The structure of rabbit retinal Müller (glial) cells is adapted to the surrounding retinal layers.

Radial glial (Müller) cells of the rabbit retina were studied by various techniques including Golgi impregnation, scanning electron microscopy, horseradish peroxidase application, and staining of enzymatically isolated cells. This combination of methods produced detailed information on the specialized morphology of the Müller cells within the different topographical regions of the retina, and of the Müller cell processes within the various retinal layers. As a general rule, the retinal periphery contains short thick Müller cells with big endfeet, whereas the thick central retina is occupied by long slender cells with small endfeet. Independent of their location within the retina, Müller cell processes were found to be adapted to the structure of the surrounding retinal layers. Within the outer and inner nuclear layers, Müller cell processes (and somata) extend thin cytoplasmic "bubbles" ensheathing the neuronal somata, as do the "velate" astrocytes in the brain. In the plexiform layers, Müller cells extend many fine side branches between the neuropil, comparable to the protoplasmic astrocytes of the brain. In the thick myelinated nerve fibre layer of the central retina the Müller cell processes are rather smooth, similar to those of fibrous astrocytes. It is concluded that the neuronal microenvironment determines the morphology of a given glial process, or even of a part of a glial process running through a specialized neuronal compartment.

A blood capillaries-bridging cell type in adult mammalian brains.

For the investigations we used coronal-sectioned series of adult brains from Wistar-rat, white mouse, cat, tree-shrew (Tupaia glis), and rhesus monkey (Macaca mulatta) in which the blood capillaries bridging cells (BCs) had been demonstrated by different silver-impregnation procedures (Golgi-Kopsch, Gallyas, Bär and Budi Santoso) and by complex staining with LFB + PAS + Hematoxylin, too. The BCs could be found in many cortical and subcortical brain areas of the 5 mammalian species under study. All investigated mammalian species showed the same morphological range of intercapillary bridges and BCs. Even between the individual brain regions as well as between the grey and white matter no difference could be determined. The BC is a small, generally spindle- or bell-shaped, rarely roundish cell bridging with its one or two smooth processes two capillaries ore precapillaries. The processes are usually attached to the blood vessels by disc- or pyramid-shaped thickenings. Usually, the bridged capillaries form bends with their crowns directed to one another. Only capillaries of the same stem were bridged. By reason of the striking morphological similarity of pericytes and BCs with regard to their soma shape, primary processes and chromatin-distribution patterns of their cell nuclei we consider the BCs as a subtype of pericytes. Our findings point to the following way of formation of the intercapillary bridges: The BC attached to the capillary either remains in this position and sends a process to another microvessel or withdraws from the vessel by means of a process and develops a second process at the opposite pole which grows towards a capillary.(ABSTRACT TRUNCATED AT 250 WORDS)

[Morphologic and histochemical changes in the secondary focus following cobalt-induced epileptogenic bioelectrical activity of the visual cortex in the adult rat]. / Morphologische und histochemische Veränderungen im Sekundärherd nach Kobalt-induzierter epileptogener bioelektrischer Aktivität im visuellen Cortex der adulten Ratte.

Implantation of cobalt-agar rods into the visual cortex of 16 adult rats induced in some of the animals epileptiform bioelectrical activity and provoked in all of them histological and histochemical changes in the region of the implantation (primary focus) as well as in some ipsilateral projection sites of the visual cortex (secondary foci). The changes within the secondary foci are demonstrated in the Corpus geniculatum laterale, pars dorsale (dLGN), by means of 18 histochemical and 5 histological methods. Together with the appearance of hyperactive and degenerating neurones combined with neuronophagy and diminution of the number of synapses a marked gliosis developed, especially an increase of microglia. The destruction of the tissue induced a depression of energy and transmitter metabolism and intensified lytic processes. This is confirmed by the decreased activities of LDH, SDH, GPDH, G6PDH, NAD(P)H-TR, GABA-T and GDH and the increased activity of acid phosphatase in the neuropil of the secondary foci. Single hyperactive nerve and glial cells were accented by high activities of those enzymes which had a reduced activity in the neuropil. Since in our experiments agar-rods without cobalt never induced histological or histochemical changes in subcortical grisea of the visual system, the secondary foci seem to result from the direct influence of the cobalt, migrating in the corticothalamic projection pathway and identifiable in the dLGN by the TIMM technique.

Structural and cytochemical features of perineuronal glial nets in the rat brain.

Perineuronal nets formed by glial cells could be visualized in different regions of the rat brain with Golgi methods. Although mostly their cellular origin was not detectable, in some cases the nets were found to originate from glial cell processes possessing characteristic features of microglia. Using the colloidal iron hydroxide binding method and carbohydrate binding lectins the perineuronal nets were shown to be enriched with anionic carbohydrate components. Some functional aspects of these structures have been discussed.

The ventral lateral geniculate nucleus of the albino rat morphological and histochemical observations.

