Hippocampal modulation of locomotor activity induced by focal activation of postsynaptic dopamine receptors in the core of the nucleus accumbens.

The locomotor effects of intra-NAcc injection of dopamine receptor agonists following discrete lesion or inhibition of the DH or the VH have been poorly investigated using only the indirect dopamine receptor agonist amphetamine. In the present study, we investigated how lidocaine in the DH or the VH modulated hyperlocomotion induced by focal injection into the NAcc core of the selective D1-like receptor agonist, SKF 38393, or coinjection of SKF 38393, and the selective D2-like receptor agonist, LY 171555; the latter pharmacological condition being required for the full expression of the postsynaptic effects of D2-like receptor agonists, and recognized to produce a locomotor response mainly mediated by D2-like postsynaptic receptors. Rats were given the D1-like receptor agonist SKF 38393 alone or in combination with the D2-like receptor agonist LY 171555 into the NAcc core, and lidocaine into the DH or the VH. Then, locomotor activity was recorded. Focal injection into the NAcc core of SKF 38393 alone or in combination with LY 171555 resulted in an increase of locomotor activity. Administration of lidocaine into the DH further potentiated the increase in locomotor activity induced by activation of D1-like receptors or co-activation of D1-like and D2-like receptors in the NAcc core. Administration of lidocaine into the VH also potentiated the increase in locomotor activity induced by D1-like receptor activation, but decreased that produced by co-activation of D1-like and D2-like receptors in the NAcc core. Taken together, these results suggest that under lidocaine-free conditions the DH may exert a tonic inhibitory modulation on hyperlocomotion mediated by D1-like and D2-like postsynaptic receptors in the NAcc core, while the VH may exert a tonic inhibitory on hyperlocomotion mediated by D1-like receptors and a tonic facilitatory control on hyperlocomotion mediated by D2-like postsynaptic receptors.