Effects of buprenorphine on motility in morphine post-dependent rats

The effects of buprenorphine (0.0125-0.2 mg kg(-1)) on the locomotor activi ty of rats were determined 1-2 months after ceasing a chronic treatment wit h morphine (20 mg kg(-1) for 28 days). In control animals buprenorphine exh ibited both depressive and stimulatory actions, as repeatedly described for morphine. In post-dependent animals buprenorphine showed a depressive effe ct similar to that observed in naive ones. On the contrary, a persistent se nsitization to the excitatory effect was observed; the degree of cross-sens itization was similar to that of morphine itself (20 mg kg(-1)). The result s are discussed in terms of persistent changes in the locomotor response to opioids, possibly correlated to both drug craving and relapse. (C) 1999 Ac ademic Press.