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Recent studies have analyzed the role of nitric oxide (NO) in pain modulation in several models of sciatic nerve injury. In the present study we have investigated NO production in lumbar dorsal root ganglia (DRG) and spinal cord (SC) over time after sciatic nerve cut. Neuronal nitric oxide synthase (nNOS)-like immunoreactivity (LI) was also determined, since the expression and activity of the enzyme do not always correlate. Nerve section induced a progressive increase in NO production in the ipsilateral L4-5 DRGs and the corresponding levels in the SC in a pattern that correlated with nNOS-LI; this increase was gradual after 7 days of survival time, more pronounced after 14 days, with the highest values detected 28 days after axotomy. This peak was followed by a progressive decrease, reaching control values 42 days after the lesion. The present study shows that nNOS upregulation is related to an increased NO production and release. The temporal pattern of NO production parallels the one observed for the expression of the enzyme, suggesting that the induction of nNOS synthesis yields a protein that is functional and highly active. [ABSTRACT FROM AUTHOR]