演題番号 : P1-a25
田中 基樹 / Motoki Tanaka:1 曽我部 正博 / Masahiro Sokabe:1
1:名大院・医・細胞生物物理学 / Dept Physiol, Nagoya Univ Grad Sch of Med, Nagoya, Japan
Many studies have demonstrated that neurosteroids promote learning and memory through modulations of the synaptic transmission in the hippocampus. However, as most of the studies were done with exogenously applied neurosteroids, how much degree endogenous neurosteroids contribute to the phenomena is poorly understood. To investigate the contribution of endogenous neurosteorids to the function of synapses in the central nervous system, we measured electrophysiologically the effect of aminoglutethimide (AG), an inhibitor of steroid biosynthesis, on the neuronal activities in the dentate gyrus of rat hippocampal slices. AG markedly decreased the basal synaptic transmission and the induction of activity dependent long-term potentiation. However, paired-pulse ratio was not affected by AG, indicating that the presynaptic transmitter release keeps its function without endogenous neurosteroids. By contrast, AG significantly reduced NMDA receptor-mediated EPSC, but not GABA receptor-mediated IPSC in granule cells. These results suggest that endogenous neurosteroids operate as potent positive modulators on the excitatory synaptic transmission by potentiating the function of postsynaptic neurons in the rat dentate gyrus under physiological condition.