Effect of ketamine on spinal cord nociceptive transmission in normal and monoarthritic rats

The effects of systemically and intrathecally administered ketamine on spin al wind-up of normal and monoarthritic rats were studied by using C-fiber r eflex responses evoked by repetitive (0.6 Hz) electric stimulation. Both sy stemic and intrathecal ketamine induced dose-dependent depression of wind-u p activity in normal rats, as revealed by the dose-related inhibitory effec ts of the drug. At the same intraperitoneal doses, ketamine produced a grea ter inhibitory effect on windup activity of monoarthritic rats, compared to normal animals. The intrathecal administration of ketamine also produced w ind-up inhibition,the efficacy being higher in the monoarthritic rats. Resu lts indicate that ketamine depresses spinal wind-up, specially in rats subm itted to chronic pain, probably due to its antagonistic properties on dorsa l horn NMDA receptors, which play a crucial role in the maintenance of chro nic pain. NeuroReport 12:1551-1554 (C) 2001 Lippincott Williams & Wilkins.