【作者】 张强；

【导师】 赵华；

【作者基本信息】 吉林大学 ， 生理学， 2016， 博士

【摘要】 甲状腺激素在中枢神经系统的发生、代谢及功能上起到至关重要的作用。甲状腺功能异常可以导致多种精神疾病,尤其是甲状腺功能低下患者通常被发现存在行动迟缓,兴趣缺失,反应迟钝,记忆力减退,社交能力下降等抑郁样行为,严重的影响甲低患者的生活质量和预后。而一些抑郁症患者有更高的风险患有甲状腺功能低下,这可能是影响疾病发展的重要原因之一。因此,探讨甲状腺功能低下所致抑郁症的发病机制对甲低抑郁症的防治,改善甲低患者的生活质量无疑具有重要的临床意义。抑郁症的发病机制复杂,目前普遍的看法是与单胺类神经递质功能失调、遗传因素、社会环境因素、个性特质、内分泌功能紊乱、脑疾病等有密切关系,其中单胺类神经递质,尤其是5-羟色胺(5-hydroxytryptamine,5-HT)递质的减少在抑郁症发病中的重要作用成为人们所关注的焦点而受到越来越多的重视。许多资料报道:抑郁患者血浆、脑脊液中5-HT水平降低,临床应用5-HT再摄取抑制剂提高中枢5-HT水平,可达到明显的抗抑郁作用,这些都反映出5-HT在抑郁症发病中具有重要的作用,并且与抑郁症发病有密切关系的其他诸多因素,最终也可通过影响5-HT系统而发挥作用。已有研究证明,下丘脑-腺垂体-甲状腺系统与中枢5-HT系统具有密切的功能联系,甲状腺素能抑制中缝背核5-HT1A受体(一个自身抑制性受体)的敏感性,从而提高5-HT水平。而丙硫氧嘧啶(一种硫脲类抗甲状腺药物)诱导的甲状腺功能低下的动物血液和一些脑区单胺类神经递质含量明显降低。临床上甲低伴有抑郁行为的病人血液中5-HT递质含量降低,说明甲低所引起的抑郁行为与中枢5-HT递质降低有密切关系。然而,甲状腺功能紊乱如何影响中枢5-HT系统,联系这两大系统的关键部位位于何处仍不清楚。大量研究证明,中缝背核是合成和释放5-HT神经递质的主要部位,损毁中缝背核区,可使脑内5-HT含量明显降低。而脑内控制中缝背核的关键部位在丘脑的外侧缰核,电刺激外侧缰核可抑制中缝背核神经元活动,两者之间有密切的纤维和功能联系。动物实验和临床抑郁症患者治疗中都证明外侧缰核在抑郁症发病中起重要作用。在四种不同的动物抑郁模型中,外侧缰核的代谢活动增强,也有实验证明损毁外侧缰核可以通过提高中背缝核内5-HT水平改善大鼠的抑郁样行为,因此外侧缰核在抑郁症发病中的作用引起了人们极大的兴趣。更有意义的是,外侧缰核与甲状腺具有密切的功能联系,在颈上神经节切除诱导的甲低大鼠中,大鼠外侧缰核的体积明显增大,两者之间存在负相关关系。在甲状腺切除所致抑郁行为大鼠中,给予丙咪嗪可降低外侧缰核的代谢达到抗抑郁作用。也有研究表明外侧缰核分布有甲状腺素受体。这些结果说明外侧缰核可能介导了下丘脑-腺垂体-甲状腺系统对中缝背核5-HT系统的影响,从而参与甲低所致抑郁症的发病过程。本实验我们应用行为学检测,组织化学方法,高效液相色谱法及WesternBlot法,检测甲状腺全切除(thyroidectomy,TD)大鼠的抑郁样行为,建立甲状腺功能低下抑郁模型,进一步观察对TD大鼠外侧缰核损毁前后以及补充甲状腺素前后其行为学变化,外侧缰核、中缝背核的活动度改变以及中缝背核内5-HT水平的变化,从而探索外侧缰核对甲低大鼠抑郁行为的影响及可能机制。实验结果如下:1.甲状腺全切术后甲状腺功能低下大鼠表现出明显的抑郁样症状,表现为强迫游泳试验中(force swimming test,FST)上窜时间明显减少而不动时间明显延长。在旷场试验中(open filed test,OFT),TD鼠的移动距离与假手术组相比明显减少。高效液相色谱法检测TD大鼠中缝背核内5-HT含量与对照组相比明显降低。这些结果充分证明了甲状腺功能减低可以导致抑郁样行为,从而成功建立甲状腺全切后大鼠的抑郁模型。2.组织化学检测外侧缰核活动度提示甲状腺功能低下抑郁大鼠外侧缰核活动度明显增高,而这种增高可以通过补充甲状腺素后恢复。Western blot检测甲低大鼠缰核中甲状腺素受体β(Thyroid hormone receptor β,THRβ),β钙调蛋白激酶 Ⅱ(βcalcium/calmodulin-dependent protein kinase Ⅱ,βCaMK-Ⅱ)表达增高。3.外侧缰核损毁或补充甲状腺素后,甲低抑郁大鼠的抑郁症状有所改善,表现为强迫游泳试验中上窜时间延长而不动时间明显缩短。在旷场试验中,缰核损毁或补充甲状腺素后,大鼠的移动距离与对照组组相比也明显增加。4.组织化学检测发现甲低大鼠中缝背核细胞色素氧化酶的活性与对照组相比明显降低,这种降低可通过补充甲状腺素后恢复。外侧缰核损毁后,高效液相色谱法检测损毁组大鼠中缝背核内5-HT含量较假损毁组明显升高。根据实验结果我们得到以下结论,甲状腺切除术后甲状腺功能低下大鼠可以出现抑郁样行为。这种抑郁样行为可能是由体内低下的甲状腺功能状态通过兴奋外侧缰核进抑制中缝背核内5-HT的合成和释放而实现的。更多还原

