Changes in rat brainstem responsiveness to somatovisceral inputs following acute bladder irritation

A number of clinical studies indicate the coexistence of multiple chronic pelvic diseases and pain syndromes. An association between various conditions related to the pelvic viscera may relate to a high degree of central visceral convergence, which is a requisite for the cross-organ coordination that is necessary for their normal functions. In the present study, a population of neurons receiving a high degree of somatovisceral convergence (those in the medullary reticular formation--MRF) was targeted in order to examine the effect of infusing a chemical irritant into one organ on the responsiveness of convergent inputs from various visceral and somatic regions of the body, using electrophysiological techniques. Acute irritation of the urinary bladder (UB) with 2% acetic acid significantly decreased the percentage of convergent MRF neuronal responses to UB distention and urethral infusion and significantly increased the percentage responding to whole body, mainly due to stimulation of the face. Irritation also produced a significant increase in the response duration of MRF neurons to distention of colon as well as the bladder (for those few UB responses that still remained). These results indicate that a pelvic/visceral pathology confined to one organ can affect at least some of the convergent responses from other regions of the body. The findings suggest that MRF neurons contribute to the cross-talk between different regions of the body under both normal and pathological conditions.