Antipoliovirus activity and mechanism of action of 3-methylthio-5-phenyl-4-isothiazolecarbonitrile

Our previous studies described the synthesis and the antiviral activity of 3,4,5-trisubstituted isothiazole derivatives that were found to be particularly effective against enteroviruses. Compound 3-methylthio-5-phenyl-4-isothiazolecarbonitrile (IS-2) exhibited an interesting anti-poliovirus activity with a high selectivity index. In the present study we investigated the mechanism of action of this compound. Studies on the time of IS-2 addition to poliovirus type 1 infected cells suggested that the compound may inhibit some early process of viral replication. In order to determine its mechanism of action, we evaluated the rate of attachment and internalization of purified [³H]uridine-labeled poliovirus to HEp-2 cells in the presence or absence of IS-2. No effect on poliovirus adsorption and internalization to host cells was detected. We also investigated the influence of the compound on virus uncoating using labeled poliovirus and measuring the radioactivity of oligoribonucleotides formed from viral RNA susceptible to ribonuclease. These experiments demonstrated that poliovirus uncoating is influenced by IS-2 action.

Bivalent phenethylamines as novel dopamine transporter inhibitors: evidence for multiple substrate-binding sites in a single transporter

Bivalent ligands--compounds incorporating two receptor-interacting moieties linked by a flexible chain--often exhibit profoundly enhanced binding affinity compared with their monovalent components, implying concurrent binding to multiple sites on the target protein. It is generally assumed that neurotransmitter sodium symporter (NSS) proteins, such as the dopamine transporter (DAT), contain a single domain responsible for recognition of substrate molecules. In this report, we show that molecules possessing two substrate-like phenylalkylamine moieties linked by a progressively longer aliphatic spacer act as progressively more potent DAT inhibitors (rather than substrates). One compound bearing two dopamine (DA)-like pharmacophoric 'heads' separated by an 8-carbon linker achieved an 82-fold gain in inhibition of [(3)H] 2beta-carbomethoxy-3beta-(4-fluorophenyl)-tropane (CFT) binding compared with DA itself; bivalent compounds with a 6-carbon linker and heterologous combinations of DA-, amphetamine- and beta-phenethylamine-like heads all resulted in considerable and comparable gains in DAT affinity. A series of short-chain bivalent-like compounds with a single N-linkage was also identified, the most potent of which displayed a 74-fold gain in binding affinity. Computational modelling of the DAT protein and docking of the two most potent bivalent (-like) ligands suggested simultaneous occupancy of two discrete substrate-binding domains. Assays with the DAT mutants W84L and D313N--previously employed by our laboratory to probe conformation-specific binding of different structural classes of DAT inhibitors--indicated a bias of the bivalent ligands for inward-facing transporters. Our results strongly indicate the existence of multiple DAT substrate-interaction sites, implying that it is possible to design novel types of DAT inhibitors based upon the 'multivalent ligand' strategy.

Lactacidosis modulates glutathione metabolism and oxidative glutamate toxicity

Lactate and acidosis increase infarct size in humans and in animal models of cerebral ischemia but the mechanisms by which they exert their neurotoxic effects are poorly understood. Oxidative glutamate toxicity is a form of nerve cell death, wherein glutamate inhibits cystine uptake via the cystine/glutamate antiporter system leading to glutathione depletion, accumulation of reactive oxygen species and, ultimately, programmed cell death. Using the hippocampal cell line, HT22, we show that lactate and acidosis exacerbate oxidative glutamate toxicity and further decrease glutathione levels. Acidosis but not lactate inhibits system , whereas both acidosis and lactate inhibit the enzymatic steps of glutathione synthesis downstream of cystine uptake. In contrast, when glutathione synthesis is completely inhibited by cystine-free medium, acidosis partially protects against glutathione depletion and cell death. Both effects of acidosis are also present in primary neuronal and astrocyte cultures. Furthermore, we show that some neuroprotective compounds are much less effective in the presence of lactacidosis. Our findings indicate that lactacidosis modulates glutathione metabolism and neuronal cell death. Furthermore, lactacidosis may interfere with the action of some neuroprotective drugs rendering these less likely to be therapeutically effective in cerebral ischemia.

