Involvement of the ventral tegmental area in locomotion elicited from the 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 area (VTA) in the motor stimulation produced by the microinjection of dopamine, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or [D-Ala2, MePhe4,Gly-ol5]enkephalin (DAMGO) into VP or the shell and core compartments of the nucleus accumbens. Initial dose-response curves revealed that dopamine was approximately equipotent at producing motor activity after microinjection into the core and shell, AMPA 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 evaluated by microinjecting the tau-aminobutyric acidB agonist baclofen into the VTA to inhibit neuronal activity. Baclofen treatment abolished the motor responses elicited by AMPA from the shell, core and VP. The motor effect of DAMGO in the VP was abolished by baclofen, whereas the response in the shell was attenuated. The motor response to dopamine was unaltered by baclofen, regardless of the injection site. These data indicate that there exist differences between the core and shell of the nucleus accumbens in the capacity of neurotransmitter analogs to elicit motor activity, and that although AMPA-induced motor activity is dependent upon neurotransmission in the VTA after microinjection into the core, shell and VP, DAMGO-induced locomotion only requires such tone after microinjection into the VP and shell.