Yokoi M, Mori K, Nakanishi S
Institute for Immunology, Kyoto University Faculty of Medicine, Japan.
Proc Natl Acad Sci U S A. 1995 Apr 11;92(8):3371-5. doi: 10.1073/pnas.92.8.3371.
Mitral/tufted cells (M/T cells) and granule cells form reciprocal dendrodendritic synapses in the main olfactory bulb; the granule cell is excited by glutamate from the M/T cell and in turn inhibits M/T cells by gamma-aminobutyrate. The trans-synaptically excited granule cell is thought to induce lateral inhibition in neighboring M/T cells and to refine olfactory information. It remains, however, elusive how significantly and specifically this synaptic regulation contributes to the discrimination of different olfactory stimuli. This investigation concerns the mechanism of olfactory discrimination by single unit recordings of responses to a series of normal aliphatic aldehydes from individual rabbit M/T cells. This analysis revealed that inhibitory responses are evoked in a M/T cell by a defined subset of odor molecules with structures closely related to the excitatory odor molecules. Furthermore, blockade of the reciprocal synaptic transmission by the glutamate receptor antagonist or the gamma-aminobutyrate receptor antagonist markedly suppressed the odor-evoked inhibition, indicating that the inhibitory responses are evoked by lateral inhibition via the reciprocal synaptic transmission. The synaptic regulation in the olfactory bulb thus greatly enhances the tuning specificity of odor responses and would contribute to discrimination of olfactory information.
二尖瓣/簇状细胞（M/T细胞）和颗粒细胞在主嗅球中形成相互的树突-树突突触；颗粒细胞被来自M/T细胞的谷氨酸激活，进而通过γ-氨基丁酸抑制M/T细胞。经突触兴奋的颗粒细胞被认为在相邻的M/T细胞中诱导侧向抑制，并优化嗅觉信息。然而，这种突触调节在多大程度上以及如何具体地促进不同嗅觉刺激的辨别仍不清楚。本研究通过对单个兔M/T细胞对一系列正常脂肪族醛类的反应进行单细胞记录，探讨嗅觉辨别的机制。该分析表明，特定的气味分子子集（其结构与兴奋性气味分子密切相关）可在M/T细胞中诱发抑制性反应。此外，谷氨酸受体拮抗剂或γ-氨基丁酸受体拮抗剂阻断相互突触传递，可显著抑制气味诱发的抑制，表明抑制性反应是通过相互突触传递的侧向抑制诱发的。嗅球中的突触调节因此极大地增强了气味反应的调谐特异性，并有助于嗅觉信息的辨别。