Gene regulation of alpha4beta2 nicotinic receptors: microarray analysis of nicotine-induced receptor up-regulation and anti-inflammatory effects

alpha4beta2 Nicotinic acetylcholine receptors play an important role in the reward pathways for nicotine. We investigated whether receptor up-regulation of alpha4beta2 nicotinic acetylcholine receptors involves expression changes for non-receptor genes. In a microarray analysis, 10 muM nicotine altered expression of 41 genes at 0.25, 1, 8 and 24 h in halpha4beta2 SH-EP1 cells. The maximum number of gene changes occurred at 8 h, around the initial increase in (3)[H]-cytisine binding. Quantitative RT-PCR corroborated gene induction of endoplasmic reticulum proteins CRELD2, PDIA6, and HERPUD1, and suppression of the pro-inflammatory cytokines IL-1beta and IL-6. Nicotine suppresses IL-1beta and IL-6 expression at least in part by inhibiting NFkappaB activation. Antagonists dihydro-beta-erythroidine and mecamylamine blocked these nicotine-induced changes showing that receptor activation is required. Antagonists alone or in combination with nicotine suppressed CRELD2 message while increasing alpha4beta2 binding. Additionally, small interfering RNA knockdown of CRELD2 increased basal alpha4beta2 receptor expression, and antagonists decreased CRELD2 expression even in the absence of alpha4beta2 receptors. These data suggest that endoplasmic reticulum proteins such as CRELD2 can regulate alpha4beta2 expression, and may explain antagonist actions in nicotine-induced receptor up-regulation. Further, the unexpected finding that nicotine suppresses inflammatory cytokines suggests that nicotinic alpha4beta2 receptor activation promotes anti-inflammatory effects similar to alpha7 receptor activation.

Overexpression of the Arabidopsis anaphase promoting complex subunit CDC27a increases growth rate and organ size

The Anaphase Promoting Complex (APC) controls CDK activity by targeting the ubiquitin-dependent proteolysis of S-phase and mitosis-promoting cyclins. Here, we report that the ectopic expression of the Arabidopsis CDC27a, an APC subunit, accelerates plant growth and results in plants with increased biomass production. CDC27a overexpression was associated to apical meristem restructuration, protoplasts with higher (3)H-thimidine incorporation and altered cell-cycle marker expression. Total protein extracts immunoprecipitated with a CDC27a antibody showed ubiquitin ligase activity, indicating that the Arabidopsis CDC27a gets incorporated into APC complexes. These results indicate a role of AtCDC27a in regulation of plant growth and raise the possibility that the activity of the APC and the rates of plant cell division could be regulated by the concentration of the CDC27a subunit.

The effect of histone deacetylase inhibitor trichostatin A (TSA) on the incorporation of 32P (Pi) and 3H-palmitic acid into the phospholipids of Tetrahymena

Histone deacetylases (HDACs) are able to control also the acetylation of tubulin. In the present experiments the effect of trichostatin A (TSA), a HDAC inhibitor was studied on the incorporation of 3H-palmitic acid and 32P to the phospholipids (PI, PIP, PS, PC, PA, PE) of Tetrahymena pyriformis, considering earlier observations on the microtubular system's influence on signalling in this unicellular eukaryote. Treatment with 1, 5, or 10 microM TSA was studied. The incorporation of hydrophobic tail component, palmitic acid was inhibited in a concentration dependent manner into all the phospholipids, except for PA, where the incorporation was increased. 32P incorporation was also inhibited. The possible relation between the microtubular system and signalling is discussed.

Antagonism by haloperidol and its metabolites of mechanical hypersensitivity induced by intraplantar capsaicin in mice: role of sigma-1 receptors

RATIONALE

We evaluated the effects of haloperidol and its metabolites on capsaicin-induced mechanical hypersensitivity (allodynia) and on nociceptive pain induced by punctate mechanical stimuli in mice.

