Golgi-like immunostaining of pituicytes and tanycytes positive for glial fibrillary acidic protein in the neurohypophysis of the Mongolian gerbil (Meriones unguiculatus)

Summary Glial cells that contain the glial fibrillary acidic protein (GFAP; the major protein constituent of glial filaments) were stained immunohistochemically in thick frozen sections of the neurohypophysis of the Mongolian gerbil (Meriones unguiculatus). The resulting Golgi-like images provided informations on cytological features and distributional patterns of tanycytes and pituicytes. In the proximal median eminence, numerous bundled processes of tanycytes were revealed. They emerged from the ependymal and subependymal layer and mostly reached the brain surface. Several tanycytic processes extended into the anatomical neural stalk. In the whole neural lobe, a dense network of GFAP-immunoreactive pituicyte processes was visualized. Stained pituicytes were highly asymmetric and exhibited a great morphological variability. Immunopositive fibers which were encountered in the intermediate lobe might be derived from pituicytes. Electron-microscopically further evidence was obtained that GFAP-positive pituicytes correspond to filament-rich fibrous pituicytes at the ultrastructural level.     

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)     

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.     

Glial cells positive for glial fibrillary acidic protein in the neurohypophysis of the Djungarian hamster (Phodopus sungorus)

Summary The presence and distribution of the glial fibrillary acidic protein (GFAP; an astrocytic marker protein associated with glial filaments) in the neurohypophysis of the Djungarian hamster (Phodopus sungorus) were investigated immunohistochemically. Our study revealed characteristic GFAP-staining patterns within the median eminence, infundibular stem and neural lobe. In the whole neurohypophysis, few glial cells showed immunoreactivity. In the neural lobe, immunopositive pituicytes appeared preferentially in the periphery. At the ultrastructural level, we found some pituicytes containing filaments, most notably in their processes. We thus demonstrated that, in contrast to the GFAP-immunoreactivity of cultured pituicytes, pituicytic GFAP-expression in vivo coincides with the presence of electron-microscopically detectable filaments.     

Immunogold electron microscopic localization of glial fibrillary acidic protein (GFAP) in neurohypophyseal pituicytes and tanycytes of the Mongolian gerbil (Meriones unguiculatus)

The post-embedding immuno gold staining (IGS) technique was used for the ultrastructural localization of glial fibrillary acidic protein (GFAP) in pituicytes and tanycytes of the neurohypophysis. IGS was applied to LR White embedded neurohypophyseal tissue of the Mongolian gerbil (Meriones unguiculatus), a species which contains abundant GFAP-positive pituicytes and tanycytes. GFAP-immunoreactivity could be demonstrated on pituicytic intermediate filaments (IF's) in situ. Thus, it was shown that pituicytes contain GFAP in its filamentous form, what had been a matter of speculation. At the ultrastructural level, gerbil tanycytes and tanycyte-like cells in the external zone of the median eminence were characterized by a great amount of densely packed IF's, which were labeled by both GFAP- or vimentin-antibodies. Sequential immunostaining of serial semithin sections with GFAP- and vimentin-antibodies revealed an invariable coexpression of the two IF proteins in somata and processes of these median eminence cells.     

Immunogold electron microscopic localization of glial fibrillary acidic protein (GFAP) in neurohypophyseal pituicytes and tanycytes of the Mongolian gerbil (Meriones unguiculatus)

Summary The post-embedding immuno gold staining (IGS) technique was used for the ultrastructural localization of glial fibrillary acidic protein (GFAP) in pituicytes and tanycytes of the neurohypophysis. IGS was applied to LR White embedded neurohypophyseal tissue of the Mongolian gerbil (Meriones unguiculatus), a species which contains abundant GFAP-positive pituicytes and tanycytes. GFAP-immunoreactivity could be demonstrated on pituicytic intermediate filaments (IF's) in situ. Thus, it was shown that pituicytes contain GFAP in its filamentous form, what had been a matter of speculation. At the ultrastructural level, gerbil tanycytes and tanycyte-like cells in the external zone of the median eminence were characterized by a great amount of densely packed IF's, which were labeled by both GFAP- or vimentin-antibodies. Sequential immunostaining of serial semithin sections with GFAP- and vimentin-antibodies revealed an invariable coexpression of the two IF proteins in somata and processes of these median eminence cells.     

