学位研究紹介

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学 位 研 究 紹 介

Comparison of the modulatory
effects on the jaw-opening reflex
among the different periods ofmastication in awake rabbits
覚醒下ウサギを用いた異なる咀嚼周期における開口反射の変調様式の検討
Division of Oral Physiology, Department of Oral BiologicalSciences, Niigata University

electrodes were implanted bilaterally on masseter anddigastric muscles. To record jaw movements, a small
cylindrical magnet and a jaw-tracking system consistsof two magnet sensors was fixed in the chin and head,respectively. To stimulate the IAN, a pair of custommade bipolar electrodes was bilaterally inserted into
the mental foramina.
To elucidate the modulatory effect, each chewing
cycle was divided into the jaw-closing (CL) and jawopening (OP) phases for preparatory period, the fast-Graduate School of Medical and Dental Sciences

closing (FC), slow-closing (SC), slow-opening (SO) andRahman Md Mostafeezur

fast-opening (FO) phases for rhythmic-chewing period

新潟大学大学院医歯学総合研究科

口腔生命科学専攻

摂食環境制御学講座

ラーマン

口腔生理学分野

モスタフィーズ

and CL, SO and FO phases for preswallow period.
To test effects of mastication on the JOR, amplitude(peak to peak) of the reflexly evoked EMG activity ofthe digastric muscle was measured and the values
were compared among the masticatory periods andbetween the chewing and non-chewing sides.

３．
Results

１．Introduction
The jaw-opening reflex (JOR) is reported to be

The JOR evoked either in the chewing or non-strongly suppressed in the jaw-closing phase thanchewing side was modulated during mastication. The

those in the jaw-opening phase only during rhythmic

modulatory pattern on the JOR was different amongchewing.

the masticatory periods. First, the JOR was not

However, the entire masticatory sequence (i.e., frommodulated in a phase-linked manner during thefood intake to just before swallow) has three

preparatory period. In addition, the modulatory effectfunctionally different masticatory periods (preparatory,

was variable (strong suppression to weak facilitation).

rhythmic-chewing and preswallow periods). Therefore,Different from the preparatory period, the JOR was

one of the aims of the study is to investigate thegenerally suppressed in a phase-linked manner during

modulatory pattern of the JOR in relation to thethe rhythmic-chewing period: the suppressive effect onphases of the chewing cycle during each of thethe JOR was less in the FO phase. The suppression ofmasticatory periods.

the JOR during this period was significant in the FC

In addition, the modulatory effects on the JOR
during mastication were investigated only for theand SC phases and the SO phase for both the chewing
and non-chewing sides.

chewing side. Therefore, the other aim of the study isLike the rhythmic-chewing period, the JOR wasto investigate if the JOR evoked in the non-chewing

suppressed in a phase-linked manner during theside is modulated in a same manner as that in thepreswallow period. Except for the FO phase in thechewing side during mastication.

chewing side, the suppressive effect was significant
throughout the chewing cycle during this period.

２．Experimental procedure

When the modulatory effect on the JOR for each of
the jaw-closing and jaw-opening phases was compared

The experiments were carried out on 10 rabbits. To

among the masticatory periods, several significant

record the EMG, teflon-coated stainless-steel wiredifferences were noted both in the chewing and non-－ 65 －66

新潟歯学会誌

chewing sides. However, the JOR evoked in thechewing side and that in the non-chewing side wereequally modulated throughout the masticatory

39
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not correlate with digastric activity.

Reference

sequence (Fig. 1).
Mostafeezur R, Yamamura K, Kurose M, Yamada Y :４．Discussion

Mastication-induced modulation of the jaw-openingreflex during different periods of mastication in awake

4.1 Modulation of the JOR during each of therabbits. Brain Res, 1254: 28-37, 2009.

masticatory period
To explain the variability in the modulatory effectduring the preparatory period, movement-generated
sensory inputs and descending inputs from the central
nervous system is considered. For the former, theinteraction of movement-generated sensory inputs andthe sensory inputs induced by the IAN stimulation
may produce either facilitatory or suppressive effects
on the JOR. For the latter, stimulation of the lingual
nerve projection locus of the cortex may produce
facilitatory effects on the JOR, whereas the stimulation
IAN projection locus may produce suppressive effects
on the JOR.
During rhythmic-chewing period, the JOR wasgenerally suppressed in a phase-linked manner.
However, the modulatory effect in the FO phase wasmore variable during cortically-induced rhythmic jaw
movements than our present findings. This, large
variability in the modulatory effects in the FO phase
may be due to the differences in the excitability of thedigastric motoneurons.
During preswallow period, the attenuation in theFig. 1
The modulatory pattern of the JOR for both the chewing
and non-chewing sides. The abscissa represents thechewing phases. The mean amplitude of the JOR isexpressed on the ordinates. (※): the amplitude of the JOR
was significantly lower than the control. (†): the amplitudeof the JOR on chewing side was significantly different
among the masticatory periods ($): the amplitude of the JOR
on non-chewing side was significantly different among themasticatory periods

suppressive effects was not prominent like therhythmic-chewing period, since the digastric activity
was smaller during preswallow period.
4. 2. Modulatory pattern of the JOR in the chewing
side and non-chewing side
The modulatory pattern of the JOR was consistent
between the chewing and non-chewing sides, although
movement-generated sensory inputs may be different
between the sides during the rhythmic-chewing andpreswallow periods. Considering this, the digastricmotoneuronal excitability and descending inputs fromthe cortex may be responsible for such modulatory
pattern of the JOR.
In case of the preparatory period, the movementgenerated sensory inputs and descending inputs fromthe cerebral cortex is considered to be responsible forthe modulation of the JOR, since the modulation does
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