The dinoflagellate Vulcanodinium rugosum, first isolated from Ingril, a French Mediterranean lagoon, is known to produce the pinnatoxins (PnTXs) and the portimines. PnTXs (A-H) constitute an emerging family of phycotoxins belonging to the cyclic imine group1,2. Interest has been focused on these fast-acting highly potent toxins because they are widely found in contaminated shellfish. Despite their highly complex molecular structure, PnTXs have been chemically synthetized by the Zakarian’s group, and demonstrated to act on various nicotinic acetylcholine receptors (nAChRs)3,4. To the best of our knowledge, neither PnTX-A nor PnTX-G and analogs, obtained by chemical synthesis with high degree of purity (> 98%), have been studied in vivo or in vitro on adult mouse and isolated nerve-muscle preparations expressing the mature muscle-type (α1)2β1εδ nAChR. Our results show that PnTX-A and PnTX-G acted on the neuromuscular system of anesthetized mice and blocked the compound muscle action potential (CMAP) in a doseand time-dependent manner with similar ID50 values (dose required to block 50% of the CMAP), as determined using an in vivo minimally invasive electrophysiological method. The decrease of CMAP induced by both toxins in vivo was reversible within 6-8 h. PnTX-A and PnTX-G, applied to isolated extensor digitorum longus (EDL) nerve-muscle preparations, blocked reversibly isometric twitches evoked by nerve stimulation. Both toxins exerted no direct action on the contractile machinery of muscle fibers, as revealed by direct muscle stimulation. In addition, PnTX-A and PnTXG blocked synaptic transmission at mouse neuromuscular junctions. PnTX-A aminoketone analog (containing an open form of the imine ring)4 had no effect on neuromuscular transmission. These results indicate the importance of the cyclic imine for interacting with adult muscle-type nAChR.