Midbrain cholinergic modulation of pain states

在美国，超过20%的成年人患有慢性疼痛，强调有必要 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年有超过6万美国人死于阿片类药物危机。而当 阿片类药物是治疗急性和慢性疼痛、包括滥用等不良副作用的非常有效的治疗方法 易耐受反复使用的止痛效果，突出非阿片类疼痛的必要性 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制作用。 从外周到中枢神经系统的上行伤害性信号是由 下行痛觉调制通路，包括腹外侧导水管周围灰质(VlPAG)及其 投射至延髓头端腹内侧(RVM)。这条途径是阿片类药物作用的关键部位， 内源性疼痛控制。虽然人们对这一回路了解很多，但像ACh这样的神经调节剂的影响 这种环路，特别是在慢性疼痛条件下，还没有被研究过。使用荧光ACH 传感器，我们将研究疼痛和其他与行为相关的刺激如何改变大脑中ACh的释放动力学。 VlPAG。利用脑片电生理学，我们将确定ACh变化背后的细胞机制 放手。最后，我们将尝试使用化学遗传学和 药理学方法。 我们的初步数据显示，桥脑脚盖(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神经元活性降低。我们还发现M2毒蛾碱型乙酰胆碱受体在 VlPAG神经元，这种疼痛增加了这些神经元的活动。这些观察将我们引向 假设慢性疼痛降低了来自PPTG的胆碱能信号，并减少了vlPAG中的M2活动， 会导致慢性疼痛症状。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传感器和体内纤维光度法来评估急性和慢性疼痛的影响。 在vlPAG中的ACh释放。我们将使用ACh的体内微透析来补充这些检测。脑片 电生理学将被用来探索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引起的 VlPAG神经元活动的变化。然后，使用化学遗传学和M2 mAChR激动剂，我们将尝试 逆转疼痛引起的vlPAG兴奋性改变。行为测试将确认 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.