Immunocytochemical localization of LH-RH in the brain and pituitary of the catfish, Clarias batrachus (Linn.)

An elaborate organization of luteinizing hormone-releasing hormone (LH-RH) immunoreactive (ir) cells and fibers was encountered in the olfactory system of Clarias batrachus. In addition to the ir structures in the olfactory nerve, peripheral area of the olfactory bulb, and the medial olfactory tract (MOT), ir cells and fibers were prominently seen in the lamellae of the olfactory organ. Perikarya showing varying degrees of intensity of immunoreaction were observed along the base of the forebrain in the nucleus preopticus basalis lateralis, nucleus preopticus periventricularis, nucleus preopticus, nucleus lateralis tuberis pars posterior, and the pituitary. Some cells were also noticed in the midbrain tegmentum. A well-defined system of ir fibers from the MOT penetrated the telencephalon and curved dorsocaudally into the pars supracommissuralis above the anterior commissure (AC); while some fibers decussate in the AC, others extended posteriorly into the diencephalon. A fairly dense network of beaded ir fibers was seen in the basal forebrain, conspicuous around the organum vasculosum laminae terminalis and caudally traceable as far as the neurohypophysis; some immunostained fibers appear to be directly contacting with the cells of the proximal pars distalis. Fibers were also witnessed in the optic chiasma and in the inner plexiform layer of the retina. Solitary fibers were noticed in certain circumscribed telencephalic areas, caudal hypothalamus, posterior commissure, midbrain tegmentum, cerebellum, and ventral medulla oblongata. The highly organized LH-RH containing system in C. batrachus is indicative of its elaborate role in synchronization of the reproductive processes and the environmental cues.     

Glucagon-like immunoreactivity in the forebrain and pituitary of the teleost, Clarias batrachus (Linn.)

The organization of glucagon-like immunoreactivity (GLI) in the olfactory system, forebrain, and pituitary was investigated in the teleost Clarias batrachus. Weak to moderate GLI was seen in some olfactory receptor neurons and basal cells of the olfactory epithelium. Intense GLI was seen in the olfactory nerve fascicles that ran caudally to the bulb, spread over in the olfactory nerve layer, and profusely branched in the glomerular layer to form tufts organized as spherical neuropils; some of the immunoreactive fibers seem to closely enfold the mitral cells. In the inner cell layer of the bulb, some granule cells were intensely immunoreactive. Although there were thick fascicles of immunoreactive fibers in the medial olfactory tracts (MOT), the lateral olfactory tracts were generally devoid of immunoreactivity. Immunoreactive fibers in the medial olfactory tract penetrated into the telencephalon from its rostral pole and entered into the area ventralis telencephali/pars ventralis where the compact fiber bundles loosen somewhat and course dorsocaudally into the area ventralis telencephali/pars supracommissuralis just above the anterior commissure. While some immunoreactive fibers decussated in the anterior commissure, fine fibers were seen in the commissure of Goldstein. Isolated immunoreactive fibers of the medial olfactory tract were traced laterally into the area dorsalis telencephali/pars lateralis ventralis and mediodorsally into the area dorsalis telencephali/pars medialis. However, a major component of the MOT continued dorsocaudally into the thalamus and terminated in the habenula. Two immunoreactive neuronal groups and some isolated cells were seen in the periventricular region of the thalamus. Although nucleus preopticus showed no immunoreactivity, some neurons of the nucleus lateralis tuberis displayed moderate GLI. Several immunoreactive cells were seen in the pars intermedia of the pituitary gland; few were encountered in the rostral pars distalis and proximal pars distalis. Immunoreactive fibers were seen throughout the pituitary gland.     

Beta-endorphin-like immunoreactivity in the forebrain and pituitary of the teleost Clarias batrachus (Linn.)

