Subcellular Imbalances in Synaptic Activity

Naoya Takahashi, Chiaki Kobayashi, Tomoe Ishikawa, Yuji Ikegaya
Cell Reports. 2016-02-01; 14(6): 1348-1354
DOI: 10.1016/j.celrep.2016.01.024

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The dynamic interactions between synaptic excitation and inhibition (E/I) shape membrane potential fluctuations and determine patterns of neuronal outputs; however, the spatiotemporal organization of these interactions within a single cell is poorly understood. Here, we investigated the relationship between local synaptic excitation and global inhibition in hippocampal pyramidal neurons using functional dendrite imaging in combination with whole-cell recordings of inhibitory postsynaptic currents. We found that the sums of spine inputs over dendritic trees were counterbalanced by a proportional amount of somatic inhibitory inputs. This online E/I correlation was maintained in dendritic segments that were longer than 50 μm. However, at the single spine level, only 22% of the active spines were activated with inhibitory inputs. This inhibition-coupled activity occurred mainly in the spines with large heads. These results shed light on a microscopic E/I-balancing mechanism that operates at selected synapses and that may increase the accuracy of neural information.

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