Electrotonic profile and passive propagation of synaptic potentials in three subpopulations of hippocampal CA1 interneurons

To elucidate the role of dendritic morphology in signal transfer, the passi ve propagation of somatic and dendritic potentials was compared in multi-co mpartment models of three interneuron subpopulations in the CA1 region. Nin e calbindin, 15 calretinin- and 10 parvalbumin-containing cells were modell ed incorporating the detailed geometry. the currents of the action potentia ls in the soma, and the AMPA, N-methyl-D-aspartate and GABA-B receptor-medi ated postsynaptic currents in the dendrites. The cable properties show char acteristic differences among the subpopulations. The morphotonic length of calbindin and calretinin cell dendrites is larger than of parvalbumin cells . Thus parvalbumin cells are more compact than calbindin or calretinin cell s unless the ratio of their axial and membrane resistivities exceeds the ra tios of the other two cell types by more than 33%. In calbindin cells, the distal parts of the extremely long dendrites that invade the alveus are vir tually isolated from the soma for passively propagating signals. The synapt ic potentials evoked at a given morphotonic distance from the soma show lar ger differences locally on the dendrites than on the soma in all subpopulat ions. Both the somatic and dendritic amplitude ratios are the smallest in P V cells. In calbindin cells the somatic amplitude of synaptic potentials ev oked at the same morphotonic distance from the soma is similar regardless o f the number of branchpoints along their path. In calretinin and parvalbumi n cells, from dendrites with long primary segments synaptic potentials reac h the soma with larger amplitude than from dendrites that are branching clo se to the soma. The dendrites with the larger impact on somatic membrane po tential are usually the dendrites that enter the stratum lacunosum-molecula re. These results indicate that dendritic morphology plays a role in changing t he effectiveness of synaptic potentials evoked at different dendritic locat ions, and in this way is likely to be an important factor in determining th e integrative properties of the different neuron populations. FC, (C) 2001 IBRO, Published by Elsevier Science Ltd, All rights reserved.