Heavy metal contamination in seafood and consumer exposure in the Gulf Cooperation Council

Dissertação para obtenção do Grau de Mestre em Tecnologia e Segurança AlimentarThe population from countries surrounded by the Gulf and Arabian Sea depend on fisheries. Industry is growing and discharges by desalination plants and refineries lead to the presence of heavy metals which accumulate in the environment and seafood. The aim is to review seafood contamination with cadmium, arsenic, lead and mercury in Saudi Arabia, Oman, Kuwait, United Arab Emirates, Bahrain and Qatar and estimate the consumer exposure to these metals. All samples of molluscs and crustaceans tested for arsenic (As) showed concentrations above maximum permitted levels, Qatar and UAE being the most contaminated. All samples from Kuwait contained lead (Pb), cadmium (Cd) and mercury (Hg). Bahrain samples contained Pb above permitted levels. On the coast of Oman and Qatar shellfish showed concentrations of Cd above permitted levels. The EWI for As from shellfish is above the PTWI for all samples. For Cd, all except shellfish from Oman, Bahrain and KSA entail a EWI above the PTWI. None of the samples, except from Kuwait, provide Pb above the PTWI and for Hg, only the clam, mussel and crab contain higher amounts. Four locations in the UAE contained fish with Cd above permitted levels. Tuna fish from KSA had higher levels of Cd and Pb. Highest levels of Hg could be found in fish from Kuwait. Bahrain and Qatar showed the highest levels of As. Hg EWI exceeded for the UAE, Kuwait and Qatar. Estimated weekly intakes of As and Cd from shellfish are extremely high and above the Provisional Tolerable Weekly Intake. Fish from these countries does not contain high levels that pose a threat to public health, except for As. The risk is probably in chronic low exposure. Risk groups should be properly advised

Caffeine, adenosine receptors, and synaptic plasticity

Copyright ©2012 IOS Press All rights reserved.Few studies to date have looked at the effects of caffeine on synaptic plasticity, and those that did used very high concentrations of caffeine, whereas the brain concentrations attained by regular coffee consumption in humans should be in the low micromolar range, where caffeine exerts pharmacological actions mainly by antagonizing adenosine receptors. Accordingly, rats drinking caffeine (1 g/L) for 3 weeks, displayed a concentration of caffeine of circa 22 μM in the hippocampus. It is known that selective adenosine A1 receptor antagonists facilitate, whereas selective adenosine A2A receptor antagonists attenuate, long term potentiation (LTP) in the hippocampus. Although caffeine is a non-selective antagonist of adenosine receptors, it attenuates frequency-induced LTP in hippocampal slices in a manner similar to selective adenosine A2A receptor antagonists. These effects of low micromolar concentration of caffeine (30 μM) are maintained in aged animals, which is important when a possible beneficial effect for caffeine in age-related cognitive decline is proposed. Future studies will still be required to confirm and detail the involvement of A1 and A2A receptors in the effects of caffeine on hippocampal synaptic plasticity, using both pharmacological and genetic approaches.The work was supported by Fundação para a Ciência e Tecnologia and Fundação Oriente

Adenosine A(2A) receptor blockade reverts hippocampal stress-induced deficits and restores corticosterone circadian oscillation

