REPEATED COCAINE ADMINISTRATION UP-REGULATES KAPPA-OPIOID AND MU-OPIOID, BUT NOT DELTA-OPIOID RECEPTORS

THE present study investigated the regulation of opioid receptors foll owing chronic repeated cocaine administration. Male Fischer rats were injected with saline or cocaine, 45 mg kg(-1) day(-1), three times dai ly at 1 h intervals for 14 days. Using quantitative in vitro autoradio graphy, the density of Kappa receptors was significantly higher in the rostral cingulate cortex, rostral caudate putamen, caudal olfactory t ubercle, and ventral tegmental area following cocaine administration. No changes in delta receptor number were detected in any brain region examined. Significant mu receptor upregulation was found in the rostra l cingulate cortex, nucleus accumbens, rostral caudate putamen, and ba solateral amygdala nucleus of the cocaine-treated animals. These resul ts suggest that enhanced dopaminergic activity can regulate mu and Kap pa opioid receptors.