Central effects of baclofen on the L-dopa induced hyperactive urinary bladder of the rat

Cystometric recordings were performed in pentobarbitone anaesthetized rats and the effects of baclofen on urinary bladder function were evaluated as their influence on bladder hyperactivity induced by 1-dihydroxyphenylalanine (L-dopa) after peripheral decarboxylase inhibition. The bladder response was inhibited by intracerebroventricularly (i.c.v., 4th ventricle, 0.1 microgram) as well as by systemically administered (10 mg/kg i.v.) baclofen. Intravenous naloxone but not i.v. bicuculline i.c.v. substance P or i.c.v. glutamate antagonized the inhibitory actions of i.c.v. or/and i.v. baclofen. It is suggested that baclofen depresses the hyperactive bladder by a central action that is unrelated to bicuculline sensitive gamma aminobutyric acid mechanisms, substance P or glutamate neurotransmission but that is possibly related to interference with opioid mechanisms.