"This provides direct confirmation of the brain's response to peripheral electrical nerve stimulation in this condition, and in particular the effect on the brainstem," Dr. Ranan Dasgupta from National Hospital for Neurology and Neurosurgery, London, told Reuters Health.

Dr. Dasgupta and colleagues used PET scanning to identify regions of brain activity relating to the perception of bladder fullness and their modulation by sacral nerve stimulation in eight women with urinary retention due to sphincter overactivity (Fowler's syndrome) and in eight healthy controls.

In healthy controls, having a full bladder was associated with enhanced activity within the anterior midbrain in a region that included the substantia nigra, as well as a second area of brainstem activation, the authors report. Bladder fullness also activated cortical centers, the researcher note in the December issue of The Journal of Urology.

In contrast, women with urinary retention showed no enhancement of midbrain regions during bladder fullness in the absence of sacral nerve stimulation. These women did, however, show activation of the same cortical centers during bladder fullness.

With the sacral stimulator switched on, patients with bladder fullness showed brain activity similar to that in healthy controls, the researchers note.

"Our findings show that urinary control depends on interactions of several brain centers including the cingulate cortex, midbrain, and pons, with evidence that sacral neuromodulation has central effects on these areas," the authors conclude.

"Importantly, our study indicates that anterior midbrain activation is necessary for perceiving bladder fullness, and details the functional interaction of anterior cingulate cortex and posterior cingulate cortex with brainstem centers."

"Further studies using functional magnetic resonance imaging are in progress," Dr. Dasgupta said, which "may shed further light on mechanisms of action of the therapy."

J Urol 2005;174:2268-2272

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