Abstract
Previous studies have shown that the jaw-opening reflex (JOR) is modulated during mastication. However in these studies, analyses have been carried out for limited period within the masticatory sequence (i.e. from food intake to just before swallow). Our aim is to study if the modulatory pattern of the JOR is consistent throughout the masticatory sequence in awake rabbits. The masticatory sequence was divided into three masticatory periods (preparatory, rhythmic-chewing and preswallow periods) based on the jaw movement patterns and the activity pattern of the jaw muscles. Electromyographic activity of the jaw-opening muscle (Digastric) and the jaw movement trajectories were recorded. Repetitive electrical stimulation (single pulse, 0.2 ms duration at a rate of 1 Hz, 1.2 times the threshold) of the inferior alveolar nerve was conducted before (for control response) and during mastication to evoke the JOR. The amplitude of the JOR was normalized to the control response and the modulatory pattern of the JOR was compared among the masticatory periods. The JOR was generally suppressed during the rhythmic-chewing and the preswallow periods; the suppressive effect was phasically weakened in the middle part of the jaw opening during the rhythmic-chewing period. On the other hand, the reflex was not only suppressed but also facilitated during the preparatory period. The results suggest that the modulatory pattern of the jaw-opening reflex is different among the masticatory periods. [Jpn J Physiol 55 Suppl:S172 (2005)]
