伏隔核区递质D-丝氨酸介导可卡因诱导的突触可塑性及行为改变

Drug addiction is a serious brain disorder with somatic, psychological, psychiatric, socio-economic and legal implications in the developed world. It is a persistent mental disorder characterized by compulsive drug craving, seeking, and ingestion despite severe adverse consequences. Previous studies have proved that plastic changes in glutamatergic synapses of the mesocorticolimbic dopamine system, which including the nucleus accumbens (NAc) that lead to enduring drug craving and addiction. We have reported chronic exposure to the psychostimulant drug induces selective downregulation of NMDA receptor NR2B subunits in the rat nucleus accumbens and the loss of NR2B further translates to the significant modulation of synaptic plasticity in the form of long-term depression at cortico-accumbal glutamatergic synapses. Based on the definite relationship between synaptic plasticity and release of D-serine from astrocytes and our preliminary results, in this program we plan to elucidate how, when, and where psychostimulant drug (cocaine) interact to control synaptic and behavioral plasticity by using the model of behavioral sensitization and conditioned place preference. Hign pressure liquid chromatography and microdialysis technique will be employed to analyze the changes of D-serine concentration in NAc, PFC, CPU, and Hippocamus after cocaine addiction. We will also perform Western blot, RT-PCR and immunohistochemistry studies to analysis the changes of serine racemase (synthetase) and D-amino acid oxidase (DAAO, metabolic enzyme) expression in NAc, PFC, CPU, and Hippocamus after cocaine addiction. Behavioral sensitization and conditioned place preference studies will be conducted to observe the behavioral effect of exogenous and endogenous D-serine on rats. Effects of exogenous and endogenous D-serine on NMDA receptor dependent-synaptic plasticity in rat NAc slices were investigated by electrophysiological methods. Our data will identify Glia-Derived D-Serine as a key regulator in the remodeling of excitatory synapses in NAc and persistent psychomotor plasticity in response to cocaine. Reversing or preventing these drug-induced D-serine dynamics and synaptic modifications may prove beneficial in the treatment of one of society's most intractable health problems.

药物成瘾是一涉及躯体反应、心理和精神卫生、恶劣社会影响等众多问题的神经精神疾病。前期研究已证实中脑边缘系统（如伏隔核,NAc）的突触可塑性是介导药物依赖的关键。我们的研究也发现：精神兴奋药物抑制NAc区NMDA受体表达和该受体依赖的突触可塑性。基于突触可塑性与D-丝氨酸之间明确的关系及预实验结果，本研究拟以D-丝氨酸为切入点，制备行为敏化和条件性位置偏爱模型，研究cocaine影响动物行为的具体机制。本项目拟利用分子生物学、高效液相色谱和微透析等技术观察药物成瘾后NAc等脑区D-丝氨酸浓度及其相关酶表达变化；利用药理学等方法探讨D-serine对大鼠成瘾行为的影响；利用电生理技术探讨D-serine对伏隔核区突触可塑性的影响。本课题以胶质细胞分泌的D-丝氨酸为桥梁，探讨由其调控的NMDA受体依赖的突触可塑性可能是药物依赖的重要机制；将为这一社会顽疾的机制研究和治疗提供新靶点。

药物成瘾是一种以强迫性觅药、 用药行为为特征并伴有身心健康、 社会功能受损的疾病；它是一涉及躯体反应、心理和精神卫生、恶劣社会影响等众多问题的神经精神疾病。药物成瘾机制涉及神经元结构的适应性和突触的可塑性改变， 药物成瘾及消退行为的形成和维持与很多经典的学习记忆模型分享了同样的分子机制。前期研究已证实中脑边缘系统（如伏隔核,NAc）的突触可塑性是介导药物依赖的关键。在此项研究中，我们利用可卡因制备药物依赖模型。使用高效液相色谱法测量模型不同脑区（主要是伏隔核区）的D-丝氨酸浓度；使用行为敏化模型及条件性位置偏爱模型观察D-丝氨酸与可卡因药物成瘾之间的关系。通过Western-blotting技术观察不同脑区（NAc区、前额皮层、海马）D-serine合成酶丝氨酸消旋酶（SR）及其降解酶D-型氨基酸氧化酶（DAAO）表达变化；同时观察药物成瘾对CREB及其上游激酶、NMDA受体的表达情况。利用电生理-场电位的手段研究D-丝氨酸对NAc区长时程削弱的影响。我们的实验结果发现：可卡因行为敏化模型，其伏隔核区及前额皮层区D-serine浓度下降，同时NAc区DAAO表达上调，SR表达下降。D-serine能够逆转行为敏化模型NAc区NMDAR受体的表达变化。同时，我们发现D-丝氨酸能够促进NAc区域的NMDA受体依赖的LTD；D-丝氨酸能够逆转NAc区域NMDA受体依赖的LTD的损伤。以上研究将深入了解D-丝氨酸调控的突触可塑性在cocaine所致模型中作用，有助于寻找崭新的药物成瘾发病的潜在靶点，为其治疗提供新的思路。