Effects of buprenorphine on motility in chronically morphine treated rats

The effects of buprenorphine (0.01-0.1 mg/kg) on the activity of nondependent and morphine dependent rats (a 20 mg/kg dose for 28 days) were determined. In naive animals buprenorphine exhibited both depressive and stimulatory actions upon the motility of rats, as repeatedly described for morphine. When buprenorphine was administered to rats chronically treated with morphine, the depressive effect disappeared (cross-tolerance to the inhibitory action); on the contrary the excitatory effect was enhanced (cross-sensitization). The results are discussed in terms of cross-sensitization to the excitatory effects in morphine dependent animals as predictor of morphine-like addictive properties in humans.