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.

Keywords: (1)EB; (10)PFA; (11)SWM; (12)ROI; (13)IHC; (14)BSA; (15)NDS; (16)TBS; (17)NF-M; (18)GFAP; (19)MBP; (2)mtDNA; (20)EM; (21)qRT-PCR; (22)Fn1; (23)Gapdh; (24)RW; (25)SCI; (26)BBB; (27)MLR; (28)MedRF; (29)PLR; (3)VLF; (30)DLF; (31)ACS; (32)PCS; (4)VC; (5)VWM; (6)EC; (7)BMS; (8)RI; (9)PBS; Basso mouse scale; Basso, Beattie, and Bresnahan; Demyelination; Ethidium bromide; Inflammation; Locomotion; Spared white matter; Spinal cord injury; anterior cord syndrome; bovine serum albumin; dorsolateral funiculus; electron microscopy; ethidium bromide; fibronectin 1; glial fibrilary acidic protein; glyceraldehyde 3-phosphate dehydrogenase; immunohistochemistry; iron eriochrome cyanine; mesencephalic locomotor region; mitochondrial DNA; myelin basic protein; neurofilament M; normal donkey serum; paraformaldehyde; phosphate buffered saline; pontomedullary locomotor region; pontomedullary reticular formation; posterior cord syndrome; quantitative real-time polymerase chain reaction; regions of interest; regularity index; running wheel; spared white matter; spinal cord injury; tris buffered saline; ventral column; ventral white matter; ventrolateral funiculus.