The Prefrontal Cortex in Neuropathic pain

描述(由申请人提供)： 疼痛是导致人们寻求医疗保健的最常见动机。当疼痛变得慢性时，它会产生几种长期影响，如抑郁、失眠、免疫功能低下、行动不便和其他长期有害后果，其中一些提示涉及到与较高认知功能有关的皮质区域。尽管过去15年发展的动物模型彻底改变了我们对慢性疼痛机制的理解，但在这些模型中获得的知识主要集中在涉及传入输入、脊髓过程和下行调制的机制上。人们对脊椎上的机制知之甚少，更不知道疼痛和皮质过程的相互作用。最近在慢性背痛患者中进行的人脑成像研究表明，即使在没有伤害性外周输入的情况下，内侧前额叶皮质也会出现过度活动。其他研究表明，慢性疼痛患者的决策任务受损，动物模型显示，阻断内侧前额叶皮质的神经元活动可逆地减少神经病理性疼痛。对炎症性疼痛的动物研究表明，前额叶皮质谷氨酸能突触传递的功能后果。所有这些观察表明，神经病理性疼痛动物的前额叶皮质可能存在功能和形态上的变化。我们将在SNI大鼠身上研究这一假设，SNI大鼠是一种高度可重复性的神经病理性疼痛模型。为比较SNI和假手术动物内侧前额叶皮质(MPFC)锥体神经元的功能和形态特征，将进行膜片钳记录和生物细胞蛋白填充神经元的形态分析。我们将比较SNI和假手术动物的树突数量和长度以及树突棘密度。免疫组织化学分析将研究神经元重组的分子标志物的表达。谷氨酸能突触传递的内在电生理特性以及药理学特性也将被研究。有核斑片记录和快速溶液交换将被用来详细研究对照组和SNI大鼠mPFC锥体神经元表达的谷氨酸受体的功能特性。我们的初步数据显示，与假手术组相比，SNI大鼠的mPFC神经元表达更高水平的c-Fos，树突树更大，树突棘密度增加，谷氨酸受体的分子组成不同。有趣的是，这些变化中有几个与受伤爪子的痛阈值有关。这些观察结果支持我们的假设，即神经病理性疼痛导致mPFC的功能重组。我们的实验的成功完成可能代表着神经病理性疼痛的细胞机制研究的一次飞跃，并开辟了新的研究领域。与公共健康相关：慢性疼痛可导致长期后果，如抑郁、失眠和饮食模式的改变，所有这些都意味着涉及到与较高认知功能有关的皮质区域；这表明疼痛可以影响这些大脑区域的功能，并可能影响这些区域的解剖组织，尽管对慢性疼痛对大脑的影响知之甚少。我们将研究神经病理性疼痛诱导的前额叶皮质的功能和形态重组；这样的实验将促进对神经病理性疼痛和皮质可塑性的细胞机制的了解，并可能导致新的治疗策略。

DESCRIPTION (provided by applicant): Pain is the most common motive leading people to seek health care. When it becomes chronic, pain can produce several long term effects such as depression, loss of sleep, depressed immune function, decreased mobility, and other long-term deleterious consequences, several of which suggest the involvement of cortical areas implicated in higher cognitive functions. Although animal models advanced over the last 15 years have revolutionized our understanding of chronic pain mechanisms, the knowledge garnered in these models has concentrated primarily on mechanisms involving afferent inputs, spinal cord processes, and descending modulation. Little is known about supraspinal mechanisms, even less so about the interaction of pain and cortical processes. Recent human brain imaging studies in chronic back pain patients indicate medial prefrontal cortical hyperactivity, even in absence of nociceptive peripheral inputs. Other studies show impairment of decision making tasks in patients suffering of chronic pain and animal models show that blocking neuronal activity in the medial prefrontal cortex reversibly decreases neuropathic pain. Animal studies on inflammatory pain show functional consequences on glutamatergic synaptic transmission in the prefrontal cortex. All these observations suggest that functional and morphological changes may be present in the prefrontal cortex of animals with neuropathic pain. We will investigate this hypothesis in SNI rats, a highly reproducible model of neuropathic pain. Patch clamp recordings and morphological analysis of biocytin filled neurons will be performed to compare the functional and morphological properties of pyramidal neurons of the medial prefrontal cortex (mPFC) of SNI and sham-operated animals. We will compare the number and length of the dendrites and the dendritic spine density in SNI and sham-operated animals. Immunohistochemical analysis will be performed to investigate the expression of molecular markers of neuronal reorganization. Intrinsic electrophysiological properties as well as the pharmacological properties of glutamatergic synaptic transmission will also be investigated. Nucleated patch recordings and fast solution exchange will be used to perform a detailed study of the functional properties of the glutamate receptors expressed in mPFC pyramidal neurons of control and SNI rats. Our preliminary data show that, compared to sham-operated counterparts, mPFC neurons from SNI rats expressed higher levels of c-Fos, have larger dendritic trees, increased dendritic spine density and different molecular composition of glutamate receptors. Interestingly, several of these changes are correlated with the pain threshold in the injured paw. These observations support our hypothesis that neuropathic pain induces functional reorganization of the mPFC. Successful completion of our experiments could represent a leap forward in the study of the cellular mechanisms of neuropathic pain and open new fields of investigation. PUBLIC HEALTH RELEVANCE: Chronic pain can cause long term consequences such as depression, loss of sleep, and changes in eating patterns, all of which imply the involvement of cortical areas implicated in higher cognitive functions; this suggests that pain can affect the function and, possibly, the anatomical organization of these brain areas, although little is known about the effect of chronic pain on the brain. We will study neuropathic pain-induced functional and morphological reorganization of the prefrontal cortex; such experiments will advance the knowledge of the cellular mechanisms of neuropathic pain and cortical plasticity, and may lead to novel therapeutic strategies.