The organization of beta-endorphin-like immunoreactivity in the olfactory system, forebrain, and pituitary of the teleost Clarias batrachus was investigated. Immunoreactivity was prominently seen in the sensory neurons and basal cells in the olfactory epithelium and in some cells in the periphery and center (granule cells) of the olfactory bulb. Immunoreactive fibers in the olfactory nerve enter the olfactory nerve layer of the olfactory bulb and branch profusely to form tufts organized as spherical neuropils in the glomerular layer. While fascicles of immunoreactive fibers were seen in the medial olfactory tracts, the lateral olfactory tracts showed individual immunoreactive fibers. Immunoreactive fibers in the medial olfactory tract extend into the telencephalon and form terminal fields in discrete telencephalic and preoptic areas; some immunoreactive fibers decussate in the anterior commissure, while others pass into the thalamus. While neurons of the nucleus lateralis tuberis revealed weak immunoreactivity, densely staining somata were seen at discrete sites along the wall of the third ventricle. Although a large population of immunoreactive cells was seen in the pars intermedia of the pituitary gland, few were seen in the rostral pars distalis and proximal pars distalis; immunoreactive fibers were seen throughout the pituitary gland.     

Seasonal changes in beta-endorphin-like immunoreactivity in the olfactory system of the female catfish, Clarias batrachus (Linn)

In the olfactory system of the catfish Clarias batrachus, beta-endorphin-like immunoreactivity was seen in several olfactory receptor neurons (ORN) and their fiber projections extending caudally over the olfactory nerve to the olfactory bulb (OB). With beta-endorphin-like immunoreactivity as a cellular marker, the olfactory system in the female fish was investigated at different stages of its annual reproductive cycle. The reproductive cycle of the fish is divisible into four distinct phases: preparatory (February-April), prespawning (May-June), spawning (July-August), and postspawning (September-January). The gonosomatic index and the immunocytochemical profile of beta-endorphin-like immunoreactivity showed distinct changes as the fish progressed from one phase to another. In the preparatory phase, limited immunoreactivity was seen in the periphery of the bulb. However, the immunoreactivity showed a robust increase as the immunolabeled fibers extended progressively deeper into the bulb toward the mitral cell layer during the prespawning and spawning phases. Significant reduction in the immunoreactivity was noticed in the olfactory nerve layer of the fish in the postspawning phase. Several granule cells showed poor to moderate immunoreactivity during the spawning phase, although no immunoreactivity was seen in the inner cell layer during the rest of the year. The beta-endorphin-like immunoreactivity in the ORN also showed season-related changes, although these were less distinct. Whereas weak immunoreactivity confined to a few ORN was noticed in the fish collected in the preparatory phase, those in the prespawning phase showed conspicuous augmentation in immunoreactivity. During the spawning phase, the sensory layer of the olfactory epithelium showed reduced, homogenous immunoreactivity. In the postspawning phase, several ORN revealed distinct granular immunoreactivity, suggesting possibilities of de novo synthesis. These annual cyclic changes in the beta-endorphin-like immunoreactivity were consistently observed over a 30-month study period that spanned three consecutive spawning phases. The results suggest that the beta-endorphin-containing ORN, their fiber projections to the OB, and several granule cells in the inner cell layer may be involved in the processing of reproduction/reproductive behavior-related signals.     

The response of nucleus preopticus neurosecretory cells to ovarian pressure in the teleost, Clarias batrachus (Linn.)

The changes undergone by the neurosecretory cells of the nucleus preopticus (NPO) were investigated histologically and immunocytochemically following pressure stimulation of the ovaries in the teleost, Clarias batrachus. Application of intraovarian pressure of 10 mm Hg revealed marked hypertrophy of the cells, while pressures of 20 and 30 mm Hg resulted in hypertrophy and exhaustion of the cells. No changes were observed when the treatment was preceded by transection of the spinal cord. The results suggest the existence of a pressure-excitable neural pathway from the ovary capable of eliciting profound cytological changes in the NPO.     

beta-endorphin and gonadotropin-releasing hormone in the forebrain and pituitary of the female catfish, Clarias batrachus: double-immunolabeling study

