Study on the induction of spontaneous transmitter release at early nerve-muscle contacts in Xenopus cultures.

During synaptogenesis, spontaneous acetylcholine release is rapidly induced by the contact of the growing neurite with the myocyte. Using Xenopus nerve-muscle co-cultures, we investigated the role of Ca2+ in the presynaptic mechanisms mediating this induction process. We found that Ca2+ influx is not necessary to induce spontaneous release and that an increase in cytosolic Ca2+ is not sufficient to trigger this release in the absence of the target cell.