Anatomical analysis of cortical projections to the auditory midbrain

描述（由申请人提供）：听觉系统包括将信息从耳朵传递到更高层次的感知的上升通路和可以修改在上升通路的每个阶段如何处理信息的下降通路。听觉皮层是大量下行投射的来源，被认为在广泛的功能中发挥作用，包括在嘈杂环境中选择性注意和理解语言。了解这些功能的进展受到有关潜在神经回路的问题的阻碍。目前的建议集中在一个最大的下降投射，从听觉皮层到中脑的下丘。一个目的是确定这些投射是否与使用神经递质GABA的中脑抑制回路直接接触。第二个目的是确定皮层的投射是否与连接中脑两侧的大的互交通路有直接的突触接触（从而可以传播皮层的影响）。这项研究将在豚鼠身上进行，这是一个在听觉功能的许多方面都得到了充分研究的模型。实验将使用多标记解剖技术，包括使用荧光神经元示踪剂来标记特定的电路元件和免疫组织化学技术来识别与这些元件相关的神经递质。该设计包括使用光学显微镜和电子显微镜进行协调研究，以便直接识别突触，这是识别神经元回路的必要步骤。该结果将为描述下行听觉通路及其与兴奋性和抑制性中脑回路的关系提供重要的一步。在gaba能回路和通往中脑的上行通路上已经做了大量的工作；目前的建议应该有助于将下行系统整合到我们对中脑gaba能机制的看法中。这可能对与衰老或损伤相关的正常功能和功能障碍（如老年性耳聋或耳鸣）以及耳蜗和脑干植入物的设计和使用具有重要意义。从训练的角度来看，所提出的实验涵盖了广泛的敏感解剖技术，包括各种多标记方法和有效结合光学和电子显微镜的策略。这种解剖训练是为了补充申请人之前在神经生理学技术方面的广泛训练。结合所有这些方法的能力将极大地扩展他将来能够解决的研究问题的范围。

DESCRIPTION (provided by applicant): The auditory system comprises ascending pathways that transmit information from the ear to higher levels for perception, and descending pathways that can modify how that information is processed at each stage of the ascending pathways. The auditory cortex is the source of massive descending projections that are considered to play a role in a wide range of functions, including selective attention and understanding speech in noisy environments. Progress in understanding these functions is hampered by questions regarding the underlying neural circuitry. The present proposal focuses on one of the largest descending projections, from auditory cortex to the inferior colliculus of the midbrain. One aim is to determine whether these projections make direct synaptic contact with midbrain inhibitory circuits that use the neurotransmitter GABA. A second aim is to determine whether the cortical projections make direct synaptic contact with the large commissural pathway that connects the two sides of the midbrain (and could thus spread the cortical effects). The study will be conducted in guinea pigs, a well-researched model for many aspects of auditory function. The experiments will use multilabeling anatomical techniques, including the use of fluorescent neuronal tracers for labeling specific circuit elements and immunohistochemical techniques for identifying the neurotransmitters associated with those elements. The design includes coordinated studies with both light and electron microscopes to allow for the direct identification of synapses, a necessary step for identifying neuronal circuits. The results will provide an important step in characterizing descending auditory pathways and their relationships to excitatory and inhibitory midbrain circuits. Considerable work has been done on GABAergic circuits and ascending pathways to the midbrain; the current proposal should help to integrate the descending systems into our view of GABAergic mechanisms in the midbrain. This may have important implications for normal function as well as dysfunction (such as presbycusis or tinnitus) associated with aging or injury and for the evolving design and use of cochlear implants and brainstem implants. From a training perspective, the proposed experiments cover a broad range of sensitive anatomical techniques, including a variety of multi-labeling methods and strategies for the effective combination of light and electron microscopy. This anatomical training is designed to complement the applicant's prior, extensive training in neurophysiological techniques. The ability to combine all these approaches will greatly expand the range of research questions that he will be able to address in the future. PUBLIC HEALTH RELEVANCE: Auditory dysfunction due to aging, damage or disease affects many people. Our ability to develop treatments or prosthetics relies in part on identifying the neuronal circuits and the neurotransmitters they use. The present proposal will characterize the connections and neurotransmitters of circuits between the auditory cortex and midbrain that are associated with a wide range of functions.