NADPH-diaphorase reactivity in articular afferents of a normal and inflamed knee joint in the cat.

The distribution of NADPH-diaphorase was studied in retrogradely labelled dorsal root ganglion cells innervating the knee joint of the cat. A strong staining reaction was found in 7.5 +/- 1.9% (mean +/- S.D. of 9 normal joints and 6393 labelled perikarya) of the articular afferents. An acute inflammation (32 h) significantly increased this proportion to 10.9 +/- 2.2% (mean +/- S.D. of 5 inflamed joints and 3933 labelled perikarya). The diameter distribution of the somata with a positive NADPH-diaphorase reaction ranged from 18 to 46 microns with a maximum at 24-28 microns. These data indicate that a small proportion of knee joint primary afferents may be able to release nitric oxide playing a role in synaptic transmission and in regulatory functions within the peripheral tissue under normal and pathophysiological conditions.