Effects of naloxone and naltrexone on memory consolidation in CD1 mice: involvement of GABAergic mechanisms.

The involvement of GABAergic mechanisms in the effects exerted by the opioid antagonists naloxone and naltrexone on memory consolidation was investigated in CD1 mice tested in a one-trial inhibitory avoidance task. In a first group of experiments posttraining administration of naloxone (2.0 and 4.0 but not 1.0 mg/kg) and naltrexone (0.5 and 1.0 but not 0.25 mg/kg), as well as those of the GABA-antagonists picrotoxin (0.5 and 1.0 but not 0.25 mg/kg) and bicuculline (0.25 and 0.5 but not 0.1 mg/kg) enhanced, whereas those of the GABA-agonist muscimol (1.0 and 2.0 but not 0.5 mg/kg) impaired retention on a 24-hr test. In a second group of experiments, picrotoxin, or bicuculline, administration enhanced, while muscimol treatment attenuated the effects of naloxone and naltrexone on retention. The results suggest that naloxone and naltrexone may influence memory consolidation in CD1 mice by interacting with the GABAergic system.