Metrifonate increases neuronal excitability in CA1 pyramidal neurons from both young and aging rabbit hippocampus.
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The effects of metrifonate, a second generation cholinesterase inhibitor, were examined on CA1 pyramidal neurons from hippocampal slices of young and aging rabbits using current-clamp, intracellular recording techniques. Bath perfusion of metrifonate (10-200 microM) dose-dependently decreased both postburst afterhyperpolarization (AHP) and spike frequency adaptation (accommodation) in neurons from young and aging rabbits (AHP: p < 0.002, young; p < 0.050, aging; accommodation: p < 0.024, young; p < 0.001, aging). These reductions were mediated by muscarinic cholinergic transmission, because they were blocked by addition of atropine (1 microM) to the perfusate. The effects of chronic metrifonate treatment (12 mg/kg for 3 weeks) on CA1 neurons of aging rabbits were also examined ex vivo. Neurons from aging rabbits chronically treated with metrifonate had significantly reduced spike frequency accommodation, compared with vehicle-treated rabbits. Chronic metrifonate treatment did not result in a desensitization to metrifonate ex vivo, because bath perfusion of metrifonate (50 microM) significantly decreased the AHP and accommodation in neurons from both chronically metrifonate- and vehicle-treated aging rabbits. We propose that the facilitating effect of chronic metrifonate treatment on acquisition of hippocampus-dependent tasks such as trace eyeblink conditioning by aging subjects may be caused by this increased excitability of CA1 pyramidal neurons. (+info)
Treating neurocysticercosis medically: a systematic review of randomized, controlled trials.
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OBJECTIVE: To summarize the evidence from randomized controlled trials on the effects of cysticidal therapy used for treating human cysticercosis. METHODS: Published and unpublished studies in any language identified through MEDLINE (1966 - June 1999) specialized databases, abstracts, proceedings and contact with experts were analysed. Those which compared, using randomized or quasi-randomized methods, any cysticidal drug with placebo or symptomatic therapy were entered in the study. Data were extracted independently by two reviewers and trial quality assessed. Meta-analysis using fixed effects models calculated provided there was no significant heterogeneity, expressed as relative risk. RESULTS: Four trials met the inclusion criteria, treating intraparenchymatous neurocysticercosis with either albendazole or praziquantel compared to placebo or no treatment. In the two trials reporting clinical outcomes, treatment was not associated with a reduction in the risk of seizures, although numbers were small (RR 0.95, 95% CI 0.59-1.51). Four trials reported radiological outcomes, and cysticidal treatment was associated with a lower risk of cyst persistence of scans taken within six months of start of treatment (RR 0.83, 95% CI 0.70-0.99). Subsidiary analysis assuming different outcomes in patients lost to follow-up did not alter the findings of the main analysis. CONCLUSIONS: There is insufficient evidence to determine whether cysticidal therapy is of any clinical benefit to patients with neurocysticercosis. The review does not exclude the possibility that more patients remain seizure-free when treated with cysticidal drugs. Further testing through placebo-controlled trials is required. (+info)
Trichlorfon induces spindle disturbances in V79 cells and aneuploidy in male mouse germ cells.
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In order to assess the effects of trichlorfon on cell division and on aneuploidy induction, we conducted an in vitro assay for spindle disturbances using V79 cells and an in vivo assay for aneuploidy induction in meiosis of male mice using multicolour fluorescence in situ hybridization (FISH) with epididymal sperm. In the in vitro assay, the chemical caused a concentration-dependent increase in the incidence of initial and full c-mitoses in the dose range 40-120 microg/ml trichlorfon. The mitotic index (MI) was decreased between 40 and 100 microg/ml trichlorfon, whereas at 120 microg/ml the MI was back to the control level, coinciding with the dramatic increase in c-mitoses. The results confirm that trichlorfon is a potent spindle poison in V79 cells. In the in vivo multicolour FISH assay, administration of trichlorfon to male mice at single doses of 200, 300 and 405 mg/kg caused a dose-dependent increase of the frequencies of disomic sperm (0.068, 0.074 and 0.134%, respectively) compared with the corresponding controls (0.046, 0.042 and 0.056%, respectively). The prevalence of X-X-8 and Y-Y-8 sperm suggests that trichlorfon affected chromosome segregation predominantly during the second meiotic division. Diploid sperm were not induced by trichlorfon treatment, indicating that no meiotic block occurred. It is concluded that trichlorfon is a potent spindle poison in V79 cells and induces aneuploidy in mouse spermatocytes during meiosis. (+info)
Metrifonate decreases sI(AHP) in CA1 pyramidal neurons in vitro.
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Metrifonate, a cholinesterase inhibitor, has been shown to enhance learning in aging rabbits and rats, and to alleviate the cognitive deficits observed in Alzheimer's disease patients. We have previously determined that bath application of metrifonate reduces the spike frequency adaptation and postburst afterhyperpolarization (AHP) in rabbit CA1 pyramidal neurons in vitro using sharp electrode current-clamp recording. The postburst AHP and accommodation observed in current clamp are the result of four slow outward potassium currents (sI(AHP), I(AHP), I(M), and I(C)) and the hyperpolarization activated mixed cation current, I(h). We recorded from visually identified CA1 hippocampal pyramidal neurons in vitro using whole cell voltage-clamp technique to better isolate and characterize which component currents of the AHP are affected by metrifonate. We observed an age-related enhancement of the slow component of the AHP tail current (sI(AHP)), but not of the fast decaying component of the AHP tail current (I(AHP), I(M), and I(C)). Bath perfusion of metrifonate reduced sI(AHP) at concentrations that cause a reduction of the AHP and accommodation in current-clamp recordings, with no apparent reduction of I(AHP), I(M), and I(C). The functional consequences of metrifonate administration are apparently mediated solely through modulation of the sI(AHP). (+info)
Short- and long-term effect of acetylcholinesterase inhibition on the expression and metabolism of the amyloid precursor protein.
