食欲素介导的神经环路异常导致抑郁症发病机理研究

Orexin is a neuropeptide that is produced in the dorsomedial hypothalamic nucleus (DMH) and the lateral hypothalamic area (LHA). It mediates eating behavior, sleep-wake cycle, reward reactions, and stress responses, all of which are physiological functions that are disturbed in depression. The mechanism of this neuronal circuit disorder remains, however, unclear. Our working hypothesis is that orexinergic neurons in DMH/LHA may directly innervate neurons in the hypothalamic paraventricular nucleus (PVN) to regulate the activity of the hypothalamo-pituitary-adrenal (HPA) axis. In addition, orexin may indirectly affect the PVN activity via modulating neurons targeting the PVN in the biological clock, the suprachiasmatic nucleus (SCN). An imbalanced regulation of this circuit may cause the over-activation of the HPA axis and depressive symptoms including decreased appetite, reduced sex drive, anxiety and sleep disturbances. We will study 1) postmortem brain material of depressive patients and of narcolepsy patients who lack orexin; 2) hypothalami of a rat depression model, of orexin knockout, orexin knock down mouse, together with 3) brain slices containing the SCN of these animals, with methods including immunocytochemistry, molecular biology, pharmacology, and electrophysiology to investigate the neuronal circuit changes in a comprehensive way. We will further validate whether the models (the nocturnal animals rat and mouse) reflect indeed the circuit changes in depression in the diurnal human. This study will help us to understand the orexin mediated neuronal circuit changes in stress and depression and may offer novel orexin related targets for antidepressant therapies.

背内侧下丘脑核（DMH）和下丘脑外侧区（LHA）神经元合成的食欲素（Orexin）直接介导了进食、睡眠—觉醒、奖赏反应、应激反应等和抑郁症症状相关的生理功能调节，其神经环路调节机制尚待阐明。根据初步证据我们提出假说：DMH/LHA中的Orexin能神经元通过直接支配下丘脑室旁核（PVN）而调节下丘脑—垂体—肾上腺（HPA）轴活性，也通过支配生物钟视交叉上核（SCN）调节其活性而间接影响HPA轴活性；该环路功能失调导致抑郁症中HPA轴过度激活和食欲、性欲降低，生物学节律紊乱等症候群。我们将在1）抑郁症患者和Orexin缺陷的发作性睡病患者脑标本，2）抑郁症动物模型、Orexin基因敲除、Orexin基因敲减小鼠下丘脑组织和SCN脑片，采用形态学、分子生物学、药理学、电生理学等方法研究DMN/LHA—SCN—PVN神经环路调节机制以验证我们的假说，寻找Orexin系统中抗抑郁药物作用靶点。

下丘脑合成的食欲素（Orexin）直接介导了进食、睡眠—觉醒、应激反应等和抑郁症症状相关的生理功能调节。我们推测orexin能神经元通过直接支配下丘脑室旁核（PVN）而调节下丘脑—垂体—肾上腺（HPA）轴活性，也通过支配生物钟视交叉上核（SCN）而间接影响HPA轴活性；该环路功能失调导致抑郁症和自杀。我们在orexin生产区下丘脑研究抑郁症患者orexin-A表达，在SCN研究GABA和血管加压素（AVP）表达；在抑郁症患者脑脊液中检测orexin-A水平；在orexin神经投射区前额叶研究orexin受体（OXR1和OXR2）的mRNA表达水平以及与自杀的关联。在观察到orexin系统变化呈现显著性别差异后，我们在常用的大鼠抑郁症模型，即慢性不可预知性应激（CUS）大鼠对比研究在人脑样本中的发现。我们发现女性抑郁症患者下丘脑orexin-A-ir总量较女性对照组显著增加并与PVN内促肾上腺皮质激素释放激素（CRH）-ir水平呈显著正相关。对照组下丘脑 orexin-A-ir表现出显著的昼夜节律，这种节律在抑郁症患者缺失。在较为年轻的个体（平均40岁），前扣带回（ACC）与背外侧前额叶（DLPFC）中均有OXR1-mRNA与OXR2-mRNA表达；而较为年长的个体（平均78岁），ACC内仅仅检测到OXR1-mRNA，DLPFC内仅仅检测到OXR2-mRNA表达。此外，死于自杀的男性抑郁症患者ACC内OXR2-mRNA水平显著高于男性对照组，而没有自杀的男性患者无此表现。抑郁症患者SCN内GAD65/67-ir、GAD67-mRNA 均显著高于对照组，男性对照组下丘脑orexin-ir 和SCN内 GAD65/67-ir 呈显著正相关而女性对照组内则无此相关性。.在CUS大鼠和急性应激大鼠，我们发现了与人类应激反应、抑郁症中类似的性别差异。此外，雌性CUS大鼠下丘脑prepro-orexin-mRNA与CRH-mRNA水平呈现显著正相关，额叶皮层内OXR1-mRNA显著升高；而雄鼠无此变化。我们继而检测了介导雄激素向雌激素转化的关键限速酶芳香化酶在抑郁症发病中的作用。.我们的发现显示orexin能系统在抑郁症中呈现出性别、年龄、脑区以及自杀特异性的改变，而且与PVN-CRH、SCN-GABA环路，继而与HPA轴活性密切相关。CUS大鼠模型orexin能系统改变仅仅部分