Avermectin B1a, a paralyzing anthelmintic that affects interneurons and inhibitory motoneurons in Ascaris.

Abstract
Avermectin B1a (AVM) is an antiparasitic agent that paralyzes nematodes without causing hypercontraction or flaccid paralysis. Using selective stimulation techniques, it was shown that AVM blocks transmission between interneuron(s) and excitatory motoneurons in the ventral nerve cord of Ascaris. It also inhibits transmission 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 the presence or absence of AVM. The results provide an explanation of how AVM may cause paralysis of nematodes.