Propagation of action potentials in dendrites depends on dendritic morphology

Action potential propagation links information processing in different regi ons of the dendritic tree. To examine the contribution of dendritic morphol ogy to the efficacy of propagation, simulations were performed in detailed reconstructions of eight different neuronal types. With identical complemen ts of voltage-gated channels, different dendritic morphologies exhibit dist inct patterns of propagation. Remarkably, the range of backpropagation effi cacies observed experimentally can be reproduced by the variations in dendr itic morphology alone. Dendritic geometry also determines the extent to whi ch modulation of channel densities can affect propagation. Thus in Purkinje cells and dopamine neurons, backpropagation is relatively insensitive to c hanges in channel densities, whereas in pyramidal cells, backpropagation ca n be modulated over a wide range. We also demonstrate that forward propagat ion of dendritically initiated action potentials is influenced by morpholog y in a similar manner. We show that these functional consequences of the di fferences in dendritic geometries can be explained quantitatively using sim ple anatomical measures of dendritic branching patterns, which are captured in a reduced model of dendritic geometry. These findings indicate that dif ferences in dendritic geometry act in concert with differences in voltage-g ated channel density and kinetics to generate the diversity in dendritic ac tion potential propagation observed between neurons. They also suggest that changes in dendritic geometry during development and plasticity will criti cally affect propagation. By determining the spatial pattern of action pote ntial signaling, dendritic morphology thus helps to define the size and int erdependence of functional compartments in the neuron.