The ventral lateral geniculate nucleus (vLGN) of albino rats (Wistar strain) has been described histologically and histochemically. Special attention was paid to the identification of cell classes in Nissl and Golgi preparations, the afferent and efferent connections of vLGN cells and the demonstration of enzymes of energy and transmitter metabolism. Topographical aspects were taken into consideration, too. The main results can be summarized as follows: In the rat vLGN, three subnuclei can be distinguished: the lateral and medial subnucleus and the intergeniculate leaflet. In the rostral vLGN, the lateral and medial subnucleus is separated by a vertical fibre bundle which contains retinal axons. Our own experiments and findings of other groups revealed that the rat vLGN is connected with numerous brain structures. There is no efferent projection to cortical regions. Afferent fibres reach the vLGN from retina, visual cortex, superior colliculus, pretectal region, zona incerta, contralateral vLGN, dorsal raphe nucleus, locus coeruleus, mesencephalic reticular formation, vestibular and dorsal tegmental nuclei. An efferent projection has been found to superior colliculus, pretectal region, dorsal lateral geniculate nucleus, contralateral vLGN, zona incerta, pontine nuclei, suprachiasmatic nucleus, lateral terminal nucleus of the accessory optic system and intralaminar nucleus of thalamus. Comparative findings suggest that the lateral subnucleus is involved in "specific projections", whereas the medial subnucleus projects to "unspecific zones". For detailed information see text. Five classes of neurons can be distinguished in Golgi and Nissl preparations. Class 1 cells are medium-sized to large with smooth thick proximal but branched spiny distal dendrites. They are confined to the lateral subnucleus and the intergeniculate leaflet. In the lateral subnucleus, class 1 cells could be identified as geniculo-tectal relay neurons (Brauer and Schober, 1982). All other classes of neurons are spineless or sparsely spined. Class 2 cells (giant neurons) of unknown function could be found in the lateral and medial subnucleus. Class 3 cells (medium-sized multipolar neurons) can mainly be found in the medial subnucleus. They are good candidates for neurons projecting to the contralateral vLGN. Class 4 cells (bipolar neurons) occupy the ventromedial part of the medial subnucleus and are very similar to cells localized in the adjacent zona incerta. Cells belonging to this type could found to be labelled by the HRP reaction product after injection of this enzyme in the pontine region.(ABSTRACT TRUNCATED AT 400 WORDS)

The glia types inthe visual system of adult rats, their shape variability, distribution patterns, and their lightoptically visible contacts to other tissue structures.

In silver impregnated coronal sections of adult rat brains the glia types of the Corpus geniculatum laterale, pars dorsalis (CGLd) an in area 17 were registered considering their form variants (FV), their intraareal distribution and their light optically demonstrable connexions to other tissue structures. Compared with the shape-determining light optically visible processes and perikarya, astrocytes show the lowest, microglial cells the greatest from variability. Transitional forms between the three glia types were not detected, but between elongated astrocytes and fiber astrocytes. An accumulation of elongated astrocytes, fiber astrocytes, and oligodendrocytes was found in the lateral zone of the CGLd, of protoplasmic astrocytes in the lateral and intermediary zones and at the rostral and caudal poles of the griseum, too. In the cortex distribution differences in the single laminae became also evident. Astrocytes were most concentrated in L I, oligodendrocytes and microglia, however, in L V. A few FV of the microglia were found to show a predominant localisation in specific laminae. Neither the total glia number nor the single glia types correlate with the neuron packing density. The frequency distribution of the FV of oligodendroglia in the CGLd and the visual cortex is similar, that of microglia, however, significantly deviating. Compared with the CGLd the oligodendrocytes of area 17 have smaller somata. Astrocytes, oligodendrocytes and microglial cells reveal structural contacts to different parts of the neurons, to blood vessels and other glial cells, too. Contacts between oligodendrocytes and microglial cells as well as astrocytes in satellite position could never be observed. In the cortex a few FV of microglia show typical connexions.

Perineuronal nets of glia.

Perineuronal nets could be visualized with some Golgi methods in the rat's brain. Nets were seen in telencephalic, diencephalic and mesencephalic structures covering somata and proximal dendrites of different neuronal types. Some nets could be found originating from microglia cells. In most cases their origin is not recognizable. These perineuronal nets seem to be identical with "Golgi nets" of late anatomists, which played an important role in the discussion between recticularists and neuronists. Some aspects of their possible functional significance are discussed.

[Variability of the relay neurons in the corpus geniculatum laterale, pars dorsalis in the albino rat]. / Untersuchungen zur Variabilität der Relais-Neuronen im Corpus geniculatum laterale, pars dorsalis (Cgl d) der Albinoratte.