Glial fibrillary acidic protein and differentiation of neonatal rat pituicytes in vitro

Summary The appearance and intracellular localisation of glial fibrillary acidic protein (GFAP) in pituicytes in neural lobe cultures of newborn rats aged 7 to 30 days were investigated by use of the indirect immunofluorescence method. GFAP-immunoreactive cells were observed mostly in the outgrowth zone. GFAP was localised in the perikaryal cytoplasm as well as in pituicyte processes. GFAP-positive pituicytes showed considerable morphological polymorphism. The presence of GFAP — astrocytic marker — in pituicytes in vitro and the evident morphological similarity to cultured astrocytes suggest the astroglial character of these cells.     

Immunohistochemical study of cells positive for glial fibrillary acidic protein (GFAP) in the human pituitary gland,with special reference to folliculo-stellate cells

Summary The cytology and the distribution of cells which contain glial fibrillary acidic protein (GFAP) were studied immunohistochemically in thick frozen sections of human pituitary glands. Immunoreactive cells were constantly demonstrated in both neuro- and adenohypophysis. In the neural lobe, an irregular network of long GFAP-positive pituicyte processes was revealed. Within this network, some asymmetric pituicytes became visible. A variable number of cells was stained in cell cords and follicles of the pars distalis and the intermediate zone. The morphology of these cells could be studied in detail, providing strong evidence to support the hypothesis that adenohypophyseal GFAP-immunoreactive cells belong to the folliculo-stellate (FS) cell system. Cells with similar cytological features in the pars distalis or the intermediate zone were found to share common immunoreactivities against GFAP and the presumable FS cell markers vimentin and S-100 protein. Our results corroborate the notion that, in the human pituitary, GFAR can be regarded as a marker protein of pituicytes and FS cells, which is expressed at varying degrees.     

Immunohistochemical study of cells positive for glial fibrillary acidic protein (GFAP) in the human pituitary gland, with special reference to folliculo-stellate cells

The cytology and the distribution of cells which contain glial fibrillary acidic protein (GFAP) were studied immunohistochemically in thick frozen sections of human pituitary glands. Immunoreactive cells were constantly demonstrated in both neuro- and adenohypophysis. In the neural lobe, an irregular network of long GFAP-positive pituicyte processes was revealed. Within this network, some asymmetric pituicytes became visible. A variable number of cells was stained in cell cords and follicles of the pars distalis and the intermediate zone. The morphology of these cells could be studied in detail, providing strong evidence to support the hypothesis that adenohypophyseal GFAP-immunoreactive cells belong to the folliculo-stellate (FS) cell system. Cells with similar cytological features in the pars distalis or the intermediate zone were found to share common immunoreactivities against GFAP and the presumable FS cell markers vimentin and S-100 protein. Our results corroborate the notion that, in the human pituitary, GFAP can be regarded as a marker protein of pituicytes and FS cells, which is expressed at varying degrees.     

Adaptation of Camelus dromedarius pars nervosa of the hypophysis to winter and summer living conditions

The aim of this work is to study the characteristics of the dromedary nervous lobe and determine how the seasons condition its organization. To this end, electron microscopy was performed and examined quantitatively on animals from winter and summer periods. The results show a higher number of cells in the nervous lobe in summer than in winter. The most abundant glial elements in winter are light pituicytes engulfing neurosecretory nerve fibers making neuroglial contact, and dark pituicytes containing numerous heterogeneous light bodies. In summer, the most distinctive glial cells may be pituicytes in a phagocytic state making contact with characteristic large light bodies that could represent a degenerative process of large neuropeptide storage. Granular pituicytes were also observed in contact with glial and neuronal components. However, lipid droplets, described in pituicytes of other mammals, were not observed in our samples. Quantitative analysis of neurovascular contacts revealed that the number of nerve terminals contacting the basal lamina did not differ between summer and winter, but the mean number of glial processes increased in winter. Our data provides evidence that the storage of neuropeptides is very marked in summer and that, associated with an autophagic and phagocytic phenomenon, this suggests an adaptation to anticipate any situation that would cause dehydration of the dromedary. Thus, in its tough environment, the animal remains permanently prepared to avoid any large water loss.     

Immunocytochemical localization of vimentin in the posterior lobe of the cat, rabbit and rat pituitary glands

The presence and distribution of vimentin, a subunit of intermediate filaments, in the neural lobe and in the pars intermedia of the cat, rabbit and rat pituitary glands were investigated immunocytochemically. In the pars intermedia, our study revealed the presence of vimentin in glial-like cells located between glandular secretory cells of the three species and in the cells of the marginal layer of the cat and rat hypophyseal cleft. In the neural lobe of the cat and rabbit pituitary glands, there was a large amount of cell processes and immunoreactive pituicytes. In contrast, in the rat neural lobe, few pituicytes exhibited immunoreactivity, and these were located principally in the posterior region near the pituitary stalk. The significance of immunoreactive vimentin in these cells is discussed.     

