Midbrain cholinergic modulation of pain states

在美国，慢性疼痛困扰着超过20%的成年人，这强调了 更全面地了解疼痛控制机制，并确定更好的疼痛治疗方法。 目前的阿片类药物危机进一步放大了这种需求，2020年有6万多美国人死亡。而 阿片类药物对急性和慢性疼痛、不良副作用，包括滥用， 对重复使用的镇痛作用的易感性和耐受性，强调了非阿片类药物疼痛的必要性 治疗这种需要促使我们研究乙酰胆碱（ACh）及其受体对疼痛的调节。 从外周到中枢神经系统的上行伤害性信号传导由 下行疼痛调节通路，包括腹外侧导水管周围灰质（vlPAG）及其 延髓头端腹内侧（RVM）的投射。该途径是阿片类药物作用的关键部位， 内源性疼痛控制虽然对这种回路了解很多，但像ACh这样的神经调质对 该回路，特别是在慢性疼痛条件下的回路尚未被研究。使用荧光乙酰胆碱 传感器，我们将调查如何疼痛和其他行为相关的刺激改变乙酰胆碱释放动力学在 vlPAG。使用脑切片电生理学，我们将确定ACh改变背后的细胞机制， release.最后，我们将尝试使用化学遗传学来逆转这些适应不良的ACh动力学， 药理学方法。 我们的初步数据表明，来自脚桥被盖（PPTg）的胆碱能投射， 调节vlPAG神经元的兴奋性。在慢性疼痛条件下，我们注意到ACh释放减少， vlPAG和PPTg中神经元活性降低。我们还发现，M2毒蕈碱AChRs表达于 vlPAG神经元，疼痛会增加这些神经元的活性。这些观察使我们 假设慢性疼痛降低了来自PPTg的胆碱能信号传导并降低了vlPAG中的M2活性， 导致慢性疼痛症状。我们进一步假设，逆转这些变化将缓解 慢性疼痛的躯体和情感症状。 我们将使用ACh传感器与体内纤维光度法来评估急性和慢性疼痛的影响 对乙酰胆碱释放的影响我们将使用ACh的体内微透析来补充这些测定。脑片 电生理学将被用来探讨疼痛引起的突触驱动和内在兴奋性的变化， PPTg胆碱能神经元投射到vlPAG。体内成像将用于评估慢性疼痛诱导的 vlPAG神经元活性的变化。然后，使用化学遗传学和M2 mAChR激动剂，我们将尝试 逆转疼痛诱导的vlPAG兴奋性变化。行为测试将证实逆转的 慢性疼痛的躯体和情感成分。更好地理解这些调节输入， 下行疼痛通路将有助于确定治疗慢性疼痛的新靶点。

Chronic pain conditions plague more than 20% of adults in the United States, emphasizing the need for a more comprehensive understanding of pain control mechanisms and identification of better pain therapies. This need is amplified further by the current opioid crisis, which killed over 60,000 Americans in 2020. While opioids are remarkably effective treatments for acute and chronic pain, adverse side effects, including abuse liability and tolerance to the analgesic effects with repeated use, highlight the need for non-opioid pain therapies. This need motivates our investigations of pain modulation by acetylcholine (ACh) and its receptors. Ascending nociceptive signaling from periphery to central nervous system is modulated by the descending pain modulatory pathway, including the ventrolateral periaqueductal grey (vlPAG) and its projections to rostral ventromedial medulla (RVM). This pathway is a crucial site of action of opioids and endogenous pain control. While much is known about this circuitry, the impact of neuromodulators like ACh on this circuit, particularly under chronic pain conditions have not been investigated. Using a fluorescent ACh sensor, we will investigate how pain and other behaviorally relevant stimuli alter ACh release dynamics in the vlPAG. Using brain slice electrophysiology, we will identify the cellular mechanisms behind alterations in ACh release. And finally, we will attempt to reverse these maladaptive ACh dynamics using chemogenetics and pharmacological approaches. Our preliminary data show that cholinergic projections from the pedunculopontine tegmentum (PPTg), modulate excitability of vlPAG neurons. Under chronic pain conditions, we noted a decrease in ACh release in vlPAG and reduced neuronal activity in PPTg. We also found that M2 muscarinic AChRs are expressed on vlPAG neurons, and that pain increases the activity of these neurons. These observations lead us to hypothesize that chronic pain lowers cholinergic signaling from PPTg and reduces M2 activity in vlPAG, contributing to chronic pain symptoms. We further hypothesize that reversing these changes will relieve somatic and affective symptoms of chronic pain. We will use an ACh sensor with in vivo fiber photometry to assess the impact of acute and chronic pain on ACh release in the vlPAG. We will complement these assays using in vivo microdialysis for ACh. Brain slice electrophysiology will be used to explore the pain-induced changes in synaptic drive and intrinsic excitability of PPTg cholinergic neurons that project to vlPAG. In vivo imaging will be used to assess chronic pain induced changes in vlPAG neuronal activity. Then, using chemogenetics and M2 mAChR agonists we will attempt to reverse the pain-induced changes in excitability of vlPAG. Behavioral testing will confirm reversal of the somatic and affective components of chronic pain. Better understanding of these modulatory inputs to descending pain pathways will help identify novel targets for treating chronic pain.