Afferents modulating VTA activity and their plasticity after self-administration

描述（由申请人提供）：腹侧被盖区（VTA）多巴胺细胞的活性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，并伴有穿插的“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成瘾药物暴露和戒断后。然而，在基线条件下和药物暴露后，对VTA特定传入的功能作用的理解受到当前技术的限制。这些研究将确定在大鼠自我给药之前或之后，VTA的活动是如何被特定事件调节的。为了分析特定传入事件的作用，我们将使用光遗传学技术，通过将光脉冲施加到表达藻类蛋白通道视紫红质2 （ChR2）的末端，可以增加选择性途径的活性。成年大鼠的特定脑区将被一种在神经元中表达ChR2的腺相关病毒感染。然后，我们将通过在VTA上施加光脉冲来确定特定通路的功能作用，以刺激来自这些区域的传入。我们将检查来自(i)桥脚被盖核（PPTg）的VTA输入，PPTg是一个对显著刺激有反应的混合谷氨酸能/胆碱能群体；（ii）局部VTA谷氨酸细胞，最近已被描述，但其功能作用尚不清楚；（iii）前内侧被盖核（RMTg），这是一种后脑结构，最近发现它向VTA发送重要的gaba能投射，但其功能作用尚不清楚。我们将评估通路特异性刺激对麻醉大鼠体内测量的细胞活性（放电速率和模式）的影响。然后，我们将通过测量刺激这些通路时产生的突触电位来确定这些体外输入的性质。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进一步测试途径的性质。目的1将研究这些途径在药物初始大鼠中的作用。目标2将在自我服用可卡因的老鼠身上进行检验。这些研究将首次确定未探索的和新的传入事件对VTA的功能作用。他们还将确定可卡因自我给药如何改变多巴胺细胞被特定事件激发的方式。这将为研究大脑奖赏通路在基线条件下的功能及其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。

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.