Motoneuron subtypes show specificity in glycine receptor channel abnormalities in a transgenic mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective loss of motoneurons. Recently we studied glycine receptors (GlyRs) in motoneurons in an ALS mouse model expressing a mutant form of human superoxide dismutase-1 with a Gly93→Ala substitution (G93A-SOD1). Living motoneurons in dissociated spinal cord cultures were identified by using transgenic mice expressing eGFP driven by the Hb9 promoter. We showed that GlyR-mediated currents were reduced in large-sized (diameter >28 μm) Hb9-eGFP⁺ motoneurons from G93A-SOD1 embryonic mice. Here we analyze GlyR currents in a morphologically distinct subgroup of medium-sized (diameter 10-28 μm) Hb9-eGFP⁺ motoneurons, presumably gamma or slow-type alpha motoneurons. We find that glycine-induced current densities were not altered in medium-sized G93A-SOD1 motoneurons. No significant differences in glycinergic mIPSCs were observed between G93A-SOD1 and control medium-sized motoneurons. These results indicate that GlyR deficiency early in the disease process of ALS is specific for large alpha motoneurons.