Figure 2.

Instrumentation and procedure for α determination by DPMD. Left: A multimode etched microfiberoptic with micron-sized tip is inserted into the overlying solution and tissue slice. Inset shows the microfiberoptic tip geometry. Fluorescence from two probes of different colors is detected simultaneously using two photomultipliers (PMT). Right: Relative fluorescence of calcein (green) and rhod-dextran (red; normalized to unity in the overlying solution and zero in water) during insertion of the microfiberoptic into the overlying solution and into a brain slice (in hippocampus). Fluorescence ratios gave α = 0.21 for both colors.