Effects of repeated administration of pentazocine on ambulatory activity in mice: comparison with the effects of morphine and methamphetamine.

Effects of single and repeated administration of pentazocine (5 times at intervals of 3-4 days) were compared with those of morphine and methamphetamine by means of ambulatory activity in mice. The interactions among these 3 drugs were also investigated. Pentazocine (25 mg/kg, s.c.), morphine (10 and 20 mg/kg, s.c.) and methamphetamine (2 mg/kg, s.c.) significantly increased the activity, and the effect progressively enhanced (defined here as development of reverse tolerance) during the repeated administration schedule. The induction of reverse tolerance to pentazocine was less dependent on the environmental conditions, and it was abolished within 2 months. A cross reverse tolerance was demonstrated from methamphetamine to pentazocine and to morphine, and from morphine to pentazocine. However, no significant cross reverse tolerance was induced from pentazocine to morphine and to methamphetamine, and from morphine to methamphetamine. The present results suggest that pentazocine possesses an ambulation-increasing effect, although the characteristics are different from that of either morphine or methamphetamine.