Region specific increase of dopamine receptor D1/D2 mRNA expression in thebrain of mu-opioid receptor knockout mice

Previous pharmacological studies have indicated the possible existence of f unctional interactions between opioidergic and dopaminergic neurons in the CNS. In this study, the expression of mRNAs encoding dopamine receptor D1/D 2 was examined to investigate whether there is a change in the dopamine pat hway of mice lacking the mu -opioid receptor by in situ hybridization techn ique. In the mu -opioid receptor knockout mice, the expression of dopamine receptor D1 mRNA was increased in the olfactory tubercle, nucleus accumbens , caudate putamen, and the layer VI of the neocortex compared with that of wild-type mice. The expression of dopamine receptor D2 mRNA was also increa sed in the olfactory tubercle, caudate putamen, and the nucleus accumbens o f mu -opioid receptor knockout mice. These results indicate that there are compensational changes in the dopaminergic systems of mu -opioid receptor k nockout mice. (C) 2001 Elsevier Science B.V. All rights reserved.