FUNCTIONAL EVIDENCE FOR THE PRESENCE OF NITRIC-OXIDE SYNTHASE IN THE DORSAL MOTOR NUCLEUS OF THE VAGUS

Background & Aims: Histochemical studies indicate that reduced nicotin amide adenine dinucleotide phosphate diaphorase, the nitric oxide synt hase-related enzyme, is present in the dorsal motor nucleus of the vag us of the cat. We have previously shown in vitro that NO synthase is p resent in this nucleus in the rat and that the excitatory effect of N- methyl-D-aspartate on these neurons is in part caused by NO formation. The aim of this study was to obtain functional evidence for the prese nce of NO synthase in the cat dorsal motor nucleus of the vagus. Metho ds: L-Glutamate, L-arginine, D-arginine, the NO donor S-nitroso-N-acet yl-penicillamine, and the NO synthase inhibitor N-G-nitro-L-arginine-m ethyl ester were unilaterally microinjected into the rostral dorsal mo tor nucleus of anesthetized cats, and antral and pyloric motility were monitored using extraluminal force transducers. Results: Microinjecti on of L-arginine increased gastric motility, whereas D-arginine had no effect. Vagotomy eliminated the L-arginine-induced increases. Microin jection of S-nitroso-N-acetyl-penicillamine increased antral motility. N-G-Nitvo-L-arginine-methyl ester prevented L-arginine from exerting an effect on gastric motility. Conclusions: Motility increases obtaine d after microinjection of L-arginine into the dorsal motor nucleus and prevention of these motility increases with microinjection of a NO sy nthase inhibitor provide functional evidence for the presence of NO sy nthase in the dorsal motor nucleus of the vagus in the cat.