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					Running Head: Validating an Animal Model of ADHD                                                  1


                                                                                          APA 6th




   Validating an animal model of attention deficit hyperactivity disorder: neural correlates of

          impulsivity in prefrontal cortex mediated by Adderall® in fetal nicotine rats



     Team Research in Testing ADHD’s Link to Impulsivity in Neuroscience (RITALIN)

                                    Team Research Proposal



 Brian Barnett, Valerie Cohen, Taylor Hearn, Emily Jones, Reshma Karilyl, Alice Kunin, Sen

                Kwak, Jessica Lee, Brooke Lubinski, Gautam Rao, Ashley Zhan




                        The University of Maryland, Gemstone Program
VALIDATING AN ANIMAL MODEL OF ADHD                                                                                                                 2




                                                         Table of Contents


Abstract ...........................................................................................................................................3
Introduction ....................................................................................................................................4
  Research Questions & Hypotheses ..............................................................................................6
  Implications ..................................................................................................................................6
Literature Review ..........................................................................................................................7
  Clinical Components ....................................................................................................................8
  Fetal Nicotine Rat Model .............................................................................................................9
  Stop-Signal Task ........................................................................................................................10
  Neurophysiology ........................................................................................................................11
  Pharmacology .............................................................................................................................12
Methodology .................................................................................................................................13
 Research Design .........................................................................................................................13
 Pilot Study ..................................................................................................................................14
 Adderall® Study..........................................................................................................................15
 Neural Recordings ......................................................................................................................16
 Fetal Nicotine Study ...................................................................................................................17
 Data Analysis .............................................................................................................................17
 Histology ....................................................................................................................................18
 Animal Care ...............................................................................................................................18
 Study Limitations .......................................................................................................................18
Conclusion ....................................................................................................................................19
Appendix A: Anticipated Budget ...............................................................................................22
Appendix B: Timeline for Team Success ...................................................................................23
Appendix C: Electrode Construction .........................................................................................24
Appendix D: Histology with Nissl Staining ...............................................................................27
Appendix E: Glossary of Terms .................................................................................................30
Appendix F: Figures ....................................................................................................................35
References .....................................................................................................................................37
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  3


                                             Abstract

Currently, the neurological basis of attention deficit hyperactivity disorder (ADHD) is not well

established; this disorder is diagnosed qualitatively using behavioral tests rather than

quantitatively. We seek to measure neural firing in the dorsal prelimbic cortex (dPL) to

determine whether it is associated with an increase in impulsivity observed in the fetal nicotine

rat model during performance of a stop-signal task. We will also establish whether Adderall®

administration alters dPL neural firing and improves stop-signal task performance of this animal

model. From these findings, we will determine the validity of fetal nicotine rats as models of

ADHD. These results will allow the fetal nicotine rat model to be used to further study the

neurological basis of ADHD.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  4


   Validating an animal model of attention deficit hyperactivity disorder: neural correlates of

           impulsivity in prefrontal cortex mediated by Adderall® in fetal nicotine rats



       ADHD is characterized by impulsivity and hyperactivity that influences one’s ability to

concentrate and regulate behavior (National Institute of Mental Health, 2007). These symptoms

usually appear in early stages of life, and in many cases, last through adulthood. Children with

ADHD are more likely to encounter academic difficulties, such as scoring poorly on exams and

withdrawing prematurely from school (Karande & Kulkarni, 2005). Recent research predicts that

ADHD affects approximately five to ten percent of school aged children (Evans, Morrill, &

Parente, 2011).

       This disorder has caused controversy due to disagreements over its diagnostic criteria, its

frequency of diagnosis, and its method of treatment. Currently there is no well-established and

experimentally verified neurological basis for ADHD, thus the disorder has been diagnosed

based on subjective, behavioral observations rather than reliable objective identifiers of the

disorder. This ineffective method of diagnosing ADHD has led to numerous misdiagnoses, rising

medical costs, and over-prescribed medication prescriptions, which can be detrimental to the

health of patients because of possible harmful side effects. Focused research in the neural basis

of ADHD will help create a concrete method for diagnosing this disorder and how to treat it.

Once a neural basis is established, doctors could use functional magnetic resonance imaging

(fMRI) brain scans to determine if the brain is malfunctioning and if the patient has a medical

disorder. This would be more accurate than diagnosing the disorder based on behaviors and

qualitative observations, benefiting health professionals, patients, and their families (Zwi,

Ramchandani, & Joughin, 2000).
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  5


       Research demonstrates that ADHD is linked to failure of the brain to control or inhibit

behavior. The stop-signal task, a popular method used in neuroscience and psychology to

measure impulsivity, has shown that those with ADHD tend to have slower inhibition response

times (Eagle & Baunez, 2010). Poor performance on these tasks is observed after

pharmacological manipulation of prefrontal cortex, notably the dPL, suggesting an association of

the prefrontal cortex with response inhibition (Aron & Poldrack, 2004; Bari et al., 2011).

Unfortunately, no single neuron recording study has been performed in conjunction with

performance on the stop-signal task, so it is still unclear what dPL signals during impulse control

in normal animals or in animal models of ADHD.

       Numerous animal models have been suggested for ADHD, but the validity of these

models remains debatable. Currently, one possible model for ADHD is the fetal nicotine rat.

These rats model the relationship noted between pregnant mothers who smoke and the increase

in children exhibiting ADHD behaviors (Wasserman, Liu, Pine, & Graziano, 2001). Research

has demonstrated that fetal exposure to nicotine leads to a dysfunction in the development of

dopaminergic and noradrenergic pathways in the brain; this dysfunction has been attributed to

notable decreases in attention span and increases in impulsivity (Muneoka et al., 1997). Our

study will serve to confirm or disprove the fetal nicotine rat as a plausible model of ADHD by

demonstrating behavioral deficits during performance of a stop-signal task, showing that task-

related activity in dPL is disrupted during stop-signal task performance, and that both behavioral

and neural deficits are corrected with administration of Adderall®.

       In order to account for these neurological differences, various pharmacological

treatments in addition to behavioral therapies are given to patients to cope with their symptoms.

One notable treatment is administering Adderall®, a mixed amphetamine salt that has been
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    6


shown to reduce ADHD symptoms in patients (Weisler, 2005). The impact of Adderall® on

neurotransmitters has been established through previous research; however, its impact on neural

firing in relation to impulsivity is yet unexamined. Neural firing in a specific brain region during

a task demonstrates that the region is involved in regulating the response. Validating the fetal

nicotine rat model could be accomplished by linking Adderall® administration with improved

performance on the stop-signal task and altered neural firing in the dPL in the model.

       In this study, we will examine this relationship in order to validate the fetal nicotine rat

model. Is there a correlation between patterns of neural firing in the dPL and variations in

impulsivity in control rats? Is this firing disrupted and impulsivity increased in fetal nicotine

rats? Will administration of Adderall® alter dPL firing and improve stop-signal task performance

in fetal nicotine rats? We hypothesize that patterns of neural firing in the dPL in control rats will

reflect the role of the dPL as an impulsivity control area. In addition, we hypothesize that fetal

nicotine rats will show increased impulsivity by having reduced neural firing in the dPL in

response to the stop-signal. Finally, we hypothesize that Adderall® administration will increase

dPL neural firing and decrease stop-signal performance in rats that exhibit increased impulsivity.

