LIGHT-MICROSCOPIC IMMUNOCYTOCHEMICAL EVIDENCE OF CONVERGING SEROTONINAND DOPAMINE TERMINALS IN VENTROLATERAL NUCLEUS-ACCUMBENS

The mesencephalic tegmentum contains monoaminergic neurons that projec t to the nucleus accumbens (NAcc), These monoaminergic neurons consist of the serotonergic (5-HT) neurons of the dorsal and median raphe and the dopaminergic (DA) neurons of the ventral tegmental area (VTA). Re cent neurochemical reports describe cocaine-induced alterations in dop amine and serotonin release in NAcc that has coincidental occurrence b oth spatially and temporally, as shown by in vivo voltammetry, There i s a functional role for 5-HT-DA interactions within the NAcc in the un derlying mechanism of action of cocaine as well as for 5-HT in A10 DA neurons in the basal or endogenous state whether or not cocaine-releva nt reward circuits are involved. Our objective was to study the neuroa natomic localization of tyrosine hydroxylase-containing (TH) and 5-HT- containing axons in the ventrolateral region of the rat NAcc, where co detection of monoamines had been assessed. The significance of this vl NAcc is its reciprocal connectivity with VTA, which contains the somat odendritic portions of the mesoaccumbens DA neurons. The results showe d that, in the vlNAcc, the core contained a dense terminal field of TH axons that had an extensive overlap with 5-HT axons in the periphery within the core, Because the in vivo electrochemical codetection of DA and 5-HT assessed in the ventral-most aspect of this overlap zone can be correlated with terminal release, a functional interaction of 5-HT and DA at postsynaptic sites in vlNAcc is possible.