Journal of neurophysiology
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1. The inhibitory effects of electrical stimulation in midbrain periaqueductal gray (PAG) and lateral reticular formation (LRF) on spinal dorsal horn neuronal responses to noxious skin heating were investigated in cats anesthetized with Nembutal and N2O. 2. Thirty-one dorsal horn units driven by electrical stimulation of the posterior tibial and/or superficial peroneal nerves at A- and C-fiber strength responded to noxious radiant heating (e.g., 50 degrees C) of the skin of the hindpaw. ⋯ In contrast, repetition of the heating series during LRF stimulation produced a parallel rightward shift in the linear temperature-response curve, with commensurate increase in response threshold. 6. The results indicate that functionally separate descending inhibitory systems are activated by stimulation of PAG and LRF. Possible inhibitory mechanisms and the functional significance of descending inhibition from PAG and LRF are discussed.