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.     

Effects on gonadal function by lesioning tanycytes in the median eminence of the rat and Japanese quail

Summary The ependymal linings of the median eminence were destroyed by electric cautery or intraventricular injection of picric acid in the rat and Japanese quail. In these animals the ventricular lumen near the median eminence disappeared due to adhesion of lesioned walls on both sides of the third ventricle. Electric lesions of the ependymal layer containing tanycytes did not induce appreciable disturbance in the estrous cycles. Rats in which tanycytes were lesioned by picric acid displayed 4-day estrous cycles after prolonged diestrus (10–22 days). After destruction of tanycytes in the quail, a photostimulated gonadal growth was observed. It is concluded that the tanycyte transport of the ventricular fluid to capillaries of the portal vessels appears unnecessary for maintenance of adenohypophysial gonadotrophic activities.Supported by a grant from the Ministry of Education of Japan and by a grant from the Ford Foundation. The authors wish to express their gratitude to Dr. B.K. Follett for providing chicken LH (IRC2) and to the late Mr. T. Asai for assay of serum LH     

Antibodies obtained by xenotransplantation of organ-cultured median eminence specifically recognize hypothalamic tanycytes

Tanycytes are specialized ependymal cells lining the infundibular recess of the third ventricle of the cerebrum. Early and recent investigations involve tanycytes in the mechanism of gonadotropin-releasing hormone (GnRH) release to the portal blood. The present investigation was performed to obtain a specific immunological marker of tanycytes and to identify the compound(s) responsible for this labeling. After 30 days of organ culture, explants of bovine median eminence formed spherical structures mostly constituted by tanycytes. These tanycyte spheres were xenotransplanted to rats, and the antibodies raised by the host animals against the transplanted living tanycytes were used for immunochemical studies of the bovine and rat median eminence. This antiserum immunoreacted with two compounds of 60 kDa and 85 kDa present in extracts of bovine and rat median eminence. The individual immunoblotting analysis of rat medial basal hypothalami showed a decrease in the amount of the 85-kDa compound in castrated rats as compared to control rats processed at oestrus and dioestrus. The antiserum, labeled as anti-P85, when used for immunostaining of sections throughout the rat central nervous system, immunoreacted specifically with the hypothalamic tanycytes. Within tanycytes, P-85 immunoreactivity was exclusively present in the basal processes. It is suggested that the 85-kDa and 60-kDa compounds correspond to two novel proteins selectively expressed by tanycytes. The possibility that they are secretory proteins involved in GnRH release is discussed. Anti-P85 appears to be the first specific marker of hypothalamic tanycytes.     

Postnatal development of glial fibrillary acidic protein (GFAP) immunoreactivity in pituicytes and tanycytes of the Mongolian gerbil (Meriones unguiculatus)

Summary The postnatal development (day of birth up to the end of the third month) of neurohypophyseal pituicytes and tanycytes of the median eminence (ME) and the medial basal hypothalamus (MBH) was studied immunohistochemically in the Mongolian gerbil (meriones unguiculatus) with antibodies directed against glial fibrillary acidic protein (GFAP; the major protein subunit of glial filaments). Weak GFAP-immunoreactivity (IR) was scattered in the neural lobe (NL), the ME and the lining of the ventral 3rd ventricle at the first postnatal days. By the end of the second postnatal week, the intensity of the IR had reached a level comparable to that of adult animals. Generally, in the whole neurohypophysis a cytoarchitectonic pattern, which essentially corresponded to adult conditions, was reached around the beginning of the second month. During the first week postnatum, solely perinuclear stainings, mostly unipolar pituicytes with short processes and isolated fibers were discernible in the NL. In the course of the second and third postnatal week, a growing number of the densely arranged pituicytes appeared in form of bi- and multipolar cells. Thickness and length of pituicyte processes, as well as their degree of branching, increased progressively in the first month. The number of GFAP-positive tanycytes in the ventral 3rd ventricle and in the ME most markedly augmented in the first week postnatum. In the MBH, long tanycyte processes emerged from the ventricular lining to cross the arcuate nucleus in large bows, delimiting groups of neurons. Ependymal and subependymal tanycytes in the ME gave rise to radial processes extending to the external zone. Moreover, in this zone several tanycyte-like cells, whose number increased considerably in the second postnatal week, contributed to the palisadal arrangement of glial processes. In the third month, the arcuate nucleus was still penetrated by many immunopositive tanycyte processes. It was characteristic of the adult staining pattern that the highly branched processes of tanycytes and tanycyte-like cells in the ME were thicker and more variable in size than the less densely arranged tanycyte processes of the MBH. The postnatal increase of GFAP-IR intensity was paralleled by a similar development of vasopressin-IR in the ME and NL, indicating that the maturation of neurohypophyseal glia is closely linked to the functional differentiation of the neurosecretory axons.     

