Dendritic Calcium Signaling in EGFP-expressing Granule Cells.
An intracellular calcium rise was elicited by a train of 4 APs at 100 Hz and measured at approximately 20–30 µM from the soma, before the first branch point of the main apical dendrite (white boxes). A. One group of immature EGFP-expressing granule cells, that were unable to fire APs (middle) had no detectable dendritic calcium rise (bottom, average and standard deviation, n = 5) in response to current injections that elicited a change in membrane potential similar in magnitude to an AP. B. More mature looking EGFP-expressing granule cells with sparsely spiny dendrites (top) were able to fire 4 APs (middle) that resulted in a detectable rise in intracellular calcium concentration in the apical dendrite (bottom, average and standard deviation, n = 5). C. Mature granule cells were densely spiny and 4 APs elicited a relatively large rise in dendritic calcium (bottom, average and standard deviation, n = 6). (Inset scale bars are 10 mV and 10 ms).