OBJECTIVES: To determine the effects of somatic stimulation, including noxious chemical stimulation of interspinous tissues, on bladder motility in the anesthetized rat.

METHODS: Changes in pressure in the previously quiescent bladder were measured in anesthetized adult female Wistar rats after various forms of noxious and innocuous somatic stimulation, including injection of the thoracic and lumbar interspinous tissues with capsaicin. Measurements were taken in both central nervous system-intact and spinalized animals, as well as in animals in whom the pelvic nerves had been transected bilaterally. Changes in bladder pressure were also measured in response to electrical stimulation of the primary dorsal ramus of lumbar spinal nerves.

RESULTS: Noxious and innocuous stimulation of the fore- and hindpaws and the skin overlying the sacrum generally failed to elicit discernible changes in bladder pressure. However, capsaicin injection of thoracic and lumbar interspinous tissues produced profound and long-lasting increases in bladder pressure. There were no significant differences in the responses to thoracic, as opposed to lumbar, stimulation. Spinalization above the level of stimulation abolished the response to capsaicin injection, as did bilateral transection of the pelvic nerves.

CONCLUSION: In general, pressure in the quiescent bladder was relatively insensitive to somatic stimulation. However, noxious chemical stimulation of the interspinous tissues produced a nonsegmentally organized, supraspinal, parasympathetically mediated reflex increase in bladder tone.

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