The functional and structural border of the neurohemal region of the median eminence

Summary In stressed rats the tanycytes of the ventrolateral wall of the third ventricle exhibit by light microscopic immunohistochemistry a positive staining for neurohormones which is distinctly limited to the distal perivascular end of the tanycyte process. Since by electron microscopic immuncytochemistry the tanycyte cytoplasm does not show any reaction product, the light microscopic reaction most likely results from a labeling of the intercellular space in the direct vicinity of the subendothelial cleft. Whether this subendothelial space is permeable to neurohormones was tested by injection of HRP¹. In the region of the arcuate nucleus 30 min after intravenous application, the marker is affixed to the membranes of the perivascular tanycyte processes in the subendothelial cleft of capillaries possessing non-fenestrated endothelia. Occasionally, HRP penetrates for a short distance between the tanycytes. Then the labeling of the intercellular cleft ends abruptly. Here, several parallel ridges of tight junctions between the perivascular distal tanycyte processes are found by the freezeetching technique. Since HRP cannot reach the subendothelial clefts of this region by passing through capillary walls due to the presence of a blood-brain barrier, it is suggested that the marker penetrates from the median eminence this far via the subendothelial extracellular space. It is prevented from spreading further by the tight junctions of the perivascular tanycyte endings. The same way may be taken by the neurohormones. Hence, a border area exists adjacent to the dorsolateral aspect of the neurohemal region of the median eminence where the tanycytes isolate the neuropil from the cerebrospinal fluid not only by their apical tight junctions, but also by basal tight junctions from the subendothelial cleft. This communicates with the perivascular space of the portal vessels.Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr. 569/2) and Stiftung VolkswagenwerkDedicated to Professor Dr. R. Ortmann on the occasion of his 65th birthday.The skilful technical assistance of Miss K. Bielenberg, Mrs. A. Hinz and Mrs. H. Prien is thankfully acknowledged     

Postnatal development of glial fibrillary acidic protein (GFAP) immunoreactivity in pituicytes and tanycytes of the Mongolian gerbil (Meriones unguiculatus)

The postnatal development (day of birth up to the end of the third month) of neurohypophyseal pituicytes and tanycytes of the median eminence (ME) and the medial basal hypothalamus (MBH) was studied immunohistochemically in the Mongolian gerbil (Meriones unguiculatus) with antibodies directed against glial fibrillary acidic protein (GFAP; the major protein subunit of glial filaments). Weak GFAP-immunoreactivity (IR) was scattered in the neural lobe (NL), the ME and the lining of the ventral 3rd ventricle at the first postnatal days. By the end of the second postnatal week, the intensity of the IR had reached a level comparable to that of adult animals. Generally, in the whole neurohypophysis a cytoarchitectonic pattern, which essentially corresponded to adult conditions, was reached around the beginning of the second month. During the first week postnatum, solely perinuclear stainings, mostly unipolar pituicytes with short processes and isolated fibers were discernible in the NL. In the course of the second and third postnatal week, a growing number of the densely arranged pituicytes appeared in form of bi- and multipolar cells. Thickness and length of pituicyte processes, as well as their degree of branching, increased progressively in the first month. The number of GFAP-positive tanycytes in the ventral 3rd ventricle and in the ME most markedly augmented in the first week postnatum. In the MBH, long tanycyte processes emerged from the ventricular lining to cross the arcuate nucleus in large bows, delimiting groups of neurons. Ependymal and subependymal tanycytes in the ME gave rise to radial processes extending to the external zone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Monoamine fluorescence in the median eminence of the Japanese quail,Coturnix coturnix japonica,following medial basal hypothalamic deafferentation

