Walton, Christine by lev17755

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									                           Christine H. Walton
   Modification of Experimental Objective and Protocol to an
 Assessment of the Effects of Electroacupuncture on VTA GABA
           Neurons in the Context of Acute Alcohol
                 Faculty Mentor: Scott C. Steffensen, Psychology/Neuroscience
Brief Explanation
Although my proposal for the ORCA grant involved the effects of nicotine on neurons in the
VTA, preliminary data showed little to no promise and my mentor and I decided to go in a
different direction.

Background
Recent studies have suggested that neurons in the ventral tegmental area (VTA) are influenced
by electroacupuncture stimulation (Lee, 2008). Previous research has found that actupuncture at
Shenmen (HT7) points suppressed a decrease of dopamine in the nucleus accumbens in rats in
ethanol-withdrawal. It also inhibited behavioral withdrawal signs of ethanol. Further
investigation suggests a role of the γ-aminobutyric acid (GABA) receptor system in acupuncture,
as GABA neurons exert great influence on the activity of dopamine-releasing neurons.
Researchers suspect that stimulation at acupuncture sites HT7 and PC6 in rats facilitates the
amelioration of effects of acute ethanol in the VTA (Lee, et al 2008). The purpose of this
experiment was to observe electrophysiological recordings of neurons in the VTA to observe
changes in neuron firing rate during electroacupuncture stimulation. Once a baseline effect of
acupuncture on “sober” neurons was established, we evaluated whether the behavioral
manifestations of the acupuncture treatment of alcohol was a reflection of changes in neuronal
activity.

Methods
We anesthetized rats with isoflurane. Extracellular potentials in anesthetized rats were recorded
by a single 3.0 M NaCl filled micropipette (5-10 M; 1-2 µm inside diameter), amplified with
an Axoprobe-1A microelectrode amplifier/headstage (Axon Instruments, Union City, CA).
Microelectrodes were placed in the VTA stereotaxically (5.7-6.2 mm posterior from Bregma, 0-1
mm from midline, and 6.5-7.5 mm ventral to brain surface).

We then inserted acupuncture needles at acupuncture sites HT7 and PC6 in the right forepaw.
Non-acupuncture control sites are located at the base of the tail. Stimulation via the acupuncture
needles was generated and controlled by the MASTER-8 Pulse Generator (AMPI, Israel). A
negative current of 1.4 mA was passed through the needles at 2 Hz, and visual twitching of the
muscle is observed to verify correct needle placement.
Neuron firing rate was measured via the micropipette, amplified, and graphed on a ratemeter
program prior to, during, and after electroacupuncture stimulation. Once a predictable effect of
electroacupuncture on VTA neuron firing rate was established, 1 g/kg ethanol was administrated
via injection into the intra-peritoneal (IP) space. Electroacupuncture stimulation continued
during ethanol injections and throughout the remainder of the experiment. Firing rate was
recorded up to 30 minutes after the IP injection.

Results




Figure 1: (A) This ratemeter shows the effects of HT7 stimulation (2 Hz, negative current at HT7
electrode, just threshold to twitch) on the firing rate of a representative VTA GABA neuron before and
after intraperitoneal injection of 1 g/kg ethanol. Note that ethanol increased the firing rate of this neuron.
(B) This ratemeter shows the effects of Tail stimulation on the firing rate of a representative VTA GABA
neuron before and after the same dose of ethanol. Note that ethanol produces its typical inhibition of
firing rate. (C) This graph summarizes the effects of HT7 vs Tail stimulation on ethanol effects on VTA
GABA neuron firing rate. There is actually an increase in firing rate with HT-7 stimulation (n=7). With the
same stimulation in the tail ethanol produces its typical inhibition (n=8). There was a significant difference
between HT-7 vs tail electroacupuncture (P=0.016, F(1,14)=7.6).

Discussion
It appears that HT7 electroacupuncture is blocking the effects of acute ethanol on VTA GABA
neurons. Sensory stimulation at non-acupuncture points in the tail did not appear to increase
firing rate or overcome the inhibition of firing rate induced by alcohol administration. Firing of
VTA GABA neurons typically acts to inhibit dopamine release by dopaminergic neurons in the
VTA; release of dopamine is associated with the reward pathway and subsequently addiction.
The observed increase in firing rate during acupuncture stimulation may suggest that it blunts or
blocks the addictive actions of alcohol in the brain. The next step is to record dopamine release
in the nucleus accumbens in anesthetized rats with medial forebrain bundle stimulation.

								
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