RESULTS

Subcutaneous administration of haloperidol or its metabolites I or II (reduced haloperidol) dose-dependently reversed capsaicin-induced (1 microg, intraplantar) mechanical hypersensitivity of the hind paw (stimulated with a nonpainful, 0.5-g force, punctate stimulus). The order of potency of these drugs to induce antiallodynic effects was the order of their affinity for brain sigma-1 (sigma(1)) receptor ([(3)H](+)-pentazocine-labeled). Antiallodynic activity of haloperidol and its metabolites was dose-dependently prevented by the selective sigma(1) receptor agonist PRE-084, but not by naloxone. These results suggest the involvement of sigma(1) receptors, but discard any role of the endogenous opioid system, on the antiallodynic effects. Dopamine receptor antagonism also appears unlikely to be involved in these effects, since the D(2)/D(3) receptor antagonist (-)-sulpiride, which had no affinity for sigma(1) receptors, showed no antiallodynic effect. None of these drugs modified hind-paw withdrawal after a painful (4 g force) punctate mechanical stimulus in noncapsaicin-sensitized animals. As expected, the control drug gabapentin showed antiallodynic but not antinociceptive activity, whereas clonidine exhibited both activities and rofecoxib, used as negative control, showed neither.

CONCLUSION

These results show that haloperidol and its metabolites I and II produce antiallodynic but not antinociceptive effects against punctate mechanical stimuli and suggest that their antiallodynic effect may be due to blockade of sigma(1) receptors but not to dopamine receptor antagonism.

Dopaminergic hypofunctions and prepulse inhibition deficits in mice lacking midkine

Midkine is a 13-kDa retinoic acid-induced heparin-binding growth factor involved in various biological phenomena such as cell migration, neurogenesis, and tissue repair. We previously demonstrated that midkine-deficient (Mdk(-/-)) mice exhibited a delayed hippocampal development with impaired working memory and increased anxiety only at the age of 4 weeks. To assess whether midkine gene could play important roles in development and maintenance of central nervous system, we investigated biochemical and behavioral parameters in dopamine and glutamate neurotransmission of Mdk(-/-) mice. The Mdk(-/-) mice exhibited a hypodopaminergic state (i.e., decreased levels of dopamine and its receptors in the striatum) with no alterations of glutamatergic system (i.e., normal level of glutamate, glutamine, glycine, d-serine, l-serine, and NMDA receptors in the frontal cortex and hippocampus). We also found prepulse inhibition deficits reversed by clozapine and haloperidol in the Mdk(-/-) mice. Our results suggested that midkine deficiency may be related to neurochemical and behavioral dysfunctions in dopaminergic system.

Severity of atypical absence phenotype in GABAB transgenic mice is subunit specific

Overexpression of GABA(B)R1a receptors in mice (R1a(+)) results in an atypical absence seizure phenotype characterized by 3- to 6-Hz slow spike-and-wave discharges (SSWDs), reduced synaptic plasticity, and cognitive impairment. Here we tested the hypothesis that increased R1 expression causes atypical absence epilepsy and is not subunit specific. GABA(B)R1b receptors were overexpressed in mouse forebrain (R1b(+)) and confirmed by immunoblot and (3)H-CGP54626A autoradiography. The R1b(+) mice showed a reduction in hippocampal long-term potentiation and GABA(A) receptor-mediated inhibitory postsynaptic currents. R1b(+) mice manifested an electrographic, pharmacological, and behavioral phenotype consistent with atypical absence seizures, though less robust than R1a(+) in terms of SSWD duration and severity of cognitive impairment. These results suggest that abnormal GABA(B)R1b function plays a lesser role in the development of atypical absence epilepsy.

The human body retention time of environmental organically bound tritium

Tritium in the UK environment causes low radiation doses to the public, but uncertainty exists in the dose coefficient for the organically bound component of tritium (OBT). This can affect the assessment of effective doses to representative persons. Contributing to that uncertainty is poor knowledge of the body retention time of OBT and how this varies for different OBT compounds in food. This study was undertaken to measure the retention time of tritium by volunteers after eating sole from Cardiff Bay, which may contain OBT from discharges from the GE Healthcare Ltd plant. Five volunteers provided samples of excreta over periods up to 150 days after intake. The results, which are presented in raw form to allow independent analysis, suggest retention of total tritium with body half-times ranging from 4 to 11 days, with no evidence (subject to experimental noise) of a significant contribution due to retention with a longer half-time. This range covers the half-time of 10 days used by the ICRP for tritiated water. The short timescale could be due to rapid hydrolysis in body tissues of the particular form of OBT used in this study. Implications for the dose coefficient for OBT are that the use of the ICRP value of 4.2 x 10(-11) Sv Bq(-1) may be cautious in this specific situation. These observations on dose coefficients are separate from any implications of recent discussion on whether the tritium radiation weighting factor should be increased from 1 to 2.

