Hypothalamo-hypophysial neurosecretory system of the teleost Trichogaster fasciatus (Bloch & Schneider) with a note on it's vascularization

The hypothalamo-hypophysial neurosecretory (HN) complex of Trichogaster fasciatus is described with the help of in situ staining technique and tissue sections. The neurons of the nucleus preopticus (NPO) give rise to fine neurosecretory axons which form the left and right main tracts. The bulk of the tracts come laterally and enter the middle portion of the neurohypophysis. However, some of them spread out and penetrate the rostral neurohypophysis as well. Hypophysial artery contributes to the formation of primary capillary plexus (PCP) which extends from the subterminal region to the extremity of the anterior neurohypophysis. Structurally, the subterminal region and the anterior neurphoyophysis can be compared to the median eminence (ME) of tetrapods as it is differentiated into ependymal, fibrous and reticular layers. Also, these areas have aboundant neurosecretory and silver positive axons suggesting the possibility of direct transmission of neurohormones into the blood.     

Anterior and posterior groups of portal vessels in the avian pituitary: incidence in forty nine species.

The hypophyseal portal vessels were studied in forty nine species of birds. The primary capillary plexus in the median eminence is single or divided into an anterior and a posterior plexus. Irrespective of whether the primary capillary plexus is single or divided, distinct, non-interconnected anterior and posterior groups of portal vessels are present in all the species investigated. The anterior group of portal vessels originates in the anterior region of the median eminence and breaks up into capillaries in the cephalic lobe of the pars distalis; the posterior group of portal vessels originates in the posterior region of the median eminence and breaks up into capillaries in the caudal lobe of the pars distalis. This type of regional distribution of portal vessels appears to be of general occurrence in the avian pituitary. The median eminence in the species investigated shows an AF-positive anterior region and an AF-negative posterior region. The pars distalis is differentiated into histologically distinct cephalic and caudal lobes. The arrangement of the portal vessels into anterior and posterior groups provides morphological basis for the view that the functions of the cephalic lobe may be controlled by the anterior median eminence, whereas those of the caudal lobe may be controlled by the posterior median eminence. However, experimental data available to date do not suggest a physiological significance to the widespread incidence of the regional distribution of portal vessels in the avian pituitary.     

Fine structure of the median eminence and the pars nervosa of the bullfrog,Rana catesbeiana

Summary The hypothalamic neurosecretory system of the bullfrog, Rana catesbeiana, was studied with light- and electron microscopy. The median eminence is roughly divided into two portions. The upper portion mostly consists of ependymal cells, glial cells and preoptico-hypophysial nerve tract, whereas in the lower portion, neurosecretory axons, glial cells, processes of glial and ependymal cells, and fine blood vessels of the hypothalamic portal vein are located. A part of the neurosecretory axons of the preoptico-hypophysial tract proceeds to the lower portion of the median eminence. These axons are arranged perpendicularly to the capillaries of the hypothalamic portal vein. The glial cells are densely located in the area of the median eminence where neurosecretory material is abundant. The neurosecretory material in the neurosecretory cells, their axons, the median eminence and the pars nervosa of the bullfrog shows a positive reaction to PAS treatment.The neurohemal area of the median eminence is occupied by many neurosecretory and non-neurosecretory axons, containing neurosecretory granules and/or synaptic vesicles. The axonal portions with the synaptic vesicles which are considered to be the nerve endings abut on the capillaries of the portal system. The size of synaptic vesicles in the axon terminals containing few neurosecretory granules is larger than those in the endings with many neurosecretory granules. Infrequently glial and ependymal processes are interposed between the nerve endings and the capillary wall.In the hilar region of the infundibulum, synapses are frequently observed between the thin fibers with or without neurosecretory granules and dendrites of non-neurosecretory neurons. The probable functions of these synapses are briefly discussed on the basis of our findings. Both in the hilar region of the infundibulum and in the pars nervosa, electron-dense neurosecretory granules of two different sizes were observed. The median eminence contains only one type of granules.The fine structure of the pars nervosa shows similar structures to those of the median eminence. Both in the median eminence and the pars nervosa, the fenestrated endothelium of the capillaries was frequently observed. The thick perivascular connective tissue space containing fibroblasts and collagen fibrils was observed both in the median eminence and the pars nervosa. Vesicles in the cytoplasm of the endothelial cells which appear to take a part in the transendothelial transport were observed.This investigation was supported in part by United States Public Health Service Research Grant, No. A-3678, to Hideshi Kobayashi from the National Institute of Arthritis and Metabolic Diseases and partly by a grant for Fundamental Scientific Research from the Ministry of Education of Japan. The authors wish to express their thanks to Prof. K. Takewaki for his kind encouragement.     

