INFUSION OF NICOTINE IN THE VENTRAL TEGMENTAL AREA OR THE NUCLEUS-ACCUMBENS OF THE RAT DIFFERENTIALLY AFFECTS ACCUMBAL DOPAMINE RELEASE

The present study examined the effects of acute, continuous infusion o f nicotine in either the ventral tegmental area or the nucleus accumbe ns on extracellular concentrations of dopamine in the nucleus accumben s by applying in vivo microdialysis in freely moving rats. Nicotine (1 000 mu M) infusion for 80 min. in the ventral tegmental area produced a long-lasting increase in accumbal dopamine, whereas similar nicotine infusion in the nucleus accumbens increased dopamine levels only with in the first 20 min. of administration. This effect was blocked by sys temic pretreatment with the nicotinic receptor antagonist mecamylamine (1 mg/kg, subcutaneously). In contrast to the effects of nicotine, N- methyl-D-aspartate infusion in the ventral tegmental area as well as i n the nucleus accumbens produced a long-lasting increase in accumbal d opamine levels. The more procounced effect of infusion of nicotine in the ventral tegmental area as compared to the nucleus accumbens on acc umbal dopamine release may be due to a lower rate or even lack of tole rance to nicotine's stimulatory action in the ventral tegmental area. These results support the notion that nicotinic receptors in the ventr al tegmental area may be of greater importance than those located in t he nucleus accumbens for mediating some of the stimulatory effects of nicotine on the reward-related mesoaccumbens dopamine system.