Contribution of capsaicin-sensitive primary afferents to mechanical hyperalgesia induced by ventral root transection in rats: the possible role of BDNF.

Objective: A recent study showed that brain-derived neurotrophic factor (BDNF) may play a role in the development of the neuropathic pain resulting from injury to motor efferent fibres, such as that in the ventral root transection (VRT) model. Capsaicin stimulation of afferent fibres was also shown to result in the release of BDNF into the spinal cord. Here, the effects of ablation of capsaicin-sensitive primary afferents (CSPAs) by local application of capsaicin on the sciatic nerve on VRT-induced mechanical hyperalgesia were observed. Methods: The paw withdrawal mechanical threshold (PWMT) was measured before and then 1 and 3 days and 1, 2, 3, 4 and 6 weeks after VRT. Results: The results showed that local application of capsaicin significantly inhibited the decrease in the PWMT induced by VRT, suggesting the inhibitory effect of locally delivered capsaicin. Furthermore, intrathecal administration of exogenous BDNF not only produced mechanical hyperalgesia but also significantly blocked the inhibitory effect of capsaicin. Conclusion: Taken together, the results of this study suggest that CSPA fibres may contribute to mechanical hyperalgesia in the VRT model.