Inhibitory action of ibotenic acid on the crayfish neuromuscular junction

The effect of ibotenic acid on the crayfish neuromuscular junction was investigated. Ibotenate reduced dose-dependently the amplitude of the excitatory junctional potentials (EJPs) elicited by repetitive stimulation of the excitatory axons. Ibotenate did not affect facilitation of successive EJPs. The decrease in the EJP amplitude caused by ibotenate was almost completely blocked by picrotoxin. A quantum analysis of extracellularly recorded EJPs demonstrated that the mean quantum content was reduced by ibotenate without remarkable change in unit size. Ibotenate increased the conductance change induced by ibotenate was observed even if the glutamate receptor was completely desensitized by the prolonged application of glutamate. From an analysis of the dose-response curve of GABA with or without ibotenate, it is suggested that ibotenate acts on the GABA receptor in the crayfish neuromuscular junction.