Several forebrain areas have been shown to project to the parabrachial nucleus (PBN) and exert inhibitory and excitatory influences on taste processing. Some sources of descending input such as the central nucleus of the amygdala (CeA) might utilize somatostatin (Sst) and/or corticotrophin-releasing hormone (Crh) to influence taste processing in the PBN (Panguluri S, Saggu S, Lundy R. 2009. Comparison of somatostatin and corticotrophin-releasing hormone immunoreactivity in forebrain neurons projecting to taste-responsive and non-responsive regions of the parabrachial nucleus in rat. Brain Res 1298:57-69; Magableh A, Lundy R. 2014. Somatostatin and corticotrophin releasing hormone cell types are a major source of descending input from the forebrain to the parabrachial nucleus in mice. Chem Senses 39:673-682). Since the predominate effect of CeA stimulation on PBN taste-evoked responses is inhibition, this study used transgenic reporter lines (Sst/TdTomato and Crh/TdTomato) and electron microscopy to assess Sst/gamma aminobutyric acid (GABA) and Crh/GABA coexpression in axon terminals within the PBN. Robust expression of Sst and Crh axon terminals was observed in the PBN. The majority of Sst-positive axon terminals were positive for GABA expression, while the majority of Crh terminals were not. The results indicate that Sst-expressing neurons, but not Crh neurons, are a source of GABAergic input to the PBN. To assess whether the CeA is a source of GABAergic input to the PBN, the CeA of Sst-cre mice was injected with cre-dependent enhanced yellow fluorescent protein (EYFP) virus and PBN tissue processed for GABA and EYFP expression. Again, the majority of EYFP Sst-positive axon terminals in the PBN coexpressed GABA. Together, the present results suggest that CeA neurons marked by Sst expression represent a major extrinsic source of GABAergic input to the PBN and this could underlie the predominate inhibitory effect of CeA stimulation on taste-evoked responses in the PBN.

中文翻译：

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比较GABA，促生长素抑制素和促肾上腺皮质激素释放激素在针对臂旁核的轴突末端的表达。

已有几个前脑区域投射到臂旁核（PBN），并对味觉加工产生抑制性和兴奋性影响。诸如杏仁核中心核（CeA）的一些下降输入来源可能利用生长抑素（Sst）和/或促肾上腺皮质激素释放激素（Crh）来影响PBN中的味觉处理（Panguluri S，Saggu S，Lundy R.2009 。投射至大鼠臂旁核味觉应答和非应答区域的前脑神经元中生长抑素和促肾上腺皮质激素释放激素免疫反应性的比较。Brain Res 1298：57-69; Magableh A，Lundy R. 2014.生长抑素和促肾上腺皮质激素释放激素细胞类型是小鼠中从前脑到臂臂旁核递减输入的主要来源（Chem Senses 39：673-682）。由于CeA刺激对PBN引起的味觉反应的主要作用是抑制，因此本研究使用转基因报告基因系（Sst / TdTomato和Crh / TdTomato）和电子显微镜评估Sst /γ氨基丁酸（GABA）和Crh / GABA共表达PBN中的轴突端子。在PBN中观察到Sst和Crh轴突末端的稳健表达。大多数Sst阳性轴突末端对GABA表达呈阳性，而大多数Crh末端不是。结果表明，表达Sst的神经元而非Crh神经元是PBN的GABA能输入的来源。为了评估CeA是否是PBN的GABA能量输入来源，向Sst-cre小鼠的CeA注射了cre依赖性增强型黄色荧光蛋白（EYFP）病毒，并对PBN组织进行了GABA和EYFP表达处理。再次，PBN中的大多数EYFP Sst阳性轴突末端共表达GABA。总之，目前的结果表明，以Sst表达标记的CeA神经元代表了PBN的GABA能输入的主要外部来源，这可能是CeA刺激对PBN引起的味觉应答的主要抑制作用。