Light and electron microscopic observation on the appearance of immunoreactive LHRH in perinatal rat hypothalamus

Summary The appearance and localization of LHRH were studied in the developing hypothalamus of perinatal rats using the unlabelled antibody method. By light microscopy, immunoreactive LHRH was first detected as brown dots on day 18.5 of gestation in the OVLT and on day 19.5 in the median eminence, respectively. When the median eminence was examined by the preembedding immunohistochemistry technique for electron microscopy, the occurrence of immunoreactive LHRH fibers could be demonstrated on day 18.5. These fibers were thin and very occasionally encountered near the surface of the lateral regions of the median eminence. The axoplasm contained a few immunopositive secretory granules and also extragranular immunoreactive products. With development, a gradual increase was noted both in number and size of nerve fibers with a concomitant accumulation of secretory granules within the axoplasm.A possible physiological significance of LHRH is discussed in relation to the onset of hypothalamo-hypophysial system in fetal life.     

Melanin-concentrating hormone stimulates the release of luteinizing hormone-releasing hormone and gonadotropins in the female rat acting at both median eminence and pituitary levels

The purpose of this study was to investigate whether melanin-concentrating hormone (MCH) acts directly on the median eminence and on the anterior pituitary of female rats regulating LHRH and gonadotropin release. In addition, immunohistochemistry was used to examine the density and distribution of MCH-immunoreactive fibers in the median eminence of proestrous rats. MCH-immunoreactive fibers were found in both the internal and external layers of the median eminence and in close association with hypophysial portal vessels. In the first series of in vitro experiments, median eminences and anterior pituitaries were incubated in Krebs-Ringer bicarbonate buffer containing two MCH concentrations (10(-10) and 10(-8) M). The lowest MCH concentration (10(-10) M) increased (P < 0.01) LHRH release only from proestrous median eminences. Anterior pituitaries incubated with both MCH concentrations also showed that 10(-10) M MCH increased gonadotropin release only from proestrous pituitaries. In the second series of experiments, median eminences and pituitaries from proestrous rats were incubated with graded concentrations of MCH. MCH (10(-10) and 10(-9) M) increased (P < 0.01) LHRH release from the median eminence, and only 10(-10) M MCH increased (P < 0.01) LH and FSH release from the anterior pituitary. The effect of MCH on the stimulation of both gonadotropins from proestrous pituitaries was similar to the effect produced by LHRH. Simultaneous incubation of pituitaries with MCH and LHRH did not modify LH but increased the FSH release induced by LHRH. The present results suggest that MCH could be involved in the regulation of preovulatory gonadotropin secretion.     

Relationship between neuropeptide Y and luteinizing-hormone-releasing hormone immunoreactivities in the hypothalamus and preoptic region

The purpose of this study was to examine the anatomical relationships of perikarya and fibers containing neuropeptide Y (NPY) and luteinizing-hormone-releasing hormone (LHRH) in the hypothalamus and preoptic region of female rats. In view of our previous report of stimulatory effects of estrogen on LHRH and NPY levels in the median eminence, animals were bilaterally ovariectomized and subsequently implanted subcutaneously with capsules containing estradiol benzoate in oil or vehicle. Following intracerebroventricular injection of colchicine, rats were perfused with fixative and their brains sectioned and processed for immunohistochemical visualization of NPY and LHRH in the same section and in consecutive sections. Estrogen treatment had no discernible effect on the distribution or relationship of these peptides. NPY-immunoreactive fibers were intimately associated with LHRH-labeled primary dendrites and perikarya in the medial preoptic region and horizontal limb of the diagonal band of Broca. Fibers containing NPY or LHRH overlapped extensively in the lateral palisade region of the median eminence and also in the subependymal and internal zones. The external zone of the median eminence displayed relatively less overlap of these peptide systems. LHRH-immunoreactive axons coursed among NPY-labeled perikarya in the arcuate nucleus and appeared to contact these cells. These results suggest that NPY-containing axons may influence LHRH-positive neurons at the cell body and also at the site of axon termination in the median eminence. LHRH-containing axons appear to contact NPY-immunoreactive perikarya in the arcuate nucleus and may interact with terminals in the median eminence. This arrangement may provide a mechanism for communication between NPY and LHRH neurons and for the neuroendocrine coordination of hypothalamic NPY and LHRH secretion before ovulation.     

