Electrical stimulation in the medullary nucleus raphe magnus inhibits noxious heat-evoked fos protein-like immunoreactivity in the rat lumbar spinal cord.

Noxious heat applied to the footpad evokes the expression of fos protein-like immunoreactivity in the rat spinal cord lumbar dorsal horn. Electrical stimulation in the medullary nucleus raphe magnus (NRM) while not evoking fos-like immunoreactivity itself, reduced significantly the number of neurons (to 50% of control) in the dorsal horn demonstrating fos protein-like immunoreactivity in response to noxious heating of the footpad. Thus descending projections from the medullary NRM appear to have direct inhibitory effects on dorsal horn neurons that receive nociceptive input from cutaneous thermal nociceptors.