Some effects of naloxone on behavior in the mouse.

The effect of naloxone on the latency of mice to enter a dark box was determined and the study of Jacob et al. (1974) on the effect of naloxone on hotplate behavior was replicated. Mice took significantly longer to enter a dark box after receiving 10 mg/kg of naloxone than did the saline controls. With the hot-plate technique, at all doses (0.1, 0.3, 1, 3, and 10 mg/kg) except the lowest (0.03 mg/kg), naloxone-treated mice jumped from the hot plate significantly sooner than did the saline controls. No effect of naloxone on paw-lick latency was found. All the data confirm the findings of Jacob et al. (1974). The hotplate results suggest that prolonged exposure to a noxious stimulus may be necessary to activate the endorphin system.