Chemical Anatomy and Synaptology of Vestibulo-Sympathetic Pathways

描述（由申请人提供）：目前了解到，动脉压力感受器控制交感神经系统张力，而前庭末端器官为前庭交感反射提供传入输入，通常增强代偿性压力反射。然而，这种整合背后的神经通路的化学解剖学、连通性和突触学在很大程度上仍然未知。提出的项目的总体目标是确定参与调解前庭-自主神经突触相互作用的神经递质和调节剂。这四个目的探讨成年大鼠这些前庭神经投射的化学解剖学和突触学，并评估前庭神经投射到尾侧和吻侧腹侧延髓（分别为CVLM和RVLM）利用不同的递质/调节剂特征和不同的突触结构安排的总体假设。目的1是确定前庭-髓质和髓质-交感神经投射神经元的位置，确定前庭投射到CVLM和RVLM的相对比例，确定这些通路所利用的初级氨基酸神经递质，并确定这些投射是否终止于CVLM和RVLM中的谷氨酸能和/或gaba能神经元。目的2是确定CVLM和RVLM的前庭末梢是否共同表达iata - rp和/或l -瓜氨酸。目的3定性分析RVLM和CVLM中前庭受体细胞的主要神经递质和调节剂，验证谷氨酸能前庭传入终止于含gabaergy / iaa - rp的CVLM神经元的中间神经元和远端树突、RVLM中gabaergy和去甲肾上腺素能树突，并直接终止于直接投射到脊髓的含谷氨酸能/ iaa - rp的RVLM神经元的体上的假设。目的4是可视化和量化前庭-交感神经突触的参数，并将验证RVLM的前庭末梢突触涉及多个递质系统之间复杂的相互作用，而CVLM的前庭-交感神经末梢突触反映了与CVLM输出神经元的直接轴-树突接触的假设。在整个项目中，前庭交感神经通路将通过组织中的顺行和逆行通道追踪来识别，并将使用额外的免疫荧光标签进一步处理以识别感兴趣的递质和调节剂。超微结构研究将使用免疫金标记来识别和量化终端和突触接触。这些研究将描述前庭投射到交感前运动髓质神经元池所利用的神经递质、调节剂和突触关节，并将对其突触结构参数进行定性分析和定量估计。这一信息目前在文献中尚不存在，但对于开发基于证据的药物治疗前庭-自主神经疾病（如体位性低血压）以及开发更特异性的抗高血压药物非常重要，这些药物不会引起致残性前庭副作用（如头晕和眩晕）。公共卫生相关性：针对交感神经系统的药物（如降压药）的直立性低血压和前庭副作用影响大量人群，特别是老年人。然而，对前庭交感神经通路的神经化学组织知之甚少。该项目将提供关于前庭神经投射到腹外侧髓质心血管神经元的化学解剖学和突触组织的基本信息，可能为改善直立性低血压和不耐受提供新的药物治疗方法，并可能导致更特异性的抗高血压药物的开发，这些药物不会引起致残性前庭副作用，如头晕和眩晕。

DESCRIPTION (provided by applicant): It is currently understood that arterial baroreceptors control sympathetic nervous system tone, while vestibular end organs provide afferent input to a vestibulo-sympathetic reflex that normally augments the compensatory baroreflex. However, the chemical anatomy, connectivity and synaptology of the neural pathways underlying this integration remain largely unknown. The overall goal of the proposed project is to identify the neurotransmitters and modulators involved in mediating vestibulo-autonomic synaptic interactions. The four aims address the chemoanatomy and synaptology of these vestibular projections in adult rats and evaluate the overall hypothesis that different transmitter/modulator signatures and distinct synaptic architectural arrangements are utilized by vestibular projections to the caudal and rostral ventrolateral medulla (CVLM and RVLM, respectively). Aim 1 is to identify the locations of vestibulo-medullary and medullo- sympathetic projection neurons, determine the relative proportions of vestibular projections to CVLM and RVLM, identify the primary amino acid neurotransmitter(s) utilized by these pathways and determine whether these projections terminate on glutamatergic and/or GABAergic neurons in CVLM and RVLM. Aim 2 is to determine whether vestibular terminals in CVLM and RVLM co-express IAA-RP and/or L-citrulline. Aim 3 is to conduct a qualitative analysis of the main neurotransmitters and modulators of vestibulo-recipient cells in RVLM and CVLM, to test the hypothesis that glutamatergic vestibular afferents terminate on interneurons and on distal dendrites of GABAergic/IAA-RP-containing CVLM neurons, GABAergic and noradrenergic dendrites in RVLM, and directly on the somata of glutamatergic/IAA-RP-containing RVLM neurons with direct projections to the spinal cord. Aim 4 is to visualize and quantify parameters of vestibulo-sympathetic synaptology, and will test the hypothesis that the synaptology of vestibular terminals in RVLM involves complex interactions among multiple transmitter systems, whereas the synaptology of vestibulo-sympathetic terminals in CVLM reflects direct axo-dendritic contacts with CVLM output neurons. Throughout the project, the vestibulo-sympathetic pathways will be identified using anterograde and retrograde tract-tracing in tissue that will be further processed using additional immunofluorescent tags to identify transmitters and modulators of interest. Ultrastructural studies will employ immunogold labels to identify and quantify terminals and synaptic contacts. These studies will characterize the neurotransmitters, modulators and synaptic articulations utilized by vestibular projections to sympathetic pre-motor medullary neuron pools and will yield qualitative analyses and quantitative estimates of parameters of their synaptic architecture. This information does not currently exist in the literature, and is important for the development of evidence-based pharmacotherapeutics for the treatment of vestibulo-autonomic disorders such as orthostatic hypotension, as well as the development of more specific anti-hypertensive medications that do not elicit disabling vestibular side-effects such as dizziness and vertigo. PUBLIC HEALTH RELEVANCE: Orthostatic hypotension and vestibular side effects of drugs targeting the sympathetic nervous system (e.g. anti-hypertensive medications) impact large populations, especially the elderly. However, little is known about the neurochemical organization of vestibulo-sympathetic pathways. This project will provide fundamental information about the chemoanatomic and synaptic organization of vestibular projections to cardiovascular neurons in the ventrolateral medulla, may suggest new drug therapies to ameliorate orthostatic hypotension and intolerance, and may lead to the development of more specific anti-hypertensive medications that do not elicit disabling vestibular side effects such as dizziness and vertigo.