Biomedical subjects

J Schnitzer

Publications and source records attributed to J Schnitzer.

At least 37 records · Page 2Linked to original sources

PubMed1991

Development of the rabbit retina. I. Size of eye and retina, and postnatal cell proliferation.

Measures of rabbit eyes and retinal wholemounts were used to evaluate the development of retinal area and shape. The retina is shown to have a horizontal axis about a third longer than the vertical axis just before birth, and to adopt an almost symmetrical shape during postnatal development to adulthood. In general, retinal thickness is shown to decrease after birth, but differently in particular retinal regions: the reduction is marked in the periphery, and less pronounced in the visual streak. As an exception, the myelinated region--after it becomes really myelinated, from 9 days p.p.--even increases in thickness. In all regions of the retina, the absolute and relative thickness of the nuclear layers decreases, whereas the relative thickness of plexiform and fibrous layers increases. Proliferation of cells within the rabbit retina was studied during the first three postnatal weeks. 3H-thymidine incorporation was used to demonstrate DNA synthesis autoradiographically in histological sections as well as in enzymatically isolated retinal cells. A first proliferation phase occurs in the neuroblastic cell layer and ceases shortly after birth in the retinal center, but lasts for about one week in the retinal periphery. We found, however, a few 3H-thymidine-labeled cells as late as in the third postnatal week. These late-labeled cells were found within the nerve fiber layer and in the inner plexiform layer. The latter cells were shown to express antigens detected by antibodies directed to the intermediate-sized filament protein vimentin, which are known to label Müller cells and neuroepithelial stem cells. This was confirmed in our preparation of enzymatically isolated cells; all cells with autoradiographically labeled nuclei revealed a characteristic elongated morphology typical for Müller radial glia (and also for early neuroepithelial stem cells). 3H-thymidine-labeled cells in the nerve fiber layer were most probably astrocytic. In analogy to the brain, we conclude that the mammalian retina undergoes a series of proliferation phases: first an early phase producing both neurons and glial cells, and then a late phase producing glial cells, e.g., in the nerve fiber layer. Most probably, the late phase within the inner nuclear layer is glial as well, i.e., consists of dividing Müller cells; it cannot be excluded, however, that there may remain some mitotically active stem cells.

Animals↗

PubMed1991

Developmental changes in the membrane current pattern, K+ buffer capacity, and morphology of glial cells in the corpus callosum slice.

Recent studies indicated that glial cells in tissue culture can express a variety of different voltage-gated channels, while little is known about the presence of such channels in glial cells in vivo. We used a mouse corpus callosum slice preparation, in which after postnatal day 5 (P5) more than 99% of all perikarya belong to glial cells (Sturrock, 1976), to study the current patterns of glial cells during their development in situ. We combined the patch-clamp technique with intracellular labeling using Lucifer yellow (LY) and subsequent ultrastructural characterization. In slices of mice from P6 to P8, we predominantly found cells expressing delayed-rectifier K+ currents. They were similar to those described for cultured glial precursor cells (Sontheimer et al., 1989). A-type K+ currents or Na+ currents were not or only rarely observed, in contrast to cultured glial precursors. LY labeling revealed that numerous thin processes extended radially from the perikaryon of these cells, and ultrastructural observations suggested that they resemble immature glial cells. In slices of older mice (P10-13), when myelination of the corpus callosum has already commenced, many cells were characterized by an almost linear current-voltage relationship. This current pattern was similar to cultured oligodendrocytes (Sontheimer et al., 1989). Most processes of LY-filled cells with such a current profile extended parallel to each other. Electron microscopy showed that these processes surround thick, unmyelinated axons. We suggest that cells with oligodendrocyte-type electrophysiology are promyelinating oligodendrocytes. In contrast to cultured oligodendrocytes, membrane currents of promyelinating oligodendrocytes in the slice decayed during the voltage command. This decay was due not to inactivation, but to a marked change in the potassium equilibrium potential within the voltage jump. This implies that, in the more mature corpus callosum, small membrane polarizations in a physiological range can lead to extensive changes in the K+ gradient across the glial membrane within a few milliseconds.

