Mihály Kálmán

Distribution of glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes in the rat brain. I. Forebrain.

SummaryIn the first of two papers dealing with the distribution of glial fibrillary acidic protein-(GFAP)-immunoreactive elements in the rat brain, the localization of immunostaining in the forebrain is systematically described. While the limbic cortex was found to contain intensely stained, evenly distributed astrocytes, the neocortex showed clearly stratified GFAP-staining, with substantially less immunoreactivity occurring in the middle layers than in the areas close to the brain surface or the white matter. A remarkably regular staining pattern was observed in the hippocampus and dentate gyrus. The striatum remained unstained in sharp contrast to the pallidum. In the diencephalon, the main thalamic nuclei were poor in GFAP-labelled elements in contrast to the internuclear border zones. In the hypothalamus, nuclei were conspicuous by their GFAP-staining. A consistent differential staining pattern was obtained in the epithalamic structures. The observed distributional pattern of diencephalic GFAP-immunoreactivity is thought to be due to different regional proliferation of the embryonic neuroepithelium of the diencephalon. The uneven distribution of GFAP-immunoreactivity in the forebrain is explained on a mainly developmental basis.

Distribution of glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes in the rat brain - II. Mesencephalon, rhombencephalon and spinal cord

SummaryThe topographical mapping of glial fibrillary acidic protein (GFAP)-immunoreactivity was performed in coronal serial sections of the rat mesencephalon, rhombencephalon and spinal cord. Relative to a background of poor or moderate overall staining of the mesencephalon, the interpeduncular nucleus, substantia nigra and the periaqueductal grey matter were prominent by their intense GFAP-immunoreactivity. The pons and particularly the medulla contained more GFAP-labelled elements compared with the mesencephalon. The spinal trigeminal nucleus and Rolando substance were distinguished by their intense staining. Large fibre tracts were usually poor in immunoreactive GFAP. In a concluding discussion, findings relevant to the GFAP-mapping of the whole rat CNS are evaluated with regard to possible reasons underlying the observed differential distribution of GFAP-immunoreactivity.

Astroglial architecture of the carp (Cyprinus carpio) brain as revealed by immunohistochemical staining against glial fibrillary acidic protein (GFAP)

Abstract The present paper is the first comprehensive study on the astroglia of a teleost fish that is based on the immunohistochemical staining of GFAP (glial fibrillary acidic protein, an immunohistochemical marker of astroglia). The ray-finned fishes (Actinopterygii) and their largest group, the Teleostei, represent a separate pathway of vertebrate evolution. Their brain has a very complex macroscopic structure; several parts either have no equivalents in tetrapods or have a very different shape, e.g., the telencephalon. The results show that the teleost brain has a varied and highly specialized astroglial architecture. The primary system is made up of radial glia, which are of ependymal origin and cover the pial surface with endfeet. The tendency is, however, that the more caudal a brain area is, the less regular is the radial arrangement. A typical radial glia dominates some parts of the diencephalon (median eminence, lobus inferior and habenula) and the telencephalon. In the rest of the diencephalon and in the mesencephalon, the course of the glial fibers is modified by brain tracts. The most specialized areas of the teleost brain, the optic tectum and the cerebellum, display elaborate variations of the original radial system, which is adapted to their layered organization. In the cerebellum, an equivalent of the Bergmann-glia can be found, although its fiber arrangement shows meaningful differences from that of mammals or birds. In the lower brain stem radial glia are confined to fibers separating the brain tracts and forming the midline raphe. A dense ependymoglial plexus covers the inner surface of the tectum and the bottom of the rhombencephalic ventricle, intruding into the vagal and facial lobes. The structure and the position of the rhombencephalic plexus suggest that it corresponds to a circumventricular organ that entirely occupies the bottom of the ventricle. Perivascular glia show an unusual form as they consist of long fibers running along the blood vessels. In the large brain tracts long glial fibers run parallel with the course of the neural fibers. At least in the diencephalon, these glial fibers seem to be modified radial fibers. Real astrocytes (i.e., stellate-shaped cells) can be found only in the brain stem and even there only rarely. The glial specialization in the various areas of the teleost brain seems to be more elaborate than that found either in amphibia or in reptiles.