Summary Monoamine fluorescence was examined in the ventral hypothalamus of the Japanese quail, Coturnix coturnix japonica after medial basal hypothalamic deafferentation. In sham-operated control birds, numerous yellow-green fluorescent fibers were observed in the median eminence and the nucleus tuberis. In the area of the paraventricular organ, a number of fluorescent fibers and cell bodies were observed. In birds with deafferented hypothalami, fluorescence disappeared both in the median eminence and the nucleus tuberis. In the area of the paraventricular organ, which was within the area of deafferentation, fluorescence of neuronal perikarya did not change, but fluorescent fibers decreased markedly in number. Disappearance of monoamine fluorescence in the median eminence and the nucleus tuberis is discussed in relation to the tanycyte absorptive function and gonadal development.Supported by Grants from the Ministry of Education to Professors T. Bando and H. Kobayashi, and a Grant from the Ford Foundation to Prof. H. Kobayashi.     

Ependymoneuronal specializations between LHRH fibers and cells of the cerebroventricular system

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

大鼠第三脑室室管膜NADPH-d阳性伸展细胞的形态与分布

应用 Ｎ Ａ Ｄ Ｐ Ｈｄ 组织化学方法研究了大鼠第三脑室视前区室管膜的伸展细胞⒚结果表明：１）第三脑室视前区室管膜存在 Ｎ Ａ Ｄ Ｐ Ｈｄ 阳性的伸展细胞,其基突伸向视前区并与神经元或毛细血管相接触;２） Ｎ Ａ Ｄ Ｐ Ｈｄ 阳性的伸展细胞在第三脑室侧壁常见、室底少见、室顶未发现其存在;３） Ｎ Ａ Ｄ Ｐ Ｈｄ 阳性的伸展细胞的形态与分布,在雌、雄大鼠间不存在明显的性别差异⒚尽管 Ｎ Ａ Ｄ Ｐ Ｈｄ 阳性的伸展细胞的生理功能不十分清楚,但本研究为伸展细胞作为脑脑脊液环路的一部分,介导下丘脑对脑脊液中化学变化的感受提供了形态学依据,并提示一氧化氮可能参与了这一过程⒚     

Uptake of peroxidase from the third ventricle by ependymal cells of the median eminence

Summary Peroxidase injected into the subarachnoid space in mice is absorbed by ependymal cells of the median eminence. The ependymal cells of the median eminence of the rat and Japanese quail absorb peroxidase injected into the third ventricle. The processes of these ependymal cells terminate at the capillaries of the primary plexus or those surrounding the ventromedial nucleus of the hypothalamus. In all three species, peroxidase is absorbed by the ependymal cells of the paraventricular organ and by those in close proximity to it. Some ependymal cells send processes to the capillaries in the lateral nucleus of the hypothalamus. These phenomena are discussed in relation to adenohypophysial function.A part of this investigation was effected while the senior author held a Visiting Professorship at the University of Giessen [Department of Anatomy (Professor A. Oksche, Director)].     