       In recent years, the dramatic increase in the number of ADHD diagnoses can be

attributed to generally qualitative observations of an individual’s behavior; the lack of a

clinically significant and verified neurological basis has resulted in significant increases of

misdiagnoses (Kim & Miklowitz, 2002). Understanding the neurological regions associated with

the pathology of ADHD would be instrumental in diagnosing patients in a consistent and

empirical manner. Research into the role of the dPL in ADHD could aid in the formulation of a

concrete diagnosis of the disorder, which may reduce incidences of misdiagnosis.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   7


       If we find that abnormal neural firing in the dPL is correlated with impulsivity in fetal

nicotine rats, this will further validate the fetal nicotine rat as an acceptable animal model of

ADHD, as the dPL is homologous to structures in the human prefrontal cortex (Quirk & Beer,

2006). The prefrontal cortex has been shown to be disrupted in ADHD patients (Aron, Fletcher,

Bullmore, Sahakian, & Robbins, 2003). After analyzing the association of the dPL and

impulsivity, we will determine whether Adderall® administration increases neural firing in the

dPL. This neural activity is associated with improved task performance in response to the stop-

signal, and will elucidate the causal relationship between alterations in increased impulsivity in

individuals with ADHD. Proving this relationship would be fundamental for health professionals

and pharmaceutical companies because they would have an empirical basis of diagnosis and

could develop more effective treatments that target dPL and areas connected to it. Further, the

precise resolution of single neuron recordings will allow us to pinpoint the signals involved in

impulsive action, allowing drugs to target those signals and not others that might lead to

unwanted side effects.



                                         Literature Review

       The first step in establishing the neural basis of ADHD is to select a rat model and verify

its validity through the use of neural recordings and pharmacological administration. In order to

find a neural basis of ADHD, we must choose a valid rat model of the disorder and integrate it

with Adderall® administration in addition to neural recording of the dPL. We will begin with an

overview of the clinical components of ADHD to assess the deficiencies in the current system of

diagnosis. We will analyze the fetal nicotine rat model, which has been shown to represent

ADHD symptoms but requires further study to validate it as an accurate model of ADHD. We
VALIDATING AN ANIMAL MODEL OF ADHD                                                                8


will then examine relevant research on the neurophysiology of ADHD, specifically that which

concerns the dPL and the neurotransmitters dopamine and noradrenaline. In addition to a

physiological basis, we will also examine the multiple behavioral factors of ADHD, one of

which is response inhibition. Inhibition of an already-initiated response is repressed in ADHD

patients and causes impulsive behavior (Oosterlaan, Logan, & Sergeant, 1998). The stop-signal

task is a strong measure of both inhibition and impulsivity. Finally, we will examine Adderall®, a

common treatment for ADHD that inhibits dopamine and noradrenaline reuptake, which then

reduces impulsivity (DuPaul & White, 2006). To the best of our knowledge, there has not been a

study of neural recording during stop-signal performance while under the influence of Adderall®.

Clinical Components

       The Diagnostic and Statistical Manual-IV (DSM-IV) is the American Psychiatric

Association’s most recently produced guide for the clinical diagnosis of ADHD. According to

the manual, the most common symptoms associated with the disorder are impulsivity,

inattention, and hyperactivity (American Psychiatric Association, 1994). Recently, there has

been a significant increase in the number of diagnoses of ADHD. From 2003 to 2007, there was

a 21.8% increase in the reported incidence of ADHD among children/adolescents between the

ages of four and seventeen (Center for Disease Control and Prevention). Although some of these

diagnoses are accurate, many are believed to be incorrect. This is due to the fact that current

methods of diagnosing ADHD as outlined by the DSM-IV rely solely on behavioral

observations. Furthermore, these guidelines do not consider that individuals within a specific

subtype can have symptoms, which vary in severity. Certain factors, such as gender, age, and

cultural background must also be taken into account when making the diagnosis (Frick & Nigg,

2011). The establishment of a neurological basis of ADHD would greatly enhance the accuracy
VALIDATING AN ANIMAL MODEL OF ADHD                                                                     9


of diagnosing the disorder. Furthermore, treatment administered to patients would be more

effective in controlling ADHD if it is able to target the specific region of the brain monitoring

the exhibition of ADHD symptoms.

Fetal Nicotine Rat Model

       The fetal nicotine rat model serves to represent various ADHD symptoms and brain

deficiencies similar to those found in humans. Fetal nicotine rats are those whose mothers were

administered nicotine while pregnant. This section of the literature review explores different rat

models that have been used in previous studies and further attempts to show the validity of the

fetal nicotine rat model.

       Sontag, Tucha, Walitza, and Lange state that the best animal model should combine face

validity, construct validity, and predictive validity (2010). Face validity is based primarily on

similarities in symptoms; therefore, an effective animal model should demonstrate three core

symptoms of ADHD to be present: attention deficit, hyperactivity, and impulsivity. Sontag et al.

also found that construct validity shows that the model corresponds to an established

pathophysiological basis of the disorder. In addition, predictive validity is the ability to predict

unknown characteristics of the neurobiology and pathophysiology of a disorder to provide

potential new treatments. In order to analyze this type of validity, drugs with similar effects in

humans and the animal model are used to validate the model. Sontag et al. analyzed the

spontaneously hypertensive rat (SHR), one example of a valid rat model that shows several

aspects of face, construct, and predictive validity. Since these rats are bred for hypertension, this

symptom serves as a confounding variable because it is not present in ADHD, which limits the

construct validity of this model. According to Sontag et al., even though there are many different
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  10


animal models that have been used to study ADHD, no model has shown all three types of

validity that are not limited by potential confounding variables.

       Although a thoroughly validated animal model of ADHD has not yet been established,

several studies have shown that problems during fetal development of brain areas such as the

prefrontal cortex that are involved in inhibition of actions linked to behavioral problems. These

behavioral problems are prevalent in the children of mothers who smoke tobacco during

pregnancy and in controlled fetal nicotine trials, which suggests a causal link between

developmental nicotine exposure and impulsivity (Wasserman et al., 2001). This provides

evidence that the fetal nicotine rat model could be a valid animal model of ADHD. Nicotine

targets certain neurotransmitter receptors in the fetal brain, which leads to deficits in the number

of brain cells, eventually creating changes in synaptic activity (Slotkin, 1998). Specifically,

prenatal nicotine exposure has been shown to lead to dysfunctions in the development of

dopaminergic and noradrenergic systems in the rat brain (Muneoka et al., 1997). Dysfunctions in

the noradrenergic system in the brain can severely decrease attention and focus, which are key

components of ADHD and measures of construct validity. These behavioral symptoms are also

present in the fetal nicotine model, and thus demonstrate face validity. Finally, it is worth noting

that, even if this rat model does not prove to be a valid model of ADHD, this research will

provide important information related to deficits observed in children prenatally exposed to

nicotine.

