Role of cholinergic afferent transmission in spinal synaptic function

描述（由申请人提供）：对中枢神经系统的体感输入在脊髓背角内的靶神经元上的初级传入突触中继处受到复杂的调节。整合和控制感觉信息的局部神经回路和过程仍然知之甚少。对该部位突触前抑制控制机制研究最透彻的是传入诱发的初级传入去极化（PAD），其中传入终末的去极化与抑制信号有关，或者矛盾地与超极化信号有关。 引起慢性疼痛的兴奋状态。这种脊髓机制有能力动态地限制或放大躯体感觉，因此，阐明PAD回路或回路亚型是如何参与的，对于解剖适应性与疾病的感觉处理有很大帮助。PAD/PSI历来被描述为多突触和GABA能。然而，我们有令人信服的证据表明，胆碱能初级传入可能会释放乙酰胆碱，并直接产生PAD以及对脊髓中间神经元产生突触作用。到目前为止，乙酰胆碱释放初级传入中枢末梢从来没有明确证明在哺乳动物。有趣的是，初级传入神经的一个亚群表达了一种最近描述的乙酰胆碱合成酶，这种酶对周围神经系统是特异性的。这一人群一直难以研究，对他们的功能知之甚少。尼古丁受体信号传导涉及调节感觉处理，包括疼痛，因此来自该感觉通路的信号传导可以独特地影响身体感觉。本研究将直接测试一个pupulmonary胆碱能初级传入神经释放ACh作为调节性递质的能力。我已经确定了一个ChAT-Cre驱动线，可能在遗传上靶向这个传入群体，使转基因方法，将使我能够表征其突触通路的基本特性。为了实现这一点，我设计了选择性激活和解剖学特征的传入人口的战略。特别是在研究突触前传入控制时，引入光遗传学策略应该会带来一个新的实验控制水平，通过分离单个神经元元件来识别通过突触前离子型受体控制传入的机制。如果一些pChAT传入被证明是突触前控制别人，一个全新的观点传入控制的机制提供了这个传入类一个独特的神经调节作用insomatosensory。

DESCRIPTION (provided by applicant): Somatosensory input to the central nervous system is complexly regulated at the primary afferent synaptic relay onto target neurons within the spinal cord dorsal horn. The local neural circuits and processes that integrate and gate sensory information are still poorly understood. The most thoroughly studied mechanism of presynaptic inhibitory control at this site is afferent-evoked primary afferent depolarization (PAD), wherein depolarization of the afferent terminal is linked to depressed signaling, or paradoxically to hyper excitable states that instigate chronic pain conditions. This spinal mechanism has the capacity to dynamically limit or magnify somatic sensation, so clarifying how PAD circuits or circuit subtypes are engaged could go a long way to dissecting adaptive versus diseased sensory processing. PAD/PSI is historically described as multisynaptic and GABAergic. However we have compelling evidence that cholinergic primary afferents may release ACh and generate PAD directly as well as produce synaptic actions on spinal interneurons. To date, acetylcholine release from primary afferent central terminals has never been unambiguously demonstrated in mammals. Intriguingly, a subpopulation of primary afferents expresses a recently described form of the acetylcholine synthesis enzyme that is specific to the peripheral nervous system. This population has been difficult to study, and little is known about their functionality. Nicotinc receptors signaling is implicated in modulating sensory processing, including pain, so signaling from this sensory pathway may uniquely influence bodily sensation. This proposal will directly test the capacity of a putatively cholinergic primary afferents to release ACh as a modulatory transmitter. I have identified a ChAT-Cre driver line that may genetically target this afferent population, enabling transgenic approaches that will allow me to characterize fundamental properties of their synaptic pathway. In order to accomplish this I have designed strategies for selective activation and anatomical characterization of this uncharacterized afferent population. In studying presynaptic afferent control in particular, introducing optogenetic strategies should bring a new level of experimental control to identifying the mechanisms controlling afferents via presynaptic ionotropic receptors by allowing individual neuronal elements to be isolated. If some pChAT afferents are shown to presynaptically control others, a completely new view on the mechanisms governing afferent control provides this afferent class a unique neuromodulatory role insomatosensation.