Immunocytochemical localization of LHRH in the median eminence,infundibular stalk,and neurohypophysis

Summary The distribution of luteinizing hormone-releasing hormone (LHRH) was studied by light-microscopic immunocytochemistry in the hypothalamo-pituitary complex of humans, monkeys, ferrets, bats, and rats. LHRH-immunoreactive fibers were identified in the median eminence of all these species, but the precise location of these fibers varied. In rats, the vast majority of LHRH fibers in the median eminence was confined to the external zone. In contrast, in bats, most of the LHRH fibers were located in the internal zone. While these two species represent opposite extremes in distribution of LHRH fibers within the median eminence, intermediate conditions were found in humans, monkeys, and ferrets, as considerable numbers of fibers occurred in both internal and external zones. In addition to fibers in the median eminence, large numbers of LHRH-immunoreactive fibers were identified traversing the infundibular stalk and entering the neural lobe of the pituitary in all species examined except the rat. In rats, only occasional fibers were observed in the infundibular stalk, and they did not project into the neural lobe. However, in humans, monkeys, ferrets, and bats, groups of LHRH-immunoreactive fibers extended well into the substance of the posterior pituitary. Most of these fibers appeared to terminate near the adenohypophysis, but others coursed away from the anterior lobe and penetrated deeper portions of the neural lobe. These observations, made in several mammalian species, indicate that multiple routes may exist in the median eminence/stalk/pituitary complex for the delivery of LHRH to the anterior pituitary.     

D1 receptor mechanisms in the median eminence and their inhibitory regulation of LHRH release

D1 receptor mechanisms in the median eminence have been studied by means of immunocytochemistry using antisera against dopamine and cyclic AMP-regulated phosphoprotein-32 (DARPP-32) and tyrosine hydroxylase (TH) and by autoradiography using the iodinated analogue of the D1 receptor antagonist SCH-23390. The co-distribution of DARPP-32 and TH immunoreactivity (IR) and of DARPP-32 and luteinizing hormone releasing hormone (LHRH) IR was analysed in the median eminence by means of computer-assisted morphometry and microdensitometry. Functional analysis involved studies on the role of D1 receptors in the regulation of LH serum levels in rats treated with nicotine in the absence and presence of the D1 receptor antagonist. LH serum levels were measured by means of radioimmunoassay procedures.The results on the co-distribution of TH and DARPP-32 IR in the median eminence which were obtained both by analysis of adjacent sections and by two-colour immunocytochemistry on the same section, demonstrated a high degree of overlap of TH and DARPP-32 IR nerve terminals and tanycytes within the medial and lateral palisade zone. Furthermore, studies on LHRH and DARPP-32 IR nerve terminals and tanycytes in the median eminence with the same methodologies demonstrated preferential overlaps within the lateral palisade zone. The overlap area was about 50% of the LHRH or DARPP-32 immunoreactive area in this region. Density maps were also obtained on the distribution of LHRH and DARPP-32 immunoreactive profiles at various rostrocaudal levels. Correlation studies demonstrated a significant and positive co-distribution of LHRH and DARPP-32 immunoreactive terminals and tanycytes within the lateral palisade zone and the subependymal layer (when all DARPP-32 positive squares were considered) of the median eminence. Instead within the medial palisade zone a significant negative correlation coefficient was found, when all the LHRH positive squares were considered.In the receptor autoradiographical analysis a weak-to-moderate labelling was obtained of the part outside the mediobasal hypothalamus using the D1 receptor radioligand [¹²⁵I]SCH-23982, while hardly any labelling was found within the median eminence and the arcuate nucleus.SCH-23390 was found to counteract, in a dose-related way, the inhibitory effects of intermittent nicotine treatment on serum LH levels. The D2 receptor antagonist raclopride in a dose of 1 mg/kg did not counteract the inhibitory effects of nicotine on serum LH levels.The present immunocytochemical, autoradiographic and functional studies suggest the existence of a D1 receptor in the median eminence which can be blocked by the D1 receptor antagonist SCH-23390 in behaviourally relevant doses and which is masked under basal conditions in the male rat. It is proposed that one type of median eminence D1 receptor is located on the axon terminals, not linked to DARPP-32, and which may make possible a rapid regulation of hypothalamic hormone release, e.g. LHRH release from the nerve terminals in the lateral palisade zone as indicated in the present morphological and functional experiments. The other type of median eminence D1 receptor may be located on the tanycytes and linked to DARPP-32. It is suggested that this D1 receptor is responsible for a long-term regulation of hypothalamic hormone release inter alia LHRH release from the terminal and preterminal parts of the LHRH axons in the lateral palisade zone and subependymal layer, respectively.     

