Pyrroloquinoline quinone (PQQ) is a naturally occurring redox cofactor that acts as ail essential oUtrient, antioxidant, and redox modulator. PQQ has been demonstrated to oxidize the redox modulatory site of N-methyl-D-aspartic acid (NMDA) receptors. Such agents are known to be neuroprotective in experimental stroke models. Therefore, we examined the possible ameliorating effect of PQQ oil spinal cord injury (SCI) in adult rats. Intraperitoneal administration of PQQ effectively promoted the functional recovery of SCI rats after hemi-transect ion, which was preceded by the attenuation of the expression of inducible nitric oxide (NO) synthase (iNOS) mRNA in the injury site. NO is involved in the secondary detrimental mechanisms and has been implicated in NMDA receptor-mediated neurotoxicity. In fact, admistration of PQQ induced significantly decreased lesion size and increased axon density adjoining the lesion area. These observations suggest that PQQ protects against the secondary damage by reducing iNOS expression following primary physical injury to the spinal cord. 2008 Elsevier Inc. All rights reserved.