The effect of cerebral ischemia on the ultrastructure of the hypothalamo-neurohypophysial system of the mongolian gerbil. The neurohypophysial axons and pituicytes.

The results of ultrastructural studies of the neurohypophysial axons and pituicytes of male mongolian gerbils subjected to experimental cerebral ischemia induced by 10 min bilateral occlusion of the common carotids are reported. In gerbils with cerebral ischemia some neurohypophysial axons were well preserved and, as regards ultrastructural organization, did not differ from the control animals. Some axons showed ultrastructural changes. They were characterized by depletion of dense cored neurosecretory granules and the appearance of optically empty vesicles. These suggest the increased secretion of neurohypophysial hormones. Moreover, the findings of intra-axonal large multilamellar bodies and externally lying tightly arranged lamellar whorls (similar to myelin sheath) were linked with simultaneous obliteration of the primary structure of certain axons. The neurohypophysis of the animals subjected to cerebral ischemia revealed the presence of 'light' ('fibrillar') and 'dark' pituicytes. The 'light' cells were characterized by large Golgi complex and the presence of fine fibrilles or fibrillar bundles which occupied a large cytoplasmic area of the cell body or of the processes. The finding of accumulated fibrilles suggests the ischemia damage of the cells. The 'dark' cells revealed the presence of dense cytoplasmic ground and the lobulated nucleus. In these cells ribosomes were predominant. The mitochondria were swollen in both varieties of pituicytes, arbitrarily designated here as 'light' ('fibrillar') and 'dark'. The results of the present study, therefore, indicate a functional susceptibility of neurosecretory axons and pituicytes to haemodynamic disturbances associated with bilateral cerebral ischemia.