Odor information is processed in the olfactory bulb (OB), which is organized into olfactory inputs, interneurons, projection neurons, and centrifugal inputs, and these various structures regulate olfactory information processing. Similar to other brain regions, the OB structures include many types of interneurons, including γ-aminobutyric acid (GABA)ergic interneurons. Many interneurons are granule cells that are found in the granule cell layer (GCL), which is a deep layer of the OB. Interestingly, these interneurons exhibit variations in GABA immunoreactivity, and previous studies have observed differing intensities among morphologically and chemically similar neuronal populations. However, the numbers and distribution patterns of cells that show variations in GABA immunoreactivity are unknown. Therefore, we observed and quantitatively analyzed this diversity in the GCL of the mouse OB using immunogold, high-voltage electron microscopy, combined with light microscopy. Consequently, our results clearly show variations in the GABA immunoreactivity among GCL interneurons, which suggested heterogeneity in the amount of GABA present in each interneuron and reflected the possibility that different amounts of neuroactive substances may be associated with different functions for the various GABAergic interneuron groups. Variations in GABA immunoreactivity could be a novel criterion for classifying interneuron subpopulations.

嗅觉信息在嗅球（OB）中处理，嗅球组织成嗅觉输入，中间神经元，投射神经元和离心输入，这些不同的结构调节嗅觉信息的处理。与其他大脑区域相似，OB结构包括多种类型的中间神经元，包括γ-氨基丁酸（GABA）增能中间神经元。许多中间神经元是在颗粒细胞层（GCL）中发现的颗粒细胞，该颗粒细胞层是OB的深层。有趣的是，这些中间神经元在GABA免疫反应性方面表现出差异，并且先前的研究已经观察到形态和化学上相似的神经元种群之间强度的差异。然而，显示GABA免疫反应性变化的细胞数量和分布模式尚不清楚。因此，我们使用免疫金，高压电子显微镜和光学显微镜观察并定量分析了小鼠OB GCL的这种多样性。因此，我们的结果清楚地表明了GCL中间神经元之间的GABA免疫反应性存在差异，这表明每个中间神经元中存在的GABA量存在异质性，并反映了不同数量的神经活性物质可能与各种GABA能性中间神经元的不同功能相关联的可能性。GABA免疫反应性的变化可能是分类神经元亚群的新标准。这表明每个中间神经元中存在的GABA量存在异质性，并反映了不同数量的神经活性物质可能与各个GABA能中间神经元组的不同功能相关的可能性。GABA免疫反应性的变化可能是分类神经元亚群的新标准。这表明每个中间神经元中存在的GABA量存在异质性，并反映了不同数量的神经活性物质可能与各个GABA能中间神经元组的不同功能相关的可能性。GABA免疫反应性的变化可能是分类神经元亚群的新标准。