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.     

On the relations between the hypothalamus and the anterior pituitary in Rana temporaria

Summary Dawson (1952) showed that, in Rana, many nerve terminals end round the capillaries of the venous portal system of the median eminence. Our observations not only confirm these facts but show as well that, besides the posterior lobe, the outer zone of the median eminence is also a centre of accumulation of neurosecretory material derived from the pre-optic nucleus. The amount of this neurosecretory material is moreover subject to a certain variation in connection with the seasons and with experimental conditions. The idea is put forward that the outer zone of the median eminence of Rana has to be considered as an analogical organ of the posterior lobe. Indeed, in the median eminence, the same morphological facts can be found, which are advanced for the conception that the posterior lobe is a centre of accumulation and a place of release of neurosecretory material originating from the pre-optic nucleus. On the basis of our observations we presume that the hypothalamo-hypophyseal neurosecretory system of Rana can be divided in two sub-units. System I ends in the posterior lobe; system II in the outer zone of the median eminence. The data of the literature indicate that the two systems also probably exist in the higher vertebrates. From these facts it is obvious that the neurosecretory material is transported from the pre-optic nucleus, via the tract, towards the outer zone of the median eminence.     

Ultrastructural characteristics of the differentiation of glandular cells in the anterior pituitary gland of collared lemmings (Dicrostonyx) from the Vrangel Island

In 15.5-, 16-, 17.5-, 18.5-, 20-day-old fetuses and newborn lemmings, the ultrastructure of the anterior lobe of the hypophysis has been studied. In the parenchyma of the 15.5-day-old fetus gland, some cells containing secretory material are revealed, but they are difficult for identification, since differentiation of their organellas is not completed and polymorphism of their granules is strongly manifested. On the 17.5th day of the prenatal development TTH-, ACTH-, LH-, STH-secreting adenocytes are detected; they include secretory granules having diameters 70--100 nm, 80--150 nm, 60--140 nm and 200--400 nm, respectively. On the 18.5th day FSH-secreting cells are identified. Lactotropocytes appear on the 20th day. The anterior lobe of the hypophysis of 17.5--18.5-day-old fetuses are characterized by a high level of the secretory activity which decreases to some extent before birth. Ultrastructure of the cellular organellas in the newborn hypophysis is similar to that in a mature animal, nevertheless, the diameter of the secretory granules does not reach the size of these elements in mature individuals.     

Relationship of the central ACTH-immunoreactive opiocortin system to the median eminence and the pituitary gland of the rat

Summary By immunocytochemical methods, the present study describes ACTH-immunoreactive fibers in the pituitary stalk and neural lobe. This opiocortin-hypothalamo-neural lobe projection arises in a bed nucleus of perikarya in the basal hypothalamus, follows supraoptico-hypophyseal fibers in the zona interna of the median eminence, and distributes throughout the neural lobe. No ACTH-immunoreactive fibers project to the zona externa; some are present in the subependymal layer and at the lateral margins of the median eminence. Further studies must identify the role of these fibers in posterior lobe function. It remains also to be determined whether this system terminates upon primary pituitary portal capillaries and delivers opiocortin neuropeptides to the adenohypophysis.Supported by NIH Grants HD-07962, NS-15345 and AM-22029The skillful technical assistance of Donna Wilson, Nancy Dembs and Jay Hocton is thankfully acknowledged     

Morphological characteristics of the structures delimiting the residual cavity of the hypophysis in rats after electrocoagulation of the median eminence of the hypothalamus]

By means of light and electron microscopy it has been shown that the remnant cavity of the hypophysis of intact and sham-operated rats on the side of the intermedial lobe is restricted with a continuous layer of epithelial cells with a well pronounced basal membrane. On the side of the frontal lobe the covering epithelium has peculiar "fenestra" through which adenocytes have free contacts with the remnant cavity. After electrocoagulation of the rostral area of the medial eminence, especially in remote postoperative terms, the remnant cavity enlarges up to gigantic size, contains a great amount of colloid, erythrocytes, fragments of cells of the anterior lobe of the hypophysis and secretory granules. The anterior epithelium is lacking on considerable areas and hence adenocytes are disposed in the cavity directly. All their organoids are preserved though a little changed, the cytomembrane is absent. On the apical surface of the posterior epithelium there appear large cytoplasmic protrusions which having separated enter the remnant cavity. The main provider of the "raw material" for colloid is likely to be the anterior lobe of hypophysis.     

