Decreased spontaneous locomotor activity in the rat induced by hypothalamic lesions

Abstract

A permanent decrease in spontaneous locomotor activity of the rat can be produced by destruction of either of two specific regions in the ventral hypothalamus at the level of the tuber cinereum. One is a lateral region which lies between the fornix and cerebral peduncle and extends from the level of the fornix downward to the base of the brain. Its rostrocaudal extent seems to be from about the level of the posterior border of the paraventricular nucleus back to, but not including, the premammillary area. The other is a medial region which seems to lie adjacent to the ventral half of the third ventricle, extending laterally from this structure only about .5^–1 mm. This region, too, appears to reach to the base of the brain. The exact rostrocaudal extent of this medial region is uncertain, but at least it does not extend rostrally into the preoptic area nor caudally into the premammillary area. Activity was decreased to a much lower level after lateral lesions than after medial lesions. Lesions in other parts of the hypothalamus did not produce hypoactivity. Hypoactivity seemed to occur independently of other signs of hypothalamic impairment.