Toxicology
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Ketamine and its stereoisomer S(+)-ketamine are widely used for sedation in pediatric anesthesia and intensive care medicine. Numerous experimental studies indicate that ketamine is potentially toxic to the developing brain. Here, we examined the long-term effects of NMDA receptor blockade on NMDA receptor subunit expression, alterations in neuronal Ca(2+)-oscillations and apoptosis. ⋯ This was accompanied by an increase in NR1 mRNA but not the NR2A and B subunit expression at the same time point. 24h following washout of the specific drug, a significant elevation of the pro-apoptotic marker BAX, as well as activated Caspase-3 positive neurons, could be detected in cultures exposed to 100μM MK801 and 25μM S(+)-ketamine. Here, we show that long-term blockade of the NMDA receptor in developing rat hippocampal neurons significantly increased NR1 subunit expression, and that this was associated with an alteration in neuronal activity. Apoptosis was only induced 24h after withdrawal of long-term blockade for high doses of S(+)-ketamine.
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Comparative Study
Sensitivity of neuroprogenitor cells to chemical-induced apoptosis using a multiplexed assay suitable for high-throughput screening.
High-throughput methods are useful for rapidly screening large numbers of chemicals for biological activity, including the perturbation of pathways that may lead to adverse cellular effects. In vitro assays for the key events of neurodevelopment, including apoptosis, may be used in a battery of tests for detecting chemicals that could result in developmental neurotoxicity. Apoptosis contributes to nervous system development by regulating the size of the neuroprogenitor cell pool, and the balance between cellular proliferation and apoptosis during neuroprogenitor cell proliferation helps to determine the size and shape of the nervous system. ⋯ The results show that all three commercially available models generated a robust source of proliferating neuroprogenitor cells, and that the assay was sensitive and reproducible when used in a multi-well plate format. There were differences in the response of rodent and human neuroprogenitor cells to a set of chemicals previously shown to induce apoptosis in vitro. Neuroprogenitor cells were more sensitive to chemical-induced apoptosis than differentiated neurons, suggesting that neuroprogenitor cells are one of the cell models that should be considered for use in a developmental neurotoxicity screening battery.
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We previously found persistent aberration of hippocampal adult neurogenesis, along with brain manganese (Mn) accumulation, in mouse offspring after developmental exposure to 800-ppm dietary Mn. Reduction of parvalbumin (Pvalb)(+) γ-aminobutyric acid (GABA)-ergic interneurons in the hilus of the dentate gyrus along with promoter region hypermethylation are thought to be responsible for this aberrant neurogenesis. The present study was conducted to examine the relationship between the induction of aberrant neurogenesis and brain Mn accumulation after oral Mn exposure as well as the responsible mechanism in young adult animals. ⋯ In contrast, 56-day oral exposure caused aberrations in neurogenesis suggestive of reductions in type 2b and type 3 progenitor cells and immature granule cells in the dentate subgranular zone. Brain Mn accumulation in 56-day exposed cases, as well as in directly Mn-injected cases occurred in parallel with reduction of Pvalb(+) GABAergic interneurons in the dentate hilus, suggesting that this may be responsible for aberrant neurogenesis. For reduction of Pvalb(+) interneurons, suppression of brain-derived neurotrophic factor-mediated signaling of mature granule cells may occur via suppression of c-Fos-mediated neuronal plasticity due to direct Mn-toxicity rather than promoter region hypermethylation of Pvalb.
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Hexachlorophene (HCP) is known to induce myelin vacuolation corresponding to intramyelinic edema of nerve fibers in the central and peripheral nervous system in animals. This study investigated the effect of maternal exposure to HCP on hippocampal neurogenesis in rat offspring using pregnant rats supplemented with 0 (controls), 100, or 300 ppm HCP in the diet from gestational day 6 to day 21 after delivery. On postnatal day (PND) 21, the numbers of T box brain 2(+) progenitor cells and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling(+) apoptotic cells in the hippocampal subgranular zone (SGZ) decreased in female offspring at 300 ppm, which was accompanied by myelin vacuolation and punctate tubulin beta-3 chain staining of nerve fibers in the hippocampal fimbria. ⋯ Although some myelin vacuolation remained, all other changes observed in HCP-exposed offspring on PND 21 disappeared on PND 77. These results suggest that maternal HCP exposure reversibly decreases type-2b intermediate-stage progenitor cells via the mitochondrial apoptotic pathway in offspring hippocampal neurogenesis at 300 ppm HCP. Neurogenesis may be affected by dysfunction of cholinergic inputs into granule cell lineages and/or GABAergic interneurons as indicated by decreased transcript levels of Chrnb2 and numbers of Chrnb2(+) interneurons caused by myelin vacuolation in the septal-hippocampal pathway.
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Diabetes mellitus is a highly prevalent metabolic disease affecting 29.1 million people or 9.3% of the population of the United States. The most prevalent form of diabetes is type 2 diabetes (T2D) which comprises 90-95% of all reported cases of diabetes. While the exact cause of T2D remains an enigma, known risk factors include age, weight, sedentary lifestyle, poor dietary habits, and genetic predisposition. ⋯ Therefore, based on the current data, chronic DDE exposure appears to have a biphasic effect on HFD-induced hyperglycemia in the male C57BL/6H mouse characterized by elevated fasting blood glucose at weeks 4 and 8 of HFD intake followed by normoglycemia upon sacrifice. In addition, chronic DDE exposure reduced HFD-induced hepatic steatosis upon sacrifice. These results indicate chronic exposure to DDE can directly affect systemic glucose and hepatic lipid metabolism and that these effects can be diet dependent.