CNR - Institute of Neuroscience CNR
Institute of Neuroscience


Botulinum neurotoxins: mechanisms of action and applications to pharmacoresistant epilepsy

Botulinum neurotoxins (BoNTs; seven serotypes, designated with letters from A to G) are the most potent poisons known. They are bacterial enzymes that act on nerve terminals to prevent transmitter release via the specific cleavage of SNARE proteins. Due to their extreme potency and specificity, BoNTs are widely exploited for scientific and therapeutic applications. In experimental settings, they represent valuable tools for the study of cellular physiology. In addition, localized injections of BoNTs are increasingly being used in the clinic for the treatment of several human diseases (e.g., dystonia and spasticity) characterized by hyperexcitability of peripheral nerve terminals. Despite this widespread use, relatively little is known on BoNT intracellular trafficking and potential central effects. Our laboratory studies the mode of action and trafficking of BoNTs in different neuronal systems in vivo. We are also exploiting the silencing properties of BoNTs for the treatment of central hyperexcitability (i.e., epileptic seizures) in animal models.

Retrograde axonal transport of botulinum neurotoxin A (BoNT/A)


Botulinum neurotoxin A (BoNT/A) exerts a long-lasting blockade of transmitter release at the neuromuscular junction via the cleavage of the synaptic protein SNAP-25. Intramuscular application of BoNT/A is a well established treatment for dystonia, spasticity and other neuromuscular pathologies. The range of clinical applications of BoNT/A is continuously increasing to include a variety of autonomic, ophtalmological, dermatological, secretory, and painful disorders. It is therefore important to fully characterize the spectrum of actions of this neurotoxin.

In particular, it was commonly believed that BoNT/A effects remain localized to the neuromuscular synapses near the injection site. There is now evidence that intramuscular injection of BoNT/A results in central nervous system effects in man and animals (Caleo et al., J Neurochem 2009). These findings are usually ascribed to plastic rearrangements subsequent to the peripheral blockade. Direct central effects are also possible, since we have recently demonstrated that BoNT/A undergoes retrograde axonal transport and is then transcytosed to central neurons, where it cleaves its substrate SNAP-25 (Antonucci et al., J Neurosci 2008; Figure 1). Ongoing experiments in the laboratory are aimed at elucidating the functional consequences of these distant actions. This knowledge may be important for clarifying the mechanisms of action of BoNT/A and for a more rational therapeutic use of this toxin.

Anti-epileptic effects of botulinum neurotoxin E (BoNT/E)


A significant proportion of focal epilepsies are resistant to systemic treatment with antiepileptic drugs and in some cases, only surgical removal of the focus can cure the disease. There is therefore an urgent need for novel approaches for pharmacoresistant epilepsy. One potential strategy is the delivery into the seizure focus of therapeutic agents with long-lasting antiepileptic action. We have probed the idea that the prolonged blockade of synaptic transmission by BoNT may be exploited for the management of focal hyperexcitability in the brain. Indeed, intracerebral injection of BoNTs inhibits excitatory glutamatergic transmission and reduces spiking activity of pyramidal neurons (Costantin et al., J Neurosci 2005). Our studies demonstrate that intracerebral injection of BoNT/E has potent anticonvulsant effects in a mouse model of chronic temporal lobe epilepsy (Antonucci et al., Epilepsia 2009; Figure 2). Administration of BoNT/E is also very effective in preventing seizure-induced neuronal loss (Figure 3).



  • Caleo M (2009) Epilepsy: synapses stuck in childhood. Nat. Med. 15:1126-7.
  • Caleo M, Schiavo G (2009) Central effects of tetanus and botulinum neurotoxins. Toxicon 54:593-9.
  • Antonucci F, Bozzi Y, Caleo M (2009) Intrahippocampal infusion of botulinum neurotoxin E (BoNT/E) reduces spontaneous recurrent seizures in a mouse model of mesial temporal lobe epilepsy. Epilepsia 50:963-6.
  • Caleo M, Antonucci F, Restani L, Mazzocchio R (2009) A reappraisal of the central effects of botulinum neurotoxin type A: by what mechanism? J. Neurochem. 109:15-24.
  • Antonucci F, Rossi C, Gianfranceschi L, Rossetto O, Caleo M (2008) Long-distance retrograde effects of botulinum neurotoxin A. J. Neurosci. 28:3689-96.
  • Antonucci F, Di Garbo A, Novelli E, Manno I, Sartucci F, Bozzi Y, Caleo M (2008) Botulinum neurotoxin E (BoNT/E) reduces CA1 neuron loss and granule cell dispersion, with no effects on chronic seizures, in a mouse model of temporal lobe epilepsy. Exp. Neurol. 210:388-401.
  • Costantin L, Bozzi Y, Richichi C, Viegi A, Antonucci F, Funicello M, Gobbi M, Mennini T, Rossetto O, Montecucco C, Maffei L, Vezzani A, Caleo M (2005) Antiepileptic effects of botulinum neurotoxin E. J. Neurosci. 25:1943-51.


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Matteo Caleo

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