Stop-Signal Task

       In clinical studies, the stop-signal task is a procedure that is generally used to measure

impulsivity (Logan, 1994). The task gauges how quickly an initiated response is inhibited (Eagle

& Baunez, 2010). In the task, the participant is trained to respond to a conditioned stimulus such
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  11


as a light turning on. On a minority of trials, another stimulus will be presented after the first one

and serves as a signal to stop the initial response. We will use the stop-signal task because it

provides a quantitative measure of motor inhibition by examining the stop signal reaction time

(SSRT) and the stop accuracy. The SSRT is the time needed by the rat to inhibit an initiated

response, and the stop accuracy is the percent of stop trials during which the subject correctly

inhibits a response (Bari et al., 2011). By obtaining and analyzing a subject’s SSRT values upon

completion of the stop-signal task, it is possible to use these values as a basis for measuring

inhibitory control and impulsivity, as a longer SSRT and lower stop accuracy would indicate

greater impulsivity and lower inhibitory control.

       Experts in the fields of clinical psychology and psychopathology have made extensive

use of SSRTs to study response inhibition in persons deemed to be generally impulsive, such as

those with ADHD (van Boxtel, van der Molen, Jennings, & Brunia, 2001). ADHD patients

exhibit elevated SSRTs, which suggest that a greater amount of time is needed to inhibit an

initiated response, have been associated with children and adult ADHD patients. This

relationship has also been demonstrated in animal models of ADHD. A high SSRT value,

therefore, is correlated to a lower level of inhibitory control and higher level of impulsivity

(Verbruggen & Logan, 2009).

Neurophysiology

       The prelimbic cortex is a subsection of the prefrontal cortex in both human and rat brains

that functions as an executive control center. The prelimbic cortex is highly correlated with

cognitive processing; subsequently, its lesioning has significant influence on motor and

behavioral tasks (del Campo, Chamberlain, Sahakian, & Robbins, 2011).
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    12


       Neurotransmitters play key roles in information processing within brain structures such

as the prelimbic cortex. The dopaminergic and noradrenergic neurotransmitter pathways are both

integral to the control of prefrontal-dependent cognitive processes such as behavioral inhibition

and impulsivity. For example, ADHD patients have decreased dopamine and noradrenaline

activity in fronto-striatal circuits (del Campo et al., 2011). This decrease results from the

potential combination of imbalances in neurotransmitter synthesis, release, receptor activation,

and neuronal responsiveness. Research shows that ADHD patients with difficulty controlling

their inhibitions have malfunctioning noradrenergic receptors while those with increased

spontaneous, unpredictable behavior have malfunctioning dopamine receptors (van Gaalen, van

Koten, Schoffelmeer, & Vanderschuren, 2006).

       The dPL is a region in the prelimbic cortex and is the focus of our research (see Figure

1). Inactivation of the dPL, such as by lesioning the region, is correlated with slower SSRTs and

mediates the effects of ADHD drugs such as atomoxetine on improving SSRTs. When

atomoxetine is used to locally block the noradrenaline reuptake in the dPL, stop-signal task

performance in SSRTs improves. Since prelimbic cortex lesions affects performance on

behavioral tasks like these, it is thought to be involved in action selection, planning, inhibition

and attention. Deficiency in these functions could result in poor performance on the stop-signal

task making dPL a strong choice for study. Further, it has been implicated in impulsivity and

ADHD and is present in both rats and humans, yet it is unclear how neural firing in the dPL

might change as a result of exposure to prenatal nicotine or Adderall®.

Pharmacology

       Various pharmacological treatments in addition to behavioral therapies are administered

to patients to manage ADHD symptoms. The three main chemical components of ADHD
VALIDATING AN ANIMAL MODEL OF ADHD                                                                 13


pharmacological treatments are atomoxetine, methylphenidate, and amphetamine. The most

common treatment for ADHD in patients is amphetamine stimulant administration, with the

mixed amphetamine salts in Adderall® being the most effective. Amphetamines have been

shown to effectively reduce hyperactivity, impulsivity, and inattention in patients with ADHD

(Weisler, 2005).

                                           Methodology

Research Design

       Our experimental design will have behavioral, neurological and pharmacological

components. The independent variable for the behavioral component will be whether or not the

mothers of the rats were administered nicotine during pregnancy; the corresponding dependent

variable will be differences in SSRT and accuracy on stop trials. The neurological independent

variable will be how neural firing in the dPL is influenced by both fetal nicotine exposure and

Adderall® administration; the dependent variable for this aspect will be variations in neural firing

of the dPL. Finally, for the pharmacological component, the independent variable is whether the

fetal nicotine rats are administered with Adderall®; the dependent variables are the changes in

both behavior and neural activity between the three rat groups.

       Our experimental design will be divided into three experiments: a pilot study to examine

the viability of fetal nicotine rats for this experiment by breeding fetal nicotine rats, an Adderall®

administration experiment in which we will divide fetal nicotine rats into a drug experimental

and a drug control group, and a fetal nicotine experiment in which we will compare unaltered

Long-Evans rats to fetal nicotine rats.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                     14


Pilot Study

       We will begin with a pilot study aimed to determine whether fetal nicotine rats can be

trained to perform the stop-signal task. Unaltered Long-Evans rats have been successfully trained

on this task before, but fetal nicotine rats may exhibit symptoms that prevent them from learning

the task. We will obtain ten male and twenty female Long-Evans rats from Charles River

Laboratory. Fetal nicotine rats will be bred using nicotine-infused water dosages. The exposure

will be equivalent to human mothers smoking 2 to 3 packs of cigarettes per day during gestation.

We will use males throughout the study because males are more even-tempered than females,

and prenatal nicotine exposure has been shown to have more dramatic effects on males (Romero

& Chen, 2004). Once rats reach a subjective satisfactory level of competence on this training

task, we will begin training on the stop-signal task.

       The stop-signal task will be conducted in aluminum boxes equipped with fluid wells and

directional lights. House lights will also be located above the wells and signal lights.

Furthermore, task control will be implemented via computer; port entry and reward retrieval are

monitored by photobeams. First, the rats will learn to associate light with reward direction (left

light leads to reward in left well). These trials will be called go trials. Once they have been able

to maintain an acceptable performance of 70% correct, stop-signal trials will be added. A

minority of the trials will have a second stimulus dictating the inhibition of the first light flash

and require a switch to the other well to receive the reward. A pseudo-random sequence in which

left and right trials are mostly random will be employed. This sequence ensures that the ratio of

right and left occurrences remains 1:1. There cannot be more than three of the same direction

trials in a row. This ensures equal sampling of all trials during the course of a session.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   15


        After a month of daily stop-signal sessions, we will evaluate the performance of the rats.

First, we will look at the differences between the percentages of correct stop trials and go trials.

If we see a significant difference based on statistical t-test analysis between these percentages,

then we can calculate an SSRT to measure the extent of impulsivity of the rat.

       The completion of the pilot study will allow us to conclude whether fetal nicotine rats are

capable of performing accurately on the stop-signal task. If we determine that the rats are

incapable of completing the task, or if we do not observe a significant between-group difference,

we will investigate other models, such as the spontaneously hyperactive rat (SHR), or try using

the delay discounting task.

Adderall® Study

       In this section of our study, we will begin by constructing the electrodes for neural

recordings. After the electrodes have been determined to be functional (see Appendix C), sixteen

fetal nicotine rats will be obtained and trained on the stop-signal task. Once training is

completed, we will perform the surgeries to implant the electrodes. To begin, rats will be

anesthetized with isoflurane, and fixed within ear bars to ensure stability throughout the surgery.

