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Long-term use of permethrin-impregnated nets does not increase Anopheles gambiae permethrin tolerance.

Vulule JM, Beach RF, Atieli FK, Mount DL, Roberts JM, Mwangi RW.

Vector Biology and Control Research Centre (Kenya Medical Research Institute), Kisumu, Kenya.

Previous use of permethrin-impregnated bednets (mosquito nets) and curtains in four Kenyan villages for one year, 1990-91, raised the permethrin LT50 of Anopheles gambiae to 2.4-fold above its baseline value, designated permethrin tolerance (PT), as measured by exposure to 0.25% permethrin-impregnated papers in W.H.O. test-kits. During 1992-93, with ongoing use of permethrin-impregnated nets and curtains, PT regressed slightly compared with the contemporary susceptibility level of An.gambiae from non-intervention villages, to 1.8-fold in 1992 and only 1.6-fold in 1993. Thus the selection pressure of impregnated nets for PT in An.gambiae appears to be minimal in our study villages, although the impact of permethrin was demonstrated by a significantly lower parous-rate of An.gambiae females in the intervention (63-66%) than in non-intervention (79%) villages, and by reduced malaria transmission (reported elsewhere). In a selected stock of An.gambiae from the study area, PT did not affect the susceptibility to deltamethrin, fenitrothion, propoxur or DDT. Bioassays described herein provide easy procedures for field-monitoring of mosquito susceptibility/tolerance/resistance to insecticides used for net impregnation in operational programmes.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8834745&dopt=Abstract permethrin Elimite



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Effects of daily dermal application of DEET and epermethrin, alone and in combination, on sensorimotor performance, blood-brain barrier, and blood-testis barrier in rats.

Abou-Donia MB, Goldstein LB, Dechovskaia A, Bullman S, Jones KH, Herrick EA, Abdel-Rahman AA, Khan WA.

Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA. donia acpub.duke.edu

DEET and permethrin were implicated in the development of illnesses in some veterans of the Persian Gulf War. This study was designed to investigate the effects of daily dermal application of these chemicals, alone or in combination, on the permeability of the blood-brain barrier (BBB) and blood-testes barrier (BTB) and on sensorimotor performance in male Sprague-Dawley rats. Groups of five rats were treated with a dermal daily dose of 4, 40, or 400 mg/kg DEET in ethanol or 0.013, 0.13, or 1.3 mg/kg permethrin in ethanol for 60 d. A group of 10 rats received a daily dermal dose of ethanol and served as controls. BBB permeability was assessed by injection of an iv dose of the quaternary ammonium compound [3H]hexamethonium iodide. While permethrin produced no effect on BBB permeability, DEET alone caused a decrease in BBB permeability in brainstem. A combination of DEET and permethrin significantly decreased the BBB permeability in the cortex. BTB permeability was decreased by treatment with DEET alone and in combination with permethrin. The same animals underwent a battery of functional behavior tests 30, 45, and 60 d after exposure to evaluate their sensorimotor abilities. All treatments caused a significant decline in sensorimotor performance in a dose- and time-dependent manner. These results show that daily dermal exposure to DEET, alone or in combination with permethrin, decreased BBB permeability in certain brain regions, and impaired sensorimotor performance.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11289702&dopt=Abstract permethrin Elimite



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Systemic application of pyrethroid insecticides evokes differential expression of c-Fos and c-Jun proteins in rat brain.

Hassouna I, Wickert H, el-Elaimy I, Zimmermann M, Herdegen T.

