The melatonin analog 5-MCA-NAT increases endogenous dopamine levels by binding NRH:quinone reductase enzyme in the developing chick retina

NRH:quinone reductase (QR2) is present in the retinas of embryonic and post-hatched (PH) chicks. 5-Methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT) is a QR2 ligand that increases cAMP levels in developing retinas, but it does not affect cAMP levels in CHO-QR2 cells. The dopamine quinone reductase activity of QR2 retrieves dopamine, which increases cAMP levels in developing retinas. The objective of the present study was to investigate whether 5-MCA-NAT increases endogenous dopamine levels in retinas from chick embryos and post-hatched chicks. Endogenous dopamine was measured by enzyme-linked immunosorbent assay (ELISA). 5-MCA-NAT increased retinal endogenous dopamine levels at all developmental stages studied and in PH chicks (−log EC50 = 11.62 ± 0.34 M). This effect was inhibited by non-selective antagonists of receptors and melatonin binding sites N-acetyl-2-benzyltryptamine (luzindole, 5 μM), but it was not inhibited by the Mel1b melatonin receptor antagonist 4-phenyl-2-propionamidotetralin (4-P-PDOT, 10 nM). The QR2 cosubstrate, N-methyl-dihydronicotinamide (NMH) (−log EC50 = 6.74 ± 0.26 M), increased endogenous dopamine levels in controls and in retinas stimulated with 5-MCA-NAT (3 nM). The QR2 inhibitor benzo[e]pyrene inhibited endogenous dopamine levels in both control (−log IC50 = 7.4 ± 0.28 M) and NMH-stimulated (at 100 nM and 1 μM benzo[e]pyrene concentrations) retinas. Theoretical studies using Molegro Virtual Docking software corroborated these experimental results. We conclude that 5-MCA-NAT increases the level of endogenous dopamine via QR2. We suggest that this enzyme triggers double reduction of the dopamine quinone, recovering dopamine in retinal development.     

Antioxidant intervention attenuates oxidative stress in children and teenagers with Down syndrome

We previously demonstrated that systemic oxidative stress is present in Down syndrome (DS) patients. In the present study we investigated the antioxidant status in the peripheral blood of DS children and teenagers comparing such status before and after an antioxidant supplementation. Oxidative stress biomarkers were evaluated in the blood of DS patients (n = 21) before and after a daily antioxidant intervention (vitamin E 400 mg, C 500 mg) during 6 months. Healthy children (n = 18) without DS were recruited as control group. The activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST), gamma-glutamyltransferase (GGT), glucose-6-phosphate dehydrogenase (G6PD) and myeloperoxidase (MPO), as well as the contents of reduced glutathione (GSH), uric acid, vitamin E, thiobarbituric acid reactive substances (TBARS), and protein carbonyls (PC) were measured. Before the antioxidant therapy, DS patients presented decreased GST activity and GSH depletion; elevated SOD, CAT, GR, GGT and MPO activities; increased uric acid levels; while GPx and G6PD activities as well as vitamin E and TBARS levels were unaltered. After the antioxidant supplementation, SOD, CAT, GPx, GR, GGT and MPO activities were downregulated, while TBARS contents were strongly decreased in DS. Also, the antioxidant therapy did not change G6PD and GST activities as well as uric acid and PC levels, while it significantly increased GSH and vitamin E levels in DS patients. Our results clearly demonstrate that the antioxidant intervention with vitamins E and C attenuated the systemic oxidative damage present in DS patients.     

Enteral nutrition feeding alters antioxidant activity in unstimulated whole saliva composition of patients with neurological disorders