Prenatal and early postnatal development of the glial cells in the median eminence of the rat

Summary The development of the glial cells of the rat median eminence (ME), including the supraependymal cells, was investigated from embryonic day (ED) 14 through postnatal day (PD) 7, and pituicyte development from ED 12 through ED 17. The anlage of the ME and neurohypophysis shows a neuroepithelial-like structure at ED 12. From ED 13 to 15, the cells of both regions start to differentiate. At the ultrastructural level, only one cell type appears. At the beginning of ED 16, glioblasts of the oligodendrocyte and astrocyte series migrate laterally (from the region of the arcuate nucleus) into the ME. Also at this time the first distinctive structural features appear in the neurohypophysial anlage, the cells of which later develop into pituicytes. Starting at ED 18, tanycytes and astrocytic tanycytes arise in the ME from local glial cells, and somewhat later oligodendroblasts and astroblasts are formed from immigrant glioblasts. Due to their common features, the pituicytes, tanycytes and astrocytic tanycytes apparently represent different forms of the same parent cell type. Microglial and supraependymal cells are first seen at ED 12. Initially, they resemble the prenatal phagocytic connective tissue cells and mature in the fetus into typical electron-dense microglia and macrophage-like supraependymal cells. Both cell types are apparently of mesodermal origin. The microglial elements of the ME probably migrate from the mesenchyma through the basement into the nervous tissue. The intraventricular macrophages of the infundibular region may originate from microglia, epiplexal cells and subarachnoid macrophages.Dedicated to Prof. I. Törö, Budapest, on the occasion of his 80th birthday     

The ultrastructure of the developing neural lobe

Summary The ultrastructure of the developing neural lobe of rats was studied. The results revealed three periods in its development. The first period lasts till the 17th day of fetal life. At its beginning the anlage of the neural lobe is formed as a mass of cells very similar in appearance and in connection with the subependymal cells of the future median eminence. During the first period the cells of the anlage differentiate into pituicytes, and the penetration of the first nerve fibres and blood vessels among them is seen. The second period is from the 18th day of fetal life till one month after birth. At its beginning the first signs of neurosecretory activity were detected. During the period increasing numbers of neurosecretory fibres penetrate into the neural lobe, and the pituicytes show morphological signs characteristic of active cells. An increase in the functional activity of the neural lobe is also detected. The third period is from the end of the 1st till the end of the third month. During this period the development of the neural lobe proceeds and at the end it has the appearance of the adult gland. During this period the pituicytes gradually lose the signs of activity and at the end of the period they look like those observed in adult animals. Considering the results from the study, together with some data from previous investigations it is suggested that the pituicytes exert some stimulating and regulative influences on the process of neurosecretion in the neural lobe.Research fellow of the Alexander von Humboldt Foundation.     

Quantitative assessment of GABA-uptake sites in the neural lobe by electron-microscopic autoradiography

Summary Distribution of (³H)GABA in the rat neural lobe was investigated 5 min after intracarotid administration using quantitative electron-microscopic autoradiography. Specificity of (³H)GABA-uptake was tested by pretreatment of control animals with nipecotic acid. It was concluded that, apart from a small fraction in the perivascular spaces, radioactivity was present exclusively in pituicytes. The results confirm and quantify earlier in-vitro observations; they are compared with recent immunocytochemical findings that reveal the presence of glutamate-decarboxylase-containing axons in the neural lobe. It is concluded that there may be GABAergic terminals that lack an uptake mechanism for exogenous transmitter. Nevertheless, (³H)GABA autoradiography is useful in demonstrating other functional components of GABAergic systems, i.e., glial cells.     

Morphology of the neural lobe of the hypophysis in rats treated with furosemide. II. Pituicytes

Following three days of furosemide administration, the characteristics of the pituicytes in the neural lobe of the rat hypophysis were studied. The pituicytes of the animals which were treated with furosemide and had access to water during the treatment showed scarce cytoplasm organelles, conferring them with a clear appearance (light pituicytes), and a frequent finding was neurosecretory axons enclosed in their own cytoplasm. In the animals deprived of water during treatment, the pituicytes were dense (dark pituicytes) elongated, with a well-developed Golgi apparatus, numerous profiles of smooth endoplasmic reticulum and frequent annular gap junctions. It is concluded that the dehydration induced by the diuretic agent is the cause of the prevalence of the dark pituicytes.     

