Motor Cortex Layer V Pyramidal Neurons Exhibit Dendritic Regression, Spine Loss, and Increased Synaptic Excitation in the Presymptomatic hSOD1G93A Mouse Model of Amyotrophic Lateral Sclerosis

Motor cortex layer V pyramidal neurons (LVPNs) regulate voluntary control of motor output and selectively degenerate (along with lower motor neurons) in amyotrophic lateral sclerosis. Using dye-filling and whole-cell patch clamping in brain slices, together with high-resolution spinning disk confocal z-stack mosaics, we characterized the earliest presymptomatic cortical LVPN morphologic and electrophysiological perturbations in hSOD1^G93A (SOD1) mice to date. Apical dendritic regression occurred from postnatal day (P) 28, dendritic spine loss from P21, and increased EPSC frequency from P21 in SOD1 LVPNs. These findings demonstrate extensive early changes in motor cortex of the SOD1 mouse model, which thus recapitulates clinically relevant cortical pathophysiology more faithfully than previously thought.