The role of beta-endorphin in modulating the gonadotropic action of gonadotropin-releasing hormone (GnRH) is well established in mammals. Although the information from teleosts also suggests that endogenous opioids modulate GnRH secretion and influence gonadotropic hormone release, the anatomical substrate in which opiate peptides and GnRH may interact has not been studied. Herein we describe the mammalian GnRH- and beta-endorphin-like immunoreactivities in the olfactory system, forebrain, and pituitary of the teleost, Clarias batrachus, using the double immunocytochemical method. While several olfactory receptor neurons showed beta-endorphin- or GnRH-like immunoreactivity, some neurons with dual immunoreactivities were also seen. GnRH- and/or beta-endorphin-like immunolabeled fascicles were seen in the olfactory nerves as they run caudally to the olfactory bulb and spread in the periphery. Several fascicles branch profusely to form tufts organized as spherical neuropils in the glomerular layer. Frequently, the innervation of the glomeruli showed a distinct pattern. While the fascicles on the medial side showed a predominance of beta-endorphin-like fibers, the majority of the fascicles on the lateral side of the bulb showed dual immunoreactivities. Several GnRH- and beta-endorphin-like immunoreactive fibers were seen in the medial olfactory tract as it extends through the telencephalon in the area ventralis telencephali/pars supracommissuralis; individual fibers with dual staining were also seen. The nucleus lateralis tuberis showed beta-endorphin- as well as GnRH-like immunoreactive neurons. While GnRH-containing cells were seen in the proximal pars distalis and pars intermedia, beta-endorphin-like cells were located throughout the pituitary; some cells in the pars intermedia showed dual immunoreactivity. The high degree of overlapping suggests the possibility of profound interplay between GnRH- and beta-endorphin-like immunoreactive systems at different levels of the neuraxis.     

Involvement of neuropeptide Y Y1 receptors in the regulation of LH and GH cells in the pituitary of the catfish, Clarias batrachus: an immunocytochemical study

Although neuropeptide Y (NPY) has been known to influence the release of luteinizing hormone (LH) and growth hormone (GH) from the pituitary gland of teleosts, the NPY receptor subtypes involved in the regulatory processes have not been fully defined. An attempt has been made to study the involvement of NPY Y1 receptors, if any, in mediating the NPY-triggered stimulation of the LH and GH secreting cells in the pituitary of the catfish, Clarias batrachus. NPY (10 ng/g of body wt) or NPY Y1 receptor agonist (Leu(31)-Pro(34)-NPY, 3 ng/g of body wt) were administered by the intracranial route and the responses by the LH and GH cells in the pituitary were investigated with the help of immunocytochemistry. Both the agents caused a highly significant decrease (P<0.001) in the immunoreactivity of LH cells. However, the treatment with NPY Y1 receptor antagonist (BIBP 3226, 1 ng/g of body wt), prior to NPY or NPY Y1 agonist, blocked the response by the LH cells; the profile of the cells was quite similar to that of the saline-injected control fish. GH cells also showed similar pattern of responses to these treatments. While NPY and NPY Y1 receptor agonist caused significant (P<0.001) decrease in the GH immunoreactivity, pretreatment with the NPY Y1 antagonist blocked the response. These results suggest that NPY may exercise a secretogogue-like action on the LH and GH cells in the pituitary of C. batrachus via NPY Y1 receptors.     

Seasonal and circadian time-dependent dual action of GH on somatic growth and ovarian development in the Asian catfish, Clarias batrachus (Linn.): role of temperature

Effect of growth hormone (GH), injected either at the morning or evening, on the somatic and ovarian development of the Asian catfish, Clarias batrachus was studied during the late quiescence and early recrudescence phase of the reproductive cycle. GH treatment during the late quiescence phase (December-January; 11L: 13D, average water temperature 16.2 ± 1°C) failed to exert any impact on the somatic or ovarian development, except that it increased plasma testosterone marginally, and decreased hepatic level of triglycerides (TG); while during the early recrudescence phase (March-April; 12.4L: 11.20D; average water temperature—28.4 ± 2 °C), GH had significant circadian time-dependent effect on somatic and ovarian development. GH injection at morning stimulated ovarian growth and development, as was evident from the dose-dependent significant increase in ovarian weight, gonadosomatic index, plasma levels of testosterone and estradiol-17β following GH treatment. The ovarian morphology also revealed the advancement in follicular development in GH treated fish. GH also induced remarkable increase in ovarian levels of TG, free cholesterol (CF) and phospholipids (PL) with concomitant declines in their hepatic levels. However, evening hour GH injection provoked appreciable increase in body weight without having any significant impact on ovarian weight and GSI. Few oocytes in the ovary of evening hour GH treated fish exhibited advanced stages of development, but number of such advanced stage oocytes was significantly much less than the morning hour GH injected fish. Ovarian TG and PL remained unchanged, while their hepatic levels were increased. The temporal synergism between GH and other intrinsic factors regulating body growth and gonadal development may be suggested herewith to be considered prior to administration of GH in fishes. This study has immense practical use in aquaculture.     

