Stimulation of avoidance behavior by buprenorphine in rats.

The effects of buprenorphine and morphine on rates and temporal patterns of avoidance responding were studied in rats. Responding was maintained under a schedule of electric shock avoidance with 30-s response-shock and shock-shock intervals during 4-h sessions. Morphine (0.3-3.0 mg/kg) increased response rates, but a dose of 10 mg/kg disrupted bar pressing. Buprenorphine increased response rates (0.003-0.03 mg/kg) and produced maximal effects that plateaued over a greater than 300-fold dose range (0.03-10 mg/kg). Disruption of bar pressing was not observed with buprenorphine. Both drugs also produced dose-related shifts in the interresponse time distribution toward increased conditional probabilities of shorter interresponse times. Morphine (10 mg/kg) and buprenorphine (0.3-10 mg/kg) virtually abolished the temporal patterning of responding in that the conditional probability of a response occurring in any 'class interval' from 0.5 to 25.5 s was close to 0.5. These results demonstrate that lower doses of buprenorphine and morphine produce similar effects on avoidance behavior in rats. At higher doses, the effects of morphine differ from those of buprenorphine in that morphine disrupts bar pressing behavior, whereas the rate-increasing effects of buprenorphine plateau over a broad dose range.