Schulz P E, Cook E P, Johnston D
Department of Neurology, Baylor College of Medicine, Houston, TX 77030, USA.
J Physiol Paris. 1995;89(1):3-9. doi: 10.1016/0928-4257(96)80546-8.
Paired-pulse facilitation (PPF) of excitatory synaptic transmission at Schaffer collateral synapses in the hippocampus was examined in relationship to long-term potentiation (LTP). PPF is a relatively simple-to-measure presynaptic form of synaptic plasticity. It is hypothesized that if the expression of LTP includes a presynaptic component, then PPF and LTP may interfere with one another. When averaged over more than 100 experiments, we observed no change in average PPF with LTP, as reported previously by a number of investigators. When individual experiments were analyzed, however, PPF significantly increased or decreased with LTP in direct relation to the initial value of PPF. There was also a linear relationship between the change in PPF and the magnitude of LTP. The PPF changes were specific to LTP and presynaptic in origin as they were input-specific and persisted with low concentrations of CNQX, GABAA and GABAB antagonists, different interstimulus intervals, and different Ca2+ concentrations. To understand the interaction between LTP and PPF, we constructed a simple model of LTP in which potential contributions by increases in three synaptic parameters were examined: the number of neurotransmitter release sites (n), the probability of release (p), and the postsynaptic unit potential (q). The data were fit by a model in which there were increases in n that changed the average p of the population, but not by a model that increased p or q alone. This is the first experimental evidence for an increase in the number of release sites with LTP, which could be due to pre- or postsynaptic mechanisms.
研究了海马体中沙费尔侧支突触兴奋性突触传递的配对脉冲易化（PPF）与长时程增强（LTP）的关系。PPF是一种相对易于测量的突触可塑性的突触前形式。据推测，如果LTP的表达包括突触前成分，那么PPF和LTP可能会相互干扰。正如之前许多研究者所报道的，在100多个实验的平均值中，我们观察到LTP时平均PPF没有变化。然而，当对单个实验进行分析时，PPF随LTP显著增加或减少，这与PPF的初始值直接相关。PPF的变化与LTP的幅度之间也存在线性关系。PPF的变化是LTP特有的且起源于突触前，因为它们是输入特异性的，并且在低浓度的CNQX、GABAA和GABAB拮抗剂、不同的刺激间隔以及不同的Ca2+浓度下仍然存在。为了理解LTP和PPF之间的相互作用，我们构建了一个简单的LTP模型，其中研究了三个突触参数增加的潜在贡献：神经递质释放位点的数量（n）、释放概率（p）和突触后单位电位（q）。数据由一个模型拟合，该模型中n增加，改变了群体的平均p，但不是由单独增加p或q的模型拟合。这是LTP时释放位点数量增加的首个实验证据，这可能是由于突触前或突触后机制。
