OPIOIDS AND STRESS: THE PAG

这项应用建议使用解剖学和电生理学相结合的方法来了解阿片类药物如何调节中脑导水管周围灰质(PAG)腹外侧区的神经元活动，并进一步了解PAG-阿片系统内的可塑性机制。申请者是一位经验丰富的超微结构神经解剖学家，并将在这一支持机制下接受电生理技术以及应激神经生物学方面的培训。PAG具有几种行为功能，但最好的特征是吗啡产生和应激诱导的止痛。Mu阿片类药物被认为通过抑制局部GABA能中间神经元从而抑制PAG的输出而作用于PAG，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发挥作用。最引人注目的是，Mu阿片受体(MOR)存在于一个很大的亚群中(约.40%的延髓投射神经元位于腹外侧侧PAG。这里，我们假设MOR可能在GABA能和非GABA能PAG神经元上起着明显的作用。这一假说将通过使用细胞内记录技术确定MOR激动剂对PAG细胞的影响来检验。研究细胞将被神经生物素填充，并用免疫组织化学标记GABA。某些应激模式，例如长期暴露在间歇性和不可避免的休克(IS)中，会对阿片系统产生长期的影响。具体地说，暴露在IS中会增强24小时后小剂量吗啡的止痛效果。PAG既参与对应激源的急性反应，也参与吗啡和应激诱导的镇痛。这表明，PAG中MOR和/或阿片受体(DOR)功能的改变可能参与了吗啡镇痛效力的改变。在具体的目标2和3中，将联合使用解剖学和电生理学方法来确定与这一现象相关的MOR和DOR功能的变化。这些研究将深入了解吗啡止痛作用的细胞机制。此外，了解应激对阿片系统的影响尤其重要，因为应激被认为是导致成瘾和复发的主要因素。

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.