Tanycyte and vascular patterns in the basal hypothalamus of Coturnix quail with reference to their possible neuroendocrine significance

Summary A well developed system of ependymal glial cells with long basilar processes stretching to the surface of the brain (tanycytes, Horstmann, 1954) has been described in the basal hypothalamus of Coturnix quail. The tanycytes both in the median eminence and the ventro-lateral hypothalamus form a link between the third ventricle and the hypophysial circulation. The processes of the ventro-lateral tanycytes terminate in the region of the infundibular sulcus in apposition to a loose network of vessels which are continuous with the primary plexus of the hypophysial portal system.Within the median eminence, the subependymal capillary network connects the vasculature of the contra-lateral sides of hypothalamus. There are no direct connections with the hypophysial portal vessels.With the aid of the light and electron microscope the ventricular ependyma was divided into a dorsal typical region and two glandular regions (ventro-lateral and ventral). Each region contains different forms of tanycyte. One of the two forms of tanycyte (designated type 3) associated with the ventro-lateral glandular ependyma has no contact with the third ventricle.Ultrastructural studies on the glandular ependyma failed to show any obvious differences between castrated, oestrogen or testosterone implanted, and sexually mature or immature quail.The possibility that the tanycyte-vascular system may have a neuroendocrine role is discussed.I am indebted to Professor A. Oksche, Dept. of Anatomy, University of Giessen for providing research facilities and to The Royal Society for additional financial support.     

Immunohistochemical and electron microscopic study of the rat hypothalamic nuclei and cell clusters under various experimental conditions

Summary In untreated, pregnant and thirsting rats the neurosecretory hypothalamic areas were investigated by means of the immunoperoxidase technique in order to demonstrate vasopressin- and oxytocin containing elements at the light- and electron microscopic level. In addition, chromalum-hematoxylinphloxin (CHP) staining and conventional double staining of ultrathin sections were used. The areas investigated included the anterior and posterior supraoptic nuclei, the paraventricular nuclei, the numerous accessory cell clusters in the region between the tractus opticus and the third ventricle as well as the median eminence. In all nuclei and in the accessory cell clusters, the number of vasopressin-reactive neurons exceeds that of oxytocin-reactive neurons. Compared with the anterior supraoptic nucleus, the posterior supraoptic nucleus and the accessory cell clusters react more heavily to prolonged thirst. In the median eminence the neurosecretory axons display close contacts with the portal vessels not only in its lateral portion but in thirsting animals also around the mid-line. There the internal layer is broadened and vasopressin-positive tanycytic processes reach the external zone. Parasagittally, fine vasopressin-positive material can be traced from the internal layer to small deposits at the portal vessels. In long term thirsting animals the typical feature of swollen axons exhibits a characteristic distribution in the median eminence and renders a distinct positive reaction to anti-vasopressin. The release of peptide hormones from the perikarya and from the axons within the nuclei as well as the mode of release within the median eminence are discussed. The significance of the positive immunostaining of the ependymal tanycytes and of some perikarya of the suprachiasmatic nucleus must be reconsidered by further studies.Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr 569/1) and Stiftung VolkswagenwerkDedicated to Professor Berta Scharrer on the occasion of her 70th birthdayThe author wishes to express her special gratitude to Dr. L.A. Sternberger for supplying the peroxidaseantiper oxidase-complex and to Dr. H. Stein (Pathologisches Institut der Universität Kiel) for supplying Anti-IgG. The skilful technical assistance of Mrs. H. Prien and Mrs. H. Schöning is thankfully acknowledged     

Immunoreactive substance P content in median eminence and pituitary gland during oestrus, dioestrus and after anterior hypothalamic deafferentation

The aim of the present study was to find a relation between the Substance P (SP) content in the median eminence and the pituitary gland in rats and hypothalamic regulaton of the oestrus cycle. SP content was measured by radioimmunoassay in female rat pituitary and median eminence during oestrus, dioestrus and after anterior hypothalamic deafferentation. SP content in rat's pituitary did not vary significantly among individual groups of animals. The greatest average SP content in rat's median eminence was found in dioestrus. Both during cyclic and constant oestrus resulting from anterior hypothalamic deafferentation SP content in median eminence was lower than in dioestrus. This fact indicates the possibility of SP involvement in the control of cyclic LH-RH release from hypothalamus.     

