Functional Organization of Inferior Colliculus

描述（由申请人提供）：本提案的总体目标是确定下核团和下丘（IC）之间发生了什么样的反应转换，每个下核团在引起这些转换时具有什么样的影响，以及这些转换可能产生什么样的功能意义。这将通过评估墨西哥无尾蝙蝠脑干听觉系统中物种特异性信号的处理来实现。它们是高度社会化的哺乳动物，使用丰富的交流手段进行各种各样的社会互动，包括母婴互动、求偶、争斗和领土。在上一个资助期进行的研究表明，IC神经元对社会沟通信号的反应经历了实质性的转变，而这些转变受到抑制的强烈影响。拟开展的研究将探讨下核团对IC的特异性抑制作用。将特别注意抑制性神经支配的三个主要来源：1）同侧DNLL; 2）外侧丘系腹侧核（VNLLc）的柱状分裂; 3）其多极分裂（VNLLm）。DNLL对IC提供GABA能抑制，而VNI. I.分裂为IC提供甘氨酸能神经支配（VNLLc）或混合的甘氨酸和GABA能神经支配（VNLLm）。总之，来自同侧DNLL和VNLL的两个分支的投射提供了IC总抑制性神经支配的一半以上。根据上述内容，提出了将回答2个主要问题的实验。首先，VNLL的两个区域的神经元如何响应物种特异性呼叫，以及它们的响应特征如何由音调和复杂信号引起，由它们接收的兴奋性和抑制性神经支配形成？这些问题将回答从每个VNLL区域的神经元记录之前，然后，而抑制被离子电渗应用荷包牡丹碱或士的宁。第二，来自同侧DNLL的GABA能输入对由音调和复合信号诱发的IC反应有什么影响，这些影响与来自VNLL亚区的甘氨酸能和/或GABA能抑制的影响相比如何？这些问题将通过记录IC神经元之前，期间和之后的可逆失活的每个较低的核来回答。这些数据将提供一个更完整的图片的抑制性放电列车，作用于IC在响应简单和复杂的信号。他们还将揭示每个核团的抑制在塑造IC对简单和复杂信号的反应中的影响，包括传达独特类别信息的通信信号。通信呼叫的处理的阐明可以提供洞察到语音的处理。抑制在此过程中的作用可能与老年人的言语知觉下降特别相关，这与听觉系统中与年龄相关的GABA能神经元的损失有关。

DESCRIPTION (provided by applicant): The overall goals of this proposal are to determine what response transformations occur between lower nuclei and the inferior colliculus (IC), what impact each lower nucleus has in causing those transformations and what functional significance might accrue to those transformations. This will be accomplished by evaluating the processing of species-specific signals in the brainstem auditory system of Mexican free-tailed bats. These are highly social mammals that employ a rich repertoire of communication calls for a wide variety of social interactions, including mother-infant interactions, courtship, agonistic encounters, and territoriality. Studies conducted during the previous grant period have shown that responses of IC neurons to social communication signals undergo substantial transformations, and those transformations are strongly shaped by inhibition. The proposed studies will investigate the specific inhibitory influences that lower nuclei have on the IC. Particular attention will be given to three main sources of inhibitory innervation; 1) the ipsilateral DNLL; 2) the columnar division of the ventral nucleus of the lateral lemniscus (VNLLc); and 3) its multipolar division (VNLLm). The DNLL provides GABAergic inhibition to the IC while the VNI.I. divisions provide either glycinergic (VNLLc) or a mixed glycineric and GABAergic innervation (VNLLm) to the IC. Together, the projections from ipsilateral DNLL and the two divisions of the VNLL provide more than half of the total inhibitory innervation of the IC. Following from the above, experiments are proposed that will answer 2 main questions. First, how do neurons in the two regions of the VNLL respond to species-specific calls and how are their response features, evoked by both tones and complex signals, shaped by the excitatory and inhibitory innervation they receive? These questions will be answered by recording from neurons in each VNLL region before and then while inhibition is blocked by iontophoretic application of bicuculline or strychnine. Second, what influences do the GABAergic inputs from the ipsilateral DNLL have on IC responses evoked by both tones and complex signals, and how do those influences compare to the influences of glycinergic and/or GABAergic inhibition fi'om the VNLL subdivisions? These questions will be answered by recording from IC neurons before, during and after reversible inactivation of each of the lower nuclei. Taken together these data will provide a more complete picture of the inhibitory discharge trains that act on the IC in response to simple and complex signals. They will also reveal what impacts the inhibition from each nucleus have in shaping IC responses to simple and complex signals, including communication signals that convey unique categories of information. The elucidation of the processing of communication calls may provide insights into the processing of speech. The roles of inhibition in this processing may be especially relevant for the decline of speech perception in the elderly, which is correlated with age related loss of GABAergic neurons in the auditory system.