3,3'-Diaminobenzidine↗

PubMed1990

Microglial cell responses in the rabbit retina following transection of the optic nerve.

The response of retinal microglial cells, which accompanies retrograde degeneration of ganglion cell axons and perikarya (induced by transection of the optic nerve), was studied in whole-mounted rabbit retinae labeled enzyme-histochemically for nucleoside diphosphatase (NDPase), which is a microglial cell marker. A few days after transection, the number of microglial cells/mm2, as well as their staining intensity, began to increase in the inner plexiform layer. The mosaic-like distribution of the star-shaped microglial cells present in the inner plexiform layer of a normal rabbit retina was preserved during ganglion cell degeneration. As in the normal retina, processes of individual cells never overlapped with those of neighboring cells in the inner plexiform layer because individual cells in the "degenerating" retina acquired shorter processes, i.e., the cells occupied a smaller territory compared to the normal retina. In the nerve fiber layer the number and staining intensity of NDPase-labeled microglial cell processes (most of which are aligned in parallel with degenerating ganglion cell axons) transiently increased and returned to normal values by 5 months post-transection. Microglial cells that are not detectably NDPase labeled in the outer plexiform layer of a normal rabbit retina acquire intense staining a few days after the nerve is cut. The functional significance of the increased NDPase activity in the plasma membrane of microglial cells during degeneration remains to be determined.

Acid Anhydride Hydrolases↗

PubMed1990

Postnatal gliogenesis in the nerve fiber layer of the rabbit retina: an autoradiographic study.

Cell proliferation was studied in the retina of rabbits at various postnatal stages. Autoradiography was performed with animals that received a single injection of 3H-thymidine and were sacrificed 1 hour later. This short survival time allowed the determination of the position of a cell undergoing DNA synthesis at that moment. Between birth and day 6, cells engaged in DNA synthesis were seen in the inner nuclear layer (INL) of the entire retina. Cytogenesis ceases in this layer after the first postnatal week. Few labeled cells were detectable in the INL at day 9; these were found close to the ora serrata. Thus neurogenesis, which is known to occur in this layer of the retina, ceases by that time. In the nerve fiber layer (NFL), labeled cells were found at all ages between birth and day 27, which was the oldest stage examined in this study. By using horizontal sections through the NFL of entire retinae, it was observed that almost all labeled cells were confined to the medullary ray region, which is the neuroglia (astrocyte and oligodendrocyte)-bearing part of the NFL. Microglial cells, the only cellular elements present in the NFL outside the medullary ray region, were rarely labeled, and thus do not play a major role in gliogenesis occurring in the NFL. In addition to neuroglia, some endothelial cells were labeled after day 9. It is concluded that gliogenesis taking place in the NFL persists after the cessation of neurogenesis, suggesting that both processes occur independently.

Aging↗

PubMed1989

Distribution and morphology of tyrosine hydroxylase-immunoreactive neurons in the developing mouse retina.

An antibody to tyrosine hydroxylase (TH), the rate-limiting enzyme in the production of catecholamines, was used to examine the morphology and distribution of catecholaminergic neurons in whole-mounted retinae of the developing and adult mouse. At adulthood TH-labeled cell bodies were located in the inner nuclear layer, stratifying mainly at the border to the inner plexiform layer (IPL). Few processes were found in the middle of the IPL. The majority of all TH-labeled cells also extended processes towards the outer plexiform layer and thus are interplexiform cells; the rest were considered to be amacrine cells. The TH-positive neurons were regularly distributed throughout the adult mouse retina. During development, the first TH-immunoreactive cells were observed by postnatal day 6 (P6) and most of them were present after the third postnatal week. The dendrites in the IPL only acquired varicosities after the eyes opened at P15. Biochemical measurements of the endogenous catecholamine content showed that at all developmental stages only dopamine was detectable, suggesting that the TH-labeled cells represent dopaminergic neurons. The content of dopamine was low before P6 and continuously increased during the following days. A strong increase in dopamine was observed during the time when varicosities formed.