Patients with neurological disorders have an increased risk of oral and systemic diseases due to compromised oral hygiene. If patients lose the ability to swallow and chew food as a result of their disorder, enteral nutrition is often utilized. However, this type of feeding may modify salivary antioxidant defenses, resulting in increased oxidative damage and the emergence of various diseases. The aim of this study was to evaluate the effects of enteral nutrition on biochemical parameters in the unstimulated whole saliva composition of patients with neurological disorders. For this, enzymatic (superoxide dismutase – SOD; glutathione peroxidase – GPx) and non-enzymatic (uric acid; ferric ion reducing antioxidant power – FRAP) antioxidant activity, as well as a marker for oxidative damage (thiobarbituric acid reactive substances – TBARS) were analyzed. Unstimulated whole saliva was collected from 12 patients with neurological disorders and tube-feeding (tube-fed group – TFG), 15 patients with neurological disorders and normal feeding via the mouth (non-tube-fed group – NTFG), and 12 volunteers without neurological disorders (control group – CG). The daily oral hygiene procedures of TFG and NTFG patients were similar and dental care was provided monthly by the same institution's dentist. All patients exhibited adequate oral health conditions. The salivary levels of FRAP, uric acid, SOD, GPx, TBARS, and total protein were compared between studied groups. FRAP was increased (p < 0.05) in the NTFG (4651 ± 192.5 mmol/mL) and the TFG (4743 ± 116.7 mmol/mL) when compared with the CG (1844 ± 343.8 mmol/mL). GPx values were lower (p < 0.05) in the NTGF (8.24 ± 1.09 mmol/min/mg) and the TFG (8.37 ± 1.60 mmol/min/mg) than in the CG (15.30 ± 2.61 mmol/min/mg). Uric acid in the TFG (1.57 ± 0.23 mg/dL) was significantly lower than in the NTFG (2.34 ± 0.20 mg/dL) and the CG (3.49 ± 0.21 mg/dL). Protein was significantly lower in the TFG (5.35 ± 0.27 g/dL) than in the NTFG (7.22 ± 0.57 g/dL) and the CG (7.86 ± 0.54 g/dL). There was no difference in the salivary flow rate and SOD between groups. Enteral nutrition in patients with neurological disorders was associated with lower oxidative damage, resulting in increased salivary antioxidant capacity. These results emphasize the importance of oral care for this population to prevent oral and systemic diseases.     

Flattening plasma corticosterone levels increases the prevalence of serotonergic dorsal raphe neurons inhibitory responses to nicotine in adrenalectomised rats

Major depression is characterized by a diminished activity of the brain serotonergic system as well as by the flattening of plasma cortisol levels. Nicotine improves mood in patients with major depression and in experimentally depressed animals by increasing brain serotonin (5-HT), noradrenaline and dopamine levels. The present study was directed to determine if flattening plasma glucocorticoid levels changes nicotine's stimulatory effects upon 5-HT DRN neurons. The experiments were performed in brain slices obtained from rats previously (14 days) adrenalectomised and implanted subcutaneously with one pellet containing 75 mg of corticosterone (Adx + CSR rats). Whole cell voltage and current clamp techniques were used to study the activity of immunocitochemically identified 5-HT DRN neurons. Administration of nicotine (1 μM) in sham-operated animals produced stimulatory effects in all 5-HT DRN neurons studied. In Adx + CSR rats however, nicotine inhibited 75% of 5-HT DRN neurons and increased the potassium-dependent inward rectifying current. The inhibitory effect of nicotine upon 5-HT DRN neurons was dependent on serotonin release inside the DRN, since it was converted into a stimulatory response by the selective antagonist of 5-HT_1A receptors N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridyl)cyclohexanecarboxamide (WAY100635, 25 nM). Adx + CSR rats also presented an increased function of 5-HT_1A autoreceptors, since, in these rats, serotonin (1–10 μM) produced a higher increase in the potassium dependent inward rectifying current in comparison with sham-operated animals. Serotonin release inside DRN was mediated by α4β2 nicotinic acetylcholine receptors since the selective antagonist of these receptors dihydro-β-erytroidine hydrobromide (DHβE, 100 nM) blocked the inhibitory effects of nicotine 5-HT DRN neurons. These data indicate that, in the experimental model of adrenalectomised rats implanted with corticosterone pellets, nicotine increases the function of 5-HT_1A receptors of 5-HT DRN neurons.     

