title: Role of timing in assessment of nerve regeneration.
abstract: Small animal models are indispensable for research on nerve injury and reconstruction, but their superlative regenerative potential may confound experimental interpretation. This study investigated time-dependent neuroregenerative phenomena in rodents. Forty-six Lewis rats were randomized to three nerve allograft groups treated with 2 mg/(kg day) tacrolimus; 5 mg/(kg day) Cyclosporine A; or placebo injection. Nerves were subjected to histomorphometric and walking track analysis at serial time points. Tacrolimus increased fiber density, percent neural tissue, and nerve fiber count and accelerated functional recovery at 40 days, but these differences were undetectable by 70 days. Serial walking track analysis showed a similar pattern of recovery. A "blow-through" effect is observed in rodents whereby an advancing nerve front overcomes an experimental defect given sufficient time, rendering experimental groups indistinguishable at late time points. Selection of validated time points and corroboration in higher animal models are essential prerequisites for the clinical application of basic research on nerve regeneration.
authors.affiliation: Department of Otolaryngology-Head & Neck Surgery, Washington University School of Medicine, Saint Louis, MO, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Brenner
authors.forename: Arash
authors.initials: A
authors.lastname: Moradzadeh
authors.forename: Terence M
authors.initials: TM
authors.lastname: Myckatyn
authors.forename: Thomas H H
authors.initials: TH
authors.lastname: Tung
authors.forename: Allen B
authors.initials: AB
authors.lastname: Mendez
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Hunter
authors.forename: Susan E
authors.initials: SE
authors.lastname: Mackinnon
mesh_terms: D000818:Animals; D016572:Cyclosporine / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008297:Male; D008866:Microsurgery / Q000534:rehabilitation; D009416:Nerve Regeneration / Q000187:drug effects / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D011917:Rats, Inbred Lew; D020127:Recovery of Function / Q000187:drug effects; D016559:Tacrolimus / Q000494:pharmacology; D013979:Tibial Nerve / Q000293:injuries / Q000503:physiopathology / Q000601:surgery; D013997:Time Factors; D014184:Transplantation, Homologous; D016138:Walking
chemical_list: D007166:Immunosuppressive Agents; D016572:Cyclosporine; D016559:Tacrolimus