Sprouting of mammalian motor nerve terminals induced by in vivo injection of botulinum type-D toxin and the functional recovery of paralysed neuromuscular junctions.

Paralysis of the mouse levator auris longus muscle by in vivo injection of Clostridium botulinum type-D neurotoxin (BoNT/D) triggered a marked outgrowth of the motor nerve from the original terminal arborization. The increase in total nerve terminal length was due to both increase in the number of terminal branches and in average branch length. Asynchronous quantal transmitter release in response to nerve impulses was a prominent feature in paralysed junctions that started 24 h after poisoning and lasted for about 15 days. The functional recovery of poisoned junctions occurred 25-30 days after poisoning and was characterized by the synchronous quantal transmitter release upon nerve stimulation that triggered synaptically evoked action potentials and muscle fibre contraction.