Pentobarbital-induced hyperactivity in mice: negligible role of opioid mechanisms.

Subhypnotic doses (10 and 20 mg/kg) of pentobarbital significantly elevated locomotor activity measured for 30 min in CD-1 mice. The hyperactivity was also observed in mice recovering from pentobarbital-induced (50 mg/kg) sleep (measurements starting 15 min after recovery of righting reflex). Naloxone in doses up to 4 mg/kg did not affect significantly the pentobarbital-induced hyperactivity in any experiment; a dose of 8 mg/kg only partially attenuated the hyperactivity induced by a dose of 20 mg/kg of pentobarbital, but did not affect significantly either the stimulatory effect of a low subhypnotic dose (10 mg/kg) or the posthypnotic hyperactivity. This suggests a negligible involvement of opioid mechanisms in the hyperactivity induced by pentobarbital.