Naloxone reduces social and exploratory activity in the rat.

Naloxone (1,2, and 4 mg/kg) produced a dose-related decrease in exploratory head-dipping in rats placed singly in a holeboard for 10 min, without a concomitant reduction in locomotor activity. Naloxone (2 mg/kg) reduced the time spent in active social interaction by pairs of rats tested in an unfamiliar or in a familiar test arena, and also reduced the amount of motor activity shown by the pairs of rats. The results are consistent with proposed roles for opiate peptides in behavioural responses to novel environments and in mediating social contact.