GnRH-LH secreting cells axis in the pituitary of the teleost Clarias batrachus responds to neuropeptide Y treatment: an immunocytochemical study

An attempt has been made to immunocytochemically visualize the effect of neuropeptide Y (NPY) on the GnRH fibers and luteinizing hormone (LH) secreting cells in the pituitary of the catfish, Clarias batrachus. Two hours following the intracranial administration of NPY at the dose of 20 ng/g body wt, a significant increase in the area occupied by the GnRH-like immunoreactive fibers, and population and size of the LH cells was observed. The treatment also resulted in considerable augmentation of immunoreactivity in the LH cells. Double immunolabeling revealed NPY fibers directly terminating on the LH cells. The results suggest that NPY may (a) stimulate some GnRH containing hypophysiotropic neuronal group in the brain, (b) promote anterograde transport of GnRH to the pituitary gland, and (c) up-regulate the LH cells.     

Changes in hypothalamic catecholamine levels in relation to season, ovariectomy, and 17 beta-estradiol replacement in the catfish, Clarias batrachus (L.)

In female Clarias batrachus, hypothalamic levels of noradrenaline (NA) and dopamine (DA) exhibited seasonal changes during different phases of the annual reproductive cycle. The NA level was high during gonadal recrudescence (prespawning and spawning phases) and low during gonadal quiescence (postspawning and resting phases). A reverse trend was noticed in the DA level. After 3 weeks of ovariectomy (Ovx), the catecholamine (CA) levels were elevated significantly in the preparatory, prespawning, and spawning phases and were unaltered in the postspawning season. Administration of 17 beta-estradiol (E2, 1.0 microgram/g BW) to 3-week Ovx fish resulted in both seasonal and differential effects on the CA levels. The NA level was significantly elevated in the preparatory phase, decreased in the prespawning and spawning phases, and remained unaltered in the postspawning season. The DA level was restored by the steroid treatment in the preparatory phase, but registered a significant elevation in the prespawning and spawning phases. In the prespawning phase, Ovx induced a significant elevation of the hypothalamic NA level after 2, 3, and 4 weeks, but was significantly low after 5 weeks. The DA level registered a significant increase after 2, 3, and 5 weeks of Ovx. Administration of E2 to 3-week Ovx fish elicited dose-dependent responses on CA levels. The administration of a low dose of E2 (0.05 microgram) caused a significant elevation of the NA level, while the 0.1 microgram dose did not alter the amine level in comparison to that of the Ovx vehicle group. The higher doses (0.5 and 1.0 microgram) of E2, however, decreased the NA level significantly below that of the sham vehicle and Ovx vehicle groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in hypothalamic monoamine oxidase activity in relation to season, ovariectomy, and 17 beta-estradiol administration in intact and ovariectomized catfish, Clarias batrachus (L.)

