A non-injurious assay to study mechanisms of transmission of noxious stimulus

虽然疼痛仍然是患者寻求医疗保健的最常见原因，但疼痛的传播和感知机制尚未完全了解。为了开发新的药物和技术来治疗疼痛，必须了解伤害性和非伤害性刺激的神经生理机制。因此，需要临床相关的疼痛动物模型来进一步了解疼痛传递机制。目前可用的研究疼痛传播的模型使用热，压力或化学刺激来施加疼痛。这些模型导致了该领域的许多发现，但有局限性。一些局限性包括这样的事实，即热和压力可能与动物的损伤有关，刺激可以非特异性地刺激几种类型的神经纤维（A β-压力，A δ-尖锐疼痛，C-缓慢燃烧疼痛），并且这些刺激可以与习惯性学习有关。为了研究伤害性刺激的传递机制，我们开发了一种新的和非损伤性的伤害性试验，优先研究伤害性刺激通过神经纤维在活体系统中的传递。我们使用神经刺激器，以不同的频率和强度向皮肤提供电刺激，并产生短暂的不适而不产生伤害。所使用的每个电频率优先刺激特定类型的疼痛纤维，并允许测量每种类型的疼痛纤维的发声阈值。在该模型中，我们将发声定义为对电刺激的疼痛回避行为，并以其为终点来测量每个疼痛纤维的电流发声阈值。与目前使用的可能产生一些组织损伤以诱导疼痛的疼痛模型不同，该测定是无损伤的，并且优先刺激每种类型的疼痛纤维。因此，它可能成为研究疼痛机制的一个有价值的工具。 我们完成了在小鼠中开发该试验的试点研究，开发了对每个频率的响应的标准值，并完全开发了控制神经刺激器的软件应用程序，并自动化了大部分方案。此外，我们正在实施升级，以实现自动数据收集和存储。我们现在正在使用该模型来研究衰老的影响，性别差异以及一氧化氮合酶在特定伤害性神经纤维中传递伤害性刺激的作用。我们正在进一步开发该模型，以评估药物干预，如吗啡与全身和局部镇痛药，不同品系和物种的动物，以及不同的疼痛模型。

Although pain is still the most common reason why patients seek health care, the mechanisms of transmission and perception of pain are incompletely understood. In order to develop new drugs and techniques to treat pain, it is imperative to undrestand the neurophysiologic mechanisms by which noxious and non-noxious stimuli are perceived. Therefore, clinically relevant animal models of pain are needed to further our understanding of the mechanisms of pain transmission. Currently available models to study transmission of pain use heat, pressure, or chemical stimulation to inflict pain. These models have led to many discoveries in the field but have limitations. Some of the limitations include the fact that heat and pressure can be associated with injury to animals, the stimuli can nonspecifically stimulate several types of nerve fibers (A beta-pressure, A delta-sharp pain, C-slow burning pain), and these stimuli can be associated with habituation learning. In order to study the mechanisms of the transmission of noxious stimuli, we developed a novel and non-injurious nociception assay to preferentially study transmission of noxious stimulus via nerve fibers in a live system. We use a neuro-stimulator that delivers electrical stimuli to the skin at different frequencies and intensities and produces transient discomfort without producing injury. Each of the electrical frequencies used preferentially stimulate a specific type of pain fiber and allows for the measure of vocalization threshold for each type of pain fiber. In the model, we define vocalization as the pain avoiding behavior to the electrical stimulus and use it as the end point to measure current vocalization threshold for each of the pain fibers. Unlike currently used pain models that may produce some tissue-injury in order to induce pain, this assay is non-injurious and preferentially stimulates each type of pain fibers. Therefore it might become a valuable tool for the study of the mechanisms of pain. We completed pilot studies for the development of this assay in mice, developed normative values for the response to each frequency, and have fully developed software application to control the neuro-stimulator, and automated a large portion of the protocol. In addition, we are implementing upgrades to enable automated data collection and storage. We are now using the model to study the impact of aging, differences in gender as well as the role of nitric oxide synthases in the transmission of noxious stimuli in specific nociceptive nerve fibers. We are further developing the model to evaluate pharmacologic interventions such as morphine with systemic and local analgesics, different strains and species of animals, and different pain models.