A comparison of intermediate filament markers for presumptive astroglia in the developing rat neocortex: Immunostaining against nestin reveals more detail, than GFAP or vimentin

The present study compares the immunopositive elements in the developing rat cortex between the day of birth (P0) and the 18th postnatal day (P18), after immunostaining against nestin, vimentin and glial fibrillary acidic protein (GFAP). Nestin immunostaining revealed more structural details than either vimentin or GFAP, or they together. While vimentin immunostaining preferred radial glia and GFAP preferred astrocytes, nestin immunostaining detected both. Stellate‐shaped astrocyte‐like cells were already seen at P0 and cells of typical astrocytic morphology were numerous at P3, and were predominating elements from P7, whereas GFAP‐immunopositive astrocytes were very scarce even at P7, and became numerous only by P11, when nestin immunopositivity started to disappear. Nestin immunostaining revealed such structures which were not seen in GFAP‐ or vimentin immunostained sections: cell body‐like structures ‘hanging’ at the end the radial fibers, seeming to divide with their fibers, or having astrocyte‐like processes. Nestin immunostaining is therefore highly recommended for studies of the glial architecture in the early post‐natal brain development.

Distribution of glial fibrillary acidic protein and vimentin-immunopositive elements in the developing chicken brain from hatch to adulthood.

Abstract The present study describes the distribution of glial fibrillary acidic protein (GFAP) and vimentin-immunopositive structures in the brain of the domestic chicken (Gallus domesticus) from hatching to maturity. The telencephalon is penetrated by a vimentin-immunopositive radial fibre system, representing a modified form of radial glia, in day-old chicks. Numerous fibres of this system persist until adulthood, mainly in the lobus parolfactorius, lamina medullaris dorsalis and lamina frontalis superior. GFAP immunoreactivity also appears in the course of development in these fibres. The distribution of GFAP-immunopositive astrocytes in the post-hatch telencephalon is like that found in adult chicken, except for the ectostriatum, in which an adult-like GFAP-immunostaining only develops during week three. This delay may be associated with a relatively slow maturation of this visual centre. In the diencephalon and in the mesencephalic tegmentum of day-old chicks GFAP-immunopositive astrocytes are confined to the border zone of several nuclei. In these areas as well as in the pons most GFAP positive astrocytes only appear gradually during the first two post-hatch weeks, although radial fibres occur only sparsely at hatch. Summarizing these results, a gradual replacement of radial fibres by astrocytes, typical of mammals, cannot be found in chicken. In the nucleus laminaris we observed a characteristic palisade of non-ependymal glia, reactive to GFAP but not to vimentin, which almost completely disappears by adulthood. We suggest that this glial system is instrumental in the development of the dendritic organisation of this nucleus. The optic tectum displays a dense array of GFAP-immunopositive radial glia at hatching, similar in this to the situation found in reptiles. However, in the tectum of reptiles this radial glia persists for the lifetime, whereas in the chick it disappears from the superficial tectal layers. This phenomenon may reflect the fact that there is no replacement of tectal cells or regeneration of retinotectal pathways in the chicken. In the early stage, the large cerebral tracts were found to contain dense accumulations of GFAP-positive cells, with peculiarly long outgrowths accompanying nerve fibres. No vimentin-immunopositivity was found in these glial elements; however vimentin was present in the glia situated at the optic chiasm, the anterior commissure and at other decussations. These structures, as well as the raphe, displayed the most intense vimentin-immunopositivity in the post-hatch chicken. This characteristic glial population may represent glial elements that have been reported to regulate fibre-crossing at the midline.

