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.     

The distribution of monoamine oxidase and acetylcholinesterase in the brain of Xenopus laevis tadpoles

Summary The distribution of monoamine oxidase (MAO) in the brain of Xenopus laevis tadpoles (stage 52–56) was studied histochemically with a modified Glenner's tryptamine-tetrazolium method. A moderate activity was observed in fibre regions of the striatum and septum (including the medial and lateral forebrain bundles), in the neuropil of the nucleus amygdalae, in the commissura anterior and commissura hippocampi, in the fibre regions of the diencephalon (including the optic chiasma), in the fibre regions of the tectum opticum and the tegmentum of the mesencephalon and in the white substance of the ventral half of the medulla oblongata. A greater MAO activity was found in the neuropil of the entire nucleus praeopticus. In the partes anterior and magnocellularis of this nucleus, MAO positive fibres are present in close contact with the perikarya, indicating a monoaminergic innervation of these neurons. The perikarya themselves did not show MAO activity. In the neurons of the nucleus praeopticus epichiasmaticus, the paraventricular organ (PVO) and nucleus infundibularis dorsalis (NID), only a slight MAO activity has been demonstrated in the perikarya, whereas a strong MAO positivity was found in the intraventricular protrusions and the neuropil. These data indicate the aminergic character of the neurons of these nuclei. From the postoptic fibre region a MAO positive tract was observed towards the developing median eminence and pars intermedia of the hypophysis. The pars nervosa and some cells of the pars distalis also contained MAO. Along the border of the aquaeduct of Silvius and the fourth ventricle, MAO positive liquor-containing neurons are also present.The distribution of acetylcholinesterase (AChE) was investigated in the hypothalamohypophysial region. AChE activity was found in the neuropil of the nucleus praeopticus magnocellularis, in the fibres of the optic chiasma and in the postoptic fibre region. The neurons of the PVO and NID were AChE negative. An AChE positive tract could be traced from the postoptic fibre region to the developing median eminence and pars nervosa. The pars distalis did not show AChE activity. However, in tadpoles reaching the metamorphic climax, ChE activity appeared in certain cells of the pars distalis; this might be related to degenerative phenomena in the acidophilic cells. The absence of AChE activity in the pars intermedia indicates a regulation of MSH release by peptidergic nerves to be unlikely.The stimulating interest and helpful advice of Prof. Dr. P. G. W. J. van Oordt is gratefully acknowledged. Thanks are also due to Mr. H. van Kooten and his co-workers for making the photographs.     

Hypothalamo-hypophysial Neurosecretory System in Normal and Hypophysectomised Catfish,Clarias Batrachus L

Two neurosecretory centers, nucleus preopticus (NPO) and nucleus lateralis tuberis (NLT), are distinguished in the hypothalamus of Clarias batrachus L. The cell bodies of NPO are grouped into nucleus preopticus magnocellularis (NPM) and nucleus preopticus parvocellularis (NPP). The NLT is recognised into three divisions: pars rostralis, pars medialis and pars ventrolateralis. The neurons of both the NLT and NPO are aldehyde-fuchsin (AF) positive. The axons from NPO run into four or five bundles ventrolaterally and caudally for some distance before all of them from either side join ventromedially into a single thick cord of neurosecretory fibers which finally enters the pars intermedia to form the neurointermediate lobe. The fibers from NLT, which are separate from the neurosecretory fibers of the NPO, anastomose in the region of the pars distalis. The neurosecretory material (NSM) of NPO is transported by axonal route whereas that of NLT is by axonal as well as ependymovascular pathways. Hypophysectomy results in the increase of AF-positive material in the neurons of NPO shortly after the operation, but later on, the material begins to deplete in them. The AF-positive material at the cut end of neurosecretory fibers, however, accumulates. The AF-positive material in the cell bodies of NLT is also depleted, but the nuclei increase in size, after hypophysectomy.     