The nerve fibres controlling the gonadotropic activity of the hypophysis of Rana temporaria

Summary In 27 adult female specimens of Rana temporaria, the total interruption of the nervous pathways to the median eminence and the hypophysis was performed, without disturbing the normal blood supply of the hypophysis. In eight cases this complete interruption persisted three months after operation. In these animals there occurred no seasonal development of the eggs, ovaries and oviducts. In the 19 other operated animals a varying degree of regeneration of the interrupted nerve fibres occurred. In these animals a varying number of ripe eggs was present, but in many of them there existed a significant difference between the weight of their ovaries compared with that of the ovaries of the control animals. In all control animals the seasonal development of the ovaries and oviducts was normal. From these and from previous experiments it could be concluded that the A. F. negative nerve fibres of the median eminence, not originating from the magnocellular neurosecretory preoptic nuclei, are responsible for the normal seasonal development of the ovaries and oviducts in Rana temporaria. It must be these nerve fibres that release gonadotropic releasing factors into the blood capillaries of the median eminence. The A. F. positive neurosecretory fibres, the portal circulation of the pars distalis and the pituicytes of the median eminence play only a secondary part during this period of control of the gonadotropic activity of the hypophysis.     

The characteristics of the hormonal profile of the central links in the regulation of adrenocortical function in rat postnatal ontogeny]

Radioimmune assay has been made of the ACTH content of the blood and adenohypophysis, as well as the content of vasopressin in the blood, median eminence, the posterior and intermediate hypophysis in 1, 3, 5, 7, and 20 days old rats and adult male rats. Comparison of the hormonal level in neurohaemal areas with that in the blood plasma suggests that transadenohypophyseal path of hypothalamic neurohormonal control of the adrenocortical function becomes essentially important only after formation of capillary plexus in the external zone of the median eminence.     

Experimental identification of a hypothalamic gonadotropic centre

Summary In a large group of adult female and male specimens of Rana temporaria all nervous pathways to the median eminence and hypophysis were extirpated without disturbing the normal blood supply of the median eminence and hypophysis. The total interruption of the nervous pathways persisted in all animals. In all animals gametogenesis and seasonal development of the gonads and of the secondary sexual characteristics were absent. In another large group of animals, the pars ventralis of the tuber cinereum of the hypothalamus was isolated from the brain. The pars ventralis retained its normal connections with the median eminence and hypophysis. The normal blood supply of the whole isolated region (pars ventralis tuberis + median eminence + hypophysis) was preserved. Four months after operation, in the majority of the animals, the isolation was still complete. In all animals, normal gametogenesis and seasonal development of the gonads and of the secondary sexual characteristics had occurred.In accordance with previous experiments, the present experiments showed that the pars ventralis tuberis contains an important gonadotropic centre. The activity of the gonadotropic centre of the pars ventralis tuberis is, at least, mainly exerted by its influence on the gonadotropic function of the pars distalis of the hypophysis. This is shown morphologically by a gradient of nuclear volume and by the mean nuclear volume of the P.A.S. positive cells of the pars distalis. The influence of the gonadotropic centre on the pars distalis is exerted by A.F.-negative nerve fibres to the median eminence. It is highly probable that all these nerve fibres end on the primary capillary network of the hypophysial portal system. The experiments strongly suggested that the axon endings of the gonadotropic centre would influence the gonadotropic activity of the pars distalis of the hypophysis by releasing of gonadotropic releasing factors into the blood capillaries of the median eminence.The gonadotropic centre of the pars ventralis tuberis is necessary for the normal gametogenesis and for the seasonal development of the gonads and of the secondary sexual characteristics. So far as concerned the gametogenesis and the seasonal development of the gonads, the function of the gonadotropic centre is largely autonomous.Exclusion of the function of a part of the pars ventralis tuberis produces quantitative, but no qualitative changes in gametogenesis.     

Evidence for the control of prolactin secretion by hypophysial posterior lobe extracts

The effect of posterior lobe extracts on prolactin secretion in vitro was compared with that of median eminence, hypothalamic (with and without median eminence) and cortex extracts. The posterior lobe extract clearly inhibited adenohypophysial prolactin secretion, showing a similar effect to that of the hypothalamic extracts. The median eminence extract showed inconstant inhibitory effects, while the cerebral cortex extracts showed no effect. The removal of the median eminence did not modify the hypothalamic inhibitory effect. Although the median eminence has always been considered to be the final common pathway for the control of adenohypophysial secretion, these results suggest that the posterior lobe may also play a physiological role in this control.     