An incision will then be made, the skull will be drilled, and the electrode will be inserted. The

incision will then be stapled together, and the rat will be administered buprenorphine and placed

into a recovery chamber. Our mentor will be able to ensure that all aspects of surgery, especially

accurate electrode placement, are performed correctly.

       The rats will need to recover postoperatively for one to two weeks (Bari et al., 2011;

Acheson et al., 2006). Buprenorphine will be administered twice during the 24-hour period

following surgery for acute pain relief. Cephalaxin 15mg/kg will be administered postoperatively

twice daily for two weeks to prevent bacterial infections.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    16


        After the recovery period, each rat will perform 240 trials in one two hour session per

day, five days per week. Given the available laboratory equipment and number of researchers

who are competent in performing the methodology, this design is highly feasible within the time

constraints of one semester. The electrode will be advanced 40 µm following each session.

Neural firing will be recorded by electrodes inserted alongside single neural cells in the dPL; a

frequency distribution of action potentials across neural membranes during trials will be plotted

as a function of time. If these plots of neural firing show an increase in activity only in response

to the stop-signal during correct ‘stop’ trials, this will allow us to establish that the brain region is

active during response inhibition rather than in anticipation of a reward or in response to the ‘go’

signal, thus correlating the dPL with regulation of impulsivity. Observation of task performance

will help us compare and contrast typical ADHD behaviors associated with rat models in this

study and those in humans (Calu, Roesch, Haney, Holland, & Schoenbaum, 2010).

        Eight of the rats will be chosen through matched random selection on stop signal

performance to receive Adderall® throughout the duration of the study. The drug will be

administrated orally in chocolate milk through a syringe. Rats assigned to the drug control group

will receive chocolate milk only. Each rat will be injected with a dose of 1 ml/kg body weight of

the animal. Drugs will be administered every three days. All dosages will be given according to a

balanced procedure (Sagvolden & Xu, 2008). We will obtain the Adderall® from Henry Schein, a

worldwide pharmaceutical distributor.

Neural Recordings

        As the rats complete trials, we will conduct single-unit recording. Neural activity will be

monitored using a computer interface in the chambers (Bryden, Johnson, Diao & Roesch, 2011).

We will screen the electrode wires prior to each trial to determine whether activity is detected. If
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    17


the electrodes are unable to detect neural firing, we will advance the electrode by 80µm. If

activity is detected, then the trial will be recorded; following the session, the electrode will be

advanced. During recordings the signals detected by the electrode will be amplified, and then be

filtered in order to identify and save specific action potential waveforms (Roesch, Calu, &

Schoenbaum, 2007).

Fetal Nicotine Study

       In this portion of our study, we will obtain eight male control rats that do not have any

genetic modifications or environmental interferences as well as eight male fetal nicotine rats.

These rats will undergo the same stop-signal training and surgery outlined above and will receive

chocolate milk through a syringe like the drug control group. They will also be subject to the

same neural recording processes. Unaltered Long-Evans rats serve as a control to the fetal

nicotine rats serving as a baseline for behavior on the stop-signal task and neural firing in the

dPL.

Data Analysis

       Data will be analyzed in MATLAB to obtain firing and behavioral information.

Wilcoxon tests, t-tests, ANOVA, and Pearson Chi-square tests will be implemented to compare

and measure relevant statistics (Bryden et al., 2011). Examples of analyses include comparative

histograms of neural firing patterns across the trial time course as well as observing the

relationship between SSRT and neural firing. When a rat’s session is analyzed, the intensity and

timing of its neural firing is compiled and aggregated with other sessions to prove an informative

comparison of neural activity of the dPL in all groups of rats.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   18


Histology

        Histological analysis will be performed to confirm that the electrodes were placed in the

correct region of the brain during surgery. See Appendix D for details (Barth, 1997).

Animal Care

        We have submitted a proposal of our study for review by University of Maryland

Institutional Animal Care and Use Committee. Throughout the study, we will adhere to the

procedures outlined in the Guide for the Care and Use of Laboratory Animals (Garber et al.,

2011). Using these guidelines, we will house our rats in appropriate cages with proper room

temperature, ventilation, and feeding. When euthanizing the rats, we will use isoflurane to place

them in a deep unconscious state. Following this, we will perfuse the rats by introducing a needle

to the circulatory system of the rat through the heart. Saline and a fixative will be pumped

through the circulatory system to preserve the brain tissue. The rats will then be sacrificed by

decapitation. The brains will be excised and then stored in a refrigerator.

Study Limitations

        Attrition effects are a main concern for our study. Factors such as fatigue, hunger, and

thirst will alter the rats’ motivation levels, which will force us to disregard trials that were

adversely affected by these conditions; that is, trials during which the rat did not complete the

entire session (Prescott et al., 2010). We will be able to control for these variables by ensuring

that the rats will not be subjected to exhaustive tests and that they will be allowed ample rest

time between trials. In order to ensure that trials are executed efficiently, we will mildly deprive

rats of water prior to completing the trials and use a thirst-based reward system. The rats will

receive 35 mL of water per day. Several hours prior to running the task, the rats will not receive
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  19


water. This lack of water will act as an incentive to motivate the rats to perform the task in order

to receive water as a reward.

       It is also necessary that the rats undergo a full recovery prior to performing the stop-

signal task by allotting recovery time after surgery. An insufficient recovery period poses a

medical risk to the rats and places the rats under additional stress that may alter the results of the

stop-signal task (Krishnan, Panigrahi, Jayalakhsmi, & Varma, 2011).

       There will also be a possibility of experimenter error in our study. A small group of team

members will build the electrodes and implant them into the rats’ brains. If the building or

implanting of the electrode differs between members, this may affect the validity of our results.

To compensate for any differences, we will follow a set of consistent procedures and electrodes

and surgeries will be divided evenly between control and experimental groups. In addition, post-

mortem histology will reveal whether or not electrode placement was correct; we will not include

data collected from incorrectly placed electrodes in our final data analysis.

       In order to account for a possible influence of age on impulsivity, we will only use male

rats of the same age. We will obtain our rats from Charles River Laboratory, and we will then

breed the rats by following an established process for exposing rats to the pharmaceuticals during

pregnancy. By accounting for these variables, we will preserve the internal validity of our

research.

                                             Conclusion

       The significant increase in the number of ADHD diagnoses made in recent years can be

attributed to the lack of an experimentally and clinically verified neurological basis of ADHD.

The criteria for diagnosing the disorder as provided by the DSM-IV is primarily composed of

qualitative observations of a patient’s behavior. The high incidences of misdiagnoses, however,
VALIDATING AN ANIMAL MODEL OF ADHD                                                                20


have shown that such observations are insufficient in generating a proper diagnosis. The

association of ADHD to a particular brain signal would be of great value to health professionals

and pharmaceutical companies by delivering drug treatments to specific regions of the brain that

modulates such a signal and would ultimately be critical for treating ADHD symptoms without

unwanted side effects.

