Axonal transport of NADPH-diaphorase and [3H]nitro-L-arginine binding, but not [3H]cGMP binding, by the rat vagus nerve

Previous studies have shown that the NO·-cGMP pathway may be functionally relevant in the nodose ganglion and at afferent terminations of the vagus nerve. The technique of unilateral vagal ligations, using double ligatures, was combined with the techniques of NADPH-diaphorase histochemistry, as an index of nitric oxide synthase (NOS) activity, and autoradiography using the radioligands [³H]nitro-L-arginine and [³H]cGMP, to examine axonal transport of NOS and cGMP-dependent effectors by the rat vagus nerve. A population of perikarya in the nodose ganglia was NADPH-diaphorase positive, and binding of both [³H]nitro-L-arginine and [³H]cGMP was found on the nodose ganglia. Following vagal ligation, NADPH-diaphorase reactivity accumulated proximal to the proximal ligature and distal to the distal ligature. Vagus nerve transection beyond the distal ligature eliminated NADPH-diaphorase reactivity at the distal ligature. Similarly, [³H]nitro-L-arginine binding was found over the nodose ganglion; and after vagal ligation, an accumulation of [³H]nitro-L-arginine binding was seen adjacent to the proximal ligature, though little binding was found adjacent to the distal ligature. No accumulation of [³H]cGMP binding was found adjacent to either the proximal or the distal ligatures. These findings suggest that the rat vagus nerve bidirectionally transports NOS, the enzyme involved in biosynthesis of NO· by nitroxidergic nerves. As anticipated, [³H]nitro-L-arginine, a competitive inhibitor of the amino acid precursor for NO·, binds only to a centrifugally transported moiety that we conjecture is NOS, while cGMP apparently is not subject to transport. These data further support the use of NO· in transmission at vagal afferent terminals. (C) 2000 Elsevier Science B.V.