Cell-specific c-Fos induction by light-triggered spike trains.

<p>(A) Immunostaining for endogenous c-Fos in CA1 area of rat hippocampal slice cultures under basal conditions (top) and 2 h after stimulation by extracellular application of 50 mM K⁺ (bottom). (B) c-Fos induction in a pyramidal neuron expressing ChR2(C128A) and cytosolic RFP after 10 stimulation pulses. Cultures were fixed 2 h after stimulation and stained for c-Fos. (C) c-Fos signal in non-stimulated cells (n = 27) and at different time points after light stimulation (n = 18, 24, 18, 25, 21). Green shaded bar indicates mean±SD of non-stimulated control cells. c-Fos induction was significant at all time points (p<0.01). (D) Significant c-Fos induction was observed after a single blue light pulse (n = 17, 15, 14, 21, 19, 11). Dashed line indicates average c-Fos signal after 50 mM K⁺ stimulation. (E) Light-triggered c-Fos induction was blocked by TTX, but not by NBQX or CPP. *: p<0.01 compared to control. (F) Green fluorescence in live organotypic slice cultures (CA3) from fosGFP transgenic mice under basal conditions (top) and 4 h after brief stimulation with 50 mM K⁺ (bottom). (G) Light-induced GFP expression in fosGFP reporter mouse neurons expressing ChR2(C128A) and RFP. (H) Light-induced GFP expression was quantified 4 h after light stimulation (10 pulses). Scale bars in (A,B,F,G): 10 µm.