Effects of chlordimeform on the electrical activity of waxmoth larva foregut

Microelectrodes were used to study the action of chlordimeform on the foregut nerve-muscle system of waxmoth larvae, Galleria mellonella. Excitatory postsynaptic potentials evoked by nerve stimulation were reversibly depressed by 2 × 10^-3M chlordimeform. All-or-none spikes elicited by transmembrane current pulses were affected by higher concentrations (up to 5 × 10^-3M) of chlordimeform. The critical membrane potential for spiking was always increased, while in some cases the amplitude and the rate of rise of the spike was reduced. Chlordimeform at 5 × 10^-3M had very little effect on the outward rectification and effective membrane resistance of these muscle fibers. These data suggest the primary action of chlordimeform, causing a disturbance of foregut activity, is an inhibition of the mechanisms which generate synaptic and action potentials.