Figure 2. More astrocytes elicit spontaneous Ca²⁺ surges in layer 1 than in layer 2/3.

A, Representative time course of spontaneous Ca²⁺ surges of astrocytes in L1. Numbers (1–6) correspond to astrocytes in Figure 1A. Each trace shows normalized fluorescence intensity of Ca²⁺ indicator OGB-1 from an individual astrocyte. Small red dots indicate period of Ca²⁺ surge. Vertical position of each trace was adjusted arbitrary to improve visibility. Scale bar: 50%. B, Number of astrocytes with at least one spontaneous Ca²⁺ surge (“active astrocyte”) per imaged area is plotted against the depth from the cortical pia. L1 had significantly more active astrocytes than L2/3. ***p<0.001, Student's t test. C, Proportion of active astrocyte for each experiment is plotted against the imaged depth. L1 had significantly higher percentage of active astrocytes than L2/3. ***p<0.001, Student's t test. D, Histograms (solid bars) and cumulative distribution (solid lines) of Ca²⁺ surge duration of astrocytes in L1 (blue) and L2/3 (red) are plotted. Vertical dotted lines indicate the mean duration of spontaneous Ca²⁺ surge. There was no significant difference in Ca²⁺ duration between L1 and L2/3. E, Histograms (solid bars) and cumulative distributions (solid lines) of Ca²⁺ surge peak of astrocytes in L1 (blue) and L2/3 (red) are plotted. L1 astrocytes had significantly higher spontaneous Ca²⁺ surge peak values. Vertical dotted lines indicate the mean Ca²⁺ surge peak (***p<0.001, Student's t test). F, Ca²⁺ surge peak values are plotted against Ca²⁺ surge duration in L1 (blue circle) and L2/3 (red triangle). There was a slight but significant correlation between Ca²⁺ peak value and duration in L1 (r≈0.24), but little correlation was observed in L2/3 (r≈0.07).