The structure and vascularization of the pars tuberalis of the hypophysis of Rana temporaria

Summary The pars tuberalis of the hypophysis of Rana temporaria presents the general structural and the cytological characteristics of an endocrine gland. It is composed of elongated cells with long, branching processes ending on the external basement membrane of the pericapillary space. The pars tuberalis cells produce secretory granules which are accumulated in the pericapillary endings of the processes.Corresponding to its separate localization, the pars tuberalis of Rana temporaria has a separate vascularization of which the efferent capillaries anastomose with the capillary plexus of the median eminence. The general direction of the blood flow of the pars tuberalis is towards the capillaries of the median eminence. Also, the secretory products of the pars tuberalis pass into the blood stream of the hypophysial portal system.Several characteristics of the pars tuberalis show that its function must be different from that of the pars distalis of the hypophysis. Moreover, in contrast with the pars distalis, the activity of the pars tuberalis is not regulated by neurohumoral factors.The results show that a role of the pars tuberalis in the regulation of the activity of the pars distalis of the hypophysis is not excluded.     

Immunocytochemical study of the GABAergic innervation of the mouse pituitary by use of antibodies against gamma-aminobutyric acid (GABA)

Summary The GABAergic innervation of the mouse pituitary, including the median eminence, was studied at light microscopic and ultrastructural levels by use of a pre-embedding immunocytochemical technique with antibodies directed against GABA. In the median eminence, a high density of GABA-immunoreactive fibers was found in the external layer where the GABAergic varicosities were frequently observed surrounding the blood vessels of the primary capillary plexus. In the internal and subependymal layers, only few fibers were immunoreactive. The intense labeling of the external layer was observed in the entire rostro-caudal extent of the median eminence. In the pituitary proper, a dense network of GABA-immunoreactive fibers was revealed throughout the neural and intermediate lobes, entering via the hypophyseal stalk. The anterior and tuberal lobes were devoid of any immunoreactivity. The GABA-immunoreactive terminals were characterized in the median eminence, and in the intermediate and posterior lobes at the electron-microscopic level. They contained small clear vesicles, occasionally associated with dense-core vesicles or neurosecretory granules. In the intermediate lobe they were seen to be in contact with the glandular cells. In the posterior lobe and in the median eminence, GABA-immunoreactive terminals were frequently located in the vicinity of blood vessels. These results further support the concept of a role of GABA in the regulation of hypophyseal functions, via the portal blood for the anterior lobe, directly on the cells in the intermediate lobe, and via axo-axonic mechanisms in the median eminence and posterior lobe.     

Developmental correlation between hypothalamic somatostatin and hypophysial growth hormone

Summary The objective of the present study was to determine, by means of immunocytochemistry, the age in fetal development at which GH is first detectable in the pituitary gland and somatostatin in the median eminence, and to correlate temporally the development of these two hormones throughout the remainder of pregnancy. Mice were studied at 15–19 days of gestation with the peroxidase-antiperoxidase (PAP) technique of Sternberger. Somatotropes in the pars distalis were initially detected at 16 days of gestation and by 17 days they were a prominent component of the parenchymal cell population of the hypophysis. These cells were ovoid and distributed uniformly throughout the pars distalis; many were located adjacent to sinusoidal capillaries. Their number and staining intensity increased by 19 days. Somatostatin was not consistently observed in the median eminence until 19 days of gestation. Reaction product indicative of the presence of somatostatin in presumptive nerve endings was located on the ventral surface of the median eminence and in the external lamina of the infundibulum in proximity to the superficial portal capillaries. Results of the present investigation support the concept that the potential for neuroendocrine control of GH secretion exists in the mouse by the end of fetal development. Several hypotheses concerning the temporal relationship between the appearance of somatostatin in the hypothalamus and of GH in the anterior pituitary gland are discussed.Supported by a Biomedical Research Support Grant (NIH RR 5417). Appreciation is extended to the National Pituitary Agency, NIAMDD for the following radioiodination-grade hormones: hGH, rPRL, rTSH, rFSH and hCG     

The origin of somatostatin fibers in the median eminence and neural lobe of Rana temporaria

