LOCALIZATION OF NITRIC-OXIDE SYNTHASE WITHIN NONADRENERGIC, NONCHOLINERGIC NERVES IN THE MOUSE ANOCOCCYGEUS

Immunocytochemical staining of whole mount preparations of the mouse a nococcygeus muscle, using antibodies to rat brain nitric oxide synthas e (NOS), revealed a dense network of NOS-immunoreactive nerve fibres r unning through the tissue. These fibres were resistant to the sympathe tic neurotoxin 6-hydroxydopamine and are therefore likely to be the no n-adrenergic nerves which mediate relaxation of this smooth muscle. Fu rther, NOS-immunoreactive fibres were absent following denervation by cold-storage (4-degrees-C; 72 h), which has been shown to abolish non- adrenergic, non-cholinergic (NANC) relaxations. The results provide st rong support for the hypothesis that the L-arginine:NO pathway is resp onsible for the generation of the NANC transmitter in the anococcygeus .