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.     

The adsorptive and transport capacity of tanycytes during the perinatal period of the rat

Summary Transport of ferritin and horseradish peroxidase from the 3rd ventricle to the median eminence was examined in rats during the perinatal life, the time when functional interrelations between hypothalamus and hypophysis are established. Protein tracers injected into the lateral ventricle are adsorbed on the apical surface of the tanycyte, mainly on its protrusions or in indentations. On the 18th day of prenatal life a few small bleblike protrusions are observed. After birth microvilli appear. In time their concentration increases to result in an increase of adsorbed substances. They are taken up by smooth and coated pinocytotic vesicles and transported to the basal portion of the cell or to the intercellular space bypassing junctional complexes. In addition to pinocytotic vesicles protein tracers fill channels of smooth ER or Golgi complex and multivesicular bodies illustrating a process probably involved in metabolic or secretory processes.     

Microglia and reactive “M” cells of degenerating central nervous system: Does similar morphology and function imply a common origin?

Summary Penetration of the median eminence and ventrolateral walls of the III ventricle by intraventricularly injected horseradish peroxidase was studied in rats. Experimental times varied between 10 to 70 min (short-term experiments) and 12 hrs to 30 days (long-term experiments).In short-term experiments, the median eminence was found to be completely stained whereas the lateral walls of the III ventricle were penetrated only up to 1 mm in depth. Spreading of the tracer takes place predominantly through the extracellular space and cellular uptake and transport do not seem to play a role during the first 70 min following the injection.In long-term experiments, the tanycytes exhibit a variety of intracellular inclusions marked by HRP precipitate. Tanycytic perikarya contain dense bodies and lipofuscin-like aggregates. Lipoprotein granules are thought to arise from these and are interpreted as lysosomal residual bodies. In tanycytic processes and perivascular endfeet, accumulations of HRP-containing tubules and polymorphous granules are encountered suggesting a transport towards the blood vessels of the portal plexus or of the arcuate and ventromedial areas, respectively. Sporadic tanycytes which are completely and evenly stained from the ventricular surface to the end of their processes were observed in the arcuate and ventromedial area. Whether this appearance can be taken as a sign of normal cell function seems doubtful. Some possible routes of transport through the median eminence—extracellular and transcellular—are summarized in a schematic drawing, taking into account the present findings and those published elsewhere in the literature.We gratefully acknowledge an Anglo-German Collaboration Grant of the Wellcome Trust enabling stimulating discussions with other workers in the field.     

The functional and structural border between the CSF-and blood-milieu in the circumventricular organs (organum vasculosum laminae terminalis,subfornical organ,area postrema) of the rat

Summary The present study continues a previous investigation on the median eminence (EM) (Krisch et al., 1978). In rats with high levels of neurohormones (LHRH, vasopressin) a limited immunohistochemical labeling of perivascular tanycyte processes can be observed surrounding capillaries in the marginal region of the organum vasculosum laminae terminalis (OVLT) and in the inner part of the subfornical organ (SFO). This labeling extends from the perivascular space a short distance along the tanycyte processes. By conventional electron microscopy and by freeze-etching, tight junctions are demonstrated at a distance from the capillary lumen which corresponds to the borderline of the immunohistochemical labeling of perivascular tanycyte processes in light microscopic preparations. The tight junctions are arranged in several parallel and helical rows and correspond to those found in the median eminence. Consequently, the immunohistochemical labeling in the OVLT and in the SFO marks the intercellular cleft. In the circumventricular organs the immunostaining labels the extension of the perivascular space characterized by the hemal milieu. The perivascular space is separated off by tight junctions from the CSF-milieu of the adjacent neuropil. Furthermore, the present study demonstrates tight junctions in the marginal region of the area postrema (AP) between the perivascular processes of the tanycytes.Supported by the Deutsche Forschungsgemeinschaft (Grant Nr. Kr. 569/2) and Stiftung VolkswagenwerkThe skillful technical assistance of Miss K. Bielenberg, Mrs. A. Hinz and Mrs. Helga Prien is thankfully acknowledged     

