Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax)

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.     

Somatotropin Release-Inhibiting Factor and Galanin Innervation in the Hypothalamus and Pituitary of Seabream (Sparus aurata)

The distribution of galanin (GAL) and somatotropin-release-inhibiting-factor (SRIF) immunoreactivity in the hypothalamus and pituitary of the sea bream (Sparus aurata) was studied by immunocytochemistry. An extensive system of neurons immunoreactive with antisera to the two peptides was identified throughout the brain with staining particularly in the hypothalamus. In the hypothalamus, GAL immunoreactive perikarya were detected principally in the nucleus preopticus and nucleus tuberis. Major nerve tracts were observed to sweep down from the hypothalamic nuclei and reached the pituitary via the preoptico-hypophysial tract. Many of the fibers had varicose swellings indicating they were secretory. SRIF immunoreactivity was distributed similarly to GAL but the network of nerve fibers was less dense; no colocalization of these two peptides was seen. SRIF immunoreactive perikarya were present in the preoptic nucleus, the tuberal nucleus, and the basolateral hypothalamus. These perikarya were large and densely staining and were predominately bipolar, although some multipolar perikarya were observed. In the pituitary GAL and SRIF immunoreactivities were confined principally to the pars distalis where fibers infiltrated between growth hormone, prolactin, and adrenocorticotrophic cells. More of the fibers were immunoreactive for SRIF than for GAL. There was no immunoreaction for GAL or SRIF in any of the pituitary cells. There is thus morphological evidence for a neuroendocrine control of the pars distalis by GAL and SRIF and for a possible functional interaction between these two systems.     

Peptidergic innervation of the adrenocorticotropic hormone (ACTH)- and growth hormone (GH)-producing cells in the pars distalis of the sea bass (Dicentrarchus labrax)

Due to its unique organization, the teleost pituitary is an ideal model in which to investigate the relationship of the nervous system with the pituitary endocrine cells. A light microscope immunocytochemical study of the sea bass pituitary revealed six different neuropeptides in nerve fibers which projected into the pituitary neurohypophysis and bordered the adenohypophysial cells. Double staining showed separate nerve fibers immunoreactive for corticotropin-releasing factor (CRF), vasotocin (VT), somatostatin (SRIF), growth hormone-releasing factor (GRF), and neurotensin (NT) in the vicinity of the adrenocorticotropic hormone-releasing cells (ACTH-cells) in the rostral pars distalis (PD). In the proximal PD cholecystokinin (CCK)-, SRIF-, GRF-, and VT-immunoreactive fibers penetrated between the growth hormone-releasing cells (GH-cells). These results suggest a possible role for CCK, GRF, SRIF, and VT in the modulation of GH-cell activity, while the synthesis and/or secretion of the ACTH-cells might be affected by the release of VT, CRF, SRIF, GRF, and NT.     

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.     

Immunohistochemical localization and radioimmunoassay of corticotropin-releasing factor in the forebrain and hypophysis of the frog Rana ridibunda

The distribution of immunoreactive corticotropin-releasing hormone (CRF) in the forebrain and pituitary of the frog Rana ridibunda was studied by means of specific radioimmunoassay and immunohistochemistry using the indirect immunofluorescence and the peroxidase-antiperoxidase techniques. Relatively high concentrations of CRF-like material were found in both chiasmatic and infundibular regions of the hypothalamus (352 +/- 11 and 422 +/- 36 pg, respectively). Large amounts of CRF were also found in neurointermediate lobe extracts. Standard curves of synthetic CRF and the dilution curves for hypothalamic or neurointermediate lobe extracts were parallel. After Sephadex G-75 gel filtration, CRF-like immunoreactivity eluted in a single peak, in the same position as synthetic ovine CRF. Reversed-phase high-performance liquid chromatography of the material purified on Sephadex G-75 revealed 5 components with CRF-like immunoreactivity. The major peak had a retention time of 22 min as compared to 25.4 min for ovine CRF and 36 min for rat CRF. The detection of CRF-like immunoreactivity in neurons was facilitated by colchicine pretreatment of the frogs. The great majority of the CRF-positive perikarya were seen in the ventral region of the preoptic nucleus. A few scattered perikarya were also observed in the dorsal preoptic nucleus and in the retrochiasmatic region. Immunoreactive fibers were found in the infundibular nucleus and in various extrahypothalamic zones. CRF-containing neurons were apparently distinct from mesotocinergic and vasotocinergic neurons. A large number of immunoreactive nerve fibers were observed in the median eminence in close contact with the capillaries of the pituitary portal plexus and in the neural lobe. A few CRF-positive fibers were detected in the intermediate lobe, whereas the distal lobe was totally negative. These results show that the diencephalon and pars intermedia-nervosa of the frog contain a peptide immunologically related to mammalian CRF.     

