Annotation. Action of pyrethroid insecticides on the vertebrate nervous system.

The neurotoxic action of the synthetic pyrethroid insecticides has received much interest in recent years, as the number of available pyrethroids and their practical applications have greatly increased. Although the majority of pyrethroids have a low oral toxicity to mammals, they may cause severe neurotoxic symptoms whenever they reach the nervous system in sufficient amount. The principal effect of pyrethroids in the vertebrate nervous system is to induce repetitive activity, particularly in the sensory nervous system. This repetitive activity originates from a prolongation of the transient increase in sodium permeability of the nerve membrane associated with excitation. Available evidence indicates that pyrethroids primarily interfere with the sodium channels in the nerve membrane. All active pyrethroids affect sodium channel gating in a similar manner, but marked differences in neurotoxic activity exist between the various pyrethroids, especially between alpha-cyano and non-cyano compounds.