Aβ1–42 Oligomers Induced a Short-Term Increase of Glutamate Release Prior to Its Depletion As Measured by Amperometry on Single Varicosities

Glutamate (Glu) is a critical neurotransmitter for neuronal communication in the nervous system. In vivo studies have shown that the concentration of Glu is reduced within the brains of those afflicted with Alzheimer's disease (AD), which is also associated with the accumulation of pathogenic amyloid-beta (Aβ). However, the effects of Aβ peptides on the level of Glu release, as well as how Aβ-mediated Glu fluctuation is initiated, remain largely unknown. Here, we fabricated a Glu electrochemical biosensor and in situ quantitatively monitored the release of Glu from a single varicosity of Aβ_1-42-insulted hippocampal neurons. We found that before the depletion of Glu after 300 min of treatment with Aβ_1-42, a short-duration (30 min) incubation with Aβ_1-42 caused a dramatic increase in vesicular Glu release compared to that of a control. Further investigation demonstrated that the density of vesicular glutamate transporter 1 (VGLUT1), which is responsible for transport of Glu into synaptic vesicles, also displayed a significant elevation and then dramatic depletion with the extension of the time of treatment with Aβ_1-42. These results indicate that at the early stage of AD, Aβ_1-42 induces excessive Glu release, which may overstimulate the N-methyl-d-aspartic acid (NMDA) receptor, resulting in excitotoxicity and damage to neurons. In this work, the amount of Glu released together with its fluctuations under Aβ_1-42 oligomers toxicity conditions was monitored for the first time, and such monitoring could provide direct and new insights for current research on Aβ_1-42-induced abnormalities in neurotransmitter release and neuron functions.