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NEURO AND ENDOCRINE CONROL IN FISH REPRODUCTION Great interaction between nervous and endocrine system Some neurons display the combination of both nervous and hormonal system which is called neurosecretory or neuroendicrine ANAOTOMY OF NERVOUS SYSTEM • Nervous system has two components, Central nervous system (CNS) and Peripheral nervous system (PNS) • THE CNS consists of brain and spinal cord. The nervous tissue other than brain and spinal cord PNS, it comprises, nerves, ganglia and receptors NERVOUS SYSTEM • Nervous system is made of two chief cells, the nerve cells and supporting cells, nerve cells are neurons and they are functional units, conduct impulses, receipt and conduction of information is impulse, receptor can be nerve cell, muscle, gland etc., transmission of message is due difference of potential between inside and outside of nerve COMPONENTS OF BRAIN • Regulating center for all the receptors, enclosed in cranium, brain is small comparison to body size, gap is filled with gelatinous matrix, brain is soft, white and coved with extensive network of blood vessels, called choroid plexi • Brain has three main divisions, Prosecephalon or fore brain, Mesencephalon or mid brain, Rhobencephalon or hind brain PROSENCEPHALON OR FORE BRAIN • The fore brain consists of two parts, Telencephalon and diencephalon • TELENCEPHALON: most anterior part of the brain, responsible for reception and conduction of smell impulses, it consists of two parts, the anterior paired olfactory bulb, and posterior two large cerebral hemispheres In addition to olfaction /smell, it also regulate aggression, sexual activity, parental behavior, maintain equilibrium to facilitate successful breeding • Ablation of forebrain in goldfish shows less response than normal ones, , tilapia neglected young ones, Cyprinidae became less cautious to a new situation, spawning was suppressed in stick leback, nest building behaviour was affected in paradise and colour vision in goldfish with the extirpation of fore brain DIENCEPHALON • It is covered dorsally by the posterior bulgings of the cerebral hemispheres. It posses cavity inside called third ventricle, it has three parts, dorsal epithalamus, lateral thalamus and ventral hypothalamus. The epithalamus contains choroid plexus in its roof, the psterior part of the roof elevates to form pineal gland or epiphysis • Epithalamus has two ganglionic masses called habinulae and also the nerve fibres from the telencephalon which connects with the thalamus, hypothalamus and the olfactory areas of the telencephalon PINEAL BODY: it has two functions, sensory and secretory functions. In sensory function it acts as chemoreceptor, and in later helps in facilitating the olfactory response to sex hormones THALAMUS • It acts as relay for center for transmitting olfactory and strait body impulses to thalamomedullar and thalamospinal tract • Hypothalamus: constitutes the floor of diencephalon. Anterior part of the hypothalamus contains peptic area. From the ventral part of hypothalamus projects a pouch like down growth, called infundibulun, the tip of the infundibulum bears hypophysis or pituitary gland THE DIENCEPHALON (FUNCTIONS) • THALAMUS: Integrating area for sensory input, it is also a relay and coordinating center between the corpus striatum, cerebral cortex and motor columns and contains significant portion of reticular system • EPITHALAMUS: Contains habenular nuclei, recevies fibre from olfactory area, transmits to motor areas of the brain stem, it receives information from light responsive pineal which is involoed in the regulation of circadian rhythems and reproductive cycles HYPOTHALAMUS • Regulation of internal environment, in contrast with the somatic sensory and motor functions of the tectum, it is visceral sensory and motor correlation area and integrates basic behavioural pathways requiring correlation of autonomic, endocrine and somatic functions. • It contains center for thermoregulation, control of water balance,and sleep, neurosecretory control of pituitory; Note: Fiber tracts in the walls of diencephalon connect the thalamic area MEDULLA • Derived from rhombencephalon, is a reflex coordinating center for information received from the muscles and joints and fro the lateral line organs, its floor contains a large part of the reticular formation which extends throuout the brain stem, it is a network of small many barnched neurons that receive and integrate information from the cord and many parts of the brain TECTUM • It is a thickened area of gray matter in the roof of mesencephalon above the aqueduct of sylvius( a canal in the mid brain connecting the 3rd and 4th ventricles of the brain), it is sensory and motor projection area and coordinating center in which motor activity is initiated • Corpus striatum: A mass of gray matter beneath the cortex and in front of the thalamus in each cerebral hemisphere CEREBRAL CORTEX • The furrowed outer layer of gray matter in the cerebrum of the brain associated with the higher brain functions as voluntary movement, coordination of sensory information, learneing