The role of dorsal columns pathway in visceral pain.

Traditionally, the dorsal column-medial lemniscus system has been viewed as a pathway not involved in pain perception. However, recent clinical and experimental studies have provided compelling evidence that implicates an important role of the dorsal column pathway in relaying visceral nociceptive information. Several clinical studies have shown that a small lesion that interrupts fibers of the dorsal columns (DC) that ascend close to the midline of the spinal cord significantly relieves pain and decreases analgesic requirements in patients suffering from cancer originating in visceral organs. Behavioral, electrophysiological and immunohistochemical methods used under experimental situations in animals showed that DC lesion lead to decreased activation of thalamic and gracile neurons by visceral stimuli, suppressed inhibition of exploratory activity induced by visceral noxious stimulation and prevented potentiation of visceromotor reflex evoked by colorectal distention under inflammatory conditions. Whereas the surgical lesion of the DC tract has proven to be clinically successful, a pharmacological approach would be a better strategy to block this pathway and thus to improve visceral pain conditions under less dramatic circumstances than cancer pain. Our finding that PSDC neurons start to express receptors for substance P after colon inflammation suggests new targets for the development of pharmacological strategies for the control of visceral pain.