[Effect of stimulating midbrain periaqueductal gray on the electrical response of somatosensory cortex to C-fiber input in cats].

The electrical responses of the somatosensory cortex (C-CEP) and spinal cord (C-SSP) to C-fiber inputs could be markedly inhibited by stimulating the periaqueductal gray (PAG), and the inhibition on C-CEP was greater than that on C-SSP. After application of cyproheptadine on the dorsal surface of the spinal cord, PAG stimulation could still inhibit C-CEP, but not C-SSP. It was suggested that PAG might inhibit C-CEP through ascending as well as descending pathways. After blocking the descending inhibitory pathway by cyproheptadine i.v. injection, cyproheptadine and naloxone could antagonize the inhibitory effect of PAG stimulation on C-CEP, indicating that endogenous opiate-like substance and serotonin might play an important role in the transmission of the ascending inhibitory pathways from PAG.