Dingledine R, Langmoen I A
Brain Res. 1980 Mar 10;185(2):277-87. doi: 10.1016/0006-8993(80)91068-9.
Intracellular recordings were obtained from CA1 pyramidal neurons in obliquely cut in vitro hippocampal slices. Recurrent IPSPs were elicited by antidromic stimulation of alvear fibers. The mechanisms by which IPSPs depress pyramidal cell excitability were investigated. Recurrent IPSPs could be reversed in sign by small hyperpolarizing currents applied through the recording electrode, indicating an increased membrane conductance. By using an AC bridge circuit it was found that the maximum impedance decrease usually occurred slightly before the peak of the IPSP. Otherwise the time course of the impedance change matched that of the IPSP itself. Inhibitory actions of the conductance increase were studied by adjusting the membrane potential to the IPSP equilibrium potential, thus allowing only the IPSP conductance to play an inhibitory role. Under these conditions non-linear summation of recurrent IPSPs with EPSPs originating in the apical dendrites could be demonstrated only during the initial 15--25 msec ofthe IPSP, which is the period of maximum conductance increase. The inhibition afforded by the hyperpolarization of the recurrent IPSP far outlasts the period of effective EPSP shunting by the inhibitory synaptic currents. The mechanisms of recurrent inhibition in the hippocampus thus appear similar to those operating in spinal motoneuron IPSPs.
在体外斜切海马脑片中从CA1锥体神经元获得细胞内记录。通过对肺泡纤维的逆向刺激诱发反复性抑制性突触后电位（IPSPs）。研究了IPSPs降低锥体细胞兴奋性的机制。通过记录电极施加小的超极化电流可使反复性IPSPs的电位反转，这表明膜电导增加。使用交流桥式电路发现，最大阻抗降低通常在IPSP峰值之前略有发生。否则，阻抗变化的时间进程与IPSP本身的时间进程相匹配。通过将膜电位调节到IPSP平衡电位来研究电导增加的抑制作用，从而仅允许IPSP电导发挥抑制作用。在这些条件下，仅在IPSP最初的15 - 25毫秒期间（即电导增加最大的时期），可以证明反复性IPSPs与源自顶树突的兴奋性突触后电位（EPSPs）的非线性总和。反复性IPSP超极化所提供的抑制作用远远超过抑制性突触电流有效分流EPSP的时期。因此，海马体中反复抑制的机制似乎与脊髓运动神经元IPSPs中的机制相似。