       Previous research has indicated that the dPL is involved in controlling impulsivity, one of

the most common symptoms of ADHD. Other studies have shown that in an individual with

ADHD, there is a reduction in the available quantity of the neurotransmitters dopamine and

noradrenaline. This effect can be counteracted by Adderall®, a common medication for ADHD

treatment. This amphetamine-based drug has been shown to increase the amount of dopamine

and noradrenaline in the dPL cortex and, consequentially, reduce impulsivity in both rat models

of ADHD. We aim to prove that the physiological signal within the dPL are disrupted in rats

with high impulsivity by conducting single-unit recordings in fetal nicotine rats and comparing

these to recordings of controls. In addition, with the administration of Adderall®, we expect that

these effects should be reversed, which will be evident by a change in the single-unit recordings

following administration in the fetal nicotine rats.

       In order to test the effects of Adderall®, we will determine the validity of the fetal

nicotine rat as a model of ADHD by establishing that impulsivity caused by fetal nicotine

exposure is a symptom of ADHD. Through the stop-signal task, we expect to see an increase in

SSRT values in the rats, which is a measure of increased impulsivity. In addition, in the single-

unit recording studies conducted during the task, we expect to see decreased dPL activity. These

results would suggest that neural firing in the dPL is correlated with impulsivity, and that

Adderall® administration alters neural firing patterns within the dPL. The findings obtained from
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  21


our research can be applied to humans because the data will be recorded from a homologous

brain area between humans and rats. Even if our results will not support our hypothesis, our

findings will contribute to further research in that we will determine the contribution of dPF to

impulsive behavior in normal rats and if this signal is disrupted in prenatally nicotine exposed

rats.
VALIDATING AN ANIMAL MODEL OF ADHD                                                 22


                               Appendix A: Anticipated Budget

Item                                  Cost per unit   Amount of   Total cost ($)
                                      ($)             item

Plexon Recording System               ~70,000         1           Provided by
                                                                  mentor

Test boxes equipped with              ~15,000         8           Provided by
photobeams                                                        mentor

Long-Evans rats                       27              10          270

Animal Care                           ~200/month      6           1200

Electrodes                            ~100            24          2400

Adderall®                             ~500            1           500

Cables                                ~800            8           Provided by
                                                                  mentor

Histology supplies (saline, stains,   ~2000           N/A         Provided by
etc.)                                                             mentor

Surgical supplies (anesthetics, etc.) ~15000          N/A         Provided by
                                                                  mentor

                                                      Total:      $4370.60
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  23


                                 Appendix B: Timeline for Success

Spring 2012

      Finalize and present thesis proposal

      Apply for IACUC approval

      Apply for grants: HHMI, NIDA

      Construct electrodes

      Create team website

Summer 2012

      Pilot study to determine if fetal nicotine rats will be able to successfully perform the stop-

       signal task

      Obtain Adderall® for study

Fall 2012

      Implant electrodes and run rats through stop-signal task and single unit neuron recording

       with experimental groups and control group: (1) fetal nicotine rats with saline. (2) fetal

       nicotine rats with Adderall® and (3) Long-evans rats.

      Outline thesis chapters

      Draft thesis chapters 1 and 2

      Present preliminary findings at Junior Colloquia

      Continue updating team website, consulting with librarian for editing thesis paper, and

       searching for conferences to attend

Spring 2013
VALIDATING AN ANIMAL MODEL OF ADHD                                                               24


      Stop-signal task and single unit neuron recordings if more rats are needed. Histology

       studies with Nissl staining for experimental and control groups to verify electrode

       location

      Present preliminary findings at Undergraduate Research Day

      Revise team thesis paper chapters 1-3 based on feedback from librarian and mentor

      Continue updating team website and searching for conferences to attend

Fall 2013

      Data analysis with ANOVA, MATLAB, t-tests, Wilcoxon tests, and chi-squared tests

      Complete thesis paper draft

      Attend senior orientation in September

      Prepare for the Team Thesis Conference rehearsal in February

      Contact and determine discussants for thesis presentation

      Continue updating team website, consulting with librarian for editing thesis paper, and

       searching for conferences to attend

Spring 2014

      Practice presentation at rehearsal

      Complete thesis paper

      Present findings at Team Thesis Conference

      Submit final thesis
VALIDATING AN ANIMAL MODEL OF ADHD                                                     25


                            Appendix C: Electrode Construction

Materials needed to construct an electrode:

      Nichrome/Formvar wire: 0.0010” bare, 0.0015” coated

      Cannula with 27 gauge thin wall diameter

      Auguts: both intact and pins from auguts that have been pushed out

      Soldering wire

      Super glue

      Flux (cleaning, purifying, and flowing agent used to aid in metal joining)

      Measuring calipers

      Silver paint

      Forceps, both blunt and sharp

      Scissors

      Constructed augut holder

      Battery

      Two alligator clip wires

      Saline solution and small beaker

      Reamers (metalworking tools used to create precise holes)

      Permanent marker

Construction of parts:

   1. Push augut pins out by hand using a cannula piece.

   2. Take cannula of 0.4 mm diameter and measure with calipers to 15 mm length and make

       sure to bevel the edge of the cannula and clean out the hole with a reamer.

   3. Cut off the narrow end of the augut pin.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                26


   4. Place cut down augut pin into a tightened holder and solder, using flux, the cannula to the

       augut pin attaching the beveled end to the pin with the beveled side facing up. The

       cannula should be straight and centered on the augut pin in all dimensions.

Construction of the electrode:

   1. Cut 11 pieces of wire at 8cm long.

   2. Gather wires and roll all wires together to create a tight bundle.

   3. Wet the ends of the bundle that will be sent through the cannula for ease.

   4. Feed the wires into the cannula and cut off the tip that was moistened.

   5. Bend the other end of the wires (near the beveled edge of the cannula) up and place a

       small drop of flux and super glue where the wires come out of the cannula.

   6. Wait for wires to dry and then carefully place the cannula on the middle pin of the augut

       that is being held by a constructed augut holder.

Under a microscope:

   1. Wrap the wires around the pins with forceps with each individual wire wrapped around

       each pin 2-3 times. Strip the ends of the wires for better conductivity. Pull the remaining

       wire with the forceps as close to the pin as possible and cut it right next to the pin. Wires

       to the left should be wrapped clockwise and wires to the right should be wrapped

       counter-clockwise.

   2. Paint the wire and pin with silver paint. Place a droplet on top of an insect pin and place

       this droplet on top of the pin and gently and slowly pull the droplet down the pin to cover

       the wire completely and to ensure that the tip of the wire is in contact with the pin.

   3. Let the first coat dry and then repaint the same way.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    27


    4. Check conductivity after both coats have dried by placing wire tips into saline solution in

        a small beaker. Then place a one side of a two-sided alligator wire onto a battery and the

        other to the beaker of saline. With another wire, connect one side to an insect pin to touch

        the flip side of the augut for each of the pins and the other side to the other part of the

        battery. Check for bubbles for each wire and if no bubbles are seen then look for a loose

        end to repaint or strip the paint with a razor blade and start over.

