Hypothalamo-hypophysial function following the lesion of tanycytes in the median eminence of the rat

Ependymal development, proliferation, and functions: a review

A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S-100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re-express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood.

Subependymal cells provide a faster response to ependymal injury than astrocytes in the hydrocephalic brain

Obstructive hydrocephalus was induced in 12-day-old rats by the infusion of kaolin into the cisterna magna. After 7 days, cortical and ependymal lesions were made with thin wire in non-hydrocephalic brains and in hydrocephalic brains. The wounds were allowed to heal for times ranging from 1 day to 10 days post-lesion, after which the animals were perfused and the brains prepared for histology. Paraffin sections of brain containing the ependymal wound were reacted for glial fibrillary acidic protein by the avidin biotin complex technique. Subependymal cells were associated with the ependymal defect from 1 day in both non-hydrocephalic and in hydrocephalic brains. Reactive astrocytes were identified in hydrocephalic wounded brains on day 3. It was not until day 6 that astrocytes and astrocytic processes were seen in association with the subependymal cells at the wound edge, and astrocytic processes were noted along the needle track in the cortex. The results suggest that the extremely rapid response of subependymal cells to ependymal injury is a mechanism distinct from the astrocytes response for repair in the brain.

Morphological feedback effect on neurons of the nucl. arcuatus (sive infundibularis) and nucl. subventricularis hypothalami due to gonadal atrophy

We have correlated the light-microscopic features in the unmyelinated hypothalamus with gonadal atrophy in 15 women of 30-111 years of age and in 7 men between 29 and 82 years. In the postmenstrual cases there is a distinct concordance of gonadal atrophy and the manifestation of nucleolar changes (augmentation, multiplication and vacuolization) in many nerve cells of the arcuate and subventricular nuclei. In younger, still fertile women this nucleolar finding was seen only rarely and sporadically, was limited to the arcuate nucleus and was absent in the subventricular nucleus. We interpret this nucleolar finding as a feedback effect. In man, too, this coincidence is obvious with age and in gonadal atrophy, with fewer nucleolar changes in old age than are seen in women. This difference is probably caused by a more rapid drop of the estradiol than of the testosterone level. - The hypertrophy of the subventricular nucleus (Sheehan and Kovacs) was also observed in our postmenstrual cases.