Function of Ret-GFL signaling in sensory neurons

描述（由申请人提供）：感觉疼痛的小直径感觉神经元被分类为伤害感受器。在胚胎发育过程中，几乎所有的伤害感受器都表达TrkA，神经营养因子NGF的受体，并依赖于NGF生存。在胚胎晚期和出生后早期，小直径无髓鞘伤害感受器（C-纤维伤害感受器）分化成两个数量大致相等的不同亚群。一个群体继续表达TrkA。另一个群体下调TrkA的表达，并表达Ret，属于GDNF家族的神经营养因子的受体。除了营养因子受体的表达，这两个亚群的C-纤维伤害感受器可以区分基于肽的表达，其结合植物凝集素，isolectin B4（IB 4）的能力，和他们的中央和外周投影的模式。表达TrkA的伤害感受器也表达肽CGRP和P物质，不结合IB 4，并投射到背角的板层I和IIo。表达Ret的伤害感受器通常不表达这些神经肽，结合凝集素IB 4，并投射到背角的LIIi。有证据表明，神经营养因子信号调节的结构和功能特性的感觉神经元在出生后的时期和成熟。由于肾脏发育不全导致的Ret基因敲除小鼠的围产期死亡限制了Ret在出生后和成熟感觉神经元中功能的研究。为了克服这一限制，我们通过将具有floxed Ret等位基因的小鼠（Ret条件小鼠）与在伤害感受器特异性启动子（钠通道a亚基1.8启动子）下表达Cre重组酶的小鼠杂交，产生了Ret仅在IB 4阳性伤害感受器中缺失的小鼠。我们将使用解剖学和行为学方法来确定Ret缺失对该小鼠中IB 4伤害感受器的结构和功能的影响。对这只小鼠的分析将使我们能够确定Ret信号在伤害感受神经元存活和维持伤害感受器结构和功能中的作用。此外，这只小鼠可能提供对IB 4伤害感受器亚群对疼痛转导的具体贡献的见解。慢性疼痛的治疗是一个主要的未满足的医疗需求。我们创造了一种新的小鼠，其中GDNF家族神经营养因子配体（GFLs）的受体Ret在伤害感受器（感知疼痛的神经元）中被删除。这种新型小鼠将使我们能够确定GFLs在伤害感受器存活和功能中的作用，并研究GFLs有效治疗慢性疼痛综合征的机制。

DESCRIPTION (provided by applicant): Small-diameter sensory neurons that sense pain are classified as nociceptors. During embryonic development virtually all nociceptors express TrkA, the receptor for the neurotrophic factor NGF, and depend on NGF for survival. During late embryonic and early postnatal life, small-diameter unmyelinated nociceptors (C-fiber nociceptors) diverge into two distinct subpopulations of roughly equal number. One population continues to express TrkA. The other population down-regulates TrkA expression and expresses Ret, the receptor for the neurotrophic factors belonging to the GDNF family. In addition to trophic factor receptor expression, these two subpopulations of C-fiber nociceptors can be distinguished based on peptide expression, their ability to bind the plant lectin, isolectin B4 (IB4), and the pattern of their central and peripheral projections. Nociceptors that express TrkA also express the peptides CGRP and substance P, do not bind IB4, and project to lamina I and IIo of the dorsal horn. Nociceptors that express Ret do not typically express these neuropeptides, do bind the lectin IB4, and project to LIIi of the dorsal horn. Evidence suggests that neurotrophic factor signaling modulates structural and functional properties of sensory neurons in the postnatal period and in maturity. Perinatal death of Ret-null mice because of kidney agenesis has limited the study of Ret function in postnatal and mature sensory neurons. To overcome this limitation, we have created a mouse in which Ret is deleted exclusively in IB4-positive nociceptors by crossing a mouse with floxed Ret alleles (Ret-conditional mouse) with a mouse expressing Cre recombinase under a nociceptor specific promoter (the sodium channel a subunit 1.8 promoter). We will use anatomical and behavioral methods to determine the effect of Ret deletion on the structure and function of IB4 nociceptors in this mouse. Analysis of this mouse will enable us to determine the role of Ret signaling in nociceptive sensory-neuron survival and in the maintenance of nociceptor structure and function. In addition, this mouse may provide insights into the specific contribution of the IB4 subpopulation of nociceptors to pain transduction. The treatment of chronic pain is a major unmet medical need. We have created a novel mouse in which Ret, the receptor for the GDNF family neurotrophic factor ligands (GFLs) is deleted in nociceptors (neurons that sense pain). This novel mouse will allow us to determine the role of the GFLs in nociceptor survival and function and to study mechanisms by which GFLs are effective in the treatment of chronic pain syndromes.