RELATIONSHIP BETWEEN DOPAMINE RELEASE IN NUCLEUS-ACCUMBENS AND PLACE PREFERENCE INDUCED BY SUBSTANCE-P INJECTED INTO THE NUCLEUS BASALIS MAGNOCELLULARIS REGION

The activity of the neurotransmitter dopamine in the nucleus accumbens is considered to be an important element in the central processing of reinforcement. Unilateral administration of the neurokinin substance P into the area of the nucleus basalis magnocellularis of rats was fou nd to be reinforcing, as assessed by the conditioned place preference paradigm. Simultaneous in vivo microdialysis showed that administratio n of substance P into the area of the nucleus basalis magnocellularis could increase extracellular concentrations of dopamine in the contral ateral nucleus accumbens. Only those animals in which the administrati on of substance P induced this increase in dopamine levels acquired pl ace preference. Furthermore, the changes in extracellular dopamine lev els after substance P administration had a bimodal time course with an acute increase (to about 160% of baseline) during the first hour afte r injection, with a low (to 120-130%) and enduring increase occurring thereafter. Interestingly, during this second increase there were indi cations for positive correlations with the degree of place preference induced by substance P. Further positive correlations with place prefe rence were found in the levels of the serotonergic metabolite 5-hydrox yindoleacetic acid. In contrast to dopamine, these were observed ipsi- and contralateral to the side of substance P administration. By combi ning the methods of in vivo microdialysis and conditioned place prefer ence it was shown that the reinforcing effect induced by unilateral su bstance P injection in the nucleus basalis magnocellularis is related to dopaminergic (and possibly serotonergic) mechanisms in the nucleus accumbens.