Department of Neuroscience & Oral Physiology, Osaka University Graduate School of Dentistry,Yamadaoka, Suita, Osaka, Japan.
Prog Brain Res. 2010;187:163-71. doi: 10.1016/B978-0-444-53613-6.00011-3.
The slow-closing phase of the mastication cycle plays a major role in the mastication of foods. However, the neuronal mechanism underlying the slow-closing phase remains unknown. The isometric contraction of jaw-closing muscles is developed through the recruitment of jaw-closing motoneurons during the slow-closing phase. It is well established that motor units are recruited depending on the order of sizes or input resistances (IRs) of motoneurons, which is known as the size principle. Two-pore-domain acid-sensitive K(+) (TASK1/3) channels are recently found to be the molecular correlates of the IR, and also found to be expressed in the masseter motoneurons. Here, we addressed the question whether spindle Ia inputs onto masseter motoneurons can induce the orderly recruitment of motoneurons in slice preparations of the rat brain using voltage-sensitive dye imaging and whole-cell patch-clamp methods. Voltage-sensitive dye imaging revealed the recruitment of many motoneurons in the whole nucleus of masseter in response to repetitive stimulation of the presumed spindle Ia inputs. Dual whole-cell recordings obtained from two adjacent motoneurons revealed the IR-ordered recruitment of motoneurons in response to repetitive stimulation of the presumed spindle Ia inputs. Thus, Ia inputs are likely to play a crucial role in the orderly recruitment of motoneurons of the trigeminal motor nucleus, which would be progressed during the slow-closing phase of the mastication cycle. Possible involvements of TASK channels in the orderly recruitment are discussed.
咀嚼周期的慢速关闭阶段在食物咀嚼中起着重要作用。然而，慢速关闭阶段的神经机制尚不清楚。在慢速关闭阶段，通过招募闭口运动神经元来发展闭口肌肉的等长收缩。众所周知，运动单位是根据运动神经元的大小或输入电阻（IR）的顺序招募的，这被称为大小原则。最近发现双孔域酸敏感 K(+) (TASK1/3) 通道是 IR 的分子相关物，并且也在咀嚼肌运动神经元中表达。在这里，我们使用电压敏感染料成像和全细胞膜片钳方法在大鼠脑切片中解决了 spindle Ia 输入是否可以诱导咀嚼肌运动神经元有序募集的问题。电压敏感染料成像显示，在对假定的 spindle Ia 输入进行重复刺激时，许多运动神经元在整个咀嚼肌核中被募集。从两个相邻运动神经元获得的双全细胞记录显示，在对假定的 spindle Ia 输入进行重复刺激时，运动神经元按 IR 顺序募集。因此，Ia 输入可能在咀嚼周期的慢速关闭阶段中对三叉运动核运动神经元的有序募集起着至关重要的作用。讨论了 TASK 通道在有序募集中的可能参与。
