Neurotrophic Mechanisms in Opiate and Cocaine Action

描述（由申请人提供）：本提案继续我们对神经营养信号通路在腹侧被盖区(VTA)-伏隔核（NAc）奖励回路中因长期暴露于鸦片或兴奋剂滥用而诱导的神经可塑性中的作用的描述。该提案有三个目的：1)描述VTA-NAc中BDNF-TrkB信号在调节对阿片类药物和可卡因的分子、细胞和行为反应中的细胞类型特异性作用；2)阐明BDNF-TrkB信号级联介导阿片类药物诱导VTA多巴胺神经元形态改变的适应性；3)描述BDNF-TrkB信号级联的适应性，该级联介导可卡因和阿片类药物诱导NAc介质棘神经元相反形态变化的能力。过去5年，我们在这些目标上都取得了重要进展，并有大量初步数据支持在拟议的新拨款期内进行高度深入和机械的研究。利用基因突变小鼠和病毒介导的基因转移，在成年动物的VTA或NAc中实现了BDNF或TrkB的高度局部敲除，我们已经证明了BDNF-TrkB信号在调节对阿片类药物和可卡因的反应中的独特作用。使用更先进的工具，现在可以在这些大脑区域内的特定神经元细胞类型中进行这种敲除，我们将描述D1与D2中含有NAc的棘神经元和VTA多巴胺神经元在这些现象中的具体影响。阿片类药物在VTA多巴胺神经元中引起的最显著的变化之一是它们的总体大小减少。这种减少是由这些神经元内BDNF信号的损伤介导的，特别是IRS-AKT通路的下调。我们现在有证据表明，这种下调是阿片类药物诱导的AKT-RHEB-mTOR信号适应的一部分。提出的实验旨在进一步建立详细的分子事件的基础上，这种形态适应。相比之下，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，神经元的树突和脊柱密度增加。我们已经证明，这些适应也涉及到BDNF信号的改变，现在我们提出进一步表征神经营养信号通路的精确变化，包括NF？介导这些适应的B信号。总之，拟议中的实验将从根本上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新的见解，这些信息可以在未来几年被挖掘出来，以确定改进的诊断测试和药物成瘾的治疗方法。

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.