Fine structure of the autapse. (a and b) Conventional electron microscopy. a, WT; b, Rab3 GEP−/−. (c and d) Rab3A immunoelectron microscopy. c, WT; d, Rab3 GEP−/−. nSV, synaptic vesicles with a normal size; sSV, synaptic vesicles with a smaller size; PSD, postsynaptic density.