Figure 6.

The fractional change in fluorescence (ΔF/F) is greater using a laser spot compared to when illumination is with an LED. Using a laser in one channel and an LED in the other, [Ca²⁺]_i or [Na⁺]_i changes were measured in alternate channels. The calcium signals (using OGB-1, 200 μm fiber, and 20× lens) in response to a single bAP were measured from a dendritic location in one cell (A) and the sodium signals (using SBFI, 200 μm fiber, and 60× lens) in response to five APs were measured from the axon of another cell (B). In each case the laser and LED signals were measured simultaneously in the two channels. For both the sodium and calcium signals the peak ΔF/F response was about twice as large using the laser. Resting fluorescence levels (F) were about the same.