Characterization of responses of primary somatosensory cerebral cortex neurons to noxious visceral stimulation in the rat.

In pentobarbital-anesthetized rats, responses of single neurons in primary somatosensory cortex (SI) to graded noxious visceral (colorectal distention, CRD) and cutaneous stimulation were recorded. One-hundred fifteen SI neurons were identified on the basis of spontaneous activity, 66 of which responded to CRD. CRD resulted in facilitation of neuronal activity in 33% and inhibition of activity in 52% of these cells. Fifteen percent had mixed facilitated/inhibited responses to varying CRD pressures. Cutaneous receptive fields were identified in 71% of CRD-responsive neurons, with low-threshold or wide dynamic range responses in most cases. Nearly all cutaneous receptive fields were small contralateral sites. Responses to CRD were independent of neuronal depth within the cortex. These data support a role of primary somatosensory cerebral cortical neurons in visceral nociception.