Gabellec Marie-Madeleine, Panzanelli Patrizia, Sassoè-Pognetto Marco, Lledo Pierre-Marie
Laboratory of Perception and Memory, CNRS URA 2182, Pasteur Institute, 25 rue du Dr Roux, 75015 Paris Cedex, France.
Eur J Neurosci. 2007 Mar;25(5):1373-83. doi: 10.1111/j.1460-9568.2007.05400.x.
Vesicular glutamate transporters (VGLUTs) mediate the packaging of the excitatory neurotransmitter glutamate into synaptic vesicles. Three VGLUT subtypes have so far been identified, with distinct expression patterns in the adult brain. Here, we investigated the spatial distribution of the three VGLUTs in the rat olfactory bulb, a brain region containing a variety of glutamate synapses, both axodendritic and dendrodendritic. Using multilabelling confocal microscopy and electron microscopic immunocytochemistry, we showed that each VGLUT isoform has a highly selective localization in olfactory bulb synapses. VGLUT1 is present at dendrodendritic synapses established by the output neurones (mitral and tufted cells) with bulbar interneurones in the glomerular layer and external plexiform layer, as well as in axonal synapses of the granule cell layer. By contrast, VGLUT2 is strongly expressed in axon terminals of olfactory sensory neurones, which establish synapses with second-order neurones in the glomerular neuropil. VGLUT2 is also found in the outer part of the external plexiform layer and in the granule cell layer but colocalizes only partially with VGLUT1. Finally, we showed that VGLUT3 is exclusively located in the glomerular neuropil, where it colocalizes extensively with the vesicular inhibitory amino acid transporter vesicular GABA transporter, suggesting that it is associated with a subset of inhibitory synapses. Together, these observations extend previous findings on VGLUT distribution in the forebrain, and suggest that each VGLUT subtype has a specific function in the distinct features of axodendritic and dendrodendritic synapses that characterize the olfactory bulb circuit.
囊泡谷氨酸转运体（VGLUTs）介导兴奋性神经递质谷氨酸包装到突触小泡中。迄今为止已鉴定出三种VGLUT亚型，在成人大脑中具有不同的表达模式。在此，我们研究了大鼠嗅球中三种VGLUTs的空间分布，嗅球是一个包含多种谷氨酸突触的脑区，既有轴树突触，也有树树突触。使用多标记共聚焦显微镜和电子显微镜免疫细胞化学技术，我们发现每种VGLUT亚型在嗅球突触中都有高度选择性的定位。VGLUT1存在于由输出神经元（二尖瓣细胞和簇状细胞）与球状层和外丛状层中的球周中间神经元建立的树树突触中，以及颗粒细胞层的轴突突触中。相比之下，VGLUT2在嗅觉感觉神经元的轴突终末中强烈表达，这些轴突终末在球状神经毡中与二级神经元建立突触。VGLUT2也存在于外丛状层的外部和颗粒细胞层中，但仅与VGLUT1部分共定位。最后，我们发现VGLUT3仅位于球状神经毡中，在那里它与囊泡抑制性氨基酸转运体囊泡GABA转运体广泛共定位，表明它与一部分抑制性突触相关。总之，这些观察结果扩展了先前关于VGLUT在前脑分布的研究发现，并表明每种VGLUT亚型在表征嗅球回路的轴树突触和树树突触的不同特征中具有特定功能。
