Responses of neurons in ventrolateral orbital cortex to noxious visceral stimulation in the rat.

In pentobarbital-anesthetized rats, responses of single neurons in ventrolateral orbital cortex (VLO) to noxious visceral (colorectal distension, CRD) and cutaneous stimulation were recorded. Of 71 neurons identified on the basis of spontaneous activity, 44 responded to CRD. CRD caused inhibition of neuronal activity in 38, facilitation of activity in four and 'mixed' responses in two of these cells. Cutaneous receptive fields were identified in 31 CRD-responsive and 10 CRD-non-responsive neurons. Cutaneous receptive fields were large and bilateral. 25 CRD-responsive cells responded only to noxious cutaneous stimulation, six had wide dynamic range responses. Six CRD-non-responsive cells responded only to noxious stimuli, four had wide dynamic range responses. No VLO neuron responded only to innocuous stimuli. These data are consistent with involvement of VLO in visceral nociception, possibly in non-discriminative aspects of nociception.