Aging↗

PubMed1989

Enzyme-histochemical demonstration of microglial cells in the adult and postnatal rabbit retina.

Enzyme-histochemical methods for thiamine pyrophosphatase (TPPase) and nucleoside diphosphatase (NDPase) were applied to wholemounted rabbit retinae to demonstrate the shape and distribution of microglial cells in early postnatal and adult animals. At birth, microglial cells were already present in the entire retina. They acquired their adult "resting shape" during the first 3 postnatal weeks. Early postnatally labeled microglial cells were scattered throughout the nerve fiber layer, the inner plexiform layer, and the outer plexiform layer (OPL); at adulthood, they were not detected in the OPL. Nissl-stained retinae revealed that the number of microglial cells continuously increased during postnatal development. The same Nissl-stained preparations were used to evaluate the topography of degenerating cells in the developing postnatal retina of the rabbit. Large numbers of degenerating pyknotic cells were observed throughout the entire retinal ganglion cell layer during the first postnatal week. Later their number decreased, and from the third postnatal week onward degenerating cells were rare. Also discussed is that the emergence of microglial cells during development may be related to cell death, whereas at adulthood the function(s) of microglial cells remains obscure. Evidence for the blood-derived origin of microglia was not obtained in this study. It is argued here that if this mode of development, which has been demonstrated for other species, is also applied to the rabbit retina, then microglia would have to migrate over considerable distances, since, postnatally, the rabbit retina is avascular for more than 1 week.

Acid Anhydride Hydrolases↗

PubMed1989

The rabbit retina: a suitable mammalian tissue for obtaining astroglia-free Müller cell cultures.

Monolayer cultures were prepared from two distinct parts of early postnatal rabbit retinae. Cell suspensions obtained from the developing medullary ray (MR) region contained neurons, Müller (glial) cells, and astrocytes, cells obtained from the remainder (peripheral) part of the retina contained neurons and Müller cells, but no astrocytes. Müller cells lack glial fibrillary acidic protein (GFAP) immunolabeling in situ but some of them acquire faint GFAP labeling in both types of cultures. Strongly GFAP-labeled cells, most likely astrocytes, were seen in MR cultures only. We propose that the periphery of the rabbit retina is ideal for obtaining astroglia-free Müller cell cultures to study their functional properties in vitro.

Animals↗

PubMed1988

Immunocytochemical studies on the development of astrocytes, Müller (glial) cells, and oligodendrocytes in the rabbit retina.

Glial markers, namely antibodies to glial fibrillary acidic protein (GFAP), vimentin, galactocerebroside (GC), 04 antigen, and 08 antigen, were used to study the development of neuroglial cells in the postnatal rabbit retina. In histological sections radially oriented Müller cells were detectable at birth. They were weakly vimentin-positive and their labeling intensity increased during further development. Few vimentin-labeled astrocytes, situated in the nerve fiber layer, were detectable at birth, but of these few many were also GFAP-positive. The number of GFAP-positive astrocytes, all of which co-labeled with vimentin antibodies, increased during the following days. From postnatal day (P) 9-10 onward, the vimentin labeling seen in GFAP-positive astrocytes began to decline. In the adult rabbit most GFAP-positive astrocytes were only weakly vimentin-stained; some astrocytes even lacked detectable amounts of vimentin. Thus, astrocytes were found to be strongly vimentin-positive at birth, and strongly GFAP-positive but weakly vimentin-labeled by adulthood. Such a transition was not observed for Müller cells, which lacked detectable amounts of GFAP at all postnatal stages studied. In single cell suspensions, cells positive for the cell surface markers 04 antigen and GC were first detected at P6-7, 08 antigen-labeled cells were found one day later. Thus, the third class of neuroglial cells in the rabbit retina, the oligodendrocytes, seems to develop about one week later than astrocytes and Müller cells.

Aging↗

PubMed1988

Astrocytes in the guinea pig, horse, and monkey retina: their occurrence coincides with the presence of blood vessels.

