Opioid inhibition of reflex urinary bladder contractions: dissociation of supraspinal and spinal mechanisms

Abstract

The supraspinal and spinal mechanisms of morphine induced inhibition of reflex urinary bladder contractions were studied in the urethane anesthetized rat. The inhibition of bladder contractions by intracerebroventricular (i.c.v.) morphine was abolished by intrathecal (i.t.) naloxone. In addition systemic reserpine (3.5–5.0 mg/kg, i.p.) abolished the inhibitory effect of both systemic morphine and i.c.v. morphine but not that of i.t. morphine. These data support the involvement of separate supraspinal and spinal mechanisms in the effects of morphine on bladder motility. The supraspinal effect appeared to be mediated indirectly via a monoaminergic system whereas the spinal action was mediated independently of monoamines. However, both the indirect supraspinal and the direct spinal mechanism involved a spinal naloxone-sensitive process possibly an endogenous enkephalinergic system.