Conditions of dominant effectiveness of distal sites of active uniform dendrites with distributed tonic inputs

This simulation study aimed at assessing linkage between the membrane properties and the effectiveness of somatopetal current transfer from activated tonic excitatory inputs homogeneously distributed along uniform dendrites. It was shown that in the dendrites having anN-shaped steady current-voltage membrane characteristic due to the negative slope within a certain range of potentials, distal sites can be more effective than proximal sites in somatopetal current transfer from tonically activated excitatory synaptic inputs. Inhomogeneous dendritic depolarization produced by these inputs should be found everywhere within a range of the negative slope. In simulated dendrites receiving, as in rat abducens motoneurons, voltage-sensitive synaptic inputs of anN-methyl-D-aspartate (NMDA) type, such spatial effects occurred at low depolarization produced by subcritical excitation. At supercritical excitation, depolarization increased and left the range of the negative slope, and proximal sites became much more effective than distal ones. It is suggested that persistent inward currents (including other than of NMDA nature) can provide similar effects.