The hypothalamo-hypophysial vascular relationship in Indian fresh-water goby, Glossogobius giuris (Ham.).920u.

The hypothalamo-hypophysial vascular relationship and intra-hypophysial vasculatisation have been described in order to understand the regulatory mechanism of hypothalamic control over the functions of the pituitary gland. In Glossogobius giuris, the disposition of the blood vessels in the head region is on typical teleostean pattern with certain modifications. The nucleus preopticus is supplied through the nucleus preopticus artery, a small blood vessel arising from the anterior branch of the posterior cerebral artery, whereas the pituitary gland receives blood through a pair of hypophysial arteries. The blood from the pituitary is drained off by the pituitary veins whch pour their blood into the supra-orbital sinus. The anterior cerebral vein after taking the blood from anterior part of the brain including the hypothalamus and the nucleus preopticus joins with the supra-orbital sinus. The hypothalamo-hypophysial portal system is absent in this fish. The saccus vasculosus receives blood from the posterior cerebral artery through a small blood vessel and is collected by a prominent saccus vasculosus vein which pours blood into the supra-orbital sinus before it joins the infra-orbital sinus to form the heat vein. There seems to be no physological connection between the saccus vasculosus and pituitary gland. The highly vascularised neurohypophysis interdigitate with the pars intermedia and extends upto the proximal pars distalis. The blood vessels are restricted to the neurohypophysial extensions only. However, in the rostral pars distalis the blood vessels are present but the neurohypophysis does not extend to this part. The blood capillaries enter the rostral pars distalis from the capillary network on the surface of pituitary gland along with the connected tissue covering of the pituitary. The neurohypophysis shows a greater vascularisation in comparison to that of the other glandular part of the pituitary gland. In the present study of Glossogobius giuris, though an extensive ramification of neurohypophysis occurs with the pars intermedia and the proximal pars distalis, the neurosecretory axons do not innervate the endocrine cells of the pituitary gland and the blood vessels are found restricted to the neurohypophysial extensions except that of the rostral pars distalis. The neuro-vascular way of hypothalamic control over the functions of the pituitary gland seems to be justified as the neurosecretory fibres have been found associated with the blood vessels.     

Hypothalamohypophysial vascular and neurosecretory link in the teleost Bagarius bagarius (Ham.).

A three-dimensional picture of the hypothalamohypophysial neurosecretory system of B. bargarius could be obtained by adopting in situ staining techniques. The paired NPO give rise to left and right neurosecretory tracts which, although they approximate as a common tract, maintain their individuality till entering the pars intermedia. The ventral hypothalamic and the hypophysial arteries take their origin from the internal carotid artery. The former contributes to the formation of the primary plexus of the median eminence and the latter enters the pituitary directly, giving rise to the neuroadreno-interface vasculature. The vasculature of the median eminence lies in close contact with the long common neurosecretory tract. Morphological evidence suggests that in B. bagarius there are three pathways of hypothalamic control of the hypophysis: (1) A direct neuroglandular pathway, where the neurosecretory axons come directly in contact with the adrenohypophysial cells. (2) An indirect neurovasculoglandular pathway, where the blood exposed to the NSM at the median eminence comes in contact with gland cells. (3) Another indirect neurovasculoglandular pathway, where the blood is exposed to NSM at the neurohypophysis prior coming in contact with the gland cells. Thus, B. bagarius has the 'median eminence equivalent' neuroadeno-interface vasculature typical of the teleosts and the median eminence comparable to the Elasmobranchs, Holocephali and primitive Actinopterygians. This shows that the pituitary portal system of teleosts is in general agreement with that of other fish groups, except that in some it is restricted to the neuroadreno-interface, whereas in others like B. bagarius it extends to the hypothalamus also. These may be termed anterior and posterior median eminence.     

