Fig. 1.

NH₄⁺transiently increases ambient glutamate and neuronal bursting in CA1 neurons. A and B show the effects of NH₄⁺ in slices prepared from wild-type (WT) and model Rett animals (RTT) as indicated. Each column presents the three panels containing the two traces showing the changes in ambient glutamate (blue) and voltage trajectories (black) measured simultaneously. Mean [Glu] traces were obtained from 12 regions of interest encircled the cells expressing glutamate sensor iGluSnFr (see Methods). Average traces are overlaid onto grey background showing ± SEM. The slice was transduced with neuronal glutamate sensor and CA1 neuron was selected to patch. The inset in the middle shows the experimental configuration. The internal solution contained Alexa 588 to visualize the neuron with dendritic tree (red). We consistently observed the repetitive glutamate spikes in naïve slices from RTT animals (B). Application of NH₄⁺ for 30 s at 0.3–10 mM (as indicated) induced stereotypic effects consisted of brief augmentation of activity with subsequent depression. The glutamate spikes coincided with burst discharges in neurons (presented as black and grey traces in respective panels). In naïve slices from WT animals (A) repetitive glutamate spikes were absent and emerged with NH₄⁺ addition. The responses were similar but had smaller amplitude. During wash-out and slow recovery ambient glutamate levels slightly elevated that was followed by appearance of glutamate spikes in WT. The mean data are summarized in Fig. 2.