Cold-water swim analgesia following pharmacological manipulation of GABA

Since increased GABA binding is observed in mice following cold-water swims (CWS) that parallels the analgesic time course, this suggests that GABA availability may modulate CWS analgesia. To test this, separate groups of rats received either the GABA agonist muscimol (75, 150, 300 μg/kg) or the GABA antagonist picrotoxin (0.25, 0.5, 1.0, 2.0 mg/kg) paired 30 min later with CWS. Neither muscimol nor the three lower picrotoxin doses significantly altered CWS analgesia or jump thresholds per se as compared to saline-treated rats. While the 2-mg/kg-picrotoxin dose potentiated CWS analgesia, it also produced convulsive activity which in itself is analgesic. These data suggest that the observed changes in GABA following CWS may not constitute necessary and sufficient conditions to explain CWS analgesia.