Injections of dopaminergic, cholinergic, serotoninergic and GABAergic drugs into the nucleus accumbens: effects on locomotor activity in the rat

Locomotor activity was elicited by injecting dopamine into the nucleus accumbens of the chronically cannulated rat. Dopamine was also injected together with cholinergic, serotoninergic and GABAergic agonists and antagonists to investigate the possible contribution to locomotor activity of these putative neurotransmitters. Carbachol elicited a transient enhancement of dopamine-stimulated activity. Atropine attenuated carbachol-stimulated enhancement but did not attenuate dopamine-stimulated activity. Serotonin attenuated dopamine-stimulated activity. The peripheral serotonin antagonist, methysergide, also attenuated locomotion. The administration of GABA elicited a bimodal response in locomotion, the lower dose eliciting a small increase in locomotion and the larger dose eliciting a reduction. The GABA antagonist, picrotoxin, elicited only increases in locomotion at all doses. These results suggest that there is not a cholinergic interneuron on the dopamine-stimulated pathway subserving locomotion but that both cholinergic and serotoninergic projections may modulate locomotor activity. Further they suggest that such modulation must be at least one inhibitory interneuron away from the dopamine synapse on the locomotor pathway. In addition, these results suggest a direct influence of GABAergic interneurons on the pathway subserving locomotor activity within the nucleus accumbens.