Effects of monosodium glutamate on the development of intraventricular axons in the rat hypothalamus.

The development of intraventricular axons in the infundibular recess of the young rat was investigated by correlative scanning and transmission electron microscopy (SEM-TEM). From the fourth through the fifteenth day of life such axons increase steadily in number. During subsequent weeks their number gradually decreases. In animals given monosodium glutamate on the fourth postnatal day there is widespread neuronal necrosis in the arcuate nucleus, and the development of intraventricular axons is greatly reduced. These findings suggest that the axons originate from the neurons of the arcuate nucleus.

A contribution to the study of the afferents to the pigeon optic tectum.

The origins of several afferent pathways to the pigeon's tectum were studied using the horseradish peroxidase tracing technique. The results confirm the presence of several previously described afferents, and add further data on intertectal and hyperstriatofugal projections. Two new sources of afferents to the tectum, located in the hypothalamus and the septum, were identified. The latter is described in greater detail.

The ventricular surface of the monkey mediobasal hypothalamus. A scanning electron microscopic study.

The ventricular lining of the infundibular recess of monkey brains of both sexes was investigated with SEM. Based on the distribution patterns of surface profiles regional differences in the tanycytic ependyma are described. Variations in the number of surface profiles were observed in females during the ovarian cycle. These variations may be an indication not only of absorptive and/or secretory activities, but may also be related to cell membrane redistribution and membrane turnover in dependence of endocrine factors. In the males such variations were not registered. An essental sexual dimorphism does not seem to exist in the tanycytic ependyma of the monkey, only the reaction pattern is different. Supraependymal macrophages (SEC) were more numerous in the ovulating females than in the males or menstruating females. In addition to these SEC some monkeys had a second SEC type which was arranged in sheets. These are interpreted to be glioses. A variable number of axons can also be found in the lower regions of the infundibular recess. Their morphology suggests the presence of several types of axons, but they do not appear to constitute an organized network. No significant sexual differences were registered in relation to the axons.

Effects of cytochalasin B on the ependyma.

In order to analyse whether or not surface morphology and intracellular skeleton are interdependent, Cytochalasin B (CB), an agent which interferes with microfilaments, was introduced ino the brain ventricular system of adult rats. Following intraventricular application of CB for different periods of time (up to 6h) the animals were sacrificed and the ventricular wall examined with both transmission and scanning electron microscopes. The first signs of cellular alteration after short periods of CB application were an increase in the number of microfilaments within the cytoplasm and the appearance of a multitude of small knobs on the surface of the cilia of the cuboidal ependymal cells, whereas the tanycytes exhibited extensive blebbing at their apical poles. When the duration of CB perfusion was lengthened, entire ciliated cells became rounded up and were loosened from the epithelium, especially in the transition zone of the third ventricle where the ependyma is composed of both tanycytes and ciliated cells. The significance of the CB-induced changes in the ependyma are discussed in relation to the ependymal surface modifications seen under physiological and other experimental conditions.

Reaction of the hypothalamic ventricular lining following systemic administration of MSG.

Monosodium glutamate (MSG) was used to create a lesion in the CNS of the infant rat. Subcutaneous injections of MSG in four day old rat pups caused a high degree of cell necrosis in the arcuate nucleus of the hypothalamus. The tanycytic ependyma overlying this nucleus was examined at different post injection intervals with both the SEM and the TEM. Four hours following treatment the tanycytic cell bodies appear swollen and their apical surfaces have lost most of their microvilli. Within 24 hours the affected ependymal area possesses a dense population of supraependymal cells. During the following days these alterations regress so that by the 14th day of life the ependymal surface of a treated animal is indistinguishable from that of a control animal. The changes taking place in the tanycytes are compared to those occurring in astrocytes within the body of the lesion. The morphological and ultrastructural features of the supraependymal cells are considered in their similarity to those of microglia.

The supraependymal cells of the rat hypothalamus: changes in their morphology and cell number during the ovarian cycle.

The number of SEC in the hypothalamus of the rat change during the ovarian cycle (5-8 cells in oestrus, 100 cells in dioestrus per ventricular surface). The changes in the number as well the morphology of the SEC support the hypothesis that they are of mesenchymal nature.

Morphology and distribution of supraependymal cells in the third ventricle of the albino rat.

The supraependymal cells (SEC) are a normal component of the wall of the cerebral ventricles. In the hypothalamic area of the third ventricle they are restricted, in healthy animals, to the ependymal projection of the hypophyseotropic area. Here the SEC show great polymorphism. In addition to bipolar, multipolar and stellate or spider-like cells, transitional forms between these types can be seen. Their perikarya and processes can either remain at some distance from the ependyma or be in close contact with it. The processes may protrude between the ependymal cells or show surface differentiations that resemble the thin cytoplasmic folds of the mesenchymal wandering cells. Considering this and the variations in the number of cells, for example during the ovarian cycle, the SEC can be interpreted as mesenchymal cells, probably related to microglial cells of the subependymal layer. It is suggested that the SEC have a phagocytotic function and may be involved in the normal renewal of the ependyma. A definitive explanation for the restriction of the SEC to the hypophyseotropic area as well as the elucidation of their function remain to be found.