Leung L S, Shen B, Kaibara T
Department of Clinical Neurological Science, University of Western Ontario, London, Canada.
Neuroscience. 1992;48(1):63-74. doi: 10.1016/0306-4522(92)90338-3.
In urethane-anesthetized rats, stimulation of the contralateral hippocampal CA1 region resulted in activation of the homotopic CA1 region. Current-source-density analysis revealed that both basal and apical dendrites were activated. However, alveolar and stratum oriens stimulation in CA1 gave about equal peak excitation of the basal and apical dendrites while CA1 stratum radiatum/moleculare and CA3c stimulation gave stronger apical than basal dendritic excitation. In chronically implanted and freely moving rats, tetanic patterned stimulation of the contralateral CA1, irrespective of depth, resulted in a robust long-term potentiation of the ipsilateral CA1 basal dendritic synapse. The population basal dendritic excitatory postsynaptic potential was initially potentiated to greater than 200% of the baseline and decayed with a 3 h time constant; it lasted at least two days. Patterned stimulation of the commissural inputs at 2 x threshold stimulus intensity seldom potentiated the apical dendritic synapse in CA1; rather, long-term depression was sometimes observed. After tetanic stimulations at 3 x threshold, a small potentiation of the apical dendritic excitation was seen in about half of the experiments. The average apical dendritic potentiation peaked at about 25% and persisted to at least one day. This study provides original evidence that the properties of long-term potentiation are different at the commissural basal dendritic and apical dendritic synapses in CA1 of the behaving rat. Basal dendritic potentiation is low-threshold, high-amplitude and decayed rapidly in the first 3 h. Apical dendritic potentiation is high-threshold, low-amplitude and not rapidly decaying. A long-lasting enhancement of synaptic transmission has been postulated as a physiological correlate of memory. This paper reports properties of this synaptic enhancement for two different types of synapses on the same cells in the behaving animal. The basal dendritic synapse on hippocampal pyramidal cells readily increased their efficacy, up to at least two days, after a brief, patterned stimulation. In the same preparation, it was difficult to obtain a long-lasting increase in the apical dendritic excitation, in contrast to studies on isolated hippocampal slices in vitro.
在氨基甲酸乙酯麻醉的大鼠中，刺激对侧海马CA1区会导致同位CA1区的激活。电流源密度分析显示，基底树突和顶树突均被激活。然而，CA1区的肺泡和原层刺激对基底树突和顶树突产生的峰值兴奋程度大致相同，而CA1区辐射层/分子层和CA3c刺激产生的顶树突兴奋强于基底树突兴奋。在长期植入且自由活动的大鼠中，无论深度如何，对侧CA1区的强直模式刺激都会导致同侧CA1基底树突突触产生强烈的长期增强。群体基底树突兴奋性突触后电位最初增强至基线的200%以上，并以3小时的时间常数衰减；它至少持续两天。以2倍阈值刺激强度对连合输入进行模式刺激很少能增强CA1区的顶树突突触；相反，有时会观察到长期抑制。在3倍阈值的强直刺激后，约一半的实验中可见顶树突兴奋有小幅度增强。顶树突平均增强峰值约为25%，并持续至少一天。本研究提供了原始证据，表明在行为大鼠的CA1区，连合基底树突和顶树突突触的长期增强特性不同。基底树突增强是低阈值、高幅度的，并且在最初3小时内迅速衰减。顶树突增强是高阈值、低幅度的，且衰减不迅速。突触传递的长期增强被认为是记忆的生理相关因素。本文报道了行为动物同一细胞上两种不同类型突触的这种突触增强特性。海马锥体细胞上的基底树突突触在短暂的模式刺激后很容易提高其效能，至少持续两天。在相同的制备中，与体外分离海马切片的研究相比，很难使顶树突兴奋产生长期增加。
