PDF(Pubmed)
Abstract：
Increases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5 μ M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump-induced hyperpolarization, in response to falling intracellular [Na+].
摘要：
随着红外激光的应用，视神经轴突的电流阈值增加，其机制仅被部分理解。在孤立的大鼠视神经中，激光照射在电刺激部位附近，通过一个灵活的光纤。光的配对应用产生了阈值的增加，而在第二次应用中降低了阈值，随着延误的增加，响应恢复，时间常数为24秒。3分钟持续时间的单次激光照射引起阈值的快速增加，随后逐渐减弱，其时间常数在40到50秒之间。光照后有时会出现后遗症，其中休息阈值降低。阈值的增加被38.6mMLi+与5μM布美他尼的组合部分阻断，一种增加折射的动作，与轴突去极化一致。评估激光对神经输入阻力的影响排除了先前建议的髓鞘阻力下降，这有助于阈值变化。这些数据似乎与轴突膜电位一致，轴突膜电位部分依赖于温度依赖性电中性钠内流，对激光的响应衰减可能是由逐渐减少的Na泵浦引起的超极化引起的，响应于下降的细胞内[Na+]。
