Department of Neuroscience, Evelyn F. and William L. McKnight Brain Institute, University of Florida, PO Box 100244, Gainesville, FL 32610-0244, USA.
Prog Neurobiol. 2012 Mar;96(3):283-303. doi: 10.1016/j.pneurobio.2012.01.007. Epub 2012 Jan 28.
In humans, heterogeneity in the decline of hippocampal-dependent episodic memory is observed during aging. Rodents have been employed as models of age-related cognitive decline and the spatial water maze has been used to show variability in the emergence and extent of impaired hippocampal-dependent memory. Impairment in the consolidation of intermediate-term memory for rapidly acquired and flexible spatial information emerges early, in middle-age. As aging proceeds, deficits may broaden to include impaired incremental learning of a spatial reference memory. The extent and time course of impairment has been be linked to senescence of calcium (Ca²⁺) regulation and Ca²⁺-dependent synaptic plasticity mechanisms in region CA1. Specifically, aging is associated with altered function of N-methyl-D-aspartate receptors (NMDARs), voltage-dependent Ca²⁺ channels (VDCCs), and ryanodine receptors (RyRs) linked to intracellular Ca²⁺ stores (ICS). In young animals, NMDAR activation induces long-term potentiation of synaptic transmission (NMDAR-LTP), which is thought to mediate the rapid consolidation of intermediate-term memory. Oxidative stress, starting in middle-age, reduces NMDAR function. In addition, VDCCs and ICS can actively inhibit NMDAR-dependent LTP and oxidative stress enhances the role of VDCC and RyR-ICS in regulating synaptic plasticity. Blockade of L-type VDCCs promotes NMDAR-LTP and memory in older animals. Interestingly, pharmacological or genetic manipulations to reduce hippocampal NMDAR function readily impair memory consolidation or rapid learning, generally leaving incremental learning intact. Finally, evidence is mounting to indicate a role for VDCC-dependent synaptic plasticity in associative learning and the consolidation of remote memories. Thus, VDCC-dependent synaptic plasticity and extrahippocampal systems may contribute to incremental learning deficits observed with advanced aging.
在人类中,随着年龄的增长,观察到海马体依赖的情景记忆能力下降存在异质性。啮齿动物已被用作与年龄相关的认知衰退模型,而空间水迷宫已被用于显示海马体依赖记忆出现和受损程度的可变性。快速获得和灵活的空间信息的中期记忆巩固受损在中年早期就出现了。随着衰老的进行,缺陷可能会扩大到包括空间参考记忆的增量学习受损。损伤的程度和时间进程与 CA1 区钙(Ca²⁺)调节和 Ca²⁺依赖性突触可塑性机制的衰老有关。具体而言,衰老与 N-甲基-D-天冬氨酸受体(NMDARs)、电压依赖性 Ca²⁺通道(VDCCs)和与细胞内 Ca²⁺储存(ICS)相关的ryanodine 受体(RyRs)的功能改变有关。在年轻动物中,NMDAR 的激活诱导突触传递的长时程增强(NMDAR-LTP),这被认为介导了中期记忆的快速巩固。从中年期开始的氧化应激会降低 NMDAR 的功能。此外,VDCC 和 ICS 可以主动抑制 NMDAR 依赖性 LTP,而氧化应激会增强 VDCC 和 RyR-ICS 在调节突触可塑性中的作用。阻断 L 型 VDCC 可促进老年动物中的 NMDAR-LTP 和记忆。有趣的是,药理学或遗传学操作以降低海马体 NMDAR 功能很容易损害记忆巩固或快速学习,通常使增量学习保持完整。最后,越来越多的证据表明 VDCC 依赖性突触可塑性在联想学习和远程记忆的巩固中发挥作用。因此,VDCC 依赖性突触可塑性和海马体外系统可能有助于解释与衰老相关的增量学习缺陷。