The dynamic transfer of 3H and 14C in mammals: a proposed generic model

Associated with the present debate regarding the potential revival of nuclear energy there is an increased interest in assessing the radiological risk to the public and also the environment. Tritium and (14)C are key radionuclides of interest in many circumstances (e.g. heavy water reactors, waste storage and fusion reactors). Because the stable analogues of these two radionuclides are integral to most biological compounds, their modelling should follow general principles from life sciences. In this paper, a model of the dynamics of (14)C and (3)H in mammals is proposed on the basis of metabolic understanding and of, as far as possible, readily available data (e.g. for organ composition and metabolism). The model is described together with validation tests (without calibration) for a range of farm animals. Despite simplifications, the model tests are encouraging for a range of animal types and products (tissues and milk), and further improvements are suggested.

Iron-loaded cardiac myocytes stimulate cardiac myofibroblast DNA synthesis

Cardiac fibrosis in iron overload disorders may arise from activation of the interstitial fibroblast. However, the cardiac myocyte, and not the fibroblast, is the main target for iron deposition. We hypothesized that fibroblasts respond to the presence of iron-loaded myocytes with increased proliferative capacity. Cardiac fibroblasts were either co-cultured with myocytes on porous filters or treated with medium conditioned by growth of myocyte cultures. In both circumstances myocytes suppressed [(3)H]thymidine incorporation by fibroblasts over 24 h, compared to stimulation of quiescent fibroblasts with fresh, unconditioned medium. However, when the myocytes were preloaded with iron, the suppressive effect was lost and DNA synthesis was restored to levels seen in unconditioned medium. This effect was not due to early events in cell cycle entry; activation of Erk at 15 min and expression of c-fos mRNA at 30 min were similar in media from control and iron-loaded myocytes. Early markers of progression of G1, namely cyclin D and phosphoretinoblastoma protein, were not significantly different in fibroblasts treated with either conditioned medium. However, cyclin E expression, a marker of the G1/S transition, was significantly increased by conditioned medium from the iron-loaded cells, compared to control-conditioned medium. We conclude that myocytes can suppress proliferation of fibroblasts by cumulative effects on late G1 events leading to DNA synthesis, and these effects are diminished with myocyte iron accumulation.

Regional differences in the vulnerability of substantia nigra dopaminergic neurons in weaver mice

Vulnerability of midbrain dopaminergic (DA) neurons in the weaver mouse was studied at postnatal (P) days 8 and 90, in chosen coronal levels throughout the anteroposterior (AP) extent of the substantia nigra pars compacta (SNc). Wild-type (+/+) and homozygous weaver (wv/wv) mice used were the offspring of pregnant dams injected in several cases with tritiated thymidine on embryonic days 11-15. DA neurons were identified for their tyrosine hydroxylase immunoreactivity. Data reveal that at P8, the frequency of both +/+ and wv/wv late-generated DA cells increases from rostral to caudal SNc. No apparent DA-cell loss was observed at P8 in the mutant genotype, irrespective of the AP level considered. However, throughout the AP, there was a significant reduction in the number of these neurons at any level in 90-day-old weavers. Comparison of P8 and P90 +/+ SNc suggests that cell death is not a major aspect in the developmental regulation of normal DA neurons, although numerical cell depletion in the postnatal development of weaver SNc probably results from the amplification of a basal cell-death process, which affected all the coronal levels studied.

