Heterogeneity of Ventral Tegmental Area Neurons and Opioid Reward

描述（由申请人提供）：美国每年约有200万人依赖或滥用阿片类药物（www.dhhs.gov）， NIDA报告称非法阿片类药物使用呈上升趋势。越来越多的证据表明，酒精消耗和奖励事件导致大脑中内源性阿片样物质的释放，因此利用相同的mu阿片样物质受体（MORs）和大脑回路参与阿片成瘾。尽管这个问题很严重，但我们只是部分地理解了MOR激活是如何引起奖励并导致成瘾的。因此，本提案的总体目标是研究有助于阿片奖励的回路。吗啡奖励需要腹侧被盖区（VTA）的MORs （Olmstead and Franklin, 1997b; Zhang et al., 2009）。VTA神经元在腹侧纹状体释放多巴胺，通常认为多巴胺在腹侧纹状体释放引起阿片奖励。然而，腹侧纹状体的损伤并不会阻断吗啡的奖励（Olmstead和Franklin， 1996,1997a； White等人，2005）。相反，内侧前额叶皮层（mPFC）的损伤确实会阻止吗啡的奖励（Tzschentke和Schmidt， 1999）。因此，本实验将重点研究mpfc投射VTA神经元的MOR控制。我们将对这一投射的详细解剖进行研究，特别是测试新发现的VTA谷氨酸神经元是否投射到mPFC。由于吗啡奖励在阿片类动物中与多巴胺无关（Bechara et al., 1992; Nader and van der Kooy, 1997），因此确定MOR激活对非多巴胺和多巴胺VTA神经元的影响至关重要。皮层突出的神经元将被逆行标记，以便在脑切片记录中识别它们，并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。记录后，使用免疫细胞化学或原位杂交，记录神经元的神经递质含量将直接鉴定为多巴胺，谷氨酸或GABA。由于电刺激mPFC是有益的（Corbett et al., 1982; Duvauchelle and Ettenberg, 1991），因此假设MOR激活会激发mPFC-突起的多巴胺和谷氨酸神经元，抑制GABA神经元。通过提高我们对阿片类奖赏回路的理解，这项工作将使涉及VTA和mPFC信号的疾病，包括成瘾、酗酒、冲动性障碍和注意缺陷多动障碍，能够更有效地治疗。

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.