Axonal transport and targeting of the t-SNAREs SNAP-25 and syntaxin 1 in the peripheral nervous system.

Axonal transport and targeting of the t-SNAREs SNAP-25 and syntaxin 1 were investigated in the rat peripheral nervous system using a stop-flow (crush) technique. In crush-operated sciatic nerves, accumulations of SNAP-25 and syntaxin 1 immunoreactivities were detected as early as 1 h after operation, indicating fast axonal transport. The amounts increased on the proximal side of the crush with time after crushing. Distal accumulations of SNAP-25, representing recycling to the cell body, were less than 10% of the proximal accumulations, but 40% for syntaxin 1, 50% for synaptobrevin II and 70% for synaptophysin. Immunoelectron microscopic studies demonstrated that SNAP-25 and syntaxin 1 are present on pleiotropic membranes within a diameter of 50 to 100 nm in axons proximal to a crush. Distal to the crush, labeling for syntaxin 1 and SNAP-25 were sparse and barely detectable, respectively. In addition, the two proteins were found in the axolemma. In nerve terminals of the spinal cord, both proteins were concentrated around small synaptic vesicles (about 50 nm in diameter), whereas only very few gold particles were observed near the presynaptic membrane or the active zones.