Intrahypothalamic connections: an electron microscopic study in the rat.

Terminal degeneration within the hypothalamus was studied by electron microsocpy 1 or 2 days (1) after carefully placed microlesions in the arcuate, anterior periventricular, ventromedial, premammilary and posterior hypothalamic nuclei and (2) after microlesions placed in the hypothalamus deafferented 3 weeks earlier. In the median eminence terminal degeneration was found after each of these lesions. Projections from the ventromedial nucleus reach the arcuate, suprachiasmatic, and anterior periventricular nuclei. Projections from the arcuate nucleus terminate in the medial preoptic, anterior periventricular, and ventromedial nuclei. After lesioning the premammillary nuclei degeneration was found in the supraoptic, arcuate, anterior hypothalamic and ventromedial nuclei.