Coding of odor molecules by neurons in mammalian olfactory bulb and cortex : Functional role of olfactory glomeruli

1)家兔主嗅球僧帽状/簇状细胞的分子感受域特性在麻醉家兔主嗅球不同区域的单个僧帽状/簇状细胞上记录细胞外锋电位反应。包括芳香族和脂肪族化合物的刺激气味分子的扩展面板的检查表明，单个二尖瓣/簇状细胞显示兴奋性尖峰响应的范围内的气味分子（分子接受范围）具有相似的构象。这些结果支持的假设，配体气味分子的构象参数在嗅球的感觉处理中发挥了关键作用。此外，这一结果与表达同种气味受体的感觉神经元集中于一个或几个肾小球的假设相一致。2）延髓局部回路神经元在气味分子编码中的功能作用采用兔主球单单位记录法，我们发现抑制反应在二尖瓣/簇状细胞通过具有与兴奋性气味分子密切相关的结构的气味分子的限定子集。药理学阻断二尖瓣/簇状细胞和颗粒细胞之间的树突突触传递显着降低了气味诱发的抑制，这表明抑制反应是通过树突突触通路的侧抑制引起的。因此，嗅球中局部回路内的突触相互作用大大增强了气味反应的调谐特异性，并有助于气味分子信息的辨别。

1) Molecular receptive range properties of mitral/tufted cells in the rabbit main olfactory bulbRecording of extracellular spike responses were made from single mitral/tufted cells in various regions of the main olfactory bulb of urethane-anesthetized rabbits. Examination with an expanded panel of stimulus odor molecules that included both aromatic and aliphatic compounds indicated that single mitral/tufted cells show excitatory spike responses to a range of odor molecules (molecular receptive range) having similar conformations. These results support the hypothesis that conformational parameters of ligand odor molecules play a key role in sensory processing in the olfactory bulb. In addition, the results are in agreement with the hypothesis that sensory neurons expressing the same type of odor receptor converge on one or a few glomeruli.2) Functional role of bulbar local circuit neurons in coding of odor moleculesUsing single unit recording in rabbit main bulb, we showed that inhibitory responses are evoked in mitral/tufted cells by a defined subset of odor molecules with structures closely related to the excitatory odor molecules. Pharmacological blockade of the dendrodendritic synaptic transmission between mitral/tufted and granule cells markedly decreased the odor evoked suppression, suggesting that the inhibitory responses are evoked by lateral inhibition via the dendrodendritic synaptic pathway. The synaptic interaction s within the local circuits in the bulb, thus, greatly enhance the tuning specificity of odor responses and contribute to discrimination of odor molecule information.