Bittner G D, Baxter D A
Department of Zoology, College of Pharmacy, University of Texas, Austin 78712.
Synapse. 1991 Mar;7(3):235-43. doi: 10.1002/syn.890070308.
Simultaneous intracellular recordings from presynaptic nerve terminals and postsynaptic muscle fibers were used to investigate the extent to which changes in presynaptic voltage may contribute to short-term facilitation and augmentation of transmitter release at neuromuscular junctions of the crayfish (Procambarus simulans) opener muscle. Presynaptic nerve terminals have an average resting membrane potential of about -80 mV, single action potentials have an average foot-to-peak amplitude of about 98 mV, and single action potentials are followed by a depolarizing after potential (DAP) of about 10 mV. During stimulus trains of 9-16 impulses at 100 Hz, amplitudes of excitatory postsynaptic potentials (EPSPs) continuously facilitate up to 100-fold. This dramatic facilitation is associated with only slight increases in the peak voltage and duration of APs for the first 2-4 pulses in such a stimulus train. Foot-to-peak total amplitude of APs usually decreases after the first pulse in a stimulus train. The data strongly suggest that short-term facilitation is not due to changes in the amplitude or duration of APs invading the presynaptic terminal. Upon cessation of a longer stimulus train, the presynaptic terminal exhibits a hyperpolarizing after potential (HAP) up to 16 mV in amplitude depending upon the frequency (10-100 Hz) and duration (1-10 sec) of the tetanic stimulation. This post-tetanic HAP decays with a time constant of 10-20 sec, which is approximately equal to the third time constant of decay in EPSP amplitude (augmentation) following tetanic stimulation. Hence, presynaptic voltage changes and/or processes associated with these voltage changes (e.g., accumulation of ions, changes in ionic conductances, etc.) may be partly responsible for augmentation of EPSP amplitudes.
通过对小龙虾（拟螯虾）开肌神经肌肉接头处的突触前神经末梢和突触后肌纤维进行同步细胞内记录，来研究突触前电压变化在多大程度上可能导致神经递质释放的短期易化和增强。突触前神经末梢的平均静息膜电位约为-80 mV，单个动作电位的平均峰峰值约为98 mV，单个动作电位之后会跟随一个约10 mV的去极化后电位（DAP）。在100 Hz的9 - 16次冲动的刺激串期间，兴奋性突触后电位（EPSP）的幅度持续易化达100倍。这种显著的易化仅与刺激串中前2 - 4个脉冲的动作电位峰值电压和持续时间的轻微增加有关。刺激串中第一个脉冲之后，动作电位的峰峰值总幅度通常会降低。数据有力地表明，短期易化并非由于侵入突触前末梢的动作电位幅度或持续时间的变化。在较长刺激串停止后，突触前末梢会出现一个超极化后电位（HAP），其幅度高达16 mV，这取决于强直刺激的频率（10 - 100 Hz）和持续时间（1 - 10秒）。这种强直后HAP以10 - 20秒的时间常数衰减，这大约等于强直刺激后EPSP幅度衰减（增强）的第三个时间常数。因此，突触前电压变化和/或与这些电压变化相关的过程（例如，离子积累、离子电导变化等）可能部分导致了EPSP幅度的增强。
