Reduction of quantum contents of synaptic potentials after postsynaptic axotomy


THE loss of synaptic transmission in the chick ciliary ganglion that is observed after the postganglionic section of the ciliary nerves is accompanied by both a decrease in acetylcholine (ACh) sensitivity of the axotomised cells and a change in the transmitter release characteristics of the presynaptic terminals1,2. Evidence for the presynaptic change included a decrease in the mean quantum content m of the excitatory postsynaptic potentials (e.p.s.p.s) and a greater susceptibility to fatigue during repetitive stimulation. The reduction in quantum content after axotomy was inferred from an increase in the coefficient of variation of the e.p.s.p. amplitude distribution in the depressed state. In the experiments reported here it was possible to measure miniature synaptic potentials (m.e.p.p.s) in axotomised preparations so that more accurate estimates of the mean quantum content of e.p.s.p.s could be made.

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