title: How muscles recover from paresis and atrophy after intramuscular injection of botulinum toxin A: Study in juvenile rats.
abstract: Botulinum toxin A (BoNT-A) is a potent biological toxin widely used for the management of skeletal muscle spasticity or dynamic joint contracture. Intramuscular injection of BoNT-A causes muscle denervation, paresis, and atrophy. This clinical effect of botulinum toxin A lasts 3 to 6 months, and injected muscle eventually regains muscle mass and recovers muscle function. The goal of the present study was to characterize the molecular and cellular mechanisms leading to neuromuscular junction (NMJ) regeneration and skeletal muscle functional recovery after BoNT-A injection. Fifty-six 1-month-old Sprague-Dawley rats were used. Botulinum toxin A was injected into the left gastrocnemius muscle at a dosage of 6 units/kg body weight. An equivalent volume of saline was injected into the right gastrocnemius muscle to serve as control. The gastrocnemius muscle samples were harvested from both hind limbs at 3 days, 7 days, 15 days, 30 days, 60 days, 90 days, 180 days, and 360 days after administration of toxin. In addition, the gastrocnemius muscles from 1-month-old rats with no injections were harvested to serve as uninjected control group. Muscle samples were processed and mRNA was extracted. Real-time polymerase chain reaction (PCR) and gene microarray technology were used to identify key molecules involved in NMJ stabilization and muscle functional recovery. More than 28,000 rat genes were analyzed and approximately 9000 genes are expressed in the rat gastrocnemius muscle. Seven days following BoNT-A injection, 105 genes were upregulated and 59 genes were downregulated. Key molecules involved in neuromuscular junction (NMJ) stabilization and muscle functional recovery were identified and their time course of gene expression following BoNT-A injection were characterized. This animal study demonstrates that following intramuscular injection of BoNT-A, there is a sequence of cellular events that eventually leads to NMJ stabilization, remodeling, and myogenesis and muscle functional recovery. This recovery process is divided into two stages (aneural and neural) and that the IGF-1 signaling pathway play a central role in the process.
authors.affiliation: Department of Orthopaedic Surgery, Wake Forest University Medical Center, Winston-Salem, North Carolina 27104, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Shen
authors.forename: Jianjun
authors.initials: J
authors.lastname: Ma
authors.forename: Cassandra
authors.initials: C
authors.lastname: Lee
authors.forename: Beth P
authors.initials: BP
authors.lastname: Smith
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Smith
authors.forename: Kim H
authors.initials: KH
authors.lastname: Tan
authors.forename: L Andrew
authors.initials: LA
authors.lastname: Koman
mesh_terms: D000818:Animals; D001284:Atrophy; D019274:Botulinum Toxins, Type A / Q000008:administration & dosage / Q000494:pharmacology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D020869:Gene Expression Profiling; D007273:Injections, Intramuscular; D007334:Insulin-Like Growth Factor I / Q000235:genetics; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D018008:Myogenin / Q000235:genetics; D009416:Nerve Regeneration; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D020411:Oligonucleotide Array Sequence Analysis; D010291:Paresis / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics; D011950:Receptors, Cholinergic / Q000235:genetics; D011978:Receptors, Nicotinic / Q000235:genetics
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; C503803:Myog protein, rat; D018008:Myogenin; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D007334:Insulin-Like Growth Factor I; C475048:MuSK protein, rat; D020794:Receptor Protein-Tyrosine Kinases; D019274:Botulinum Toxins, Type A