Suppression of the jaw-opening reflex by periaqueductal gray stimulation is decreased by paramedian brainstem lesions.

Electrical stimulation of the midbrain periaqueductal gray region (PAG) suppresses the tooth pulp-evoked jaw-opening reflex (TP-JOR). In the present study the pathways that mediate this suppression were investigated by placing brainstem lesions in lightly anesthetized cats. Parasagittal lesions that interrupted the afferent and efferent connections of the medullary and pontine raphe nuclei attenuated (but did not abolish) suppression of the TP-JOR evoked by PAG stimulation. This result provides further evidence that medial brainstem structures partially mediate the effects of PAG stimulation in the trigeminal system.