Animal Models for Study of Neurotransmitter Function/Neu

在过去的一年里，我们继续研究神经精神疾病的遗传和分子机制。我们的主要重点一直是肾上腺素能系统，我们继续使用5-羟色胺转运蛋白（5-HTT）敲除小鼠模型，在这个实验室开发的破坏肾上腺素能功能的模型。先前我们描述了这种小鼠的行为表型，表现为焦虑增加。进一步的行为表征表明，这种小鼠也表现出强烈的行为绝望。动物模型中的行为绝望被认为与人类中报告的抑郁状态平行，减轻人类抑郁的药物减少了动物模型中的行为绝望。因此，这些小鼠代表了反映不存在抑郁症的动物模型，并且是研究可能起作用以承受抑郁状态或从抑郁状态恢复的分子机制的有用模型。特别是，这种动物可能有助于阐明慢性选择性5-羟色胺转运体抑制剂（SSRIs）缓解抑郁症的作用。 血清素的功能与冲动和攻击性有关。血清素功能和攻击性之间存在反比关系。5-HTT敲除小鼠表现出攻击性降低。我们已经发现，尽管5-HTT敲除小鼠在整个组织制备物中显示5-羟色胺的基因剂量耗尽，但细胞外空间中的5-羟色胺水平升高，反映了缺乏从细胞外空间去除5-羟色胺的转运蛋白。因此，在5-HTT敲除小鼠中缺乏攻击性和行为绝望可能是细胞外空间中5-羟色胺可用性增加的结果。 如前所述，在5-HTT敲除小鼠中5-HT 1A表达和功能降低。我们认为，这种下调5-HT 1A受体是由于过量的5-HT在突触。此外，我们还发现，除了5-HT 1A受体的改变，这些小鼠还显示出5-HT 2A/C受体以区域特异性方式的表达改变。5-HT 2A/C受体在杏仁核中增加，杏仁核是与攻击性相关的大脑区域。正在研究5-羟色胺及其突触前和突触后受体沿着相关的细胞内信号通路在焦虑、抑郁和攻击性表达中的作用。 我们在神经内分泌和其他神经递质功能中5-羟色胺相互作用的研究也取得了进展。由于压力可能是抑郁和焦虑发展的主要因素，我们研究了5-HTT敲除小鼠的压力反应。5-HTT敲除小鼠显示出的神经内分泌特征可能与慢性应激产生的特征相似。尽管5-HTT基因敲除小鼠血浆肾上腺素的基础水平不变，但血浆中肾上腺素的分泌增加，同时肾上腺组织中肾上腺素的消耗以及垂体ACTH的消耗也增加。我们正在调查的假设，血清素在适应压力的能力中起着至关重要的作用。 由于压力往往会导致焦虑状态加剧，这可以通过作用于血清素和GABA系统的药物来缓解。我们已经开始研究血清素和GABA系统的相互作用。5-HTT基因敲除小鼠在行为和分子水平上显示出GABA能功能的改变。我们正在测试的假设，这种改变GABA功能可能反映了缺乏能力，这些小鼠适应压力，以及假设，过量的细胞外5-羟色胺在发展过程中可能会改变GABA系统。 我们还微调了我们的手术和HPLC程序，使我们能够将大脑和其他组织中神经递质和激素的变化与血浆中的变化联系起来。由于中枢神经内分泌功能的外周指标很少，这些技术将使我们能够描述中枢神经系统神经内分泌改变与外周神经系统神经内分泌改变的可能相关性。这对于将从动物身上收集的基础科学数据与从人类受试者身上收集的数据相关联至关重要。 5-羟色胺可能对神经元细胞具有营养作用，并且SSRI已显示出增加某些神经元细胞的活力。我们的同事已经证明，5-HTT敲除小鼠对氧化应激的抵抗力更强。5-HTT敲除小鼠从胚胎第一天起在缺乏5-羟色胺转运蛋白的情况下发育，因此代表了研究慢性5-羟色胺转运蛋白阻断以及细胞外5-羟色胺过量的发育作用的有效模型。考虑到这一点，我们正在研究5-羟色胺转运蛋白和某些神经营养因子（如BDNF）在神经元功能、存活和发育中的作用。我们已经成功地开发了一个小鼠神经元干细胞系，目前正在开发一个神经元干细胞系来自5-HTT基因敲除小鼠，以进一步研究的作用，5-羟色胺转运蛋白在发育中的神经系统。 虽然焦虑通常但并不总是与抑郁症共病，但我们对这个模型感兴趣，因为它与焦虑但不抑郁的动物有关。解除这种关系可能有利于抑郁症和焦虑症的适当治疗。我们正在继续研究抑郁症和焦虑症中5-羟色胺的分子机制和关系，并调查缺乏5-HTT对发育的影响。

In the last year we have continued to investigate the genetic and molecular mechanisms underlying neuropsychiatric diseases. Our primary focus has been on the serotonergic system and we have continued to use the serotonin transporter (5-HTT) knockout mouse model developed in this laboratory as a model of disrupted serotonergic function. Previously we described a behavioral phenotype of this mouse as one displaying an increase in anxiety. Further behavioral characterization has shown that this mouse also exhibits robust lack of behavioral despair. Behavioral despair in animal models is believed to parallel depressive states reported in humans and drugs that alleviate depression in humans decrease behavioral despair in animal models. Thus these mice represent an animal model that reflects an absence of depression and are a useful model in which to study the molecular mechanism that may be acting to withstand or recover from depressive states. In particular, this animal may be useful in elucidating the effects of chronic selective serotonin transporter inhibitors (SSRIs) that underlie remission of depression. Serotonin function has been linked to impulsivity and aggression. There is an inverse relationship between serotonin function and aggression. The 5-HTT knockout mice show a decrease in aggression. We have discovered that although 5-HTT knockout mice show a gene-dose depletion of serotonin in whole tissues preparations, serotonin levels in the extracellular space are elevated reflecting the lack of transporters to remove serotonin from the extracellular space. Thus the lack of aggression and behavioral despair in the 5-HTT knockout mice may be a result of increased availability of serotonin in the extracellular space. As previously reported there is a decrease in 5-HT1A expression and function in 5-HTT knockout mice. We suggest that this downregulation of the 5-HT1A receptors is due to the excess 5-HT in the synapse. Furthermore we have discovered that in addition to 5-HT1A receptor alterations these mice also show altered expression of 5-HT2A/C receptors in a regionally specific manner. 