Glycinergic Innervation of Motoneurons Is Deficient in Amyotrophic Lateral Sclerosis Mice

Abstract

Altered motoneuron excitability is involved in amyotrophic lateral sclerosis pathobiology. To test the hypothesis that inhibitory interneuron innervation of spinal motoneurons is abnormal in an amyotrophic lateral sclerosis mouse model, we measured GABAergic, glycinergic, and cholinergic immunoreactive terminals on spinal motoneurons in mice expressing a mutant form of human superoxide dismutase-1 with a Gly933 Ala substitution (G93A-SOD1) and in controls at different ages. Glutamic acid decarboxylase, glycine transporter-2, and choline acetyltransferase were used as markers for GABAergic, glycinergic, and cholinergic terminals, respectively. Triple immunofluorescent labeling of boutons contacting motoneurons was visualized by confocal microscopy and analyzed quantitatively. Glycine transporter-2-bouton density on lateral motoneurons was decreased significantly in G93A-SOD1 mice compared with controls. This reduction was absent at 6 weeks of age but present in asymptomatic 8-week-old mice and worsened with disease progression from 12 to 14 weeks of age. Motoneurons lost most glycinergic innervation by 16 weeks of age (end-stage) when there was a significant decrease in the numbers of motoneurons and choline acetyltransferase-positive boutons. No significant differences in glutamic acid decarboxylase-bouton densities were found in G93A-SOD1 mice. Reduction of glycinergic innervation preceded mitochondrial swelling and vacuolization. Calbindin-positive Renshaw cell number was decreased significantly at 12 weeks of age in G93A-SOD1 mice. Thus, either the selective loss of inhibitory glycinergic regulation of motoneuron function or glycinergic interneuron degeneration contributes to motoneuron degeneration in amyotrophic lateral sclerosis. (Am J

Aberrant Regulation of DNA Methylation in Amyotrophic Lateral Sclerosis: A New Target of Disease Mechanisms

“…It is not yet clear whether the abnormality in ALS mouse motor neuron neurotransmission is autonomous or non-autonomous and related to primary abnormalities in spinal interneurons. Other studies of transgenic mouse models of ALS show that interneurons degenerate before motor neurons [91], and motor neurons become deficient in glycinergic innervation early in the course of the disease [103], leading to the hypothesis that ALS is initiated in interneurons [104]. This hypothesis has been supported by recent work modeling ALS in Drosophila [105] and in clinical studies of ALS patients [106].…”

Mitochondrial Pathobiology in Parkinson's Disease and Amyotrophic Lateral Sclerosis

“…high -mSOD1 undergo prominent degeneration; about 80% of lumbar motor neurons are eliminated by end-stage disease [98,161]. Subsets of spinal interneurons degenerate before motor neurons in G93A…”

“…high -mSOD1 [98] and some are the glycinergic Renshaw cells [161]. Unlike the degeneration of motor neurons in human ALS [143], motor neurons in these mice do not degenerate with a morphology resembling any form of apoptosis or apoptosis-necrosis hybrids [12,98,147,160].…”

“…high -mSOD1 mice more closely resembles a prolonged necrotic-like cell death process [98,160] involving early-occurring mitochondrial damage, cellular swelling, and dissolution [98,[161][162][163][164][165][166]. Biochemically, the death of motor neurons in G93A highmSOD1 is characterized by somal and mitochondrial swelling and formation of DNA single-strand breaks prior to double-strand breaks occurring in nuclear DNA and mtDNA [98].…”

“…EM studies of motor neurons in G93A high mice have shown that the outer mitochondrial membrane (OMM) remains relatively intact to permit formation of megamitochondria [160,161]. Moreover, early in the disease of these mice, mitochondria in dendrites in spinal cord ventral horn undergo extensive cristae and matrix remodeling, while few mitochondria in motor neuron cell bodies show major structural changes [160].…”