SEX-DIFFERENCES IN OPIOID AND N-METHYL-D-ASPARTATE MEDIATED NONOPIOIDBITING FLY EXPOSURE INDUCED ANALGESIA IN DEER MICE

There is evidence for sex differences in responses to noxious stimuli and in the expression and mediation of analgesia. In particular, resul ts of investigations with swim stress and the more ethologically appro priate stress of predator odor exposure have suggested sex differences in N-methyl-D-aspartate (NMDA) receptor system involvement in the med iation of analgesia. Whether or not this sex difference generalizes to other environmental stressors is, however, not clear. Biting flies ar e a natural aversive stimuli commonly encountered by wild and domestic animals and humans. The present study examined the opioid and non-opi oid mediated nociceptive (50 degrees C hot plate) responses of reprodu ctive male and female deer mice, Peromyscus maniculatus, exposed to bi ting fly attack. A 30 min exposure to biting flies (stable flies, Stom oxys calcitrans (L.)) elicited a naloxone sensitive, opioid-mediated a nalgesia that was of a greater magnitude in males than in female deer mice. In contrast, a 5 min exposure to biting flies elicited a 'on-opi oid' analgesia that was of similar magnitude in both sexes and insensi tive to both naloxone and the specific kappa opiate antagonist, nor-bi naltorphimine. In male mice this non-opioid analgesia was antagonised by the competitive NMDA antagonist, NPC 1262, while in reproductive fe males the biting fly-induced analgesia was insensitive to NPC 12626. T hese results show that there are sex differences in NMDA involvement i n the mediation of the non-opioid analgesia arising from brief exposur e to the stress of biting fly attack. These data from a common, natura l environmental challenge support the presence of basic sex difference in NMDA involvement in the mediation of stress-induced analgesia. (C) 1998 International Association for the Study of Pain. Published by El sevier Science B.V.