To implant the electrode, holes will be drilled in predetermined positions on the rat’s skull for

anchoring screws that will hold the electrode in place, and a somewhat larger central hole will be

made for insertion of the electrode itself. With a microscope, the outermost layers of the

membranes that cover the brain will be cut away from this central hole and the microelectrode

will be inserted into the brain tissue. The electrode will be inserted further into the brain at a rate

of 100 microns/minute until it is near a single neuron so that recording can begin. The electrode

will then be screwed to the skull and fastened using grip cement and dental acrylic.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   28


                            Appendix D: Histology with Nissl Staining

        In order to ensure that the electrodes in the study were, in fact, recording from the dPL

we will perform histological analysis. Histology is the study of animal tissue under a microscope,

as well as the techniques that prepare the tissue for microscope study. To be viewed by light

microscopy, tissue must be stained in order to trace fiber tracts and receptor types. First, brain

tissue must be isolated by sacrificing the animal of interest and then perfusing it to drain blood.

Blood may interfere with the staining process so instead a fixative is added into the vascular

system, which also helps harden the brain. The brain is then removed, sectioned into thin slices,

and stained with cresyl violet. Once it is stained, structures can be identified using an atlas of the

rat brain.

Materials need for histology:

       Fixed rat brain

       Cryostat or microtome to section the brain accurately

       Microscope slides

       For the stain solution (1.5 L of 0.25% thionin):

             o   1428 mL distilled water

             o   54 mL 0.1M sodium hydroxide (NaOH)

             o   18 mL glacial acetic acid

             o   3.75 g thionin

To create stain:

    1. Mix distilled water, sodium hydroxide, and acetic acid. Heat until just boiling, then add

        thionin and reflux for 45 minutes with stirring.
VALIDATING AN ANIMAL MODEL OF ADHD                                                               29


   2. Cool to room temperature, then decant 1000 mL of the solution in a dark bottle. Decant

       the remainder of the solution into another dark bottle and store this excess.

   3. Keep stain at 37 degrees Celsius. Filter solids out before each use.

To perform a Nissl stain:

   1. Mount dried, sliced tissue on slides.

   2. Defat the tissue in a fume hood in a solution of equal parts concentrated chloroform and

       ethanol for one hour.

   3. Soak tissue in 100% ethanol twice for two minutes at a time, followed by 95% ethanol,

       70% ethanol, and 50% ethanol each for two minutes at a time. Dip twice in distilled water

       twice.

   4. To stain, soak tissue for 20 seconds in 0.25% thionin, followed by two dips in distilled

       water twice.

Dip in 50% ethanol, 70% ethanol, 95% ethanol twice, and 100% ethanol twice for 4 minutes

each, followed by 4 minute soaks in ortho-dimethylbenzene, meta-dimethyl benzene, and para-

dimethylbenzene. Let dry thoroughly.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   30


                                 Appendix E: Glossary of Terms

Action potential

        A neuron contains a plasma membrane with a voltage differential caused by ion pumps

and ion channels. When a neuron is at rest, it has a resting potential of -70 millivolts. When it

receives electrical signals from dendrites of other neurons to its axon, it reaches a threshold

potential of -55 millivolts. At this point, an action potential occurs and the membrane potential

shoots up to around +100 millivolts. This potential travels to dendrites of the neuron and is

passed on to other axons.

Amphetamines

        Amphetamines, from alpha-methylphenethylamine, are psychostimulant drugs which

increase alertness and focus. This class of drugs works by modulating the dopaminergic and

noradrenergic neurotransmitters in specific region of the brain. Modulation is achieved by

altering the DA reuptake protein, preventing the reuptake of DA.

Animal/Rat models

        Animal models are used to represent various diseases and are evaluated based on three

criteria: face validity, construct validity, and predictive validity. Face validity is the model’s

ability to display major symptoms of the disease. Similarities to the disease’s pathophysiology

exemplify construct validity. Predictive validity is present when the model responds in a similar

fashion to drugs designed to alleviate the disease. An excellent animal model for a disease will

display all three forms of validity.

Augut

        The augut is a connector crimp tool that allows for smooth cable connections during

usage. This is mainly used for electrode construction.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  31


Cannula

        A small flexible tube placed into a body cavity or blood vessel, which is used to insert a

surgical instrument, drain off fluid, or administer medication. For our research, we will

surgically implant the cannulas into the rats to deliver the electrodes to the dPL.

Dorsal prelimbic cortex

        The dorsal prelimbic (dPL) cortex is located within the PFC, the brain region that serves

as the primary control for complex cognitive behaviors. Because this area controls higher-level

executive functions, it stands to reason that the dPL would be involved in controlling

impulsivity; this assumption has been supported by various studies. Lesioning the dPL has been

shown to impair decision-making involving information regarding actions the subject is about to

perform; hence, inactivation of the dPL has also been shown to increase stop-signal reaction

times (Bari et al., 2011).

Impulsive action

        In the stop-signal task, impulsive action can be observed when the rats fail to change

direction or when a premature response occurs. Essentially, impulsive action happens when there

is no behavioral inhibition. Impulsive action can be distinguished from impulsive choice, which

occurs when decisions are made without any consideration. Rats exhibit impulsive choice when

they choose a smaller immediate reward as opposed to a larger delayed reward.

Impulsive action neural circuit

        When recording the subject’s neural activity, it is important to remember that neural

signals are rarely a lone signal. Rather, they tend to take complex pathways through various

brain regions to achieve the desired physical output. For impulsive action, this circuit includes

the PFC, orbitofrontal cortex, anterior cingulated cortex, and nucleus accumbens. Therefore,
VALIDATING AN ANIMAL MODEL OF ADHD                                                                   32


when a drug is administered to a single region of the brain it will only affect that area, not the

entire circuit in which the signal is traveling. For this study, we will be administering drugs

systematically, which will affect the entire brain, not just the dPL.

Neural circuit

       The neural circuit represents multiple brain regions through which a neural signal passes

through to execute a physical action.

Neuroplasticity

       Also known as brain plasticity, neuroplasticity is the ability of the brain to reorganize

existing connections between neurons. When a particular brain region is damaged, the intact

neurons of functional brain regions are able to grow new nerve endings to connect to damaged

brain cells or to other functional neurons to form a new network of signaling. In this way, the

brain is still able to perform necessary functions even if the regions normally responsible for

performing these functions are injured.

Neurotransmitters

       A neurotransmitter is a chemical that transmits signals from a neuron to another cell via a

synapse, the structure between a neuron and another cell. A neurotransmitter leaves the

presynaptic neuron, crosses the synapse, and arrives in the postsynaptic neuron. Noradrenaline

(NA), also known as norepinephrine, is a neurotransmitter that commonly influences alertness

and one’s reward system. Dopamine (DA), another neurotransmitter, is a precursor to

norepinephrine in the biosynthesis, involved in cognitive functions including attention. Reuptake

is the process in which a neurotransmitter, such as DA or NA, is reabsorbed into a neuron after it

has transmitted the neural impulse. Neurotransmitters can also be degraded extracellularly by

acetylcholinesterase. Due to the large molecular size of neurotransmitters, reuptake can only be
VALIDATING AN ANIMAL MODEL OF ADHD                                                                 33


achieved with specific transporter proteins that carry the molecules across the cellular

membrane.

Nissl Stain

       The nissl stain is a histological procedure used to identify differences in neurons and

therefore differences in brain areas. The stain colors the RNA molecules (most likely ribosomal

RNA (rRNA) blue, which are in the cytoplasm of the cell at the neuron’s time of death. The stain

stains the RNA molecules (most likely ribosomal RNA (rRNA)) that are in the cytoplasm of the

cell at the time of the death of the neuron blue. This stain shows RNA molecules and the rough

endoplasmic reticulum, an organelle in the cell, which modifies proteins to make them functional

for the cell to use, has rRNA on the surface of the organelle. The stain shows the structural

features of the neurons. After reviewing the stains, we will use a brain atlas to identify the brain

region we are in.