Dynamic alterations in luteinizing hormone-releasing hormone (LHRH) neuronal cell bodies and terminals of adult rats

Summary 1. The decapeptide lueteinizing hormone-releasing hormone (LHRH) is synthesized in neuronal cell bodies diffusely distributed across the basal forebrain and is secreted from neuronal terminals in the median eminence. Once secreted, LHRH enters the portal vessels and is then transported to the anterior pituitary, where it modulates the synthesis and secretion of gonadotropins, which are essential to gonadal function and reproduction.2. Because of the difficulties encountered in studying these diffusely distributed neurons, we have developed strategies which combine immunocytochemistry and computer-assisted techniques to examine individual LHRH neuronal cell bodies, as well as the entire population of LHRH neurons from the diagonal band of Broca to the mammillary bodies. In addition, we have examined LHRH neuronal terminals in the median eminence using computer-assisted imaging techniques to examine individual terminals by electron microscopy or across all rostral-caudal regions of the median eminence by light microscopy. In our most recent studies using confocal microscopy, we have examined the relationships of LHRH terminals to glial processes.3. These studies reveal a very dynamic system of LHRH neuronal cell bodies and terminals. The population of neurons in which LHRH can be detected varies as a function of time after gonadectomy, during the estrous cycle, and during the preovulatory surge of LH during the afternoon of proestrus. Dynamic changes are also observed in LHRH terminals in the median eminence as a function of time after gonadectomy and in specific rostral-caudal regions of the median eminence during the preovulatory surge of LH. Finally, confocal microscopy reveals that LHRH terminals are prevented from contacting the basal lamina of the brain by glial end-feet.4. We are currently examining the hypothesis that these relationships change as a function of endocrine milieu and, therefore, participate in the modulation of LHRH secretion. Ongoing studies focus on defining the sites of action and synergy of multiple sources of regulation of LHRH secretion and their relative importance to ensuring reproductive success.     

LHRH-like system in the brain of Xenopus laevis daud

Summary Rabbit antiserum to synthetic LHRH was used with the immunofluorescence technique to identify the LHRH-secreting neurons and their axonal pathways in the brain of Xenopus laevis. Three groups of immunoreactive neurons were identified: the first, in the telencephalon, is a paired group of cells scattered near the two telencephalic ventricles; the second group lies near the preoptic recess; the third group occurs in the ventral wall of the infundibulum. Two principal neuronal pathways were observed: Fibres originating from the dorsally located telencephalic neurons converge on the cephalic median plane where they form a single bundle behind the telencephalic furrow. This bundle descends towards the anterior border of the preoptic recess where it divides into two nerve bundles which pass on either side of the preoptic recess, run above the optic chiasma then cross the infundibular floor and finally terminate in the median eminence. The second pathway is more direct. The more ventrally located telencephalic LHRH cells give rise to this second pathway. Their axons converge with the other LHRH fibres near the lateral border of the preoptic recess. Most of the LHRH nerve fibres terminate in the median eminence although some terminate near the paired pars tuberalis. No reaction was observed after the use of antiserum absorbed with synthetic antigen.Equipe de Recherche associée C.N.R.S. n 492. This work was financed by the D.G.R.S.T., Contract n 7470046     

