A Sensory Map for Sulfated Steroids in the Accessory Olfactory Bulb

描述（由申请人提供）：在这个提案中，我们描述了一组实验，旨在测试感觉信号是如何在副嗅觉系统的第一突触上表示的。辅助嗅觉系统检测与动物行为反应有关的化学信号，从攻击到生殖的神经内分泌控制。鼻子中的感觉神经元投射到副嗅球，在那里来自表达相同受体类型的神经元的轴突共同聚集在被称为肾小球的小区域。在层状副嗅球的单一层内，单个受体类型在肾小球亚群内汇聚。在这些肾小球内，感觉神经元在二尖瓣细胞上突触，二尖瓣细胞编码感觉信号并向嗅球外投射。感觉神经元和二尖瓣细胞的反应模式在肾小球中是否具有空间相关性尚不清楚。除了与二尖瓣细胞的连接外，感觉神经元还驱动肾小球抑制性中间神经元的活动。GABA(A)和(B)受体在突触前和突触后均表达；这些抑制受体是各种电路和感觉处理任务的候选效应器，从输入的缩放和规范化到对其他动物气味的特定记忆的编码。然而，实际上对抑制在肾小球内形成反应的程度一无所知。例如，目前尚不清楚这种抑制是否是“横向的”（意思是，它在对应不同受体的肾小球之间起作用），以及抑制对球的输出神经元（二尖瓣细胞）的后果是什么。为了研究肾小球激活的特异性和抑制机制，我们将利用这样一个事实，即肾小球内感觉神经元终末的信号水平可以通过钙浓度的变化进行光学测量，从而使整个群体对刺激的反应可以通过光学记录。在目的1中，我们将使用已知的硫酸类固醇来驱动感觉神经元和二尖瓣细胞的活动，以确定副嗅球内肾小球激活的空间模式。我们预测不同配体对肾小球的激活在功能上是分离的，并且具有固定的空间分布。在目的2中，我们将确定抑制性神经传递在形成共激活肾小球反应中的作用。将通过对单个硫酸类固醇的反应来确定肾小球群体，然后在群体同时被激活时测量抑制相互作用。GABA(A)和GABA(B)受体的作用将通过GABA(A)和(B)拮抗来测量。我们预测感觉神经元突触前末端的gaba能抑制将发生在肾小球内和相邻的协同活性肾小球之间。如果成功，这些实验将为最近的观察提供机制基础，例如二尖瓣细胞相对于感觉神经元的雌激素硫酸盐反应性降低和性别特异性气味对抗。

DESCRIPTION (provided by applicant): In this proposal we describe a set of experiment designed to test how sensory signals are represented at the first synapse of the accessory olfactory system. The accessory olfactory system detects chemical signals pertinent to behavioral responses ranging from aggression to neuroendocrine control of reproduction in animals. Sensory neurons in the nose project to the accessory olfactory bulb, where axons from neurons expressing the same receptor type co-converge on small regions of neuropil called glomeruli. Individual receptor types converge within subsets of glomeruli in a single lamina of the laminar accessory olfactory bulb. Within these glomeruli, sensory neurons synapse on mitral cells, which encode sensory signals and project out of the olfactory bulb. It is unknown whether the response patterns of the sensory neurons and mitral cells have a spatial correlate in the glomeruli. In addition to connections with mitral cells, sensory neurons drive activity in glomerular inhibitory interneurons. GABA(A) and (B) receptors are expressed both pre- and post-synaptically; these inhibitory receptors are candidate effectors for a variety of circuit and sensory processing tasks from scaling and normalization of inputs to the encoding of specific memories for the scent of other animals. However, virtually nothing is known about the degree to which inhibition shapes responses within the glomeruli. For example, it is unknown whether the inhibition is "lateral" (meaning, it acts between glomeruli corresponding to different receptors), and what the consequences of inhibition are for the output neurons of the bulb, the mitral cells. To examine the specificity of glomerular activation and mechanisms of inhibition, we will exploit the fact that the levels of signaling in sensory neuron terminals within the glomeruli are optically measurable as changes in calcium concentration, thus rendering the entire population response to a stimulus amenable to optical recording. In Aim 1, we will identify the spatial patterns of glomerular activation within the accessory olfactory bulb using sulfated steroids known to drive activity in both sensory neurons and mitral cells. We predict that glomerular activations by different ligands will be functionally separate and have stereotyped spatial distributions. In Aim 2, we will determine the role of inhibitory neurotransmission in shaping the responses of co-activated glomeruli. Populations of glomeruli will be identified by responses to individual sulfated steroids, and then the inhibitory interactions will be measured when the populations are simultaneously activated. The role of both GABA(A) and GABA(B) receptors will be measured, via GABA(A) and (B) antagonism. We predict that GABAergic inhibition of sensory neuron pre-synaptic terminals will occur both within glomeruli and between adjacent co-active glomeruli. If successful, these experiments will provide a mechanistic basis for recent observations such as diminished estrogen sulfate responsiveness of mitral cells relative to sensory neurons and sex-specific odor opponency.