and memory • Pons: Band of nerve fibres in the brain connecting the lobes of mid brain, medulla and cerebrum • Lamina terminalis: Thin sheet of tissues which marks rostral • Anterior commissure: It is a bundle of nerve fibres(white matter) connecting the two cerebral hemispheres across the midline and placed in the front of the columns of the fornix(junction between posterior eyelid and eye ball) • Optic recess: At the junction of the floor and anterior wall of the third ventricle, immediate above optic chiasma the ventricle presents small angular recess or diverticulum(Tubular sac branching off from a canal or cavity) • Cerebral peduncle: A bundle of myelinated neurons joining different parts of the brain • Corpus mammillare: Two rounded structures under surface of brain that form terminals of the fornix ENDOCRINE GLANDS • Ductless glands, they release their product directly into blood or lymph • On the basis of organization they can be classified as : • Discrete endocrine glands; pituitory, thyroid and pineal • Organ containg both endocrine and exocrine functions, it is kidney, gonads, and intestine, kidney contains, heterotrophic thyroid follicles, interenal and corpuscles of stanius Scattered cells with endocrine functions, they are different neuroendocrines, they are • Present in digestive tract and are called paracrine (eg. Somatostatin), they are gastrointestinal peptides, hormone or paracrine agent has not been cleared CHEMICAL CLASSIFICATION • Steroid hormones (testosterone and estradiol) • Protein (peptide hormones), eg. Insulin, and those secreted by hypophysis, thyroid, interenal tissue and pancreatic tissue • Aminoacid analogues are nor epinephrine and epinephrine PITUITORY OR HYPOPHYSIS • Same central part in endocrin signalling as in mammals, it is ectodermal in origin, mesoderm inside which supplies blood to PG • It is located below the diencephalon (hypothalamus), behind the optic chiasma and anterior to saccus vasculosus and is attached to the diencephalon by a stalk or infundibulum, short thick walled hollw infundibular stalk contains a lumen which continues with the third ventricle SHAPE AND SIZE • Oval, compressed dorsoventrally, PG has 472.9 micron length, 178 micron width, 360 micron depth in mature fish and weighs 0.5 gram, it is completely surrounded by a delicate connective tissue capsule ANATOMY OF GALAND • Microscopically it is composed of two parts • Adenohypophysis: glandular part originated from oral ectoderm • Neurohypophysis, nervous part, originated from infundibular region of the brain, both parts are present in close association GENERAL DIVISION • Proadenohypophysis or Rostral pars distalis, lying dorsal to the mesoadenohypophysis in the form of thin strip • Mesoadenohypophysis or proximal pars distalis, lying almost inbetween the rostral pars distalis and pars intermedia • Metadenohypophysis or pars intermedia, lying at the dorsal tapering end of PG • On the basis of immunocytochemistry, the cells are classified according to the hormones released by the proadenohypophysis, if they produce adrenocorticotrophic hormones, they are called ACTH cells, if they secrete thyroid stimulatimg hormones they are called thyrotrops, if they secrete FSH, then called gonado trops • The teleost hypothalamopituitory is unique amongst vertebrates, as there is direct innervation of pars distalis by neurosecretory neurons of FUNCTION OF ADENOHYPOPHYSIS OR PG • Cells of PG secret hormones, they are stored in the form of granules present in cytoplasm, the cells can be acidophilc, basophilic, or their binding affinity with ribonucleoproteins, they can be chromphobes if they repel dye or chromophilic if they stron affinity to dye PRO ADENOHYPOPHYSIS • It contains cells which secrete prolactin and corticotropin exclusively in addition to other hormones • MESOADENOHYPOPHYSIS: Proximal pars distalis contains cell which produce, gonadotropin(GtH) and growth hormone(GH), Thyrotropin cells may be in either of them META ADENOHYPOPHYSIS • Encompasses more neurohypophysial tissue than any other region • PINEAL BODY: Roof of diencephalon bears pineal body(epiphysis), it secrets melatonin, which concentrates the pigment of melanophores of fishes, inhibits gonadal development and is involved in circadian rhythems, an enzyme hydroxyindole-o-methyltransferase participates in the synthesis of melatonin NEUROHYPOPHYSIS • It comprises connective tissue, neuroglia cells (class of cells in brain and spinal cord that form the supporting structure for nearons and provide them with loosely tangled network of insulation)and nerve fibres, these nerve fibres are scattered horizontally along the dorsal part of the adenohypophysis, interspread with granular material, large irregulary shaped amorphous masses (having no definite shape) and large nuclei, these masses are called herring bodies, have intimate relation with the diencephalic neurosecretory cells HORMONES OF PITUITORY • 7 various hormones, one-cell type- one hormone concept • Cell secreting hormones not localized in a specific region but spread over in part of adenohypophysis • Hormones secreted by PG are