Locomotor activity and accumbens fos expression driven by ventral hippocampal stimulation require D-1 and D-2 receptors

Numerous studies have suggested that excitatory projections from the ventra l hippocampus to the nucleus accumbens modulate locomotor activity in rats. Furthermore, the ability of ventral hippocampal neurons to alter locomotor activity may involve the dense dopaminergic innervation found in the nucle us accumbens. The purpose of this study was to: (i) more fully characterize the locomotor effects of acute alterations in ventral hippocampal activity ; (ii) ascertain the influence of dopamine agonists and antagonists on loco motor changes produced by altered ventral hippocampal activity; and (iii) u se immediate early gene induction to determine whether dopamine antagonists alter the response of nucleus accumbens neurons to ventral hippocampal sti mulation. By comparing a variety of excitatory amino acid agonists, it was found that ventral hippocampal infusion of N-methyl-D-aspartate elevated lo comotor activity in a subconvulsive manner, while other excitatory amino ac id receptor agonists did not. Inactivation of the ventral hippocampus achie ved by lidocaine infusion did not suppress ongoing locomotor activity, nor did it affect amphetamine-induced increases in locomotor activity. Increase s in locomotor activity induced by ventral hippocampal N-methyl-D-aspartate infusion were blocked by systemic administration of haloperidol (a D-2 rec eptor antagonist), SCH-23390 (a D-1 receptor antagonist) or reserpine. Cell ular expression of the protein product of the immediate early gene, c-fos, was dramatically increased in the nucleus accumbens shell after ventral hip pocampal N-methyl-D-aspartate infusion, and haloperidol, SCH-23390 and rese rpine attenuated this effect. These results suggest that the increases, but not decreases, in ventral hip pocampal activity have a measurable effect on ongoing rates of locomotion, and that this effect requires both D-1 and D-2 receptors. Moreover, the stu dies of Fos expression suggest that dopamine receptor antagonists attenuate neuronal responses to ventral hippocampal stimulation within the nucleus a ccumbens, a brain region important in the generation and maintenance of loc omotor activity. (C) 1999 IBRO. Published by Elsevier Science Ltd.