Minocycline prevents chronic restraint stress-induced vulnerability to developing cocaine self-administration and associated glutamatergic mechanisms: a potential role of microglia

Stressful experience-induced cocaine-related behaviors are associated with a significant impairment of glutamatergic mechanisms in the Nucleus Accumbens core (NAcore). The hallmarks of disrupted glutamate homeostasis following restraint stress are the enduring imbalance of glutamate efflux after a cocaine stimulus and increased basal concentrations of extracellular glutamate attributed to GLT-1 downregulation in the NAcore. Glutamate transmission is tightly linked to microglia functioning. However, the role of microglia in the biological basis of stress-induced addictive behaviors is still unknown. By using minocycline, a potent inhibitor of microglia activation with anti-inflammatory properties, we determined whether microglia could aid chronic restraint stress (CRS)-induced glutamate homeostasis disruption in the NAcore, underpinning stress–induced cocaine self-administration. In this study, adult male rats were restrained for 2 h/day for seven days (day 1–7). From day 16 until completing the experimental protocol, animals received a vehicle or minocycline treatment (30 mg/Kg/12h i.p.). On day 21, animals were assigned to microscopic, biochemical, neurochemical or behavioral studies. We confirm that the CRS-induced facilitation of cocaine self-administration is associated with enduring GLT-1 downregulation, an increase of basal extracellular glutamate and postsynaptic structural plasticity in the NAcore. These alterations were strongly related to the CRS-induced reactive microglia and increased TNF-? mRNA and protein expression, since by administering minocycline, the impaired glutamate homeostasis and the facilitation of cocaine self-administration were prevented. Our findings are the first to demonstrate that minocycline suppresses the CRS-induced facilitation of cocaine self-administration and glutamate homeostasis disruption in the NAcore. A role of microglia is proposed for the development of glutamatergic mechanisms underpinning stress-induced vulnerability to cocaine addiction.

应激性体验引起的可卡因相关行为与尾壳核核心（NAcore）谷氨酸能机制的显著损害密切相关。应激后谷氨酸稳态紊乱的特征在于可卡因刺激后谷氨酸外流持续的失衡以及NAcore中GLT-1下调导致的细胞外谷氨酸基础浓度的增加。谷氨酸传递与微胶质细胞的机能紧密相连。然而，微胶质细胞在应激诱导的成瘾行为生物学基础中的作用仍不明确。本研究通过使用具有抗炎特性的强效微胶质细胞激活抑制剂米诺环素，确定了微胶质细胞是否能够辅助慢性束缚应激（CRS）诱导的NAcore谷氨酸稳态破坏，从而奠定应激诱导的可卡因自我给药的基础。在本研究中，成年雄性大鼠每日束缚2小时，连续七天（第1-7天）。从第16天开始直至完成实验方案，动物接受溶剂或米诺环素治疗（30 mg/Kg/12h 腹腔注射）。在第21天，动物被分配到显微镜、生化、神经化学或行为研究。我们证实，CRS诱导的可卡因自我给药的促进与NAcore中持续的GLT-1下调、基础细胞外谷氨酸的增加以及突触后结构可塑性增强有关。这些改变与CRS诱导的活化微胶质细胞以及TNF-? mRNA和蛋白质表达的增加密切相关，因为通过给予米诺环素，受损的谷氨酸稳态和可卡因自我给药的促进得以预防。我们的发现首次证明了米诺环素可以抑制CRS诱导的可卡因自我给药促进和NAcore谷氨酸稳态破坏。我们提出微胶质细胞在发展支撑应激诱导的可卡因成瘾易感性的谷氨酸能机制中发挥一定作用。