In the present study the distribution of astrocytes in the nerve fiber layer (NFL) has been studied in the sparsely vascularized retinae of the guinea pig and horse and in the richly vascularized retina of the Old World monkey (Cercopithecus aethiops) using immunocytochemical methods. In the guinea pig retina glial fibrillary acidic protein (GFAP)-positive astrocytes could not be detected. They were found, however, in the myelinated region of the optic nerve. The optic nerve head and a small retinal region immediately adjacent to it contained few vimentin-positive astrocytes. Histological sections confirmed the restriction of astrocytes to a small retinal region and showed that this is also the only retinal area that is vascularized. Astrocytes showing GFAP and vimentin immunoreactivity were absent from most of the horse retina. They were found only in a narrow zone close to the optic disc, which is also the only region of the horse retina that is vascularized. Thus, as in the rabbit retina (Schnitzer: J. Comp. Neurol. 240:128-142, 1985), in the guinea pig and horse retina astrocytes are not present ubiquitously in the NFL but coexist with blood vessels. In the monkey retina, GFAP-positive astrocytes were found ubiquitously in the NFL. Astrocytes were absent from the avascular foveal region only. It is suggested that the concurrence of retinal astrocytes and intraretinal vascularization may be a feature common to many, if not all, mammalian species.

Animals↗

PubMed1988

The development of astrocytes and blood vessels in the postnatal rabbit retina.

Antibodies to glial fibrillary acidic protein (GFAP) have been used to study the shape and location of astrocytes in whole mount preparations of developing postnatal rabbit retina. At all developmental stages GFAP-positive astrocytes were detectable. At birth, they were few in number and only weakly labelled. With further development, their number as well as their labelling intensity increased. Following Nissl counterstaining it was observed that GFAP-positive astrocytes, always situated in the nerve fibre layer, are capable of cell division during about the first 4 postnatal weeks. GFAP-positive astrocytes were always confined to a wing-shaped area extending horizontally from both sides of the optic nerve head. It is suggested that astrocytes are not generated in the entire rabbit retina, which is in clear contrast to the second glial cell type of the rabbit retina, the Müller cell; and it has been concluded that the confinement of astrocytes to the medullary rays region in the adult rabbit is established during ontogenesis, and is not due to a secondary restriction of astrocytes to this region. Horizontal sections cut through entire rabbit retinae at various postnatal stages revealed that the first intraretinal blood vessels are not found before postnatal day 9. This is more than 1 week later than the first astrocytes are detectable. It is suggested that, at least in the rabbit, retinal astrocytes do not co-migrate with blood vessel endothelial cells from the optic disc into the retina, a hypothesis considered recently for the cat retina. It was, however, not possible to decide unequivocally if, in this material, astroglial progenitors are derived from retinal neuroepithelial cells or invade the retina from the optic nerve head.

Animals↗

PubMed1987

Retinal astrocytes: their restriction to vascularized parts of the mammalian retina.

The distribution of astrocytes has been studied in whole-mounted horse and monkey retinae by the immunocytochemical localization of glial fibrillary acidic protein (GFAP). In the horse, astrocytes were found to be restricted to a narrow zone close to the optic nerve head. This is also the only region of the horse retina that is vascularized. In the monkey, astrocytes were found ubiquitously in the nerve fiber layer of the retina, apart from the avascular fovea centralis which lacked astrocytes. These observations strongly suggest that retinal astrocytes co-occur with blood vessels, a feature which may be common among mammals.

Animals↗

PubMed1987

Immunocytochemical localization of S-100 protein in astrocytes and Müller cells in the rabbit retina.

The localization of S-100 protein was studied in histological sections of retinae from adult rabbits. By use of double-immunolabeling techniques it was shown that most but not all radially oriented vimentin-positive Müller cells were co-labeled by an antiserum to S-100 protein. Glial fibrillary acidic protein-positive astrocytes, which in the rabbit retina are restricted to the medullary rays formed by myelinated optic nerve fibers, consistently showed S-100 protein immunoreactivity. The present report shows that, with respect to S-100 protein staining, Müller cells represent a heterogeneous population of glial elements.

