Cabanes C, Viana F, Belmonte C
Instituto de Neurociencias, Universidad Miguel Hernández-Consejo Superior de Investigaciones, 03550, San Juan Alicante, Spain.
J Neurophysiol. 2003 Oct;90(4):2219-31. doi: 10.1152/jn.00299.2003.
Intracellular recordings were employed to study the effects of temperature on membrane properties and excitability in sensory neurons of the intact guinea pig trigeminal ganglion (TG) maintained in vitro. Neurons were classified according to the shape and duration of the action potential into F (short-duration, fast spike) and S (long duration, slow spike with a "hump") types. Most type F (33/34) neurons had axons with conduction velocities >1.5 m/s, while only 30% (6/23) of type S neurons reached these conduction speeds suggesting differences in myelination. Cooling reduced axonal conduction velocity and prolonged spike duration in both neuronal types. In F-type neurons with strong inward rectification. cooling also increased the excitability, augmenting the input resistance and reducing the current firing threshold. These effects were not observed in S-type neurons lacking inward rectification. In striking contrast to results obtained in cultured TG neurons, cooling or menthol did not induce firing in recordings from the acutely isolated ganglion. However, after application of submillimolar concentrations (100 microM) of the potassium channel blocker 4-aminopyridine (4-AP), 29% previously unresponsive neurons developed cold sensitivity. An additional 31% developed ongoing activity that was sensitive to temperature. Only neurons with strong inward rectification (mostly F-type) became thermosensitive. Cooling- and 4-AP-evoked firing were insensitive to intracellular application of 4-AP or somatic membrane hyperpolarization, suggesting that their action was most prominent at the level of the axon. The lack of excitatory actions of low temperature in the excised intact ganglion contrasts with the impulse discharges induced by cooling in trigeminal nerve terminals of the same species, suggesting a critical difference between cold-transduction mechanisms at the level of the nerve terminals and the soma.
采用细胞内记录法，研究温度对体外培养的完整豚鼠三叉神经节（TG）感觉神经元膜特性和兴奋性的影响。根据动作电位的形状和持续时间，将神经元分为F（短持续时间、快速锋电位）型和S（长持续时间、带有“驼峰”的慢锋电位）型。大多数F型（33/34）神经元的轴突传导速度>1.5 m/s，而只有30%（6/23）的S型神经元达到这些传导速度，这表明髓鞘形成存在差异。冷却降低了两种神经元类型的轴突传导速度，并延长了锋电位持续时间。在具有强内向整流的F型神经元中，冷却还增加了兴奋性，提高了输入电阻并降低了电流发放阈值。在缺乏内向整流的S型神经元中未观察到这些效应。与培养的TG神经元中获得的结果形成鲜明对比的是，冷却或薄荷醇在急性分离的神经节记录中未诱导发放。然而，在应用亚毫摩尔浓度（100 microM）的钾通道阻滞剂4-氨基吡啶（4-AP）后，29%先前无反应的神经元产生了冷敏感性。另外31%的神经元产生了对温度敏感的持续活动。只有具有强内向整流的神经元（大多为F型）变得对温度敏感。冷却和4-AP诱发的发放对细胞内应用4-AP或体细胞超极化不敏感，这表明它们的作用在轴突水平最为突出。在切除后的完整神经节中低温缺乏兴奋作用，这与同一物种三叉神经末梢冷却诱导的冲动发放形成对比，表明神经末梢和胞体水平的冷转导机制存在关键差异。
