Roles of the rostroventromedial medulla and the spinal 5-HT(1A) receptor in descending antinociception induced by motor cortex stimulation in the neuropathic rat.

Electric stimulation of the primary motor cortex (M1) has been effective in suppressing pain-related responses in neuropathic as well as healthy control animals. We studied whether the rostroventromedial medulla (RVM) or the spinal 5-HT(1A) receptor contributes to antinociception induced by stimulation of M1 in neuropathic animals. Assessments of the noxious heat-evoked limb withdrawal reflecting spinal nociception was performed in rats with spinal nerve ligation-induced peripheral neuropathy under light pentobarbital anesthesia. Spinal antinociception induced by electric stimulation of M1 was reduced following block of the RVM with intramedullary injection of muscimol, a GABA(A) receptor agonist, or following intrathecal administration of WAY-100635, a 5-HT(1A) receptor antagonist. The results indicate that the RVM and the descending serotonergic pathway acting on the spinal 5-HT(1A) receptor contribute to spinal antinociception induced by M1 stimulation in neuropathic animals. Copyright 2010 Elsevier Ireland Ltd. All rights reserved.