Ependymoneuronal specializations between LHRH fibers and cells of the cerebroventricular system

Summary Light-and electron-microscopic immunocytochemistry (LM-ICC and EM-ICC) were used to visualize luteinizing hormone-releasing hormone (LHRH) in fibres associated with ventricular ependyma and tanycytes of the median eminence. LM-ICC suggests that LHRH fibers appear to enter the third ventricle. However, with EM-ICC, LHRH fibers are in fact found within ependymal canaliculi formed by adjacent ependymal cells. The canaliculi contain other myelinated and unmyelinated axons in addition to immunoreactive LHRH fibers. Thin slips of ependymal and tanycyte processes project into the canaliculi and enclose axons to varying degrees. At the median eminence many LHRH fibers bend sharply downwards from their ventricular course and travel with tanycytic processes towards their common destination — the perivascular space of the hypophysial-portal vascular system. Here, EM-ICC reveals that LHRH fibers closely contact basal processes of tanycytes. Lateral processes from tanycytes form glioplasmic sheaths which surround some individual LHRH fibers. A few LHRH terminals contact the perivascular space directly but more often are separated from the perivascular space by intervening glia. It is hypothesized that: (1) glia of this region responds to the physiological state of the animal and may determine the degree of LHRH secretion by varying the extent of glial investment of LHRH terminals; and (2) may play a role during development by providing direction and support for LHRH fibers similar to that described for radial and other glial cells.     

The distribution of LHRH in the hypothalamus of the thirsting rat

Summary Prolonged thirst provokes an activation of the LHRH system which enables the visualization of fiber connections not seen in untreated control animals. This type of experimental stress situation increases the number of LHRH-containing fibers in the organum vasculosum laminae terminalis and in the median eminence. The number of LHRH-producing cells in the preoptic nucleus is increased and the fiber connection between this area and the median eminence can be observed. The tanycytes and the perikarya of the arcuate nucleus do not react with the antibody against LHRH. Moreover, during thirst, a network of LHRH-containing fibers is observed in the medial mammillary nucleus. The results obtained at the light microscopic level have been confirmed and supplemented by electron microscopic immunocytochemical observations.Supported by the Stiftung Volkswagenwerk and the Deutsche Forschungsgemeinschaft (Grant No. Kr 569/1) Acknowledgements. The author is greatly indebted to Dr. M. Dubois (Lab. de Physiol. de la Reprod., Nouzilly/France) for the generous gift of the LHRH antibody, and to Dr. L.A. Sternberger (Edgewood Arsenal, Maryland/USA) for supplying the peroxidase-antiperoxidase-complex. The skillful technical assistance of Mrs. H. Prien is thankfully acknowledged     

Hypothalamic contents of LHRH and catecholamines during the ovulatory cycle of the hen (Gallus domesticus)

Concentrations of LHRH, dopamine, noradrenaline and adrenaline in the anterior hypothalamus-preoptic region (AH-POR) and posterior hypothalamus-median eminence (PH-me) were determined in hens killed at different times in relation to the first ovulation of a sequence. The occurrence of a preovulatory rise in plasma LH concentration 4-6 h before the expected time of ovulation was confirmed. This rise in plasma LH was accompanied by a significant (P less than 0.01) 50% reduction in the LHRH content of the AH-POR and PH-me while the subsequent fall in plasma LH was accompanied by a restoration of the LHRH content of both regions to their former levels. Although no significant fluctuations in the hypothalamic content of either dopamine, noradrenaline or adrenaline were detected during the ovulatory cycle, significant correlations between LHRH content and catecholamine content were observed in the AH-POR (P less than 0.05) and PH-me (P less than 0.01). Thus mean levels of each amine followed the same temporal pattern as LHRH content with minimum values being observed shortly before the peak of the preovulatory surge of LH. These findings support the conclusion that an enhanced secretion of LHRH from the median eminence, possibly associated with an increased activity of catecholaminergic neurones, is a prerequisite for the preovulatory release of LH in the hen.     

