Wim Blyweert

Interstitial cells of the bladder: the missing link?

INTRODUCTIONThe innervation and function of the bladder wall is stillsomewhat enigmatic. Different aetiological mechanisms forbladder overactivity have been proposed. Neurogeniccauses are well known. For the idiopathic forms, however,explanations remain to be established.Previously researchers have focused on efferent andafferent innervation and on smooth muscle physiology;recent research papers show a shift of interest to the roleof the urothelium and the suburothelium. The sensingfunction of the urothelium is being investigated as well asthe role of a strange type of myofibroblast-like or intersti-tial cell, located in the suburothelium and in betweendetrusor muscle bundles.In this paper the authors try to integrate the current datain an intriguing hypothesis. If these interstitial cells proveto have a role in integrating the information coming fromthe urothelium and nerves they would be able to modulatedetrusor contractility; this would mean a leap forward inour understanding of bladder overactivity. Since similarcells are also present in the gut and other organs, theinteraction between the mucosal lining and the underlyingsmooth muscle might become an interesting research area.CLASSICAL VIEWS ONBLADDER OVERACTIVITYUrgency and urge incontinence are very common symp-toms, having a large impact on quality of life and beingaccountable for major healthcare expense. Underlyingdetrusor overactivity has a wide variety of causes, manyof which are still considered to be idiopathic. The conditionis also present in patients with neurological disorders likemultiple sclerosis and spinal cord lesions.The normal micturition reflex requires efferent nerveinput from the spinal cord to the bladder and afferent inputfrom the bladder to the central nervous system. The afferentnerves transmit information regarding bladder fullness anddiscomfort to the brain and consist of two types of nervefibres. The myelinated and fast-conducting Ay-fibres pro-ject sensations of fullness and wall tension to the centralregulatory centres of micturition through interneuroneslocated in the spinal cord. Normal micturition occursthrough a spino-bulbo-spinal reflex arc initiated by theseAy-fibres. Unmyelinated C-fibres connect to the motorinnervation of the bladder through spinal interneurones.These C-fibres transmit noxious and painful sensations. Incats with chronic spinal cord transection these additionalpathways create a spinal reflex arc and mediate automaticmicturition resulting in neurogenic detrusor overactivity.