Immunocytochemical identification of melanin-concentrating hormone in the brain and pituitary gland of the teleost fishes Oncorhynchus keta and Salmo gairdneri

Summary Melanin-concentrating hormone (MCH) has been purified from the chum salmon pituitary. Its complete amino acid sequence has recently been established. To identify the precise site of origin of MCH, immunostaining was performed in the brain and pituitary gland of the chum salmon and the rainbow trout using a highly sensitive and specific antiserum raised against synthetic MCH. In these two salmonid species immunoreactivity for MCH was detected in neurons and neuronal processes in the pars lateralis of the nucleus lateralis tuberis (NLT) in the basal hypothalamus. Numerous positive-staining processes of these MCH-neurons project to the pituitary gland, extending into neurohypophysial tissues within the pars intermedia and, to a lesser extent, into the pars distalis. No pituitary cells showed cross-reactivity. These results suggest that MCH is biosynthesized in the neurons of the NLT/pars lateralis and released in the neurohypophysis. On the other hand, prominent but less numerous MCH-positive processes could be traced to the pretectal area in which projection of both optic and pineal fibers has been detected using tracers. This observation suggests that the synthesis and/or release of MCH might be under the influence of either of these photosensory neurons. Moreover, the existence of an extrahypothalamic projection from MCH-positive neurons suggests that, in addition to melanin-concentration, MCH might be involved in other neuronal functions, perhaps serving as neuromodulator in the brain.     

Evidence for corticotropin releasing factor (CRF) synthesis in the preoptic nucleus of Xenopus laevis tadpoles

Summary For the study of the hypothalamo-hypophysial system of Xenopus laevis tadpoles, hypothalamic lesions were made by means of the electrocoagulation technique. Lesioning of the ventral region of the preoptic nucleus resulted in a decrease of the number of ACTH cells in the pars distalis of the pituitary gland and in a diminution of the PAS-positive reaction of these cells. In addition, regeneration of the neurosecretory cells of the ventral region of the preoptic nucleus observed 6 weeks after lesioning was accompanied by the reappearance of normal PAS-positive ACTH cells in the pars distalis. It is suggested that the neurosecretory cells of the ventral region of the preoptic nucleus of Xenopus laevis tadpoles are related to the ACTH synthesizing cells, probably by producing CRF.Dedicated to Prof. Dr. med. W. Bargmann on the occasion of his 70th birthdayThe authors thank Prof. Dr. J.C. van de Kamer for his interest, Prof. Dr. P.G.W.J. van Oordt for his many helpful comments, and Messrs. H. van Kooten, E. van der Vlist, J.J. van der Vlis and M.C.A. van Pinxteren for preparing the illustrations     

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     

Nucleus praeopticus and nucleus lateralis tuberis of Salmo salar and Salmo gairdneri: Structure and relationship to the hypophysis

Summary The nucleus praeopticus (NPO) is located on both sides of the preoptic recess and is composed of a pars parvocellularis and a pars magnocellularis. Only in the rainbow trout does the pars magnocellularis consist of separately located medium-sized cells and very large cells. Cytologically, three cell types can be distinguished: 1) unipolar cells ending in the cerebrospinal fluid (CSF), 2) bipolar cells also ending in the CSF and forming an axon, and 3) multipolar cells which generally do not have a direct connection with the ventricle.Axons originate from the cell bodies forming the paired preopticohypophysial tract that runs along the border of the diencephalon and the optic tract. A considerable number of NPO fibers leading to the hypophysis makes close contact with the cell bodies of the pars lateralis of the nucleus lateralis tuberis, indicating a functional relationship. Most NPO fibers terminate in the caudal part of the neurohypophysis, around blood capillaries and at the basal lamina of the pars intermedia. Far fewer fibers appear to terminate near the boundary of the neurohypophysis and the rostral and proximal pars distalis.The nucleus lateralis tuberis (NLT) is located in the caudal hypothalamus, beginning at the rostral end of the horizontal commissure and extending caudally beyond the hypophysial stalk. It consists of the partes rostralis, medialis, lateralis and ventrolateralis. In both species the p. rostralis contains small subependymal neurons and some larger ones. Only in the p. medialis of the Atlantic salmon are large cells present. In both species the most prominent part is the p. lateralis, which consists solely of large cells. Cells situated between the p. medialis and the p. lateralis are grouped in the p. ventrolateralis. It was impossible to trace the axons originating in the NLT, since the cyto- and axoplasm could not be stained specifically.The structure of the NPO and NLT in the two salmonid species is compared with that of other teleosts.     

