Presynaptic acetylcholine receptors at the excitatory amino acid synapse in locust muscle

Acetylcholine (greater than or equal to 10(-5) M) applied in the bathing medium to the excitatory nerve-muscle junction of the locust caused a dose-dependent increase in the frequency of spontaneous miniature potentials and in the mean quantal content of evoked potentials. The statistical characteristics of the spontaneous release process were also modified, high frequency bursts of spontaneous potentials and "giant' miniature potentials occurring in the presence of acetylcholine. The response, which was dependent on extracellular calcium concentration, consisted of two distinct phases; these could be induced or abolished selectively by nicotinic and muscarinic drugs, respectively. The results suggest the presence, in low density, of two types of cholinergic receptors on the excitatory motor nerve terminals of the locust. The acetylcholine-induced channels may admit calcium ions. The possible role of these presynaptic receptors is discussed.