Synaptic mechanisms underlying reward seeking and compulsive drug use

项目一：谷氨酸和多巴胺从中脑多巴胺神经元传输共享类似的释放特性，但不同的可卡因的影响。（Adrover，Shin和Alvarez，J. Neuroscience 2014）腹侧被盖区和延髓核（NAc）之间的突触传递与奖励动机行为密切相关，并被认为在成瘾中发生改变。除了多巴胺（DA），谷氨酸被包装和释放的中脑边缘DA神经元的一个子集，引发EPSC到中等多刺神经元在NAc。关于DA中脑末梢谷氨酸释放的性质和调节以及可卡因的作用知之甚少。使用光遗传学方法选择性地激活中脑DA纤维，我们比较了使用快速扫描循环伏安法和全细胞记录在小鼠脑切片中测量的DA瞬变和EPSC的性质和调制。DA受体D2 R激动剂抑制DA瞬变和EPSC，并显示出明显的成对脉冲抑制，需要2分钟才能完全恢复。多巴胺使EPSC的振幅降低了50%，但增强了中脑DA神经元的整体DA传递。AMPA和NMDA受体介导的EPSCs同样受到可卡因的抑制，表明突触前作用机制。DA神经元D2 R的药理学阻断和基因缺失阻止了可卡因对EPSC的抑制，并引起DA瞬时峰的较大增加，证实了突触前D2 R的参与。这些研究结果表明，急性可卡因抑制DA和谷氨酸释放中脑DA神经元通过突触前D2 R，但有差异的整体影响，其在NAc的传输。我们推测，可卡因，通过阻断DA再摄取，抑制DA瞬变和促进DA和谷氨酸从这些终端释放的反馈抑制。 项目2：反复酗酒改变乙醇饮用模式并抑制纹状体GABA能传递。（Wilcox等人，Neuropsychopharmacology 2014） 对大量和狂欢式乙醇饮用的神经生物学的研究受到大多数小鼠品系显示的低水平的自愿乙醇消耗的限制（Crabbe等人，2011年）。最近，间歇性接触乙醇的模型已经显示出在小鼠中引起狂欢样饮酒和与酒精相关的血液乙醇浓度（BEC）（罗兹等人，2005年）。该模型被称为在黑暗中饮酒，它利用小鼠的昼夜节律模式，在两小时的饮酒时间内实现可靠的高水平消费。 C57 BL/6 J小鼠达到高于80 mg/dl的BEC，并显示出中毒的迹象，如运动障碍（罗兹等人，2007年）。DID是一种稳健的范例，已成功用于研究调节酗酒样乙醇消耗的神经元回路和信号（Sprow，2012）。尽管这种间歇性获取模式取得了成功，但人们对获得自愿乙醇饮用的机制并不完全了解。在这项研究中，我们在实验室建立了DID，并表明它产生了可靠的自愿乙醇摄入量和血液乙醇浓度的上升。我们的特点是饮用模式的小鼠间歇性获得乙醇使用lickometers记录每回合的高时间分辨率超过数周的自愿乙醇消费，并分析了纹状体神经元的突触形态后2天和30天的最后一次乙醇狂欢。这些结果代表了对酒精领域的一个新颖而重要的贡献，因为他们确定了瓶子交换，DID的一个组成部分，作为一种可能的机制，间歇性访问通过诱导小鼠以更高的速度饮酒来促进自愿乙醇饮酒行为的获得。 随着时间的推移，小鼠改变了他们的乙醇饮用模式，并在每次DID开始时增加了饮用速度。 更快的乙醇饮用与更高的BEC相关，并且在治疗6周后观察到对乙醇的偏好增强。有趣的是，没有变化，无论是纹状体或小脑棘密度，和缩短的棘长度被认为只是短暂的，这表明这些行为的变化发生独立的长期变化，在大脑中的突触形态。

Project 1: Glutamate and dopamine transmission from midbrain dopamine neurons share similar release properties but are differentially affected by cocaine.(Adrover, Shin and Alvarez, J. Neuroscience 2014)Synaptic transmission between ventral tegmental area and nucleus accumbens (NAc) is critically involved in reward-motivated behaviors and thought to be altered in addiction. In addition to dopamine (DA), glutamate is packaged and released by a subset of mesolimbic DA neurons, eliciting EPSCs onto medium spiny neurons in NAc. Little is known about the properties and modulation of glutamate release from DA midbrain terminals and the effect of cocaine. Using an optogenetic approach to selectively activate midbrain DA fibers, we compared the properties and modulation of DA transients and EPSCs measured using fast-scan cyclic voltammetry and whole-cell recordings in mouse brain slices. DA transients and EPSCs were inhibited by DA receptor D2R agonist and showed a marked paired-pulse depression that required 2 min for full recovery. Cocaine depressed EPSCs amplitude by 50% but enhanced the overall DA transmission from midbrain DA neurons. AMPA and NMDA receptor-mediated EPSCs were equally inhibited by cocaine, suggesting a presynaptic mechanism of action. Pharmacological blockage and genetic deletion of D2R in DA neurons prevented the cocaine-induced inhibition of EPSCs and caused a larger increase in DA transient peak, confirming the involvement of presynaptic D2R. These findings demonstrate that acute cocaine inhibits DA and glutamate release from midbrain DA neurons via presynaptic D2R but has differential overall effects on their transmissions in the NAc. We postulate that cocaine, by blocking DA reuptake, prolongs DA transients and facilitates the feedback inhibition of DA and glutamate release from these terminals. Project 2: Repeated binge-like ethanol drinking alters ethanol drinking patterns and depresses striatal GABAergic transmission.(Wilcox et al., Neuropsychopharmacology 2014) Research into the neurobiology of heavy and binge-like ethanol drinking has been limited by the low-levels of voluntary ethanol consumption shown by most mouse strains (Crabbe et al., 2011). Recently, a model of intermittent access to ethanol has been shown to elicit binge-like drinking and pharmacologically relevant blood ethanol concentrations (BECs) in mice (Rhodes et al., 2005). Termed Drinking in the Dark, this model takes advantage of the circadian patterns of mice to achieve reliably high levels of consumption in a two hour drinking session. C57BL/6J mice reach BECs higher than 80 mg/dl, and show signs of intoxication such as motor impairment (Rhodes et al., 2007). DID is a robust paradigm that has been successfully used to investigate neuronal circuits and signals that modulate binge-like ethanol consumption (Sprow, 2012). Despite the success of this intermittent access model, the mechanisms underlying the acquisition of voluntary ethanol drinking are not completely understood. In this study, we established DID in our laboratory and showed that it produces reliable escalation of voluntary ethanol intake and blood ethanol concentration. We characterized the drinking pattern of mice with intermittent access to ethanol using lickometers to record each bout with high temporal resolution over many weeks of voluntary ethanol consumption, and analyzed the synaptic morphology of striatal neurons 2 days and 30 days after the last ethanol binge. The results represent a novel and important contribution to the alcohol field because they identify the bottle exchange, an integral part of DID, as a likely mechanism by which intermittent access facilitates the acquisition of voluntary ethanol drinking behavior by inducing mice to drink at a higher rate. Over time, mice change their ethanol drinking pattern and increase the speed of drinking at the beginning of each DID session. Faster ethanol drinking is associated with higher BEC, and an enhanced preference for ethanol was observed after 6 weeks of treatment. Interestingly, no changes were detected in either striatal or accumbal spine density, and a shortening of spine length was seen only transiently, suggesting that these behavioral changes occur independent of long-term changes in synaptic morphology in brain.