Abstract
Effects of mastication on the jaw-opening reflex (JOR) were studied in awake rabbits. The JOR was evoked by unilateral low-intensity electrical stimulation of the inferior alveolar nerve either chewing or non-chewing side before (control) and during mastication. The entire masticatory sequence (from food intake to just before swallow) was divided into three functionally different masticatory periods (preparatory, rhythmic-chewing and preswallow periods) based on the jaw movements and the related activity pattern of the jaw muscles, and each chewing cycle in each period was further divided into jaw-closing and jaw-opening phases. Then amplitude of the JOR was compared 1) among the masticatory periods and 2) between the stimulation sides (i.e. chewing or non-chewing sides). Overall, the JOR was suppressed during mastication. Although the suppressive effect on the JOR did not differ between the stimulation sides, considerable differences were noted in the suppressive effect among the masticatory periods. During rhythmic-chewing and preswallow periods, the JOR was strongly suppressed in the jaw-closing phase (8 to 20% of the control), but the suppressive effect was phasically weakened (30 to 61% of the control) in the late part of the jaw-opening phase. On the other hand, such phase-dependent fluctuation in the suppressive effect was not observed during the preparatory period. The findings suggest that neural mechanisms modulating the JOR during the preparatory period may be different from other masticatory periods. [J Physiol Sci. 2006;56 Suppl:S189]
