Abstract
Carbachol was injected into a presynaptic cholinergic neuron in the buccal ganglion of Aplysia and the quantal aspects of the Cl- -dependent postsynaptic response to a prolonged stimulation were analyzed by a statistical fluctuation method. The calculated amplitude of the miniature postsynaptic current was increased with respect to control. Statistical fluctuation analysis was also used to analyze the postsynaptic response obtained during ionophoretic application of acetylcholine and carbachol. The calculated unitary channel current was found to be greater for carbachol than for acetylcholine. This increase could explain the larger miniature postsynaptic current seen after intracellular injection of carbachol into the presynaptic neuron if carbachol was released at the synapse as a false transmitter. This conclusion was supported by the observation that it was possible to restore transmission at a synapse previously blocked by presynaptic intracellular injection of acetylcholinesterase with a presynaptic injection of carbachol.