Early Excitability Changes in Lumbar Motoneurons of Transgenic SOD1G85R and SOD1G93A-Low Mice

Abstract

This work characterizes the properties of wild-type (WT) mouse motoneurons in the second postnatal week and compares these at the same age and in the same conditions to those of two different SOD1 mutant lines used as models of human amyotrophic lateral sclerosis (ALS), the SOD1G93A low expressor line and SOD1G85R line, to describe any changes in the functional properties of mutant motoneurons (Mns) that may be related to the pathogenesis of human ALS. We show that very early changes in excitability occur in SOD1 mutant Mns that have different properties from those of WT animals. The SOD1G93A-Low low expressor line displays specific differences that are not found in other mutant lines including a more depolarized membrane potential, larger spike width, and slower spike rise slope. With current pulses SOD1G93A-Low were hyperexcitable, but both mutants had a lower gain with current ramps stimulation. Changes in the threshold and intensities of Na+ and Ca2+ persistent inward currents were also observed. Low expressor mutants show reduced total persistant inward currents compared with WT motoneurons in the same recording conditions and give arguments toward modifications of the balance between Na+ and Ca2+ persistent inward currents. During the second week postnatal, SOD1G93A-Low lumbar motoneurons appear more immature than those of SOD1G85R compared with WT and we propose that different time course of the disease, possibly linked with different toxic properties of the mutated protein in each model, may explain the discrepancies between excitability changes described in the different models.