The role of GABAergic neuronal system in learning and memory was investigated using the step-down typed passive avoidance and rapidly learned conditioned suppression tasks in mice. GABA antagonists, picrotoxin and bicuculline, or a GABA synthesis inhibitor, 3-mercaptopropionic acid (3-MP), were administered just after the training test. All of these drugs caused amnesia: they shortened the step-down latency (SDL) and attenuated the conditioned suppression of motility in the retention test conducted 24 h after the administration. Furthermore, we investigated the effect of GABA receptor agonists, muscimol and baclofen, or a GABA transaminase inhibitor, aminooxyacetic acid (AOAA), on these amnesia models. GABA agonists showed an antiamnesic action as follows: in the passive avoidance task, 1) picrotoxin-induced amnesia was antagonized by muscimol, baclofen and AOAA. 2) Bicuculline-induced amnesia was antagonized by muscimol and AOAA but not by baclofen. 3) 3-MP-induced amnesia was antagonized only by muscimol. 4) In the rapidly learned conditioned suppression task, picrotoxin-, bicuculline- and 3-MP-induced amnesia were antagonized by muscimol, baclofen and AOAA. These results suggest that the GABAergic neuronal system plays an important role in the memory retention of passive avoidance and rapidly learned conditioned suppression tasks.
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