Benzodiazepine-Induced Glutamate Receptor Plasticity

描述(由申请人提供)：反映对包括苯二氮类药物(BZS)在内的各种滥用药物的身体依赖的戒断综合征潜在的神经生理机制尚不清楚。利用一个公认的慢性BZ治疗的大鼠模型，我们已经确定了海马区兴奋性氨基酸受体的变化，这些变化与焦虑样行为有关，这是一种戒断的迹象。CA1神经元的改变包括alpha-amino-3-hydroxy-5-methyl-4-isozaxolepropionic酸受体电流幅度和电导的增加，以及AMPAR结合和GluR1亚单位水平的增加。当AMPAR电流增加时，N-甲基-D-天冬氨酸受体(NMDAR)诱发的电流、NMDA效应和NR2B亚基水平降低。戒断期间的NMDA拮抗剂治疗逆转了NMDAR的下调，允许更长时间的焦虑样行为表达。AMPAR拮抗剂治疗可阻止随后的AMPAR上调。这些发现表明，AMPAR功能的增强通过NMDAR依赖的海马通路参与了BZ诱导的戒断，并使人想起了海马兴奋性突触活动依赖可塑性的机制。类似的机制可能与BZ戒断时的行为可塑性有关。工作假说是，海马CA1区神经元兴奋性突触的局部重塑是BZ身体依赖的核心特征，表现为戒断诱导的焦虑样行为，具有与活动依赖性突触可塑性相似的基本特征。三个特定的假设集中在CA1神经元EAAR突触在停用1周氟氮安定治疗后发生的功能和结构变化的亚单位依赖性。在停药后的特定时间点，当焦虑样行为表现出来时，将使用全细胞和向外贴片技术在海马片和急性分离的CA1神经元中研究AMPA和NMDAR的功能。第一个目标是使用GluR1亚单位选择性神经生理学和药理学工具来探索AMPAR通道的特性。第二个目标将使用类似的方法来研究CA1突触NMDAR功能降低对NR2B亚单位的依赖。第三个目的是利用光镜和电子显微镜免疫组织化学方法研究CA1突触上AMPAR和NMDAR的结构变化，这些结构变化有助于海马兴奋功能的变化和焦虑样行为的发生。通过更好地了解戒断现象背后的神经生理机制，可以找到治疗滥用药物身体依赖的合理方法。

DESCRIPTION (provided by applicant): The neurophysiological mechanisms underlying withdrawal syndromes reflecting physical dependence on a variety of drugs of abuse, including the benzodiazepines (BZs), are unknown. Using a well-established rat model of chronic BZ treatment, we have identified changes in hippocampal excitatory amino acid receptors temporally associated with anxiety-like behavior, a sign of withdrawal. CA1 neuron changes include increases in alpha-amino-3-hydroxy-5-methyl-4-isozaxolepropionic acid receptor (AMPAR) current amplitude and conductance, and increases in AMPAR binding and GluR1 subunit levels. When AMPAR currents increase, N-methyl-D-aspartate receptor (NMDAR)-evoked currents, NMDA efficacy and NR2B subunit levels are reduced. NMDA antagonist treatment during withdrawal reverses NMDAR down regulation, allowing more prolonged expression of anxiety-like behavior. AMPAR antagonist treatment prevents subsequent AMPAR upregulation. These findings suggest that enhanced AMPAR function contributes to BZ-induced withdrawal through NMDAR-dependent hippocampal pathways, and are reminiscent of well-described mechanisms underlying activity-dependent plasticity of hippocampal excitatory synapses. Similar mechanisms may be involved in behavioral plasticity during BZ withdrawal. The working hypothesis is that localized remodeling of hippocampal CA1 neuron excitatory synapses is a central feature underlying BZ physical dependence, expressed as withdrawal-induced anxiety-like behavior, and has essential characteristics analogous to those associated with activity-dependent synaptic plasticity. Three specific hypotheses focus on the subunit dependence of the functional and structural alterations that occur at CA1 neuron EAAR synapses after withdrawal from 1-week flurazepam treatment. AMPA and NMDAR function will be studied at selected time-points after drug removal, when anxiety-like behavior is expressed, using whole-cell and outside-out patch techniques in hippocampal slices and acutely dissociated CA1 neurons. The first aim will be to explore AMPAR channel properties using GluR1 subunit-selective neurophysiological and pharmacological tools. The second aim will use a similar approach to study the NR2B-subunitdependence of decreased NMDAR function at CA1 synapses. The third aim is to use light microscopic and electron microscopic immunohistochemical approaches to investigate the structural changes in AMPARs and NMDARs at CA1 synapses that contribute to changes in hippocampal excitatory function and to anxiety-like behavior. Rational approaches to the treatment of physical dependence on drugs of abuse can emerge from a better understanding of the neurophysiological mechanisms underlying withdrawal phenomena.