proteins or polypeptides TWO TYPES OF HORMONES • I: those regulates the function of other endocrine glands, such hormones are called tropins or tropic hormones e.g. • Thyrotropin activates thyroid gland • Adrenocorticotropic hormones activate adrenal cortex • Gonadotropin FSH and LH (Gonads, steroids) • II: which directly regulates the specific enzymatic reactions in various body cells or tissues, the hormones are melanin hormones and melanophore stimulating hormone, Thyrotropin hormone is secreted from proadenohypophysis and stimulates activity of thyroid hormones GONADOTROPIN • Gonadotropin cells are richly found in proximal pars distalis, where they form solid rim of cells in cyprinodonts but in eels and salmonids they are present in proximal pars ditalis and rostral pars distalis, gonadotroph is under the control of gonadotropin releasing hormone, •Neurosecretory stimuli may pass along the nerve fibres piercing the lamina that separates the neuro from • adenohypophysis and penetrating into endocrine parenchyma of pars distalis • Two types of nerve fibres, A and B, Fibres of A type remain in contact with hormone producing cells, including gonadotrops, b type fibres form synaptic contact with a large granular vesicle Adenocorticotropic hormone • ACTH is secreted from the cells located between rostral pars distalis and neurohypophysis, secretion is stimulated by hypothalamus through cortitropic releasing factor,Prolactin, Released from proadeno hypophysis, growth hormone from mesoadenohypophysis, Melanocyte stimulating hormone from meta- adenohypophysis USE OF PITUITORY HORMONES IN INDUCED BREEDING/ REPRODUCTION • Have practical applications • Injection or implantation force or stimulate spawning of certain fishes of great economic value • Synthesis of sex hormones in gonad is controlled by pituitary gonadotropin • PG extract Containing, GtH taken fro sexually mature male or female, hasten spawning process, other hormone analogues are also used, ovaprim, physex leo(HCG), dry PG REPRODUCTION Three types Bisexual, Hermaphrodite (Perca, Stizostedion, Micropterus) Parthenogenic(gynogenesis; developemnt of youngones without fertilization)(Poecilia formosa) Most predominant bisexual HISTOLOGY Ovary contains supporting tissue called stroma, which contain oogonia and oocytes, oogonium (germ cell) after multiplication develops into primary oocyte, at early stages of development oogonium is large cell with a large nucleus, prominent nucleolus and chromophobic cytoplasm, on multiplication cell size reduces and chromosome number is halved HEMOPOIETIC(made of blood) EPIGONAL(come after) ORGAN(HEO) Gonads both testes and ovaries are associated with HOE and extend back to cloaca Female reproductive organ:It comprises ovary, oviduct Ovaries in relation with oviduct and transport of ova can be distinguished into three types THREE TYPES Cytovarian type: Lumen of ovary is connected with oviduct, both oviducts join to open out through genital pore, mature oocytes released by ovulation into ovarian lumen and then pass through the oviduct and goes into water through genital pore •In semicytovarian type , oocytes pass through funnel shaped transparent groove which opens into genital pore, oviduct degenerate partially or completely, ova are coelomic cavity and then carried through the pores or funnel (Notopteridae, Osteoglassidae) Gymnovarian type not continuous with oviduct, oocytes ovulated in coelomic or peritoneal cavity and then move to oviduct by cilia STIMULANTS • External environment:Light, tempertaure, rainfall, food , photperiod, salinity affect brain by mdifying activities of specific neurohormones and neurotransmitters in order to regulate secretion rate of gonadotropin releasing hormone(GnRH) and dopamine from hypothalamus • Release of PG Gonadotropin(GtH) is under dual hypothalamic control, secretion is stimulated by GnRH and inhibited by dopamine, at the end of hypothalamic-PG- gonadal axis, GtH stimulates gametogenesis and steroidogenesis gonadotropic hormones can be activated by hypophysation, PG extracts, gonadotropins HORMONES OF THE GONADS • Testes, androgens, testosterone, 11- ketotestosterone • Female produces 2 principal classes of hormones, oestrogens which include estradiol-17B and oestrone and • progestagens are 17alpha-20B- dihydroprogesterone and 17alpha- hydroxyprogesterone ENZYMES REQUIRED FOR STEROIDOGENESIS IN THE OVARY Glucose-6 phosphate dehydrogenase(G-6PDH) 3 beta-hydroxysteroid dehydrogenase(3 beta HSD) 17 beta hydroxysteroid dehydrogenase(17 beta HSD) and 20 beta hydroxy steroid dehydrogenase(20 beta HSD) VITELLOGENESIS Ovary contains numerous oocytes in different stags of development and degeneration Follicular atresia is degenerative process by which oocytes at various stages are lost even during ovulation, they do not synthesize steroid hormones and no any endocrine function VITELLOGENESIS Degenrating follicles are of two types viz corpora lutea (is a temporary endocrine structure in mammals, involved in production of estrogen and progestogen, which is needed to maintain the endometrium) and corpora atretica (being in a state of atresia; without