Point mutations in the para-orthologous sodium channel α-subunit of the head louse (M815I, T917I and L920F) are associated with permethrin-and DDT-resistance. These mutations were inserted in all combinations using site-directed mutagenesis at the corresponding amino acid sequence positions (M827I, T929I and L932F) of the house fly para-orthologous voltage-sensitive sodium channel α-subunit (Vssc1 WT ) gene and heterologously co-expressed with the sodium channel auxiliary subunit of house fly (Vsscβ) in Xenopus oocytes. The double mutant possessing M827I and T929I (Vssc1 MITI /Vsscβ) caused a ~4.0 mV hyperpolarizing shift and the triple mutant, Vssc1 MITILF / Vsscβ, caused a ~3.2 mV depolarizing shift in the voltage dependence of activation curves. Vssc1 MITI /Vsscβ, Vssc1 TILF /Vsscβ and Vssc1 MITILF /Vsscβ caused depolarizing shifts (~6.6, ~7.6 and ~8.8 mV, respectively) in the voltage dependence of steady-state inactivation curves. The M827I and L932F mutations reduced permethrin sensitivity when expressed alone but the T929I mutation, either alone or in combination, virtually abolished permethrin sensitivity. Thus, the T929I mutation is the principal cause of permethrin resistance in head lice. Comparison of the expression rates of channels containing single, double and triple mutations with that of Vssc1 WT /Vsscβ channels indicates that the M827I mutation may play a role in rescuing the decreased expression of channels containing T929I.
We previously described methods for age-grading female Aedes aegypti (L.) by gas chromatographic (GC) analysis of whole-body cuticular hydrocarbon patterns. Two regression models were developed that were based on the age-dependent, relative abundance of 2 cuticular hydrocarbons, pentacosane (GC peak 1) and nonacosane (GC peak 5). We have refined this method so that only the legs are required to age individual females. Two new regression models were developed that also use the relative abundance of a 3rd cuticular hydrocarbon, octacosane (GC peak 4). These models improve the overall accuracy of the cuticular hydrocarbon method for aging female mosquitoes, especially for older females from 132 to 165 degree-days (DD) of age (12-15 calendar days at 28 degrees C). The correlation coefficients (R2) for the best-fitted linear regression models for aging females from 0 to 132 and 0-165 DD were 0.80 and 0.81, respectively (P < 0.001 in all cases). The use of leg cuticular hydrocarbons for estimating the age of female Ae. aegypti has a significant advantage over whole-body extracts as indicated by the decreased variability associated with the relative abundance of pentacosane and the expanded range over which the models were able to predict age accurately by the addition of the relative abundance of octacosane.
The ability to clone, express, and electrophysiologically measure currents carried by voltage-gated ion channels has allowed a detailed assessment of the action of pyrethroids on various target proteins.Recently, the heterologous expression of various rat brain voltage-gated sodium channel isoforms in Xenopus laevis oocytes has determined a wide range of sensitivities to the pyrethroids, with some channels virtually insensitive and others highly sensitive. Furthermore, some isoforms show selective sensitivity to certain pyrethroids and this selectivity can be altered in a state-dependent manner. Additionally, some rat brain isoforms are apparently more sensitive to pyrethroids than the corresponding human isoform. These finding may have significant relevance in judging the merit and value of assessing the risk of pyrethroid exposures to humans using toxicological studies done in rat.Other target sites for certain pyrethroids include the voltage-gated calcium and chloride channels. Of particular interest is the increased effect of Type II pyrethroids on certain phosphoforms of the N-type Ca(v)2.2 calcium channel following post-translational modification and its relationship to enhanced neurotransmitter release seen in vivo.Lastly, parallel neurobehavioral and mechanistic studies on three target sites suggest that a fundamental difference exists between the action of Types I and II pyrethroids, both on a functional and molecular level. These differences should be considered in any future risk evaluation of the pyrethroids.
Gas chromatography with flame-ionization detection was used to measure the time-associated, quantitative changes in the cuticular hydrocarbons of female Aedes aegypti (L.). Cohorts of unstressed Ae. aegypti, Rockefeller strain, were reared and held at 3 constant temperatures (24, 28, and 30 degrees C). Five females from each cohort were taken at 33 degree-day (DD) intervals from 0 to 231 DD (using 17 degrees C as the threshold temperature). Quantitative changes over time of cuticular hydrocarbons associated with gas chromatographic peaks 1 and 5 were identified as having promise for age grading. The relative abundance of peak 1 (pentacosane) decreased linearly from 0 to 132 DD, whereas peak 5 (nonacosane) increased linearly over the same period. Suboptimal larval conditions (crowded and starved), which resulted in physiological stress (decreased size), had negligible effect on the relative abundance of pentacosane and nonacosane. Additionally, the rate of change in the relative abundance of pentacosane and nonacosane were the same for both a recently colonized Chachoengsao (Thailand) strain of Ae. aegypti compared with the long-colonized Rockefeller (Caribbean) strain over a 0-99 DD interval. Two linear regression models, one based on the relative abundance of pentacosane and the other on the logit transformation of these values, were developed for aging female Ae. aegypti. A blind study using laboratory-reared mosquitoes and a mark-release-recapture experiment using field mosquitoes validated these age-grading models and produced promising results for aging females up to 132 DD (19, 12, and 10 calendar days at 24, 28 and 30 degrees C, respectively). Therefore the regression models, based on the relative abundance of these 2 cuticular hydrocarbons, appeared to be a useful approach for age-grading Ae. aegypti up to at least 12 d of age regardless of environmental conditions (temperature and stress) and population history (origin and colonization time).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.