Axonal degeneration in the Trembler-j mouse demonstrated by stimulated single-fiber electromyography.
The Trembler-j (Tr-j) mouse is a naturally occurring mutant with a point mutation in the peripheral myelin protein-22 gene causing severe peripheral nerve demyelination. It is a genetically homologous murine model for Charcot-Marie-Tooth disease type 1A (CMT 1A). Our prior pilot studies using stimulated single-fiber needle electromyograpy (SSFEMG) showed increased jitter in 60-day-old Tr-j mice compared to age-matched, wildtype animals. The aim of this study was to better elucidate the etiology of increased jitter in Tr-j mice and test the following hypotheses: (1) the increased jitter in Tr-j mice is due to turnover of endplates secondary to axonal degeneration with reinnervation and not to conduction block secondary to demyelination of motor nerve axons; and (2) aging Tr-j mice demonstrate increased jitter and fiber density compared with younger mutant mice due to progressive motor axon loss. SSFEMG studies performed on 60- and 140-day-old mice indicated that average mean consecutive difference (MCD) and fiber density estimates (FDE) were significantly increased in Tr-j mice at both ages compared to age-matched wildtypes. FDE also increased substantially in older mutant mice. Intraperitoneal neostigmine injections produced significant reductions in average MCD in Tr-j mice, suggesting that impaired neuromuscular transmission is an early pathologic feature in these mice and likely reflects distal axonal degeneration. Our findings corroborate our prior pilot study, although in a much larger number of animals across a wider age span. Our study also indicates that SSFEMG, performed in a serial fashion, is a useful, noninvasive method of detecting progressive axon loss in this murine model of CMT 1A. This technique may be a valuable tool to study the affects of genetic or pharmaceutical interventions in murine models of peripheral neuropathy. Muscle Nerve, 2007.
Meekins
Gregg D
GD
Department of Neurology, University of Washington Medical Center, Seattle, Washington 98195, USA.
Carter
Gregory T
GT
Emery
Michael J
MJ
Weiss
Michael D
MD
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000367:Age Factors; D000818:Animals; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D004252:DNA Mutational Analysis / Q000379:methods; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D051379:Mice; D008810:Mice, Inbred C57BL; D008818:Mice, Neurologic Mutants / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D009154:Mutation; D009185:Myelin Proteins / Q000235:genetics; D009388:Neostigmine / Q000494:pharmacology; D009410:Nerve Degeneration / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*
D002800:Cholinesterase Inhibitors; D009185:Myelin Proteins; C489545:Pmp22 protein, mouse; D009388:Neostigmine