Characterization of Thalamic Neuronal Responses to Urinary Bladder Distention, Including the Effect of Acute Spinal Lesions in the Rat

Chronic visceral pain has proved to be difficult to treat. This study characterized urinary bladder distention (UBD)–evoked responses of neurons located within the ventrobasal group of the thalamus. Units were also characterized for responses to cutaneous stimuli and colorectal distention (CRD). In addition, the effects of spinal lesions on UBD-evoked responses were examined in a subset of neurons. After a stable response to UBD was established, 3 sequential lesions of the spinal cord at the mid-cervical level were performed, and responses to UBD were determined 1 and 5 minutes later. A majority of the neurons in the ventrobasal group of the thalamus were excited by UBD, demonstrated graded responses to graded distention pressures, and responded to cutaneous stimulation. No correlation between the magnitude of the responses of thalamic neurons to UBD and CRD was found. UBD-evoked thalamic neuronal activity was significantly attenuated after dorsal midline lesions of the spinal cord. The present study is a quantitative description of ventrobasal thalamic neuronal responses to UBD in the rat and provides direct neurophysiologic evidence that nociceptive information from the urinary bladder to the ventrobasal group of the thalamus ascends via a dorsal midline pathway.PerspectiveThe effect of dorsal midline lesions is of profound clinical interest because it points to a potential treatment for urinary bladder pain, such as that which is characteristic of interstitial cystitis. Further research might reveal pharmacologic approaches to modulate this pain pathway and result in novel treatments for interstitial cystitis.