Immunohistochemical localization of corticotropin-releasing factor (CRF)-containing neurons in the hypothalamus of the Japanese quail,Coturnix coturnix

Immunohistochemical localization of corticotropin-releasing factor (CRF)-like immunoreactivity in the brain of the Japanese quail was studied by means of the peroxidase anti-peroxidase (PAP) method. CRF-immunopositive perikarya of parvocellular neurons were observed mainly in the nucleus praeopticus medialis and nucleus paraventricularis. Additional perikarya were also detected in the nucleus hypothalamicus posterior medialis in the hypothalamus and in the non-hypothalamic nucleus accumbens, nucleus septalis lateralis and nucleus dorsomedialis and dorsolateralis thalami. No CRF immunoreaction was found to coexist with the vasotocin (Vt)-containing system in comparative examination of consecutive sections treated with anti-vasopressin (Vp) serum. The CRF-immunoreactive fibers were detected mainly in the external layer of the anterior median eminence but not in its posterior division. Unilateral adrenalectomy induced the marked reduction in number of the CRF immunopositive fibers in the anterior median eminence.     

Effect of long-term suppression and long-term stimulation of ACTH secretion on the ultrastructure of tanycytes[]

The ultrastructure of the tanycyte ependyma in males of Wistar albino rats (160--180 g of weight) was studied under experimental long-term suppression of ACTH secretion and its long-term stimulation. The former effect was accomplished by daily (for 8 days) intraperitoneal administration of dexamethasone phsophate; the stimulation of ACTH secretion was achieved by bilateral adrenalectomy. The long-term suppression of the hypophyseal adrenocorticotrophic function was followed by the ultrastructural markers of an increased transport and secretory activity in the tanycytes (mainly in beta-tanycytes, i. e. the ependyma lining floor of the third ventricle): the increased amount of microvesicles in the Golgi area and in the vicinity of the particular membranous cavity system (MCS, according to the authors' definition), the appearance of some figures of exocytosis, the elevated amount of lipid inclusions. On the contrary, the long-term stimulation of ACTH secretion was followed by the ultrastructural changes of the opposite character. The data obtained are in agreement with the previously established fact that there is a negative correlation between the tanycyte activity and the hypophyseal adrenocorticotrophic activity. It is supposed that this correlation is regulated by a feedback mechanism and attest to the involvement of tanycytes in the inhibitory control of ACTH secretion. A possible substrate inhibiting ACTH secretion by the tanycytes is discussed.     

Ultrastructural changes in the median eminence of the rat following deafferentation of the basal hypothalamus

Summary This report concerns a light and electron microscopic investigation of the median eminence and dorsal infundibular stem of the rat following surgical isolation (deafferentation). Using a modification of the Halász technique, the basal hypothalamus, including the arcuate nucleus and median eminence were surgically isolated from surrounding structures. Special attention was directed to the contact (external) zone of the median eminence and rostral infundibulum where tuberohypophyseal axons as well as ependymal cell processes abut upon the abluminal basement membrane of the portal perivascular space. The results of this study to date suggest that 9, 20, and 40 days following surgical isolation, there is a distinct increase in the population of tuberohypophyseal dense core vesicles. It is suggested that deafferentation abolishes inhibitory and excitatory input that serves to modify the cellular dynamics of tuberohypophyseal neurosecretory elements. Comments are also made on the presence of cistern-like structures in the lateral median eminence; the presence of vesicle-like inclusions in terminal ependymal processes is discussed in relationship to the role that ependyma may play in linking the third ventricle with the adenohypophysis.This research was supported by USPHS Grants NB 08171 and AM 10002. The authors are indebted to the excellent technical assistance provided by G. Krobisch Dudley. Further, the authors wish to express their thanks to Dr. Adolph Weindl for his valuable advice and criticism, and to Matilde Holzwarth for her helpful assistance.