38 Golgi-impregnated relay cells from the Wistar rat's dLGN were investigated considering their possible differentiation into 2 types using camera lucida drawings with a magnification of 800. The following criteria were taken into account: 1. size of neurons (perikarya, size of dendritic domains) 2. structure of dendrites (number of dendrites, branching points, distribution of dendritic density in relation to the perikaryon, surface structures of dendrites). It was tried to correlate the investigated parameters quantitatively and qualitatively. The results showed that inspite of a missing clear subdivision into 2 types there exists a trend towards developing a second type of relay cells.

[Enzyme histochemical examinations of the visual system of the adult rat following unilateral enucleation]. / Enzymhistochemische Untersuchungen am visuellen System der adulten Ratte nach unilateraler Enucleation.

12 adult white lab-rats were enucleated and after a survival period of 1, 3, 7 and 30 days the activities of GABA-T, GDH, LDH, SDH and GPDH were demonstrated histochemically in the Tractus opticus (To), Corpus geniculatum laterale, pars dorsalis (CGLd) et ventralis (CGLv), Colliculus superior (Cs) and Nucleus olivaris praetectalis (Nop). Since the ipsi- and contralateral grisea are always in the same tissue section the enzyme activities can be quantitatively compared by visual impression without a greater mistake. In To enucleation caused a hypertrophy of astrocytes together with an increase of the activities of GABA-T, GDH, LDH, and GPDH in these cells. The reactions indicate a more intensive metabolism in connection with the myelin degradation. In CGLd, CGLv, Cs and Nop following enucleation there appeared contralaterally a graded loss in the activities of GDH, LDH, GPDH, and GABA-T; only SDH scarely changed its activity. The fastest and strongest reaction was found in Cs and Nop, while CGLd and CGLv reacted later and to a less degree. In CGLv the enzyme reaction was limited to the lateral part of the nucleus. As diminution of activity is caused by degeneration of the retinal terminals the effected enzymes must be localised in cytoplasma and mitochondria of these terminals. Taking into account findings from literature the following is concluded from the time patterns, the degree of diminution of the enzyme activities and the relation of retinal to extraretinal terminals in the individual nuclei: GABA probably acts as a transmitter in interneurons of CGLd, Cs, and Nop. Glutamate is a transmitter in Cs and Nop.

[Axon-like glial extensions in the pars ventralis of the corpus geniculatum laterale (CGLv) of the albino rat]. / Axonähnliche Gliafortsätze in der Pars ventralis des Corpus geniculatum laterale (CGLv) der Albinoratte.

In sections of the Corpus geniculatum laterale, pars ventralis (CGLv) of adult albino rats impregnated according to Golgi-Kopsch, structures are visible very similar to long unbranched axons with large boutons en passage. Within the CGLv these axon-like structures can be followed parallel to the optic tract. Generally they take a ventro-dorsal, exceptionally a dorso-ventral course. As well in Golgi-Kopsch material as in sections in which glial cells are specifically impregnated the described structures could be traced to cells mainly located subpial in the Tractus opticus. Within the optic tract these axon-like structures change their appearance looking similar as the numerous other processes originating from these cells too. These other processes take a course right-angled to the optic fibers and in general they don't bear axon-like structures as described. In our opinion based also on investigations of Nissl-stained sections the origination cells represent a specialized type of astroglia of until now unknown function.

[From Paul Flechsig to the Paul Flechsig Institute for Brain Research. Development of brain research at the Karl Marx University]. / Von Paul Flechsig zum Paul-Flechsig-Institut für Hirnforschung. Die Entwicklung der Hirnforschung and der Karl-Marx-Universität.

A review is given on the development of the brain research institute of the Karl-Marx-University of Leipzig during the directorates of Paul Flechsig (1883-1920), Richard Arwed Pfeifer (1925-1957), and Wolfgang Wünscher (1957-1971).

[Problems and experience in the light optical and histological presentation of glia cells]. / Probleme und Erfahrungen bei der lichtoptischen histologischen Darstellung der Gliazellen

1. 8 histological techniques and 13 modifications derived from those were tested on usefulness for the demonstration of glial cells in the adult rat brain. From these methods the impregnation techniques of Golgi-Kopsch, Valenzuela y Chacón and Rio del Hortega were modified according to a scheme of variance to find out the optimal variants. 2. The impregnation quality depends on the animal species, the animal age, the health of brains, the brain area, the balanced proportion of the treatment stages and the biochemical state of the glial cells. 3. The silver impregnation techniques are not so specific that only one glial type is stained, but one type prevails. The silver carbonate procedure according to Hortega allows to impregnate oligodendrocytes, microglial cells and astrocytes in frozen as well as in paraffin sections. The method of Golgi-Kopsch is more suited for oligodendrocytes and microglial cells than for astrocytes. Following the procedure of Valenzuela y Chacón especially astrocytes, but also microglial cells allow impregnation in both frozen and paraffin sections. 4. The different demonstration qualities of the proved methods call for critical examination of absolute measurements of cell size, length of processes and ramification density. 5. The presence of cell groups of different disposition towards impregnation within a glial type speaks for a biochemical inhomogeneity of the glial types.