Spinal neurophysiologic correlates of the analgesic actions of intravesical dimethyl sulfoxide and capsaicin in the rat.

Peripheral analgesia produced by the intravesical instillation of dimethyl sulphoxide (DMSO) and capsaicin has been used to treat visceral pain originating in the urinary bladder. The present study sought to determine the neurophysiologic consequences of the intravesical instillation of these compounds by measuring spinal neuronal responses evoked by urinary bladder distension (UBD) in the rat. Subjects were spinally transected, decerebrate female Sprague-Dawley rats. The effect of 0.5 mL of solution of 10% or 50% DMSO, 100 micromol/L capsaicin, or the same volume of saline instilled into the bladder on excitatory neuronal responses to UBD was studied by using single-unit extracellular recordings of L6-S2 dorsal horn spinal cord neurons. Fifty-six dorsal horn neurons that were excited by UBD in a graded fashion were identified. All neurons were also excited by noxious or non-noxious cutaneous stimuli. Two hours after intravesical instillation, solutions of 50% DMSO or 100 micromol/L of capsaicin produced a reduction of the slope of stimulus-response functions for neuronal activity evoked by graded UBD. These data support a local effect of intravesical 50% DMSO or capsaicin and suggest the use of this model to study novel peripheral treatment strategies for bladder pain.