Vigor of visceromotor responses to urinary bladder distension in rats increases with repeated trials and stimulus intensity.

This methodological study characterized visceromotor responses (VMRs) as abdominal contractile responses to urinary bladder distension (UBD) in the female rat. Electromyographic activity of the abdominal musculature was used as a measure of the VMR. Similar to previously characterized cardiovascular responses to UBD, VMRs to UBD demonstrated an initial sensitization period whereby repeated presentation of UBD stimuli led to increase vigor of the VMR. Graded UBD produced graded VMRs, therefore stimulus-response functions could be constructed. The intravenous administration of the opioid fentanyl produced a reduced vigor of the VMR in a fashion consistent with its analgesic effect. The present report supports the utility of this model for studies of urinary bladder nociception.