Figure 3.

Delay between Schaffer collateral stimulation and evoked astrocyte or neuronal Ca²⁺ responses and AMPA and NMDA receptor currents. (A,C) Astrocyte in stratum radiatum (A) and CA1 pyramidal neuron (B) each filled with 150 μM OGB-1 Ca²⁺ indicator dye. Boxed regions of interest in subcellular compartments correspond to the fluorescence traces in (C,D). Boxes were placed all over the visible astrocyte but only a few are shown for clarity. Cells were given 10 min to recover after removal of the whole-cell patch clamp pipette prior to Schaffer collateral stimulation. The stimulating electrode was placed 75 μm from the recorded cells. (C,D) Schaffer collateral stimulation at 50 Hz for 1s produced astrocytic Ca²⁺ elevations after ~3 s in the first responding process of this specific astrocyte (C), while neuronal Ca²⁺ elevations occurred almost instantaneously in proximal neuronal compartments in this example as well as all other recorded neurons (n = 4) (D). (E) Astrocyte Ca²⁺ elevations occurred on average after ~8 s in the first responding compartment (n = 4 cells). Response initiation times were defined as the first data point that preceded two successive data points that were ≥3 S.D. above the mean baseline noise. We have observed that the astrocytic Ca²⁺ responses to the first stimulation are faster and more reliable than subsequent stimulations, so only the responses to the first stimulation were calculated. (F) In the same conditions, fEPSPs (n = 5 slices) and whole-cell CA1 neuronal NMDA eEPSCs (n = 16 cells, 16 slices) were evoked after ~5 and 4 ms, respectively, in response to single depolarizing pulses (0.05 Hz) to the Schaffer collaterals.