Distribution of LHRH in the rat and mouse brain with special reference to the tanycytes

Summary The distribution of luteinizing hormone-releasing hormone (LHRH) was studied in the rat and mouse brain by means of light and electron microscopic immunohistochemistry using the peroxidase-antiperoxidase method. An immunoreactive product to LHRH antiserum was found near the blood vessels of the vascular organ of the lamina terminalis. In the arcuate nucleus-median eminence region, an immunoreactive material occurred bilaterally in the hypothalamic tissue around the tuberoinfundibular sulci. Electron microscopy revealed that immunoreactive fibers observed light microscopically contain numerous granules 100–130 nm in diameter. No immunoreactive product was located in the tanycytes of the median eminence, the perikarya of hypothalamic neurons, and the parenchyma of several circumventricular organs (subfornical organ, subcommissural organ, pineal organ, area postrema).Supported by grants from the Ministry of Education of Japan and the Ford Foundation     

Effect of protein deficiency on some hypothalamic and pituitary hormones in growing male lambs. An immunohistochemical study

Growing male lambs were fed with diets containing 14.0, 10.8 and 7.6% protein for 3 months to determine their effects on the content of hypothalamic LHRH and SRIH and pituitary LH and GH, using immunohistochemical methods. Lowering the concentration of dietary proteins caused marked changes in the immunoreactivity of these hormones. The immunoreactive (IR) content of LHRH stored in the median eminence was enhanced, and the proportion of LH cells and their IR content increased. Opposite effects were observed in the SRIH/GH system; IR SRIH content stored in the median eminence markedly diminished, and, although hyperplasia of GH cells was observed, their IR content was diminished. This study indicates that prolonged restrictions of protein in the diet of growing male sheep affects the immunoreactive content of the investigated hormones. It seems that they suppress LHRH/LH release and augment GH release, possibly via suppression of hypothalamic somatostatin.     

Immunocytochemistry of luteinizing hormone-releasing hormone,vasopressin, and corticotropin following deafferentation of the basal hypothalamus of the male rat brain

Summary Luteinizing hormone-releasing hormone (LHRH), vasopressin, and corticotropin systems were examined by immunocytochemical methods in male rats 2 to 20 days after deafferentation of the basal hypothalamus. Axonal degeneration of the vasopressin system (whose perikarya lie rostral to the island) and the corticotropin system (whose perikarya lie within the island) was examined and compared with the response of the LHRH system.Vasopressin immunoreactive staining was absent in the internal zone of the median eminence 10 and 20 days after deafferentation. Disruption of the efferent projections of the opiocortin system caused the loss of almost all fiber staining outside the island by the 5th postoperative day. LHRH staining in the median eminence was modestly reduced in 5 days, considerably reduced in 10 days and negligible 20 days after deafferentation. At 10 and/or 20 days after deafferentation densely stained fibers of all three systems were observed on both sides of the cut. Invasive vasopressinergic fibers reached the lateral median eminence by the 20th postoperative day.This study reports on the response of three neuropeptide systems after complete deafferentation and demonstrates that regeneration can occur across the knife cut.Supported by: NIH Grants AM-22029 and Program Project NS-15345, and USPHS grant 5T32 GM-07136-06The authors wish to express their appreciation to Ms. Barbara Dolf for her technical assistance.     