Coexistence of tyrosine hydroxylase and growth hormone-releasing factor in a subpopulation of tubero-infundibular neurons of the rat

The distribution of growth hormone-releasing factor (GRF) and tyrosine hydroxylase (TH), a marker for dopamine neurons in this region, was analyzed in the mediobasal hypothalamus with indirect immunofluorescence histochemistry and an elution-restaining procedure. TH-like immunoreactivity was present in most GRF-immunoreactive cells in the ventral part of the arcuate nucleus (ventral A12 dopamine cell group). Dopamine cells in the dorsal A12 group and, for example, in the hypothalamic A14 cell group seemed to lack GRF peptide. Partly overlapping GRF- and TH-immunoreactive fibers in the median eminence were observed, indicating possible coexistence of the two compounds also in nerve endings close to portal vessels. These findings suggest that a subpopulation of A12 dopamine neurons produces, stores and releases a GRF-like peptide. Possible interactions of GRF and dopamine in the control of growth hormone secretion are discussed.     

Immunocytochemical localization of growth hormone-releasing hormone-like peptide in the brain of the tiger frog,Rana tigrina

Using antisera directed against carp growth hormone-releasing hormone (cGHRH), we found more extensive brain distribution of GHRH-like immunoreactive (ir) neurons in the tiger frog, Rana tigrina, than reported in previous studies, which employed mammalian GHRH antibodies. In the telencephalon, GHRH-ir perikarya were present in the pallium dorsale, pallium laterale (pars dorsalis and pars ventralis), pallium mediale, nucleus entopeduncularis, amygdala pars medialis, and in the ventral portion of the lateral preoptic area. Most GHRH somata were present in the nucleus infundibularis ventralis located around the third ventricle, extending from the region posterior to the optic chiasma to the caudal end of infundibulum. In the thalamic region, GHRH-ir perikarya occurred in the area ventrolateralis thalami, the nuclei posterocentralis thalami, and the posterolateralis thalami. The ir cell bodies in the nucleus posteroventralis tegmenti mesencephali represented the caudal-most brain GHRH perikarya. Extensive GHRH-ir fibers occurred around the nonreactive cells in the ventral preoptic area and ventral area of the infundibulum. GHRH-ir fibers were present in the outer layers of the median eminence, but not in the neural lobe or pars distalis of the pituitary gland. This wider neuroanatomical distribution of GHRH-like peptide in the brain of R. tigrina should, provide the basis for future studies to establish the exact role of GHRH-like peptides in anuran brain.     

Immunohistochemical localization of gonadotropin releasing hormones in the brain and pituitary gland of the Nile perch,Lates niloticus (Teleostei,Centropomidae)

