Presynaptic inhibition of tooth pulp afferents in the trigeminal nucleus during REM sleep

In order to find whether presynaptic inhibition of tooth pulp afferents is enhanced in any phase of sleep or wakefulness, the orthodromic mass response of the trigeminal nucleus to electrical stimulation of the ipsilateral tooth pulp and the antidromic mass response of the tooth pulp to stimulation of the trigeminal nucleus were recorded in the cat. Both responses were stable in amplitude during different phases of sleep and wakefulness. However, attenuation of the orthodromic response and augmentation of the antidromic one were sometimes observed during the burst of rapid eye movements during paradoxical sleep, suggesting that presynaptic inhibition is massively enhanced only on those occasions.