Involvement of capsaicin-sensitive fibers in spinal NMDA-induced glutamaterelease

The activation of spinal NMDA receptors can evoke glutamate release through the production of nitric oxide (NO) within-the spinal cord, resulting in p ain-relating behavior. In this study, we investigated the involvement of ca psaicin-sensitive primary afferents in this phenomenon using in vivo intrat hecal microdialysis. Intrathecal NMDA perfusion evoked increases in the con centrations of NO metabolises and glutamate and in pain-related behavior in both neonatal capsaicin and vehicle-treated Key words: Glutamate; Neonatal capsaicin; Nitric oxide; NMDA rats. Although the degrees of increase in NO metabolises in capsaicin- and vehicle-treated rats were not significantly different, capsaicin-treated rats showed significantly smaller increases in glutamate concentration and pain-related behavior than did vehicle-treated rats. Our results showed-that glutamate release from capsaicin-sensitive p rimary afferent terminals is involved in spinal NMDA-induced pain. (C) 2001 Lippincott Williams & Wilkins.