The use of functional-MRI in the imaging of the central regulation of micturition in the healthy male and female.

Overactive bladder is a condition characterized by urgency, frequency and urge
incontinence. A relatively new treatment is to inject Botulinum toxin A in the
bladder wall. This appears to be effective and is rapported to reduce
complaints in 70-80% of the patients. As yet the precise working mechanism is
unclear. One of the theories is that Botulinum toxin A has an effect on the
afferent part of the micturition innervation pathway.
The micturition process is coordinated in the brainstem. The pontine
micturition center (PMC) causes excitation of parasympathetic bladder
motoneurons in the sacral spinal cord. By releasing acetylcholine in the
synaptic junction these motoneurons initiate detrusor contraction. The afferent
pathway of the micturition control system consists of Aδ-fibers, which respond
to stretch of the bladder wall. In this way the periaqueductal gray (PAG) in
the brainstem is continuously informed about the bladder content. There exist
strong connections between various limbic system related brain structures and
the PMC, which are believed to be inhibitory. Probably the urge to void is
suppressed by the emotional system, until there is an appropriate opportunity
to void.
There are two theories concerning the cause of overactive bladder. The first
one relies on increased sensitivity of peripheral afferent fibres; the second
on lesions in the central pathway described above. Lack of inhibition of the
urge signal would mean a constant urge to void, hence the overactive bladder.

The eventual aim of the study is to determine the effects of Botulinum toxin
injections in the bladder on overactive bladder.
The objective of this initial study is to determine what brainstructures are
activated in respond to increasing volumes of the bladder and micturition.

The study will be prospective as healthy volunteers will undergo a set of
fMRI-scans before and after their bladder has been filled using a transurethral
catheter and during micturition.

The study is performed in healthy subjects who will undergo catheterization and
filling of the bladder. This means a minor risk of urinary tract infection.
Also they will undergo an fMRI-scan prior to and after filling of the bladder
with saline and during micturition. If the contra-indications are taken into
account, the MRI has no known side effects or complications.