Affiliative behavior in voles: effects of morphine, naloxone, and cross-fostering.

Species differences in affiliative behavior were examined in prairie and montane voles. Unfamiliar male-female pairs were placed in a test-cage for 2 hr and side-by-side huddling was recorded during the third hour. Prairie vole pairs spent a mean of 31.2 minutes in contact whereas montane voles were in contact only 1.3 minutes. In order to examine the effects of experience on affiliative differences, pups of each species were cross-fostered. Fostered prairie vole parents did not survive longer than 7 days, whereas fostered montane voles were successfully weaned; cross-fostering had no effect on their huddling behavior when tested as adults. The effects of morphine (5 and 10 mg/kg) and naloxone (5 and 10 mg/kg) on side-by-side contact were evaluated in both species. Morphine (10 mg/kg) reduced huddling duration and activity levels in prairie voles. There were no other drug effects in either species.