Summary A light microscopic immunocytochemical study of the brain of frogs with hypothalamic lesions was performed in order to obtain evidence concerning the origin of somatostatin fibers in the median eminence and neural lobe of the hypophysis. The results indicate that the somatostatin fibers of the neural lobe originate from somatostatin perikarya located in the prechiasmatic part of the hypothalamus and possibly also in the telencephalon. The somatostatin neurons of the pars ventralis tuberis cinerei do not send axons to the neural lobe. The frog median eminence contains axon terminals of somatostatin neurons located in the pars ventralis of the tuber cinereum. Many other somatostatin fibers of the frog median eminence originate from somatostatin neurons located outside the tuber cinereum. Most of these neurons probably lie in the preoptic hypothalamic region.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Influence of thyroid hormone on the development of preoptic-hypothalamic monoaminergic neurons in tadpoles of Bufo bufo japonicus

The effect of thyroid hormone on the development of diencephalic monoaminergic neurons was studied in tadpoles of Bufo bufo japonicus. Monoamine-containing neurons in the preoptic recess organ (PRO) appeared later than those in the paraventricular organ (PVO) and nucleus infundibularis dorsalis (NID). After deprivation of thyroidal primordium no fluorescent neurons developed in the PRO. Development of monoaminergic neurons in the PVO and NID was not affected by thyroidectomy. Thyroxine treatment brought about the fluorescent neurons in the PRO of the thyroidectomized tadpoles. Fluorescent terminals in the median eminence became conspicuous around the capillaries which penetrated to the median emience, when the tadpoles reached late prometamorphic stage. In the median eminence of thyroidectomized tadpoles, the monoaminergic axon terminals did not develop. Thyroxine induced both the fluorescent terminals and the capillary penetration in the median eminence of the thyroidectomized tadpoles. In the tadpoles hypophysectomized at tail-bud stage, thyroxine induced neither the fluorescent terminals nor the capillaries in the median eminence.     

Distribution pattern in the human pituitary and hypothalamus of a new neuropeptide: The C-terminal glycoprotein-fragment of human pro-pressophysin (CPP)

Summary The distribution pattern of CPP-containing neurons and fibers in the human pituitary and hypothalamus was studied with a specific antiserum to human CPP and the unlabeled antibody technique. Immunoreactive CPP was found in the magnocellular neurons of the supraoptic nucleus (SON), the paraventricular nucleus (PVN) and in neurons scattered in the supraoptic hypophyseal tract. CPP-containing parvocellular neurons were found in the suprachiasmatic nucleus (SCN). The CPP-containing fibers from the magnocellular neurons formed a tract coursing through the median eminence and the pituitary stalk to the posterior lobe of the hypophysis. In contrast, no such fibers from the SCN projected to SON, PVN and the median eminence. This pattern is identical to that of vasopressin and its associated neurophysin-containing neurons and fibers and strongly supports the concept that CPP is a part of the common precursor for vasopressin and neurophysin II. The biological importance of human CPP other than being a precursor fragment remains to be elucidated.To whom requests for reprints should be addressed     

Organization and development of the perivascular space system in the neurohypophysis of the laboratory mouse

Summary The organization of the system of perivascular space around the capillaries in the neurohypophysis was studied in the adult and developing laboratory mouse by the use of histological silver impregnation and electron microscopical techniques.In the median eminence short and long extensions, arising mainly from the shallow space around capillary loops of the primary plexus of the portal system, formed radiations into the adjacent neural tissue of the external zone. The tissue of the neural lobe was separable into non-vascular regions dominated by undilated portions of neurosecretory nerve fibres and pituicytes, and neurovascular regions with perivascular space extensions forming an extensive system of connections between neighbouring capillaries.In the median eminence, the system of extensions of the perivascular space was estimated to increase the neurovascular contact surface area by at least 50%, implying an increased efficiency of the organ without a notable increase of its volume. The possibility that the ramifications of the perivascular space imply an enhanced uptake rate into the bloodstream and a subsequent increased concentration of the neurohormones in the portal blood, was discussed.During development of the median eminence, differentiation of perivascular space extensions of the adult type started in the juvenile of about three weeks of age, when shallow capillary loops had been formed. In the neural lobe, perivascular space ramifications were already present when the internal capillaries were formed and were fairly frequent in ten-day young. At the age of three to four weeks the organization of the system was similar to that of the adult animal.     

