Lesions of the mid-spinal trigeminal complex are effective in producing perioral thermal hypoalgesia

The hypoalgesic effects of lesions in the rat spinal trigeminal complex at the levels of subnucleus interpolaris and caudal subnucleus oralis were investigated. Lesions of the trigeminal tract, nucleus, or adjacent reticular formation resulted in significant elevations in escape latencies to noxious thermal stimulation of the ipsilateral perioral area. The nuclear lesions were significantly more effective in producing latency elevations than were the reticular formation lesions. Behavioral and anatomical evidence is presented suggesting that the mid-spinal trigeminal complex, including the ascending trigeminal intranuclear pathways, participate in perioral thermal nociception.