Differential labeling of the vestibular complex following unilateral injections of horseradish peroxidase into the cat and rat locus coeruleus

In anaesthetized cats, lumbar dorsal horn neurons were excited by brief noxious radiant heating of glabrous hindpaw skin. These nociceptive responses were inhibited by concomitant repetitive electrical stimulation of the ipsilateral deep radial nerve. Noxious heat responses were linearly correlated with skin temperature during heating. The slope of this stimulus-response function was decreased, and the response threshold increased, by deep radial nerve stimulation. Microinjection of lidocaine into the medullary raphe attenuated the inhibition induced by deep radial nerve stimulation. The results indicate that in the cat, ‘diffuse noxious inhibitory controls’ (DNIC) involve medial medullary regions.