Ultrastructure of the Area Postrema of the Bat / 대한해부학회지

This study was undertaken to investigate the ultrastructure of the neurons, neuroglial cells and capillaries in the area postrema[AP] of the Oriental discolured bat, Vespertilio superans. The AP of the bat was a single midline structure at the most caudal portion of the fourth ventricle. Most neurons in the AP were small cells, but their ultrastructure were similar to the typical neurons located elsewhere in the central nervous system. Astroglial cells and oligodendrocytes were also observed and showed their typical ultrastructure. Ultrastructural features of neurons, astroglial cells and oligodendrocytes were not changed during hibernating cycles. However, microglial cells were only found in the hibernating AP ; these cells were located in the parenchyma and near the blood vessels of the AP. Since the microglial cytoplasm was filled with phagocytotic inclusions, the nuclei of the these cells were eccentrically located. Phagocytotic cytoplasmic inclusions were shown to be composed of a dense irregular peripheral region and the pale round central region. A Large vacant space was often found in the electron lucent central region. Continuous and fenestrated capillaries surrounded by pericytes were found in the bat`s AP. Especially, Phagocytotic inclusions were found in the pericyte cytoplasm of the hibernating AP, and this result supports suggestion that pericytes might be phagocytotic cells. On the basis of the distributions of phagocytotic tells[pericytes and microglial cell], ultrastructure of these cells, morphology of their cytoplasmic inclusions, and the appearance of phagocytotic activity of the pericytes during the hibernating stage when microglial cells were observed, it can be concluded that pericytes may also participates in the formation of rrlicroglial cells. Tanycytes were also found in the bat AP.

THE ULTRASTRUCTURAL CHARACTERISTICS AND THEIR FUNCTIONAL SIGNIFICANCES OF THE ARCUATE NUCLEUS AND MEDIAN EMINENCE / 解剖学报

The ultrastructural characteristics of the arcuate and median eminence in the rat have been studied by means of folmaldehyde-osmic acid fixation method. The observations showed that there are two kinds of neurons (dark and light) in the arcuate nucleus which might be responsible for producing both dopamine and releasing hormones. The tanycytes of the ependyma of the third ventricle run longitudinally through various zones of the median eminence and reach the perivascular space of the portal capillaries. The neurosecretory substance-containing nerve terminals may travel between ependymal cells or end around the basal membrane of the capillaries of the median eminence, even keep close to the endothelial fenestrae of "open-type capillary". The axo-somatie and axo-dendritic synapses are formed at the soma and dendrites of neurons of the arcuate nucleus. Both agranular type and granular type axo-axonic synapses are encountered in the fibrous zone of the median eminence. There are also synaptic connections between the basic processes and the large granular vesicles containing nerve terminals in the palisade zone of the median eminence. The ultrastructural characteristics mentioned above suggest that (1) the releasing (or inhibiting) hormones of the hypothalamus might be released into the portal capillaries from nerve terminals directly or into the cerebro-spinal fluid of the third ventricle and then uptaken by the tanycytes, and transported to the portal capillaries by their processes. (2) each step of synthesis, storage, transport and release of the releasing (or inhibiting) hormones could be regulated by nervous mechanism