Neuronal pathways to the margin of the hypothalamic median eminence and to the pituitary stalk of the rat. I. A golgi and degeneration study.

The course and termination of nerve fibres approaching the median eminence from lateral direction were studied in Golgi specimens and by the axon-degeneration technique. Varicose nerve fibres could be traced from an area corresponding to the medial and superficial portion of the medial forebrain bundle. They run immediately underneath the free ventral surface of the hypothalamus. Parasagittal knife-cuts placed at various distances (0.5 to 1.4 mm) from the midline resulted in a large number of degenerated axon fragments along the margin of the median eminence, on both sides of the tuberoinfundibular sulcus. Scattered degenerated fragments were found in the lateral part of the palisade zone as well as in the pituitary stalk. No degeneration could be seen in the abo9ve mentioned areas if the cut was as far as 1.8 mm from the midline. Degenerated axon fragments appeared as soon as 5 hours following the lesion indicating that the time course of ultrastructural degenerative alterations is remarkably fast in this fibre system.