Inhibition of the spinal transmission of nociceptive information by supraspinal stimulation in the cat

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Abstract
In cats anesthetized with .alpha.-chloralose or sodium pentobarbitone a study was made of the effects of supraspinal electrical stimulation on the excitation of dorsal horn neurones by noxious and non-noxious cutaneous stimuli. Stimulation near the dorsal raphe of the midbrain non-selectively reduced the responses of neurons to both noxious and non-noxious stimuli. I.v. naloxone (0.3-0.6 mg/kg) had no effect on this inhibition. Electrical stimulation near the medullary raphe selectively reduced the excitation of dorsal horn neurons by noxious cutaneous stimuli. Excitation of neurons by deflection of hairs was unaffected. The inhibition of nociceptive responses outlasted the period of raphe stimulation by up to 6 min. I.v. naloxone (0.6-1.0 mg/kg) also failed to affect this selective inhibition.