Effects of hypothalamic lesions on central gray stimulation induced escape behavior and on withdrawal reactions in the rat.

The effects of unilateral--medial or lateral--hypothalamic lesions were studied with regard to both switch-off (i.e., escape) responding induced by central gray (CG) stimulation and responsiveness of the same animals to peripherally-applied electrical or thermal stimulation. Medial hypothalamic (MH) lesions were found to reduce--but not abolish--the efficiency of CG stimulations applied on the side of the MH lesion, while the efficiency of contralaterally applied CG stimulations remained unchanged. Furthermore, such lesions enhanced the responsiveness to peripheral nociceptive stimuli on whatever body side they were applied. Lateral hypothalamic lesions were found to only slightly--or not at all--affect the efficiency of CG stimulations, while they enhanced the responsiveness to peripheral nociceptive stimuli on either side of the body. These results suggest that the hypothalamus does not exert a univocal control over both centrally induced escape behavior and peripherally induced withdrawal reactions.