[Median eminence of the hypothalamus in hypophysectomized rats: its structure and ultrastructure].

The median eminence of the hypothalamus of intact and hypophysectomized rats has been studied by means of light and electron microscopy. Paraldehyde-fuchsin (PAF)-positive material is revealed in the external zone of the median eminence in 2-5 days after the operation. The PAF-positive material is also accumulated in the neurosecretory fibres localized around subependymal blood vessels. A2 fibres containing granules of 100-150 nm in diameter and B type fibres with granules up to 100 nm in diameter are seen in the external zone of the median eminence in intact rats. Besides, A1 fibres with granules of 120-200 nm in diameter are found near hypophyseal portal vessels in hypophysectomized animals. All type terminals make contact with blood vessels in the subependymal zone of the median eminence of hypophysectomized rats. It is suggested that terminals of the neurosecretory fibres of types A2 and B permanently make contact with the primary portal capillaries in the external zone of the median eminence, while A1 fibres ingrow in the median eminence in the course of postoperative reparation.