Colorectal distension-induced suppression of a nociceptive somatic reflex response in the rat: modulation by tissue injury or inflammation.

Inhibition of somatic nociception by conditioning noxious visceral stimulation was studied under pathophysiological conditions in rats. Viscero-somatic inhibition was enhanced following visceral inflammation and reduced by a somatic heat injury. The enhancement was reversed by an N-methyl-D-aspartate (NMDA) receptor antagonist. These changes in viscero-somatic inhibition may be explained by corresponding changes in excitatory drives evoked by conditioning and test stimulation, although disinhibition may contribute to reduction of inhibition following somatic injury.