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

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Abstract
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 present study we used immunocytochemical labeling for the Fos protein product of the c-fos proto-oncogene to determine the location of lumbar spinal nociresponsive neurons that are inhibited by a spatially remote noxious stimulus. Repetitive hindpaw pinch evoked pronounced Fos-like immunoreactivity in the superficial and deep laminae of the lumbar spinal cord. Placing the tail in 50°C water before each hindpaw pinch significantly reduced Fos-like immunoreactivity in these regions. These data demonstrate that nociresponsive neurons in both the superficial and deep laminae of the spinal cord are sensitive to inhibition by a spatially remote noxious conditioning stimulus.