A novel role for midbrain glutamate co-transmitting neurons in alcohol drinking and motivated behaviors

项目总结 青少年早期饮酒是患酒精使用障碍(AUD)风险的最佳预测指标之一 在以后的生活中。一般来说，青少年更有可能报告酒精带来的积极、有益的影响，而更少的 负面影响，这可能导致更大的饮酒量倾向。分子 酒精奖励敏感性增强的潜在机制尚不清楚，但如果被发现，可能会导致 减少虐待责任的新方法，并以专为青少年量身定做的方式治疗AUD 和成年人。谷氨酸信号与AUDS的易感性和发病机制密切相关。近期 临床前的研究进一步完善了这一观察结果，表明一组表达 囊泡谷氨酸转运蛋白2(VGLUT2)与药物奖赏的调节密切相关。我们有 发现这种不同的VGLUT2谷氨酸能神经元亚群也是多巴胺能的。我们也 发现谷氨酸增强了活性依赖的囊泡多巴胺的加载和释放。因此，虽然谷氨酸 和多巴胺都分别与酒精、谷氨酸和 多巴胺也可以协同作用来调节对酒精的敏感性。值得注意的是，VGLUT2表达式为 发育调节，表达在青春期达到峰值，并随着年龄的增长而下降，这可能解释了 为什么青少年对酒精的有益影响特别敏感。此外，我们发现很强的 VGLUT2在谷氨酸/多巴胺共传递神经元中表达的性别差异 相对于男性，女性表达更多的VGLUT2。因此，VGLUT2的表达也可以解释为什么女性 对酒精奖励有不同的敏感度。直到最近，还很难从功能上剖析 谷氨酸神经元的亚群，包括那些共同传递多巴胺的亚群，特别是在大鼠中。然而， 我们现在可以选择性地控制谷氨酸/多巴胺神经元中VGLUT2的表达，并回答以下几个问题 关键问题：1)酒精如何改变TH/VGLUT2终末谷氨酸和多巴胺的共同释放 在mNAcSh中；2)在mVTA谷氨酸/多巴胺神经元中VGLUT2表达水平的操纵 在男性和女性以及关键发育阶段有区别地修改酒精强化和动机 阶段(即青春期和成年期)？我们的中心假设是：i)谷氨酸/多巴胺的量- 根据基础条件下VGLUT2的表达水平和年龄和性别的不同，释放会有所不同 对酒精的反应(目标1)；ii)操纵VGLUT2表达水平将改变酒精强化和 动机行为(目标2)。使用分子、成像和行为工具的组合，我们将明确地 确定中脑谷氨酸能神经元亚群在酒精强化和酒精刺激中的机制作用 激励，并推动未来发展新的、更有效的酒精使用障碍干预措施。

PROJECT SUMMARY Early adolescent alcohol use is one of the best predictors of risk for developing an alcohol use disorder (AUD) later in life. Generally, adolescents are more likely to report positive, rewarding effects of alcohol and fewer negative effects, which can lead to an increased propensity to consume larger volumes of alcohol. The molecular mechanisms underlying enhanced sensitivity to alcohol reward are poorly understood, but if identified, could lead to novel methods for reducing abuse liability and treating AUD in a manner that is uniquely tailored to adolescents and adults. Glutamate signaling is strongly implicated in the vulnerability to and pathogenesis of AUDs. Recent preclinical work has further refined this observation by showing that a population of neurons that express vesicular glutamate transporter 2 (VGLUT2) are strongly implicated in modulating drug reward. We have discovered that this distinct subpopulation of VGLUT2+ glutamatergic neurons is also dopaminergic. We also found glutamate potentiates activity-dependent vesicular dopamine loading and release. Thus, while glutamate and dopamine have both been individually implicated in the reinforcing effects of alcohol, glutamate and dopamine may also act synergistically to regulate sensitivity to alcohol. Notably, VGLUT2 expression is developmentally regulated, with expression peaking in adolescence and decreasing with age, which may explain why adolescents are particularly sensitive to the rewarding effects of alcohol. Additionally, we discovered strong sex differences in the expression of VGLUT2 including in glutamate/dopamine co-transmitting neurons, with females expressing more VGLUT2 relative to males. Thus, VGLUT2 expression may also explain why females are differentially sensitive to alcohol reward. Until recently, it has been difficult to functionally dissect subpopulations of glutamate neurons, including those that co-transmit dopamine, particularly in rats. However, we can now selectively control expression of a VGLUT2 in glutamate/dopamine neurons, and answer several key questions: 1) how does alcohol alter co-release of glutamate and dopamine from TH+/VGLUT2+ terminals in the mNAcSh?; 2) does manipulation of levels of VGLUT2 expression in mVTA glutamate/dopamine neurons modify alcohol reinforcement and motivation differentially in males and females and across key developmental stages (i.e., adolescence and adulthood)? Our central hypotheses are: i) Amount of glutamate/dopamine co- release will vary according to age and sex based on levels of VGLUT2 expression under basal conditions and in response to alcohol (Aim 1); ii) Manipulating levels of VGLUT2 expression will alter alcohol reinforcement and motivated behaviors (Aim 2). Using a combination of molecular, imaging, and behavioral tools, we will definitively identify the mechanistic role of subpopulations of midbrain glutamatergic neurons in alcohol reinforcement and motivation, and drive future development of new, more effective interventions for alcohol use disorder.