Effects of pyrethroids

Induction of repetitive activity in the nervous system is the principal effect of pyrethroids. Repetitive activity originates from a prolongation of the transient increase in sodium permeability of the nerve membrane associated with excitation. All pyrethroids affect sodium channel gating in a similar manner, although Type II pyrethroids are significantly more neurotoxic than Type I pyrethroids. 

Riviere, J.L., J. Bach, and G. Grolleau. 1983. Effect of pyrethroid insecticides and N-(3,5-dichlorophenyl) dicarboximide fungicides on microsomal drug-metabolizing enzymes in the Japanese quail (Cotumix cotumix). Bull. Environ. Contam. Toxicol. 31 479-485. 

Vijverberg, H.P.M., G.S.F. Ruigt, and J.V.D. Bercken. 1982. Structure-related effects of pyrethroid insecticides on the lateral-line sense organ and on peripheral nerves of the clawed frog, Xenopus laevis. Pestic. Biochem. Physiol. 18 315-324. 

To deal with flying insects, the volatilization of pyrethroids is the first requirement and volatilization energy is needed for this property. In the case of crawling insects, persistent and residual effects of pyrethroids are required after residual application to floors and walls. 

Recent results that examined the effect of pyrethroids on voltage-gated sodium channels expressed in human embryonic kidney (HEK293) cells grown in... 

Taken together, the limited experiments conducted using neuronal cell cultures illustrate a distinct difference in the way that pyrethroids modify ion conductance and subsequent neurotransmitter release under resting and depolarized conditions. Continued efforts utilizing recent new tools like automated patch-clamp systems and MEAs to assess the effects of pyrethroids on the kinetics and voltage-dependent gating of ion channels in primary cultures or transfected cells is likely to provide new insight into the neurotoxicity of pyrethroids [79, 82]. 

Shafer TJ, Meyer DA (2004) Effects of pyrethroids on voltage-sensitive calcium channels a critical evaluation of strengths, weaknesses, data needs, and relationship to assessment of cumulative neurotoxicity. Toxicol Appl Pharmacol 196 303-318... 

Lund AE, Narahashi T (1983) Kinetics of sodium channel modification as the basis for the variation in the nerve membrane effects of pyrethroids and DDT analogs. Pestic Biochem Physiol 20 203-216... 

Hossain MM, Suzuki T, Sato I, Takewaki T, Suzuki K, Kobayashi H (2004) The modulatory effect of pyrethroids on acetylcholine release in the hippocampus of freely moving rats. Neurotoxicology 25 825-833... 

Table 2 ED30 for acute effects of pyrethroids on motor activity in rats...

The effects of pyrethroids on acoustic startle response (ASR) were examined to detect the effects on sensorimotor function. Pyrethroids show various effects on ASR (Table 3). Crofton and Reiter reported that non-cyano pyrethroids showed no effect on the latency, while they increased the amplitude. a-Cyano pyrethroids showed increase or no change on the latency, while various effects on the amplitude were observed [30, 31]. Fenvalerate showed effects similar to non-cyano pyrethroids. In studies by Hijzen et al. [32, 33], the results of permethrin and deltamethrin on the amplitude were consistent with the findings by Crofton and Reiter, but cypermethrin induced contradictory effects. NAK 1901 showed similar effects to other non-cyano pyrethroids. The reason for the inconsistency of effects of pyrethroids on startle response remains unsolved. 

Wolansky MJ, Gennings C, DeVito MJ et al (2009) Evidence for dose-additive effects of pyrethroids on motor activity in rats. Environ Health Perspct 117 1563-1570... 

Wolansky MJ, Gennings C, Crofton KM (2006) Relative potencies for acute effects of pyrethroids on motor function in rats. Toxicol Sci 89 271-277... 

Hijzen TH, Beun RD, Slangen JL (1988) Effects of pyrethroids on the acoustic startle reflex in the rat. Toxicol 49 271-276... 

Stein EA, Washburn M, Walczak C et al (1987) Effects of pyrethroid insecticides on operant responding maintained by food. Neurotoxicol Teratol 9 27-31... 

Similarly, the reductions in toxicity observed in laboratory toxicity tests where exposure is modified (either through the addition of sediment or by removal to clean water) are also apparent in the field. Field effect concentrations are generally observed to occur at concentrations around three to ten times above those based on standard laboratory data. Dissipation and degradation are therefore clearly the critical factors in mitigating effects of pyrethroids under field conditions. This provides reassurance that preliminary ecological risk assessments based on... 

Table 7 Field trial results investigating effects of pyrethroids on honeybees...

The toxic effects of some pesticide mixtures are additive, particularly when their toxic mechanisms are identical. The additive effects of the organophosphates chlorpyrifos and diazanon were demonstrated in one study. T Another study found the s-triazine herbicides atrazine and cyanazine to show additive toxic effects. Not all mixtures of similar pesticides produce additive effects, however. In one study, mixtures of five organophos-phate pesticides (chlorpyrifos, diazinon, dimethoate, acephate, and malathion) were shown to produce greater than additive effects when administered to laboratory animals. Another article discusses nonsimple additive effects of pyrethroid mixtures. Despite the similarities in their chemical structure, pyrethroids act on multiple sites, and mixtures of these produce different toxic effects. 10 ... 

The effect of pyrethroids on the stretch receptor neuron is described in more detail by Chalmers and Osborne (8). These results agree with earlier studies on the insect neuromuscular junction in which the actions of pyrethroids were interpreted entirely on the basis of their actions on the sodium channels of the presynaptic axons (SO ... 

Direct effects of pyrethroid insecticides on giant axons in the abdominal nerve cord (microelectrode recordings). 

Effects of pyrethroid molecules on isolated axons (current-clamp experiments). 

Effects of Pyrethroids on Mouse Brain Sodium Channels... 

Our initial studies in this system employed deltamethrin at a high concentration (10 pM) to characterize the effects of pyrethroids on... 

We explored the potency of pyrethroid action in this system using deltamethrin, NRDC 157 (3-phenoxybenzyl [lR,cis]-3-( 2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate the non-cyano analog of deltamethrin), and their nontoxic enantiomers as test compounds ( Table II). Deltamethrin produced half-maximal enhancement of veratridine-dependent activation at 25 nM, whereas NRDC 157 was approximately tenfold less potent and the nontoxic enantiomers were inactive. These findings demonstrate that the effect of pyrethroids on mouse brain sodium channels is both potent and stereospecific for toxic isomers. The relative potencies of deltamethrin and NRDC 157 in this assay also agree well with their... 

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