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The electrophysiological and pharmacological properties of the voltage-gated Ca2+ channels in MC3T3-E1 cells were analyzed using the perforated whole-cell patch-clamp technique. When the voltage was depolarized by step pulses from a holding potential of -104mV, the cells displayed transient inward currents (-4.25±0.25pA/pF, n=16) in 10mM Ba2+ solution. The activation threshold for the inward Ba2+current was about -60mV and the peak existed between -40 and -20mV. The steady state activation and inactivation properties of the inward Ba2+ current generated a window current in the range of -70 to -40 mV. Gd2+ (0.1mM) inhibited the inward Ba2+ currents by about 60%. Ni2+ (0.1mM, a blocker for T-type and R-type Ca2+ channels at this concentration), nifedipine (5μM, L-type Ca2+ channel blocker), ω-conotoxin GVIA (3μM, N-type Ca2+ channel blocker) and ω-agatoxin TK (200nM, a P/Q-type Ca2+ channel blocker) did not inhibit the currents. Bay K 8644 (0.5μM, a dihydropyridine agonist for L-type Ca2+ channel) also did not affect the Ba2+ currents. The results suggest that Ca2+ channels with novel properties are expressed in MC3T3-E1 cells.

本研究は人工ニューラルネットワークを用いて, ウサギの飲水時, ペレット咀嚼時, パン咀嚼時のそれぞれの下顎運動パタンの特徴を解析したものである。無麻酔, 無拘束下に導出されたウサギの摂食時咀嚼筋発火パタンをもとに, 3層パーセプトロン型の人工ニューラルネットワークをバックプロパゲーション学習法によって構築した。学習時には用いなかった咀嚼筋発火パタンに対するこのネットワークによる識別結果を調べ, 従来生理学的データ解析に用いられてきた, 発火タイミングや, 振幅を比較する解析方法と比較した。その結果, 咬筋活動からは従来の方法でも3種の下顎運動パタンを識別できたが, 人工ニューラルネットワークを用いると顎二腹筋活動からもそれぞれの下顎運動パタンを識別することが可能であった。それゆえ, 本手法が曖昧な情報を含む筋電図の解析に有用であることが明らかとなった。

無麻酔・無拘束下のウサギのリズミカルな咀嚼運動に対する嚥下の影響を調べた。咀嚼時と嚥下時に下顎運動軌跡と咬筋, 顎二腹筋, 甲状舌骨筋の筋電図を記録した。固形飼料の咀嚼運動中の嚥下の影響は5つのタイプに分類される。 (1) 嚥下が下顎運動の開口相に影響し休止期を示すもの (OPタイプ), (2) 閉口相に影響し休止期を示すもの (CLタイプ), (3) 閉口相と開口相の両方に影響し休止期を示すもの (CL/OPタイプ), (4) 閉口と開口の両相に対して影響しないもの (Non-influタイプ), (5) 不十分な閉口相を引き起こし, 長い休止期の後に開口相に移行させるもの (Pタイプ)。観察された嚥下の52%がOPタイプ, 26%がCLタイプ, 12%がCL/OPタイプで10%が他のタイプであった。CLタイプとCL/OPタイプでの閉口相の変調は, 固形飼料の咀嚼中歯根膜からの入力による咬筋活動の抑制に関与し, OPタイプとCL/OPタイプでの開口相の変調は, 咽頭性入力による顎二腹筋活動の抑制に関与すると結論できる。

To elucidate the effects of food consistency on chewing patterns, the electromyographic (EMG) activity of the masticatory muscles (masseter, digastric and mylohyoid) and jaw movement orbits were recorded in freely moving rabbits during chewing two foods with a different texture (bread and uncooked rice). When the hard food was tested, the burst duration of the masseter increased on both sides, but no significant differences in the burst duration were observed in either the digastric or mylohyoid muscles. The burst timings varied between the bread and rice chewings, especially in the offset time of bilateral masseter bursts and the onset time of mylohyoid bursts. The amplitudes of masseter and mylohyoid on both sides were obviously affected by food texture. Although the cycle time and fast closing time were consistent between the foods, the slow closing time during hard food chewing was significantly longer than that during soft food chewing. The results indicated that food consistency greatly influenced both amplitude andburst duration in the closer activities, but influenced neither amplitude nor burst duration in the digastric muscle as a primary jaw opener. In the case of mylohyoid muscle, the food texture affected the amplitude alone. This suggests an additional role of the muscle in tongue manipulations to that as a jaw opener.

The taste organ in the frog tongue is situated at the summit of the fungiform papilla. Morphologically, the frog taste organ is usually called the taste disk rather than taste bud. It comprises many taste cells which respond to various taste stimuli with depolarizing receptor potentials. There are many axon terminals at the base of the taste cell layer in the frog, and it has been found that there exists a chemical synapse between a frog taste cell and a gustatory axon terminal. It is considered that a depolarizing receptor potential in a taste cell elicited by a taste stimulus may release a transmitter from the cell, and then the postsynaptic potential in the axon terminal membrane evoked by the transmitter may trigger an initiation of gustatory neural impulses.Although it has been supposed that gustatory neural impulses may be initiated at the first node of Ranvier on the gustatory nerve fiber, obvious evidence has not been obtained until recently. In order to clarify the initiation site of gustatory neural impulse, it is important to examine the course of single gustatory nerve fibers within the fungiform papilla as giving attention to the spatial position of nodes of Ranvier.The purpose of the present experiment was to examine histologically the sensory innervation of the frog taste disk and to determine electrophysiologically the initiation site of gustatory neural impulses.