Perisomatic-Targeting Granule Cells in the Mouse Olfactory Bulb

Inhibitory interneurons in the hippocampus and neocortex are differentiated into several morphological and functional subtypes that innervate distinct subcellular domains of principal neurons. In the olfactory bulb (OB), odor information is processed by local neuronal circuits that include the major inhibitory interneuron, granule cells (GCs). All GCs reported to date target their inhibitory output synapses mainly to dendrites of mitral cells (MCs) and tufted cells (TCs) in the external plexiform layer (EPL). Here we identified a novel type of GC that targets output synapses selectively to the perisomatic region of MCs. In the OB of adult transgenic mice expressing green fluorescent protein (GFP) under the control of nestin gene regulatory regions, we observed cells in the granule cell layer (GCL) that have GC-like morphology and strongly express GFP (referred to as type S cells). Type S cells expressed NeuN and GAD67, molecular markers for GCs. Intracellular labeling of type S cells revealed that their dendrites did not enter the EPL, but formed branches and spines within the GCL, internal plexiform layer, and mitral cell layer. Type S cells typically had huge spines at the ends of the apical dendrites. Some of the terminal spines attached to the perisomatic region of MCs and formed dendrosomatic reciprocal synapses with a presumed granule-to-mitral inhibitory synapse and a mitral-to-granule excitatory synapse. These findings indicate the morphological differentiation of GCs into dendritic-targeting and perisomatic-targeting subsets, and suggest the functional differentiation of the GC subsets in the processing of odor information in the OB. J. Comp. Neurol. 515:409-426, 2009. (C) 2009 Wiley-Liss, Inc.

海马体和新皮质中的抑制性中间神经元分化为几种形态和功能亚型，它们支配主要神经元的不同亚细胞区域。在嗅球（OB）中，气味信息由局部神经元回路处理，其中包括主要的抑制性中间神经元——颗粒细胞（GCs）。到目前为止，所有报道的颗粒细胞都将其抑制性输出突触主要靶向于外丛状层（EPL）中的 mitral细胞（MCs）和簇状细胞（TCs）的树突。在此，我们鉴定出一种新型的颗粒细胞，它选择性地将输出突触靶向于MCs的胞体周围区域。在巢蛋白基因调控区控制下表达绿色荧光蛋白（GFP）的成年转基因小鼠的嗅球中，我们观察到颗粒细胞层（GCL）中的一些细胞具有类似颗粒细胞的形态并强烈表达GFP（称为S型细胞）。S型细胞表达NeuN和GAD67，这是颗粒细胞的分子标记。对S型细胞进行细胞内标记显示，它们的树突不进入EPL，而是在GCL、内丛状层和mitral细胞层内形成分支和棘突。S型细胞通常在顶端树突的末端有巨大的棘突。一些末端棘突附着在MCs的胞体周围区域，并与假定的颗粒细胞到mitral细胞的抑制性突触以及mitral细胞到颗粒细胞的兴奋性突触形成树突 - 胞体交互突触。这些发现表明颗粒细胞在形态上分化为靶向树突和靶向胞体周围的亚群，并暗示了颗粒细胞亚群在嗅球气味信息处理中的功能分化。《比较神经学杂志》2009年第515卷第409 - 426页。（C）2009威利 - 利斯公司。