Wojtowicz J M, Atwood H L
Department of Physiology, University of Toronto, Ontario, Canada.
J Neurosci. 1988 Dec;8(12):4667-74. doi: 10.1523/JNEUROSCI.08-12-04667.1988.
Long-term facilitation (LTF) of synaptic transmission was investigated in the crayfish opener muscle to determine the factors necessary for its induction and expression. LTF was induced without action potentials by intracellular depolarization of presynaptic nerve terminals. Following induction, the synaptic transmission was enhanced by about 80% for a period of several hours. Intracellular recordings from pre- and postsynaptic cells, combined with ionic and pharmacological tests, permitted dissection of LTF into 2 phases: an initial tetanic phase that depended on the presence of both sodium and calcium ions and a subsequent long-lasting phase. This latter long-lasting enhancement of synaptic transmission was induced by repeated depolarizations of synaptic terminals but did not depend on the influx of sodium or calcium ions or on intracellular release of calcium ions. Both tetanic and long-lasting phases of LTF are attributable to activity of a single neuron, i.e., they are homosynaptic phenomena. Furthermore, LTF is associated with an increase of quantal release, whereas the size of quanta remains unchanged. During the long-lasting phase of LTF, the nerve terminal releases more transmitter for a given depolarization than before induction of LTF. Thus, the locus of LTF is presynaptic. Our findings suggest the presence of a voltage-dependent mechanism in the presynaptic membrane different from voltage-gating of Na or Ca channels. Such a mechanism may be important in the establishment of long-lasting synaptic changes at the crayfish neuromuscular junction and perhaps in other neural systems.
在小龙虾开肌中研究了突触传递的长期易化（LTF），以确定其诱导和表达所需的因素。通过对突触前神经末梢进行细胞内去极化，在无动作电位的情况下诱导出LTF。诱导后，突触传递在数小时内增强了约80%。对突触前和突触后细胞进行细胞内记录，并结合离子和药理学测试，可将LTF分为两个阶段：一个初始强直相，该相依赖于钠离子和钙离子的存在；以及随后的持久相。突触传递的这种持久增强是由突触末梢的重复去极化诱导的，但不依赖于钠离子或钙离子的内流，也不依赖于细胞内钙离子的释放。LTF的强直相和持久相均归因于单个神经元的活动，即它们是同突触现象。此外，LTF与量子释放的增加相关，而量子大小保持不变。在LTF的持久期，对于给定的去极化，神经末梢释放的递质比LTF诱导前更多。因此，LTF的位点在突触前。我们的发现表明，突触前膜中存在一种与Na或Ca通道的电压门控不同的电压依赖性机制。这种机制可能在小龙虾神经肌肉接头处以及可能在其他神经系统中持久突触变化的建立中起重要作用。
