Presynaptic transmitter content controls the number of quanta released at a neuro-neuronal cholinergic synapse.

In the buccal ganglion of Aplysia the overloading of the cholinergic presynaptic neuron by exogenous acetylcholine (AcCho) led to an enhancement of the postsynaptic response. The deprivation of choline in the presynaptic neuron by extra- and/or intracellularly applied choline oxidase to prevent AcCho synthesis resulted in a decrease of the postsynaptic response. In both cases, the size of the calculated miniature postsynaptic current (i.e., the size of the quantum) remained unchanged. It was concluded that, for a given stimulation, the number of quanta released (i.e., the quantal content) is directly related to the quantity of AcCho available for release in the presynaptic neuron.