The risk and associated factors of methamphetamine psychosis in methamphetamine-dependent patients in Malaysia

ObjectiveThe objective of this study was to determine the risk of lifetime and current methamphetamine-induced psychosis in patients with methamphetamine dependence. The association between psychiatric co-morbidity and methamphetamine-induced psychosis was also studied.MethodsThis was a cross-sectional study conducted concurrently at a teaching hospital and a drug rehabilitation center in Malaysia. Patients with the diagnosis of methamphetamine based on DSM-IV were interviewed using the Mini International Neuropsychiatric Interview (M.I.N.I.) for methamphetamine-induced psychosis and other Axis I psychiatric disorders. The information on sociodemographic background and drug use history was obtained from interview or medical records.ResultsOf 292 subjects, 47.9% of the subjects had a past history of psychotic symptoms and 13.0% of the patients were having current psychotic symptoms. Co-morbid major depressive disorder (OR = 7.18, 95 CI = 2.612–19.708), bipolar disorder (OR = 13.807, 95 CI = 5.194–36.706), antisocial personality disorder (OR = 12.619, 95 CI = 6.702–23.759) and heavy methamphetamine uses were significantly associated with lifetime methamphetamine-induced psychosis after adjusted for other factors. Major depressive disorder (OR = 2.870, CI = 1.154–7.142) and antisocial personality disorder (OR = 3.299, 95 CI = 1.375–7.914) were the only factors associated with current psychosis.ConclusionThere was a high risk of psychosis in patients with methamphetamine dependence. It was associated with co-morbid affective disorder, antisocial personality, and heavy methamphetamine use. It is recommended that all cases of methamphetamine dependence should be screened for psychotic symptoms.     

Biobehavioral and neuroendocrine correlates of antioxidant enzyme activity in ovarian carcinoma

Increased levels of reactive oxygen species (ROS) such as superoxide anions and hydrogen peroxide have been reported in many cancer cells and they have been implicated in carcinogenesis and tumor progression. Antioxidant enzymes, such as Manganese Superoxide Dismutase (MnSOD or SOD2) and Glutathione Peroxidase-1 (GPx1), act coordinately to neutralize ROS. These enzymes are also thought to contribute to cancer cell resistance to conventional radio-chemo-therapies. Although some relationships have been reported between psychosocial factors and the regulation of antioxidant enzymes, little is known about these relationships in the context of cancer progression.The current study investigated the levels of MnSOD and GPx1in confirmed serous, high-grade tumor tissue from 60 ovarian cancer patients, and explored the relationship between the activity of these enzymes, the levels of tumor norepinephrine (NE), and patient mood as determined via pre-operative questionnaires. MnSOD activity was positively related to depressed mood (p = 0.025) and tumor NE (p = 0.023). In contrast, GPx1 activity was inversely related to fatigue (p = 0.015) and tumor NE (p = 0.009), and was positively associated with vigor (p = 0.024). These findings suggest that psychological state and adrenergic signaling are linked with antioxidant enzyme activity in ovarian cancer and may have implications for patient treatments and outcomes.     

Methamphetamine-induced expression of zif268 mRNA is prevented by haloperidol in mice lacking μ-opioid receptor

We investigated the role of μ-opioid receptor (μ-OR) and dopamine receptor in the modulation of methamphetamine (METH)-induced expression of zif268 mRNA in the striatum of mice. Four groups of wild-type and μ-OR knockout mice were given a single daily intraperitoneal injection of saline (control; group 1) or METH (10 mg/kg; groups 2–4) for 7 consecutive days. On day 11 (after 4 abstinent days), groups 1 and 2 were challenged with saline, group 3 was challenged with METH (10 mg/kg), and group 4 was challenged with dopamine receptor antagonist haloperidol (0.06 mg/kg, subcutaneous injection) plus METH (10 mg/kg). Two hours after the last saline or METH injection, mouse brain tissues were taken for zif268 mRNA analysis using in situ hybridization histochemistry. In comparison to corresponding saline control group (group 1), striatal zif268 mRNA levels were unchanged in group 2 and increased in group 3 in both wild-type and μ-OR knockout mice and without genotype difference. METH challenge-enhanced expression of zif268 mRNA was completely abolished by pre-administration of haloperidol (group 4) in μ-OR knockout mice but not in wild-type mice. The results suggest a crosstalk of the two neurotransmitter systems in modulation of METH-induced IEG expression, because only in μ-OR knockout mice in which dopamine receptors were blocked were METH-induced zif268 expression abolished. METH-induced zif268 expression was not altered in μ-OR knockout mice without blockade of dopamine receptors or wild-type mice with blockade of dopamine receptors.     

