Histochemical Evidence for Localized Inhibition of Cholinesterase in the House Fly1

Abstract

Histochemical demonstration of cholinesterase (ChE) activity and inhibition in Musca domestica L. (Diptera: Museidae) central nervous system was observed using thiocholine substrates incubated with cryostat frozen sections. Topical application of organophosphorus (OP) and carbamate insecticides showed that the brain of the fly was a secondary site of action for the toxicants, while the peripheral regions of the thoracic ganglion were the primary areas of ChE inhibition. Inhibition with the OP compounds seemed to penetrate into the neuropile of the ganglia with time. No penetration further than the perineurium occurred with the carbamates. Reactivation of ChE was noted in dead flies with both the OP and carbamate compounds. The possible importance of the peripheral ChE of the thoracic ganglion is considered in conjunction with symptomology of poisoning.