Animal Models For Study Of Neurotransmitter Function/neu

我们的主要关注点是5-羟色胺能系统，我们继续使用本实验室开发的5-HTT基因敲除小鼠模型作为5-羟色胺能系统功能紊乱的模型。在此之前，我们描述了这种小鼠的一种行为表型，即焦虑增加。进一步的行为特征表明，这只小鼠也表现出强烈的缺乏行为绝望。动物模型中的行为绝望被认为与人类中报道的抑郁状态相似；缓解人类抑郁的药物减少了动物模型中的行为绝望。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(SSRI)缓解抑郁的机制。5-羟色胺的功能与冲动和攻击性有关。5-HTT基因敲除小鼠表现出攻击性的减少。我们发现，尽管5-HTT基因敲除小鼠表现出整个组织中5-羟色胺的基因剂量耗竭，但细胞外空间的5-羟色胺水平升高，反映出缺乏从细胞外空间移除5-羟色胺的转运体。因此，5-HTT基因敲除小鼠缺乏攻击性和行为绝望可能是细胞外空间5-羟色胺可获得性增加的结果。正如先前报道的那样，在5-HTT基因敲除的小鼠中，5-HT1A的表达和功能都降低了。此外，我们还发现，除了5-HT1A受体的改变外，这些小鼠还表现出区域性的5-HT2A/C受体表达的改变。杏仁核中的5-HT2A/C受体增加，杏仁核是大脑中与攻击有关的区域。5-羟色胺及其突触前和突触后受体以及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正在被研究。我们在5-羟色胺在神经内分泌和其他神经递质功能中的相互作用的研究方面也取得了进展。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基因敲除小鼠的压力反应。5-HTT基因敲除小鼠表现出可能与慢性应激产生的神经内分泌相似的神经内分泌特征。尽管5-HTT基因敲除小鼠的基础血浆肾上腺素水平没有变化，但血浆中肾上腺素的分泌增加，肾上腺组织中的肾上腺组织和脑下垂体ACTH对短暂的应激刺激做出反应。我们正在研究一种假设，即5-羟色胺在适应压力的能力中起着关键作用。压力通常会导致高度的焦虑状态，这可以通过同时作用于5-羟色胺和GABA系统的药物来缓解。我们已经开始研究5-羟色胺和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都表现出GABA能功能的改变。我们正在测试一种假设，即这种改变的GABA功能可能反映了这些小鼠缺乏适应压力的能力，以及一种假设，即发育过程中过量的细胞外5-羟色胺可能会改变GABA系统。我们还微调了我们的手术和高效液相程序，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5-羟色胺能功能的外周测量很少，这些技术将使我们能够描述中枢神经系统中神经内分泌变化与外周神经内分泌变化的可能相关性。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进行关联将是至关重要的。5-羟色胺可能对神经细胞有营养作用，SSRIs已被证明可以提高某些神经细胞的活力。我们的同事已经证明，5-HTT基因敲除小鼠对氧化应激更具抵抗力。5-HTT基因敲除小鼠从胚胎第一天起就在缺乏5-羟色胺转运体的情况下发育，因此是研究慢性5-羟色胺转运体阻断和细胞外5-羟色胺过量对发育影响的有效模型。考虑到这一点，我们正在研究5-羟色胺转运体和某些神经营养因子，如BDNF在神经元功能、生存和发育中的作用。为了进一步研究5-羟色胺转运体在神经系统发育中的作用，我们已经成功地建立了一种小鼠神经干细胞系，目前正在开发一种来源于5-HTT基因敲除小鼠的神经干细胞系。虽然焦虑经常但不总是伴随着抑郁，但我们对这个模型很感兴趣，因为它与焦虑但不抑郁的动物有关。单独评估这种关系可能有利于为焦虑症和抑郁症设计适当的治疗方法。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，以及缺乏5-HTT对发育的影响。

Our primary focus is 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; drugs that alleviate depression in humans decrease behavioral despair in animal models.This animal may be useful in elucidating the mechanisms of chronic selective serotonin transporter inhibitors (SSRIs) that underlie remission of depression. Serotonin function has been linked to impulsivity 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. 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 of pituitary ACTH in response to brief stress stimuli. We are investigating the hypothesis that serotonin plays a critical role in the ability to adapt to stress. 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. Separately evaluating this relationship may be advantageous to designing appropriate treatment for anxiety disorder as well as depression. 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.