Morphine analgesia in grouped and isolated rats.

The effects of long-term isolation of young adult male rats on the analgesic effects of morphine were investigated. Isolated rats developed altered patterns of behavior, including muricidal behavior in some animals. Analgesic activity of morphine was assessed with both the tail compression and the hot plate methods. The results indicate that chronically isolated rats, whether developing muricidal behavior or not, show no alteration in either pain thresholds or in their response to morphine-induced analgesia.