Types and spatial distribution of vasoactive intestinal polypeptide (VIP)-containing synapses in the rat visual cortex

SummaryIn the rat visual cortex vasoactive intestinal polypeptide (VIP)-containing structures were studied by means of light and electron microscopy and image analysis. VIP-immunoreactive axon terminals were found to form symmetric synapses with small dendritic shafts, dendritic spines and somata of pyramidal cells and interneurons. VIP-terminals often occured in pairs with VIP-negative, asymmetric synapses on the same postsynaptic structure. VIP-immunostained dendrites and perikarya were contacted by a purely asymmetric and a mixed population of VIP-negative terminals, respectively. Synaptic connections between two VIP-neurons are seldom as compared to the other types of VIP-synapses. Quantitative studies obtained by the image analysis of VIP-stained boutons and dendritic particles in light microscopic preparations suggest a distinct laminar distribution. Dendritic particles are most frequent in layers I–II, whereas axonal boutons have three laminar accumulations: at the border of layers I–II, in layer IV and layer VI. Together with previous results, the present findings argue for a non-random spatial distribution of VIP-boutons.

Glial fibrillary acidic protein-immunopositive structures in the brain of a Crocodilian, Caiman crocodilus, and its bearing on the evolution of astroglia.

Caiman crocodilus, as a representative of the order Crocodilia, was used in immunohistochemical studies. Immunohistochemical procedures were performed on free‐floating sections using a monoclonal antibody against porcine glial fibrillary acidic protein (GFAP) and employing standard avidin‐biotin complex methodology. The astroglia of Caiman exhibited robust immunoreactivity to the antibodies raised against mammalian GFAP. In Caiman, the predominant GFAP‐immunopositive elements are the radial ependymoglia, similar to other reptiles. The regional variability of glial architecture in Caiman, however, seems greater than in other reptiles so far examined, although it is less compared with chickens. We suggest that this finding corresponds to a more advanced “regional adaptation” of the glial structure in Caiman compared with other reptiles. The main feature that distinguishes the astroglia of Caiman from those of other reptiles is the widespread occurrence of GFAP‐immunopositive astrocytes. These cells are limited in lizards and snakes, are not present in turtles, but are found in every major brain area in Caiman. However, even in Caiman, astrocytes are only intermingled with radial glia and are not the predominant glial element of any brain area. The occurrence of astrocytes does not correlate with brain wall thickness. Despite their origin from different ancestral groups of stem reptiles (synapsid or diapsid), mammals and birds exhibit some common general features in their glial architecture and GFAP distribution: 1) predominance of astrocytes and 2) absent or limited GFAP immunopositivity of several brain areas. The present study demonstrates that, even in Caiman, a representative of the reptilian group most closely related to birds, these features are present only in part, suggesting that, in mammals and birds, they have evolved independently. J. Comp. Neurol. 431:460–480, 2001.

Distribution of glial fibrillary acidic protein-immunopositive structures in the brain of the red-eared freshwater turtle (Pseudemys scripta elegans)

The distribution of glial fibrillary acidic protein (GFAP)-immunoreactivity is described in serial Vibratome sections of the turtle brain. The results are discussed in relation to our previous studies of rat and chicken brains. In the turtle brain, the distribution of GFAP-positive elements is rather evenly abundant as compared to that observed in the chicken and rat. The GFAP-positive structures are fibers of different length and orientation, but the stellate cells are not GFAP-positive. The basic systems is the radial ependymoglia, directed from the ventricles toward the outer surface of the brain. This system also contains some transverse and randomly oriented fibers. The cell bodies are not usually GFAP-positive. The large brain tracts could be recognized by their weak immunostaining, but gray matter nuclei could not be identified on the basis of immunostaining against GFAP. The layers of the optic tectum could be distinguished, as well as the gray and white matter of brain stem and spinal cord and the molecular and granular layers of the cerebellum. In the cerebellum, a fiber system resembling the Bergmann-fibers, a strong midline raphe and coarse transverse fibers could be observed. These latter fibers have no equivalent in other cerebella. Their perikarya proved also to be GFAP-positive, and seemed to be dividing in the adult turtle brain. We conclude that the appearance of GFAP-positive stellate cells had a great importance in the evolution of avian and mammalian brains strengthening the thicker brain walls and assisting in the formation of local differences of GFAP-immunoreactivity in different brain areas.

