Snake presynaptic neurotoxins with phospholipase A2 activity induce swelling of synaptic boutons and exoxytosis of synaptic vesicles

摘要

The mechanisms of action of four snake presynaptic phospholipase A2 neurotoxins\udwere investigated in cultured neurons isolated from various parts of the rat\udbrain. Strikingly, physiological concentrations of notexin, beta-bungarotoxin,\udtaipoxin or textilotoxin induced a dose-dependent formation of discrete bulges at\udvarious sites of neuronal projections. Neuronal bulging was paralleled by the\udredistribution of the two synaptic vesicle markers synaptophysin I (SypI) and\udvesicle-attached membrane protein 2 (VAMP2) to the bulges, and by the exposure of\udthe luminal domain of synaptotagmin on the cell surface. These neurotoxins\udinduced glutamate release from cultured neurons similarly to the known evoked\udrelease of acetylcholine from neuromuscular junctions. In addition, partial\udfragmentation of F-actin and neurofilaments was observed in neurons, but not in\udastrocytes. These findings indicate that these snake presynaptic neurotoxins act \udwith by same mechanism and that the observed phenotype results from the fusion of\udsynaptic vesicles with the plasma membrane not balanced by an adequate membrane\udretrieval. These changes closely resemble those occurring at neuromuscular\udjunctions of intoxicated animals and fully qualify these primary neuronal\udcultures as pertinent models for studying the molecular mode of action of these\udneurotoxins.