In the present study we investigated the distribution of gonadotropin-releasing hormones (GnRH) in the brain of Lates niloticus and their association with different pituitary cell types using immunohistochemical techniques. We found immunoreactive (ir) chicken GnRH-II (cGnRH-II) and mammalian GnRH (mGnRH) as the main components of the GnRH-ir system within the brain of the Nile perch. The results indicate that mGnRH and cGnRH are localized in different neurons: mGnRH-ir perikaria were observed in the preoptic region particularly in the organum vasculosum laminae terminalis (OVLT) and in the nucleus lateralis tuberis pars posterior (NLTP) of the mediobasal hypothalamus. These cell bodies are located along a continuum of ir-fibers that could be traced from the olfactory nerve to the pituitary. mGnRH-ir fibers were detected in many parts of the brain (olfactory bulbs, ventral telencephalon, hypothalamus, and mesencephalon) and in the pituitary. cGnRH-ir cell bodies are restricted to the optic tract, but few scattered fibers could be detected in different parts of the brain. The pituitary exhibited very few cGnRH-II ir fibers, contrasting with an extensive mGnRH innervation. Moreover, mGnRH-ir fibers were targeting the three areas of the pituitary gland: rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). Double immunolabeling studies showed GnRH-ir fibers in close proximity with prolactin (PRL)- and adrenocorticotropic hormone (ACTH)-producing cells in the RPD, growth hormone (GH)-producing cells in the PPD, gonadotropins (GTHs)-producing cells in the PPD in the external border of the PI, and with somatolactin (SL)- and alpha-melanocyte stimulating hormone (alpha-MSH)-producing cells in the PI. Our results showed direct morphological evidence for a close association of GnRH-ir fibers with the different adenohypophysial cell types. These results suggest a multiple role of GnRH in the regulation of various pituitary hormones' release.     

Immunohistochemical studies on peptide neurons in the hypothalamus of the bullfrog Rana catesbeiana

The hypothalamus of the bullfrod Rana catesbeiana was examined immunohistochemically by using the indirect immunoperoxidase and the peroxidase-antiperoxidase (PAP) methods. Seven kinds of bioactive peptides were demonstrated in different neuronal somata and fibers located in the preoptic and infundibular areas of the bullfrog. The preoptic nucleus contains β-endorphin-, substance P-, and calcitonin-immunoreactive cells and fibers in its anterior part. Neuronal somata immunoreactive for somatostatin are scattered in the magnocellular preoptic nucleus. Pancreatic polypeptide (PP)-, calcitonin-, somatostatin-, gastrin-, methionine (Met)-enkephalin-, and substance P-immunoreactive neurons and fibers are found in the nucleus infundibularis ventralis. Met-enkephalin-immunoreactive cells occurs also in the ventral part of the nucleus infundibularis dorsalis.Most of the peptide neurons in the bullfrog hypothalamus are multipolar in shape, whereas some are cerebrospinal fluid (CSF)-contacting in type. This type includes substance P- and somatostatin-immunoreactive neurons in the preoptic nucleus and calcitonin-immunoreactive ones in the nucleus infundibularis ventralis. Immunoreactive substances often are gathered to the knobbed end of the CSF-contacting neuronal process and this finding supports the view that neurosecretions may be released into the CSF. Some, if not all, of the above mentioned neurons containing Met-enkephalin-, β-endorphin-, calcitonin-, gastrin-, and somatostatin-like immunoreactivities send their axons to the median eminence, where they are beaded in shape surrounding the blood capillaries, suggesting the release these bioactive substances into the hypothalamo-hypophyseal portal circulation. Possible regulation of the adenohypophyseal secretion by these neuronal peptides are proposed. In the neurohypophysis, somatostatin-, and Met-enkephalin-like immunoreactivities are localized in the nerve terminals abutting on the blood capillaries. Through the general circulation these peptides presumably exert certain unknown actions in remote targets.     

Thyrotropin-releasing hormone (TRH): Immunohistochemical distribution in tadpole and frog brain

The anatomical localization of immunoreactive TRH (IR-TRH) was demonstrated by the peroxidase-antiperoxidase technique in the brain and pituitary gland of larval and adult Rana catesheiana. In the adult frog main sites of IR-TRH are perikarya and neuronal fibers in the preoptic and infundibular nuclei of the hypothalamus and in the amygdala and diagonal band of Broca of the telencephalon. In addition, TRH-positive neuronal fibers and endings were found in the septum, pallium, and brain stem as well as in the preoptico-hypophyseal tract, the external zone of the median eminence (which matures during late larval stages), and the pars nervosa; fibers were less extensive in the pars intermedia, and were absent from the pars distalis. In early larval stages, the magnocellular nucleus of the posterior preoptic area is the main site of immunoreactive perikarya. During late stages the extensive adult pattern of distribution of IR-TRH becomes established. The study represents the first immunohistochemical demonstration of IR-TRH in larval anurans, and serves as a basis for clarification of the neuroendocrine regulation of metamorphosis.     