Methylmercury-induced developmental toxicity is associated with oxidative stress and cofilin phosphorylation. Cellular and human studies

Environmental exposure to methylmercury (MeHg) during development is of concern because it is easily incorporated in children’s body both pre- and post-natal, it acts at several levels of neural pathways (mitochondria, cytoskeleton, neurotransmission) and it causes behavioral impairment in child. We evaluated the effects of prolonged exposure to 10–600 nM MeHg on primary cultures of mouse cortical (CCN) and of cerebellar granule cells (CGC) during their differentiation period. In addition, it was studied if prenatal MeHg exposure correlated with altered antioxidant defenses and cofilin phosphorylation in human placentas (n = 12) from the INMA cohort (Spain).Exposure to MeHg for 9 days in vitro (DIV) resulted in protein carbonylation and in cell death at concentrations ≥200 nM and ≥300 nM, respectively. Exposure of CCN and CGC to non-cytotoxic MeHg concentrations for 5 DIV induced an early concentration-dependent decrease in cofilin phosphorylation. Furthermore, in both cell types actin was translocated from the cytosol to the mitochondria whereas cofilin translocation was found only in CGC. Translocation of cofilin and actin to mitochondria in CGC occurred from 30 nM MeHg onwards. We also found an increased expression of cortactin and LIMK1 mRNA in CGC but not in CCN. All these effects were prevented by the antioxidant probucol.Cofilin phosphorylation was significantly decreased and a trend for decreased activity of glutathione reductase and glutathione peroxidase was found in the fetal side of human placental samples from the highest (20–40 μg/L) MeHg-exposed group when compared with the low (<7 μg/L) MeHg-exposed group.In summary, cofilin dephosphorylation and oxidative stress are hallmarks of MeHg exposure in both experimental and human systems.     

Dopamine elevates intracellular zinc concentration in cultured rat embryonic cortical neurons through the cAMP-nitric oxide signaling cascade

Zinc ion (Zn^2 +), the second most abundant transition metal after iron in the body, is essential for neuronal activity and also induces toxicity if the concentration is abnormally high. Our previous results show that exposure of cultured cortical neurons to dopamine elevates intracellular Zn^2 + concentrations ([Zn^2 +]_i) and induces autophagosome formation but the mechanism is not clear. In this study, we characterized the signaling pathway responsible for the dopamine-induced elevation of [Zn^2 +]_i and the effect of [Zn^2 +]_i in modulating the autophagy in cultured rat embryonic cortical neurons. N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), a membrane-permeable Zn^2 + chelator, could rescue the cell death and suppress the autophagosome puncta number induced by dopamine. Dopamine treatment increased the lipidation level of the endogenous microtubule-associated protein 1A/1B-light chain 3 (LC3 II), an autophagosome marker. TPEN added 1 h before, but not after, dopamine treatment suppressed the dopamine-induced elevation of LC3 II level. Inhibitors of the dopamine D1-like receptor, protein kinase A (PKA), and NOS suppressed the dopamine-induced elevation of [Zn^2 +]_i. PKA activators and NO generators directly increased [Zn^2 +]_i in cultured neurons. Through cell fractionation, proteins with m.w. values between 5 and 10 kD were found to release Zn^2 + following NO stimulation. In addition, TPEN pretreatment and an inhibitor against PKA could suppress the LC3 II level increased by NO and dopamine, respectively. Therefore, our results demonstrate that dopamine-induced elevation of [Zn^2 +]_i is mediated by the D1-like receptor-PKA-NO pathway and is important in modulating the cell death and autophagy.     

