Population differences in benzodiazepine sensitive male scent-induced analgesia in the deer mouse, Peromyscus maniculatus.

We compared opioid and nonopioid involvement in the mediation of scent-induced analgesia in two populations of deer mice, Peromyscus maniculatus; P. m. artemisiae from a mainland region and P. m. angustus from a small marine island. Exposure to bedding taken from the soiled home cage of an isolated (dominant aggressive) male resident elicited a significant increase in the nociceptive responses of male deer mice from mixed sex pairs, with the island population of mice displaying significantly greater analgesic responses than the mainland animals. In the mainland population of mice, the large amplitude analgesia induced by the scent of a conspecific was insensitive to the opiate antagonist, naloxone, but could be blocked by either the benzodiazepine antagonist, Ro 15-1788, or agonist, diazepam. Exposure to the scent of individuals from the island population elicited a lower amplitude analgesia that was sensitive to both the opiate and benzodiazepine manipulations. In the island population, both the lower amplitude analgesia induced by the scent of a conspecific and the higher amplitude analgesic elicited by the scent of a mainland animal was blocked by naloxone and only partially reduced by the benzodiazepine manipulations. Bedding treated with the peppermint also induced analgesia, with the island mice displaying a markedly greater analgesic response than the mainland animals. In both populations of deer mice the peppermint-induced analgesia was blocked by naloxone and insensitive to the benzodiazepine manipulations. These findings are considered in terms of their possible ecological significance and relations to the differences in agonistic and social behaviors between island and mainland populations of deer mice and other small rodents.