Neurotrophic Mechanisms in Opiate and Cocaine Action

描述（由申请人提供）：该提案继续我们对神经营养信号通路在慢性暴露于阿片类或兴奋剂滥用药物的腹侧被盖区（VTA）-丘脑核（NAc）奖赏回路中诱导的神经可塑性中的作用的表征。该提案有三个目标：1）描述BDNF-TrkB信号在VTA-NAc中调节对阿片类药物和可卡因的分子、细胞和行为反应的细胞类型特异性作用; 2）描述介导阿片类药物诱导VTA多巴胺神经元形态学变化的能力的BDNF-TrkB信号级联中的适应;以及3）描绘BDNF-TrkB信号级联中的适应，其介导可卡因和阿片类药物诱导NAc中等多刺神经元中相反形态学变化的能力。在过去的5年里，我们在每个目标上都取得了重要进展，并有大量的初步数据支持在拟议的新资助期内进行高度深入和机制性的研究。使用遗传突变小鼠和病毒介导的基因转移，这使得高度本地化的成年动物的腹侧被盖区或NAc内的BDNF或TrkB的敲除，我们已经证明了不同的作用，BDNF-TrkB信号在调节阿片类药物和可卡因的反应。使用更先进的工具，现在使这种敲除在特定的神经元细胞类型在这些大脑区域内，我们将表征的具体影响D1与D2含有NAc中等多刺神经元，腹侧被盖区多巴胺神经元，在这些现象。阿片类药物在腹侧被盖区多巴胺神经元中引起的最引人注目的变化之一是它们的整体尺寸减小。这种减少是由这些神经元内BDNF信号传导的损伤介导的，特别是IRS-AKT通路的下调。我们现在有证据表明，这种下调是AKT-RHEB-mTOR信号转导中阿片类药物诱导的整体适应的一部分。拟议的实验旨在进一步建立详细的分子事件，这种形态适应的基础。相反，可卡因和阿片类药物引起NAc中棘神经元的明显变化：可卡因增加，而阿片类药物减少，神经元的树突分支和棘密度。我们已经表明，这些适应也涉及改变BDNF信号，现在提出进一步表征神经营养信号通路的精确变化，包括NF？调节这些适应的B信号。总之，拟议的实验将为阿片类药物和兴奋剂改变VTA-NAc神经元的戏剧性方式提供全新的见解，这些信息可以在未来几年中被挖掘出来，以确定改进的药物成瘾诊断测试和治疗方法。 公共卫生相关性：这项资助的目的是研究神经营养信号通路在小鼠药物滥用模型中的作用，作用于大脑的奖励回路。我们研究了长期暴露于滥用药物对大脑奖励区域内这些复杂信号通路的水平和活性的影响。然后，我们通过使用遗传突变小鼠或病毒介导的基因转移来操纵奖励区域中特定信号蛋白的活性，并研究这些操纵的分子、细胞和行为后果。总之，这些研究有望提供关于滥用药物如何在长期服用后改变大脑奖励回路的全新信息，并为开发改进的诊断测试和更有效的药物成瘾治疗提供新的线索。

DESCRIPTION (provided by applicant): This proposal continues our characterization of the role of neurotrophic signaling pathways in the neural plasticity induced in the ventral tegmental area (VTA)-nucleus accumbens (NAc) reward circuit by chronic exposure to opiate or stimulant drugs of abuse. The proposal has three Aims: 1) to delineate the cell-type specific actions of BDNF-TrkB signaling in the VTA-NAc in regulating molecular, cellular, and behavioral responses to opiates and cocaine; 2) to delineate the adaptations in BDNF-TrkB signaling cascades that mediate the ability of opiates to induce morphological changes in VTA dopamine neurons; and 3) to delineate the adaptations in BDNF-TrkB signaling cascades that mediate the ability of cocaine and opiates to induce opposite morphological changes in NAc medium spiny neurons. We have made important progress in each of these Aims over the past 5 years, and have substantial preliminary data to support highly penetrating and mechanistic studies over the proposed new grant period. Using genetic mutant mice and viral-mediated gene transfer, which has enabled highly localized knockouts of BDNF or TrkB within the VTA or NAc of adult animals, we have demonstrated distinct roles for BDNF-TrkB signaling in regulating responses to opiates and cocaine. Using more advanced tools, which now enable such knockouts in specific neuronal cell types within these brain regions, we will characterize the specific influence of D1 vs. D2 containing NAc medium spiny neurons, and VTA dopamine neurons, in these phenomena. One of the most dramatic changes that opiates induce in VTA dopamine neurons is a decrease in their overall size. This decrease is mediated by an impairment in BDNF signaling within these neurons, specifically, downregulation of the IRS-AKT pathway. We now have evidence that this downregulation is part of overall opiate-induced adaptations in AKT-RHEB-mTOR signaling. The proposed experiments are designed to further establish the detailed molecular events that underlie this morphological adaptation. In contrast, cocaine and opiates induce distinct changes in NAc medium spiny neurons: cocaine increases, whereas opiates decrease, the neurons' dendritic arborizations and spine density. We have shown that these adaptations too involve altered BDNF signaling, and now propose to further characterize the precise changes in neurotrophic signaling pathways, including changes in NF?B signaling that mediate these adaptations. Together, the proposed experiments will provide fundamentally new insight into the dramatic ways in which opiates and stimulants change VTA-NAc neurons, information which could be mined in future years to define improved diagnostic tests and treatments for drug addiction. PUBLIC HEALTH RELEVANCE: The objective of this grant is to study the role of neurotrophic signaling pathways, acting in the brain's reward circuits, in drug abuse models in mice. We investigate the influence of chronic exposure to drugs of abuse on levels and activity of these complex signaling pathways within brain reward regions. We then manipulate the activity of specific signaling proteins in reward regions by use of genetic mutant mice or viral mediated gene transfer, and study the molecular, cellular, and behavioral consequences of these manipulations. Together, these studies promise to provide fundamentally novel information concerning how drugs of abuse alter the brain's reward circuits after chronic administration, and to offer new leads toward the development of improved diagnostic tests and more effective treatments of drug addiction.