Electron microscopy of the ventricular lining associated with the hypothalamus and median eminence of prepubertal female horses.

Scanning electron microscopy showed that cells in the infundibular recess of prepubertal female horses were devoid of cilia and sparsely covered with stubby microvilli and small blebs, whereas superior ventricular areas were covered with cilia. Ciliated ependymal cells in supraoptic-suprachiasmatic areas were associated with extensive blebbing, and folded tissue adjacent to the inferior borders of the mamillary body displayed distinct bands of cilia regularly interrupted by areas of sparsely ciliated cells which appeared to be undergoing ciliogenesis. Arcuate ependymal areas had well developed basal tanycyte processes separated by large intercellular spaces. Basal tanycyte processes usually terminated as encapsulating processes around supendymal nerve endings or fibre bundles. The end feet of tanycyte processes encapsulating nerve terminations contained granules and vesicles similar to those found in the neurone, suggesting leaching of neuropeptides from this area of the hypothalamus into CSF. Secretion of substances into CSF was also suggested by scanning electron microscopy observations of blebbing on the apical surfaces of cells. Undeveloped apical microvilli suggest that transport of substances from the CSF to central endocrine tissues and vasculature is probably minimal in prepubertal female horses. However, the ultrastructural observations do suggest that substances may be transferred from the hypothalamic nuclei into the CSF.