Intradermal capsaicin inhibits lumbar dorsal horn neuronal responses to colorectal distention

Abstract

The purpose of this study was to examine the effect of cutaneous inflammation on the responses of viscerosomatic convergent dorsal horn neurons to graded colorectal distension (CRD) and cutaneous mechanical stimulation. Responses of single viscerosomatic neurons in the lumbar dorsal horn of the rat spinal cord to CRD and to cutaneous stimuli were recorded before and 50 min after cutaneous inflammation induced by intradermal injection of capsaicin in the receptive field (RF) or in the ipsilateral and contralateral forepaw. Capsaicin injection in the RF induced an increase in the spontaneous activity of dorsal horn neurons, an expansion in the size of their RF and facilitated their responses to cutaneous stimuli. An injection placed in the center of the RF attenuated the responses to noxious CRD. Capsaicin injection in the forepaw caused a significant decrease in the responses to CRD but not to cutaneous stimuli. These results indicate that the inhibitory effects, evoked by cutaneous inflammation, can modulate the responses of dorsal horn neurons to CRD, independent of its effect on the responses to cutaneous mechanical stimuli.