Arai A, Black J, Lynch G
Center for the Neurobiology of Learning and Memory, University of California, Irvine 92717-3800.
Hippocampus. 1994 Feb;4(1):1-9. doi: 10.1002/hipo.450040103.
Responses to theta pattern stimulation, and the long-term potentiation (LTP) they induce, were compared in the basal versus apical dendrites of neurons in field CA1 of hippocampus. A series of 10 theta bursts produced more than twice as much LTP in basal synapses as in their apical counterparts as measured with field EPSPs. This confirms earlier field potential studies showing that the maximum degree of potentiation (the LTP ceiling) is considerably greater in stratum oriens than stratum radiatum. Experiments with whole-cell clamp recording obtained similar results, indicating that synapses at different loci on the same neuron reach different LTP ceilings following prolonged theta burst stimulation. The basal synapses also required fewer theta bursts to reach their LTP ceiling than did the apical synapses. Tests with paired-pulse facilitation and an antagonist of the NMDA receptor gave no indication that the greater LTP in basal synapses was qualitatively different from the lesser effect obtained in apical contacts. Intracellular recording revealed significant differences between basal versus apical responses to single theta bursts and trains of bursts: the within-burst depolarization was greater and the between-burst hyperpolarization was smaller for the basal dendritic responses. These two variables have previously been proposed to influence the magnitude of LTP and the observed differences between basal versus apical synapses are in accord with this hypothesis. Together with recently described immunocytochemical results, the findings reported here suggest that variations in LTP across dendritic subfields of hippocampus reflect a differential distribution of a subclass of GABAergic interneurons.
在海马体CA1区神经元的基底树突与顶端树突中，对theta模式刺激的反应以及它们所诱导的长时程增强（LTP）进行了比较。通过场兴奋性突触后电位（field EPSPs）测量，一系列10次theta爆发在基底突触中产生的LTP是其顶端对应突触的两倍多。这证实了早期的场电位研究，表明在海马体的原层（stratum oriens）中，增强的最大程度（LTP上限）比辐射层（stratum radiatum）要大得多。全细胞膜片钳记录实验得到了类似的结果，表明在长时间的theta爆发刺激后，同一神经元上不同位点的突触达到不同的LTP上限。基底突触达到其LTP上限所需的theta爆发次数也比顶端突触少。成对脉冲易化测试和NMDA受体拮抗剂测试均未表明基底突触中更大的LTP在性质上与顶端突触中较小的LTP有差异。细胞内记录显示，基底树突与顶端树突对单个theta爆发和爆发序列的反应存在显著差异：基底树突反应在爆发内的去极化更大，爆发间的超极化更小。此前有人提出这两个变量会影响LTP的大小，而观察到的基底突触与顶端突触之间的差异与这一假设相符。结合最近描述的免疫细胞化学结果，本文报道的研究结果表明，海马体树突亚区LTP的变化反映了一类GABA能中间神经元的差异分布。
