抄録
It has been hypothesized that hippocampal mossy fiber terminals of young rodents release GABA in addition to glutamate. Using whole cell-clamp recordings in mouse slice preparations, I re-examined this possibility with paying attentions about the conditions to evoke monosynaptic GABAergic responses by stimulation of mossy fibers. Strong stimulus to the stratum granulosum of dentate gyrus or stimulus to the stratum lucidum of CA3 region elicited IPSCs in CA3 neurons in the presence of glutamate receptor antagonists 10 μM CNQX and 25 μM D-AP5, and these putative "monosynaptic IPSCs" were abolished by addition of GABAA receptor antagonist 100 μM picrotoxin. In contrast, weak stimulus to the stratum granulosum never elicited IPSCs in the presence of CNQX and D-AP5. The responses to weak and strong stimuli also displayed differential sensitivity to group II mGluR agonist DCG-IV; application of 1 μM DCG-IV almost abolished the responses to weak stimulus and left substantial responses to strong stimulus which were inhibited by further application of picrotoxin. These results suggested that strong stimulus to stratum granulosum causes monosynaptic IPSCs by stimulating inhibitory interneurons in addition to mossy fibers, and mossy fiber terminals themselves may not release GABA. [J Physiol Sci. 2006;56 Suppl:S85]
