Zhang Chunzhao, Szabó Gábor, Erdélyi Ferenc, Rose James D, Sun Qian-Quan
Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071, USA.
J Comp Neurol. 2006 Dec 20;499(6):1000-15. doi: 10.1002/cne.21166.
The neural circuits of the piriform cortex mediate field potential oscillations and complex functions related to integrating odor cues with behavior, affective states, and multisensory processing. Previous anatomical studies have established major neural pathways linking the piriform cortex to other cortical and subcortical regions and major glutamatergic and GABAergic neuronal subtypes within the piriform circuits. However, the quantitative properties of diverse piriform interneurons are unknown. Using quantitative neural anatomical analysis and electrophysiological recording applied to a GAD65-EGFP transgenic mouse expressing GFP (green fluorescent protein) under the control of the GAD65 promoter, here we report a novel inhibitory network that is composed of neurons positive for GAD65-EGFP in the posterior piriform cortex (PPC). These interneurons had stereotyped dendritic and axonal properties that were distinct from basket cells or interneurons expressing various calcium-binding proteins (parvalbumin, calbindin, and calretinin) within the PPC. The GAD65-GFP neurons are GABAergic and outnumbered any other interneurons (expressing parvalbumin, calbindin, and calretinin) we studied. The firing pattern of these interneurons was highly homogenous and is similar to the regular-spiking nonpyramidal (RSNP) interneurons reported in primary sensory and other neocortical regions. Robust dye coupling among these interneurons and expression of connexin 36 suggested that they form electrically coupled networks. The predominant targets of descending axons of these interneurons were the dendrites of Layer III principal cells. Additionally, synapses were found on dendrites and somata of deep Layer II principal neurons and Layer III basket cells. A similar interneuronal subtype was also found in GAD65-EGFP-negative mouse. The extensive dendritic bifurcation at superficial lamina IA among horizontal afferent fibers and unique axonal targeting pattern suggests that these interneurons may play a role in direct feedforward inhibitory and disinhibitory olfactory processing. We conclude that the GAD65-GFP neurons may play distinct roles in regulating information flow and olfactory-related oscillation within the PPC in vivo.
梨状皮层的神经回路介导场电位振荡以及与将气味线索与行为、情感状态和多感官处理整合相关的复杂功能。先前的解剖学研究已经确定了连接梨状皮层与其他皮层和皮层下区域的主要神经通路，以及梨状回路内主要的谷氨酸能和γ-氨基丁酸能神经元亚型。然而，不同梨状中间神经元的定量特性尚不清楚。利用定量神经解剖学分析和电生理记录，应用于在GAD65启动子控制下表达绿色荧光蛋白（GFP）的GAD65-EGFP转基因小鼠，我们在此报告了一种新的抑制性网络，其由梨状后皮质（PPC）中GAD65-EGFP阳性神经元组成。这些中间神经元具有刻板的树突和轴突特性，与PPC内的篮状细胞或表达各种钙结合蛋白（小白蛋白、钙结合蛋白和钙视网膜蛋白）的中间神经元不同。GAD65-GFP神经元是γ-氨基丁酸能的，并且数量超过了我们研究的任何其他中间神经元（表达小白蛋白、钙结合蛋白和钙视网膜蛋白）。这些中间神经元的放电模式高度一致，类似于在初级感觉和其他新皮层区域报道的规则放电非锥体（RSNP）中间神经元。这些中间神经元之间强大的染料偶联和连接蛋白36的表达表明它们形成了电偶联网络。这些中间神经元下行轴突的主要靶点是III层主细胞的树突。此外，在深层II层主神经元和III层篮状细胞的树突和胞体上发现了突触。在GAD65-EGFP阴性小鼠中也发现了类似的中间神经元亚型。水平传入纤维之间在浅表层IA的广泛树突分支和独特的轴突靶向模式表明，这些中间神经元可能在直接前馈抑制和去抑制嗅觉处理中发挥作用。我们得出结论，GAD65-GFP神经元可能在体内调节PPC内的信息流和嗅觉相关振荡中发挥独特作用。
