Gastrointestinal smooth muscles and sphincters spasms: treatment with botulinum neurotoxin

More than fifty years following the discovery that botulinum neurotoxins inhibit neuromuscular transmission, these powerful poisons have become drugs with many indications. First used to treat strabismus, local injections of botulinum neurotoxin are now considered a safe and efficacious treatment for neurological and non-neurological conditions. One of the most recent achievements in the field is the observation that botulinum neurotoxin is a treatment for diseases of the gastrointestinal tract. Botulinum neurotoxin is not only potent in blocking skeletal neuromuscular transmission, but also block cholinergic nerve endings in the autonomic nervous system. The capability to inhibit contraction of smooth muscles of the gastrointestinal tract was first suggested based on in vitro observations and later demonstrated in vivo; it has also been shown that botulinum neurotoxin does not block non adrenergic non cholinergic responses mediated by nitric oxide. This has further promoted the interest to use botulinum neurotoxin as a treatment for overactive smooth muscles and sphincters, such as the lower esophageal sphincter to treat esophageal achalasia, or the internal anal sphincter to treat anal fissure. Information on the anatomical and functional organization of innervation of the gastrointestinal tract is a prerequisite to understand many features of botulinum neurotoxin action on the gut and the effects of injections placed into specific sphincters. This review presents current data on the use of botulinum neurotoxin to treat diseases of the gastrointestinal tract and summarizes recent knowledge on the pathogenesis of disorders of the gut due to a dysfunction of the enteric nervous system.