PHENYLPYRAZOLES, A NEW CLASS OF PESTICIDES - AN ELECTROPHYSIOLOGICAL INVESTIGATION INTO BASIC EFFECTS

Phenylpyrazoles constitute a newly developed class of pesticides that may exert direct excitatory effects on the nervous system. Basic electrophysiological effects were investigated in vitro in the sciatic nerve and the lateral-line sense organ of the clawed frog, Xenopus laevis, by recording nerve activity extracellularly. In the slowly adapting stretch receptor organ of the crayfish, Astacus sp., effects on the membrane potential of the neurone were recorded using intracellular microelectrodes. Both in the sciatic nerve and in the lateral-line sense organ the main effect of phenylpyrazoles was to decrease the survival time of the isolated preparation. In the isolated crayfish stretch receptor organ a similar decrease of the survival time was accompanied by a depolarization of the stretch receptor neurone membrane. The depolarizing effect of the phenylpyrazoles is not caused by a modification of the tetrodotoxin-sensitive voltage-dependent Na+ channels, nor by an effect on the picrotoxin-sensitive neurotransmission mediated by γ-aminobutyric acid. The phenylpyrazoles neither act by inhibiting the electrogenic Na/K pump. Although the cause of the phenylpyrazole-induced membrane depolarization remains to be elucidated, it is concluded that the underlying mechanism is distinct from that of the pyrethroid insecticides. © 1991.