Proliferation of glial cells in vivo induced in the neural lobe of the rat pituitary by lithium

Lithium salts are widely used for treatment of psychiatric illness. Lithium also affects cell proliferation. During investigation of the effect of lithium chloride on the central nervous system (CNS) of nephrectomized rats, we noted numerous mitotic figures in the neural lobe of the pituitary. Morphologic criteria established that the mitotic cells were astrocytes, the supporting glial cells of the CNS, also known as pituicytes. Equimolar doses of chlorides of chemically related cations (sodium, potassium, rubidium) had no such effect.     

QUANTITATIVE LYSOSOMAL ENZYME ACTIVITY CHANGES IN THE NEURAL LOBE OF THE RAT FOLLOWING WATER DEPRIVATION AND LACTATION

—The activities of five lysosomal enzymes, acid phosphatase, β-glucosidase, β-glucuronidase, β-galactosidase and N-arylamidase (classified according to Marks (1970)) were measured by means of sensitive microchemical techniques in frozen-dried rat neural lobe tissue after experimental and physiological stimulation of hormone release from the hypothalamo–neurohypophysial system i.e. water deprivation (3 and 6 days), delivery and lactation (10 days). During all conditions of stimulation increases of 29 to 106 per cent were measured for lysosomal enzyme activity, expressed as mmol/ng DNA/h. With histochemical staining methods the acid phosphatase activity appears to be mainly localized in the pituicytes, but it was impossible to visualize the microchemically measured acid phosphatase activity increase within the two main compartments of the neurohypophysis, i.e. axonal endings and the neurohypophysial glial cells, the pituicytes.     

Morphological characteristics of pituicytes in different functional stages

Summary Most of the pituicytes of normal rats show relatively few indications of metabolic activity. This situation remains unchanged after two days of dehydration. From the third to the eighth day of dehydration, a considerable hypertrophy of the majority of pituicytes takes place. During this period proliferative and degenerative processes occur. After eight days of dehydration the pituicytes show an increase of degenerative processes and indications of decreased activity. Only one type of pituicytes in three different morphofunctional stages is considered to represent the basic cellular component of the neural lobe. A relationship between these stages and the release of neurosecretory material from the nerve endings is discussed.Partially supported by Unesco and Ibro post-doctoral fellowships.     

Ultrastructural changes and proliferation of pituicytes in mouse posterior lobe during water deprivation and rehydration

Ultrastructural changes and proliferation of pituicytes during water deprivation and rehydration were studied in the posterior lobe of C57BL/Tw mice. Deprivation for 3 days brought about a significant increase in the number of electron-dense bodies (lysosomes) in pituicyte perikarya and their processes. The frequency of pituicytes enclosing neurosecretory axons in their cytoplasm significantly decreased as compared with that of the controls. 12-hour rehydration following deprivation for 3 days induced extensive development of rough endoplasmic reticulum and Golgi apparatus and an increase in frequency of neurosecretory axons enwrapped by pituicyte cytoplasm. However, at 2 days of rehydration the morphology of pituicytes was no more different from that of the controls. Mitotic figures of pituicytes were not encountered throughout the deprivation period of 6 days, but rehydration for 12 h and 1, 2, or 3 days following deprivation for 3 or 6 days was effective in eliciting an increase in mitotic activity. The present results indicate that pituicytes in the mouse posterior lobe are intimately related with the secretory mechanism of neurosecretory material from the neurosecretory axons and that the proliferation of pituicytes is stimulated in conditions of reaccumulation of neurosecretory material.     

Differential immunocytochemical staining for glial fibrillary acidic (GFA) protein,S-100 protein and glutamine synthetase in the rat subcommissural organ,nonspecialized ventricular ependyma and adjacent neuropil

Summary Antibodies raised against glial fibrillary acidic protein (GFA), S-100 protein (S100) and glutamine synthetase (GS) are currently used as glial markers. The distribution of GFA, S100 and GS in the ependyma of the rat subcommissural organ (SCO), as well as in the adjacent nonspecialized ventricular ependyma and neuropil of the periaqueductal grey matter, was studied by use of the immunocytochemical peroxidase-antiperoxidase technique. In the neuropil, GFA, S100 and GS were found in glial elements, i.e., in fibrous (GFA, S100) and protoplasmic astrocytes (S100, GS). The presence of S100 in the majority of the ventricular ependymal cells and tanycytes, and the presence of GFA in a limited number of ventricular ependymal cells and tanycytes confirm the glial nature of these cells. The absence of S100, GFA and GS from the ependymocytes of the SCO, which are considered to be modified ependymal cells, suggests either a non-astrocytic lineage of these cells or an extreme specialization of the SCO-cells as glycoprotein-synthesizing and secreting elements, a process that may have led to the disappearance of the glial markers.