By using mechanical nerve ligation or nerve pinch technique, we provid
e evidence that nitric oxide synthase (NOS) is transported in the preg
anglionic sympathetic axons, while postganglionic axons lack NOS trans
port. This finding corroborates the preganglionic sympathetic terminal
as the site of NO synthesis, which is known to affect ganglionic tran
smission. Both vasoactive intestinal polypeptide (VIP) and substance P
(SP) containing neurons of the nodose ganglion transport NOS in their
axons. These results therefore suggest that NOergic innervation of au
tonomically innervated tissues is of parasympathetic and/or sensory, r
ather than sympathetic, origin.