Figure 2. Synaptically activated Ca²⁺ waves in a neocortical pyramidal neuron.

These waves can be easily evoked with repetitive focal synaptic stimulation in acute slices. In this experiment, a pyramidal neuron was loaded with the low-affinity indicator furaptra (300 μM) via a patch electrode on the soma and stimulated via a tungsten electrode (dashed arrow) at 100 Hz for 0.25 s (a and c). Two views of the resulting changes in intracellular calcium concentration ([Ca²⁺]_i) are shown. Part b shows a pseudocolour line scan of the fluorescence changes along a selected series of pixels in a. The timescale for b is the same as for the optical and electrical traces shown below in d. Part d shows the time course of the fluorescence changes at the regions of interest (ROIs), which are indicated by coloured rectangles in c. The time courses and amplitudes of the delayed responses differ at the four ROIs. This figure illustrates that two waves initiated at different locations in dendrites (close to branch points) can be propagated along the main dendrite in both directions. In this cell, the waves did not propagate into the soma. ΔF/F, relative change in fluorescence. Figure courtesy of W.N.R.