Potential of casein as a nutrient intervention to alleviate lead (Pb) acetate-mediated oxidative stress and neurotoxicity: First evidence in Drosophila melanogaster

Understanding the interaction between dietary protein deficits and neurotoxicants such as lead (Pb) is critical since oxidative stress is a common denominator under such conditions. The Drosophila system is an extensively used model to investigate the interaction between nutrients and environmental toxicants. Accordingly, we have examined the hypothesis that casein (CSN) enrichment has the propensity to attenuate Pb-associated phenotype, oxidative stress and neurotoxicity in Drosophila melanogaster. Exposure of young (2–3 d) and adult flies (10–12 d old) to Pb acetate (0–20 mM, 7 d) in the medium resulted in a concentration dependent mortality and the survivors exhibited a hyperactive phenotype. While males showed higher susceptibility to Pb among both age groups, young flies were relatively more susceptible than adults. Pb exposure (5–10 mM, 5 d) among young flies caused robust oxidative stress as evidenced by markedly elevated levels of reactive oxygen species with concomitant perturbations in the activities of antioxidant enzymes (diminished SOD and elevated thioredoxin reductase) and altered redox state. Further, Pb caused significant elevation in the activity of acetylcholinesterase and dopamine levels. In a satellite study, we assessed the modulatory effect of CSN-enriched diet (1–2%) on Pb intoxication in terms of lethality, hyperactivity, oxidative stress and neurotoxicity. CSN markedly offset Pb-induced lethality and diminished the hyperactivity response. While CSN enrichment among Pb (5 mM) treated flies caused further elevation in ROS levels and thioredoxin reductase activity, the SOD levels were restored to normalcy. Further, CSN improved the activity levels of complex I–III and restored the dopamine levels. Our data suggest that Pb-induced toxicity in the Drosophila system may be predominantly mediated through oxidative stress mechanisms and the propensity of casein-enriched diet to abrogate such responses. Hence, we propose that enrichment of diet with protein such as casein may be a useful approach to alleviate Pb associated adverse effects in children.     

Persistence of the benefit of an antioxidant therapy in children and teenagers with Down syndrome

This study examined the effect of an antioxidant intervention in biomarkers of inflammation and oxidative stress (OS) in the blood of Down syndrome (DS) children and teenagers during four different stages. A control group was composed by healthy children (n = 18), assessed once, and a Down group composed by DS patients (n = 21) assessed at the basal period (t₀), as well as after 6 months of antioxidant supplementation (t₁), after 12 months (after interruption of the antioxidant intervention for 6 months) (t₂), and again after further 6 months of antioxidant supplementation (t₃). Biomarkers of inflammation (myeloperoxidase activity – MPO and levels of IL-1β and TNF-α) and OS (thiobarbituric acid reactive substances – TBARS, protein carbonyls – PC), reduced glutathione (GSH), uric acid (UA) and vitamin E levels, as well as antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST) and gamma-glutamyltransferase (GGT) activities, were measured after each period. After the antioxidant supplementation, the activities of SOD, CAT, GPx, GR, GGT and MPO were downregulated, while TBARS contents were strongly decreased, the contents of GSH and vitamin E were significantly increased, and no changes in G6PD and GST activity as well as in UA and PC levels were detected. After the interruption of the antioxidant therapy for 6 months, DS patients showed elevated GPx and GGT activities and also elevated UA and TBARS levels. No changes in SOD, CAT, GR, GST, G6PD and MPO activities as well as in GSH, vitamin E, PC, TNF-α and IL-1β levels were detected. The results showed that the antioxidant intervention persistently attenuated the systemic oxidative damage in DS patients even after a relatively long period of cessation of the antioxidant intervention.     

Minocycline protects,rescues and prevents knockdown transgenic parkin Drosophila against paraquat/iron toxicity: Implications for autosomic recessive juvenile parkinsonism

