Nicotine attenuates iNOS expression and contributes to neuroprotection in a compressive model of spinal cord injury

Primary impact to the spinal cord results in stimulation of secondary processes that potentiate the initial trauma. In the present study, we hypothesized that the altered expression of nitric oxide synthase (NOS) may contribute to these effects. Recent evidence indicates that nicotine can exert potent antioxidant and neuroprotective effects in spinal cord injury (SCI). Therefore, the aim of the present study was to evaluate whether the administration of nicotine can influence expression of inducible NOS (iNOS) and/or neuronal NOS (nNOS) in injured spinal cords. Adult male Long-Evans rats were subjected to a moderate contusion model of SCI and received a single intraperitoneal injection of either saline or nicotine (0.35, 3.5, or 7 mg/kg) 2 hr after trauma. SCI dramatically increased iNOS (but not nNOS) mRNA and protein levels in microglial cells in the thoracic and lumbar regions of spinal cords. iNOS overexpression resulted in increased nitrotyrosine formation, decreased number of NeuN (neuronal nuclei)-immunoreactive cells, and up-regulation of inflammatory genes. Most importantly, these effects were markedly attenuated by nicotine acting via a receptor-mediated mechanism. These data may have significant therapeutic implications for the targeting of nicotine receptors in the treatment of compressive spinal cord trauma.