The actin cytoskeleton and neurotransmitter release: An overview

Here we review evidence that actin and its binding partners are involved in the release of neurotransmitters at synapses. The spatial and temporal cha racteristics of neurotransmitter release are determined by the distribution of synaptic vesicles at the active zones, presynaptic sites of secretion. Synaptic vesicles accumulate near active zones in a readily releasable pool that is docked at the plasma membrane and ready to fuse in response to cal cium entry and a secondary, reserve pool that is in the interior of the pre synaptic terminal. A network of actin filaments associated with synaptic ve sicles might play an important role in maintaining synaptic vesicles within the reserve pool. Actin and myosin also have been implicated in the transl ocation of vesicles from the reserve pool to the presynaptic plasma membran e. Refilling of the readily releasable vesicle pool during intense stimulat ion of neurotransmitter release also implicates synapsins as reversible lin ks between synaptic vesicles and actin filaments. The diversity of actin bi nding partners in nerve terminals suggests that actin might have presynapti c functions beyond synaptic vesicle tethering or movement. Because most of these actin-binding proteins ale regulated by calcium, actin might be a piv otal participant in calcium signaling inside presynaptic nerve terminals. H owever, there is no evidence that actin participates in fusion of synaptic vesicles. (C) 2000 societe francaise de biochimie et biologie moleculaire / Editions scientifiques et medicales Elsevier SAS.