Effect of implantation of an extra nerve on the recovery of neuromuscular transmission from botulinum toxin.

1. The common peroneal nerve was implanted into soleus in the mouse and 2 weeks later a sublethal dose of botulinum toxin injected causing a block of neuromuscular transmission at the terminals of the soleus nerve. Most muscle fibres became innervated by the common peroneal nerve. 2. Recovery of neuromuscular transmission at the soleus nerve terminals was delayed in the common peroneal nerve implanted muscles. 3. Stimulation of the soleus nerve after botulinum-evoked subthreshold end-plate potentials (e.p.p.s) in virtually every fibre tested in unoperated muscles. In common peroneal nerve-implanted muscles stimulation of the soleus nerve failed to evoke e.p.p.s in about 40% of fibres tested and where e.p.p.s were recorded their amplitudes were generally smaller. 4. When the common peroneal nerve was cut 2 months after botulinum, neuromuscular transmission at soleus nerve terminals occurred after 4 weeks. When the common peroneal nerve was cut 6 months after botulinum, transmission was found at soleus nerve terminals within 1 week. 5. Recovery of transmission at soleus nerve terminals from the effects of botulinum toxin is delayed if the muscle fibres become innervated by the common peroneal nerve and a proportion of soleus nerve terminals cease to release acetylcholine (ACh) until after the peroneal nerve has been cut.