NMDA RECEPTOR BLOCKADE AND SPINAL-CORD ISCHEMIA DUE TO AORTIC CROSS-CLAMPING IN THE RAT MODEL

Recent brain research proposes that, during ischemia, synaptically rel eased excitatory amino acid neurotransmitters accumulate at toxic conc entrations with ensuing neuronal death. Their action is mediated by th e receptor subtype N-methyl-D-aspartate (NMDA). The protective effect of NMDA receptor blockade with intrathecal MgSO4 and MK-801 was invest igated during spinal cord ischemia induced by aortic occlusion of 12 m inutes. Male Sprague-Dawley rats, 250-300g, underwent intrathecal admi nistration of 20 mu L of normal saline (SA n = 16), MgSO4 1M (MG n = 1 6), or MK-801, 25 mM solutions (MK n = 16) in a randomized order. Afte r 2 hours, the animals underwent occlusion of the thoracic aorta and s ubclavian arteries for 12 min. An additional control group (CO n = 16) underwent occlusion for 12 minutes, without intrathecal injection. Th e animals were scored according to their functional performance (LS = lesion score) each day for four days by a blinded observer. Mean LS we re calculated for each group at a given day. Treatment and control gro ups were not different at day 1 (P = 0.302). Group MG was improved fro m groups SA (P = < 0.0039) and CO (P = < 0.0048) at day 4. This study demonstrates that although intrathecal NMDA receptor blockade with MgS O, or MK-801 does not prevent paraplegia due to spinal cord ischemia i n the rat, it could however influence the rate of recovery after ische mic injury.