Extravascular circulation in the pituitary of Mugil cephalus (Teleostei)

Summary Extravascular circulation in the pituitary of Mugil cephalus was investigated by injecting live fish with horseradish peroxidase and studying the distribution of the enzyme in the gland. The principal components of the extravascular circulatory system are the pericapillary spaces, and, arising from them, the interlobular and circumhypophyseal spaces. Extensions of these spaces penetrate the glandular parenchyma of the pars distalis, where they merge with pericellular spaces. In the neurohypophysis, pericapillary spaces are connected to the periaxonal spaces.Capillaries penetrating from the proximal neurohypophysis into the pars distalis are accompanied by neurosecretory axons. These axons form a mass of tissue which is limited near the capillaries by the pericapillary spaces and near the adenohypophysis by the interlobular spaces. Toward the interior of the adenohypophysis the amount of nervous tissue accompanying the capillaries progressively diminishes, thus reducing the distance between pericapillary and interlobular spaces. Within the pars distalis, the neurosecretory axons accompanying the capillaries are sparse, and the secretory and stellate cells are mostly located directly adjacent to the pericapillary spaces. In the neuro-intermediate lobe, interlobular spaces outline the neuro-adenohypophyseal boundary.The relationship between extravascular spaces and hormone-secreting cells varies in the different regions of the adenohypophysis depending upon the type of neurosecretory innervation in the respective region. In the regions of prolactin and gonadotropin cells, where neurosecretory axons are in direct contact with the secretory cells, the hormone-secreting and stellate cells are adjacent to the pericapillary spaces. In the regions of ACTH and STH cells, secretory and stellate cells are found adjacent to the interlobular spaces, which are interposed between the cells and the neurosecretory axons.Abbreviations AH adenohypophysis - CH circumhypophyseal - DNH distal neurohypophysis - HRP horseradish peroxidase - NH neurohypophysis - NS neurosecretory - PD pars distalis - PI pars intermedia - PPD proximal pars distalis - RNH rostral neurohypophysis - RPD rostral pars distalis This research was supported by a grant from the National Council for Research and Development, Israel, and the GKSS Geesthacht-Tesperhude, Federal Republic of Germany     

Vascularization of the pituitary of the Australian lungfish and Neoceratodus forsteri

The vascularization of the brain and the pituitary region of the Australian lungfish, Neoceratodus forsteri is described from serial section reconstruction. The distal lobe has no direct arterial blood supply and receives blood solely from a pituitary portal system basically similar to that of other sarcopterygians. The primary capillary plexus of the median eminence receives its arterial blood from the infundibular arteries, which on their way distribute some small branches to the prechiasmatic region. The primary plexus also receives capillaries from the adjacent pial hypothalamic plexus. The primary capillary plexus of the median eminence comprises a rostral 'uncovered' and caudal 'covered' part which are not sharply delineated. Distinct portal vessels connect the 'uncovered' rostral part of the primary plexus with the secondary capillary plexus supplying the rostral subdivision of the pars distalis. The 'covered' caudal part of the primary plexus merges into the proximal subdivision of the pars distalis, apparently without formation of distinct portal vessels. The primary plexus has some connections with the plexus intermedius via a hypophysial stem capillary plexus. The plexus intermedius has a substantial arterial supply and gives off capillaries to the parenchyma of the pars intermedia. The adenohypophysis is drained into an unpaired hypophysial vein. The significance of the vascular pathways is discussed from comparative, functional, and evolutionary viewpoints.     

Ultrastructural features of the developing hypothalamo-hypophysial axis in the rat

Summary Nerve fibres containing granular vesicles first appear in the median eminence of the rat on the 16th foetal day while secretory granules in the cells of the adenohypophysis are not present till the 17th foetal day. These observations suggest that the differentiation and early activity of pars distalis cells may depend on substances elaborated at nerve terminals in the median eminence. Although the loops of the primary plexus of portal vessels do not develop until the 4th postnatal day, substances released by nerve fibres in the neurohypophysis could reach the pars distalis through vessels already present at the 15th foetal day in the mesenchyme between the diencephalon and the adenohypophysis. This view is supported by the fact that the earliest cells to exhibit ultrastructural evidence of secretory activity are in the rostral pole of the pars distalis, the first region of the gland to become vascularized. The earliest granules to appear in the cells of the pars distalis correspond to those which are considered to contain mucoprotein hormones; somatotrophin type granules were seen only in postnatal tissues.The finding that, in the median eminence, the development of granular vesicles precedes that of agranular vesicles is discussed with reference to the times at which neurosecretory materials and monoamines become detectable in the region.We should like to thank Miss Ann Pearson, Mr. D. Burns, and Mr. J. Nailon for their technical assistance, and Mr. J. Simmons, F.R.P.S., for his help in the preparation of illustrations. This work was supported by grants from the National Health and Medical Research Council of Australia.     

