Kulagina I. Structure-dependent features of the spatial-temporal patterns of autorythmical activity of neurons

Thesis is devoted to the study of the biophysical mechanisms and laws that determine the influence of geometry and active membrane properties of dendrites on formation of intrinsic complex patterns of electrical activity of neurons. Investigations were performed on model neurons of different types (neocortical pyramidal neurons, cerebellar Purkinje neurons, motor neurons of the brain stem and spinal cord) with active properties of the dendritic membrane and complex geometry of dendritic arborizations, both natural, derived from computer reconstruction of in vivo stained cells, and modified by the virtual dissection of individual structural elements in order to specify the functional roles of the latter. For the first time we disclosed the biophysical mechanisms determining the generation of a variety of both simple and complex, including stochastic, intrinsic patterns of output signals in neurons with the dendrites having complex metrically asymmetrical branching geometry and nonlinear electrical membrane properties. For the first time subtle organization of the electrical states of excitable membranes was revealed as the possibility of the existence of multiple excitation states, which differ in levels, time of occurrence and life-time of the membrane depolarization, which tends to self-maintaining. It was for the first time established that neurons of different types, which significantly differ in structure and membrane properties of their dendrites, share common laws of links between the complexity and regularity of the temporal pattern at the cell output and the intensity of tonic synaptic excitation, uniformly distributed along the dendrites. Common are the generation of simple periodical pulse patterns of low or high frequency at, respectively, low or high excitation intensity, and the generation of complex periodical or stochastic patterns at excitation intensity in a certain intermediate range. The feature is the dependence of the latter on the size of the dendritic branching: the larger arborization the smaller intensities in this characteristic range. For the first time we determined the specific roles of the size, complexity, and metrical asymmetry of the dendritic branching as well as kinetic properties of ion channels populating the dendritic membrane in the formfion of the features of spatial-temporal patterns of intrinsic electrical activity of neurons of different types.