Heterogeneity of Ventral Tegmental Area Neurons and Opioid Reward

描述（由申请人提供）：在美国，每年约有200万人依赖或滥用阿片类药物（www.dhhs.gov），NIDA报告说，非法阿片类药物的使用正在增加。越来越多的证据表明，酒精消费和奖励事件导致内源性阿片类药物在大脑中的释放，因此利用相同的μ阿片受体（MORs）和阿片类药物成瘾中涉及的大脑回路。尽管这个问题的严重性，我们只是部分了解莫尔激活如何引起奖励并导致成瘾。因此，本提案的总体目标是研究有助于阿片类药物奖励的回路。腹侧被盖区（VTA）中的MOR是吗啡奖赏所必需的（Olmstead和富兰克林，1997 b; Zhang等人，2009年）。腹侧被盖区神经元在腹侧纹状体中释放多巴胺，人们通常认为腹侧纹状体中释放的多巴胺会引起阿片类药物奖励。然而，腹侧纹状体的损伤不阻断吗啡奖赏（Olmstead和富兰克林，1996，1997 a;白色等人，2005年）。相反，内侧前额叶皮层（mPFC）的损伤确实会阻断吗啡奖赏（Tzschentke和施密特，1999）。因此，所提出的实验集中于mPFC投射VTA神经元的莫尔控制。将研究这种投射的详细解剖，特别是测试新发现的腹侧被盖区谷氨酸神经元是否投射到mPFC。因为吗啡奖赏在阿片类药物未处理的动物中是多巴胺非依赖性的（Bechara等人，1992年; Nader和货车der Kooy，1997），确定莫尔激活对投射到mPFC的非多巴胺和多巴胺VTA神经元的影响至关重要。皮质投射神经元将被逆行标记，使得它们可以在脑切片记录期间被识别，并且将在这些标记的神经元中电生理地测量突触前和突触后莫尔激动剂效应。记录后，使用免疫细胞化学或原位杂交将记录的神经元的神经递质内容直接鉴定为多巴胺、谷氨酸或GABA。由于mPFC的电刺激是有益的（Corbett等人，一九八二年; Duvauchelle和Ettenberg，1991），假设莫尔激活将激发投射mPFC的多巴胺和谷氨酸神经元，并抑制GABA神经元。通过提高我们对阿片类药物奖励所涉及的电路的理解，这项工作将使涉及VTA和mPFC信号传导的疾病，包括成瘾，酒精中毒，冲动性障碍和注意缺陷多动障碍的治疗开发更加有效。 公共卫生相关性：拟议研究的总体目标是确定负责阿片类药物成瘾的潜在大脑回路。由于大脑阿片受体也会在饮酒、进食和其他自然奖励后被激活，因此同样的回路也会导致其他疾病，如酗酒和暴饮暴食。通过确定阿片类药物奖励和成瘾的大脑通路，这项工作将使更多的针对性治疗这些成瘾性疾病的开发成为可能。

DESCRIPTION (provided by applicant): Approximately 2 million people are dependent on or abuse opioids in the USA each year (www.dhhs.gov), and NIDA reports that illicit opiate use is on the rise. Accumulating evidence indicates that alcohol consumption and rewarding events cause the release of endogenous opioids in the brain, therefore utilizing the same mu opioid receptors (MORs) and brain circuits involved in opiate addiction. In spite of the magnitude of this problem, we only partially understand how MOR activation causes reward and leads to addiction. Therefore overall objective of this proposal is to investigate the circuits that contribute to opioid reward. MORs in the ventral tegmental area (VTA) are required for morphine reward (Olmstead and Franklin, 1997b; Zhang et al., 2009). VTA neurons release dopamine in the ventral striatum, and it is commonly thought that dopamine released in the ventral striatum causes opioid reward. Yet, lesions of the ventral striatum do not block morphine reward (Olmstead and Franklin, 1996, 1997a; White et al., 2005). Instead, lesions of the medial prefrontal cortex (mPFC) do block morphine reward (Tzschentke and Schmidt, 1999). Therefore the proposed experiments focus on MOR control of mPFC-projecting VTA neurons. Detailed anatomy of this projection will be studied, in particular to test whether the newly discovered VTA glutamate neurons project to the mPFC. Because morphine reward is dopamine-independent in opiate na¿ve animals (Bechara et al., 1992; Nader and van der Kooy, 1997), it is critical to determine the effects of MOR activation on both the non-dopamine and dopamine VTA neurons that project to the mPFC. Cortical-projecting neurons will be retrogradely labeled so that they can be identified during brain slice recordings, and pre- and postsynaptic MOR agonist effects will be measured electrophysiologically in these labeled neurons. Following recordings, the neurotransmitter content of the recorded neurons will be directly identified as dopamine, glutamate, or GABA using immunocytochemistry or in situ hybridization. Since electrical stimulation of the mPFC is rewarding (Corbett et al., 1982; Duvauchelle and Ettenberg, 1991), it is hypothesized that MOR activation will excite mPFC-projecting dopamine and glutamate neurons, and inhibit GABA neurons. By improving our understanding of the circuitry involved in opioid reward, this work will enable more effective therapeutic development for disorders that involve VTA and mPFC signaling, including addiction, alcoholism, impulsivity disorders and attention deficit hyperactivity disorder. PUBLIC HEALTH RELEVANCE: The overall goal of the proposed research is to determine the underlying brain circuitry responsible for opiate addiction. Because brain opiate receptors are also activated following alcohol consumption, food consumption, and other natural rewards, the same circuitry also contributes to other disorders such as alcoholism and overeating. By determining the brain pathways involved in opiate reward and addiction, this work will enable more targeted treatments to be developed for these addiction disorders.