An image of SAB synapses on head muscle from a wild type worm double labelled with antibodies directed against the synaptic vesicle protein RAB3 (in red) and the active zone marker Rim (in green). Rim decorates one, and occasionally two subdomains of each synaptic varicosity in SAB neurons. Immunohistochemistry is a technique we use extensively to examine the structure of synapses, and subsynaptic structures such as the active zone. Antibodies directed against different structural elements of the synapse are valuable reagents in the our studies of assembly of the presynaptic density. Image from Koushika et al, Nature Neuroscience, 2001.