Cyclic changes in hypothalamic monoamine oxidase (MAO) activity were noted during the annual ovarian cycle of Clarias batrachus, with a high level in the preparatory phase and a low level in the spawning phase. Administration of 17 beta-estradiol (E2) daily for 3 days induced both season- and dose-dependent responses in enzyme activity. In the preparatory phase, 0.05, 0.1, and 0.5 microgram/g doses of E2 enhanced enzyme activity in a dose-dependent manner, with significant changes being observed in the latter two dose groups. Administration of 1.0 and 10.0 micrograms/g doses decreased enzyme activity, with a significant difference elicited by the latter dose. In the spawning phase, enzyme activity was significantly elevated by 0.05 and 0.1 microgram/g doses. MAO activity decreased insignificantly in the 0.5 and 1.0 microgram/g groups and significantly in the 10.0 micrograms/g E2 group. Enzyme activity decreased significantly 2, 3, and 4 weeks after ovariectomy (prespawning phase), in a time-dependent manner, and increased after 5 weeks (not significantly different from the sham control value) and 6 weeks. Administration of E2 to 3-week ovariectomized fish elicited dose-dependent effects on MAO activity. E2 injections at 0.05 and 0.1 microgram/g doses not only restored the ovariectomy-induced decrease, but also elevated enzyme activity significantly compared with the sham + vehicle control. The higher doses (0.5 and 1.0 microgram/g) were ineffective in restoring enzyme activity, which decreased significantly in the 1.0 microgram/g group compared with ovariectomy and sham control values.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitric oxide: An autocrine regulator of Leydig cell steroidogenesis in the Asian catfish, Clarias batrachus

Nitric oxide has been recognized as an important inter- and intra-cellular modulator of testicular steroidogenesis in higher vertebrates with conflicting results. Moreover, its role in regulation of testicular steroidogenesis in ectothermic vertebrates is non-existent. The present study was, therefore, undertaken to examine whether Leydig cells of a freshwater catfish, Clarias batrachus produce nitric oxide (NO), if so, does it regulate its steroidogenic activity? The purified Leydig cells were stained histochemically for NADPH-diaphorase (NADPH-d) activity, and immunocytochemically for neuronal and inducible nitric oxide synthase (nNOS and iNOS) like molecules. Leydig cells were also incubated with NOS inhibitor, N-nitro-l-arginine methyl ester (l-NAME), and NO donor, sodium nitroprusside (SNP). NO and testosterone released in incubation medium were analyzed. A distinct positive NAPDH-d staining was observed in Leydig cells. These cells also exhibited immunoprecipitation of variable intensity with nNOS and iNOS antibodies. Further, l-NAME treatment caused significant suppression in NO production and elevation in testosterone secretion by Leydig cells. On the contrary, exposure of Leydig cells to SNP resulted in increased NO production with concomitant decline in testosterone level. Thus, the present study reports NO production by Leydig cells in fish for the first time, which appears to inhibit its own androgen production.     

Immunocytochemical evidence for peptidergic (GnRH) and dopaminergic innervation of the gonadotropic cells in the pituitary of the African catfish, Clarias gariepinus

The proximal pars distalis (PPD) of the pituitary of the African catfish, Clarias gariepinus, was studied with immunocytochemical methods at the ultrastructural level. Anti-serum raised against synthetic mammalian luteinizing hormone-releasing hormone (LHRH) was applied on Lowicryl-embedded pituitaries and the antigenic sites were visualized with protein A-gold. In nerve fibers contacting the gonadotropic cells, granulated vesicles with a diameter of 90-120 nm were labeled after this procedure, whereas the glandular cells were not labeled. For the immunocytochemical demonstration of dopaminergic fibers, the preembedding method was performed on Vibratome sections, using highly specific antibodies against dopamine. Immunoreactivity was restricted to fibers containing granulated vesicles with a diameter of approximately 80 nm and terminating on gonadotropic cells. The present data support the results of earlier in vivo and in vitro studies on the catfish pituitary, indicating a dual neuroendocrine regulation of the gonadotropic cells.     

Diurnal variations in prolactin secretion and serum Na+ and K+ concentrations in the freshwater catfish. Clarias batrachus

Variations in the pituitary gland and blood serum prolactin levels along with Na+ and K+ ions concentrations during 24 hr period were studied in Clarias batrachus. Prolactin secretion exhibited clear diurnal rhythm. Peaks in the prolactin content of pituitary and serum were recorded at early photophase 06.00 and 09.00 hr respectively. Troughs in the both pituitary and serum were noticed during mid darkphase at zero hour (24.00 hr). The concentration of serum Na+ and K+ ions also demonstrated marked diurnal changes but unlike prolactin levels, the highest cation concentrations were encountered during mid darkphase and the lowest at the middle of photophase. Apparently, there was no relationship between changes in prolactin secretion and Na+ and K+ ions concentrations.     

