Benzodiazepine-Induced Glutamate Receptor Plasticity

描述（由申请人提供）：反映对多种滥用药物（包括苯二氮卓类药物（BZs））的身体依赖的戒断综合征的神经生理机制尚不清楚。使用一个成熟的大鼠慢性BZ治疗模型，我们已经确定了海马兴奋性氨基酸受体的变化与焦虑样行为（戒断症状）暂时相关。CA1神经元的变化包括α -氨基-3-羟基-5-甲基-4-异丙烯丙酸受体（AMPAR）电流振幅和电导的增加，AMPAR结合和GluR1亚基水平的增加。当AMPAR电流增加时，n -甲基- d -天冬氨酸受体（NMDAR）诱发电流、NMDA功效和NR2B亚基水平降低。戒断期间NMDA拮抗剂治疗逆转NMDA下调，允许更长的焦虑样行为表达。AMPAR拮抗剂治疗可防止随后的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bz诱导的戒断，并使人联想到海马兴奋性突触活动依赖可塑性的良好机制。类似的机制可能涉及BZ戒断过程中的行为可塑性。工作假设是海马CA1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，并具有与活动依赖性突触可塑性相关的基本特征。三个特定的假设集中在停用氟西泮治疗1周后CA1神经元EAAR突触发生的功能和结构改变的亚基依赖性。AMPA和NMDAR功能将在药物去除后的特定时间点进行研究，当焦虑样行为表达时，使用海马切片和急性解离的CA1神经元的全细胞和外向贴片技术。第一个目标将是利用GluR1亚基选择性神经生理和药理学工具探索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功能下降的nr2b亚单位依赖性。第三个目的是利用光镜和电镜免疫组织化学方法研究CA1突触ampar和NMDARs的结构变化，这些结构变化有助于海马兴奋功能的改变和焦虑样行为。对戒断现象背后的神经生理机制有了更好的理解，就可以找到治疗药物滥用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.