Galanin-like immunoreactivity in the brain of the snake Bothrops jararaca

The distribution of galanin-like immunoreactive perikarya and nerve fibers in the brain of the snake Bothrops jararaca was studied by means of immunohistochemistry using an antiserum against porcine galanin. Immunoreactive neurons were only detected in the infundibular recess nucleus. Immunoreactive fibers were found in the telencephalic, diencephalic and mesencephalic areas such as the dorsal cortex, nucleus accumbens, lamina terminalis, preoptic area, mediodorsal region of the supraoptic nucleus, subfornical organ, nucleus of the paraventricular organ, subcommisural organ and periventricular grey region. The habenula, paraventricular nucleus, infundibular recess nucleus and hypothalamo-hypophyseal tract presented denser innervations. The outer layer of the median eminence displayed numerous fibers located close to the portal system, while scarce fibers were seen in the inner median eminence and neural lobe of the hypophysis. The distribution of labelled neurons in the brain of this snake was more restricted than that described in a turtle. The wide hypothalamic and extrahypothalamic distribution of labelled fibers suggests that galanin peptides may have hypophysiotropic, neuromodulator and neurotransmitter roles in the snake B. jararaca.     

Colocalization of somatostatin receptors and growth hormone-releasing factor immunoreactivity in neurons of the rat arcuate nucleus.

Recent studies from our group have demonstrated an association of [125I]-labeled somatostatin (SRIF)-binding sites with a subpopulation of arcuate (ARC) neurons. The distribution of these cells was similar to that of growth hormone-releasing factor (GRF)-immunoreactive neurons, which led us to propose that at least some SRIF receptors may be directly localized to GRF-containing cells. To test this hypothesis, we have visualized radiolabeled SRIF-binding sites and GRF immunoreactivity (ir) in adjacent sections of the hypothalamus, by combined radioautography and immunohistochemistry. Adult male rats were sacrificed by decapitation and the brains were rapidly frozen and serially sectioned on a cryostat. Fifteen pairs of adjacent 6-microns-thick sections, taken at 100-microns intervals through the rostrocaudal extent of the ARC nucleus, were alternately processed for [125I]-SRIF radioautography and GRF immunohistochemistry. GRF-ir and [125I]-SRIF-labeled cells were mapped at each level and quantified with the aid of a camera lucida. The maps were subsequently superimposed to determine the extent of [125I]-SRIF/GRF-ir colocalization. GRF-ir perikarya [13.2 +/- 4.4 (mean +/- SE) cells per section] were mainly localized in the ventrolateral portion of the ARC nucleus and predominated within the caudal-most tier. [125I]-SRIF-labeled cells (35.6 +/- 6.5 cells per section) were more numerous, more evenly distributed, and extended further rostrally and caudally than GRF-ir cells. Superimposition of the camera lucida maps indicated that, overall, 33.5 +/- 10.8% of the GRF-ir cells were labeled with [125I]-SRIF in adjacent sections.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Immunohistochemical localization of thyrotropin-releasing hormone in the brain of carp, Cyprinus carpio

The localization of immunoreactive thyrotropin-releasing hormone (IR-TRH) in the forebrain and pituitary of carp was studied immunohistochemically using the peroxidase-antiperoxidase technique. In the hypothalamus. IR-TRH was present in the neuronal processes extending from the preoptic nucleus (NPO) to the nucleus recessus lateralis (NRL). Cell bodies appeared to be present in the inside of the medial NRL. Most of these neurons were fusiform and bipolar. Immunoreactive-beaded fibers streamed from the anterior part of the NRL toward the nucleus posterioris periventriculas and nucleus lateral tuberis pars posterioris. Vertical strands of the beaded fibers ran in the nucleus lateral tuberis pars anterioris. In the pituitary, the reaction product was found in the neural lobe, where intense immunoreactivity was evident along neural fibers entering the intermediate lobe. Staining could be detected only rarely in the anterior lobe. IR-TRH-beaded fibers were present in the olfactory stalk as well as in the caudal and inner parts of the olfactory bulb. In contrast to the high concentration of IR-TRH in the olfactory bulb, immunohistochemical data from this work indicated weak immunoreactivity in this region.     

