Module 10: Figure neocortical Ca2+ wave
Dendritic Ca2+ signals in layer 5 neocortical pyramidal neurons.
In the panels at the top, Ca2+ responses were measured in a series of small squares (superpixels) running down a length of the long dendritic region of a neocortical neuron to produce a series of line scans that were then stacked up to produce the spatiotemporal plots shown on the right. The dashed arrowhead on the left marks the position of the stimulating electrode used to stimulate one of the dendritic branches at 100 Hz for 0.5 s. A patch electrode on the soma (not shown) was used to activate two back-propagating action potentials (spikes) that occurred over 30 ms. The traces on the bottom illustrate the changes in Ca2+ concentration that occurred in a small dendritic region (white box). Synaptic input alone induced a brief opening of voltage-operated channels (VOCs), resulting in a small but rapid increase in Ca2+, followed by a slower secondary phase that may have resulted in some release from internal stores. Back-propagating spikes alone caused a somewhat larger early increase in Ca2+ concentration, which decayed back to the resting level. However, when the synaptic response was followed 0.5 s later by the spikes, there was a very much larger secondary increase in Ca2+ concentration. It seems that the inositol 1,4,5-trisphosphate (InsP3) produced by the synaptic activity acted synergistically with the Ca2+ generated by the spikes to produce a very large dendritic Ca2+ signal. Reproduced from Larkum, M.E., Watanabe, S., Nakamura, T., Lasser-Ross, N. and Ross, W.N. (2003) Synaptically activated Ca2+ waves in layer 2/3 and layer 5 rat neocortical pyramidal neurons. J. Physiol. 549:471–488, with permission from Blackwell Publishing; see Larkum et al. 2003.