5-HT2A/C receptors are increased in the amygdala, a brain region associated with aggression. The role of serotonin and its pre- and post- synaptic receptors along with associated intracellular signally pathways in the expression of anxiety, depression, and aggression are being investigated. We have also made progress in the study of the interaction of serotonin in neuroendocrine and other neurotransmitter functions. As stress can be a major factor in the development of depression and anxiety we studied the stress responses in 5-HTT knockout mice. 5-HTT knockout mice display a neuroendocrine profile that may parallel that produced by chronic stress. Although basal levels of plasma epinephrine are unchanged in 5-HTT knockout mice, there is an enhanced secretion of epinephrine in to the plasma with coincidental depletion in adrenal tissues as well as depletion in of pituitary ACTH. We are investigating the hypothesis that serotonin plays a critical role in the ability to adapt to stress. As stress often results in a heightened state of anxiety, which can be moderated by drugs that act on both the serotonin and GABA systems. We have begun investigating the interaction of serotonin and the GABA system. 5-HTT knockout mice display altered GABAergic function at both the behavioral and molecular levels. We are testing the hypothesis that this altered GABA function may reflect a lack of ability of these mice to adapt to stress as well as the hypothesis that excess extracelluar serotonin during development may alter the GABA system. We have also fine-tuned our surgical and HPLC procedures to allow us to correlate alterations of neurotransmitters and hormones in the brain and other tissues with that in plasma. As there are few peripheral measures of central serotonergic function, these techniques will allow us to describe possible correlations of neuroendocrine alterations in the central nervous system with that of the periphery. This will be critical in correlating basic science data collected in animals with that from human subjects. Serotonin may have a trophic effect on neuronal cells and SSRIs have been shown to increase the viability of certain neuronal cells. Our colleagues have shown that 5-HTT knockout mice are more resistant to oxidative stress. The 5-HTT knockout mice develop in the absence of serotonin transporter from embryonic day one and thus, represent a potent model in which study the developmental effects of chronic serotonin transporter blockade as well as extracellular serotonin excess. With this in mind, we are investigating the role of the serotonin transporter and certain neurotrophic factors such as BDNF in neuronal function, survival, and development. We have successfully developed a mouse neuronal stem cell line and are currently developing a neuronal stem cell line derived from 5-HTT knockout mice in order to further investigate the role of the serotonin transporter in the developing nervous system. Although anxiety is often, but not always, co-morbid with depression, we are interested in this model as it relates to an anxious but not depressed animal. Un-teasing this relationship may be advantageous in appropriate treatment for depression as well as anxiety. We are continuing to study the molecular mechanisms and relationship between serotonin in depression and anxiety as well as investigating the developmental effects of the lack of 5-HTT.