Melanin-concentrating hormone (MCH) immunoreactive hypophysial neurosecretory system in the teleost Poecilia latipinna: light and electron microscopic study

Neurons containing immunoreactivity for melanin-concentrating hormone (MCH) were located in the brain of the teleost Poecilia latipinna by light microscopic (peroxidase antiperoxidase) and electron microscopic (immunogold) methods. Neuronal cell bodies were found in the tuberal hypothalamus, mostly within the nucleus lateralis tuberis, pars lateralis, containing MCH-immunoreactive granules up to 150 nm in diameter. From here bundles of immunoreactive fibers could be traced through the preoptic area as far forward as the olfactory bulb, and through the posterior hypothalamus up into the pretectal thalamus and midbrain. The main projection was, however, to the neurohypophysis, where MCH fibers were observed to form contacts with pituicytes, basement membranes around blood vessels, and the endocrine cells of the pars intermedia. Occasionally MCH-immunoreactive terminals were also seen near the corticotrophs of the rostral pars distalis. These results support the hypothesis that MCH may act as a systemic hormone, a central neurotransmitter, and a modulator of pituitary function.     

Growth Hormone Inhibits the Hypophysectomy-Induced Expression of Galanin in Hypothalamic Neurons of the Toad (Bufo arenarumHensel)

The expression of the neuropeptide galanin was analyzed by immunohistochemistry in magnocellular and preoptic hypothalamic neurons of toads following hypophysectomy (HPX) and pars distalectomy (PDX). There was a marked increase in the galanin-like immunoreactive expression in magnocellular hypothalamic cells 3 days after HPX, followed by a decrease to normal levels after 7 days. No changes in the expression of galanin were detected after PDX in these neurons when compared to controls. Moreover, 7 days after HPX or PDX the number of cells expressing galanin was significantly increased in the preoptic area, where numerous intraependymal cells were intensely immunoreactive. The hypophysis grafts into the hind limb in HPX or PDX animals prevented increased galanin-like immunoreactivity in preoptic cells but not in magnocellular neurons. Similarly, PDX toads given growth hormone showed no GAL-LI in the intraependymal preoptic cells. These results suggest the presence of a regional regulation of galanin expression in the preoptic area by hypophyseal hormones, in particular growth hormone.     

Chronological appearance of the different hypophysial hormones in the pituitary of sea bass larvae (Dicentrarchus labrax) during their early development: an immunocytochemical demonstration

Antisera raised against chum salmon prolactin (PRL), rainbow trout growth hormone (GH), mammalian adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH) were used to study the chronological appearance of immunoreactivity for PRL, GH, ACTH, TSH, LH, and melanocyte-stimulating hormone (MSH) in the pituitary of sea bass larvae (Dicentrarchus labrax) during the first 26 days after hatching. The anti-ACTH gives positive immunostaining in the ACTH cells as well as in the MSH cells; however, the two cell types can easily be distinguished by their different localization in the pituitary: ACTH in the rostral pars distalis, MSH in the pars intermedia. The first day after hatching cells immunoreactive for TSH, GH and ACTH could already be noticed, ACTH reacted strong in the pars intermedia but very weak in the rostral pars distalis. Cells immunopositive for PRL became visible between Days 9 and 15. With anti-LH, no positive reaction could be obtained during the first 26 days after hatching.     

