Public release date: 1-Apr-2008

Could Botulinum Toxin Be Bad for You?

Botulinum toxins (BoNTs) are used increasingly to treat maladies from spasms and migraines to obesity and wrinkles. It has been assumed that the toxin remains localized at the injection site, where it cleaves proteins involved in vesicle fusion, thereby blocking neurotransmitter release. But now Antonucci et al. demonstrate that BoNT/A is retrogradely transported along microtubules, transcytosed, and taken up by afferent terminals. When BoNT/A was injected into one hippocampus in rats, it cleaved its target [synaptosomal-associated protein of 25 kDa (SNAP-25)] in the contralateral hippocampus, resulting in reduced neuronal activity. Similarly, when BoNT/A was injected into the superior colliculus or whisker pads, SNAP-25 was cleaved in the retina and facial nucleus, respectively. In the retina, BoNT/A remained active for at least 25 d after injection. Although cleaved SNAP-25 was detected only in afferents that projected directly to the injection site, it is not clear whether further transcytosis would occur over time.