Suppression of the nociceptive jaw-opening reflex by stimulation of the red nucleus

We studied the effect of stimulation of the red nucleus (RN) on the jaw-opening reflex (JOR) in anesthetized rats. The JOR was evoked by electrical stimulation of the tooth pulp of a lower incisor, and was recorded as the electromyographic responses of the anterior belly of the digastric muscle, bilaterally. Conditioning electrical stimulation of the RN was found to suppress the JOR bilaterally. Microinjection of monosodium glutamate into the RN also suppressed the JOR bilaterally. The suppressive effect of the magnocellular part of the RN was significantly larger than that of the parvicellular part of the RN. These results imply that the RN is involved in control of the JOR evoked by noxious stimulus.

► The jaw-opening reflex was evoked by stimulation of the tooth pulp.
► Electrical stimulation of the red nucleus suppressed the jaw-opening reflex.
► Injection of glutamate into the red nucleus also suppressed the jaw-opening reflex.
► Suppression by magnocellular part was larger than that by parvicellular part.
► The red nucleus may be involved in coordinating the motor response to pain.