Recently, investigators have observed the interesting phenomenon that botulinum neurotoxin (BoNT) may provide significant benefit in the reduction of certain types of pain. However, the mechanistic basis for this phenomenon is unclear, since an interaction between the terminals of the sensory nervous system and BoNTs is not well understood. Is there a direct effect of BoNT on primary sensory neurons associated with pain? In an effort to address this, a study of the neuropeptide content of sensory neurons demonstrating sensitivity to BoNT serotype A was undertaken in murine primary sensory neurons in culture. The SNARE protein SNAP-25, the intracellular target of BoNT A, was developmental expressed in embryonic dorsal root ganglia culture and cleaved by BoNT A (10-8M) in a time dependent manner. Cleavage of SNAP-25 was detected in a select population of DRG neurons by immunofluorescence, that were double-labeled with some pain-related neuropeptides, including CGRP, galanin, GABA and nociceptin, but not with substance-P and glutamate. It has previously been reported that BoNT A blocks the release of substance-P, and glutamate in the spinal dorsal horn and decreases the sensitivity of pain transduction from spinal cord to brain. Our preliminary results suggest that the release of certain neuropeptides related to pain transmission or modulation in primary sensory neurons may be selectively altered by BoNT A. Thus, a potential mechanism for pain relief by BoNT A may be mediated by toxine-induced interference of multiple pain related factors.