an opening)., in former the enclosed oocytes are removed from follicles by invading granulosa cells and ingrowing theca cells Egg in the beginning is without yolk but vitellogenesis takes place later on (atresia) VITELLOGENESIS In oviparus and ovoviviparus vertebrates, blood of mature female contains calcium binding lipiphosphoprotein, vitellogenin, synthesized in liver under stimulation of female sex steroids From plasma it passes to oocytes where it gives yolk protein lipovitellin and phosvitin In Vitellogenesis accummulation of yolk substance starts, cytoplasm changes from basophilic to acidophilic state VITELLOGENESIS Three essential yolk substances, yolk vesicles, yolk globules and oil droplets Yolk vesicles contain glycoprotein, later become cortical alveoli and take part in perivitelline space (a space between the oocyte and the zona pellucida) Outer most layer Yolk globules are made of mainly lipoprotein with some carbohydrates and other substances Oil droplets contain glycerides and small amount of cholesterol On completion of vitellogenesis, movement of germinal vesicle, fusion of yolk granules and grouping of oil droplets occur •Chromosomes Becomes thread like in nucleus(leptotene stage), zygotene, pachytene, diplotene, and finally diaknesis a At this stage of development oogonium is surrounded by a single layer of follicle cells which in turn are surrounded by stromal cells, other layers are MEIOSIS MATURE OOCYTE Components; Theca cell layer, interspersed with blood vessels, basement membrane, layer of granulosa cells, , then zona radiata layer which encloses germinal vesicle TYPES OF EGGS Unfertlized eggs are opaque and heavier than water, they can be floating and non floating, adhesive or non adhesive Eggs of Common carp are adhesive and non floating, while those of Catla(light red), Labeo rohita(reddish), Labeo calbasu(bluish), Cirrhinus mrigala(brownish) are non floating and non adhesive Eggs of Clarias batrachus and Heteroneustes fossilis are adhesive, non filamentous and green in colour Eggs of Notopterous notopterous and Notopterous chitala are yellowish Eggs of Channa punctatus and Channa striatus are floating and amber in colour MALE REPRODUCTIVE ORGANS Paired structures, situated on either side, below the kidney, Have two major functions; production of spermatozoa (spermatogenesis) and production of sterods(steroidogenesis) Size of testis becomes enormous during breeding season Testis may be sac like or lobulated, rounded or triangular, nevertheless they are suspended from the dorsal body wall by mesentery call mesorchia, they are well vascularized and contain nerve fibres HISTOLOGY Each testis is enclosed in connective tissue sheath, tunica propria of connective tissue priject into the lumen forming tubes Blind end is site of primary spermatocytes Tubular structure consists of two parts, interstitial and lobular Former consists of interstitial cells, fibroblasts, blood and lymph vessels Later is distinguished into germ and somatic cells, somatic cells analogue to Leydig cells are positive for lipid and cholesterol and produces steroid hormones • Another type of cells in interstitium are sertoli cells(cyst cells) around spermatogonic cells, they supply nutrients to to the germinal cells STAGES OF SPERMATOGENESIS Stage I:Presence of only large spermatogonia, immature stage Stage II:spermatogonia multiply in testis by mitosis until many are present, then spermatogenesis starts,Spermatogonia increases in size to become a primary spermatocyte(2n)(PS) Stage III:rapid enlargement of testis volume. PS goes under Ist Meiotic division(2n to n) and gives 2 secondary spermatocytes(SS) (each with n chromosomes but duplicated) •Sex cells are at all stages of spermatogenesis. SS in turn divide(IInd meiotic division), Spermatids (n) Following II nd meiotic division each matures to spermatozoa at the end of this stage Much of cytoplasm is lost and nucleus compacts to small head with haploid DNA and acrosome with lysins (enzymes), behind the head is a midpiece which includes two centrioles and tightly coiled mitochondria which supply energy for newly formed flagellar tail that provides motility Stage IV:End of spermatogenesis process, some gonad channels are filled up with mature spermatozoa, in others spermatogenesis is continued Stage V:Spread of mature spermatozoa Stage VI: Resorption of remaining spermatozoa Fig. 5. Schematic diagram of telomere dynamics during spermatogenesis. Large circles (khaki, green, blue, and azure) and crescents (navy blue) represent nuclei of spermatogenic cells. Intermediate spermatogonia (In), type B spermatogonia (B), preleptotene spermatocytes (PL), leptotene spermatocytes (L), zygotene spermatocytes (Z), pachytene spermatocytes (P), diplotene spermatocytes (D), secondary spermatocytes (2nd), round spermatids (steps 1–8), elongating spermatids (steps 9–12), and elongated spermatids (steps 13–16). Telomeres are indicated as red dots within the nuclei. Blue and pink arrows indicate the presence of telomere extension activity and DNA replication activity, respectively.
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