PROLONGED ETHANOL INTAKE INCREASES D-2 DOPAMINE-RECEPTOR EXPRESSION IN THE RAT-BRAIN

Dopamine via interaction with its receptor is known to be involved in the behavioral and endocrine actions in the mammalian brain. Behaviora l effects produced by ethanol appear to be due to its actions on the d opaminergic system. In the present study using in situ hybridization h istochemistry and RNase protection assay, the effect of prolonged etha nol intake on the expression of D-2 dopamine receptor mRNA was examine d in the rat brain. Specific D-1 and D-2 receptor mRNA signals were de tected in the caudate putamen, nucleus accumbens, olfactory tubercle, hippocampus, dentate gyrus, and amygdaloid complex of the rat brain. W ithin the hypothalamus, the level of receptor mRNA was low in most nuc lei with a somewhat higher level in the arcuate nucleus. Only the supu rachiasmatic nucleus showed moderate to dense dopamine receptor mRNAs. Prefrontal cortex showed hybridization signals but their intensity wa s very low. A considerable amount of D-2 mRNA was localized in the sub stantia nigra but D-1 mRNA was not. Ethanol (10%) intake for 5 weeks i ncreased both the density of hybridization signal and number of cells expressing D-2 dopamine receptor mRNA in the caudate putamen, and nucl eus accumbens, but not in the olfactory tubercle. RNase protection ass ay revealed about a 1.5-fold increase in the D-2 dopamine receptor mRN A level in the corpus striatum. These results provide a basis for the involvement of dopamine D-2 receptor expression in alcoholism.