Neuronal nitric oxide synthase like-immunoreactivity and nitrate levels in rat dorsal root ganglia and spinal cord after sciatic nerve axotomy

M.F. CORONEL; M.C. DEFAGOT; P.L. MUSOLINO; M.J. VILLAR

Orlando, USA

Congreso; Society for Neuroscience; 2003

Society for Neuroscience

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 nitrate levels (nitrate is the major end product of NO) in lumbar dorsal root ganglia (DRG) and spinal cord (SC) over time in a model of peripheral neuropathy.  A correlation with the immunostaining of neuronal nitric oxide synthase (nNOS) was also done. Animals subjected to peripheral axotomy were perfused after different survival times (1, 3, 7, 14, 28 days) and the ipsilateral and contralateral L4-5 DRGs, as well as the corresponding levels of the SC, were removed. The tissues were processed for standard ABC immunohistochemistry using nNOS antibodies. Animals destined for nitrate determination were decapitated following similar survival times and their DRGs and lumbar SC were homogenized in sucrose 0,32M. The homogenates were centrifuged at 27000 rpm for 90 min. In the supernatants, nitrate levels were determined using the NO Analyser 280 (Sievers). Nerve section induced a progressive increase in the number of nNOS-immunoreactive cells in the ipsilateral DRGs, reaching the highest values 28 days after axotomy. An increased number of positive fibers and terminals was observed in the ipsilateral dorsal horn of the SC. Nitrate levels were also increased in the ipsilateral DRGs and SC, reaching a peak 7 and 3 days after axotomy, respectively. This temporal discordance between nNOS-like immunoreactivity and nitrate levels could be due to a decreased enzyme activity secondary to a negative feedback mechanism resulting from a previously increased NO production. Another possibility is that normal NO degradation pathways may be altered by the presence of some metabolite that could be trapping NO, modifying in this way the total amount of nitrate produced.