Figure 4. High dose Aβ42 has a biphasic effect on electrical network activities.

A. A representative experiment. Under calcium-free conditions, a PC was recorded after delivery of three extracellular stimuli. The bursts became briefer after 500 nM Aβ42 was applied for 13 min. (2nd panel). After Aβ was applied for ≥30 min., the responses became paradoxically stronger as evidenced by the broader bursts and tonic firing that followed the 3^rd evoked burst (3^rd panel). Spontaneous responses were also enhanced (followed the 2^nd evoked burst in the 3rd panel). The excessive activity recovered on washout for 20 min. (lower panel). B. Statistical analysis: Compared with the control, the average duration (left panel) and occurrence (right panel) of evoked responses was significantly reduced after 500 nM Aβ42 was applied for ≤25 min. (duration: p = 0.017; occurrence: p = 0.002, n = 10, not including the cells that later showed tonic responses during prolonged application). The inhibition disappeared with Aβ applications for more than 30 min. (duration: p = 0.509; occurrence: p = 0.137). On washout, responses were similar to the control (duration: p = 0.332) but appeared less frequently (occurrence: p = 0.006). Note: “*”, p<0.05; “**”, p<0.01.