Ultrastructural study of the uptake of peroxidase by the rat median eminence

An active role of the ependymal cells (tanycytes) of the median eminence in the transport of hypothalamic hormones has been recently suggested. In order to investigate the fate of material present in the cerebrospinal fluid, a protein tracer, horse-radish peroxidase (HRP) was injected into the left lateral ventricle of rats. Two minutes after the injection, HRP had largely diffused between tanycytes and hypendymal cells. As soon as 5 min after the injection, HRP had completely penetrated all the layers of the median eminence. A few labelled vesicles and lysosomes were occasionally seen in ependymal and glial cells. At longer time intervals (20 min, 1 and 4 hrs), a reaction was observed in the lumen of fenestrated capillaries of the pituitary portal plexus. In many nerve endings of the external zone, vesicles and lysosomes were seen to contain HRP. An interesting observation was the localization of HRP between nerve endings and cells in both the pars nervosa and the pars intermedia of the pituitary gland. No reaction was recorded in the anterior pituitary and the kidney. Seventeen hours after the injection, the extracellular space was free of reaction but a few positive intracellular structure were still found. These results clearly indicate that some material from the third ventricle can rapidly diffuse between cells and axons of the median eminence to reach the fenestrated capillaries of the pituitary portal plexus and the posterior pituitary without involving an active transport by tanycytes.     

Vascular Connections in the Pituitary of Anolis carolinensis with Special Reference to the Pars intermedia

The pituitary vascular system of Anolis carolinensis is similar to that of other lizards. Distinct portal vessels connect the primary plexus of the median eminence with the secondary plexus of the pars distalis. The primary plexus has some connections with the neural lobe. The neural lobe plexus is fed by separate arteries, and drains into the pars intermedia. The latter lobe receives its blood supply by this route. The pituitary is drained into the vena retrohypophysea. The findings are discussed in relation to existing theories regarding the neurovascular control of the pars intermedia.     

Distributional pattern of oxytocin- and vasopressin-immunoreactivity in the neurohypophysis of the Djungarian hamster (Phodopus sungorus)

Summary The topography of oxytocin (OT)- and vasopressin (VP)-containing axons of the hypothalamo-neurohypophyseal system was studied in the neurohypophysis of the Djungarian hamster (Phodopus sungorus) by means of immunohistochemistry. Compared with other mammalian species, the neurohypophysis of Phodopus shows some peculiarities. Accumulations of OT-immunoreactivity around the distal vessels of the primary portal plexus can be observed in the distal median eminence and neural stem. This staining pattern indicates that OT is secreted into portal blood. In the neural lobe, OT- and VP-immunopositive fibers terminate in different areas. The vast majority of the OT-containing axons is distributed in the dorsal part of the neural lobe. In contrast, VP-containing axons are mainly found in the centre of the neural lobe up to the pars intermedia.     

The distribution of monoamine oxidase and acetylcholinesterase in the hypothalamus and its relation to the hypothalamo-hypophysial neurosecretory system in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary The distribution of monoamine-oxidase and acetylcholinesterase activities in the hypothalamus of the White-crowned Sparrow has been studied in relation to the hypothalamohypophysial neurosecretory system. The enzyme activities, as revealed by the methods employed, are unaffected during photoperiodically induced testicular growth. Monoamine oxidase has a distribution distinctly different from that of the aldehyde-fuchsin positive neurosecretory material in that there is high activity in the peripheral palisade layers of both the anterior and posterior divisions of the median eminence. Intimate contact is made between these areas with the primary vessels of the hypophysial portal system. A second concentration of activity lies in a layer between the ependymal cells and the neurosecretory material of the fiber tract. In general, monoamine oxidase appears to be associated with glial elements and non-neurosecretory axons. The pars nervosa has little or no monoamine-oxidase activity. The distribution of acetylcholinesterase activity in the anterior division of the median eminence is very similar to that of the aldehyde-fuchsin positive neurosecretory neurons; however, acetylcholinesterase also occurs in the posterior division without associated neurosecretory fibers. These distribution of enzyme activities are considered in relation to possible adrenergic and cholinergic mechanisms in the median eminence.Dedicated to Professor Berta Scharrer in honor of her 60th birthday.Supported by grant NB-01353 from the National Institutes of Health to Professor Farner. This investigation was conducted while Doctor Kobayashi was a National Science Foundation Senior Foreign Scientist at Washington State University. We are indebted to Doctor Christian Da Lage, Laboratoire de Histologie, Falculté de Médecine de Paris, for the preliminary development of some of the techniques used in these investigations.     