Specific inhibition of kynurenate synthesis enhances extracellular dopamine levels in the rodent striatum

Fluctuations in the endogenous levels of kynurenic acid (KYNA), a potent alpha7 nicotinic and NMDA receptor antagonist, affect extracellular dopamine (DA) concentrations in the rat brain. Moreover, reductions in KYNA levels increase the vulnerability of striatal neurons to NMDA receptor-mediated excitotoxic insults. We now assessed the role of a key KYNA-synthesizing enzyme, kynurenine aminotransferase II (KAT II), in these processes in the rodent striatum, using KAT II KO mice-which have reduced KYNA levels-and the selective KAT II inhibitor (S)-4-(ethylsulfonyl)benzoylalanine (S-ESBA) as tools. S-ESBA (applied by reverse dialysis) raised extracellular DA levels in the striatum of KYNA-deficient mice threefold and caused a much larger, 15-fold increase in wild-type mice. In the rat striatum, S-ESBA produced a 35% reduction in extracellular KYNA, which was accompanied by a 270% increase in extracellular DA. The latter effect was abolished by co-infusion of 100 nM KYNA. Intrastriatal S-ESBA pre-treatment augmented the size of a striatal quinolinate lesion by 370%, and this potentiation was prevented by co-infusion of KYNA. In separate animals, acute inhibition of KAT II reduced the de novo synthesis of KYNA during an early excitotoxic insult without enhancing the formation of the related neurotoxic metabolites 3-hydroxykynurenine and quinolinate. Taken together, these results provide further support for the concept that KAT II is a critical determinant of functionally relevant KYNA fluctuations in the rodent striatum.

Glyceroneogenesis is the dominant pathway for triglyceride glycerol synthesis in vivo in the rat

Triglyceride synthesis in mammalian tissues requires glycerol 3-phosphate as the source of triglyceride glycerol. In this study the relative contribution of glyceroneogenesis and glycolysis to triglyceride glycerol synthesis was quantified in vivo in adipose tissue, skeletal muscle, and liver of the rat in response to a chow diet (controls), 48-h fast, and lipogenic (high sucrose) diet. The rate of glyceroneogenesis was quantified using the tritium ([(3)H(2)]O) labeling of body water, and the contribution of glucose, via glycolysis, was determined using a [U-(14)C]glucose tracer. In epididymal and mesenteric adipose tissue of control rats, glyceroneogenesis accounted for approximately 90% of triglyceride glycerol synthesis. Fasting for 48 h did not alter glyceroneogenesis in adipose tissue, whereas the contribution of glucose was negligible. In response to sucrose feeding, the synthesis of triglyceride glycerol via both glyceroneogenesis and glycolysis nearly doubled (versus controls); however, glyceroneogenesis remained quantitatively higher as compared with the contribution of glucose. Enhancement of triglyceride-fatty acid cycling by epinephrine infusion resulted in a higher rate of glyceroneogenesis in adipose tissue, as compared with controls, whereas the contribution of glucose via glycolysis was not measurable. Glyceroneogenesis provided the majority of triglyceride glycerol in the gastrocnemius and soleus. In the liver the fractional contribution of glyceroneogenesis remained constant (approximately 60%) under all conditions and was higher than that of glucose. Thus, glyceroneogenesis, in contrast to glucose, via glycolysis, is quantitatively the predominant source of triglyceride glycerol in adipose tissue, skeletal muscle, and liver of the rat during fasting and high sucrose feeding.

Functional mutations in mouse norepinephrine transporter reduce sensitivity to cocaine inhibition

The transporters of dopamine, norepinephrine and serotonin are molecular targets of cocaine, amphetamine, and therapeutic antidepressants. The residues involved in binding these drugs are unknown. We have performed several rounds of random and site-directed mutagenesis in the mouse norepinephrine transporter and screened for mutants with altered sensitivity to cocaine inhibition of substrate uptake. We have identified a triple mutation that retains close to wild-type transport function but displays a 37-fold decrease in cocaine sensitivity and 24-fold decrease in desipramine sensitivity. In contrast, the mutant's sensitivities to amphetamine, methamphetamine, and methylphenidate are only slightly changed. Our data reveal critical residues contributing to the potent uptake inhibitions by these important drugs. Furthermore, this drug-resistant triple mutant can be used to generate a unique knock-in mouse line to study the role of norepinephrine transporter in the addictive effects of cocaine and the therapeutic effects of desipramine.