Electron-microscopic investigation of the innervation of the pars distalis of the hypophysis in adult Rana temporaria L.

Summary In the pars distalis of the hypophysis of adult Rana temporaria, three types of nerve-fiber profiles were found at two distinct sites, in both lateral parts of the bordering regions of the anterior lobe with the intermediate lobe of the hypophysis. The first type of nerve-fiber profile consists of bundles of very fine axonal elements (diameter: <0.7 m). The second type is formed by larger nerve fibers (diameter up to 4 m) containing a few neurosecretory granules of approximately 100 nm. The third type of nervefiber profile resembles the second type but these nerve fibers make synaptoid contacts on at least two different types of glandular cells. The possible functional significance of these nerve fibers in the pars distalis is discussed.No nerve fibers were found (1) in the central part of the bordering region of the pars distalis with the intermediate lobe, (2) at the bordering region with the median eminence and (3) with the neurohypophysial stalk, and (4) in all other parts of the pars distalis.     

Hypophysiotropic neurons in the goldfish hypothalamus demonstrated by retrograde transport of horseradish peroxidase

Summary The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only — the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The distribution of monoaminergic structures was studied in the proximal neurosecretory contact region and neurohypophysis of the lamprey by light and electron microscopic radioautography. Only weak radioautographic reactions were found in the proximal neurosecretory contact region 1 h after injection of 3H-dopamine. High-resolution radioautography revealed some labeled neurosecretory terminals mainly in contact with the basement membrane of the connective tissue layer separating the proximal neurosecretory contact region from the hypophysial pars distalis. The number of silver grains as well as the number of neurosecretory terminals marked by the presence of labeled dopamine was much higher in the neurohypophysis of the same species. In the latter, labeled neurosecretory terminals were found in contact with the connective tissue layer containing blood vessels of the general circulation. Some neurosecretory terminals make synaptoid contacts with tanycyte perikarya and their basal processes. According to their ultrastructure and the size of their granules, the labeled neurosecretory terminals are identical with the B type terminals described in both neurohemal regions (transmission electron microscopy). No labeled neurosecretory terminals were observed in the proximal neurosecretory contact region and the neurohypophysis of lampreys treated with the serotonin precursor, 3H-5-hydroxytryptophan.     

Structure of the neurohypophysis and the hypothalamo-hypophysial vascularization in the teleost Channa punctatus Bloch.

In C. punctatus the median eminence includes the subterminal region of the hypothalamus and the anterior neurohypophysis. It is formed of ependymal, fibrous and reticular layers as in the tetrapods. Primary capillary plexus extends from the subterminal region to the extremity of the anterior neurohypophysis. Only few portal vessels from the hypothalamus enter in the pars distalis. All the components of pituitary including the pars intermedia are irrigated by the secondary plexus formed from the portal vessels emerging out of the anterior neurohypophysis. The neurosecretory axons and the ependymal cells are in close morphological contact with the primary plexus. Several axons have perivascular endings at the median eminence. Some axons were found to be only silver or aldehyde fuchsin positive whereas some others take up both. The silver positive axons were abundant in the pars distalis and the AF positive ones were more concentrated in the pars intermedia with greater accumulation of neurosecretory material.     

