Kratskin Igor, Kenigfest Natalia, Rio Jean Paul, Djediat Chakib, Repérant Jacques
Department of Otorhinolaryngology, Head and Neck Surgery, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4283, USA, and Institut National de la Santé, U-616, Hôpital de la Salpêtrière, Paris, France.
Neurosci Lett. 2006 Jul 10;402(1-2):121-5. doi: 10.1016/j.neulet.2006.03.077. Epub 2006 May 22.
The olfactory input to the brain is carried out by olfactory nerve axons that terminate in the olfactory bulb glomeruli and make synapses onto dendrites of glutamatergic projection neurons, mitral and tufted cells, and GABAergic interneurons, periglomerular cells. The dendrites are reciprocally connected through asymmetric synapses of mitral/tufted cells with periglomerular cells and symmetric synapses of the opposite direction. Transmission at the first synapse in the olfactory pathway is regulated presynaptically, and this regulation is mediated, in part, by metabotropic GABAB receptors that, when activated, inhibit transmitter release from the olfactory nerve. Functional GABAB receptors are heterodimers composed of the GABAB1 and GABAB2 subunits. Studies using double immunofluorescence have shown colocalization of both subunits in the glomerular neuropil, and ultrastructural studies have localized GABAB1 to extrasynaptic, synaptic, and perisynaptic sites on the plasma membrane of olfactory nerve terminals. We studied the subcellular localization of GABAB2 in the mouse olfactory glomeruli using a subunit-specific antibody and preembedding immunogold labeling. Immunoreactivity for GABAB2 was associated with symmetric dendrodendritic synapses of periglomerular cells with mitral/tufted cells and was localized to the extrasynaptic plasma membrane of presynaptic dendrites, and extrasynaptic, synaptic, and perisynaptic sites on the plasma membrane of postsynaptic dendrites. The results suggest that postsynaptic, and perhaps presynaptic, GABAB receptors may be expressed at GABAergic synapses between dendrites of periglomerular interneurons and projection neurons. Immunolabeling was observed at junctions of the olfactory nerve with mitral/tufted cell dendrites, providing ultrastructural evidence for the expression of the GABAB2 subunit at the primary olfactory synapse.
大脑的嗅觉输入由嗅觉神经轴突完成，这些轴突终止于嗅球的肾小球，并与谷氨酸能投射神经元、二尖瓣细胞和簇状细胞以及GABA能中间神经元（球周细胞）的树突形成突触。这些树突通过二尖瓣/簇状细胞与球周细胞的不对称突触以及相反方向的对称突触相互连接。嗅觉通路中第一个突触处的传递在突触前受到调节，这种调节部分由代谢型GABAB受体介导，该受体激活时会抑制嗅觉神经递质的释放。功能性GABAB受体是由GABAB1和GABAB2亚基组成的异二聚体。使用双重免疫荧光的研究表明，这两个亚基在肾小球神经纤维网中共定位，超微结构研究已将GABAB1定位到嗅觉神经末梢质膜上的突触外、突触和突触周部位。我们使用亚基特异性抗体和预包埋免疫金标记研究了GABAB2在小鼠嗅觉肾小球中的亚细胞定位。GABAB2的免疫反应性与球周细胞与二尖瓣/簇状细胞的对称树突-树突突触相关，并定位于突触前树突的突触外质膜以及突触后树突质膜上的突触外、突触和突触周部位。结果表明，突触后以及可能的突触前GABAB受体可能在球周中间神经元和投射神经元树突之间的GABA能突触处表达。在嗅觉神经与二尖瓣/簇状细胞树突的连接处观察到免疫标记，为GABAB2亚基在初级嗅觉突触处的表达提供了超微结构证据。