Maternal separation (MS) is an early life stress model that induces permanent changes in the central nervous system, impairing hippocampal long-term potentiation (LTP) and spatial working memory. There are compelling evidences for a role of hippocampal adenosine A(2A) receptors in stress-induced modifications related to cognition, thus opening a potential window for therapeutic intervention. Here, we submitted rats to MS and evaluated the long-lasting molecular, electrophysiological and behavioral impairments in adulthood. We then assessed the therapeutic potential of KW6002, a blocker of A(2A) receptors, in stress-impaired animals. We report that the blockade of A(2A) receptors was efficient in reverting the behavior, electrophysiological and morphological impairments induced by MS. In addition, this effect is associated with restoration of the hypothalamic-pituitary-adrenal axis (HPA-axis) activity, as both the plasma corticosterone levels and hippocampal glucocorticoid receptor expression pattern returned to physiological-like status after the treatment. These results reveal the involvement of A(2A) receptors in the stress-associated impairments and directly in the stress response system by showing that the dysfunction of the HPA-axis as well as the long-lasting synaptic and behavioral effects of MS can be reverted by targeting adenosine A(2A) receptors. These findings provide a novel evidence for the use of adenosine A(2A) receptor antagonists as potential therapy against psychopathologiesWe acknowledge Alexandre de Mendonca, David Blum and Rodrigo Cunha for helpful discussions. VLB is thankful to Joao Baiao and Carla Batalha for technical assistance. VLB has been awarded a PhD fellowship from Fundacao para a Ciencia e Tecnologia (BD/63041/2009). LVL is funded by Fundacao para a Ciencia e Tecnologia (PTDC/SAU-NEU/099853/2008) and by EU programme Egide-Pessoa. YB and CEM were funded by the Ministry for Education and Research (BMBF, Grant number 01EW0911) in the frame of ERA-NET NEURON

Glutamate-induced depression of EPSP–spike coupling in rat hippocampal CA1 neurons and modulation by adenosine receptors

The presence of high concentrations of glutamate in the extracellular fluid following brain trauma or ischaemia may contribute substantially to subsequent impairments of neuronal function. In this study, glutamate was applied to hippocampal slices for several minutes, producing over-depolarization, which was reflected in an initial loss of evoked population potential size in the CA1 region. Orthodromic population spikes recovered only partially over the following 60 min, whereas antidromic spikes and excitatory postsynaptic potentials (EPSPs) showed greater recovery, implying a change in EPSP–spike coupling (E–S coupling), which was confirmed by intracellular recording from CA1 pyramidal cells. The recovery of EPSPs was enhanced further by dizocilpine, suggesting that the long-lasting glutamate-induced change in E–S coupling involves NMDA receptors. This was supported by experiments showing that when isolated NMDA-receptor-mediated EPSPs were studied in isolation, there was only partial recovery following glutamate, unlike the composite EPSPs. The recovery of orthodromic population spikes and NMDA-receptor-mediated EPSPs following glutamate was enhanced by the adenosine A1 receptor blocker DPCPX, the A2A receptor antagonist SCH58261 or adenosine deaminase, associated with a loss of restoration to normal of the glutamate-induced E–S depression. The results indicate that the long-lasting depression of neuronal excitability following recovery from glutamate is associated with a depression of E–S coupling. This effect is partly dependent on activation of NMDA receptors, which modify adenosine release or the sensitivity of adenosine receptors. The results may have implications for the use of A1 and A2A receptor ligands as cognitive enhancers or neuroprotectants

Adenosine A2A receptors facilitate synaptic NMDA currents in CA1 pyramidal neurons

© 2018 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.Background and purpose: NMDA receptors play a key role in both synaptic plasticity and neurodegeneration. Adenosine is an endogenous neuromodulator and through membrane receptors of the A2A subtype can influence both synaptic plasticity and neuronal death. The present work was designed to evaluate the influence of adenosine A2A receptors upon NMDA receptor activity in CA1 hippocampal neurons. We discriminated between modulation of synaptic versus extrasynaptic receptors, since extrasynaptic NMDA receptors are mostly associated with neurodegeneration while synaptic NMDA receptors are linked to plasticity phenomena. Experimental approach: Whole-cell patch-clamp recordings were obtained to evaluate NMDA receptor actions on CA1 pyramidal neurons of young adult (5-10 weeks) male Wistar rat hippocampus. Key results: Activation of A2A receptors with CGS 21680 (30 nM) consistently facilitated chemically-evoked NMDA receptor-currents (NMDA-PSCs) and afferent-evoked NMDA-currents (NMDA-EPSCs), an action prevented by an A2A receptor antagonist (SCH58261, 100 nM) and a PKA inhibitor, H-89 (1 μM). These actions did not reflect facilitation in glutamate release since there was no change in NMDA-EPSCs paired pulse ratio. A2A receptor actions were lost in the presence of an open-channel NMDA receptor blocker, MK-801 (10 μM), but persisted in the presence of memantine, at a concentration (10 μM) known to preferentially block extrasynaptic NMDA receptors. Conclusion and implications: These results show that A2A receptors exert a positive postsynaptic modulatory effect over synaptic, but not extrasynaptic, NMDA receptors in CA1 neurons and, therefore, under non-pathological conditions may contribute to shift the dual role of NMDA receptors towards enhancement of synaptic plasticity.Work supported by LISBOA-01-0145-FEDER-007391, project co-funded by FEDER through POR Lisboa 2020 (Programa Operacional Regional de Lisboa) from PORTUGAL 2020 and Fundação para a Ciência e Tecnologia, (FCT), by an FCT project (PTDC/DTP-FTO/3346/2014), and by a Twinning action (SynaNet) from the EU H2020 programme (project number: 692340). F.M.M. was in receipt of SFRH/BD/89582/2012 FTC fellowship, and D.M.R. is in receipt of a fellowship from Instituto de Medicina Molecular (IMM/BI/38-2017).info:eu-repo/semantics/publishedVersio