II. Institute of Physiology, University of Heidelberg, Germany.

Expression of the c-Fos and c-Jun transcription factor was investigated by immunocytochemistry in the thalamus, hypothalamus, hippocampus and cortex of adult rats following intraperitoneal application of proconvulsant doses of the pyrethroid insecticides, cypermethrin and permethrin. Pyrethroid insecticides are used world-wide and their uptake, e.g., by nutrition and inhalation evokes severe neurological symptoms in animals and humans, but their effects on neuronal gene expression has not been elucidated. Cypermethrin induced a strong expression of c-Fos and c-Jun in all the thalamic nuclei, except the ventro-posterior complex and substantia nigra, and in all the hypothalamic nuclei. In general, the immunoreactivities (IR) persisted for 8 h on their maximal levels, and were still above control levels after 24 h in several thalamic and hypothalamic areas. c-Fos-IR was strongly increased in all cortical layers with a predominance in the superficial layers II-IV, whereas c-Jun-IR was only slightly increased. In the hippocampus, cypermethrin induced a weak expression of c-Fos, but not of c-Jun, in the dentate gyrus and CA-3 area. Permethrin that has a lower pharmacological potency, evoked a similar pattern of c-Fos and c-Jun expression, however, intensity and persistence of the neuronal labeling were less pronounced. Our results demonstrate that the neurotoxic effects of pyrethroid insecticides comprise molecular genetic alterations in the brain such as early and lasting induction of Fos and Jun transcription factor proteins. These changes in the neuronal program are prominent in the hypothalamus and thalamus that are involved in the regulation of the autonomic and visceral nervous systems.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8856738&dopt=Abstract permethrin Elimite



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Effects of the pyrethroid insecticide permethrin on membrane fluidity.

Moya-Quiles MR, Munoz-Delgado E, Vidal CJ.

Departamento de Bioquimica y Biologia Molecular A, Facultad de Biologia, Edificio de Veterinaria, Campus de Espinardo, Universidad de Murcia, Spain.

The interaction of permethrin with dimyristoyl- (DMPC), dipalmitoyl- (DPPC) and distearoyl- (DSPC) bilayers has been investigated by differential scanning calorimetry (DSC) and DPH and TMA-DPH fluorescence anisotropy. In experiments performed by DSC, we show that the addition of permethrin to liposomes, in a 5:1 phospholipid/pyrethroid ratio, decreases the phase transition temperature (Tm) of DMPC, DPPC and DSPC by 3.2, 2.3 and 1.1 degrees C, respectively. Furthermore, DSC profiles reveal that permethrin decreases the cooperativity for the phase transition of DMPC, DPPC and DSPC membranes. DPH and TMA-DPH fluorescence anisotropy experiments show that permethrin increases membrane fluidity at temperatures below the Tm. The results are discussed in terms of a preferential localization of permethrin in the hydrophobic core of the membrane, where it diminishes the lipid packing in the gel phase and has no effect in the liquid-crystalline phase.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8907239&dopt=Abstract permethrin Elimite



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Factors Influencing Pyrethroid Resistance in a Permethrin-Selected Strain of the Soybean Looper, Pseudoplusia includens (Walker)

Thomas JD, Ottea JA, Boethel DJ, Ibrahim S.

Department of Entomology, Louisiana Agricultural Experiment Station, Baton Rouge, Louisiana, 70803

Cytochrome P450 monooxgenase activity toward p-nitroanisole was measured in larvae of three strains of soybean looper, Pseudoplusia includens (Walker), including a laboratory susceptible (S) strain, a resistant (R) strain selected for several generations with permethrin, and a nonselected (NS) strain from the same field collections as the R strain. Activity was significantly higher in R strain larvae than in the S and NS strains (1.8- and 1.4-fold, respectively), and there was no significant difference between activity in the S and NS strains. Resistance to the alpha-cyano pyrethroids deltamethrin and cypermethrin was similar to or higher than that observed with permethrin (RR = 70.0, 62.4, 145.3 and 12.1, 32.3, and 27.0 for permethrin, deltamethrin, and cypermethrin in R and NS strains, respectively). The R strain was less resistant (RR = 4.3) to tefluthrin, a pyrethroid with a fluorinated-phenyl alcohol moiety, and a nonester (ether) pyrethroid, BRC 429 (RR = 17.7). Piperonyl butoxide (PB) significantly increased the toxicity of each insecticide tested in the R and NS strains. In addition, penetration of 14C-cypermethrin was decreased significantly at 24 hr after treatment when R strain larvae were pretreated with PB, with 21.1% of the applied dose unpenetrated in PB-treated larvae and 7.6% unpenetrated in larvae not treated with PB.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8980024&dopt=Abstract permethrin Elimite