Chromatographic and biologic analysis of ME and OVLT LHRH

The luteinizing hormone (LH)-releasing activities a pooled rat organum vasculosum lamina terminalis (OVLT) and median eminence (ME) tissues were evaluated for chromatographic and biologic similarity and compared to those of synthetic decapeptide LH-releasing hormone (LHRH). The LHRH detected in these extracts appeared similar chromatographically (Sephadex G-25) to synthetic LHRH. These extracts, as well as synthetic LHRH, were also capable of stimulating dose dependent gonadotropin release form cultures rat gonadotrophs. These findings suggest a physiological role of the LHRH present in the rat OVLT in the control of gonadotropin secretion.     

In vivo and in vitro studies on the appearance of LHRH neurons in the hypothalamus of perinatal rats

Summary Ontogenetic development of LHRH-containing neurons was studied by fluorescence and enzyme immunohistochemistry in rats. In in vitro studies, the tissues of the septal-chiasmatic and mediobasal hypothalamic areas of fetal rats on day 16.5 or 18.5 of gestation were trypsinized separately for dissociation of the neural cells, and cultured for several days. Immunopositive reaction against LHRH was first detected in nerve cells derived from both areas of the hypothalamus of the fetuses on days 16.5 and 18.5 of gestation, after 8 and 6 days culture, respectively. The cells were small, and seemed to be bipolar in morphology indicating an axon and arborized dendrites. Immunopositive material occurred in the cell soma as well as in the cellular processes. In in vivo studies, immunopositive material, possibly deposited in nerve fibers, appeared first in OVLT and simultaneously in the external layer of the median eminence of fetuses on day 20.5 of gestation. The immunoreactive fibers increased in number in both parts with development, especially after birth in the median eminence. No immunopositive material was detected within any neural cell bodies nor in the cytoplasm of any ependymal cells.This work was financed by the Ministry of Education, Japan. No. 257008. We would like to thank Dr. Katsuhiko Saito (Department of Surgery, Tokushima University) for his kind advice on the preparation of the antibody used for the immunofluorescence study.     

Immunohistochemical identification of corticotropin releasing factor-containing neurons projecting to the stalk-median eminence of the rat

The site of origin of CRF-containing projections to the rat median eminence was studied with immunofluorescence for CRF in combination with the retrograde transport of True blue. After the injection of True blue into the median eminence, retrogradely-labeled CRF producing neurons were identified in the medial division of the paraventricular nucleus and the periventricular nucleus. CRF neurons in the preoptic region had no positive dye. The present findings demonstrate that CRF neurons in the paraventricular and periventricular nuclei project directly to the median eminence.     

LHRH in the human hypothalamus. Immunohistochemical mapping in normal newborn infants or in sudden death infants

The topographical distribution of neurons containing LHRH has been investigated in newborn hypothalamus using the peroxidase anti-peroxidase technique. In control subjects, LHRH immunoreactive (LHRH-IR) perikarya have been mainly observed essentially in the infundibular nucleus. The preoptic region displayed a moderate density of LHRH-IR cell bodies. High LHRH innervation was observed in the anterior hypothalamus in the lamina terminalis and in the mediobasal hypothalamus in the median eminence, and in the peri- and paraventricular regions. In sudden death infant syndrome, a comparable mapping was observed, except a low density in the mediobasal peri- and paraventricular areas.     

A comparison of neuropeptide immunocytochemistry in fluid-fixed and freeze-dried brains

Summary Immunocytochemical staining of luteinizing hormone-releasing hormone (LHRH), somatostatin, and neurophysin was compared in rat brains fixed with 1) formalin, 2) Bouin's solution, 3) freeze-dried (FD), or 4) freeze-dried + paraformaldehyde vapor perfused (FDV). The distribution of LHRH fibers was similar in all preparations; however, beads of granular reaction product often appeared finer and more numerous in the median eminence of FD- and FDV brains. Positively stained LHRH perikarya were not observed in any of the preparations. In contrast, somatostatin-immunoreactive perikarya were present in the fluid-fixed and FD brains, although few were observed in FDV brains. Somatostatin-immunoreactive fibers were present in all preparations, but appeared most numerous in the median eminence of FD brains. Staining of neurophysin-containing perikarya and fibers was similar in all preparations. These observations suggest that the FD brain can provide a suitable tissue substrate for immunocytochemistry, demonstrating staining comparable to or surpassing that of more conventional preparations. However, staining of antigens in FD brain was not uniformly successful and may depend on stereochemical characteristics of each antigen as well as properties of the primary antisera used in the staining procedure.     

