Neuromuscular contacts in the developing rat soleus depend on muscle activity

Neuromuscular transmission of the rat soleus muscle was interrupted by blocking the response of the postsynaptic membrane with alpha-bungarotoxin (alpha-BTX) at two different stages of postnatal development, i.e., at birth and at 10 days. The effect of this treatment on the maintenance of synaptic contacts was studied using histological and electrophysiological criteria. Following treatment at birth fewer muscle fibres were polyneuronally innervated 5-7 days later. After this initial loss of synaptic contacts, the subsequent rate of synapse elimination was slower than in control animals, so that even at 3 weeks muscles treated with alpha-BTX at birth had higher levels of polyneuronal innervation than their unoperated controls. Thus, interference with the response of the postsynaptic membrane at birth has prolonged effects on synaptic development. In muscles treated with alpha-BTX at 10 days the elimination of polyneuronal innervation was arrested and more neuromuscular contacts preserved.