Animals↗

PubMed1986

Immunocytochemical studies on astroglia of the cat retina under normal and pathological conditions.

The cell density and morphology of astrocytes in whole-mounted adult cat retinae have been studied by immunocytochemical localization of glial fibrillary acidic protein (GFAP). There was a peak density at the optic nerve head of about 2,000 astrocytes/mm2 dropping to approximately 200 astrocytes/mm2 in the far periphery. In the central area there was a local minimum of astrocyte density. Whereas the processes of astroglia in the outermost retinal periphery were radially arranged, thus giving the cells a characteristic star-shaped appearance, the majority of astroglial processes in the central region of the retina were aligned in parallel with the ganglion cell axon bundles. To study the correlation between optic nerve fibres and astrocytes, ganglion cell axons were caused to degenerate following photocoagulation lesions close to the optic disc. Postlesion the processes of astrocytes in the central retina lost their directional preference and linearity, thus appearing to develop a star-shaped morphology typical of astroglia in the far periphery of normal retinae. The density of astrocytes decreased by approximately 50% on the optic disc side of the lesions and by up to 80% on the peripheral side of the lesions. The results show that the morphology and number of astrocytes vary as a function of their proximity to optic nerve fibres and to the density of these fibres.

Animals↗

PubMed1986

The shape and distribution of astrocytes in the retina of the adult rabbit.

Astrocytes stained by antibodies to glial fibrillary acidic protein (GFAP) were examined in whole-mount preparations of retinae from adult rabbits and found to be restricted to the medullary rays. Astroglial cells exhibited a variety of shapes that varied between two extreme morphologies. One extreme was an astrocyte that possessed a few sturdy primary processes as well as finer processes and was strongly GFAP positive. The other extreme was an astroglial cell that displayed a star-shaped appearance; its perikarya gave rise to a few thin, radially oriented processes, which were rather weakly GFAP positive. The majority of astroglial processes were aligned with the ganglion-cell axons, but some of their processes were in contact with capillaries. It has been proposed that astrocytes are specifically associated with ganglion-cell axons. Their restriction to the medullary rays in the retina of the rabbit suggests, however, that their physiological role is also concerned with the vascular system.

Animals↗

PubMed1986

Shape and distribution of astrocytes in the cat retina.

Astrocytes in the adult cat retina were stained by immunocytochemical localization of glial fibrillary acidic protein (GFAP), a major constituent of the astrocytic intermediate filaments. Their density in whole mounted retinae showed a peak of about 2000 astrocytes/mm2 at the optic nerve head and dropped to approximately 200 astrocytes/mm2 in the far periphery. At the central area a prominent local minimum of astrocyte density was found. The shape of astrocytes changed from a stellate form in the outermost retinal periphery to an elongated form in the central part of the retina with the majority of astroglial processes aligned in parallel with the ganglion cell axons. Results in the cat retina suggest a close correlation between astrocytes and optic nerve fibers, the latter presumably being involved in the establishment of the astrocytic network.

Animals↗

PubMed1985

Distribution and immunoreactivity of glia in the retina of the rabbit.

Glial markers, namely antibodies to glial fibrillary acidic protein (GFAP), vimentin, galactocerebroside (GC), and 08 antigen, were used to study the occurrence and location of neuroglial cells in adult rabbit retinae. Müllerian glia were vimentin-positive, lacked detectable amounts of GFAP, and were found in all parts of the rabbit retina. The neuronal A-type horizontal cells were labeled by vimentin antibody only in the superior retina and at the medullary rays but not in the inferior retina. They lacked GFAP in all regions. Astroglia showing GFAP and vimentin immunoreactivity were absent from most of the superior and inferior retina, being found only in the myelinated area of the ganglion cell axon bundles, the medullary rays. Thus the rabbit retina differs from the retinae of all mammals studied to date by this restriction of astroglia to just one area. The medullary rays, which are known to be myelinated, were labeled by the antibodies to GC and 08 antigen. Boycott and Hopkins ('84) found, using whole-mounted rabbit retinae stained by the reduced silver method of Richardson, that all neurons in the ganglion cell layer of the rabbit retina have a cilium, while cells that have only a diplosome are either neuroglia or microglia. By using this criterion as a basis to differentiate between neurons and glia, the absence of neuroglia from the nerve fiber layer outside the medullary rays was confirmed in the same silver-stained material. Thus, the data obtained from immunocytochemistry and conventional silver staining agree closely. It has been concluded that, at least in the adult, significant lengths of ganglion cell axons extend without astroglial sheaths.

