Reduced Excitability and Increased Neurite Complexity of Cortical Interneurons in a Familial Mouse Model of Amyotrophic Lateral Sclerosis.

Rosemary M Clark,Tracey C Dickson,Catherine A Blizzard,Mariana Brizuela

doi:10.3389/fncel.2018.00328

Abstract

Cortical interneurons play a crucial role in regulating inhibitory-excitatory balance in brain circuits, filtering synaptic information and dictating the activity of pyramidal cells through the release of GABA. In the fatal motor neuron (MN) disease, amyotrophic lateral sclerosis (ALS), an imbalance between excitation and inhibition is an early event in the motor cortex, preceding the development of overt clinical symptoms. Patients with both sporadic and familial forms of the disease exhibit reduced cortical inhibition, including patients with mutations in the copper/zinc superoxide-dismutase-1 (SOD1) gene. In this study, we investigated the influence of the familial disease-causing hSOD1-G93A ALS mutation on cortical interneurons in neuronal networks. We performed whole-cell patch-clamp recordings and neurobiotin tracing from GFP positive interneurons in primary cortical cultures derived from Gad67-GFP::hSOD1G93A mouse embryos. Targeted recordings revealed no overt differences in the passive properties of Gad67-GFP::hSOD1G93A interneurons, however the peak outward current was significantly diminished and cells were less excitable compared to Gad67-GFP::WT controls. Post hoc neurite reconstruction identified a significantly increased morphological complexity of the Gad67-GFP::hSOD1G93A interneuron neurite arbor compared to Gad67-GFP::WT controls. Our results from the SOD1 model suggest that cortical interneurons have electrophysiological and morphological alterations that could contribute to attenuated inhibitory function in the disease. Determining if these phenomena are driven by the network or represent intrinsic alteration of the interneuron may help explain the emergence of inhibitory susceptibility and ultimately disrupted excitability, in ALS.

Highlights

Amyotrophic lateral sclerosis (ALS) is the most common and severe form of motor neuron (MN) disease
Previous studies have demonstrated that mutant hSOD1G93A can perturb neuronal excitability during development, which may contribute to cellular vulnerability in disease (Kuo et al, 2004; van Zundert et al, 2008; Martin et al, 2013; Wainger et al, 2014; Devlin et al, 2015)
We focus on investigating cortical interneuron excitability in neuronal culture by examining firing patterns and membrane properties of interneurons in Gad67GFP::hSOD1G93A cultures

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is the most common and severe form of motor neuron (MN) disease It is clinically characterized by selective loss of the upper and lower MNs in the primary motor cortex and spinal cord, resulting in progressive motor system failure and death within 3–5 years of diagnosis (Talbot, 2014; Brown and Al-Chalabi, 2017). Accumulating evidence from several clinical and experimental studies suggests the disease pathogenesis may center on altered regulation of MN excitability (Turner and Kiernan, 2012; Clark et al, 2015; Geevasinga et al, 2016) In both sporadic and familial forms of ALS, patients have been found to present with neurophysiological alterations described as hyperexcitability (Vucic and Kiernan, 2006; Vucic et al, 2008; Geevasinga et al, 2015). In ALS, hyperexcitability likely results from dysfunctional inhibition exerted by GABAergic interneurons, as well as intrinsic changes to sodium (Na+) and potassium (K+) channel function on MNs (Geevasinga et al, 2016; Do-Ha et al, 2018)

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