Central effects of tetanus and botulinum neurotoxins

Tetanus neurotoxin (TeNT) and botulinum neurotoxins (BoNTs; from A to G) are metalloproteases that act on nerve terminals to prevent exocytosis. They are extensively exploited for the study of cellular physiology. Moreover, BoNTs are also employed in clinical neurology for the treatment of several disorders characterized by hyperexcitability of peripheral nerve terminals. This review summarizes recent studies that have provided a deeper understanding of the mode of action of TeNT and BoNTs. TeNT and BoNTs bind with extreme specificity and are internalized at the neuromuscular junction. We first examine the retrograde transport mechanisms by which TeNT gains access to the central nervous system. We also discuss recent findings indicating that, besides their well known local actions at the neuromuscular junction, BoNTs can also affect central circuits.