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.dhs.gov)，NIDA报告称，非法阿片类药物的使用正在增加。越来越多的证据表明，饮酒和奖励事件导致大脑中内源性阿片类药物的释放，因此利用与阿片成瘾有关的相同的MU阿片受体(MORS)和大脑回路。尽管这个问题很严重，但我们对MOR的激活如何导致奖赏和成瘾只有部分了解。因此，这项提议的总体目标是调查有助于阿片类药物奖励的回路。吗啡奖赏需要腹侧被盖区(VTA)的MORS(Olmstead和Franklin，1997b；Zhang等，2009)。VTA神经元在腹侧纹状体释放多巴胺，通常认为腹侧纹状体释放的多巴胺引起阿片类奖赏。然而，腹侧纹状体的损伤并不能阻止吗啡奖励(Olmstead和Franklin，1996,1997 a；White et al.，2005)。相反，内侧前额叶皮质(MPFC)的损伤确实阻断了吗啡奖励(Tzschentke和Schmidt，1999)。因此，本实验的重点是对投射mPFC的VTA神经元进行MOR控制。对这一投射的详细解剖将被研究，特别是测试新发现的VTA谷氨酸神经元是否投射到mPFC。由于吗啡奖赏在鸦片类NA动物中是不依赖多巴胺的(Bechara等人，1992；Nader和van der Kooy，1997)，因此确定MOR激活对投射到mPFC的非多巴胺和多巴胺VTA神经元的影响是至关重要的。皮质投射神经元将被逆行标记，以便在脑片记录中识别它们，并将在这些标记的神经元中测量突触前和突触后的MOR激动剂效应。在记录之后，记录的神经元的神经递质含量将通过免疫细胞化学或原位杂交被直接鉴定为多巴胺、谷氨酸或GABA。由于电刺激mPFC是有回报的(Corbett等人，1982；Duvuchelle和Ettenberg，1991)，因此假设MOR激活将兴奋mPFC投射多巴胺和谷氨酸的神经元，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信号的疾病的治疗开发成为可能，包括成瘾、酒精中毒、冲动障碍和注意缺陷多动障碍。 与公共健康相关：拟议研究的总体目标是确定导致阿片成瘾的潜在大脑回路。由于大脑阿片受体在饮酒、进食和其他自然奖励后也会被激活，同样的电路也会导致其他疾病，如酗酒和暴饮暴食。通过确定参与鸦片奖励和成瘾的大脑通路，这项工作将使人们能够为这些成瘾障碍开发更有针对性的治疗方法。

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.