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 label led 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 afferen ts. An acute inflammation (32 h) significantly increased this proporti on to 10.9 +/- 2.2% (mean +/- S.D. of 5 inflamed joints and 3933 label led perikarya). The diameter distribution of the somata with a positiv e NADPH-diaphorase reaction ranged from 18 to 46 mu m with a maximum a t 24-28 mu m. These data indicate that a small proportion of knee join t primary afferents may be able to release nitric oxide playing a role in synaptic transmission and in regulatory functions within the perip heral tissue under normal and pathophysiological conditions.