Role of spinal nitric oxide synthase-dependent processes in the initiation of the micturition hyperreflexia associated with cyclophosphamide-induced cystitis.

The aim of this study was to examine the participation of nitrergic neurotransmission in the initiation of micturition hyperreflexia associated to cyclophosphamide (CP)-induced cystitis in rats. Micturition threshold volume was significantly reduced 4 h after CP administration (100 mg/kg, i.p.); this reduction was attenuated by intra-arterially injected N(G)-nitro-l-arginine-methyl ester (l-NAME), a non selective nitric oxide synthase (NOS) inhibitor, but not by intravesical infusion of S-methyl-l-thiocitrulline (l-SMTC), another structurally different NOS inhibitor. Interestingly, l-NAME failed to affect micturition threshold volume in normal rats. The magnitude of isolated detrusor strips contractions elicited by either carbachol or nerve activation was significantly reduced in CP-treated rats but was unaffected by the addition of N(G)-nitro-l-arginine (l-NOARG), a nonselective NOS inhibitor. In contrast, intrathecal l-NAME and l-SMTC but not N(G)-nitro-d-arginine-methyl ester (d-NAME) administration augmented the micturition threshold volume in CP-treated rats in an l-arginine preventable manner. As with the systemic injection, intrathecal l-NAME also did not affect the micturition threshold volume in normal rats. Four hours after CP injection, the number of neuronal NOS immunoreactive or nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) positive neurons in spinal lumbosacral segments (L6-S2) was not altered whereas the number of c-Fos immunoreactive neurons increased significantly in the dorsal gray commissural nucleus (DGC), the parasympathetic sacral nucleus (PSN) and lamina X of these segments. Ca(2+)-dependent, but not Ca(2+)-independent NOS activity increased significantly in spinal L6-S2 segments but not in thoracic segments of CP-treated rats. These data indicate that the micturition hyperreflexia observed in the initial hours of CP-induced cystitis is associated with an increase in Ca(2+)-dependent NOS activity in spinal L6-S2 segments suggesting an increased production of nitric oxide (NO). The increased production of NO in these spinal segments appears to be necessary for the initiation of the micturition hyperreflexia.