Differential Cholinergic Modulation of Ca Transients Evoked by Backpropagating Action Potentials in Apical and Basal Dendrites of Cortical Pyramidal Neurons

Cho K-H, Jang H-J, Lee E-H, Yoon SH, Hahn SJ, Jo Y-H, Kim M-S, Rhie D-J. Differential cholinergic modulation of Ca transients evoked by backpropagating action potentials in apical and basal dendrites of cortical pyramidal neurons. J Neurophysiol 99: 2833–2843, 2008. First published April 16, 2008; doi:10.1152/jn.00063.2008. The effect of the cholinergic agonist carbachol (CCh) on backpropagating action potential (bAP)–evoked Ca transients in distal apical and basal dendrites of layer 2/3 pyramidal neurons in the primary visual cortex of rats was studied using whole cell recordings and confocal Ca imaging. In the presence of CCh (20 M), initial bAP-evoked Ca transients were followed by large propagating secondary Ca transients that were restricted to proximal apical dendrites 40 m from the soma. In middle apical dendrites (41–100 m from the soma), Ca transients evoked by AP bursts at 20 Hz, but not by single APs, were increased by CCh without secondary transients. CCh failed to increase the bAP-evoked Ca transients in distal apical dendrites (101–270 m from the soma). In contrast, in basal dendrites, CCh increased Ca transients evoked by AP bursts, but not by single APs, and these transients were relatively constant over the entire length of the dendrites. CCh further increased the enhanced bAP-evoked Ca transients in the presence of 4-aminopyridine (200 M), an A-type K channel blocker, in basal and apical dendrites, except in distal apical dendrites. CCh increased large Ca transients evoked by high-frequency AP bursts in basal dendrites, but not in distal apical dendrites. CCh-induced increase in Ca transients was mediated by InsP3-dependent Ca 2 -induced Ca -release. These results suggest that cholinergic stimulation differentially increases the bAP-evoked increase in [Ca ]i in apical and basal dendrites, which may modulate synaptic activities in a location-dependent manner.