Inhibitory effect of entopeduncular nucleus on the jaw-opening reflex induced by the tooth pulp stimulation

The effect of stimulation of the entopeduncular nucleus (EP) on the jaw-opening reflex (JOR) was studied in the cat anesthetized with sodium pentobarbital. JOR was quantified by the digastric electromyogram. The conditioning stimulation (train of 33 pulses at 330 Hz, 0.5 ms duration, 50-400 microA) of the EP powerfully inhibited the JOR induced by the tooth pulp stimulation. Conditioning stimulation with 300 microA produced inhibition which continued approximately 400 ms from the cessation of the stimulation. The injection of monosodium glutamate into EP elicited inhibition of the JOR that lasted about 15 min. Additionally, the conditioning stimulation inhibited the JOR induced by the stimulation of trigeminal rostral and caudal nuclei in a similar manner but not jaw-opening response induced by the stimulation of the trigeminal motor nucleus. Therefore, it is possible that the excitation of the EP exerts inhibitory modulation of JOR at the motor nucleus rather than the trigeminal sensory nucleus.