MORPHOLOGICAL AND FUNCTIONAL EVIDENCE AGAINST A SENSORY AND SYMPATHETIC ORIGIN OF NITRIC-OXIDE SYNTHASE-CONTAINING NERVES IN THE RAT LOWER URINARY-TRACT

To establish which type of nerves (parasympathetic, sympathetic or sen sory) produce nitric oxide in the rat lower urinary tract, chemical de nervation of primary afferents and sympathetic nerves was carried out by systemic treatment with capsaicin and 6-hydroxydopamine, respective ly, followed by identification of neuronal nitric oxide synthase immun oreactivity. Functional in vitro studies were also performed to examin e whether the synthesis and release of nitric oxide was affected follo wing treatment with the respective neurotoxins. Nerve fibres immunorea ctive for substance P and calcitonin gene-related peptide were found i n control tissue, but could not be detected following capsaicin treatm ent. In comparison, nitric oxide synthase-immunoreactive fibres appear ed to be unaffected by capsaicin treatment. Administration of 6-hydrox ydopamine resulted in a complete disappearance of tyrosine hydroxylase -immunoreactive nerves, whereas nitric oxide synthase-containing nerve fibres did not appear to be affected by the treatment. In ultrastruct ural studies, nitric oxide synthase immunoreactivity, as studied by co lloidal gold particles, was found in the axoplasm and not in associati on with intraneuronal structures or synaptic vesicles. Gold particles representing substance P immunoreactivity were seen as clusters associ ated with large granular vesicles. In consecutive sections of nerve fi bres, substance P and nitric oxide synthase were not found in the same axon profile. In functional studies on urethral tissue, application o f capsaicin (1 mu M) produced a long-lasting relaxation. The nitric ox ide synthase inhibitor N-G-nitro-L-arginine (0.1 mM) had no effect on this response. Systemic treatment with capsaicin or 6-hydroxydopamine had no effect on nerve-evoked, nitric oxide-mediated relaxations. The data suggest that nitric oxide synthase-containing nerves in the rat l ower urinary tract do not belong to nerve populations sensitive to eit her the sympathetic neurotoxin, 6-hydroxydopamine, or the sensory neur otoxin, capsaicin. Copyright (C) 1997 IBRO.