Proportion of NADPH-diaphorase reactive sympathetic efferents innervating the normal and inflamed knee joint of the cat.

To determine whether postganglionic sympathetic efferents may be a source of nitric oxide in normal and inflamed knee joints, the distribution of NADPH-diaphorase was studied in retrogradely labelled neurons of the paravertebral sympathetic ganglia in the cat. In these ganglia, a strong NADPH-diaphorase staining reaction was found in 3-7% (segments L2-L5) and 14-17% (segments L6 and L7) of the neurons. Only 2.5 +/- 1.2% (mean +/- SD, 4 normal joints), of 2207 labelled neurons showed a positive staining reaction. During a unilateral inflammation (32 h), this proportion slightly increased to 5.0 +/- 1.2% (unaffected joints of 4 animals, 2510 labelled perikarya) and 5.4 +/- 2.8% (inflamed joints of 4 animals, 2578 labelled perikarya). However, these increases only attained statistical significance between the values obtained from control animals and from the normal sides of animals with a monoarthritis. Thus, the data indicate that in the sympathetic innervation of the normal and inflamed knee in the cat, the release of nitric oxide has little or no importance.