A new animal model for stress-induced transition from acute to chronic pain

描述（由申请人提供）：从急性疼痛到慢性疼痛的转变可能是由复杂的机制组合引起的。重要的是开发一种有用的临床前动物模型，可以复制人类状况的复杂性。先前的研究表明，心理社会和社会环境因素与慢性术后疼痛的发展有关。在我们的初步研究中，我们发现强迫游泳应激显著增强了足底切开诱导的氨基-3-羟基-5-甲基-4-异氧唑丙酸（AMPA）受体磷酸化，并大大延长了足底切开诱导的疼痛，但单独强迫游泳应激不会产生疼痛行为；我们还发现AMPA受体GluA1磷酸化位点Ser831的靶向突变显著抑制应激诱导的切口疼痛延长。因此，应激可能通过调节AMPA受体磷酸化诱导疼痛过渡。最近，我们进一步发现，强迫游泳应激显著增加GluA1膜表面表达和GluA2内化，从而增强脊髓背角神经元突触AMPA受体从Ca2+不透性（含GluA2）到Ca2+透性（缺乏GluA2）的转换。这种开关会增加Ca2+内流并进一步激活Ca2+依赖性蛋白激酶，从而促进AMPA受体磷酸化和其他磷酸化触发的活性。这种正反馈循环可能有助于应激诱导疼痛转变的分子机制。因此，我们假设AMPA受体磷酸化的调节和磷酸化触发的突触AMPA受体从Ca2+不渗透到Ca2+渗透的转换有助于应激诱导从急性到慢性疼痛转变的关键机制。为了解决这一中心假设，我们将把足底切开与不同水平的应激结合起来，建立一个新的动物模型来研究疼痛过渡（特定目的1），我们将在我们的疼痛过渡模型（特定目的2）中研究应激对AMPA受体活性的调节（磷酸化、转运、突触靶向和亚基组成变化）。我们将研究磷酸化触发的AMPA受体从Ca2+不渗透到Ca2+渗透的转换在应激诱导的疼痛转变中的作用（特定目的3）。本研究的总体目标是建立一种新的动物模型用于疼痛转移研究，并为疼痛转移模型的特征提供关键证据。这些研究将证明应激产生的AMPA受体调控在急性到慢性疼痛转变中的作用，并为慢性术后疼痛的发病机制提供新的线索。

DESCRIPTION (provided by applicant): The transition from acute to chronic pain is likely to result from a complex combination of mechanisms. It is important to develop a useful preclinical animal model that can replicate the complexity of the human condition. Previous studies have shown that psychosocial and socio-environmental factors are involved in the development of chronic postsurgical pain. In our preliminary studies, we found that forced swim stress significantly enhances plantar incision-induced �-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor phosphorylation and greatly prolongs plantar incision-induced pain, but forced swim stress alone does not produce pain behaviors; we also found that targeted mutation of AMPA receptor GluA1 phosphorylation site Ser831 significantly inhibits stress-induced prolongation of incisional pain. Thus, stress may induce pain transition by regulating AMPA receptor phosphorylation. Recently, we further found that forced swim stress significantly increases GluA1 membrane surface expression and GluA2 internalization and thereby enhances synaptic AMPA receptor switch from Ca2+-impermeable (GluA2-containing) to Ca2+-permeable (GluA2-lacking) in the spinal dorsal horn neurons. This switch will increase Ca2+ influx and further activate Ca2+-dependent protein kinases, thereby promoting AMPA receptor phosphorylation and other phosphorylation-triggered activities. This positive feedback loop may contribute to the molecular mechanisms that underlie stress- induced pain transition. Therefore, we hypothesize that regulation of AMPA receptor phosphorylation and phosphorylation-triggered synaptic AMPA receptor switch from Ca2+-impermeable to Ca2+-permeable contribute to a key mechanism by which stress induces the transition from acute to chronic pain. To address this central hypothesis, we will combine plantar incision with different levels of stress to develop a new animal model to study pain transition (specific aim 1), we will investigate stress-produced regulation of AMPA receptor activities (phosphorylation, trafficking, synaptic targeting, and subunit composition change) in our pain transition model (specific aim 2), and we will investigate the role of phosphorylation-triggered switch of AMPA receptors from Ca2+-impermeable to Ca2+-permeable in stress-induced pain transition (specific aim 3). The overall goal of this proposal is to develop a new animal model for pain transition study and provide critical evidence to characterize the pain transition model. The proposed studies will demonstrate the role of stress- produced AMPA receptor regulation in the transition from acute to chronic pain and shed new light on the pathogenesis of chronic postsurgical pain.