ABSTRACT
The cord dorsum potential evoked by stimulation in the ventrolateral aspect of periaqueductal grey (PAG-CDP) was recorded from the dorsal surface of the spinal lumbosacral cord in rats. PAG stimulation with the same parameters as for producing PAG-CDP inhibited the C discharges of convergent neurons in spinal dorsal horn. There was a positive correlation between the time course of the inhibitory effect of PAG on convergent neurons and the duration of the slow wave of PAG-CDP. a positive correlation also presented between the latencies of the PAG inhibition and the slow wave. Furthermore, the PAG inhibition did not appear when the intensity of PAG stimulation was below the threshold of PAG-CDP. These results indicate that the presynaptic inhibition is involved in the PAG inhibition of the C discharges of convergent neurons in spinal dorsal horn.