Enhanced role of adenosine A2A receptors in the modulation of LTP in the rat hippocampus upon ageing

Adenosine neuromodulation depends on a balanced activation of inhibitory A1 (A1R) and facilitatory A2A receptors (A2AR). Both A1R and A2AR modulate hippocampal glutamate release and NMDA-dependent long-term potentiation (LTP) but ageing affects the density of both A1R and A2AR. We tested the effects of selective A1R and A2AR antagonists in the modulation of synaptic transmission and plasticity in rat hippocampal slices from three age groups (young adults, 2–3 month; middle-aged adults, 6–8 months; aged, 18–20 months). The selective A2AR antagonist SCH58261 (50 nm) attenuated LTP in all age groups, with a larger effect in aged ()63 ± 7%) than in middle-aged adults ()36 ± 9%) or young adult rats ()36 ± 9%). In contrast, the selective A1R antagonist DPCPX (50 nm) increased LTP magnitude in young adult rats (+42 ± 6%), but failed to affect LTP magnitude in the other age groups. Finally, in the continuous presence of DPCPX, SCH58261 caused a significantly larger inhibition of LTP amplitude in aged ()71 ± 45%) than middle-aged ()28 ± 9%) or young rats ()11 ± 2%). Accordingly, aged rats displayed an increased expression of A2AR mRNA in the hippocampus and a higher number of glutamatergic nerve terminals equipped with A2AR in aged (67 ± 6%) compared with middle-aged (34 ± 7%) and young rats (25 ± 5%). The results show an enhanced A2AR-mediated modulation of LTP in aged rats, in accordance with the age-associated increased expression and density of A2AR in glutamatergic terminals. This age-associated gain of function of A2AR modulating synaptic plasticity may underlie the ability of A2AR antagonists to prevent memory dysfunction in aged animals

Presynaptic A2A adenosine receptors dampen CB1 cannabinoid receptor-mediated inhibition of corticostriatal glutamatergic transmission

Background and Purpose Both CB1 cannabinoid and A2A adenosine receptors (CB1Rs and A2ARs) control synaptic transmission at corticostriatal synapses, with great therapeutic importance for neurological and psychiatric disorders. A post-synaptic CB1R-A2AR interaction has already been unraveled, but the presynaptic A2AR-mediated control of presynaptic neuromodulation by CB1Rs remains to be defined. Since the corticostriatal terminals provide the major input of the basal ganglia, understanding the interactive nature of converging neuromodulation on them will provide us with novel powerful tools to understand the physiology of corticostriatal synaptic transmission and interpret changes associated with pathological conditions. Experimental Approach Here we employ selective presynaptic tools to study the putative presynaptic interaction between the two neuromodulator systems. Pharmacological manipulation of CB1R and A2AR was carried out in isolated nerve terminals used for flow synaptometry, immunoprecipitation, radioligand binding, ATP and glutamate release measurement, as well as in whole-cell patch-clamp recordings in horizontal corticostriatal slices. Results Flow synaptometry showed that A2AR are extensively co-localized with CB1R-immunopositive corticostriatal terminals, and A2AR co-immunoprecipitated CB1R in these purified terminals. A2AR activation decreased CB1R radioligand binding and decreased the CB1R-mediated inhibition of high-K+-evoked glutamate release in corticostriatal terminals. Accordingly, A2AR activation prevented CB1R-mediated paired-pulse facilitation and attenuated the CB1R-mediated inhibition of synaptic transmission in glutamatergic synapses of corticostriatal slices. Conclusions and Implications These results show that presynaptic A2AR dampens CB1R-mediated inhibition of corticostriatal terminals. This constitutes a thus far unrecognized mechanism to shut-down the potent CB1R-mediated presynaptic inhibition, enabling a frequency-dependent enhancement of synaptic efficacy at corticostriatal synapses