Prefrontal cortex

       The prefrontal cortex (PFC) is part of the frontostriatal circuit, which is known to control

higher-level executive functions, including inhibition. Within the PFC is the dorsal prelimbic

area, the primary region of study in this investigation.

Single-unit neural recording

       Single-unit neural recordings will be procured by implanting a Schoenbaum electrode

into the subjects’ dorsal prelimbic area of their prefrontal cortex. These electrodes take

extracellular recordings of the changes in electrical potential, thereby measuring when the

neuron fires, indicating neural activity.
VALIDATING AN ANIMAL MODEL OF ADHD                                                                    34


Stop-signal task

       The stop-signal task is a behavioral measure of impulsivity. Subjects are first trained on

the task, learning how to respond correctly to the visual input (e.g. right light ⇒go right). When

the task begins, subjects are directed to go to the right or left well and, if they choose the correct

side, they are rewarded with a quantity of water with 10% sucrose. The time it takes for the

subject to complete this task is defined as the “go reaction time.” This sequence makes up a

majority (80%) of trials, so the subjects become accustomed to going to the same side the light

flashes. However, during the other 20% of trials, a primary light will flash, directing the subject

to one side, while the subject in en route to the directed well, the opposite side’s light flashes,

instructing the subject to change direction. The time it takes the subject to correct their direction

is defined as the “stop reaction time.” If the subject does not change direction, this is considered

an incorrect response (see Figure 2).

       The dependent variable of the stop-signal task is the time it takes the subjects to correct

their response after the second light flashes, which is affected by the independent variable, the

time between the primary flash and the secondary flash. These times are measured by

photosensors across the well that, when broken, record the difference in time.
VALIDATING AN ANIMAL MODEL OF ADHD                                                              35


                                      Appendix F: Figures




Figure 1. Rat brain coronal cross section with the dPL circled (Eagle & Baunez, 2010). The

areas of the brain shown (from left to right): pre-genual cingulated cortex (CG), prelimbic cortex

(PL), infralimbic cortex (IL), orbitofrontal cortex (OF), dorsomedial striatum (DMStr),

dorsolateral striatum (DLStr), nucleus accumbens core (NAcbC), nucleus accumbens shell

(NAcbS), and subthalamic nucleus (STN).
VALIDATING AN ANIMAL MODEL OF ADHD                                                           36




Figure 2. Diagram of the stop-signal task (Eagle & Baunez, 2010). The levers shown in this

diagram would be wells in our experiment.
VALIDATING AN ANIMAL MODEL OF ADHD                                                               37


                                           References

Acheson, A., Farrar, A. M., Patak, M., Hausknecht, K. A., Kieres, A. K., Choi, S., ... Richards, J.

       B. (2006). Nucleus accumbens lesions decrease sensitivity to rapid changes in the delay

       to reinforcement. Behavioural Brain Research, 173(2), 217-228. doi: S0166-

       4328(06)00346-9

American Psychiatric Association. (1994). Diagnostic and Statistical Manual of Mental Diseases

       (DSM-IV) (4th ed.) Washington, DC.

Aron, A. R., Fletcher, P. C., Bullmore, E. T., Sahakian, B. J., & Robbins, T. W. (2003). Stop-

       signal inhibition disrupted by damage to right inferior frontal gyrus in humans. Nature

       Neuroscience, 6, 1115-1116. Doi: 10.1038/nn1003

Aron, A. & Poldrack, R. (2004). The cognitive neuroscience of response inhibition: relevance for

       genetic research in attention-deficit/hyperactivity disorder. Society of Biological

       Psychiatry, 57, 1285-1292. doi: S0006-3223(04)01106-0

Bari, A., Mar, A.C., Theobald, D.E., Elands, S.A., Oganya, K.C., Eagle, D.M. & Robbins, T.W.

       (2011). Prefrontal and monoaminergic contributions to stop-signal task performance in

       rats. Journal of Neuroscience, 31, 9254-9263. doi: 10.1146/annurev-clinpsy-032511-

       143150

Barth, D. (1997). Neuroscience Methods- VII. Histology I: An Introduction [PDF document].

       Retrieved from http://psych.colorado.edu/~dbarth/.

Bryden, D. W., Johnson, E. E., Diao, X., & Roesch, M. R. (2011). Impact of expected value on

       neural activity in rat substantia nigra pars reticulata. European Journal of Neuroscience,

       33(12), 2308-2317. doi: 10.1111/j.1460-9568.2011.07705.x
VALIDATING AN ANIMAL MODEL OF ADHD                                                              38


Calu, D. J., Roesch, M.R., Haney, R.Z., Holland, P.C., Schoenbaum, G., (2010). Neural

       correlates of variation in event processing during learning in central nucleus of amygdala.

       Neuron, 68, 991-1001. doi:10.1016/j.neuron.2010.11.019

Center for Disease Control and Prevention. (2010). Increasing prevalence of parent-reported

       attention-deficit/hyperactivity disorder among children — united states, 2003 and 2007

       [Data file]. Retrieved from http://www.cdc.gov/mmwr/pdf/wk/mm5944.pdf

Curatolo, P., D'Agati, E., & Moavero, R. (2010). The neurobiological basis of ADHD. Italian

       Journal of Pediatrics, 36(1), 79. doi: 1824-7288-36-79

Del Campo, N., Chamberlain, S. R., Sahakian, B. J., & Robbins, T. W. (2011). The roles of

       dopamine and noradrenaline in the pathophysiology and treatment of attention-

       deficit/hyperactivity disorder. Biological Psychiatry, 69(12), e145-157. doi: S0006-

       3223(11)00260-5

DuPaul, G. J., & White, J. P. (2006). ADHD: Behavioral, Educational, and Medication

       Interventions. Education Digest: Essential Readings Condensed for Quick Review, 71(7),

       57-60.

Eagle, D. M., & Baunez, C. (2010). Is there an inhibitory-response-control system in the rat?

       Evidence from anatomical and pharmacological studies of behavioral inhibition.

       Neuroscience Biobehavioral Review, 34(1), 50-72. doi: S0149-7634(09)00100-6

Evans, W.N., Morrill, M.S., & Parente, S. T. (2010). Measuring inappropriate medical diagnosis

       and treatment in survey data: the case of ADHD among school-age children. Journal of

       Health Economics, 29(5), 657-673. doi:10.1016/j.jhealeco.2010.07.005
VALIDATING AN ANIMAL MODEL OF ADHD                                                                  39


Frick, P. J., & Nigg, J. T. (2011). Current issues in the diagnosis of attention deficit hyperactivity

       disorder, oppositional defiant disorder, and conduct disorder. Annual Review of Clinical

       Psychology, 19(35), 1-31. doi:10.1146/annurev-clinpsy-032511-14315

Garber, J. C., Barbee, R. W., Bielitzki, J. T., Clayton, L. A., Donovan, J. C., Hendriksen, C. F.