Antidepressants modulate the in vitro inhibitory effects of propofol and ketamine on norepinephrine and serotonin transporter function

Norepinephrine transporter (NET) and serotonin transporter (SERT) proteins regulate norepinephrine (NE) and serotonin via their reuptake function and are targets of antidepressants action. Several intravenous (IV) anesthetics have been shown to inhibit NET and SERT. The interactions between antidepressants and anesthetics on transporter function, however, are not well studied. We examined the effect of different IV anesthetics on NET and SERT function, with and without chronic antidepressant pretreatment, by measuring NE or 5-hydroxytryptamine (5-HT) uptake and determined NET and SERT protein expression via immunoblotting. Both ketamine and propofol inhibited NET dose-dependently (propofol 10(-4)M -22%+/-5.6%, and propofol 10(-3)M -35%+/-5.7%; ketamine 10(-4)M -23%+/-4.1% and ketamine 10(-3)M -73%+/-2.9%); and SERT (propofol 10(-4)M -11%+/-4.3% and propofol 10(-3)M -23%+/-3.8%; ketamine 10(-4)M -29%+/-5.2% and ketamine 10(-3)M -63%+/-6.4%). Etomidate and thiopental had no effect on either NET or SERT function. Desipramine and fluoxetine, specific inhibitors of NET and SERT, respectively, both enhanced the inhibitory effects of propofol but reduced the inhibitory effects of ketamine on NET and SERT functions. IV anesthetics treatment did not change transporter protein expression in the presence of its respective inhibitor. Our results demonstrate that both ketamine and propofol inhibited SERT and NET function, but the inhibition was differentially modulated by antidepressants. Therefore, in the clinical context, this would suggest that patients receiving antidepressant treatments might have altered response to IV anesthetics in an agent-specific manner.

Presynaptic mGlu1 and mGlu5 autoreceptors facilitate glutamate exocytosis from mouse cortical nerve endings

The effects of mGlu1 and mGlu5 receptor activation on the depolarization-evoked release of [3H]d-aspartate ([3H]D-ASP) from mouse cortical synaptosomes were investigated. The mGlu1/5 receptor agonist 3,5-DHPG (0.1-100microM) potentiated the K+(12mM)-evoked [3H]D-ASP overflow. The potentiation occurred in a concentration-dependent manner showing a biphasic pattern. The agonist potentiated [3H]D-ASP exocytosis when applied at 0.3microM; the efficacy of 3,5-DHPG then rapidly declined and reappeared at 30-100microM. The fall of efficacy of agonist at intermediate concentration may be consistent with 3,5-DHPG-induced receptor desensitization. Facilitation of [3H]D-ASP exocytosis caused by 0.3microM 3,5-DHPG was prevented by the selective mGlu5 receptor antagonist MPEP, but was insensitive to the selective mGlu1 receptor antagonist CPCCOEt. In contrast, CPCCOEt prevented the potentiation by 50microM 3,5-DHPG, while MPEP had minimal effect. Unexpectedly, LY 367385 antagonized both the 3,5-DHPG-induced effects. A total of 0.3microM 3,5-DHPG failed to facilitate the K+-evoked [3H]D-ASP overflow from mGlu5 receptor knockout (mGlu5-/-) cortical synaptosomes, but not from nerve terminals prepared from the cortex of animals lacking the mGlu1 receptors, the crv4/crv4 mice. On the contrary, 50microM 3,5-DHPG failed to affect the [3H]D-ASP exocytosis from cortical synaptosomes obtained from crv4/crv4 and mGlu5-/-mice. Western blot analyses in subsynaptic fractions support the existence of both mGlu1 and mGlu5 autoreceptors located presynaptically, while immunocytochemistry revealed their presence at glutamatergic terminals. We propose that mGlu1 and mGlu5 autoreceptors exist on mouse glutamatergic cortical terminals; mGlu5 receptors may represent the "high affinity" binding sites for 3,5-DHPG, while mGlu1 autoreceptors represent the "low affinity" binding sites.

