DIFFUSE NOXIOUS INHIBITORY CONTROLS REDUCE THE EXPRESSION OF NOXIOUS STIMULUS-EVOKED FOS-LIKE IMMUNOREACTIVITY IN THE SUPERFICIAL AND DEEP LAMINAE OF THE RAT SPINAL-CORD

Behavioral and electrophysiological studies have shown that a noxious stimulus applied to one part of the body can reduce the response to a subsequent noxious stimulus elsewhere on the body. This phenomenon is referred to as diffuse noxious inhibitory controls (DNIC). In the pres ent study we used immunocytochemical labeling for the Fos protein prod uct of the c-fos proto-oncogene to determine the location of lumbar sp inal nociresponsive neurons that are inhibited by a spatially remote n oxious stimulus. Repetitive hindpaw pinch evoked pronounced Fos-like i mmunoreactivity in the superficial and deep laminae of the lumbar spin al cord. Placing the tail in 50-degrees-C water before each hindpaw pi nch significantly reduced Fos-like immunoreactivity in these regions. These data demonstrate that nociresponsive neurons in both the superfi cial and deep laminae of the spinal cord are sensitive to inhibition b y a spatially remote noxious conditioning stimulus.