Localization of acetylcholinesterase in a crustacean neuromuscular system

1. The localization of acetylcholinesterase (AChE) was studied by light and electron microscopy (LM and EM) at the neuromuscular junctions (NMJs) of the abdominal superficial flexor muscle (SFM) and the claw adductor muscle (CAM) of the crayfish in view of reported pharmacological evidence of cholinergic transmission at the former but not at the latter site. 2. Survey of LM with the copper-thiocholine method disclosed staining for AChE, but not for butyrocholinesterase (BuChE), at numerous NMJs of the SFM; neither enzyme was detected at any NMJs of the CAM. 3. With the bis-(thioacetoxy) aurate (I) method, EM examination showed AChE-staining at NMJs of the SFM to be confined to the postjunctional membrane. 4. The published and present findings suggest a unique situation of more than one excitatory transmitter for the skeletal neuromuscular system in the crustacean studied.