A comparative study of the ultrastructure of the median eminence,infundibular stem and neural lobe of the hypophysis of the rat

Summary The ultrastructure of the infundibulum has been studied and compared with that of neural lobe in normal rats. The neurohemal areas of the median eminence are similar to those of the stem but differ from those of neural lobe. The infundibular axons which end around the primary capillaries of the portal system are of a significantly finer caliber. Secondly they contain a different vesicle population. They lack the large (1500 Å–2100 Å) neurosecretory vesicles so abundant in neural lobe axon terminals but contain a smaller (less than 1000 Å) type of vesicle with an osmiophilic center. These dense-core vesicles are consistently present in the many infundibular levels examined, although they are not as numerous as the neurosecretory ones of neural lobe. They are outnumbered by vesicles of the synaptic type, whereas in neural lobe the neurosecretory ones predominate. Another difference involves the electron lucent, neurosecretory vesicle. These are abundant in neural lobe axons, but comparable aggregations of them have not been seen in infundibular axon endings of the neurohemal areas. In contrast, the internal zone of median eminence and the interior of the stem display, in addition to the fine axons, many large fibers which by size and content match the ones of neural lobe. However, careful study indicates that these are axis cylinders and not axon endings.These observations lead to the conclusion that the small calibered axons which terminate around the infundibular capillaries of the portal system constitute a separate group, and are clearly distinguishable at the ultrastructural level from the large supraoptico-neurohypophyseal axons. The latter normally traverse the infundibulum but terminate in neural lobe.This investigation was supported by U.S.P.H.S. Research Grant 5 RO 1 NB 02321-05, National Institute of Neurological Diseases and Blindness. — The author is particularly indebted to Mrs. Nora Tong for her excellent technical assistance throughout the course of this study.     

The topography of mesotocin and vasotocin systems in the brain of the domestic mallard and japanese quail: Immunocytochemical identification

Summary The neurosecretory systems producing mesotocin (MT) and vasotocin (VT) (the avian homologues of oxytocin and vasopressin, respectively) were characterized in the brains of the domestic mallard and Japanese quail by means of indirect immunofluorescence techniques using specific antisera. In the anterior preoptic region, including the organum vasculosum of the lamina terminalis, and at different levels of the supraoptic and paraventricular nuclei, separate mesotocin- and vasotocin-producing neurons were identified. Mesotocinergic and vasotocinergic neurons were also located in the tuberomammillary area, among the ectomammillary tract fibers. The supraoptico-neurohypophysial tract, formed by vasotocin- and mesotocincontaining axons, enters the internal zone of the median eminence and ends in the posterior lobe of the pituitary. The external zone of the rostral median eminence appears to contain vasotocin and mesotocin fibers, which terminate in close contact with the capillaries of the hypophysial portal system.With contributions by Dr. B. Kerdelhué, Laboratoire des Hormones Polypeptidiques du CNRS, 91190 Gif-sur-Yvette, France     

Immunohistochemical localization of gonadotropin-releasing hormone (GnRH) in the fetal and early postnatal mouse brain.

The objectives were to (a) determine the age in development when GnRH is first detectable in the brain and (b) observe the distribution of GnRH throughout the fetal and early postnatal period. GnRH was localized immunohistochemically in fetal (15, 16, 17 and 19 days of gestation) and early postnatal (1- and 7-day-old) mice with the peroxidase-antiperoxidase (PAP) method of Sternberger. In the organum vasculosum of the lamina terminalis (OVLT) and in the median eminence of the fetus, GnRH was first detected at 17 days of gestation. In the OVLT, GnRH was found ventral to the preoptic recess of the third ventricle near the ventral surface of the brain. In addition, GnRH was located adjacent to the superficial portal capillaries near the surface of the median eminence. At 19 days of gestation, the distribution of GnRH was similar to that observed at 17 days and there was a marked increase in amount. In the newborn mouse, GnRH was undetectable in the OVLT and its content in the median eminence was decreased as compared to that observed in the fetus. By the seventh postnatal day, a considerable accumulation of GnRH had occurred in the OVLT and median eminence. In the OVLT, it was associated with capillaries ventral to the preoptic recess, and its distribution in the median eminence was similar to that in the adult mouse. In both the OVLT and median eminence of the fetal and early postnatal mouse GnRH appeared to be stored in axons and axon endings, but was not detectable in nerve cell bodies or ependymal cells. These observations suggest that the potential for neuroendocrine control of gonadotropin secretion exists in the fetal mouse early as 17 days of gestation.     

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.