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We have investigated the acute and chronic effect of metrifonate (MTF) and dichlorvos (DDVP), respectively the prodrug and active acetylcholinesterase inhibitor, on the secretory processing of the amyloid precursor protein (APP) in SH-SY5Y neuroblastoma cells. We demonstrate that the acute treatment of SH-SY5Y cells with both compounds results in an increased secretion of the soluble fragment of APP (sAPPalpha) into the conditioned media of cells, with a pattern correlated to the level of acetycholinesterase inhibition. The regulation of APP processing in these conditions is mediated by an indirect cholinergic effect on muscarinic receptors, as demonstrated by inhibition with atropine. We have also followed APP expression and metabolism after long-term treatment with metrifonate. Treated cells showed reduced AChE activity after 24, 48 h and also following 7 days of repeated treatment, a time point at which increased AChE expression was detectable. At all time points sAPPalpha release was unaffected suggesting that enhanced sAPPalpha release by MTF is transitory, nevertheless the sensitivity of cholinergic receptors was unchanged, as indicated by the fact that cholinergic response can be elicited similarly in untreated and treated cells. APP gene expression was unaffected by long-term AChE inhibition suggesting that increased short-term sAPPalpha release does not elicit compensatory effects. (+info)
Galantamine is an allosterically potentiating ligand of neuronal nicotinic but not of muscarinic acetylcholine receptors.
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Galantamine (Reminyl), an approved treatment for Alzheimer's disease (AD), is a potent allosteric potentiating ligand (APL) of human alpha 3 beta 4, alpha 4 beta 2, and alpha 6 beta 4 nicotinic receptors (nAChRs), and of the chicken/mouse chimeric alpha 7/5-hydroxytryptamine3 receptor, as was shown by whole-cell patch-clamp studies of human embryonic kidney-293 cells stably expressing a single nAChR subtype. Galantamine potentiates agonist responses of the four nAChR subtypes studied in the same window of concentrations (i.e., 0.1-1 microM), which correlates with the cerebrospinal fluid concentration of the drug at the recommended daily dosage of 16 to 24 mg. At concentrations >10 microM, galantamine acts as an nAChR inhibitor. The other presently approved AD drugs, donepezil and rivastigmine, are devoid of the nicotinic APL action; at micromolar concentrations they also block nAChR activity. Using five CHO-SRE-Luci cell lines, each of them expressing a different human muscarinic receptor, and a reporter gene assay, we show that galantamine does not alter the activity of M1-M5 receptors, thereby confirming that galantamine modulates selectively the activity of nAChRs. These studies support our previous proposal that the therapeutic action of galantamine is mainly produced by its sensitizing action on nAChRs rather than by general cholinergic enhancement due to cholinesterase inhibition. Galantamine's APL action directly addresses the nicotinic deficit in AD. (+info)
Experimental study of the effect of a series of phosphoroorganic pesticides (Dipterex and Imidan) on embryogenesis.
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Experiments conducted on pregnant Wistar rats show that chlorophos (Dipterex) has embroyotoxic and teratogenic effects after oral introduction in a 80 mg/kg dose during a critical period of embryogenesis. Embryotoxic and teratogenic effects are absent during the introduction of 8 mg/kg of the pesticide. The oral introduction of phthalophos (Imidan) in a 30 mg/kg dose once on day 9 of pregnancy and the introduction of a 1.5 mg/kg dose daily throughout the course of pregnancy caused increased postimplantation mortality of embryos. A dose of 30 mg/kg of phthalophos on day 9 or day 13 of pregnancy causes developmental abnormalities, including hyponathia and hydrocephaly. A 0.06 mg/kg phthalophos dose does not affect the course of embryogenesis in white rats. Thus the organophosphate pesticides Dipterex and Imidan exhibit embryotoxic and teratogenic effects at doses which significantly exceed the acutal amounts of the pesticide that can enter the human organism. (+info)
Cloning, mutagenesis, and expression of the acetylcholinesterase gene from a strain of Musca domestica; the change from a drug-resistant to a sensitive enzyme.
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Insect acetylcholinesterase (AChE) is known to be a primary target of organophosphorus and carbamate insecticides. However chronic exposure to these chemicals has led to resistance to applied insecticides, due usually to mutation of the AChE gene. Analysis of the AChE gene (hm) of Musca domestica (the housefly), which is cloned in this report, reveals the relationship between mutation and insecticide resistance. The 2,076 bp hm encodes a mature protein of 612 amino acids (67 kDa), and an 80 residue signal peptide. Unlike the enzyme of 'sensitive' strains, the AChE used in this study was resistant to the organophosphorus insecticide, trichlorphon. DNA sequencing showed that this AChE is identical to that of the sensitive strains with the exception of three amino acids Met-82, Ala-262, and Tyr-327. Site-directed mutagenesis of the Ala-262 and Tyr-327 residues largely restored sensitivity to the insecticide, suggesting that these two residues are the key structural elements controlling sensitivity. In addition to these residues, Glu-234 and Ala-236 in the conserved sequence FGESAG are thought to play a role in modulating sensitivity to organophosphorus insecticides. (+info)