Animals↗

PubMed1984

Some immature tetanus toxin-positive cells share antigenic properties with subclasses of glial cells. An immunofluorescence study in the developing nervous system of the mouse using a new monoclonal antibody S1.

Monoclonal antibody S1 reacts in monolayer cultures with the cell surfaces of oligodendrocytes and a subclass of astrocytes derived from early postnatal mouse cerebellum, cerebrum and spinal cord, as well as with some glial cells in mouse retina but not in dorsal root ganglia. At earlier developmental stages S1 antigen is present in addition to oligodendrocytes and astrocytes on some tetanus toxin-positive neurons. S1 antigen is a developmentally early marker, detectable already in freshly trypsinized single cell suspensions from cerebella of 13-day-old embryos. Immunocytolysis of S1 antigen-bearing cells leads to reappearance of S1 positive glial cells but not tetanus toxin receptor-positive neurons. S1 antigen is also expressed in rat, rabbit, chicken and human. When cultured cells are permeabilized with denaturing agents, S1 antibody not only labels cell surfaces of some glial cells and, depending on the developmental stage, some neuronal cells but also intracellular components of all astrocytes, oligodendrocytes, neurons and fibroblasts.

Animals↗

PubMed1984

Specificity of monoclonal antibody N1 for cell surfaces of mouse central nervous system neurons.

Monoclonal antibody N1 reacts by indirect immunofluorescence with the cell surface of tetanus toxin-positive neurons from early postnatal mouse cerebellum. In freshly trypsinized single cell suspensions from early postnatal mouse cerebellum, 5-10% of all viable cells express N1 antigen on their surface. After 3-24 h of maintenance in vitro all N1 antigen-positive cells are tetanus toxin-positive. After culture periods of 3-4 days, most (approximately 90%) tetanus toxin-positive cells express N1 antigen on their surface. When horse serum-supplemented medium (HSSM) is used for cultivation, neurons begin to lose N1 antigen from their surface after about one week in vitro, until after two weeks in vitro, N1 antigen is no longer detectable, although some tetanus toxin-positive neurons can be shown to survive in culture. In defined medium, however, N1 antigen-positive neurons can still be detected after 34 days in vitro, the longest culture period examined so far. Complement-dependent immunocytolysis deletes all N1 antigen-positive and approximately 90% of all tetanus toxin-positive neurons from cultures. The remaining neurons reveal a morphology different from the one of the majority of small neurons, the granule cells. They have slightly larger cell bodies and several branched and unbranched cellular processes. Neonatal cerebellar cells show the same temporal sequence of appearance and disappearance of N1 antigen on most tetanus toxin-positive neurons in HSSM, and a persistence of N1 antigen on neurons in defined medium. N1 antigen becomes first detectable at embryonic day 17, and never becomes detectable in cell cultures derived from cerebella of younger mice. At all stages studied, N1 antigen expression is restricted to tetanus toxin-positive neurons, while it is absent from the cell surfaces of astrocytes, oligodendrocytes and fibroblasts. N1 antigen is also found in cultures derived from early postnatal mouse cerebrum, but is not detected in cultures derived from mouse retina, spinal cord, dorsal root ganglion, and embryonic telencephalon. It is also not detectable in cerebellar cultures from rabbit, rat, chicken and human. When N1 antibody is applied to fixed cultures where intracellular antigens are accessible, all cell types are labeled intracellularly, with astrocytes and fibroblasts revealing a fibrillary, vimentin-like staining pattern.

Animals↗