Frequency Facilitation at Mossy Fiber–CA3 Synapses of Freely Behaving Rats Contributes to the Induction of Persistent LTD via an Adenosine-A1 Receptor-Regulated Mechanism

Frequency facilitation (FF), comprising a rapid and multiple-fold increase in the magnitude of evoked field potentials, is elicited by low-frequency stimulation (LFS) at mossy fiber–CA3 synapses. Here, we show that in freely behaving rats, FF reliably occurs in response to 1 and 2Hz but not in response to 0.25-, 0.3-, or 0.5-Hz LFS. Strikingly, prolonged (∼600 s) FF was tightly correlated to the induction of long-term depression (LTD) in freely moving animals. Although LFS at 2 Hz elicited unstable FF and unstable LTD, application of LFS at 1 Hz elicited pronounced FF, as well as robust LTD that persisted for over 24 h. This correlation of prolonged FF with LTD was absent at stimulation frequencies that did not induce FF. The adenosine-A1 receptor appears to participate in these effects: Application of adenosine-A1, but not adenosine-A3, receptor antagonists enhanced mossy fiber synaptic transmission and occluded FF. Furthermore, adenosine-A1 receptor antagonism resulted in more stable FF at 1 or 2 Hz and elicited more potent LTD. These data support the fact that FF contributes to the enablement of long-term information storage at mossy fiber–CA3 synapses and that the adenosine-A1 receptor may regulate the thresholds for this process

Caffeine Consumption Prevents Diabetes-Induced Memory Impairment and Synaptotoxicity in the Hippocampus of NONcZNO10/LTJ Mice

Diabetic conditions are associated with modified brain function, namely with cognitive deficits, through largely undetermined processes. More than understanding the underlying mechanism, it is important to devise novel strategies to alleviate diabetes-induced cognitive deficits. Caffeine (a mixed antagonist of adenosine A1 and A2A receptors) emerges as a promising candidate since caffeine consumption reduces the risk of diabetes and effectively prevents memory deficits caused by different noxious stimuli. Thus, we took advantage of a novel animal model of type 2 diabetes to investigate the behavioural, neurochemical and morphological modifications present in the hippocampus and tested if caffeine consumption might prevent these changes. We used a model closely mimicking the human type 2 diabetes condition, NONcNZO10/LtJ mice, which become diabetic at 7–11 months when kept under an 11% fat diet. Caffeine (1 g/l) was applied in the drinking water from 7 months onwards. Diabetic mice displayed a decreased spontaneous alternation in the Y-maze accompanied by a decreased density of nerve terminal markers (synaptophysin, SNAP25), mainly glutamatergic (vesicular glutamate transporters), and increased astrogliosis (GFAP immunoreactivity) compared to their wild type littermates kept under the same diet. Furthermore, diabetic mice displayed up-regulated A2A receptors and down-regulated A1 receptors in the hippocampus. Caffeine consumption restored memory performance and abrogated the diabetes-induced loss of nerve terminals and astrogliosis. These results provide the first evidence that type 2 diabetic mice display a loss of nerve terminal markers and astrogliosis, which is associated with memory impairment; furthermore, caffeine consumption prevents synaptic dysfunction and astrogliosis as well as memory impairment in type 2 diabetes