Defference in physiological and mophological properties between jaw-closing and opening motoneurons

用全细胞膜片钳记录新生大鼠脑干切片上的咬肌运动神经元(MaMN)和二腹运动神经元(DiMN)，研究张口型和闭口型运动神经元的放电特性。MaMns的输入电阻和膜时间常数均小于DiMns。MaMNS的尖峰后中时程后超极化(MAHP)波幅小于DiMNS，NaMNS的mAHP持续时间短于DiMNS。MaMns的mAHP尾电流衰减时间常数比DiMns的短。在apamin？-agatoxin IVA、？-芋螺毒素CV1a和Ni^&lt；2+&gt；存在的情况下，通过激活Ca^&lt；2+&gt；激活的K^+通道而产生mAHP的钙内流通过钙成像被监测。注入1-S电流脉冲诱发的放电频率(F)与膜去极化(V)关系的斜率在MaMN比DIMN更陡峭。F-V关系斜率与mAHP的幅度和持续时间相关，apamin可消除MaMns和DiMns之间f-V关系斜率的差异。我们的结论是，与DiMns相比，MaMN中较小和较短的mAHP导致f-V关系的斜率更陡峭。闭合和张口运动神经元的这种放电特性可能有助于将咀嚼驱动信号从咀嚼中枢模式产生器传导到适当的闭合和张口肌活动中。

Whole cell patch clamp recordings were made from masseter motoneurons (MaMNs) and digastric motoneurons (DiMNs) in neonatal rat brainstem slice preparations to study firing properties of jaw-closing and opening motoneurons. Input resistance and membrane time constant of MaMNs were smaller than those of DiMNs. Amplitude of the post-spike medium-duration afterhyperpolarization (mAHP) in MaMNs was smaller than that of DiMNs and duration of the mAHP in NaMNs was shorter than that of DiMNs. Decay time constant of the mAHP tail current in MaMNs was shorter than that in DiMNs. Ca^<2+> influx producing the mAHP through activation of Ca^<2+>-activated K^+ channel was monitored using Ca^<2+> imaging, in the presence of apamin ? -agatoxin IVA, ? -conotoxin CV1A and Ni^<2+>. The slope of the relationship between firing frequency (f) and membrane depolarization (V) induced by injection of 1-s current pulses was steeper in MaMNs than the slope in DiMNs. The slope of the f-V relationship were correlated with amplitude and duration of the mAHP and the difference in the slope of the f-V relationship between MaMNs and DiMNs was abolished by apamin. We conclude that smaller and shorter mAHP in MaMNs results in steeper slope of the the f-V relationship, compared with DiMNs. Such firing properties of jaw-closing and opening motoneurons might contribute to transduction of masticatory drive signal from central pattern generator of mastication to appropriate activities of jaw-closing and opening muscles.