SV2A and SV2B knockout mice were obtained from the Jackson Laboratory. Rat cDNAs encoding SV2A, SV2B, and SV2C were generously provided by R. Janz (Houston, TX). They were cloned into a lentiviral vector (Lox-Syn-Syn) as we previously described 7 (link). This vector contains two separate neuronal-specific synapsin promoters. One promoter drives expression of SV2 and the other one drives expression of GFP as a marker. Human cDNA encoding SV2C was obtained from PlasmID repository of Harvard Medical School. Human monoclonal antibody against HCA (RAZ-1) was generously provided by J. Marks (San Francisco, CA). Mouse monoclonal antibodies against VAMP2 (Cl 69.1), SNAP-25 (Cl 71.2), Syp (Cl 7.2) were generously provided by E. Chapman (Madison, WI) and are available from Synaptic Systems (Göttingen, Germany). SV2 (pan-SV2) was also provided by E. Chapman (Madison, WI) and it is available from The Developmental Studies Hybridoma Bank (AB2315387, Iowa City, IA). The following antibodies were purchased from indicated vendors: mouse monoclonal antibody against actin (Sigma, A2228); rabbit polyclonal antibody against synapsin (Millipore, Ab1543p); chicken polyclonal antibody against GFP (Aves lab, GFP-1020). Purified BoNT/A1 of Hall-A strain and BoNT/D of D1873 strain were generously provided by E. Johnson (Madison, WI).