Afferents modulating VTA activity and their plasticity after self-administration

描述(申请人提供)：腹侧被盖区(VTA)的多巴胺细胞的活动在奖励和动机中起着关键作用。在体内，这些细胞不规则地放电，并穿插着“爆发”事件；这种活动模式是局部和远端结构产生的兴奋性和抑制性输入的结果。此外，这些输入的可塑性发生在暴露和戒除成瘾药物之后。然而，无论是在基线条件下还是在药物暴露后，对VTA的特定传入神经的功能作用的了解都受到当前技术的限制。这些研究将确定在大鼠服用可卡因之前或之后，VTA的活动如何受到特定传入细胞的调节。为了剖析特定传入细胞的作用，我们将使用光遗传学技术，通过向表达藻类蛋白通道视紫红质2(ChR2)的末端施加光脉冲，可以增加选择性通路的活性。成年大鼠的特定脑区将感染一种腺相关病毒，以检测神经元中ChR2的表达。然后，我们将通过在VTA中应用光脉冲来刺激每个区域的传入，来确定特定通路的功能作用。我们将研究来自(I)脚桥脑被盖核(PPTg)的输入，这是一个对显著刺激做出反应的谷氨酸/胆碱能混合群体；(Ii)局部VTA谷氨酸细胞，其功能作用最近已被描述；以及(Iii)旋转内侧被盖核(RMTg)，这是一种新近被发现的后脑结构，向VTA发送重要的GABA能投射，但其功能作用尚不清楚。我们将评估特定路径刺激对体内测量的麻醉大鼠细胞活动(放电率和模式)的影响。然后，我们将在体外通过测量刺激这些通路产生的突触电位来确定这些输入的性质。我们还将确定这种突触输入的整合方式。最后，我们将通过进行免疫组织化学研究来进一步测试这些通路的性质。目的1将研究这些通路在药物依赖大鼠中的作用。目标2将在自我注射可卡因的大鼠身上进行检测。这些研究将首次确定未被探索的和新的VTA传入神经的功能作用。他们还将确定可卡因自身给药如何改变特定传入刺激多巴胺细胞的方式。这将为大脑奖赏通路在基线条件下的运作方式以及自我给药后的可塑性提供重要信息。这些研究将为控制成瘾行为的神经回路提供新的见解。 与公共健康相关：这些研究将确定在大鼠服用可卡因之前或之后，大脑奖励区域腹侧被盖区的活动是如何受到特定输入的调节的。为了剖析特定输入的作用，我们将使用一种名为光遗传学的新技术，通过在脑细胞附近施加光脉冲来增加选择性脑细胞的活动。这些研究将为控制成瘾行为的神经回路提供新的见解。

DESCRIPTION (provided by applicant): The activity of dopamine cells of the ventral tegmental area (VTA) plays a critical role in reward and motivation. In vivo, these cells fire irregularly, with interspersed "burst" events; this pattern of activity is the consequence of excitatory and inhibitory inputs arising locally and from distal structures. In addition, plasticity of these inputs occurs after exposure and withdrawal from addictive drugs. However, understanding the functional role of specific afferents to the VTA, both in baseline conditions and after exposure to drugs, has been limited by current technology. These studies will establish how the activity of the VTA is modulated by specific afferents, before or after cocaine self-administration in rats. To dissect the role of specific afferents, we will use the technique of optogenetics whereby the activity of selective pathways can be increased with pulses of light applied to the terminals that express the algae protein channelrhodopsin 2 (ChR2). Specific brain regions of adult rats will be infected with an adeno-associated virus for ChR2 expression in neurons. We will then determine the functional role of specific pathways by applying light pulses in the VTA, to stimulate the afferents from each of these regions. We will examine inputs to the VTA from (i) the pedunculopontine tegmental nucleus (PPTg), a mixed glutamatergic/cholinergic population that responds to salient stimuli; (ii) local VTA glutamate cells, which have recently been described but whose functional role is unclear; and (iii) the rostromedial tegmental nucleus (RMTg), a hindbrain structure recently identified that sends important GABAergic projections to the VTA but whose functional role is unknown. We will evaluate the consequence of pathway-specific stimulation on cell activity (firing rates and patterns) measured in vivo in anesthetized rats. Then, we will determine the nature of these inputs in vitro, by measuring synaptic potentials generated upon stimulation of these pathways. We will also determine the manner in which such synaptic input is integrated. Finally, we will further test the nature of the pathways by performing immunohistochemistry studies. Aim 1 will examine the role of these pathways in drug-naove rats. Aim 2 will examine it in rats that have self-administered cocaine. These studies will be the first to determine the functional role of unexplored and novel afferents to the VTA. They will also determine how cocaine self-administration modifies the way dopamine cells are excited by specific afferents. This will provide important information on the manner in which brain reward pathways function in baseline conditions, and their plasticity after self-administration. These studies will provide novel insights on neural circuits that control addictive behavior. PUBLIC HEALTH RELEVANCE: These studies will establish how the activity of a brain reward area known as the ventral tegmental area is modulated by specific inputs before or after cocaine self-administration in rats. To dissect the role of specific inputs, we will use a novel technique called optogenetics whereby the activity of selective brain cells can be increased with pulses of light applied in proximity of the brain cells. These studies will provide novel insights on neural circuits that control addictive behavior.