Central GABAergic innervation of neurointermediate pituitary lobe: biochemical and immunocytochemical study in the rat.

Activity of glutamic acid decarboxylase GluDCase, the biosynthetic enzyme of gamma-aminobutyric acid (GABA) was measured in low-speed homogenate supernatant of the neural and intermediate (neurointermediate) lobe (28--30 pmol of CO2 per microgram of protein per hr) and of the anterior lobe (2--4 pmol of CO2 per microgram of protein per hr). In the neurointermediate lobe, stalk transection reduced the GluDCase activity by more than 95%. By using an antiserum to rat brain GluDCase and the unlabeled antibody--peroxidase method of Sternberger, GluDCase immunoreactivity was localized in many terminals within the neurointermediate lobe of the hypophysis. In pars intermedia, immunoreactive terminals occurred in apposition to secretory cells and to glial cells and were near nonimmunoreactive axonal profiles; in pars neuralis they were apposed to pituicytes and to unlabeled axons including the neurosecretory terminals and were along fenestrated portal capillaries. GluDCase immunoreactive axons terminals exhibited diverse morphological features and would not have been identified as a distinct population without the GluDCase antiserum. No GluDCase-immunoreactivity was found in the anterior pituitary lobe. Stalk transection abolished GluDCase immunoreactivity in the neurointermediate lobe. These data provide biochemical and morphological evidence for a central GABAergic innervation of neural and intermediate lobes of the hypophysis.     

Central GABAergic innervation of the pituitary in goldfish: a radioautographic and immunocytochemical study at the electron microscope level

The GABAergic innervation of the goldfish pituitary was studied at the light and electron microscope levels by means of radioautography after in vitro incubation in tritiated gamma-aminobutyric acid (GABA) and immunocytochemistry using antibodies against GABA. Following incubation of pituitary fragments in a medium containing tritiated GABA, a selective uptake of the tracer was observed within the digitations of the neurohypophysis. Silver grain clusters were also observed in the adenohypophyseal tissue. At the electron microscope level, this uptake was found to correspond to nerve endings containing small clear and dense-core vesicles. These labeled profiles were located mainly in neurohypophyseal digitations in close apposition with the basement membrane separating the neurohypophysis from the adenohypophysis. However, they were also encountered in direct contact with most adenohypophyseal cell types in the different lobes. These results were confirmed by immunocytochemical data demonstrating the presence of numerous GABA immunoreactive fibers in both anterior and neurointermediate lobes. They were found either in the digitations of the neurohypophysis or in the adenohypophysis in direct contact with the glandular cells with a distribution and an ultrastructural aspect similar to those observed by radioautography. These data demonstrate that the pituitary of teleosts receives a massive GABAergic innervation. Although physiological data providing a functional significance for such an innervation are lacking, the present study suggests that, as already documented in mammals, GABA may be involved in the neuroendocrine regulation of pituitary functions in teleosts.     

Purification of gonadotropic hormone from the pituitary of the African catfish, Clarias gariepinus (Burchell), and the development of a homologous radioimmunoassay

Glycoprotein gonadotropic hormone (GTH) was purified from 2000 pituitaries of male and female African catfish, Clarias gariepinus. The first step was chromatography on concanavalin A-Sepharose followed by filtration on Ultrogel Aca 54, chromatography on DEAE-cellulose, and filtration on Ultrogel Aca 54, respectively. Finally, the purified fractions were analyzed by polyacrylamide gel electrophoresis. The gonadotropic activity in the different fractions was characterized using two tests: the radioimmunoassay for carp gonadotropin-beta subunit was used to quantify the immunoreactive GTH and a cAMP accumulation test was applied to measure the GTH biological activity. The purified glycoprotein GTH was used to raise antibodies and to develop a radioimmunoassay. This resulted in an assay with a variation between assays of approximately 4%, a precision of 4-8%, and an accuracy of 4-8%. GTH levels can be measured over a range of 0.8 to 12.5 ng/ml.     

