Potentiation of thalamic responses to colorectal distension by visceral inflammation.

Responses of single viscerosensitive units in the ventral posterolateral (VPL) nucleus of the thalamus to cutaneous stimuli and graded colorectal distension (CRD) were recorded before and after colon inflammation by mustard oil (MO). The spontaneous firing rate increased around 25 min after the injection of MO. Responses to CRD obtained after this time increased significantly. In contrast, responses to cutaneous stimuli were attenuated and no substantial variations in the size of the cutaneous receptive fields were observed. A lesion of the dorsal column (DC) at T10 dramatically decreased the background activity and almost totally abolished the responses to CRD and to innocuous cutaneous stimuli but did not significantly affect the responses to noxious cutaneous pinch. These results indicate that colon inflammation potentiates thalamic responses to visceral stimuli while decreasing those to cutaneous stimuli.