Diffuse noxious inhibitory controls (DNIC) involve trigeminothalamic and spinothalamic neurones in the rat.

Fifty-eight lumbar dorsal horn and trigeminal nucleus caudalis neurones which could be activated by both innocuous and noxious peripheral stimuli have been recorded in the anaesthetized rat. Using transcutaneous electrical stimulation to produce A and C fibre activity in these neurones from the hindpaw or facial receptive fields the ability of a distant noxious (mechanical or thermal) stimulus applied to the nose, tail, ears and paws to inhibit the neuronal activity was demonstrated. These effects have been termed diffuse noxious inhibitory controls (DNIC). DNIC produced powerful long-lasting inhibitions on all units studied in accordance with our previous results. Approximately 40% of these convergent neurones could be antidromically activated from the contralateral ventrobasal thalamus. Similar neuronal characteristics, effects of DNIC and proportions of projection cells were found in both the dorsal horn and trigeminal complex. However, the spinothalamic tract cells conducted more rapidly than the trigeminothalamic neurones. These results indicate that DNIC can produce comparable effects on the thalamic representation of the efferent activity of these spinal cord and trigeminal neurones. The possible role of DNIC in nociception is discussed.