Tanaka E, Yasumoto S, Hattori G, Niiyama S, Matsuyama S, Higashi H
Department of Physiology, Kurume University School of Medicine, Kurume 830-0011, Japan.
J Neurophysiol. 2001 Sep;86(3):1095-103. doi: 10.1152/jn.2001.86.3.1095.
The mechanisms underlying the depression of evoked fast excitatory postsynaptic currents (EPSCs) following superfusion with medium deprived of oxygen and glucose (in vitro ischemia) for a 4-min period in hippocampal CA1 neurons were investigated in rat brain slices. The amplitude of evoked fast EPSCs decreased by 85 +/- 7% of the control 4 min after the onset of in vitro ischemia. In contrast, the exogenous glutamate-induced inward currents were augmented, while the spontaneous miniature EPSCs obtained in the presence of tetrodotoxin (TTX, 1 microM) did not change in amplitude during in vitro ischemia. In a normoxic medium, a pair of fast EPSCs was elicited by paired-pulse stimulation (40-ms interval), and the amplitude of the second fast EPSC increased to 156 +/- 24% of the first EPSC amplitude. The ratio of paired-pulse facilitation (PPF ratio) increased during in vitro ischemia. Pretreatment of the slices with adenosine 1 (A1) receptor antagonist, 8-cyclopenthyltheophiline (8-CPT) antagonized the depression of the fast EPSCs, in a concentration-dependent manner: in the presence of 8-CPT (1-10 microM), the amplitude of the fast EPSCs decreased by only 20% of the control during in vitro ischemia. In addition, 8-CPT antagonized the enhancement of the PPF ratio during in vitro ischemia. A pair of presynaptic volleys and excitatory postsynaptic field potentials (fEPSPs) were extracellularly recorded in a proximal part of the stratum radiatum in the CA1 region. The PPF ratio for the fEPSPs also increased during in vitro ischemia. On the other hand, the amplitudes of the first and second presynaptic volley, which were abolished by TTX (0.5 microM), did not change during in vitro ischemia. The maximal slope of the Ca(2+)-dependent action potential of the CA3 neurons, which were evoked in the presence of 8-CPT (1 microM), nifedipine (20 microM), TTX (0.5 microM), and tetraethyl ammonium chloride (20 mM), decreased by 12 +/- 6% of the control 4 min after the onset of in vitro ischemia. These results suggest that in vitro ischemia depresses the evoked fast EPSCs mainly via the presynaptic A1 receptors, and the remaining 8-CPT-resistant depression of the fast EPSCs is probably due to a direct inhibition of the Ca(2+) influx to the axon terminals.
在大鼠脑片中研究了海马CA1神经元在灌流缺乏氧气和葡萄糖的培养基（体外缺血）4分钟后诱发的快速兴奋性突触后电流（EPSCs）抑制的潜在机制。体外缺血开始4分钟后，诱发的快速EPSCs幅度下降至对照的85±7%。相反，外源性谷氨酸诱导的内向电流增强，而在存在河豚毒素（TTX，1μM）时获得的自发性微小EPSCs在体外缺血期间幅度未改变。在常氧培养基中，通过配对脉冲刺激（间隔40毫秒）诱发一对快速EPSCs，第二个快速EPSC的幅度增加至第一个EPSC幅度的156±24%。配对脉冲易化率（PPF比率）在体外缺血期间增加。用腺苷1（A1）受体拮抗剂8-环戊基茶碱（8-CPT）预处理切片以浓度依赖性方式拮抗快速EPSCs的抑制：在存在8-CPT（1-10μM）时，体外缺血期间快速EPSCs的幅度仅下降至对照的20%。此外，8-CPT拮抗体外缺血期间PPF比率的增强。在CA1区辐射层近端部分细胞外记录一对突触前群峰电位和兴奋性突触后场电位（fEPSPs）。fEPSPs的PPF比率在体外缺血期间也增加。另一方面，被TTX（0.5μM）消除的第一个和第二个突触前群峰电位的幅度在体外缺血期间未改变。在存在8-CPT（1μM）、硝苯地平（20μM）、TTX（0.5μM）和四乙铵氯化物（20mM）时诱发的CA3神经元Ca(2+)依赖性动作电位的最大斜率在体外缺血开始4分钟后下降至对照的12±6%。这些结果表明，体外缺血主要通过突触前A1受体抑制诱发的快速EPSCs，而剩余的8-CPT抗性快速EPSCs抑制可能是由于对轴突终末Ca(2+)内流的直接抑制。
