钙离子依赖的胶质细胞源性谷氨酸释放在海洛因复吸中的作用

The "net balance" between glutamate release and elimination is termed "glutamate homeostasis", which regulates synaptic activity and plasticity. Glutamate release is both neuronal and astrocytic, while glutamate elimination is largely through glial transporters. Although an impairment in glutamate homeostasis has been considered as a mechanism underling the biological vulnerability to relapse for drug addiction, it is unclear how extrasynaptic glutamate is regulated by astrocytes, and how astrocyte-regulated glutamate affects synaptic neurotransmission in the nucleus accumbens of rats trained to self-administer heroin. The overarching hypothesis in this proposal that the abnormality of glia-neuron signaling mediated by calcium-dependent glutamate exocytosis from astrocyte (Ca-glia-Glu) may contribute to the impaired glutamate homeostasis, which is a candidate pathophysiology in heroin addiction. Three specific aims are proposed to investigate glutamate-mediated astrocyte-neuron signaling in heroin-addicted animals. Aim #1: the glutamate homeostasis (the basal extrasynaptic glutamate levels and uptake) in the nucleus accumbens in heroin-extinguished animals. Aim #2: the function of Ca-glia-Glu and presynaptic glutamatergic autoreceptor (mGluR2/3) in heroin-extinguished animals. Aim #3: the restoration of impaired glutamate homeostasis by rescuing Ca-glia-Glu to prevent the heroin relapse. This study will explore an unanticipated mechanism of heroin-induced deficiency in glutamate homeostasis involving heroin-induced changes in Ca-glia-Glu and mGluR2/3. The findings by this study will link to an innovative pharmacotherapeutic theory to prevent relapse based on understanding astrocyte/neuron signaling in an animal model of heroin addiction.

谷氨酸平衡失调及神经可塑性的损伤在药物成瘾动物中长期存在，并且在导致成瘾药物复吸的生物学脆弱性中扮演着极其重要的角色，然而其病理机制尚不清楚。本项目的中心假说是在海洛因成瘾动物的腹隔核中，钙离子依赖的胶质细胞源性谷氨酸释放(Ca-glia-Glu)的改变是造成谷氨酸平衡失调的原因；这一病理改变是导致海洛因复吸的生物学脆弱性的潜在机制。我们首先将确认在成瘾动物长期戒断后是否存在慢性谷氨酸平衡失调现象。其后，为了探索形成谷氨酸平衡失调的形成机制，我们将调查Ca-glia-Glu释放和谷氨酸自身受体mGluR2/3的功能是否有所改变。最后，我们将证明修复Ca-glia-Glu释放功能可以恢复谷氨酸平衡，并预防海洛因复吸。本项目将围绕着海洛因成瘾动物的Ca-glia-Glu功能改变及其病理生理学和行为学意义进行充分研究，并在此基础上探索新的预防复吸的药物治疗理论。

药物成瘾行为即使在长期戒断也极其容易再次复发。这表明成瘾个体在复吸行为上存在着复杂并且持久的生物学脆弱性。药物成瘾的动物模型研究已经显示在长期戒断后觅药行为再发生时，伴随着突触外谷氨酸的显著增加。然而，导致突触外谷氨酸平衡改变的病理机制、及其与药物复吸行为的相关性依然不为人所知。因此，我们研究了1) 海洛因成瘾动物伏隔核中的谷氨酸转运蛋白（GLT-1）及谷氨酸回收功能；2) 海洛因成瘾动物谷氨酸突触外溢出现象与与复吸的相关性；3) 海洛因成瘾动物伏隔核胶质细胞源性谷氨酸释放的改变与复吸的相关性；4) 比较CaMKII在海洛因及可卡因成瘾动物在复吸时的不同作用。我们发现成瘾动物伏隔核中，星形胶质细胞表面G-蛋白偶联受体导致的谷氨酸释放显著减少，谷氨酸转运蛋白表达及回收功能受到损害，以及谷氨酸负反馈受体mGluR2/3功能受损；由此导致复吸时过渡的谷氨酸突触外溢。揭示钙离子/钙调蛋白依赖的蛋白激酶II（CaMKII）及其下游信号可能与海洛因及可卡因成瘾动物不同的觅药冲动相关，为有针对性地治疗药物成瘾的复吸提供了潜在靶点。本项目揭示了成瘾动物伏隔核谷氨酸稳态失衡的病理机制，具有重要的科学价值。据此，我们探索了预防成因动物复吸的新药理学靶点：1) 慢性给予Ceftriaxone促进GLT-1表达，纠正胶质细胞功能，可以防止谷氨酸突触外溢；2) 脂肪酸酰胺水解酶（FAAH）抑制剂URB-597可抑制内源性大麻素成分花生四烯酸乙醇胺（AEA）分解，增加了成瘾动物胶质细胞源性谷氨酸释放；上述治疗方案平衡中枢谷氨酸稳态，抑制条件性线索或药物点燃所导致的海洛因复吸，具有潜在的临床应用前景。