CNS involvement in overactive bladder: pathophysiology and opportunities for pharmacological intervention.

The pathophysiology of overactive bladder (OAB) syndrome is complex, and involves both peripheral and CNS factors. Several CNS disorders are associated with OAB, e.g. stroke, spinal cord injury, Parkinson's disease and multiple sclerosis, and in each disorder the pathophysiology of OAB can be multifactorial. Irrespective of cause or pathophysiology of OAB, antimuscarinic drugs are the first line of pharmacological treatment. However, adverse effects and limited efficacy makes alternative therapeutic principles desirable. Most alternative drugs used for the treatment of OAB have a peripheral site of action, mainly affecting efferent or afferent neurotransmission or the detrusor muscle itself. New targets for pharmacological intervention may be found in the CNS. Several CNS transmitters/transmitter systems are known to be involved in micturition control, but few drugs with a defined CNS site of action (e.g. baclofen, imipramine and duloxetine) have been used for the treatment of voiding disorders. GABA, glutamate, opioid, serotonin, noradrenaline (norepinephrine), and dopamine receptors and mechanisms are known to influence micturition, and drugs influencing these systems could potentially be developed for the treatment of OAB. Preclinical studies in different animal models have shown that modulation of normal micturition and detrusor overactivity by drugs acting within the spinal cord or supraspinally is possible. Promising results have been obtained in such models, e.g. with drugs interfering with GABA mechanisms, serotonin 5-HT1A receptors, mu-opioid receptors and alpha-adrenoreceptors. However, considering the limited predictability of existing animal models for efficacy in humans, positive proof of concept studies in humans are mandatory. Such studies are scarce and further investigations are needed.