Activity-Dependent Plasticity of Astroglial Potassium and Glutamate Clearance

Figure 2

Short-term plasticity of astroglial potassium and residual currents quantified using two different methods. Simultaneous recordings of field excitatory postsynaptic potentials (fEPSPs) and synaptically evoked astroglial currents were carried out in hippocampal CA1 region upon stimulation of Schaffer collaterals. (a, h) Two different methods used to quantify astroglial currents are illustrated. fEPSPs (top) and astroglial currents (bottom) during the first four stimulations of a 10 Hz train are shown. The peak amplitude of each response was measured either in reference to (a) the prestimuli baseline, taken just before each stimulation (astroglial facilitation) or (h) to the initial resting baseline (), taken before the first stimulation (astroglial summation). Scale bars = 0.05 mV for fEPSP, 20 pA for astroglial currents, 25 ms. (b, d, and f) Sample traces are shown for fEPSPs (top) and pharmacologically isolated astrocytic potassium (bottom, blue) and residual (bottom, green) currents in response to (b) paired-pulse stimulation (interpulse interval = 40 ms; scale bars = 0.5 mV for fEPSP, 20 pA for astroglial currents, 25 ms), (d) repetitive stimulation (10 Hz for 30 s; scale bars = 0.2 mV for fEPSP, 40 pA for astroglial currents; 5 s for astroglial currents and 50 ms for fEPSP), and (f) tetanic stimulation (100 Hz for 1 s; scale bars = 0.2 mV for fEPSP, 20 pA for astroglial currents; 7.5 s for astroglial currents and 60 ms for fEPSP). Quantifications using (c, e, and g) astroglial facilitation or (i, j, and k) astroglial summation methods are shown for (c, i) paired-pulse ratio, and normalized fEPSP slope and astrocytic current amplitudes during (e, j) repetitive or (g, k) tetanic stimulation. Numbers indicate extracted traces before (1), during (2), and after (3, 4) each stimulation. Mean ± SEM are shown for (c), (e), (g), (i), (j), and (k).