Gilly William F, Teal P, Graves Edward E, Lo Jackei, Schneider M Bret, Zasio Reese, Adler John R
Biology, Hopkins Marine Station, Stanford University, Pacific Grove, USA.
Radiation Oncology, Stanford University School of Medicine, Stanford, USA.
Cureus. 2021 Feb 3;13(2):e13110. doi: 10.7759/cureus.13110.
Ionizing radiation is clinically used to treat neurological problems and reduce pathological levels of neural activity in the brain, but its cellular-level mechanisms are not well understood. Although spontaneous and stimulated synaptic activity has been produced in rodents by clinically and environmentally relevant doses of radiation, the effects on basic excitability properties of neurons have seldom been reported. This study examined the effects of focused ionizing radiation on synaptic transmission and action potential generation in the squid giant-fiber system, which includes the giant synapse between a secondary interneuron and the tertiary giant motor axons. Radiation of 140-300 Gy was delivered to a stellate ganglion of a living squid over several minutes, with the contralateral stellate ganglion serving as an internal control. No qualitative changes in the efficacy of synaptic transmission were noted in conjunction with stimulation of the input to the giant synapse, although in one irradiated ganglion, the refractory period increased from about 5 ms to more than 45 seconds. Small but significant changes in the action potential recorded from the giant motor axon in response to electrical stimulation were associated with an increased maximum rate of fall and a shortened action potential duration. Other action-potential parameters, including resting potential, overshoot, the maximum rate of the rise, and the refractory period were not significantly changed. Attempts to account for the observed changes in the action potential were carried through a Hodgkin-Huxley model of the action potential. This approach suggests that an increase in the maximum voltage-gated potassium conductance of about 50% mimics the action potential shortening and increased rate of fall that was experimentally observed. We propose that such an effect could result from phosphorylation of squid potassium channels.
电离辐射在临床上用于治疗神经问题并降低大脑中神经活动的病理水平，但其细胞水平的机制尚未完全了解。尽管临床和环境相关剂量的辐射已在啮齿动物中产生自发和刺激的突触活动，但对神经元基本兴奋性特性的影响却鲜有报道。本研究考察了聚焦电离辐射对鱿鱼巨大纤维系统中突触传递和动作电位产生的影响，该系统包括二级中间神经元和三级巨大运动轴突之间的巨大突触。在几分钟内将140 - 300 Gy的辐射施加到一只活鱿鱼的星状神经节上，对侧星状神经节作为内部对照。在刺激巨大突触的输入时，未观察到突触传递效能的定性变化，不过在一个受辐照的神经节中，不应期从约5毫秒增加到超过45秒。在对电刺激的反应中，从巨大运动轴突记录到的动作电位有微小但显著的变化，表现为最大下降速率增加和动作电位持续时间缩短。其他动作电位参数，包括静息电位、超射、最大上升速率和不应期均无显著变化。通过动作电位的霍奇金 - 赫胥黎模型来解释观察到的动作电位变化。该方法表明，电压门控钾电导最大值增加约50%可模拟实验观察到的动作电位缩短和下降速率增加。我们认为这种效应可能是鱿鱼钾通道磷酸化的结果。