Immunohistochemistry of the hypothalamic neuropeptides and anterior pituitary cells in the Japanese quail

The pars distalis of the avian adenohypophysis consists of well-defined cephalic and caudal lobes which are distinct in their cellular constituents. Immunocytochemical investigations on the pituitary hormones of the pars distalis of the Japanese quail reveal five types of secretory cells, adenocorticotropin (ACTH) cells, prolactin (PRL) cells, thyroid-stimulating hormone (TSH) cells, growth hormone GH (STH) cells, and FSH/LH (gonadotropic) cells. The ACTH cells, TSH cells, and PRL cells are restricted to the cephalic lobe, and GH (STH) cells are confined to the caudal lobe, while FSH/LH cells are distributed throughout the cephalic and caudal lobes. The median eminence of birds has distinct anterior and posterior divisions, each with different neuronal components. The avian hypophysial portal vessels also consists of two groups, anterior and posterior. The peculiar arrangement and distribution of the avian hypophysial portal vessels are possibly related to the distribution of neuropeptides in the two divisions of the median eminence and to the cytological and functional differentiation of two lobes of the pars distalis. The localization of perikarya and fibers containing luteinizing hormone releasing hormone (LHRH), somatostatin, vasotocin, mesotocin, corticotropin-releasing factor (CRF), vasoactive intestinal polypeptide (VIP), glucagon, metenkephalin, and substance P in the hypothalamus and median eminence of the Japanese quail has been investigated by means of immunohistochemistry using antisera against the respective neuropeptides. LHRH-, somatostatin-, VIP-, met-enkephalin-, and substance P-immunoreactive fibers are localized in the external layer of the anterior and posterior divisions of the median eminence, while CRF- and vasotocin-reactive fibers are demonstrated only in the external layer of the anterior division of the median eminence. The metenkephalin fibers are thicker in the anterior median eminence but the substance P fibers are more abundant in the posterior division. Mesotocin fibers occur only in the internal layer of the median eminence and neural lobe.     

Immunohistochemical localization of the luteinizing hormone releasing hormone (LHRH)-containing structures in the central nervous system of the domestic fowl

Summary The location of LHRH-containing neuronal elements was investigated in the domestic fowl by means of immunohistochemical techniques. LHRH antisera were raised against synthetic LHRH in the rabbit. The antiserum used in the present study cross-reacted with LHRH of mammalian and avian tissues.LHRH-immunoreactive perikarya are located in the preoptic and in the septal areas, and in the bulbus olfactorius; however, no LHRH-immuno-reactive perikarya were found in the tuberal part of the hypothalamus. LHRH-immunoreactive fibers course from these areas toward the median eminence mainly along the wall of the third ventricle in the form of a periventricular network. Originating from the same cell groups other fibers run caudally immediately above the optic chiasma, forming the median bundle of the tractus preoptico-infundibularis. The third bundle running toward the OVLT is named the tractus preoptico-terminalis. In addition to these structures, LHRH-containing fibers and terminals were also present in different regions of the limbic system, in the dorsal part of the hippocampus, in the tuberculum and bulbus olfactorius, as well as in the optic lobe, nuclei commissurales tectales, organon subcommissurale, periaqueductal area, and pars ventralis mesencephali.The general distribution of the LHRH system in the chicken corresponds principally to that described previously in rodents (Sétáló et al. 1976, 1978). However, some subtle differences were demonstrated between the location of the LHRH system in birds and mammals.