Figure 8. Mapping the location of astrocyte calcium responses. A, The proportion of responders (astrocytes experiencing >2 of 10 synchronized Ca2+ elevations evoked by ChR2 photostimulation) were calculated for the three apical dendrite subregions depicted in G (average values: primary, 53.3 ± 8.9%, N = 9; secondary, 33.4 ± 8.7%, N = 8; and tertiary, 13.8 ± 3.7%, N = 7). Averages for primary and tertiary dendritic regions were significantly different (p = 0.0077, ANOVA with Dunnett's comparison with the primary dendritic region). B, The vertical distance to cell soma was determined for each astrocyte along the apical dendrites of CA1 cells. Distances were plotted for each astrocyte against the number of synchronized responses (0, 260.8 ± 10.6 μm, n = 137; 1, 239.1 ± 12.4 μm, n = 93; 2, 203.3 ± 14.7 μm, n = 76; 3, 166.3 ± 15.7 μm, n = 46; 4, 152.2 ± 19.0 μm, n = 35; 5, 161.0 ± 17.6 μm, n = 23; 6, 136.8 ± 20.6 μm, n = 18; 7, 157.5 ± 26.3 μm, n = 12; 8, 138.3 ± 11.1 μm, n = 19; 9, 185.7 ± 62.0 μm, n = 3). The averages were significantly different (p < 0.0001, ANOVA with Dunnett's comparison with the first column are indicated on graph), indicating that responders are closer to the neuronal soma. C, Astrocytes in the primary subregion showed the greatest maximum response when compared with the other subregions (average values: primary, 72.9 ± 4.7%, N = 7; secondary, 52.9 ± 9.2%, N = 7; and tertiary, 41.7 ± 6.5%, N = 6) (p = 0.021, ANOVA with Dunnett's comparison). D, Astrocyte to dendrite distance did not determine the level of response (p = n.s.). E, Responders are, on average, farther away from main dendrites than from any other dendrite (two-tailed Mann–Whitney test). F, Astrocytes to dendrites (either any or main dendrites) distance is not significantly different (two-tailed Mann–Whitney test) when the window of detection is reduced from 15 to 5 s. G, Two-dimensional schematic illustrating the location of responders along the apical dendrites of CA1 cells.