Effect of Long-Term Oxybutynin Administration on c-Fos Expression in Spinal Neurons: Inhibition of Antimuscarinics on Bladder Afferents in Conscious Rats

ObjectivesTo investigate the effect of long-term administration of oxybutynin on afferent input from the bladder by evaluating c-Fos expression in the spinal cord.MethodsUsing an osmotic pump, long-term administration of oxybutynin (4 weeks) was performed in the rat. The effects of oxybutynin (2 doses) on the urodynamic parameters were determined by continuous cystometry in conscious rats. After cystometry, c-Fos expression in the spinal cord was measured by immunohistochemistry.ResultsThe long-term administration of low-dose oxybutynin (0.36 mg/kg/d) significantly increased the micturition interval and bladder capacity, but it did not affect micturition pressure. However, administration of high-dose oxybutynin (3.6 mg/kg/d) significantly decreased the micturition pressure and increased the residual volume. In the rats that received low-dose oxybutynin, the number of c-Fos–positive neurons in the spinal cord was significantly lower than that in controls.ConclusionsAdministration of low-dose oxybutynin decreased the c-Fos expression induced by continuous infusion of saline into the bladder. This result suggests that the antimuscarinic drug oxybutynin at clinically recommended doses can exert an inhibitory effect on afferent input from the bladder during the storage phase without affecting detrusor contractions.