Downregulation of kappa opioid receptor mRNA levels by chronic ethanol andrepetitive cocaine in rat ventral tegmentum and nucleus accumbens

The combination of ethanol and cocaine is commonly abused by human addicts which has serious clinical consequences. Here, the effects of separately an d concurrently administered ethanol and 'binge' cocaine on kappa opioid rec eptor (KOR) mRNA in the ventral tegmental area (VTA) and nucleus accumbens (NAc) of rats were studied. KOR mRNA was down-regulated in both brain regio ns during concurrent as well as separate treatment with these drugs. In the VTA, the most pronounced decrease was obtained following combined treatmen t with ethanol and 'binge' cocaine. In the NAc, the strongest decrease was observed in the 'binge' cocaine group. This profound decrease of KOR mRNA i n regions important for brain reward suggests a potential role of the KOR s ystem in the abuse of cocaine and ethanol. (C) 1999 Elsevier Science Irelan d Ltd. All rights reserved.