SPINAL-CORD NADPH-DIAPHORASE HISTOCHEMICAL STAINING BUT NOT NITRIC-OXIDE SYNTHASE IMMUNOREACTIVITY INCREASES FOLLOWING CARRAGEENAN-PRODUCEDHINDPAW INFLAMMATION IN THE RAT

Recent reports suggest that NADPH-diaphorase (NADPH-d) may be a histoc hemical marker for neuronal nitric oxide synthase (nNOS) in the centra l nervous system. Carrageenan-produced unilateral hindpaw inflammation in the rat results in a bilateral increase in NADPH-d in spinal cord neurons. This suggests there would be a bilateral increase in NO, whic h mediates thermal hyperalgesia. However, carrageenan-produced unilate ral hindpaw inflammation results in hyperalgesia of the inflamed hindp aw only. This study determined (1) if neurons that labeled for NADPH-d following carrageenan-produced unilateral hindpaw inflammation coloca lized nNOS, and (2) whether there was an increase in nNOS-ir neurons f ollowing inflammation. Following unilateral hindpaw inflammation, doub le labeling of tissue sections and single labeling of alternate serial sections revealed a lack of colocalization or mismatch between NADPH- d histochemical activity and nNOS-like immunoreactivity in neurons in lamina I, the dorsolateral funiculus and lamina X. Quantitative analys is showed no difference in the number of nNOS-ir neurons and NADPH-d l abeled neurons in the superficial laminae of the spinal cord in non-in flamed animals. Following unilateral hindpaw inflammation, there was a 34% increase in the number of NADPH-d labeled neurons but no increase in the number of nNOS-ir neurons. These results indicate that nNOS-im munoreactive neurons and NADPH-diaphorase stained neurons are not iden tical and that nNOS does not increase as a result of hindpaw inflammat ion, leaving the source of NO involved in thermal hyperalgesia followi ng injury in question.