Kapur A, Yeckel M F, Gray R, Johnston D
Division of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA.
J Neurophysiol. 1998 Apr;79(4):2181-90. doi: 10.1152/jn.1998.79.4.2181.
The requirement of postsynaptic calcium influx via L-type channels for the induction of long-term potentiation (LTP) of mossy fiber input to CA3 pyramidal neurons was tested for two different patterns of stimulation. Two types of LTP-inducing stimuli were used based on the suggestion that one of them, brief high-frequency stimulation (B-HFS), induces LTP postsynaptically, whereas the other pattern, long high-frequency stimulation (L-HFS), induces mossy fiber LTP presynaptically. To test whether or not calcium influx into CA3 pyramidal neurons is necessary for LTP induced by either pattern of stimulation, nimodipine, a L-type calcium channel antagonist, was added during stimulation. In these experiments nimodipine blocked the induction of mossy fiber LTP when B-HFS was given [34 +/- 5% (mean +/- SE) increase in control versus 7 +/- 4% in nimodipine, P < 0.003]; in contrast, nimodipine did not block the induction of LTP with L-HFS (107 +/- 10% in control vs. 80 +/- 9% in nimodipine, P > 0.05). Administration of nimodipine after the induction of LTP had no effect on the expression of LTP. In addition, B- and L-HFS delivered directly to commissural/associational fibers in stratum radiatum failed to induce a N-methyl--aspartate-independent form of LTP, obviating the possibility that the presumed mossy fiber LTP resulted from potentiation of other synapses. Nimodipine had no effect on calcium transients recorded from mossy fiber presynaptic terminals evoked with the B-HFS paradigm but reduced postsynaptic calcium transients. Our results support the hypothesis that induction of mossy fiber LTP by B-HFS is mediated postsynaptically and requires entry of calcium through L-type channels into CA3 neurons.
通过L型通道的突触后钙内流对于诱导苔藓纤维输入到CA3锥体神经元的长时程增强（LTP）的需求，针对两种不同的刺激模式进行了测试。基于以下建议使用了两种类型的LTP诱导刺激：其中一种，即短暂高频刺激（B-HFS），在突触后诱导LTP，而另一种模式，即长时间高频刺激（L-HFS），在突触前诱导苔藓纤维LTP。为了测试钙流入CA3锥体神经元对于由任何一种刺激模式诱导的LTP是否必要，在刺激期间添加了L型钙通道拮抗剂尼莫地平。在这些实验中，当给予B-HFS时，尼莫地平阻断了苔藓纤维LTP的诱导[对照组增加34±5%（平均值±标准误），而尼莫地平组为7±4%，P<0.003]；相比之下，尼莫地平并未阻断L-HFS诱导的LTP（对照组为107±10%，尼莫地平组为80±9%，P>0.05）。在LTP诱导后给予尼莫地平对LTP的表达没有影响。此外，直接施加于辐射层联合/联合纤维的B-HFS和L-HFS未能诱导出一种不依赖N-甲基-D-天冬氨酸的LTP形式，排除了假定的苔藓纤维LTP是由其他突触的增强所导致的可能性。尼莫地平对用B-HFS范式诱发的苔藓纤维突触前终末记录的钙瞬变没有影响，但减少了突触后钙瞬变。我们的结果支持这样的假设，即B-HFS诱导苔藓纤维LTP是通过突触后介导的，并且需要钙通过L型通道进入CA3神经元。
