Spontaneous multiquantal release at synapses in guinea‐pig hypogastric ganglia: evidence that release can occur in bursts.

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Abstract
A study was made of some properties of the spontaneous synaptic potentials recorded in cells of the hypogastric ganglia of guinea pigs. The distribution of the amplitudes of the spontaneous synaptic potnetials arising from a single preganglionic fiber was multimodal, with peaks at roughtly integral multiples of a unit peak. The amplitudes of the larger spontaneous potentials were consistent with them being the result of synchronous or near-synchronous release of 2 or more unit-sized quanta (multiquantal release). The proportion of multiquantal potentials observed was dependent on the extracellular Ca2+ concentration. When the stochastic properties of the spontaneous potentials were examined, the spontaneous release process was not random and independent but appeared to be clustered. Indeed, the probability of occurrence of a unit spontaneous synaptic potential was greatly enhanced during the 40-60 ms immediately following any given spontaneous synaptic potential. When unit spontaneous potentials were excluded from the analysis, the multiquantal potentials were still clustered although the clustering wwas less marked than that seen in the over-all process. The multiquantal spontaneous potentials apparently arose from the release of unit quanta in short high frequency bursts and a mathematical model incorporating such a mechanism could describe the spontaneous quantal release process.