Somatostatin in the brain and the pituitary of some teleosts

Summary Immunocytochemical investigations show that somatostatin (SRIF)-like immunoreactive material is present in the brain and the pituitary of nine different species of teleosts. In the brain, immunoreactive perikarya and fibers are observed in the preoptic periventricular nucleus, the entopeduncular nucleus, the anterior periventricular nucleus, and the nucleus lateralis tuberis. In the pituitary, SRIF-like-immunoreactive fibers occur in the proximal pars distalis (PPD), which contains the growth hormone (GH)-secreting cells. Nerve fibers are scattered among GH cells (cyprinids), or end on the basal lamina at the neuroglandular interface of the PPD (eel, salmonids). In the eel, the proximal neurohypophysis does not penetrate deeply into the PPD that is very poorly vascularized. In some species, e.g. Myoxocephalus, SRIF-like immunoreactive fibers are also observed in the caudal neurohypophysis, and even among MSH cells of the pars intermedia.In long-term starved carps and eels, the amount of SRIF-like material in the pituitary is clearly reduced. A possible role of SRIF in the concomitant stimulation of GH cells is discussed.     

Immunohistochemical demonstration of alpha-1-antitrypsin in the islet cells of human pancreas

Summary Using the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level, it has been shown that, in the dipnoan preoptico-hypophysial neurosecretory system, vasotocin and mesotocin are synthesized in separate neurons. In the preoptic nuclei, the perikarya of these two types of neurosecretory neurons are not located preferentially. The two types of neurosecretory perikarya give rise to separate vasotocinergic and mesotocinergic axons, respectively. The dipnoan median eminence and neural lobe contain separate vasotocinergic and mesotocinergic nerve fibres, the general distribution of which is described. In the pars distalis and the pars intermedia of the hypophysis, neurohypophysial hormone-containing nerve fibres have not been found.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk OnderzoekThe authors are greatly indebted to Prof. Dr. Hyder, Department of Zoology, University of Nairobi, Kenya for kindly supplying us with the fixed material used in this study     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The proximal neurosecretory contact region (PNCR) of the lamprey, a homologue of the median eminence of tetrapods, was studied by light, fluorescence and electron microscopy. Paraldehyde fuchsin-positive neurosecretory fibers are seen mainly in the central part of the rostral subdivision of the PNCR. The Falck-Hillarp technique reveals a weak, mainly diffuse yellow-green fluorescence in the PNCR. The ultrastructure of the tanycyte layer of the PNCR is very similar to that in the neurohypophysis of the same species, although the funnel-shaped protrusions of the third ventricle in the rostral part of the PNCR are more frequent than in the neurophypophysis. Peptidergic A1 and A2 neurosecretory fibers are characterized by neurosecretory granules of 120-200 nm and 100-150 nm in diameter, respectively. Monoaminergic B type fibers contain granules 80-100 nm in diameter. Neurosecretory terminals and the vascular endfeet of tanycytes make contact with the basement membrane of the avascular connective tissue layer separating the PNCR from the hypophysial pars distalis. It is suggested that both peptide and monoamine neurohormones diffuse through the thick connective tissue septa into the underlying blood vessels which supply the pars distalis and thus affect the function of its glandular cells.     

Ultrastructural identification of catecholaminergic fibers in the goldfish pituitary

Summary The monoaminergic innervation of the goldfish pituitary gland was studied by means of light- and electronmicroscopic radioautography after in vitro administration of ³H-dopamine. The tracer was specifically incorporated and retained by part of the type-B fibers innervating the different lobes of the pituitary. In the rostral pars distalis labeled fibers were most frequently observed in contact with the basement membrane separating the neurohypophysis and the adenohypophysis. In the proximal pars distalis and the pars intermedia, labeled profiles were detected in the neural tissue and in direct contact with the different types of secretory cells.According to the previous data concerning the uptake and retention of tritiated catecholamines in the central nervous system, it is assumed that the labeled fibers are mainly catecholaminergic (principally dopaminergic). This study provides morphological evidence for a neuroendocrine function of catecholamines in the goldfish.     

