Abstract
Avermectin B1a (AVM) is an antiparasitic agent that paralyzes nematodes without causing hypercontraction or flaccid paralysis. Using selective stimulation techniques, we have shown that AVM blocks transmission between interneuron(s) and excitatory motorneurons in the ventral nerve cord of Ascaris. It also inhibits transmissin between inhibitory motoneurons and muscle but has little effect on excitatory neuromuscular transmission. Picrotoxin can reverse the AVM-induced block of interneuron-excitatory motoneuron transmission but has no effect on the inhibitory motoneuronal synapse in either the presence or absence of AVM. Our results provide an explanation of how AVM may cause paralysis of nematodes.