Monoamine oxidase in the hypothalamo-hypophysial region of the teleosts,Anguilla japonica and Oryzias latipes

Summary Distribution of monoamine oxidase (MAO) was histochemically examined in the hypothalamo-hypophysial region of the eel (Anguilla japonica) and the medaka (Oryzias latipes) with a modified Glenner's tryptamine-tetrazolium method. The hypothalamic neurosecretory cells showed very weak MAO activity in their perikarya. MAO-positive fibers were present in close contact with the neurosecretory cells, suggesting that monoaminergic fibers participate in the control of neurosecretory cell activity. The nucleus lateralis tuberis (NLT) contained cells exhibiting strong MAO activity. These cells must be monoaminergic neurons.In the anterior region of the neurohypophysis of both eel and medaka, two bundles of MAO-positive fibers originating from the NLT proceed down along each side of the third ventricle into the pars distalis. This suggests that monoaminergic neurons of the NLT are involved in the release of hormones from the pars distalis. In addition to these tracts, numerous MAO-positive fibers proceed backward from the post-optic area and end around the blood capillaries located between the neurohypophysis and the pars intermedia in both species.I wish to express my gratitude to Prof. H. Kobayashi for his valuable advice during the course of this study. I am indebted to Prof. S. Uchida, Ocean Research Institute, University of Tokyo, for supplying the eels.     

Identification of adenohypophysiotropic neurohormone producing neurosecretory cells in Rana temporaria

Summary By means of electron microscopy, in the median eminence of Rana temporaria, the terminal arborizations of axons of six different types of neurosecretory cells, located in the pars ventralis of the tuber cinereum, were identified. In addition, phenomena connected with the release of neurosecretory material from the axon terminals of these neurosecretory cells into the blood capillaries of the median eminence are described.Preliminary results suggested the existence, in the median eminence, of additional different neurosecretory axon types which could also belong to corresponding neurosecretory cell types probably located in the apical part of the pars ventralis of the tuber cinereum. Moreover, in the external region of the normal median eminence, separate monoaminergic nerve fibres were tentatively identified. Arguments are adduced which plead (1) against the assumption that the ependyma or the pituicytes of the median eminence could produce adenohypophysiotropic hormones; (2) against the inference that the ependymal cells of the median eminence might be involved in the transport of adenohypophysiotropic hormones from the cerebrospinal fluid into the blood capillaries of the median eminence.     

An in situ Study of the Hypothalamic Neurosecretory System of the Freshwater Catfish Ailia coila (Ham.)

The hypothalamo-neurohypophysial complex of Ailia coila is well demonstrated with the help of in situ staining procedure. Both pars magnocellularis and pars parvocellularis components of the nucleus preopticus contribute to the formation of the right and the left main neurosecretory tracts. Anterior one third of these tracts are loosely set and posteriorly they became more compact. From the posterior two thirds of the main tracts several pairs of lateral tracts were given off which join at the midline to form the paired median tracts. The median and the main tracts jointly enter the pituitary as the common tract. The common tract on entering the pituitary often divides into two or more branches and enter the pars intermedia independently. The rostral pars distalis is least innervated by the neurosecretory axons. Since the proximal pars distalis has varying amount of AF-positive cells, and the pars intermedia has the bulk of the neurosecretory axons both these regions are stained dark in the in situ preparations. Bulk preparations provide a clear topographic picture of the entire neurosecretory system, which is very difficult to visualise in tissue sections and in their reconstructions.     