Cyclical mitotic activity in the adeno-hypophysis of Rana temporaria

Summary In the pars distalis, the pars intermedia and the pars tuberalis of the hypophysis of Rana temporaria, an annual mitotic cycle is described.In the pars distalis there exists a gradient of mitotic activity, corresponding to a gradient of distribution of the PAS positive cells.In the pars distalis, the rate of cell degeneration and of cell renewal of the PAS positive cells seems to be faster than of the orange G positive cells.The replacement of degenerated PAS positive cells of the pars distalis seems to occur mainly during the months immediately following on the period of maximal activity of the PAS positive cells.     

Ultrastructural characterization of neurosecretory fibres immunoreactive for vasotocin,isotocin, somatostatin,LHRH and CRF in the pituitary of a teleost fish,Poecilia latipinna

Summary Using the electron-microscopic immunogold method, vasotocin, isotocin, somatostatin (SRIF), gonadotrophin-releasing hormone (LHRH) and corticotrophin-releasing factor (CRF)-like immunoreactivities were localized in separate neurosecretory fibres in the pituitary of a teleost fish Poecilia latipinna. Antigenicities were preserved in sections of conventionally fixed tissue, except in the case of LHRH and CRF-like substances which were sensitive to osmium postfixation. Under the same fixation conditions, ultrastructural differences were observed between the 5 fibre types, and morphometric analysis of their granule sizes revealed significant differences in mean diameter except between vasotocin and isotocin fibres.Terminal-like regions of each type were identified on blood vessels, glial cells or other fibres in the neurohypophysis, on the basement lamina of the adenohypophysis, or directly on adenohypophysial endocrine cells. The fibres containing the two neurohypophysial hormones, originating from separate preoptic perikarya, were intermingled with, and may form endings near all the adenohypophysial cell types except those secreting prolactin. Although both types had similar mean granule diameters, the granules in the vasotocin fibres (mean 135 nm) were markedly less electron dense than those in the isotocin fibres (mean 140 nm). SRIF-immunoreactive fibres (mean 101 nm) appeared to form synapse-like endings on the somatotrophs, and a few thyrotrophs in the proximal pars distalis, and near the pars intermedia cells. An LHRH-positive type (mean 103 nm) contacted only the gonadotrophs of the proximal pars distalis. The rarer CRF-like fibres (mean 116 nm) appeared to project mainly towards the pars intermedia, but a few appeared to terminate rostrally near the adrenocorticotrophic cells.The significance of these observations is discussed in relation to the direct neurosecretory control of adenohypophysial function in teleosts.     

The influence of social rank on adenohypophysial cell activity in Salmo irideus

Summary In nine cell types of the adenohypophysis in untreated adult rainbow trout, histologically different activity phases, seasonal changes in activity, and the relation between certain cell types and the interrenal gland, thyroid or gonads were investigated by light and, occasionally, by electron microscopy. Special attention was given to the effect of social rank on the synthetic activity in adenohypophysial cells of trout kept in small groups in which a social hierarchy with one (light) dominant and several (dark) submissives is established.Cell types in the rostral pars distalis were azocarminophil (I) or amphiphil (II). Proximal pars distalis cell types were slightly basophil (IV), orangeophil (V), strongly basophil (VI) or chromophobe (VII). In the pars intermedia, cell types were amphiphil (VIII) or very slightly basophil (IX). Type III was a non-secretory supporting (?) cell.Histologically different activity phases abounded in type IV cells, which mainly occurred in the proximal pars distalis but were also found dispersed in the rostral pars distalis, the pars intermedia and the neurohypophysis.Influences of social rank were pronounced in type IV cells. Phases with a high synthetic activity were exclusively found in submissive animals, phases with a low synthetic activity occurred in dominants. As a positive relation existed between type IV cell activity and the social rank dependent activity of the interrenal gland, it was suggested that type IV cells produce ACTH.In (dominant) male trout treated with DOCG or ACTH, colloid-containing type IV cell phases, reflecting accumulation of the secretory product, were found. This supported the earlier suggestion that ACTH in the trout is produced in the basophil type IV cells and not, as reported in the literature, in cells comparable to type II.The author is greatly indebted to Miss M.C. Wentzel, Miss I. Stulen, Mr. J. Veening and Dr. J.G. van Rhijn for their help with histological techniques, interrenal cell measurements and statistical aspects     

