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Maximizing Your Minis

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Science  11 Jul 2003:
Vol. 301, Issue 5630, pp. 145
DOI: 10.1126/science.301.5630.145b

Resting neurons release the contents of individual synaptic vesicles spontaneously and at random intervals. The ensuing miniature postsynaptic potentials (colloquially referred to as minis), which correspond to individual quanta of the postsynaptic response, are too small to initiate firing of an action potential in the postsynaptic cell.

Sharma and Vijayaraghavan recorded miniature excitatory postsynaptic currents (mEPSCs) from voltage-clamped pyramidal cells before, during, and after local application of nicotine. Nicotine increased the fraction of large mEPSCs (consistent with the concerted release of multiple quanta) and stimulated high-frequency bursts of mEPSCs. This increase in mEPSC amplitude and frequency depended on release of calcium from intracellular stores that was secondary to calcium influx through presynaptic nicotinic acetylcholine receptors (nAChRs). When the voltage clamp was removed, nicotine application initiated bursts of action potentials in the postsynaptic cells. Thus, calcium influx through presynaptic nAChRs supports a mechanism whereby impulses can be generated in the postsynaptic cell in the absence of firing in the presynaptic neuron. — EA

Neuron 38, 929 (2003).

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