Activity-Dependent Electrical Asymmetry of Dendrites as a Factor Determining the Repertoire of Intrinsic Firing Patterns of Neurons

Metrical asymmetry induced by the inequality of lengths and/or diameters of sister branches of dendrites is a common feature of complex dendritic arborizations in neurons of different types. A consequence of this structural feature is the electrical asymmetry, namely the inequality of passive electrical transfer along metrically asymmetrical branches and, correspondingly, different electrical states of those branches. In our previous studies, it was shown that, for any pair of dendrite branches with a given metrical asymmetry, the asymmetry of their passive transfer functions is characteristically modified with changes in the specific membrane conductance, which depends on the intensity of activation of dendritic synapses. We have investigated in detail the relationships of metrical asymmetry and synaptic activity-dependent transfer properties typical of the dendritic arborizations in different-type neurons (reconstructed pyramidal neurons of the neocortex and hippocampus, cerebellar Purkinje neurons, brainstem neurons, and spinal motoneurons), on the one hand, and the output discharge patterns generated by a given neuron when its dendrites receive synaptic signals of different intensities, on the other hand. In all examined neurons, the repertoire of output discharge patterns critically depended on synaptically induced dynamical changes in the electrical asymmetry of the dendritic arborization. These facts show that the parametric sensitivity of dynamic transfer functions of complex dendritic arborizations with active membrane properties plays a significant role in the formation of output discharge patterns. The latter can be determined by multiple metastable electrical states of metrically asymmetrical branches and sub-trees of the given arborization.