[Inhibition of nociceptive responses of spinal dorsal horn neurons by periaqueductal gray stimulation (author's transl)].
In order to analyze analgesic effects of periaqueductal gray stimulation, experiments were carried out in nitrous oxide anesthetized cats. Spinal dorsal horn neurons receiving C-fiber inputs from the posterior tibial and/or superficial peroneal nerves were excited by noxious heat stimulation of the ipsilateral hindpaw. The evoked spike discharges were inhibited by repetitive stimulation of the periaqueductal gray at currents 300--900 microamperemeter. Effective sites for inhibition were distributed throughout the ventral half of the periaqueductal gray bilaterally. A monotonous relationship was found between stimulus intensity (skin temperature) and number of spike discharges; As predicted by Stevens' law, the number of spike discharges psi grew as a power function: psi = K(psi--psi0)beta where psi is the stimulus intensity, psi0 is the effective threshold, and K is a slope constant of the spike discharges versus stimulus intensity curve depending upon neurons. The exponent beta was approximately 1.0. The periaqueductal gray stimulation resulted in a decrease in the slope constant kappa, without alteration either in the threshold constant psi0 or in the exponent beta.
D000200:Action Potentials; D000818:Animals; D002415:Cats; D004558:Electric Stimulation; D006358:Hot Temperature; D008636:Mesencephalon / Q000502:physiology*; D009433:Neural Inhibition; D009619:Nociceptors / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*