Reproduction phase-related expression of GnRH-like immunoreactivity in the olfactory receptor neurons,their projections to the olfactory bulb and in the nervus terminalis in the female Indian major carp Cirrhinus mrigala (Ham.)

The reproductive biology of the Indian major carp Cirrhinus mrigala is tightly synchronized with the seasonal changes in the environment. While the ovaries show growth from February through June, the fish spawn in July-August to coincide with the monsoon; thereafter the fish pass into the postspawning and resting phases. We investigated the pattern of GnRH immunoreactivity in the olfactory system at regular intervals extending over a period of 35 months. Although no signal was detected in the olfactory organ of fish collected from April through February following year, distinct GnRH-like immunoreactivity appeared in the fish collected in March. Intense immunoreactivity was noticed in several olfactory receptor neurons (ORNs) and their axonal fibers as they extend over the olfactory nerve, spread in the periphery of the olfactory bulb (OB), and terminate in the glomerular layer. Strong immunoreactivity was seen in some fascicles of the medial olfactory tracts extending from the OB to the telencephalon. Some neurons of the ganglion cells of nervus terminalis showed GnRH immunostaining during March; no immunoreactivity was detected at other times of the year.Plexus of GnRH immunoreactive fibers extending throughout the bulb represented a different component of the olfactory system; the fiber density showed a seasonal pattern that could be related to the status of gonadal maturity. While it was highest in the prespawning phase, significant reduction in the fiber density was noticed in the fish of spawning and the following regressive phases. Taken together the data suggest that the GnRH in the olfactory system of C. mrigala may play a major role in translation of the environmental cues and influence the downstream signals leading to the stimulation of the brain-pituitary-ovary axis.     

Localization of the neuronal form of nitric oxide synthase (bNOS) in the diencephalon and pituitary gland of the catfish,Synodontis multipunctatus: an immunocytochemical study

The distribution of the neuronal form of nitric oxide synthase (bNOS) was investigated in the brain and pituitary gland of the catfish, Synodontis multipunctatus. Immunoreactive neurons were found mainly in the nucleus praeopticus periventricularis, the parvocellular and supraoptic subdivisions of the nucleus praeopticus, the nucleus recessus lateralis and the nucleus recessus posterioris. In addition, some scattered bNOS labeled somata were noted in the dorsal hypothalamic area. A few positive cells in the adenohypophysis and some reactive fibers in the pituitary stalk were also seen. Our results are compatible with the notion that the cells expressing bNOS in the diencephalon and hypophysis are involved in the control of hormone regulation. Moreover, the presence of bNOS positive cells in the rostral pars distalis of the pituitary gland supports a role of nitric oxide in osmoregulation.     

Maturational gonadotropin from the African catfish, Clarias gariepinus: purification, characterization, localization, and biological activity.

A gonadotropic hormone of the African catfish, Clarias gariepinus, was was purified and chemically characterized. Its biological activity was tested and its localization in the gonadotropic cells of the pituitary demonstrated. An ethanolic extract of 500 pituitaries of adult male and female African catfish was subjected to ion-exchange chromatography on DE-52. The 31- to 38-kDa fraction was further purified on Sephadex G-75. On rpHPLC over an ODS 120T column two major components appeared as single bands after SDS-PAGE. From the amino acid composition and sequence analysis of these fractions, compared with those of salmon and carp GTH II-alpha and salmon GTH II-beta it was concluded that they represent catfish GTH alpha- and II-beta-subunits. The biological activity of the complete hormone (the 31- to 38-kDa fraction from the G-75 column) was tested on the production of 11 beta-hydroxyandrostenedione and 17 alpha-hydroxy-20 beta-dihydroprogesterone by catfish testis in vitro. Polyclonal antibodies were raised against the purified beta-subunit. Immunocytochemical study using these showed them to bind specifically to hypophysial gonadotropic cells. To date only one form of GTH has been demonstrated in the African catfish.