ACTIVITY-DEPENDENT ACTION-POTENTIAL INVASION AND CALCIUM INFLUX INTO HIPPOCAMPAL CA1 DENDRITES

The temporal and spatial profile of activity-evoked changes in membran e potential and intracellular calcium concentration in the dendrites o f hippocampal CA1 pyramidal neurons was examined with simultaneous som atic and dendritic patch-pipette recording and calcium imaging experim ents. Action potentials are initiated close to the soma of these neuro ns and backpropagate into the dendrites in an activity-dependent manne r; those occurring early in a train propagate actively, whereas those occurring later fail to actively invade the distal dendrites. Consiste nt with this finding, dendritic calcium transients evoked by single ac tion potentials do not significantly attenuate with distance from the soma, whereas those evoked by trains attenuate substantially. Failure of action potential propagation into the distal dendrites often occurs at branch points. Consequently, neighboring regions of the dendritic tree can experience different voltage and calcium signals during repet itive action potential firing. The influence of backpropagating action potentials on synaptic integration and plasticity will therefore depe nd on both the extent of dendritic branching and the pattern of neuron al activity.