Compression of the facial nerve caused increased nitric oxide synthase activity in the facial motor nucleus.

Nitric oxide synthase activities in the facial motor nucleus were studied in rats after unilateral compression of the facial nerve. Using a radiometric assay which measured the total soluble nitric oxide synthase activities in the facial motor nucleus and the surrounding tissues, it was found that nitric oxide synthase activities were markedly increased during facial paralysis that resulted from compression of the facial nerve. The subsequent decrease in nitric oxide synthase activities between postoperative days 20 and 40 coincided with the recovery of facial functions. In contrast, staining with NADPH-diaphorase histochemistry revealed that the diaphorase activities in the facial motor neurons were markedly increased between days 20-40 when the total activities as measured biochemically were in decline. However, staining of the vascular endothelium was increased on postoperative day 7 when the total activity was high. It is suggested that the increase in total nitric oxide synthase activities immediately after facial nerve compression may be predominantly endothelial. Since the increase in neuronal NADPH-diaphorase reactivity coincided with the recovery of facial functions, increased neuronal nitric oxide synthase may be a contributing factor to the restoration of facial innervation. The results of this study show that biochemical measurements of soluble nitric oxide synthase activities in tissue homogenates and NADPH-diaphorase histochemical staining in tissue sections may represent two distinct populations of nitric oxide synthase.(ABSTRACT TRUNCATED AT 250 WORDS)