INVOLVEMENT OF THE VENTRAL TEGMENTAL AREA IN LOCOMOTION ELICITED FROMTHE NUCLEUS-ACCUMBENS OR VENTRAL PALLIDUM

This study was designed to evaluate the role of the circuit containing the nucleus accumbens, ventral pallidum (VP) and ventral tegmental ar ea (VTA) in the motor stimulation produced by the microinjection of do pamine, lpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or [D-Ala(2),MePhe(4), Gly-ol(5)]enkephalin (DAMGO) into VP or the sh ell and core compartments of the nucleus accumbens. Initial dose-respo nse curves revealed that dopamine was approximately equipotent at prod ucing motor activity after microinjection into the core and shell, AMP A was more effective in the core, whereas DAMGO was more potent in the shell. A role for the VTA in the motor responses elicited by dopamine , AMPA or DAMGO microinjection into the shell, core or VP was evaluate d by microinjecting the tau-aminobutyric acid(B) agonist baclofen into the VTA to inhibit neuronal activity. Baclofen treatment abolished th e motor responses elicited by AMPA from the shell, core and VP. The mo tor effect of DAMGO in the VP was abolished by baclofen, whereas the r esponse in the shell was attenuated, The motor response to dopamine wa s unaltered by baclofen, regardless of the injection site. These data indicate that there exist differences between the core and shell of th e nucleus accumbens in the capacity of neurotransmitter analogs to eli cit motor activity, and that although AMPA-induced motor activity is d ependent upon neurotransmission in the VTA after microinjection into t he core, shell and VP, DAMGO-induced locomotion only requires such ton e after microinjection into the VP and shell.