中脑腹侧被盖区-腹侧海马多巴胺能投射通路调控慢性痛诱发抑郁的机制研究

Chronic pain often induce depression, and the latter further aggravates the pain sensation, forming a vacious cycle of mutual promotion. Recent studies demonstrate that both midbrain ventral tegmental area (VTA) and the ventral hippocampus are important brain areas associated with the functional regulation of chronic pain induced depression. Our preliminary data showed that the expression of tyrosine hydroxylase (TH) was decreased obviously in the VTA of mice suffered with chronic pain for more than 8 weeks, and companied with remarkable depression-like behavior. Meanwhile, the specific activation of VTA-ventral hippocampal dopaminergic nerve terminals could obviously revise the animals’ depression-like behavior, which implied that the dopaminergic neurons in VTA-hippocampus pathway might be involved in the regulation process of chronic pain induced depression. To identify this hypothesis, this project intends to build chronic pain induced depression animal model, and combining tract-tracing techniques with optogetics, morphology, molecular biology, pharmacological genetics, and electrophysiology to investigate the functional and morphological plasticity changes of the dopaminergic neurons in VTA-hippocampus projection pathway in the process of chronic pain induced depression, and the influence on the functional activity and key neural mechanism of postsynaptic neurons in hippocampus. So as to clarify that VTA-hippocampus dopaminergic projection may be an important pathway to regulate chronic pain induced depression, which may provide novel strategies for the clinical intervention of chronic pain and depression interaction, and new targets for prevention of depression occurrence on patients with chronic pain.

慢性痛常诱发抑郁，而后者又会加重疼痛，形成相互促进的恶性循环。新近研究表明中脑腹侧被盖区（VTA）和腹侧海马可能参与了慢性痛诱发抑郁的功能调控。我们的预实验观察到慢性痛8周时，小鼠VTA内TH的表达显著下降，并伴有明显的抑郁样行为；特异性激活VTA-腹侧海马内DA能神经终末可明显改善动物的行为学表现，提示VTA-海马投射通路内DA能神经元参与了慢性痛诱导抑郁的产生和调控过程。为了证实此假设，本项目拟构建慢性痛诱发抑郁动物模型，综合运用束路追踪结合行为学、光遗传学、形态学、分子生物学、药理遗传学和电生理学等技术，检测VTA-腹侧海马DA能投射通路在调控慢性痛诱发抑郁过程中DA能神经元功能和形态结构的可塑性变化，及其对海马内突触后神经元的功能活动的影响和关键神经机制，明确VTA-海马DA能投射可能是调控慢性痛诱发抑郁的重要通路，为临床上干预慢性痛与抑郁交互恶化，尽早预防其发生提供新的策略和靶点

临床上慢性痛常伴有抑郁症的发生，两者相互促进而难以治疗。本课题综合运用化学遗传学、光遗传学和药理学等方法，研究腹侧被盖区（VTA）到腹侧海马（vHPC）的多巴胺能投射通路调控慢性痛诱发抑郁共病的机制。结果显示：①VTA内DA能神经元向vHPC内谷氨酸能和GABA能神经元发出直接纤维投射；且VTADA-vHPC通路参与急性伤害性信息的传递。②cuff模型术后8周，慢性痛组小鼠自主活动能力无变化，未出现焦虑样行为；但部分cuff组小鼠则出现了明显的抑郁样行为（susceptible组），同时可见VTA内多巴胺能神经元被抑制但GABA能神经元被激活；其余cuff组小鼠则未出现抑郁样行为（resilient组）。③利用化学遗传学技术特异性激活VTA-vHPC通路，可明显改善susceptible组小鼠的抑郁样行为，但对各组机械痛阈无影响。④利用caspase3技术特异性凋亡向vHPC发出直接纤维投射的VTA内神经元，可引起正常小鼠出现抑郁样行为，但未出现机械痛阈的改变。⑤利用TH-Cre小鼠结合光遗传学技术，以pahsic模式特异性激活VTADA-vHPC通路，可明显改善susceptible组小鼠的抑郁样行为；但对各组机械痛阈亦无影响。⑥利用光遗传学结合药理学方法，当phasic光刺激分别结合多巴胺D1受体抑制剂（SCH23390）或结合多巴胺D2受体抑制剂（sulpiride）时，均可引起resilient组小鼠出现抑郁样行为，同时可以阻断phasic激活VTADA-vHPC通路在susceptible组产生的抗抑郁作用；但SCH23390可引起sham组小鼠出现抑郁样行为，而sulpiride未观察到此现象。以上结果证明，VTADA-vHPC投射通路在慢性痛诱发抑郁共病的发生和发展中起到关键作用，其机制可能主要是通过vHPC内D1R/D2R而发挥作用。