Ultrastructure of the neurohypophysis of the teleost Poecilia latipinna in relation to neural control of the adenohypophysial cells

Summary The structure of the neurohypophysis of Poecilia latipinna (green molly, sailfin molly) was studied with the electron microscope. Profile diameters of neurosecretory granules in the non-myelinated neurohypophysial nerve fibres were measured and mathematically corrected for error due to section thickness. Six different types of nerve fibres could be distinguished by statistical classification of their granules and by other ultrastructural features. One fibre-type (type B) contained granules with a mean diameter of 85 nm, and the other five types (types Ala, Alb, A2, A3 and A4) all contained granules with mean diameters greater than 100 nm. Synaptic contacts were observed between type B fibres and all the adenohypophysial cell-types, although in the case of the ACTH cells the synapses were separated from the cell membrane by a continuous double basement membrane. Type A fibres were observed to contact the cells of the proximal pars distalis and pars intermedia, but did not form synapses. However, synapses occurred between type A fibres and pituicytes, and between type A fibres and the pericapillary basement membrane in the interior of the neurohypophysis. The possible roles of the different types of nerve fibres in controlling the adenohypophysial cells are discussed in the context of evidence from other teleosts.We thank Mr. W.A. Thomson and Mr. D.I. Hollingworth for technical assistance, and Dr. D.I.C. Pearson (Department of Physics, University of Nancy, Nancy, France) for advice on mathematical analysis and computer programs. The work was carried out during the tenure of an S.R.C. Research Studentship by T.F.C.B.     

Immunocytochemical studies on the pituitary pars distalis of the Japanese long-fingered bat,Miniopterus schreibersii fuliginosus

Summary Immunocytochemical studies were performed to describe the characteristics of cell types and their distribution in the pars distalis of Japanese long-fingered bat, Miniopterus schreibersii fuliginosus, collected at various stages of the reproductive cycle. Six distinct cell types have been identified in the pars distalis by the unlabeled immunoperoxidase technique and by the ABC method. Growth hormone (GH) and prolactin (PRL) cells were immunostained with antisera against chicken GH and ovine PRL. The GH-immunoreactive cells were round or oval orangeophilic cells distributed throughout the pars distalis with prominent aggregation in the posterolateral region. The PRL cells were pleomorphic carminophilic cells that occurred in small groups within the central and dorsocaudal regions of the pars distalis. They were sparsely distributed in the central region of the pars distalis in the hibernating bats, but increased significantly in the pregnant and lactating bats. The adrenocorticotropic (ACTH) cells were large round or polygonal amphophilic cells in the rostroventral and ventrolateral regions of the pars distalis. The thyrotropic (TSH) cells were small rounded or polygonal and distributed mainly in the ventrolateral region of the pars distalis. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) cells were identified immunocytochemically with antisera against the specific beta subunits of ovine LH and rat FSH. There were two populations of LH and FSH cells, one aggregated in the zona tuberalis and the other scattered singly throughout the rest of the pars distalis. The aggregated cells were immunoreactive with both antisera directed to LH and FSH, while scattered cells were reactive solely with antiserum to either LH or FSH and exhibited seasonal variations. In females, the proportional volume of the pars distalis occupied by LH cells was significantly reduced during pregnancy and lactation. No evidence of involution was observed in pars distalis cells except for PRL cells in males or females during hibernation.