Effects of dorsal raphe stimulation on escape induced by medial hypothalamic or central gray stimulation.

Electrical stimulation of the ventral part of the mesencephalic central gray affects escape responding induced by stimulation of either the medial hypothalamus (MH) or dorsal central gray (CG) in the rat. The sign and magnitude of the effect appeared to depend on the following factors: (1) The location of the site stimulated in the ventral central gray and the intensity of the stimulation. A stimulation of the dorsal raphe nucleus (DR) which induced a marked rewarding and a low aversive effect reliably suppressed MH or CG induced escape. Stimulation of sites located at the boundary between DR and central gray enhanced escape at low intensities and suppressed it at higher intensities. When located more laterally in the ventral central gray, the stimulation induced less rewarding and more marked aversive effects and it reliably enhanced MH or CG induced escape. (2) The kind of stimulation applied (monopolar or bipolar). (3) The location of the site (MH or CG) from which the stimulation-induced escape responses were obtained.