Evidence that inhibition of a nociceptive flexion reflex by stimulation in the rostroventromedial medulla in rats occurs at a premotoneuronal level.

The amplitude of the hamstring monosynaptic reflex was measured before and during stimulation of the rostroventromedial medulla (RVM) in the lightly anaesthetized rat. The RVM was stimulated at currents sufficient to completely inhibit a paw withdrawal reflex evoked by noxious heat. At these currents, RVM stimulation produced no significant change in monosynaptic reflex amplitude, evidence that inhibition occurs at a premotoneuronal level.