The role of nigral and thalamic output pathways in the expression of oral stereotypies induced by amphetamine injections into the striatum

Microinjections of amphetamine into the ventrolateral striatum (VLS) elicit a striking behavioral syndrome characterized by compulsive oral and foreli mb motor stereotypies, The neural pathways that mediate these behavioral re sponses downstream fr om the striatum have not yet been identified. Ln a se ries of experiments, we investigated the involvement of the substantia! nig ra pars reticulata (SNr) and the ventromedial nucleus of the thalamus (VMT) in the mediation of this behavioral syndrome. We demonstrated that lidocai ne-induced reversible inactivation of the SNr reduced amphetamine-induced s tereotyped biting and gnawing behaviors, suggesting that the nigral output pathway plays a significant role in the expression of these behavioral resp onses. In rum, injections of lidocaine into the VMT only transiently reduce d amphetamine-stimulated biting and increased stereotyped gnawing and paw n ibbling, suggesting that the expression of oral stereotypies induced by amp hetamine injections into the VLS is not dependent on thalamocortical feedba ck. (C) 2000 Elsevier Science B.V. All rights reserved.