Elsevier

Neurobiology of Disease

Volume 37, Issue 2, February 2010, Pages 370-383
Neurobiology of Disease

A systematic study of brainstem motor nuclei in a mouse model of ALS, the effects of lithium

https://doi.org/10.1016/j.nbd.2009.10.017Get rights and content

Abstract

Transgenic mice expressing the human superoxide dismutase 1 (SOD-1) mutant at position 93 (G93A) develop a phenotype resembling amyotrophic lateral sclerosis (ALS). In fact, G93A mice develop progressive motor deficits which finally lead to motor palsy and death. This is due to the progressive degeneration of motor neurons in the ventral horn of the spinal cord. Although a similar loss is reported for specific cranial motor nuclei, only a few studies so far investigated degeneration in a few brainstem nuclei. We recently reported that chronic lithium administration delays onset and duration of the disease, while reducing degeneration of spinal motor neuron. In the present study, we extended this investigation to all somatic motor nuclei of the brain stem in the G93A mice and we evaluated whether analogous protective effects induced by lithium in the spinal cord were present at the brain stem level. We found that all motor but the oculomotor nuclei were markedly degenerated in G93A mice, and chronic treatment with lithium significantly attenuated neurodegeneration in the trigeminal, facial, ambiguus, and hypoglossal nuclei. Moreover, in the hypoglossal nucleus, we found that recurrent collaterals were markedly lost in G93A mice while they were rescued by chronic lithium administration.

Introduction

Amyotrophic lateral sclerosis (ALS) is a progressive, devastating neurodegenerative disease that affects primarily motor neurons (MN) of the spinal cord, brainstem and motor cortex (Wijesekera and Leigh, 2009, Cleveland and Rothstein, 2001). The clinical symptoms include weakness, muscle atrophy and fasciculations, death occurs in 3–5 years from diagnosis (Rowland and Shneider, 2001).

When the motor nuclei of the brainstem are involved at the onset of disease (roughly, 25% of cases), the clinical outcome is the most severe leading to death in less than 1 year from diagnosis (Kühnlein et al., 2008). In fact, the involvement of the brainstem leads to dysarthria, dysphagia and impairment of swallowing and breathing all due to a damage of hypoglossal, trigeminal and ambiguus nuclei. Also the facial nucleus is affected and contributes to these symptoms (Kusaka et al., 1988, Hartmann et al., 1989). In contrast, oculomotor nuclei are relatively spared (Gizzi et al., 1992, Okamoto et al., 1993).

Based on the knowledge of inherited ALS in humans, a variety of mouse strains have been generated. Among these, the most studied is the G93A mouse, where a point mutation in the human gene coding the enzyme superoxide dismutase type-1 (SOD1) leads to a 93 glycine/alanine substitution. These mice develop a rapidly progressive MN disease, which leads to hindlimb paralysis and death (Gurney et al., 1994, Ripps et al., 1995, Gurney, 1997). This phenotype recapitulates several clinical and histopathological features of both familial and sporadic forms of the human disease (Gurney et al., 1994, Gurney, 1997, Newbery and Abbott, 2001). Although lumbar spinal cord is the site of onset and it is mostly affected, MN degeneration also occurs at higher levels of the cord and brainstem. It is surprising that, despite brainstem degeneration was described in this mouse model, and the brainstem involvement leads to the worst prognosis of ALS in humans, only a few studies investigated the brainstem motor nuclei in the G93A mouse.

Therefore, we decided to analyze the entire population of somatic brainstem motor nuclei of the G93A mouse also including the parasympathetic nucleus dorsalis of the vagus.

Within these nuclei, we counted the degeneration occurring at the end of the natural course of the disease, and we evaluated the effects of lithium. In fact, recent reports (Shin et al., 2007, Fornai et al., 2008a, Fornai et al., 2008b, Feng et al., 2008, Pasquali et al., 2009) indicate that chronic lithium administration protects G93A mice from MN degeneration (Shin et al., 2007; for a review, see Pasquali et al., 2009 ; Young, 2009) and rescues the behavioural and pathological deficit occurring following a spinal cord transection (Dill et al., 2008). These effects are concomitant with lithium-induced increased neuron number and decreased gliosis as shown both in degenerating (Fornai et al., 2008a, Fornai et al., 2008b) and lesioned (Su et al., 2007, Su et al., 2009) spinal cords as well as lithium-induced sprouting of corticospinal (Dill et al., 2008) and rubrospinal (Yick et al., 2004) tracts.

Section snippets

Animals

We used male mice from our own colony originated from the G93A mouse strain originally obtained from the Jackson laboratories (Bar Harbor, ME, USA). Selective breeding maintained the transgene in the hemizygous state in an F1 hybrid C57BL6xSJL genetic background. Colony maintenance and screening for the presence of the human transgene were performed as described (Spalloni et al., 2006). In addition, we replicated the experiments in G93A mice directly purchased from Jackson laboratories (Bar

Results

Chronic lithium administration extended the survival time and significantly improved the motor function of the G93A mouse used in this study, confirming our previous publication (Fornai et al., 2008a, Fornai et al., 2008b). In Supplementary Fig. 1, presented are the results of the motor function tests (Rotarod, PaGe and stride length) and the survival time. In this experimental context, the increased neuron number and the decreased vacuolization in the spinal cord were confirmed here as shown

Discussion

In the present paper, we analyzed all brainstem motor nuclei in the G93A mouse showing the reliability of this experimental model to reproduce the bulbar involvement of ALS. Moreover, by profiting of this experimental setting, we characterized the effects of lithium in counteracting the loss of brainstem motor neurons thus extending previous findings obtained in the spinal cord.

In fact, ALS is characterized by the degeneration of motor neurons in the spinal cord, brainstem, and motor cortex (

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