Fig. 1
Oligomeric Aβ induces calcium overload in the healthy mouse brain. a A new experimental setting was designed to specifically address the effect of oAβ on calcium homeostasis in vivo. Wild-type C57BL/6 mice were injected with an AAV-CBA-YC3.6 and a cranial window was installed 4 weeks later. After a first imaging session at baseline, the window was opened and WtCM, TgCM or depleted TgCM was topically applied for 1 hour before reimaging again the exact same fields of view. b Neurites, consisting of dendrites and axons, filled with YC3.6 were imaged before and after treatment with TgCM, WtCM or depleted-TgCM. Images were pseudocolored according to calcium concentration (Scale bar = 20 μm). c Individual neurites were selected for measuring YFP and CFP ratio and calculating resting calcium levels. Distribution curves of [Ca2+] i (YFP/CFP ratio on the lower x-axis and [Ca2+] i on the upper x-axis) are presented before (purple curve) and after treatment (red curve) for each experimental group. Acute exposure to TgCM, but not to WtCM or immunodepleted-TgCM, resulted in a shift in the [Ca2+] i distribution towards higher ratio values, i.e. higher calcium concentrations. The black line indicates the threshold for calcium overload which represents 2 SD above the mean of ratios measured from all mice before treatment. The percentage of neurites with calcium overload before (purple) and after (red) treatment is noted on the graphs. Calcium overload was only significantly increased in the TgCM treated group from 3.09 to 25.82% (p < 0.0001 Fisher exact test). d YFP/CFP ratios before and after treatment with WtCM, TgCM or depleted TgCM represented for each neurite. The red traces account for the neurites that showed an increase of ≥10% in YFP/CFP ratio after topical application of CM. e The relative change in ratio was calculated for each neurite and the mean + SEM of each group is presented (linear mixed effects model fitted with treatment group as fixed effect and mouse as random effect ** p = 0.0012, *p = 0.0183)