NEUROPHARMACOLOGICAL ASPECTS OF ADAPTIVE PAIN INHIBITION IN MURINE VICTIMS OF AGGRESSION

This review outlines recent research on a subset of physiological resp onses in murine ''victims'' or aggression. In a typical resident-intru der paradigm, the detailed study of intruders has revealed that exposu re to conspecific attack (and related stimuli) is associated with two forms of analgesia which appear to be integral components of the murin e defensive repertoire. In response to intense/enduring attack, intrud er mice display a profound, long-lasting and opioid-mediated analgesia . This reaction is highly correlated with defensive immobility and may function to reduce involuntary cues to further attack. In contrast, t he inhibition of pain reactivity in mice tested immediately upon the d isplay of defeat is less intense, shorter-tasting, non-opioid in natur e and may function to facilitate active defenses such as escape. As th is form of pain inhibition is also evident in intruders exposed to the scent of an aggressive male conspecific, a possible anticipatory defe nsive function linked to mechanisms of anxiety has been proposed. This hypothesis is supported by 1) the prevention of defeat analgesia by a range of antianxiety drugs (benzodiazepines, 5-hydroxytryptamine(1A) [5-HT1A] receptor agonists, and 5-HT3 receptor antagonists) and 2) the effects of social defeat on behavior in the elevated plus-maze model of anxiety. These findings are discussed in relation to coping mechani sms in murine ''victims'' of aggression. (C) 1995 Wiley-Liss, Inc.