Functional consequences of ethidium bromide demyelination of the mouse ventral spinal cord

Abstract

Ethidium bromide (EB) has been extensively used in the rat as a model of spinal cord demyelination. However, this lesion has not been addressed in the adult mouse, a model with unlimited genetic potential. Here we characterize behavioral function, inflammation, myelin status and axonal viability following bilateral injection of 0.20 mg/mL ethidium bromide or saline into the ventral white matter (VWM) of female C57Bl/6 mice. EB-induced VWM demyelination significantly reduced spared VWM and Basso Mouse Scale (BMS) scores persisting out to 2 months. Chronic hindlimb dysfunction was accompanied by a persistent inflammatory response (demonstrated by CD45+ immunofluorescence) and axonal loss (demonstrated by NF-M immunofluorescence and electron microscopy; EM). These cellular responses differ from the rat where inflammation resolves by 3–4 weeks and axon loss is minimal following EB demyelination. As these data suggest that EB-injection in the mouse spinal cord is a non-remyelinating lesion, we sought to ask whether wheel running could promote recovery by enhancing plasticity of local lumbar circuitry independent of remyelination. This did not occur as BMS and Treadscan® assessment revealed no significant effect of wheel running on recovery. However, this study defines the importance of descending ventral motor pathways to locomotor function in the mouse as VWM loss results in a chronic hindlimb deficit.

Curcumin decreases astrocytic reaction after gliotoxic injury in the rat brainstem

“…Other evidences suggest that although EB does intercalate both chromosomal and mitochondrial DNA, it only affects mtDNA transcription 26 . So, an injection of EB into the white matter is likely to affect mtDNA in all cells of the lesion site, although neurons and endothelial cells appear to be less sensitive than glia in rodent models 4 . Astrocyte disappearance due to the gliotoxic effect and direct mechanical damage due to intracisternal injection are identified as factors capable of disturbing the blood-brain barrier, thus allowing monocyte and lymphocyte infiltration.…”

“…Ethidium bromide (EB) injections in the white matter of the central nervous system (CNS) are known to act like a gliotoxin, causing local oligodendroglial and astrocytic death, leading to primary demyelination, neuroinflammation, blood-brain barrier disruption and Schwann cell invasion due to the glia limitans breakdown 1,2,3,4 . Surviving astrocytes present a vigorous reaction around the injury site with increased immunoreactivity to the specific cell marker glial fibrillary acidic protein (GFAP), as well as re-expression of vimentin 3 .…”

Propentofylline reduces glial scar development following gliotoxic damage in the rat brainstem

“…However, other evidences suggest that while EB does intercalate both chromosomal and mitochondrial DNA, it only affects transcription of mtDNA 27 . So, it is likely that EB injection into the white matter compromises mtDNA in all cells in the lesion site although neurons and endothelial cells appear to be less sensitive than glia in rat models 3 . After trauma, blood-brain barrier dysfunction is immediately observed as well as activation of inflammatory cells including microglia, astrocytes and invading monocytes/macrophages 1,2,3 .…”

“…Both oligodendrocyte and astrocyte loss are hallmarks within the epicenter of an EB lesion while axons remain unaffected. The mechanism of selective glial death has been suggested to occur through EB's action as a minor-groove DNA intercalator 3 . However, other evidences suggest that while EB does intercalate both chromosomal and mitochondrial DNA, it only affects transcription of mtDNA 27 .…”

“…It is widely described that ethidium bromide (EB) injection in the white matter of the central nervous system (CNS) acts like a gliotoxin causing local oligodendroglial and astrocytic death, with consequent demyelination (although the naked axons remained preserved), blood-brain barrier disruption and Schwann cell invasion due to the glia limitans breakdown 1,2,3 . Surviving astrocytes presented a vigorous reaction around the injury site with increased immunoreactivity to the specific cell marker glial fibrillary acidic protein (GFAP) and reexpression of vimentin (VIM) 2 .…”