Blockade of non-opioid analgesia in intruder mice by selective neuronal and non-neuronal benzodiazepine recognition site ligands.

Abstract

In male mice, the biologically significant experience of social defeat is associated with an acute non-opioid form of analgesia. Recent studies have shown that this reaction is sensitive to certain benzodiazepine receptor ligands but is unaffected by others. The present experiments were designed to assess the possibility that activity at "non-neuronal" benzodiazepine binding sites might account for this unusual pharmacological profile. Our results show that defeat analgesia was blocked by clonazepam (0.06-3 mg/kg), Ro05-4864 (2.5-20 mg/kg), Ro05-5115 (20 mg/kg), PK11195 (5-20 mg/kg) and PK14067 (10-20 mg/kg). Furthermore, when given in combination, subthreshold doses of PK11195 (2.5 mg/kg) and clonazepam (0.03 mg/kg) totally prevented defeat analgesia. All of these effects were observed in the absence of intrinsic activity on basal nociception. Together with earlier findings, current data imply that inhibition of defeat analgesia by ligands for neuronal and/or non-neuronal benzodiazepine recognition sites is most probably unrelated to their activity at these sites. Alternative explanations for the overall patterns of results are considered.