Immunohistochemical Localization of Growth Hormone and Prolactin in the Pituitary Gland of Acipenser güldenstaedti Brandt (Chondrostei)

Abstract Prolactin (LTH) and growth hormone (GH) containing cells in A. güldenstaedti have been localized by means of anti-ovine prolactin and anti-bovine growth hormone respectively, coupled indirectly to peroxidase, and localized histochemically with hydrogen peroxide as substrate and 3,3′-diaminobenzidine as capturing agent. The distribution of the anti-prolactin positive cells has been demonstrated and correlated histologically with the acidophilic cells both in the rostral and proximal pars distalis. This cell type is elongated and arranged in follicles in the rostral pars distalis; in the proximal pars distalis they are smaller and oval, without any special orientation. Neither of the other cell types which are scattered among these acidophils contain prolactin. The anti-bovine growth hormone positive cells are evenly distributed in the proximal pars distalis above the hypophysial cleft, and some are also found in the pars intermedia. The anti-GH positive cells have been correlated histologically with the amphiphilic cells in the proximal pars distalis. These cells are arranged in cell cords in close contact with the secondary capillary plexus, near its origin from the primary capillary plexus covering the median eminence.     

Morphometric analysis of the formation of the external zone of the median eminence of the rat hypothalamus in the perinatal period

Morphometric electron microscopy data were obtained using a semiautomatic image analysis which demonstrate that the main stages of formation of the external zone of median eminence in the rat hypothalamus take place during the perinatal period. From the 20th day of prenatal period to the 9th day of postnatal period, the length of contact between the neurosecretory axons and the primary portal plexus increases twice, whereas that between the basal processes of ependyma cells and the primary portal plexus by a factor of 1.5. At the same time, the number of secretory granules and microvesicles in axons and that of pinocytotic vesicles in the basal processes markedly increases. Regional differences in the distribution of vesicular structures were noted in neonatal animals: secretory granules were more numerous in the axon swellings remote from the external basal lamina; pinocytotic vesicles were more numerous in the basal processes which terminated in the medial median eminence.     

Aminergic Innervation of the Cranial and Caudal Neurosecretory Systems in the Teleost Gillichthys mirabilis

Abstract Numerous fluorescent varicosities surround most of the caudal neurosecretory neurons and also regularly occur among pars intermedia cells of the adenohypophysis in the teleost, Gillichthys mirabilis. The color of the varicosities, as well as their responses to pharmacological treatments, is diagnostic of catecholaminergic neurons and processes. No fluorescence characteristic of monamines is found in the rostral pars distalis, in the proximal pars distalis or in the cells of the nucleus lateralis tuberis (NLT), although fluorescent varicosities are found within the ventral hypothalamus in the vicinity of the NLT. Bilateral clusters of fluorescent cell bodies are located in the ventral hypothalamus (posterior to the NLT); some of these cells border the neurohypophysis. Fluorescent tracts from these cell clusters extend to a pair of elongate nuclei of nonfluorescent neurons which are surrounded by fluorescent varicosities. Alteration of osmotic conditions did not effect the fluorescence, except for the caudal neurosecretory cells of fish exposed to fresh water for long periods. Adrenergic nervous input thus seems to be an important component of both the cranial and caudal neurosecretory systems.     

Pituitary cytology of the chimaeroid fish Hydrolagus colliei (Lay and Bennett).

The pituitary of Hydrolagus colliei is divided into the adenohypophysis, neurohypophysis and an oral Rachendachhypophyse. The adenohypophysis is further divided into rostral and proximal pars distalis and neurointermediate lobe. The neurohypophysis is restricted to the pars intermedia only. The rostral pars distalis is composed of acidophils, chromophobes, lightly PAS+ cells and amphiphils. The amphiphils were stained with Heidenhain's iron haematoxylin and lead haematoxylin also. The proximal pars distalis is formed of cyanophils where the granules are AF and PAS positive, acidophils, chromophobes and H.Pb+ cells. The pars intermedia has perviascular amphiphils which are H.Pb+, lightly PAS+ cells and chromophobes. Few AF+ cells were also identified. All the component parts of the adenohypophysis have follicular cavities which are probably developed from the hypophysial cavity, which is well seen in the young specimen as a single cavity extending antero-posteriorly throughout the adenohypophysis.     

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.