Proenkephalin mRNA levels in rat striatum are increased and decreased, respectively, by selective D 2 and D 1 dopamine receptor antagonists

Abstract

Rats were treated for 3 days with the selective D 1 dopamine receptor antagonist SCH23390 (250 μg/kg i.p., 3 × daily), the selective D 2 dopamine receptor antagonist YM-09151-M (500 μg/kg i.p., 2 × daily), or saline. The levels of striatal proenkephalin mRNA were then assayed by in-situ hybridisation histochemistry, using a synthetic oligonucleotide probe. Following YM-09151-M treatment, proenkephalin mRNA levels were dramatically raised in the striatum, compared to animals receiving vehicle injections. In contrast, rats treated with SCH23390 showed decreased striatal levels of proenkephalin mRNA. The results demonstrate that selective D 2 receptor blockade leads to enhanced proenkephalin gene expression in rat striatum, while selective D 1 receptor antagonism has the opposite effect.