【Abstract】 Thyroid hormone plays an important role in the development,metabolism and function of most organs,and the disturbance of thyroid function could result in dysfunction of many organs.It has been reported that hypothyroidism has a close relationship with psychiatric disorders such as depression.The patients with hypothyroidism usually present with various kinds of depression-like behavior as cognitive dysfunction,apathy,dull reaction and poor sociability,which severely affects the life quality and its prognosis.While,some depression patients are more prone to suffer from hypothyroidism,which might be an important risk factor in the development of depression.So,there will be an important clinical significance to find out the mechanism of depression that induced by hypothyroidism,which could be beneficial for the prevention and treatment of the patient with hypothyroidism-induced depression.The pathogenesis of depression is complicated,it might closely related to monoamine neurotransmitter disorder,social environment,individual characteristic,endocrine changes and mental diseases.The deficiency of monoamine neurotransmitter,especially serotonin(5-hydroxytryptamine,5-HT),is focused on because of its important role in the onset of depression.It is reported that 5-HT levels in serum and cerebrospinal fluid declines in depression patients,serotonin uptake inhibitor has already been used as anti-depressive treatment in clinic,which undoubtly demonstrates that the 5-HT plays a key role in depression,and other factors related to depression also work via affecting the 5-HT system.Other studies argue there has a close functional interaction between hypothalamus-pituitary-thyroid(HPT)axis and serotonin system.5-HT levels could be elevated by thyroid hormone by inhibiting 5-HT 1A receptors in dorsal rapheal nuclei(DRN).Monoamine neurotransmitter is lower in serum and some brain region of rats with hypothyroidism induced by Propylthiouracil.Decreased serum 5-HT levels could also be found in hypothyroidism with depressive-like behavior,which indicates the depressive-like behavior resulting from hypothyroidism is associated with the declined central serotonin neurotransmitter.But the mechanism underlying the effects of thyroid disorders on the central serotonin system is unknown and the key region that connects the HPT axis and serotonin systems has yet not to be identified.DRN is the principal part of the 5-HT synthesis and release,DRN lesion could result in significant decreased central 5-HT levels.The key region that controls the DRN is lateral habenular nucleus(LHb).Neuron activity in DRN could be inhibited by electrical stimulation on LHb,and there exists a complicated functional projection between them.Lots of evidence show that LHb acts as a key point in depression both in experimental animals and in clinical patients.Activity of LHb is obviously increased in the four different animal models of depression.Other research indicates depressive-like behavior could be improved by the increased 5-HT levels induced by LHb lesion.What’s more,there exits a close functional connection between LHb and thyroid,an enlarged LHb size could be detected in hypothyroidism rats induced by the excision of cervical neural ganglion.Dynaprin could exert an antidepressive effect on depressive rats by decreasing the metabolism of LHb,Other studies show that the thyroid hormone receptors exist in LHb,which indicates LHb may involved in the pathogenesis of depression resulting from hypothyroidism by mediating the effect of hypothalamus-pituitary-thyroid axis on 5-HT system in DRN.In our work,we used behavior tests,histochemistry,high efficiency liquid chromatography and Western blot to measure depressive behavior of thyroidectomy(TD)rats,and then,to observe the changes of depressive-like behavior,neural activity of LHb and DRN,5-HT levels in DRN after LHb lesion and thyroid hormone supplement on TD rats,further to discuss the role of LHb in depressive-like behavior of rats induced by hypothyroidism and the underlying mechanism.The results are list as follow:1.The behavior test showed depressive-like behavior was obvious in TD rats with prolonged immobility time and decreased climbing time in ’force swimming test(FST).The movement distance was also declined in TD rats comparing with the sham rats in open-field test(OST).High efficiency liquid chromatography showed the 5-HT levels of DRN were decreased in TD rats compared with the sham.It reveals that the depressive-like behavior could be induced by hypothyroidism in TD rats.2.Histochemistry manifested the COX activity in LHb of TD rats was much higher than that of the sham,which could be restored after thyroid hormone supplement of TD rats.Western blot showed the expression of thyroid hormone receptor β(THR)and β calcium/calmodulin-dependent protein kinase Ⅱ(βCaMK-Ⅱ)were up regulated.These changes could recovered by thyoird hormone supply.3.After LHb lesion or thyroid hormone supplement,the depressive-like behavior of TD rats were improved.In FST,the climbing time was increased and the time spent immobile was decreased compared with the sham,and the mobile distance was increased in OFT.4.The COX activity in DRN of TD rats was decreased compared with the sham,which could be reversed after thyroid hormone supplement.High efficiency liquid chromatography showed 5-HT levels of DRN in TD rats were increased after LHb lesion.According to our results,we conclude that depressive like behavior could be induced by hypothyroidism in TD rats,which results from the decreased 5-HT level of DRN that was attributed to the inhibitory effect from the excited LHb.更多还原