       M., . . .Würbel, H. (2011). Guide for the care and use of laboratory animals eighth

       edition. Washington, DC: The National Academies Press.

Joyce, B. M., Glaser, P. E., & Gerhardt, G. A. (2007). Adderall produces increased striatal

       dopamine release and a prolonged time course compared to amphetamine isomers.

       Psychopharmacology (Berlin), 191(3), 669-677. doi: 10.1007/s00213-006-0550-9

Karande, S. & Kulkarni, M. (2005). Poor school performance. The Indian Journal of Pediatrics,

       72(11), 961-967. doi: 10.1007/bf02731673

Kim, E.Y., & Miklowitz, D.J. (2002). Childhood mania, attention deficit hyperactivity disorder

       and conduct disorder: a critical review of diagnostic dilemmas. Bipolar Disorders: An

       International Journal of Psychiatry and Neurosciences, 4(4), 215-225.

       doi: 10.1034/j.1399-5618.2002.01191.x

Krishnan, S., Panigrahi, M., Jayalakshmi, S., & Varma, D. R. (2011). Neuroplasticity in

       hemispheric syndrome: an interesting case report. Neurology India, 59(4), 601-604. doi:

       10.4103/0028-3886.84346

Larsson, J. O., Larsson, H., & Lichtenstein, P. (2004). Genetic and environmental contributions

       to stability and change of ADHD symptoms between 8 and 13 years of age: a

       longitudinal twin study. Journal of the American Academy of Child and Adolescent

       Psychiatry, 43(10), 1267-1275. doi: S0890-8567(09)61581-1
VALIDATING AN ANIMAL MODEL OF ADHD                                                               40


Muneoka, K., Ogawa,T., Kamei, K., Muraoka, S., Tomiyoshi, R., Mimura, Y., … Takigawa, M.

       (1997). Prenatal nicotine exposure affects the development of the central serotonergic

       system as well as the dopaminergic system in rat offspring: involvement of route of drug

       administrations. Developmental Brain Research, 102(1), 117-126. doi: 10.1016/S0165-

       3806(97)00092-8.

National Institutes of Health, US Department of Health and Human Services. (2007). Attention

       deficit hyperactivity disorder. NIH. 49 pages. Retrieved from:

       http:/www.nimh.nih.gov/health/publications/adhd/nimhadhdpub.

Oosterlaan, J., Logan, G. D., & Sergeant, J. A. (1998). Response Inhibition in AD/HD, CD,

       Comorbid AD/HD+CD, Anxious, and Control Children: A Meta-analysis of Studies with

       the Stop Task. Journal of Child Psychology and Psychiatry, 39(3), 411-425. doi:

Prescott, M., Brown, V., Flecknell, P., Gaffan, D., Garrod, K., Lemon, R., & ... Whitfield, L.

       (2010). Refinement of the use of food and fluid control as motivational tools for

       macaques used in behavioural neuroscience research: report of a working group of the

       NC3Rs. Journal of Neuroscience Methods, 193(2), 167-188.

       doi:10.1016/j.jneumeth.2010.09.003

Quirk, G. J. & Beer, J. S. (2006). Prefrontal involvement in the regulation of emotion:

       convergence of rat and human studies. Current Opinion in Neurobiology, 16(6), 723-727.

       doi: 10.1016/j.conb.2006.07.004

Roesch, M.R., Calu, D.J., Schoenbaum, G. (2007). Dopamine neurons encode the better option

       in rats deciding between differently delayed or sized rewards. Nature Neuroscience,

       10(12), 1615-1623. doi:10.1038/nn2013
VALIDATING AN ANIMAL MODEL OF ADHD                                                              41


Romero, R. D., & Chen, W.-J. A. (2004). Gender-related response in open-field activity

       following developmental nicotine exposure in rats. Pharmacology Biochemistry and

       Behavior, 78(4), 675-681. doi: 10.1016/j.pbb.2004.04.033

Sagvolden, T., & Xu, T. (2008). l-Amphetamine improves poor sustained attention while d-

       amphetamine reduces overactivity and impulsiveness as well as improves sustained

       attention in an animal model of attention-deficit/hyperactivity disorder (ADHD).

       Behavioral and Brain Functions, 4(3), 1-12. doi: 10.1186/1744-9081-4-3

Sallee, F. R., & Smirnoff, A. V. (2004). Adderall XR: long acting stimulant for single daily

       dosing. Expert Review of Neurotherapeutics, 4(6), 927-934. doi:

       10.1586/14737175.4.6.927

Slaats-Willemse, D., Swaab-Barneveld, H., de Sonneville, L., van der Meulen, E., & Buitelaar, J.

       (2003). Deficient response inhibition as a cognitive endophenotype of ADHD. Journal of

       the American Academy of Child and Adolescent Psychiatry, 42(10), 1242-1248. doi:

       S0890-8567(09)61988-2

Slotkin, T.A., (1998). Fetal nicotine or cocaine exposure: which one is worse?. Journal of

       Pharmacology and Experimental Therapeutics. 285: 931-945.

Sontag, T. A., Tucha, O., Walitza, S., & Lange, K. W. (2010). Animal models of attention

       deficit/hyperactivity disorder (ADHD): a critical review. ADHD Attention Deficit and

       Hyperactivity Disorders, 2(1), 1-20. doi: 10.1007/s12402-010-0019-x

Thapar, A., Fowler, T., Rice, F., Scourfield, J., van den Bree, M., Thomas, H., . . . Hay, D.

       (2003). Maternal smoking during pregnancy and attention deficit hyperactivity disorder

       symptoms in offspring. American Journal of Psychiatry, 160(11), 1985-1989.
VALIDATING AN ANIMAL MODEL OF ADHD                                                             42


Van Boxtel, G. J. M., van der Molen, M. W., Jennings, J. R., Brunia, C. H. M. (2001). A

       psychophysiological analysis of inhibitory motor control in the stop-signal paradigm.

       Biological Psychology, 58(3), 229-262. doi: 10.1016/S0301-0511(01)00117-X

van Gaalen, M.M., van Koten, R., Schoffelmeer, A., & Vanderschuren, L. (2006). Critical

       involvement of dopaminergic neurotransmission in impulsive decision making.

       Biological Psychiatry, 60, 66–73. doi:10.1016/j.biopsych.2005.06.005

Verbruggen, F., & Logan, G. D. (2009). Models of response inhibition in the stop-signal and

       stop-change paradigms. Neuroscience and Biobehavioral Review, 33(5), 647-661. doi:

       S0149-7634(08)00144-9

Wasserman, G. A., Liu, X., Pine, D. S., & Graziano, J. H. (2001). Contribution of maternal

       smoking during pregnancy and lead exposure to early child behavior problems.

       Neurotoxicology and Teratology, 23(1), 13-21. doi: S0892-0362(00)00116-1

Weisler, R. H. (2005). Safety, efficacy and extended duration of action of mixed amphetamine

       salts extended-release capsules for the treatment of ADHD. Expert Opinion on

       Pharmacotherapy, 6(6), 1003-1018. doi: 10.1517/14656566.6.6.1003

Zwi, M., Ramchandani, P., Joughin, C. (2000). Evidence and belief in ADHD. British Medical

       Journal, 321, 975-976. doi: 10.1136/bmj.321.7267.975

				
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