Nociceptor Maturation and Response to Peripheral Injury

描述(申请人提供)：疼痛感觉神经元，或伤害性感受器，在生命早期特别容易受到组织创伤和炎症的影响，越来越多的证据表明，新生儿的外周炎症可以导致中枢伤害性神经回路和疼痛相关行为的永久性改变。这些变化在多大程度上反映了伤害性感受器外周终末的永久性局部变化尚不清楚，尽管这种知识对于理解驱动或帮助维持成人伤害性感受功能变化的因果机制至关重要。我们最近在新生小鼠上的工作表明，有髓伤害性感受器的外周末端在炎性伤害后的几天内会发生显著的解剖和生理变化；相比之下，其他皮肤伤害性感受器基本上没有受到影响，因此对有髓伤害性感受器的影响可能是了解早期组织创伤后成人疼痛状态变化的关键。拟议的实验将直接检验使用成年小鼠体内三叉神经制剂的有髓伤害性感受器终末永久改变的可能性。这种新的制剂首次赋予成年动物标记生理鉴定的皮肤感觉神经元的外周终末的能力。这些研究的总体目标是确定正常成年动物皮肤中有髓伤害性感受器终末的形态多样性，以及新生儿早期的外周炎症是否会导致这些终末的永久性改变。通过细胞内记录，神经元将使用一套全面的自然皮肤刺激进行生理学表征，然后通过神经生物素的离子导入进行整体标记。标记神经元的外周终末将在皮肤切片中重建，以允许直接确认个别生理识别的皮肤感觉神经元的功能形态。对正常成人(即NAOVE)的分析将为分析新生儿炎症后这些结局的潜在变化提供关键背景。将在两种不同的实验诱导的新生小鼠面部皮肤炎症模型中检查外周终末潜在的长期变化；将比较新生儿佐剂诱导的炎症和卡拉胶诱导的炎症的长期影响，以分析持续和急性炎症状态在产生有髓伤害感受器终末永久性变化方面的潜在差异。这些结果将与成年后实验诱导的炎症反应进行比较，以确定有髓伤害性感受器的外周终末是否保持对成人组织创伤的反应能力，从而在一生中保持可塑性。这些研究的结果将对疼痛系统的这一重要组成部分的早期成熟以及这些传入细胞对早期扰动的敏感性提供前所未有的理解。这些信息将对未来儿科疼痛管理战略的制定和将这些战略转化为有效实践至关重要。 与公共卫生相关越来越多的证据表明，新生儿的外周炎症可以导致疼痛回路和行为的永久性改变。这些永久性影响在多大程度上是由早期炎症对痛觉终端或皮肤中伤害性感觉神经元的不可逆转影响所驱动的，目前尚不清楚。这项拟议的工作将确定正常成年小鼠皮肤伤害性感受器终末的形态多样性，并确定早期炎症是否会导致这些终末的永久性变化。

DESCRIPTION (provided by applicant): Pain sensory neurons, or nociceptors, are particularly vulnerable to tissue trauma and inflammation during early life, and there is mounting evidence that peripheral inflammation in newborns can lead to permanent alterations in central nociceptive circuitry and pain-related behaviors. The extent to which these changes reflect permanent local alterations in the peripheral terminals of nociceptors is unknown, although such knowledge is critical to understanding causal mechanisms that either drive or help maintain altered nociceptive functioning in adults. Our recent work in neonatal mice has shown that the peripheral terminals of myelinated nociceptors undergo dramatic anatomical and physiological alterations within days of an inflammatory insult; by contrast, other cutaneous nociceptors were largely unaffected, and thus effects on myelinated nociceptors may be key to understanding altered adult pain states following early tissue trauma. The proposed experiments will directly examine the potential for permanent changes in myelinated nociceptor terminals using an in vivo trigeminal preparation in adult mice. This new preparation confers the ability, for the first time, to label the peripheral terminals of physiologically identified skin sensory neurons in adult animals. The overall goals of these studies are to determine the morphological diversity of myelinated nociceptor terminals in the skin of normal adult animals, and whether peripheral inflammation in early neonatal life results in permanent alterations of these endings. Through intracellular recordings, neurons will be physiologically characterized using a comprehensive suite of natural skin stimuli and then labeled in their entirety through iontophoresis of Neurobiotin. The peripheral terminals of labeled neurons will be reconstructed in skin sections to allow direct confirmation of functional morphology of individual physiologically identified skin sensory neurons. Analyses in normal (i.e., naove) adults will provide a critical backdrop for analyzing potential changes in these endings following neonatal inflammation. Potential long-term alterations in peripheral endings will be examined in two different models of experimentally induced inflammation in facial skin of newborn mice; the long-term effects of neonatal adjuvant-induced and carrageenan-induced inflammation will be compared to analyze potential differences between persistent versus acute inflammatory states in producing permanent alterations in myelinated nociceptor terminals. These results will be compared with the effects of experimentally induced inflammation in adulthood to determine whether the peripheral terminals of myelinated nociceptors retain the ability to respond to adult tissue trauma and therefore remain plastic throughout life. The results of these studies will provide an unprecedented understanding of the early maturation of this vital component of the pain system and the susceptibility of these afferents to early perturbation. This information will be pivotal to the development of future strategies in pediatric pain management and the translation of these strategies into effective practice. PUBLIC HEALTH RELEVANCE There is mounting evidence that peripheral inflammation in newborns can lead to permanent alterations in pain circuitry and behaviors. The extent to which these permanent effects are driven by irreversible effects of early inflammation on the terminals of pain-sensing, or nociceptive sensory neurons in the skin is unknown. The proposed work will determine the morphological diversity of nociceptor terminals in the skin of normal adult mice, and determine whether early inflammation leads to in permanent alterations in these endings.