Dorso-ventral variation in the attenuating effect of lateral hypothalamic stimulation on the switch-off response elicited from the mesencephalic central gray area.

Previous experiments have shown that the lateral hypothalamus (LH) is a heterogeneous structure with respect to self-stimulation and aversion. Specifically it has been reported that stimulation of the dorsal LH region entails consequences which are both more rewarding and more aversive than those due to ventral LH stimulation [5, 7, 8, 16, 18]. The aim of the present study was to compare the effects of electrical stimulation applied to either the dorsal or the ventral regions of the LH on the switch-off response elicited by activation of the dorsal part of the mesencephalic central gray area (CG). This experiment was performed using BALB/c mice. The results obtained show that whatever the LH site, hypothalamic stimulation reduces the aversive effects of CG stimulation; however, ventral LH activation was more effective than the dorsal one. In addition, a close relationship was observed between the tolerance in regard to LH stimulation alone, and the tolerance in regard to combined CG/LH stimulation. These data suggest that the more marked aversive consequences of dorsal LH stimulation represent a limiting factor for the attenuating effect on CG escape responding.