Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Duesseldorf, Germany; Institute of Neuro- und Sensory Physiology, Medical Faculty, Heinrich-Heine-University, Duesseldorf, Germany.
Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University, Duesseldorf, Germany; Result Medical GmbH, Duesseldorf, Germany.
Exp Neurol. 2017 Apr;290:41-52. doi: 10.1016/j.expneurol.2017.01.003. Epub 2017 Jan 6.
Accumulation of ammonium and glutamine in blood and brain is a key factor in hepatic encephalopathy (HE) - a neuropsychiatric syndrome characterized by various cognitive and motor deficits. MRI imaging identified abnormalities notably in the basal ganglia of HE patients, including its major input station, the striatum. While neurotoxic effects of ammonia have been extensively studied, glutamine is primarily perceived as "detoxified" form of ammonia. We applied ammonium and glutamine to striatal and cortical cells from newborn rats cultured on microelectrode arrays. Glutamine, but not ammonium significantly increased spontaneous spike rate with a long-lasting excitation outlasting washout. This effect was more prominent in striatal than in cortical cultures. Calcium imaging revealed that glutamine application caused a rise in intracellular calcium that depended both on system A amino acid transport and activation of ionotropic glutamate receptors. This pointed to downstream glutamate release that was triggered by intracellular glutamine. Using an enzymatic assay kit we confirmed glutamine-provoked glutamate release from striatal cells. Real-time PCR and immunocytochemistry demonstrated the presence of vesicular glutamate transporters (VGLUT1 and VGLUT2) necessary for synaptic glutamate release in striatal neurons. We conclude that extracellular glutamine is taken up by neurons, triggers synaptic release of glutamate which is then taken up by astrocytes and again converted to glutamine. This feedback-loop causes a sustained long-lasting excitation of network activity. Thus, apart from ammonia also its "detoxified" form glutamine might be responsible for the neuropsychiatric symptoms in HE.
血液和大脑中氨和谷氨酰胺的积累是肝性脑病 (HE) 的一个关键因素 - 一种以各种认知和运动缺陷为特征的神经精神综合征。MRI 成像在 HE 患者的基底节中发现了明显的异常，包括其主要输入站纹状体。虽然氨的神经毒性作用已经得到了广泛的研究，但谷氨酰胺主要被认为是氨的“解毒”形式。我们将氨和谷氨酰胺应用于新生大鼠的纹状体和皮质细胞，这些细胞在微电极阵列上培养。谷氨酰胺而非铵显著增加了自发尖峰率，其持久的兴奋持续时间超过了冲洗时间。这种作用在纹状体培养物中比在皮质培养物中更为明显。钙成像显示，谷氨酰胺的应用导致细胞内钙的增加，这既依赖于系统 A 氨基酸转运，也依赖于离子型谷氨酸受体的激活。这表明细胞内谷氨酰胺触发了下游谷氨酸的释放。使用酶测定试剂盒，我们证实了纹状体细胞中由谷氨酰胺引发的谷氨酸释放。实时 PCR 和免疫细胞化学显示了存在囊泡谷氨酸转运体（VGLUT1 和 VGLUT2），这对于纹状体神经元中的突触谷氨酸释放是必要的。我们得出结论，细胞外谷氨酰胺被神经元摄取，触发谷氨酸的突触释放，然后被星形胶质细胞摄取并再次转化为谷氨酰胺。这种反馈环导致网络活动的持续持久兴奋。因此，除了氨之外，其“解毒”形式谷氨酰胺也可能是 HE 中神经精神症状的原因。
