Liquorkontaktneurone im Nucleus infundibularis

Scanning and Transmission Electron Microscopy of the Ependymal Lining of the Third Ventricle

In its simplest form, the ependyma of the third ventricle consists of a single layer of cuboidal cells. Although these typical mural cells constitute the greater part of the lining of the ventricle, a specialized variety of ependymal cell (the tanycyte) can also be distinguished within circumscribed areas of the ventricular wall. Although such cells are found scattered throughout the dorsoventral extent of the third ventricle, they are particularly numerous along the ventrolateral walls and floor. The regional variation in the surface morphology of the ventricle walls as evident with the scanning electron microscope is consistent with this pattern of tanycyte distribution. Ultrastructural studies have established that the tanycyte is a fundamentally distinct cell with a long basal process extending into the subjacent neuropil and frequently directed toward a capillary wall. This unique morphology conforms closely to its three-dimensional appearance as demonstrated with the scanning electron microscope. The significance of ependymal tanycytes particularly of the third ventricle derives largely from the connections they establish between the ventricular lumen and vasculature of the median eminence. This intriguing structural relationship has led to the suggestion that ependymal cells and cerebrospinal fluid of the third ventricle may be involved in the regulation of adenohypophysial activity. Evidence indicating the functional involvement of specialized ependymal cells in the neuroendocrine control of pituitary activity is reviewed.

Hypothalamic neuroendocrine correlates of cutaneous burn injury in the rat: I. Scanning electron microscopy

Rats were given a standard scald burn on 60% of the body surface or only a sham burn and were sacrificed at intervals from 6 hr to 14 days later. Serum thyroxine (T4), free thyroxine index (FT4I) and triiodothyronine (T3) were depressed compared to values in respective shams as early as 6 hr post-burn. T4 and FT4I were less depressed on post-burn days (PBD) 2-3 than on PBD 1 and then exhibited a further fall. T3 remained depressed through PBD 14. Pineal melatonin content was elevated at 6 hr and fell to the normal daytime range in subsequent samples. The ventral portion of the diencephalon was prepared for scanning electron microscopy. Only in the burned rats and beginning on PBD 2, large numbers of supraependymal neurons (SEN) appeared in the ventricular space attached to the inferior walls and floor of the third cerebral ventricle. Transmission electron microscopy was used to confirm the neuronal nature of the SEN. Viewed by scanning electron microscopy, these persisted through PBD 14. SEN were interconnected by cables of their neurites exhibiting varicosities on individual neurites as they passed over perikarya of other SEN. Some SEN were seen to be only partially emerged from the underlying tissue and others were seen to send a thick process into the hypothalamic tissue. These observations indicate that after peripheral injury there is marked plasticity of the brain in an area thought to control the endocrine systems that show abnormalities after such a peripheral injury. The timing, location and nature of these anatomic changes indicate the possibility that at least some aspects of central nervous orchestration of the endocrine metabolic response to injury may be related to the emergence of a neuronal system receiving or sending messages through the cerebrospinal fluid and/or through new neurite circuits along the surface of the third ventricular wall. These structures may appear in response to initial primary hormonal changes and/or may play a role in maintaining the post-injury hormonal milieu manifested in part by a subsequent second fall in serum T4.

Surface fine structure of supraependymal elements and ependyma of hypothalamic third ventricle of mouse

The ependymal surface of the hypothalamic third ventricle of the adult female and male mouse was examined with the scanning electron microscope. The material was dried with the critical point method. Supraependymal cells, exhibiting a variety of forms, lie among the cilia of the rostrodorsal two-thirds of the ventricle. The cell bodies are usually between 8 and 10 mu in diameter and have dividing pseudopodial processes which may be broad or narrow, flat or stout, smooth or varicosed. The textured surfaces of the cells seen in this material appear to have no cilia, microvilli or membraneous folds though they may have small bleb-like protrusions. Some cells and adjacent cilia bear clusters of friable-looking material that may be secretory. In several female mice, mounds of debris, that could be degenerating cells or secretory material, were seen in intimate association with clusters of cells. The cells' processes extend over and through the surface of the mound. While some supraependymal cells may be neurons or glia, it is suggested that many of the cells seen may be morphological variants of one cell line, mononuclear phagocytes. Sausage-shaped structures at the end of long cilia-like stalks are described and their possible identity discussed.