Dendritic Ca2+ action potentials in neocortical pyramidal
neurons have been characterized in brain slices, but their presence and role
in the intact neocortex remain unclear. Here we used two-photon microscopy
to demonstrate Ca2+ electrogenesis in apical dendrites of deep-layer
pyramidal neurons of rat barrel cortex in vivo. During whisker stimulation,
complex spikes recorded intracellularly from distal dendrites and sharp waves
in the electrocorticogram were accompanied by large dendritic [Ca2+
] transients; these also occurred during bursts of action potentials
recorded from somata of identified layer 5 neurons. The amplitude of the [Ca
2+] transients was largest proximal to the main bifurcation, where
sodium action potentials produced little Ca2+ influx. In some
cases, synaptic stimulation evoked [Ca2+] transients without
a concomitant action potential burst, suggesting variable coupling between
dendrite and soma.
