Genetic Animal Models for the Study of Serotonin

5-羟色胺神经递质系统及其关键组件之一--5-羟色胺转运体(SERT)是该项目的主要目标。临床科学实验室(LCS)SERT基因敲除小鼠的发展为研究SERT和5-羟色胺受体提供了新的活工具，SERT和5-羟色胺受体是世界上使用的数量最多的神经精神药物的靶分子。在5-羟色胺基因敲除小鼠中发现了30多种神经化学、行为和其他表型变化。由此得到的数据有助于指导LCS和其他实验室研究最近在人类SERT基因中发现的多种功能变异。 我们研究的广泛目标是更好地了解5-羟色胺神经递质系统及其在生理、行为和人类疾病，特别是神经精神疾病中的作用。5-羟色胺几乎参与了所有已知的生理功能。5-羟色胺转运体(SERT)在5-羟色胺释放后循环，从而终止5-羟色胺在其受体上的作用。 为了更好地了解5-羟色胺的功能，我们建立了一个小鼠模型，它要么缺乏5-羟色胺转运体，要么5-羟色胺转运体的表达减少了50%。这些SERT-/-和+/-小鼠细胞外液5-羟色胺(5-HT)浓度有基因比例的增加。即，+/+小鼠的SERT缺陷分别是+/+小鼠的9倍和5倍，自受孕以来就存在SERT缺陷。同时，SERT-/-小鼠细胞内可释放的5-羟色胺缺乏50%。这些小鼠在第四层皮质桶区域也有组织学异常，这在过去的一年中被证明导致了用葡萄糖利用技术测量的对胡须刺激的反应的功能障碍。 在焦虑模型中，SERT缺陷小鼠表现出明显更多的焦虑样行为。类似地，这些小鼠的HPA和交感肾上腺系统在处理和生理盐水注射等轻微应激刺激的反应中有更大的激活，血浆ACTH和肾上腺素增加，而脑下垂体和肾上腺激素显著减少。通过5-羟色胺1A受体拮抗剂的治疗，焦虑行为可以恢复到接近正常的水平。 通过含有1A序列的重组腺病毒在下丘脑中恢复5-HT1A受体数目，这些异常的焦虑反应没有变化，尽管异常的应激反应被纠正。由于5-羟色胺对神经细胞具有营养作用，我们正在研究5-羟色胺转运体和某些神经营养因子(如BDNF)对神经元功能、存活和发育的作用。我们已经成功地建立了SERT x BDNF双基因敲除小鼠模型，以进一步研究5-羟色胺转运体和BDNF在神经系统发育中的作用，因为人类遗传学研究分别表明这两个基因与情感性和其他神经精神疾病的发展有关。在过去的一年里，我们报道了缺乏一个BDNF等位基因的SERT-/-小鼠有更明显的细胞内单胺缺乏，也有更大的应激反应异常和焦虑相关行为。

The serotonin neurotransmitter system and one of its key components, the serotonin transporter (SERT), is the primary target of this project. The development of the SERT knockout mouse in the Laboratory of Clinical Science (LCS) provided a new living tool to study SERT and serotonin receptors, the target molecules for the largest numbers of neuropsychiatric drugs used in the world. 30-plus neurochemical, behavioral and other phenotypic changes have been discovered in the serotonin knockout mouse. The resulting data is helping to guide the LCS and other laboratories in investigations of the multiple functional variants recently discovered in the human SERT gene. The broad goal of our studies is a better understanding of the serotonin neurotransmitter system and its contributions to physiology, behavior and human disorders, especially neuropsychiatric disorders. Serotonin has been implicated in almost every physiological function known. The serotonin transporter (SERT) recycles serotonin after its release, thereby terminating the action of serotonin at its receptors. In our attempt to better understand serotonin's function, we have generated a mouse model which either lacks the serotonin transporter or has a 50% reduction in serotonin transporter expression. These SERT -/- and +/- mice have gene-proportionate increases in extracellular fluid serotonin (5-HT) concentrations. i.e., 9- and 5-fold excesses respectively over +/+ mice, with the SERT deficiency present since conception. At the same time, the SERT -/- mice have a 50% deficit of intracellular, releasable 5-HT. These mice also have histological abnormalities in layer IV cortex barrel fields which were demonstrated in the past year to lead to functional impairment in responses to whisker stimulation as measured using glucose utilization techniques. In models of anxiety, the SERT deficient mice exhibit markedly greater anxiety-like behaviors. Similarly, these mice have substantially greater activation of the HPA and sympathoadrenal systems in responses to minor stressful stimuli such as handling and saline injections, with high plasma ACTH and epinephrine increases, and more marked reductions in pituitary and adrenal gland hormones. The anxiety behaviors are restored to near normal levels by treatment with a serotonin 1A receptor antagonist. These abnormal anxiety responses were unchanged by restorations of 5-HT1A receptor number via recombinant adenovirus containing 1A sequences in the hypothalamus, although the abnormal stress responses were corrected. As serotonin has a trophic effect on neuronal cells, we are investigating the role of the serotonin transporter and certain neurotrophic factors such as BDNF on neuronal function, survival, and development. We have successfully developed a SERT x BDNF double knockout mouse model to further investigate the role of the serotonin transporter and BDNF in the developing nervous system, as human genetic studies have separately implicated both genes in the development of affective and other neuropsychiatric disorders. In the past year, we reported that SERT -/- mice who lacked one BDNF allele had more marked intracellular monoamine deficiencies and also had greater stress-response abnormalities and anxiety-related behaviors.