Large synapses with many active zones are expected to produce large EPSCs and reliably produce action potentials in postsynaptic cells. Therefore, Mc Laughlin et al. Were surprised at a recent report that at one of the largest synapses in the mammalian brain—the auditory calyx of Held—presynaptic potentials evoked by auditory stimuli did not reliably produce postsynaptic spikes. The presynaptic calyx has hundreds of active zones, and the synapse is so large that presynaptic and postsynaptic responses can be measured with a single extracellular electrode. McLaughlin et al. Suspected that prepotentials not associated with a postsynaptic response were actually spikes from nearby axons that did not synapse on the postsynaptic cell. They showed that this was the case by measuring interspike intervals at cat calices. They found that prepotentials associated with a postsynaptic response sometimes occurred within the refractory period of a prepotential that did not produce a response, indicating that they were produced by different neurons.
Security at the Calyx of Held
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