GFAP-immunopositive structures in spiny dogfish, Squalus acanthias, and little skate, Raia erinacea, brains: differences have evolutionary implications

GFAP expression patterns were compared between the brains of a spiny dogfish (Squalus acanthias) and a little skate (Raia erinacea). After anesthesia, the animals were perfused with paraformaldehyde. Serial vibratome sections were immunostained against GFAP using the avidin-biotin method. Spiny dogfish brain contained mainly uniformly-distributed, radially arranged ependymoglia. From GFAP distribution, the layered organization in both the telencephalon and the tectum were visible. In the cerebellum, the molecular and granular layers displayed conspicuously different glial structures; in the former a Bergmann glia-like population was found. No true astrocytes (i.e., stellate-shaped cells) were found. Radial glial endfeet lined all meningeal surfaces. Radial fibers also seemed to form endfeet and en passant contacts on the vessels. Plexuses of fine perivascular glial fibers also contributed to the perivascular glia. Compared with spiny dogfish brain, GFAP expression in the little skate brain was confined. Radial glia were limited to a few areas, e.g., segments of the ventricular surface of the telencephalon, and the midline of the diencephalon and mesencephalon. Scarce astrocytes occurred in every brain part, but only the optic chiasm, and the junction of the tegmentum and optic tectum contained large numbers of astrocytes. Astrocytes formed the meningeal glia limitans and the perivascular glia. No GFAP-immunopositive Bergmann glia-like structure was found. Astrocytes seen in the little skate were clearly different from the mammalian and avian ones; they had a different process system – extra large forms were frequently seen, and the meningeal and perivascular cells were spread along the surface instead of forming endfeet by processes. The differences between Squalus and Raia astroglia were much like those found between reptiles versus mammals and birds. It suggests independent and parallel glial evolutionary processes in amniotes and chondrichthyans, seemingly correlated with the thickening of the brain wall, and the growing complexity of the brain. There is no strict correlation, however, between the replacement of radial ependymoglia with astrocytes, and the local thickness of the brain wall.

Heterogeneous occurrence of aquaporin-4 in the ependyma and in the circumventricular organs in rat and chicken

Aquaporins are selective water channel proteins critical in volume homeostasis. In the CNS AQP4 predominates, localized mainly in the glia limitans, the perivascular endfeet and ependyma. The present immunofluorescent study reveals the distribution of aquaporin-4 in the circumventricular organs in rat and chicken brains. The ventricular ependyma (especially in the third one), the subfornical organ, the area postrema, the rat pineal body (in part), and the vascular organ of lamina terminalis were marked by intense immunopositivity. Several areas, however, proved to be immunonegative: the central canal, the subcommissural organ, the ependymal zone of the median eminence in rat but its whole thickness in chicken, the subtrochlear organ, and the paraventricular organ. The immunostaining of the lateral septal and subseptal organs were similar to their environment. Results on developing rats suggested that the aquaporin-4 immunonegativity is a secondary phenomenon. Surveying other structural and functional features, no clear explanation of the heterogeneous occurrence of aquaporin-4 was found. The absence of aquaporin-4 seems to correlate with some features of the “ependymal organs” (thickened, pseudostratified ependyma, presence of blood–brain barrier) and with the avoidance of GFAP. On the other hand, the organs rich in aquaporin-4 have features of the “hypendymal organs” (glial and vascular plexus but no blood–brain barrier). There are organs, however, which do not fit into either group completely, i.e. the lateral septal and subseptal organs. Presence of tight junctions coincides with the absence of aquaporin-4 in the ependyma of spinal cord, the subcommissural organ and the ependyma of median eminence.