Input integration around the dendritic branches in hippocampal dentate granule cells
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Recent studies have shown that the dendrites of several neurons are not simple translators but are crucial facilitators of excitatory postsynaptic potential (EPSP) propagation and summation of synaptic inputs to compensate for inherent voltage attenuation. Granule cells (GCs)are located at the gateway for valuable information arriving at the hippocampus from the entorhinal cortex. However, the underlying mechanisms of information integration along the dendrites of GCs in the hippocampus are still unclear. In this study, we investigated the input integration around dendritic branches of GCs in the rat hippocampus. We applied differential spatiotemporal stimulations to the dendrites using a high-speed glutamate-uncaging laser. Our results showed that when two sites close to and equidistant from a branching point were simultaneously stimulated, a nonlinear summation of EPSPs was observed at the soma. In addition, nonlinear summation (facilitation) depended on the stimulus location and was significantly blocked by the application of a voltage-dependent Ca2+ channel antagonist. These findings suggest that the nonlinear summation of EPSPs around the dendritic branches of hippocampal GCs is a result of voltage-dependent Ca2+ channel activation and may play a crucial role in the integration of input information.
KeywordsHippocampus Dendrite Excitatory postsynaptic potentials summation Uncaging Supralinear amplification
We thank Dr. Fujii of Yamagata Univ., Dr. Sakai of Tamagawa Univ., and Drs. Hong and Nishiyama of New York Univ. for valuable discussions and advice on the physiological experiments. This work was supported by the Global COE Program at Tamagawa University and Strategic Research Foundation for Private Universities and by NEXT KAKENHI Grants (Numbers 19200014 and 20500278).
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