Cholecystokinin receptor binding in morphine analgesia: tolerance, withdrawal and abstinence

The effect of morphine treatment on cholecystokinin (CCK) receptor binding in rat cerebral cortex was investigated. Subcutaneous implantation and removal of Alzet miniosmotic pumps, releasing morphine, permitted us to establish the phases of initial analgesia, tolerance to the analgesic action of morphine, morphine withdrawal and abstinence. CCK receptor binding in rat cerebral cortex never differed from the values obtained from animals implanted with saline-releasing minipumps. The results of the present study suggest that the putative changes in the interaction between opioidergic and CCKergic neurotransmission at different stages of morphine treatment and withdrawal are not caused by changes of CCK receptor binding properties.