Autosomal recessive Juvenile Parkinsonism (AR-JP) is a chronic, progressive neurodegenerative disorder caused by mutation in the PARKIN gene, and invariably associated with dopaminergic (DAergic) neuronal loss and brain iron accumulation. Since current medical therapy is symptomatic and lacks significant disease-modifying effects, other treatment approaches are urgently needed it. In the present work, we investigate the role of minocycline (MC) in paraquat (PQ)/iron-induced neurotoxicity in the Drosophila TH > parkin-RNAi/+ (w[*]; UAS-parkin-RNAi; TH-GAL4) fly and have shown the following: (i) MC increased life span and restored the locomotor activity of knockdown (KD) transgenic parkin flies in comparison with the control (vehicle) group; (ii) MC at low (0.1 and 0.3 mM) and middle (0.5 mM) concentrations protected, rescued and prevented KD parkin Drosophila against PQ toxicity. However, MC at high (1 mM) concentration aggravated the toxic effect of PQ; (iii) MC protected and rescued DAergic neurons against the PQ toxic effect according to tyrosine hydroxylase (TH) > green-fluorescent protein (GFP) reporter protein microscopy and anti-TH Western blotting analysis; (iv) MC protected DAergic neurons against PQ/iron toxicity; (v) MC significantly abridged lipid peroxidation (LPO) in the protection, rescue and prevention treatment in TH > parkin-RNAi/+ flies against PQ or iron alone or combined (PQ/iron)-induced neuronal oxidative stress (OS). Our results suggest that MC exerts neuroprotection against PQ/iron-induced OS in DAergic neurons most probably by the scavenging activity of reactive oxygen species (ROS), and by chelating iron. Therefore, MC might be a potential therapeutic drug to delay, revert, or prevent AR-JP.     

Sertraline reduces glutamate uptake in human platelets

Mitochondrial damage and declines in ATP levels have been recently attributed to sertraline. The effects of sertraline on different parameters were investigated in washed platelets from 18 healthy male volunteers, after 24 h of drug exposure. Sertraline toxicity was observed only at the highest concentrations, 30 and 100 μM, which significantly reduced platelet viability to 76 ± 3% and 20 ± 2%, respectively. The same concentrations significantly decreased total ATP to 73 ± 3% and 13 ± 2%, respectively. Basal values of glycogen were not significantly affected by sertraline treatment. Glutamate uptake was significantly reduced after treatment with 3, 30 and 100 μM, by 28 ± 6%, 32 ± 5% and 54 ± 4%, respectively. Our data showed that sertraline at therapeutic concentrations does not compromise platelet viability and ATP levels, but they suggest that in a situation where extracellular glutamate levels are potentially increased, sertraline might aggravate an excitotoxic condition.     

Ascorbic acid efficiently enhances neuronal synthesis of norepinephrine from dopamine

Ascorbic acid enhances synthesis of norepinephrine from dopamine in adrenal chromaffin cells by serving as a co-factor for chromaffin granule dopamine β-hydroxylase (DβH). However, there is controversy regarding in situ kinetics of the ascorbate effect in chromaffin cells, as well as whether they apply to neuronal cells. In this study we evaluated the stimulation of norepinephrine synthesis from dopamine in cultured SH-SY5Y neuroblastoma cells. These cells contained neither ascorbate nor norepinephrine in culture, but when provided with dopamine, they generated intracellular norepinephrine at rates that were stimulated several-fold by intracellular ascorbate. Ascorbate-induced increases in norepinephrine synthesis in dopamine-treated cells were linear over 60 min, despite saturation of intracellular ascorbate. Norepinephrine accumulation after 60 min of incubation with 100 μM dopamine was half-maximal at intracellular ascorbate concentrations of 0.2–0.5 mM, which fits well with the literature K_m for ascorbate of DβH using dopamine as a substrate. Moreover, these ascorbate concentrations were generated by initial extracellular ascorbate concentrations of less than 25 μM due to concentrative accumulation by the ascorbate transporter. Treatment with 100 μM dopamine acutely increased cellular superoxide generation, which was prevented by ascorbate loading, but associated with a decrease in intracellular ascorbate when the latter was present at concentrations under 1 mM. These results show that ascorbate promptly enhances norepinephrine synthesis from dopamine by neuronal cells that it does so at physiologic intracellular concentrations in accord with the kinetics of DβH, and that it both protects cells from superoxide and by providing electrons to DβH.     

