Regulation and immunhistochemical localization of nitric oxide synthases and soluble guanylyl cyclase in mouse spinal cord following nociceptive stimulation

The localization and regulation of neuronal nitric oxide synthase (nNOS), i nducible nitric oxide synthase (iNOS) and soluble guanylyl cyclase (sGC) we re assessed in the spinal cord of mice stimulated by an intraplantar inject ion of zymosan. Both, nNOS and iNOS were upregulated in the dorsal horns of the spinal cord in response to the zymosan challenge. While nNOS was found in neurons of superficial laminae iNOS occurred in astrocytes. Thus, astro cytes mig ht be involved in the processing of nociceptive stimuli. Expressi on of sGC was not affected by zymosan treatment. It was found exclusively i n nerve fibers suggesting that it was predominantly localized to the presyn aptic neuron. This supports the hypothesis that nitric oxide (NO) acts as r etrograde messenger in spinal nociceptive processing. (C) 2000 Elsevier Sci ence Ireland Ltd. All rights reserved.