Hypothalamic interconnections of somatostatin and growth hormone releasing factor neurons

Combined immunohistochemical labelling for neurons containing growth hormone (GH) releasing factor (GRF) or somatostatin and single labelling immunohistochemistry combined with Fluorogold retrograde transport labelling were used to examine whether somatostatin or GRF neurons might be reciprocally innervated. Occasional somatostatin-immunoreactive neurons in the periventricular preoptic area were found to be closely approached by GRF-immunoreactive fibres, providing possible evidence of scant innervation of somatostatin neurons by GRF cells. In contrast, many GRF-immunoreactive neurons in the arcuate nucleus appeared to have somatostatin-immunoreactive fibres closely applied to their perikarya suggesting that GRF neurons might be innervated by somatostatin cells. Combined retrograde tracing and fluorescence immunohistochemistry revealed few somatostatin-immunoreactive neurons doubly labelled following injections of Fluorogold in the basal hypothalamus. Occasional GRF-immunoreactive neurons in the basal hypothalamus were doubly labelled following PO/AHA injections of Fluorogold. Numerous somatostatin-immunoractive perikarya were observed in the periventricular arcuate region in colchicine-pretreated animals. We conclude that GH-regulating neurons do not have strong reciprocal innervation. The innervation of GRF neurons by somatostatin fibres may be derived from local somatostatin neurons.     

Galanin in the hypothalamo-hypophyseal system

In the rat median eminence immunoreactive galanin nerve fibers and terminals are present in high numbers in the external layer, and fibers in moderate numbers are seen in the internal layer. The possible sources of these galanin-containing fibers were studied by means of radioimmunoassay and immunohistochemistry in rats with different types of hypothalamic lesions. Galanin-like neurons were found both (1) in the magnocellular hypothalamo-neurohypophyseal system and (2) in the parvocellular hypothalamo-median eminence-anterior pituitary system. Cell bodies containing galanin-like immunoreactivity were localized in the supraoptic, magnocellular paraventricular and accessory magnocellular neurons with axons traversing the internal layer and terminating in the posterior pituitary. Surgical isolation of these neurons from the median eminence resulted in a marked depletion of immunoreactive galanin from the internal layer of the median eminence and the posterior pituitary. Due to the retrograde accumulation of axonally transported substances in cells proximal to the lesions, immunoreactive galanin-like cells became visible in the supraoptic and paraventricular nuclei ipsilateral to the knife cuts, and levels of galanin-like immunoreactivity increased in these nuclei 7 days after bilateral transections of the hypothalamo-hypophyseal tract. Immunoreactive galanin fibers in the external layer of the median eminence around the portal capillaries were found to be of paraventricular and arcuate nucleus origin. Bilateral paraventricular lesions caused marked (70%) reduction in levels of galanin-like immunoreactivity in the median eminence. The remaining 30% of the galanin immunoreactivity in the external layer may arise from the arcuate nucleus, which contains a great number of galanin-containing cell bodies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical localization of corticotropin-releasing factor in the brain and corticotropin-releasing factor and thyrotropin-stimulating hormone in the pituitary of chinook salmon (Oncorhynchus tshawytscha)

This report describes the distribution of corticotropin-releasing factor (CRF)-like immunoreactivity in the brain and the contiguous localization of CRF- and thyrotropin-stimulating hormone (TSH)-like immunoreactivity in the pituitary of hatchery-reared, juvenile chinook salmon (Oncorhynchus tshawytscha). Results show that CRF-immunoreactive cell bodies exist in the parvocellular and magnocellular nuclei of the preoptic area and in a ventral hypothalamic region corresponding to the nucleus lateralis tuberis. CRF-immunoreactive fibers are observed along the rostral edge of the hypothalamus, in the pituitary stalk, and in the pituitary gland. Within the pituitary, CRF-immunoreactive fibers, with terminal-like boutons, were distinguishable in the neurohypophysis, pars distalis (PD), and pars intermedia (PI). In the PD, the CRF-immunoreactive fibers terminate in regions that contain TSH-positive pituitary cells. From this study, we conclude that CRF-immunoreactive fibers travel through, and terminate in, the neurohypophysis. CRF-immunoreactive fibers were also observed to terminate within the basement membrane and within the PD and PI of the adenohypophysis. Furthermore, the contiguous localization of CRF-immunoreactive fibers and TSH-immunoreactive pituitary cells suggests that CRF may mediate release of TSH.