Ventral tegmental stimulation modulates centrally induced escape responding.

Electrical stimulation of the ventromedial tegmentum (VT) exerts a dual effect on escape responding, induced by stimulating either the medial hypothalamus (MH) or the dorsal part of the central gray matter (CG), namely a suppressant effect which reduces MH or CG induced escape responses and a facilitating one which increases these same responses. The relative magnitude of these effects appears to depend on both the location of the VT stimulation site and the stimulation intensity applied. Furthermore, VT stimulation is often more effective in suppressing escape responding induced by MH as opposed to CG stimulation. VT stimulation has clear rewarding effects but seems to have also aversive effects. The VT sites whose stimulation induces escape suppression seem to yield less marked aversive effects than those sites whose stimulation induces escape facilitation. Furthermore, a negative correlation was found to exist between the escape rate induced by a combined CG/VT or MH/VT stimulation and the self-stimulation rate yielded by these VT sites. These results suggest that the effects of a VT stimulation on escape responding induced by electrical brain stimulation are somehow related to the rewarding and/or aversive effects of this same VT stimulation.