A comparative study of selective stimulation of raphe nuclei in the cat in inhibiting dorsal horn neuron responses to noxious stimulation.

Consistent inhibition of cord nociceptive neurons was obtained at low levels of stimulation (5 V or 50-100 micro A) within raphe magnus. Less consistently and with higher stimulus intensities, inhibition was observed on stimulating raphe pallidus. Still less frequently, and generally only with stimulation in the 20 V or 500 micro A range, inhibition was observed in raphe dorsalis, raphe obscurus and centralis superior. No inhibition could be obtained by stimulation in linearis intermedias or linearis rostralis. Nearly all midline sites where inhibition of cord nociceptive neurons was observed were those within or in immediate proximity to raphe nuclei.