The Effect of Piperazine on Toad and Earthworm Muscle Membrane Potentials

Antagonism Between Chlorpyrifos and Flaxedil in Toad and Earthworm Neuromuscular Transmission

“…Therefore, the possible effects of chlorpyrifos on earthworm extrasynaptic action potentials were also excluded from this study [14] . Previous work [4][5][6] reported a long neuromuscular latency, or junctional delay, in the earthworm. In the present work, the latency, or junctional delay, measured in the earthworm preparations (12.3 ms) in normal Ringer was more than six times longer than that (1.8 ms) in the toad preparations under threshold flaxedil.…”

“…2) and interstimulus interval (Fig. 3) in both toad and earthworm as predicted [4][5][6][11][12][13] . When the graphs are examined horizontally along the abscissa, the first impression is that chlorpyrifos increased the depolarizing rate (Fig.…”

“…One of these mechanisms is a facilitated cholinergic synaptic transmission due to inhibition of the enzyme cholinesterase [1][2][3] . The purpose of this article is to test this cholinesterase inhibition by chlorpyrifos in the little studied neuromuscular transmission of the earthworm [4][5][6] by comparing it to the well studied neuromuscular transmission in the frog [7,8] .…”

“…For instance, a postsynaptic action potential was never evoked in the South American earthworm, Amynthas hawayanus (nee, Pheretima hawayana), muscle membrane by a single threshold, or overthreshold electrical stimulus to its presynaptic nerve in normal earthworm Ringer [5,6] . Moreover, a graded spike potential [4][5][6] , which may be equivalent to the frog action potential, can only be evoked by summing two threshold stimuli even when the preparation is in the normal earthworm Ringer. These characteristics suggest that neuromuscular transmission in the earthworm has a much lower excitability than that of the frog.…”

“…Two electrophysiological parameters, the depolarizing rate of the endplate potential evoked by a single threshold stimulus after blocking its action potential by flaxedil and the interstimulus interval of paired threshold stimuli to evoke an action potential after blockage by flaxedil, will be used to measure neuromuscular excitability. As there is little knowledge of neuromuscular transmission in South American frogs of the Leptodactylus and Physalaemus genera, the South American toad, Bufo ichthyricus, will be used in this work because its neuromuscular transmission in normal frog Ringer is known [4] to be similar to that of North American frogs of the genus Rana [7,8] .…”