Additive inhibition of human α1β2γ2 GABAA receptors by mixtures of commonly used drugs of abuse

Yearly, exposure to drugs of abuse results in ∼1 million emergency department visits in the US. In ∼50% of the visits, stimulant drugs like cocaine and amphetamine-like substances (e.g. 3,4-methylenedioxymethamphetamine (MDMA, the main active ingredient of ecstasy)) are involved, whereas in ∼60% multiple drugs are involved. These drugs induce higher dopamine and serotonin levels resulting in drug-induced toxicity. Since GABA receptors (GABA-R) provide the main inhibitory input on dopaminergic and serotonergic neurons, drug-induced inhibition of GABA-R could contribute to higher neurotransmitter levels and thus toxicity.We therefore investigated the effects of combinations of commonly abused stimulant drugs (cocaine, MDMA, 3,4-methylenedioxyamphetamine (MDA) and meta-chlorophenylpiperazine (mCPP)) on the function of the human α₁β₂γ₂ GABA_A receptor (hGABA_A-R), expressed in Xenopus oocytes, using the two-electrode voltage-clamp technique.These drugs concentration-dependently inhibited the GABA-evoked current (mCPP > cocaine > MDMA > MDA). Most drug combinations decreased the GABA-evoked current stronger than the single drug. Additivity was observed during combined exposure to low concentrations of cocaine and mCPP as well as during combined exposure to MDA with cocaine or mCPP. However, combinations containing MDMA mainly resulted in sub-additivity or no additivity.At drug concentrations relevant for clinical toxicology, co-exposure to ≥2 drugs can decrease the GABA-evoked current in an additive manner. Thus, in patients exposed to multiple drugs, inhibitory GABA-ergic input is reduced more prominently, likely resulting in higher brain dopamine levels. As this will increase the risk for drug-induced toxicity, treatment of drug-intoxicated patients with drugs that enhance GABA-ergic input should be further optimized.     

Vitamin D status and cognitive performance in community-dwelling adults: A dose-response meta-analysis of observational studies

Low vitamin D status is linked with poorer cognition in adults while findings in relation to high levels are mixed. We performed a systematic review and meta-analyses to examine dose–response associations between 25-hydroxyvitamin D (25OHD) levels and cognitive performance in community-dwelling adults. Thirty-eight observational studies were included in dose–response meta-analyses. Positive, nonlinear associations were identified between baseline 25OHD levels and global cognition in cross-sectional and longitudinal analyses, and for performance in memory and executive function in longitudinal analyses. When restricted to studies involving older adults, the pattern emerged for specific domains in cross-sectional analyses. Poorer performance was associated with low 25OHD levels, while a sharp improvement was associated with levels up to 60–70 nM/L. Further improvement was observed only for longitudinal global cognition. Our findings support the association between low vitamin D and poorer cognition and suggest levels of at least 60 nM/L are associated with better cognition during ageing.     

Nitrous oxide related behavioral and histopathological changes may be related to oxidative stress

Nitrous oxide (N₂O) toxicity can result in myelin loss and hyperhomocysteinemia similar to cobalamin (Cbl) deficiency. Studies on N₂O exposure can help in understanding the mechanism of demyelination. In view of paucity of studies on N₂O toxicity in rats this study was undertaken. Six male wistar rats were exposed to 1.5 L/min N₂O with 1:1 O₂ for 90 min daily for 1 month. After 1-month exposure blood homocysteine (HCY) and oxidative stress parameters glutathione (GSH) and total antioxidant capacity (TAC) were measured. Brain and spinal cord was subjected to histopathological examination. The neurobehavioral changes, oxidative stress parameters and histopathological changes were correlated with serum B12 and HCY level. After 1-month exposure, the rats appeared sluggish, lethargic and developed predominantly hind limb weakness for 1–1.5 h. In the exposed group, the total distance traveled (2001.66 ± 118.27 cm; p = 0.037), time moving (80.16 ± 5.7 s; p = 0.028), number of rearing (10.33 ± 1.45; p = 0.014) and grip strength (1042.40 ± 51.3 N; p = 0.041) were significantly decreased whereas, resting time significantly increased (219.83 ± 5.7 s; p = 0.030) compared to controls. Serum HCY level was significantly increased (20.56 ± 1.296 μm/ml; p = 0.0007) in the exposed group. However, serum B12 and folic acid levels were not significantly different. GSH significantly decreased (2.21 ± 0.60 mg/dl; p = 0.018) along with TAC (0.76 ± 0.16 Trolox_Eq_mmol/l; p = 0.036). The histopathological studies revealed shrinkage and vacuolation of neurons in cerebral cortex, focal myelin loss, vacuolation in subcortical white matter and spinal cord. N₂O exposure results in behavioral alterations, hyperhomocysteinemia, cortical and spinal cord demyelination which were associated with decrease GSH and TAC highlighting pathophysiological role of oxidative stress.     

