Behavioral effects of microinjections of SR 95103, a new GABA-A antagonist, into the medial hypothalamus or the mesencephalic central gray.

The behavioral effects of unilateral microinjections of SR 95103, a new GABA-A receptor antagonist, into periventricular structures were studied. When injected into the medial hypothalamus (MH) or into the dorsal part of the mesencephalic central gray (CG), SR 95103 produced a dose-dependent behavioral activation together with jumps. However, the characteristics of this behavioral activation differed according to whether SR 95103 was injected into the MH or into the CG. The behavioral activation was found to be attenuated by pretreatment with THIP, a GABA receptor agonist. When injected into the CG or into the deep layers of the superior colliculus, SR 95103 proved to affect the rat's reactivity to tactile stimuli as evidenced by ipsilateral 'neglect' combined with contralateral hyperreactivity expressed as withdrawal reactions and jumping. Similar results were obtained following microinjections of bicuculline methiodide at the same sites. These data confirm that in both the MH and the CG, GABA-A receptors are involved in the neural control of the generation and/or expression of aversive effects. The data further suggest that at the level of the CG and the deep layers of the superior colliculus, GABA is also involved in the gating of sensory information towards the substrate underlying the generation of such aversive effects.