电鱼小脑浦肯野细胞对急性缺氧的功能反应

Functional responses of mormyrid cerebellar Purkinje cells to acute hypoxia insult

目的:通过研究急性缺氧对电鱼(mormyrid electric fish)小脑浦肯野细胞(Purkinje cell,PC)的功能影响,阐明缺氧耐受动物神经元在缺氧条件下的电生理特征。方法:采用全细胞膜片钳记录法,观察急性缺氧对电鱼小脑主神经元PC膜电位、兴奋性和平行纤维(parallel fiber,PF)-PC突触传递的影响。结果:(1)短暂缺氧使电鱼小脑PC膜电位发生迅速而持久的超极化,可持续30 min以上,同时伴随自发放电频率的显著下降。谷氨酸AMPA受体阻断剂CNQX不影响PC缺氧性超极化的产生,但可阻断缺氧性超极化的持续存在;而GABAA受体阻断剂Bicuculline则完全阻断缺氧性超极化的产生,并使膜电位在缺氧开始后发生短暂的去极化。(2)缺氧使PC诱发动作电位的阈值增高,频率减低,幅值减小。(3)急性缺氧使刺激PF诱发的PC兴奋性突触后电流(excitatorypostsynaptic current,EPSC)呈现长时程增强(long term potentiation,LTP),同时使EPSC双脉冲增强现象(pair-pulsefacilitation,PPF)显著衰减。CNQX逆转了PF EPSC的缺氧性LTP,表现为长时程抑制(Long Term Depression,LTD);而Bicuculline则使PF EPSC的缺氧性LTP增强。结论:耐缺氧动物电鱼小脑神经元的缺氧反应特征与哺乳类动物显著不同,AMPA受体和GABAA受体均参与电鱼小脑PC的缺氧性超极化和PF LTP的产生,表明维持GABA能突触和谷氨酸能突触活动的适度平衡,可能是电鱼以及其他耐缺氧动物脑保护机制的关键。

Objective： To evaluate the electrophysiological characteristics of neuron in anorexia tolerant animal under hypoxia condition by discovering the functional responses of Mormyrid cerebellar Purkinje cells（PCs） to acute hypoxia insuit. Methods：The whole cell patch clamp was used for the intraceUular recording from PCs of the mormyrid cerebellar slices to evaluate the changes of the membrane potential and the excitability of PCs and the PF-PC synaptic transmission induced by acute hypoxia insult. Results： （ 1 ） PCs show a rapid and significant hyperpolarization with a decreased spontaneous firing rate following the onset of hypoxia episode and last persistently for more than 30 minutes. AMPA receptor antagonist CNQX did not affect the initiating of the hyperpolarization, but prevented the hypoxia hyperpolarization from long lasting. GABAA receptor antagonist BicucuUine completely block the hypoxia hyperpolarization, and induced a briefhypopolarization immediately following hypoxia episode. （2） An increased threshold of active potential and a decreased frequency of active potential induced by the injection of depolarized current into PCs body were shown following hypoxia episode. The amplitude of active potential of PCs was also decreased by hypoxia. （3） Acute hypoxia induced mormyrid cerebellar PF-PC excitatory postsynaptic current（EPSC） long-term potentiation （LTP） with a decreased pair-pulse facili- tation（PPF）. CNQX reversed PF EPSC LTP induced by hypoxia episode to long term depression（LTD）. Bicuculline enhanced hypoxia LTP of PF EPSC. Conclusion ： The functional responses of mormyrid cerebellar PCs to hypoxia insult were quite different from that of mammalian. Both of AMPA receptor and GABAA receptor contribute to the hypoxia hyperpolarization and PF EPSC LTP, suggesting that a balance between GABAergic and Glutamatergic synaptic activities is required for the protective responses of mormyrid neuron under hypoxia condition and probably also for the other anoxia tolerant ani- mals as well .