[Effect of sodium nitroprusside on the spontaneous and induced responses of rat spinal cord dorsal horn neurons].

ABSTRACT

The present study was performed on anesthetized and paralyzed Wistar rats. Extracellular recordings were made from the lumbar enlargement of the spinal cord using carbon filament electrodes. NO donor sodium nitroprusside (SNP) was locally microdialyzed to the spinal cord, and effects of NO on spontaneous response and the responses induced by mechanical stimulation of the hind-foot were observed. After dialyzing for 10~20 min, SNP at a concentration of 1 micromol/L increased the induced responses to innocuous mechanical stimulation and decreased those to noxoius mechanical stimulation. The induced responses to both innocuous and noxious mechanical stimulations were all decreased after dialyzing the same dose of SNP for 20~30 min. The decrease was shown within 7~15 min dialysis when SNP was used at a concentration of 20 micromol/L. SNP at both concentrations of 1 and 20 micromol/L increased spontaneous spikes of the recorded spinal units. These effects were shown preferentially in deep units. The data suggest that in the deeper neurons of the spinal cord NO of different concentrations has different effects on transmission of nociceptive and nonnociceptive signals induced by mechanical stimulation, and No is involved in the antinociception in spinal neurons and facilitates their spontaneous activity.