Neuromuscular Transmitters in the Horseshoe Crab

Most arthropod species use glutamate as their principal excitatory neuromuscular transmitter, but we present evidence that this role is played by acetylcholine in walking legs of the horseshoe crab, Limulus polyphemus. Agonists of cholinergic transmission enhance neuronally evoked contractions, while antagonists inhibit these contractions. Videorecording and electrical recording were both used to gather this data. Considering the lineage of arthropod taxa, cholinergic innervation of arthropod muscle may predate the glutamatergic innervation of crustaceans and insects