Pharmacokinetic,neurochemical, stereological and neuropathological studies on the potential effects of paraquat in the substantia nigra pars compacta and striatum of male C57BL/6J mice

The pharmacokinetics and neurotoxicity of paraquat dichloride (PQ) were assessed following once weekly administration to C57BL/6J male mice by intraperitoneal injection for 1, 2 or 3 weeks at doses of 10, 15 or 25 mg/kg/week. Approximately 0.3% of the administered dose was taken up by the brain and was slowly eliminated, with a half-life of approximately 3 weeks. PQ did not alter the concentration of dopamine (DA), homovanillic acid (HVA) or 3,4-dihydroxyphenylacetic acid (DOPAC), or increase dopamine turnover in the striatum. There was inconsistent stereological evidence of a loss of DA neurons, as identified by chromogenic or fluorescent-tagged antibodies to tyrosine hydroxylase in the substantia nigra pars compacta (SNpc). There was no evidence that PQ induced neuronal degeneration in the SNpc or degenerating neuronal processes in the striatum, as indicated by the absence of uptake of silver stain or reduced immunolabeling of tyrosine-hydroxylase-positive (TH⁺) neurons. There was no evidence of apoptotic cell death, which was evaluated using TUNEL or caspase 3 assays. Microglia (IBA-1 immunoreactivity) and astrocytes (GFAP immunoreactivity) were not activated in PQ-treated mice 4, 8, 16, 24, 48, 96 or 168 h after 1, 2 or 3 doses of PQ.In contrast, mice dosed with the positive control substance, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 10 mg/kg/dose × 4 doses, 2 h apart), displayed significantly reduced DA and DOPAC concentrations and increased DA turnover in the striatum 7 days after dosing. The number of TH⁺ neurons in the SNpc was reduced, and there were increased numbers of degenerating neurons and neuronal processes in the SNpc and striatum. MPTP-mediated cell death was not attributed to apoptosis. MPTP activated microglia and astrocytes within 4 h of the last dose, reaching a peak within 48 h. The microglial response ended by 96 h in the SNpc, but the astrocytic response continued through 168 h in the striatum.These results bring into question previous published stereological studies that report loss of TH⁺ neurons in the SNpc of PQ-treated mice. This study also suggests that even if the reduction in TH⁺ neurons reported by others occurs in PQ-treated mice, this apparent phenotypic change is unaccompanied by neuronal cell death or by modification of dopamine levels in the striatum.     

Serum paraoxonase and arylesterase activity and oxidative status in patients with multiple sclerosis

The aim of this study was to investigate serum paraoxonase and arylesterase activities, and to determine oxidative status via the measurement of total oxidant status (TOS), total antioxidant status (TAS) and the oxidative stress index (OSI) in patients with relapsing-remitting multiple sclerosis (RRMS). Results were compared with data from healthy controls. A total of 60 subjects, including 30 newly diagnosed and untreated patients with RRMS (20 females, 10 males, 18–40 years of age) and 30 healthy controls (20 female, 10 male 20–40 years of age) were enrolled in this study. The oxidative status of the RRMS patients was measured by TOS, TAS and estimation of the OSI was made by a new automated method. Paraoxonase (PON1) and arylesterase activities were measured spectrophotometrically. TAS levels of RRMS patients were significantly lower than that of controls (p < 0.05). TOS levels of RRMS patients were higher than that of controls (p < 0.05). PON1 and arylesterase activities of RRMS patients were lower, but not significantly, than those of controls (p > 0.05). There was no correlation between serum PON1 activity and OS? in patients with RRMS (p > 0.05). Hypercholesterolemia was not observed in multiple sclerosis patients. In conclusion, although the mechanism underlying the significant reduction of TAS levels of multiple sclerosis patients compared with those of controls is unknown, the results imply that endogenous antioxidants may have been exhausted by increased oxidative stress and we believe that additional antioxidant treatment might be beneficial for these patients.