そしゃく運動中の延髄網様体ニューロンの活動様式 下あご運動およびそしゃく筋筋電図との相関

Abstract

Inhibitory premotor neurons projecting to the jaw closer motoneurons (IM neurons) and excitatory premotor neurons projecting to the jaw opener motoneurons (ED neurons) in the bulbar reticular formation were shown to be involved in the inhibition of the jaw closer motoneurons and the excitation of the jaw opener motoneurons during the jaw-opening phase of the cortically induced masticatory rhythm in the immobilized cats. The present study analyzed the role of these bulbar reticular neurons in the control of the natural masticatory jaw movements during food ingestion in the chronically prepared unanesthetized cats. The single unit activity was recorded from 40 bulbar reticular neurons which modulated the firing frequency in the same rhythm as the masticatory jaw movement. Thirty-four neurons showed a burst during the jaw-opening phase (opening type), while the remaining 6 neurons showed a burst during the jaw-closing phase (closing type) . By averaging the full-rectified EMG of the masticatory muscle by the spikes of the reticular neurons, 4 neurons were found to be the IM neurons and the other 4 neurons the ED neurons. All these premotor neurons belonged to the opening type. A posi tive correlation was found between 1) the instantaneous firing frequency (IFF) and the velocity of the jaw movements in 4 of 6 opening type neurons (2 of 3 IM neurons and 2 of 3 ED neurons) and in 3 of the 6 closing type neurons, 2) the IFF and the jaw displacement in 3 of the 6 opening type neurons (2 of 3 IM neurons and 1 of 3 ED neurons) and in 2 of the 6 closing type neurons, 3) the number of spikes in a burst and the duration of the jaw-opening phase or the jawclosing phase as well as the maximum displacement and/or velocity of the jaw movement in 16 tested neurons and 4) the maximum firing frequency and the maximum displacement and/or velocity of jaw movement in the 16 tested neurons. It was concluded that the bulbar reticular neurons were involved in the control of the velocity and displacement of ja movement during mastication by modulating the firing frequency and the number of spikes in a burst.