Disruption of dopamine transport by DDT and its metabolites

Epidemiological studies suggest a link between pesticide exposure and an increased risk of developing Parkinson's disease (PD). Although studies have been unable to clearly identify specific pesticides that contribute to PD, a few human studies have reported higher levels of the organochlorine pesticides dieldrin and DDE (a metabolite of DDT) in post-mortem PD brains. Previously, we found that exposure of mice to dieldrin caused perturbations in the nigrostriatal dopamine system consistent with those seen in PD. Given the concern over the environmental persistence and reintroduction of DDT for the control of malaria-carrying mosquitoes and other pests, we sought to determine whether DDT and its two major metabolites, DDD and DDE, could damage the dopamine system. In vitro analyses in mouse synaptosomes and vesicles demonstrated that DDT and its metabolites inhibit the plasma membrane dopamine transporter (DAT) and the vesicular monoamine transporter (VMAT2). However, exposure of mice to either DDT or DDE failed to show evidence of nigrostriatal damage or behavioral abnormalities in any of the measures examined. Thus, we report that in vitro effects of DDT and its metabolites on components of the dopamine system do not translate into neurotoxicological outcomes in orally exposed mice and DDT appears to have less dopamine toxicity when compared to dieldrin. These data suggest elevated DDE levels in PD patients may represent a measure of general pesticide exposure and that other pesticides may be responsible for the association between pesticide exposure and PD.

Effects of deposit-feeding macrofauna on benthic bacteria, viruses, and protozoa in a silty freshwater sediment

In microcosm experiments, we simultaneously tested the effects of increased numbers of deposit-feeding macrofauna (chironomids, oligochaetes and cladocerans) on the standing stock, activities and interactions of heterotrophic bacteria, viruses, and bacterivorous protozoa (heterotrophic nanoflagellates and ciliates) in the aerobic layer of a silty littoral freshwater sediment. On average, bacterial secondary production was stimulated between 11 and 29% by all macrofaunal groups compared to control experiments without macrofauna addition. Bacterial standing stock increased significantly by 8 and 13% in case of chironomids and cladocerans, respectively. Oligochaetes and chironomids produced significant negative effects on viral abundance while the results with cladocerans were inconsistent. The addition of oligochaetes and chironomids resulted in a significant decrease by on average 68 and 32% of viral decay rates, respectively, used as a measure of viral production. The calculated contribution of virus-induced lysis to benthic bacterial mortality was low, with 2.8 to 11.8% of bacterial secondary production, and decreased by 39 to 81% after the addition of macrofauna compared to the control. The abundances of heterotrophic nanoflagellates were significantly reduced by 20% by all tested macrofauna groups, while ciliates showed inconsistent results. The importance of heterotrophic nanoflagellate grazing on benthic bacteria was very low (<1% of bacterial secondary production) and was further reduced by elevated numbers of macrofauna. Thus, the selected deposit feeding macrofauna groups seem to have several direct and indirect and partly antagonistic effects on the benthic bacterial compartment through the enhancement of bacterial production and the reduction of virus-induced cell lysis and protozoan grazing.

NMDA receptor blockade augmented nicotine-evoked dopamine release from rat prefrontal cortex slices

Nicotine evokes dopamine release through activation of nicotinic acetylcholine receptors, and tobacco cigarette smoking is more prevalent among individuals diagnosed with schizophrenia. Blockade of ionotropic glutamate (NMDA) receptors can induce changes in central dopamine and glutamate circuits, which models the symptoms of schizophrenia. The effect of the NMDA receptor antagonist, ketamine, on the effect of nicotine in rat prefrontal cortex was examined using a slice superfusion assay in which cortical slices were preloaded with [(3)H] dopamine. A wide range of ketamine concentrations (0.1-300 microM) did not evoke [(3)H] overflow from slices, indicating that NMDA receptor blockade did not induce dopamine release. Ketamine, at concentrations that model the symptoms of schizophrenia (1-10 microM), augmented the effect of nicotine (1-100 microM) to evoke [(3)H] overflow from slices and decreased the threshold nicotine concentration to evoke [(3)H] overflow. This indicates that NMDA receptor blockade increased the potency and efficacy of nicotine to evoke dopamine release from prefrontal cortex slices, suggesting that ketamine induced hypersensitivity to nicotine. The present results support a role for nicotinic acetylcholine receptors in the pathophysiology and treatment of schizophrenia.

