The midgut epithelium of mosquitoes adjusts cell proliferation and endoreplication to respond to physiological challenges.

BACKGROUND: Hematophagous mosquitoes transmit many pathogens that cause human diseases. Pathogen acquisition and transmission occur when female mosquitoes blood feed to acquire nutrients for reproduction. The midgut epithelium of mosquitoes serves as the point of entry for transmissible viruses and parasites. RESULTS: We studied midgut epithelial dynamics in five major mosquito vector species by quantifying PH3-positive cells (indicative of mitotic proliferation), the incorporation of nucleotide analogs (indicative of DNA synthesis accompanying proliferation and/or endoreplication), and the ploidy (by flow cytometry) of cell populations in the posterior midgut epithelium of adult females. Our results show that the epithelial dynamics of post-emergence maturation and of mature sugar-fed guts were similar in members of the Aedes, Culex, and Anopheles genera. In the first three days post-emergence, ~ 20% of cells in the posterior midgut region of interest incorporated nucleotide analogs, concurrent with both proliferative activity and a broad shift toward higher ploidy. In mature mosquitoes maintained on sugar, an average of 3.5% of cells in the posterior midgut region of interest incorporated nucleotide analogs from five to eight days post-emergence, with a consistent presence of mitotic cells indicating constant cell turnover. Oral bacterial infection triggered a sharp increase in mitosis and nucleotide analog incorporation, suggesting that the mosquito midgut undergoes accelerated cellular turnover in response to damage. Finally, blood feeding resulted in an increase in cell proliferation, but the nature and intensity of the response varied by mosquito species and by blood source (human, bovine, avian or artificial). In An. gambiae, enterocytes appeared to reenter the cell cycle to increase ploidy after consuming blood from all sources except avian. CONCLUSIONS: We saw that epithelial proliferation, differentiation, and endoreplication reshape the blood-fed gut to increase ploidy, possibly to facilitate increased metabolic activity. Our results highlight the plasticity of the midgut epithelium in mosquitoes' physiological responses to distinct challenges.

Tissue distribution of levo-methadone in nonpregnant and pregnant female and male mice: effect of SKF 525-A 1,2.

Male, nonpregnant and pregnant female (15-17 gestational days) mice were injected i.p. with saline or SKF 525-A (50 mg/kg) and 1 hour later with levo-3H-1-methadone (205 mug/kg; 0.8 and 5 mg/kg). Levels of free methadone were examined in some or all of the following tissues: brain, plasma, liver, lung, spleen, kidney, heart, eye, placenta, amniotic fluid, whole fetus, fetal brain and liver. In saline controls, the methadone concentrations in several adult tissues, whole fetuses, fetal brain and liver reached peak levels at 15 minutes and were negligible at 24 hours. Tissue levels of methadone increased in a dose-related manner; however, the brain/plasma concentration ratios with the three doses were almost unity at 15 minutes, 1 hour and 3 hours. Among adult tissues with high concentrations were the lung, liver, kidney and spleen; the brain in contrast contained very low concentrations. No notable differences were detected in the tissue levels of methadone in males and nonpregnant females; however, in pregnant mice significantly higher levels were observed in the lung and the liver. Fetal brain, liver and whole fetus concentrations were approximately similar. At 15 minutes, the fetal brain contained about 3 times more methadone than the maternal brain and the difference increased at subsequent times. Nonpregnant females excreted somewhat larger amounts of 3H in the urine than did pregnant females. SKF 525-A markedly enhanced and prolonged the concentrations of methadone in all the adult and the fetal tissues and lowered urinary excretion of total radioactivity in nonpregnant and pregnant females. Marked increases in tissue radioactivity after SKF 525-A might be due to a combination of effects involving inhibition of drug metabolism, altered tissue distribution and lower urinary excretion.