The involvement of the mediodorsal nucleus of the thalamus and the midbrain extrapyramidal area in locomotion elicited from the ventral pallidum

Motor activity is regulated by projections from the nucleus accumbens to the ventral pallidum, but it is unclear which efferents regulate behavioral output from the ventral pallidum. Motor activity was elicited pharmacologically by microinjecting either the mu opioid receptor agonist, Tyr-D-Ala-Gly-NmePhe-Gly-OH (DAMGO) or the glutamate receptor agonist, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA) into the ventral pallidum. The involvement of efferent projections was determined by microinjecting the local anesthetic procaine into the mediodorsal nucleus of the thalamus (MID) or the midbrain extrapyramidal area (MEA) prior to administering DAMGO or AMPA into the ventral pallidum. The motor activity induced by DAMGO was blocked by procaine microinjected into either the MD or the MEA. In contrast, procaine microinjected into the MD did not block motor activity elicited by AMPA while procaine into the MEA abolished the behavioral activation. These data indicate that the involvement of efferent projections from the ventral pallidum to either the MD or MEA in motor activation depends upon the type of receptor stimulated in the ventral pallidum. (C) 1999 Elsevier Science H.V. All rights reserved.