OPIOIDS AND STRESS: THE PAG

本申请提出使用组合的解剖学和电生理学手段来理解阿片类物质如何起作用以调节腹外侧导水管周围灰质（PAG）中的神经元活动，并且进一步理解PAG-阿片类物质系统内的可塑性机制。申请人是一名经验丰富的超微结构神经解剖学家，将在该支持机制下接受电生理技术和应激神经生物学方面的培训。PAG维持几种行为功能，但已被最好地表征为吗啡产生和应激诱导的镇痛的部位。Mu阿片类药物被认为通过抑制局部GABA能中间神经元并随后解除PAG输出而在PAG中起作用，然而，一些解剖学观察表明Mu阿片类药物可能通过其他机制起作用。最引人注目的是，μ阿片受体（莫尔）存在于一个大的亚群（约100个）。40%）的延髓投射神经元。在这里，我们假设莫尔可能对GABA能与非GABA能PAG神经元有不同的功能。将通过使用细胞内记录技术确定莫尔激动剂对PAG细胞的作用来检验该假设。研究的细胞将充满神经生物素，并对GABA进行化学标记。某些应激模式，例如长时间暴露于间歇性和不可避免的休克（IS）对阿片系统具有长期持续的影响。具体地说，暴露于IS在24小时后增强了低剂量吗啡的镇痛作用。PAG参与对应激的急性反应以及吗啡和应激诱导的镇痛。这表明PAG中莫尔和/或δ阿片受体（DOR）功能的变化可能参与IS产生的吗啡镇痛效力的变化的假设。在特定目标2和3中，将同时使用解剖学和电生理学方法来确定与该现象相关的莫尔和DOR功能的变化。这些研究将有助于深入了解吗啡镇痛作用的细胞机制。此外，了解压力对阿片系统的影响是特别重要的，因为压力已被牵连作为一个主要因素，有助于成瘾和复发的药物寻求行为。

This application proposes using combined anatomical and electrophysiological means to understand how opioids function to modulate neuronal activity in the ventrolateral periaqueductal gray (PAG) and furthermore to understand mechanisms of plasticity within the PAG-opioid system. The applicant is an experienced ultrastructural neuroanatomist and will be trained under this support mechanism in electrophysiological techniques, as well as in stress neurobiology. The PAG subserves several behavioral functions but has been most well characterized as a site of morphine-produced and stress-induced analgesia. Mu opioids are thought to act in the PAG by inhibiting local GABAergic interneurons and subsequently disinhibiting PAG output, however, several anatomical observations suggest the mu opioids may act through additional mechanisms. Most strikingly, mu opioid receptor (MOR) is present on a large subpopulation (approx. 40%) of medullary projecting neurons in the ventrolateral PAG. Here we hypothesize the MOR may function distinctly on GABAergic vs. nonGABAergic PAG neurons. This hypothesis will be tested by determining the effects of MOR agonists on PAG cells using intracellular recording techniques. Studied cells will be filled with neurobiotin and immunohistochemically labeled for GABA. Certain stress paradigms, for example a prolonged exposure to intermittent and inescapable shock (IS) have long lasting effects on the opioid system. Specifically, exposure to IS potentates the analgesic effects of low doses of morphine 24 hours later. The PAG is involved in both the acute response to stressors, and morphine and stress induced analgesia. This suggests the hypothesis that changes in MOR and/or delta opioid receptor (DOR) functioning in the PAG may participate in IS produced changes in morphine's analgesic potency. In Specific Aims 2 and 3, anatomical and electrophysiological methods will be used in concert to determine the changes in MOR and DOR function relating to this phenomenon. These studies will shed insight into the cellular mechanisms that underlie morphine's analgesic effects. Furthermore, understanding stress effects on the opioid system are particularly important since stress has been implicated as a major factor contributing to addiction and relapse to drug seeking behavior.