Astrocytes display complex and localized calcium responses to single-neuron stimulation in the hippocampus - PubMed (original) (raw)

Properties of evoked calcium events in astrocytes. A, Bath application of the CB1 receptor antagonist AM251 (2 μ

m

) did not modify the number of astrocytes showing evoked synchronized responses (n = 136, N = 8). Inhibiting astrocytic metabotropic glutamate receptors mGluR5 and mGluR1 with MPEP (50 μ

m

) and LY367385 (LY; 100 μ

m

), respectively, significantly reduced the responsiveness of astrocytes (n = 111, N = 8). Inhibiting glial glutamate transporter with TFB–TBOA (100 n

m

) did not significantly change the proportion of responding astrocytes (n = 126, N = 7). Both 12 h slice treatment with the VAMP/synaptobrevin toxin TeNT (100 ng/ml, n = 135, N = 9) and blocking gap junctions and hemichannels with CBX (20 μ

m

, n = 135, N = 7) had no effect on evoked calcium responses. However, when applied with CBX, the P2Y1–2 purinergic receptor antagonist suramine (100 μ

m,

n = 110, N = 7) blocked the astrocyte responses. The pannexin-1 blocker probenecid (1 m

m,

n = 119, N = 8) also strongly inhibited evoked calcium increase. B, Pharmacological compounds used in A had less pronounced effects on the evoked calcium frequency elevations. CTRL in A and B refers to ChR2 stimulation at 25 Hz for 1 s in the absence of inhibitors. C, Representative traces (20 superimposed) of evoked responses when TFB–TBOA was bath applied. During some stimuli, TFB–TBOA caused a highly synchronized astrocyte calcium response across the astrocyte population. Arrowheads show the timing of neuronal excitation. D, Superimposed mean trace of evoked events recorded in CA1 while stimulating Schaeffer collaterals in nontreated (black line; n = 120 events, N = 6) and TeNT-treated (gray line; n = 140, N = 7) slice cultures. Bar graph shows the mean values of peak maximum amplitude of control (black bar) and TeNT-treated (gray bar) slices (p < 0.0001, Student's _t_ test). **_E_**, Astrocyte responsiveness when the detection window of calcium events was reduced to 5 s. ChR2-evoked synchronized response (black bars; _n_ = 124, _N_ = 7) and eGFPf controls (gray bars; _n_ = 105, _N_ = 7) are shown. **_F_**, Astrocytes showing >1 of 10 evoked synchronized responses (instead of 2 with a 15 s detection window) had significant responses above background. G, Using both 5 and 15 s time windows gives the same amount of evoked astrocyte responses.