Removing TRPV1-expressing primary afferent neurons potentiates the spinal analgesic effect of delta-opioid agonists on mechano-nociception

Most delta-opioid receptors are located on the presynaptic terminals of primary afferent neurons in the spinal cord. However, their presence in different phenotypes of primary afferent neurons and their contribution to the analgesic effect of delta-opioid agonists are not fully known. Resiniferatoxin (RTX) is an ultra-potent transient receptor potential vanilloid type 1 channel (TRPV1) agonist and can selectively remove TRPV1-expressing primary afferent neurons. In this study, we determined the role of delta-opioid receptors expressed on TRPV1 sensory neurons in the antinociceptive effect of the delta-opioid receptor agonists [D-Pen(2),D-Pen(5)]-enkephalin and [D-Ala(2),Glu(4)]-deltorphin. Nociception was measured by testing the mechanical withdrawal threshold in the hindpaw of rats. Changes in the delta-opioid receptors were assessed using immunocytochemistry and the [(3)H]-naltrindole radioligand binding. In RTX-treated rats, the delta-opioid receptor on TRPV1-immunoreactive dorsal root ganglion neurons and afferent terminals in the spinal cord was diminished. RTX treatment also significantly reduced the maximal specific binding sites (31%) of the delta-opioid receptors in the dorsal spinal cord. Interestingly, intrathecal injection of [D-Pen(2),d-Pen(5)]-enkephalin or [D-Ala(2),Glu(4)]-deltorphin produced a large and prolonged increase in the nociceptive threshold in RTX-treated rats. These findings indicate that loss of TRPV1-expressing afferent neurons leads to a substantial reduction in presynaptic delta-opioid receptors in the spinal dorsal horn. However, the effect of delta-opioid agonists on mechano-nociception is paradoxically potentiated in the absence of TRPV1-expressing sensory neurons. This information is important to our understanding of the cellular sites and mechanisms underlying the spinal analgesic effect of delta-opioid agonists.

The potential use of methotrexate in the treatment of falciparum malaria: in vitro assays against sensitive and multidrug-resistant falciparum strains

The anti-malarial activity of the anti-cancer drug methotrexate against chloroquine-sensitive T9-96 and the multidrug-resistant K1 strains of Plasmodium falciparum was assessed in vitro. Mean IC50 values of 0.32 +/- 0.05 nM and 48.02 +/- 4.40 nM were obtained for T9-96 and K1, respectively, indicating methotrexate's high potency against both sensitive and resistant P. falciparum strains in vitro. Our results suggest that methotrexate is potentially effective against falciparum malaria in short-term, low-dose regimens, minimizing the risk of toxicity. This, along with the practical advantages of methotrexate, warrants the clinical investigation of methotrexate in human cases of falciparum malaria.

Role of liver and plasma lipoproteins in selective transport of n-3 fatty acids to tissues: a comparative study of 14C-DHA and 3H-oleic acid tracers

We conducted a study aimed at a direct comparison of the plasma dynamics and uptake of docosahexaenoic (DHA) and oleic (OA) fatty acids by various organs. 14C-DHA and 3H-OA were intravenously co-injected into mice. At 5 min after injection, more than 40% of the 14C-DHA, but less than 20% of the 3H-OA, labels was associated with the liver. Heart uptake of 14C-DHA was three to four times greater compared to the 3H-OA label. Brain incorporation of 14C-DHA slowly rose to 0.7% at 24 h, but it remained at the 1-1.5% level for 3H-OA. Total 14C activity in plasma reached 2% of the injected dose at 20 min and leveled off at 0.5% after 1.5 h. Fifteen percent of 14C-DHA plasma activity at 30 min was associated with non-esterified fatty acids, whereas about 85% was recovered in triglycerides in very low-density lipoprotein (VLDL) and LDL fractions. Only 30% of 3H-OA derived activity was found in the VLDL fraction at 30 min. All 3H activity in plasma at later time points was in catabolite fractions. These findings demonstrate that liver plays an important role in the initial selectivity for DHA. It is likely that DHA is specifically taken up by liver, esterified, loaded into lipoproteins, and then delivered to brain, heart, and other target tissues.