title: Botulinum A toxin stimulates neurite branching in nerve-muscle cocultures.
abstract: In addition to skeletal muscle paralysis, type A botulinum toxin commonly causes sprouting of motor axons in various experimental whole-animal systems. The use of type A botulinum toxin in clinical treatment of muscle spasm disorders is becoming increasingly popular. The eventual, unwanted return of involuntary activity in the treated muscles may be a consequence of such axon sprouting. We have developed a coculture model allowing the quantification of botulinum toxin-induced sprouting that shows promise for future studies on its mechanism and control. Chick embryo ciliary ganglion motor neurons were cocultured with chick leg muscle cells. The presence of type A botulinum toxin in the coculture medium was correlated with significantly increased branching frequency of neurites. Toxin-increased branching frequency occurred even when the neurons and muscle cells were separated from each other on the culture dishes, suggesting a presynaptic effect of toxin. Cocultures incubated in the presence of curare, a post-synaptic blocker, had control levels of neurite branching, ruling out the possibility that simple synaptic blockade causes sprouting but again supporting the hypothesis of a pre-synaptic activity of botulinum toxin.
authors.affiliation: T.H. Morgan School of Biological Sciences, University of Kentucky, Lexington 40506-0225.
authors.forename: P H
authors.initials: PH
authors.lastname: Bonner
authors.forename: A F
authors.initials: AF
authors.lastname: Friedli
authors.forename: R S
authors.initials: RS
authors.lastname: Baker
mesh_terms: D000818:Animals; D001905:Botulinum Toxins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D004594:Electrophysiology; D005726:Ganglia, Parasympathetic / Q000166:cytology / Q000187:drug effects; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000187:drug effects; D009132:Muscles / Q000166:cytology / Q000187:drug effects / Q000294:innervation*; D016501:Neurites / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D001905:Botulinum Toxins