The ambulation-increasing effect of buprenorphine in mice: comparison with the effect of morphine.

Effects of buprenorphine on ambulatory activity in mice were studied, and the result s were compared with those of morphine. Buprenorphine, at 0.01-3 mg/kg s.c., increased the mouse's ambulatory activity in a dose-dependent manner with Straub tail-reaction. The effect reached to the maximum level at 10-20 min and persisted for 2-3 hr after the administration. The overall activity counts for 3 hr were almost identical when 1 mg/kg of buprenorphine and 10 mg/kg of morphine were administered. Naloxone, 0.01-1 mg/kg s.c., reduced the ambulation-increasing effect of both buprenorphine and morphine, but the reducing-action of naloxone was stronger for morphine than for buprenorphine. However, the combined administration of buprenorphine and morphine demonstrated no significant modification in individual drug effects. On the other hand, the ambulation-increasing effect of buprenorphine and morphine were enhanced by combined s.c. administration of methamphetamine (1 mg/kg), cocaine (10 mg/kg), scopolamine (0.5 mg/kg), or caffeine (10 mg/kg). Such enhancing effects of methamphetamine and cocaine were much greater for buprenorphine than for morphine. In contrast, haloperidol (0.05 mg/kg), pilocarpine (2 mg/kg), and N6-(L-2-phenylisopropyl)-adenosine (0.1 mg/kg) reduced the ambulation-increasing effect of buprenorphine or morphine. The modification by pilocarpine was more marked for morphine than for buprenorphine. The present results indicate that buprenorphine and morphine possess differential effectiveness on dopaminergic and/or cholinergic systems.