A SEGMENTAL CHRONIC PAIN SYNDROME IN RATS ASSOCIATED WITH INTRATHECALINFUSION OF NMDA - EVIDENCE FOR SELECTIVE ACTION IN THE DORSAL HORN

We explored the effects of chronic lumbar intrathecal NMDA infusion (m ini-osmotic pumps) in Sprague-Dawley rats on motor and sensory axon in tegrity. Several different infusion protocols, each given over a 4 wee k period were examined: 0.15 M NMDA in phosphate buffered saline; phos phate buffered saline without NMDA; and 0.20 M magnesium sulfate plus 0.15 M NMDA; 0.35 M NMDA. In two additional protocols, 0.15 M NMDA or phosphate buffered saline were infused for a total of 8 weeks. Within 1-2 weeks of the onset of NMDA, but not phosphate buffered saline infu sions, the rats exhibited irritability, circling, biting and excessive grooming resulting in loss of hair, and skin ulcerations from autotom y localized to lumbar and sacral innervated dermatomes. Co-infusion of NMDA with magnesium sulfate almost completely prevented these finding s. The behavioural changes were not associated with abnormalities of s ensory or motor conduction. Intrathecal infusion of NMDA induces a chr onic ''central'' experimental pain disorder in rats, localized to the cord segment with the greatest exposure to the infusion, without invol vement of peripheral sensory axons and sparing the axonal integrity of anterior horn cells.