Fine-Tuning of Spike Timing

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Science  18 Jul 2008:
Vol. 321, Issue 5887, pp. 318
DOI: 10.1126/science.321.5887.318c

Neurons in layer III of the entorhinal cortex send projections along the perforant pathway that reaches area CA1 of the hippocampus. In addition to well-documented excitatory connections, there is also an important feedforward inhibitory circuit; monosynaptically activated interneurons form inhibitory synapses on CA1 pyramidal cells and thus control the timing of spiking of their target neurons. Feedforward inhibition limits the temporal summation of excitatory potentials and generates a narrow temporal window of excitability during which postsynaptic targets can fire action potentials. One important component of this feedforward inhibitory circuit is the neurogliaform cells, which frequently target the distal dendrites of excitatory neurons. Neurogliaform cells are known to be interconnected extensively through gap junctions, which has led to the hypothesis that feedforward inhibition of CA1 pyramidal cells might be highly synchronized. Price et al. found that stimulation of neurogliaform cells evoked GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) with a slow decay in pyramidal cells. The IPSCs also had a small but robust GABAB receptor component. Furthermore, these synapses were also subject to presynaptic GABAB receptor-mediated control. It thus makes physiological sense that these inhibitory neurogliaform-to-pyramidal cell synapses are finely tuned to control the integration time for one of the major excitatory pathways into the hippocampus. — PRS

J. Neurosci. 28, 6974 (2008).

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