The location of brainstem neurones tonically inhibiting dorsal horn neurones of the cat.

In an investigation of the origin of tonic descending inhibition of dorsal horn neurones by impulses in unmyelinated primary afferents, brainstem regions were electrolytically lesioned. With each neurone studied, tonic descending inhibition was measured before and after brainstem lesions by cooling a segment of spinal cord cephalic to the recording site. Such inhibition was not reduced by lesions of areas which, when stimulated, produce analgesia. These included the periaqueductal grey and the raphé areas of the midbrain and pons-medulla. Tonic descending inhibition was reduced by bilateral lesions of the ventrolateral caudal medulla in the region of the lateral reticular nuclei. Lateral reticular areas may have a functional role in the control of pain.