REGIONAL AND CELLULAR-DISTRIBUTION OF SEROTONIN 5-HYDROXYTRYPTAMINE(2A) RECEPTOR MESSENGER-RNA IN THE NUCLEUS-ACCUMBENS, OLFACTORY TUBERCLE, AND CAUDATE-PUTAMEN OF THE RAT

This paper describes the regional and cellular distribution of seroton in 5-hydroxytryptamine(2a) (5-HT2a) receptor mRNA in (sub)regions of t he rat striatum by using in situ hybridization. Our results indicate t hat 5-HT2a mRNA is distributed heterogeneously in this brain region. R egional densitometry of autoradiograms from striatal sections hybridiz ed with isotope-labeled cRNA probes showed that mRNA levels were highe st in the olfactory tubercle, lower in the nucleus accumbens, and lowe st in the caudate-putamen. In the nucleus accumbens, the average mRNA levels in the shell were higher than those in the core. These data sug gest a particular relevance for the 5-HT2a receptor for olfactory tube rcle-and shell-related functions. Therefore, in the nucleus accumbens and the olfactory tubercle, the cellular localization of 5-HT2a mRNA w as investigated by determining the colocalization of 5-HT2a mRNA with enkephalin mRNA or dynorphin mRNA. 5-HT2a mRNA was found in enkephalin ergic as well as dynorphinergic neurons. Thus, there does not seem to be a differential distribution of this receptor in the output routes o f the ventral striatum. In all of the subregions investigated (core, m edial shell, and lateral shell of the nucleus accumbens and the olfact ory tubercle), only subpopulations of the total enkephalinergic and dy norphinergic populations were found to contain 5-HT2a mRNA. For enkeph alin, the percentage colocalization was higher in the lateral shell (6 1%) compared with the other subregions (38-45%). For dynorphin, the pe rcentage colocalization was higher in the olfactory tubercle (68%) tha n in the other subregions (34-43%). The differences in (sub)regional m RNA levels and in colocalization with opioids suggest a considerable r egional differentiation in the effects of 5-HT2a mediated neurotransmi ssion in the striatum. (C) 1997 Wiley-Liss, Inc.