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Background: The use of Alzheimer’s disease (AD) models obtained by intracerebral infusion of amyloid-β (Aβ) has been increasingly reported in recent years. Nonetheless, these models may present important challenges. Objective: We have focused on canonical mechanisms of hippocampal-related neural plasticity to characterize a rat model obtained by an intracerebroventricular (icv) injection of soluble amyloid-β42 (Aβ42). Methods: Animal behavior was evaluated in the elevated plus maze, Y-Maze spontaneous or forced alternation, Morris water maze, and open field, starting 2 weeks post-Aβ42 infusion. Hippocampal neurogenesis was assessed 3 weeks after Aβ42 injection. Aβ deposition, tropomyosin receptor kinase B levels, and neuroinflammation were appraised at 3 and 14 days post-Aβ42 administration. Results: We found that immature neuronal dendritic morphology was abnormally enhanced, but proliferation and neuronal differentiation in the dentate gyrus was conserved one month after Aβ42 injection. Surprisingly, animal behavior did not reveal changes in cognitive performance nor in locomotor and anxious-related activity. Brain-derived neurotrophic factor related-signaling was also unchanged at 3 and 14 days post-Aβ icv injection. Likewise, astrocytic and microglial markers of neuroinflammation in the hippocampus were unaltered in these time points. Conclusion: Taken together, our data emphasize a high variability and lack of behavioral reproducibility associated with these Aβ injection-based models, as well as the need for its further optimization, aiming at addressing the gap between preclinical AD models and the human disorder.

Introduction Nanoparticles (NPs), as drug delivery systems, appear to be a promising tool for prolonged therapeutic strategies as they allow a controlled drug release over time. However, most of the studies found in the literature simply contemplate the use of a single or low number of dosages with low NPs concentrations. In the context of chronic diseases, like Alzheimer's disease, cancer or human immunodeficiency virus (HIV), where the therapeutic scheme is also chronic, studies with numerous repeated dosages are often neglected. Methods We screened different NPs, polymeric and lipid-based, in a repeated-dose toxicity study, to evaluate the safety and tissue distribution of promising nanocarriers to be used in the treatment of long-lasting diseases. Results After administrating 24 high concentrated doses of the selected NPs intraperitoneally (i.p.) (3 times a week for 2 months), animals have presented NPs accumulation in different tissues. However, neither toxicity, bodyweight changes nor clinical signs of disease were observed. Discussion This work demonstrates no general adverse effects upon the studied NPs repeated-dose exposure, indicating the most promising NPs to be used in the different therapeutic circumstances, which may be useful in chronic diseases treatment.

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Copyright © 2021, © SAGE Publications, Background: Cognitive deficits profoundly impact on the quality of life of patients with schizophrenia. Alterations in brain derived neurotrophic factor (BDNF) signalling, which regulates synaptic function through the activation of full-length tropomyosin-related kinase B receptors (TrkB-FL), are implicated in the aetiology of schizophrenia, as is N-methyl-D-aspartate receptor (NMDA-R) hypofunction. However, whether NMDA-R hypofunction contributes to the disrupted BDNF signalling seen in patients remains unknown. Aims: The purpose of this study was to characterise BDNF signalling and function in a preclinical rodent model relevant to schizophrenia induced by prolonged NMDA-R hypofunction. Methods: Using the subchronic phencyclidine (PCP) model, we performed electrophysiology approaches, molecular characterisation and behavioural analysis. Results: The data showed that prolonged NMDA-R antagonism, induced by subchronic PCP treatment, impairs long-term potentiation (LTP) and the facilitatory effect of BDNF upon LTP in the medial prefrontal cortex (PFC) of adult mice. Additionally, TrkB-FL receptor expression is decreased in the PFC of these animals. By contrast, these changes were not present in the hippocampus of PCP-treated mice. Moreover, BDNF levels were not altered in the hippocampus or PFC of PCP-treated mice. Interestingly, these observations are paralleled by impaired performance in PFC-dependent cognitive tests in mice treated with PCP. Conclusions: Overall, these data suggest that NMDA-R hypofunction induces dysfunctional BDNF signalling in the PFC, but not in the hippocampus, which may contribute to the PFC-dependent cognitive deficits seen in the subchronic PCP model. Additionally, these data suggest that targeting BDNF signalling may be a mechanism to improve PFC-dependent cognitive dysfunction in schizophrenia., The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was 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 European Union’s Horizon 2020 research and innovation programme under grant agreement No 692340 (SynaNet) and No 952455 (EpiEpinet) and GAPIC (20180014). SRT was in receipt of SFRH/BD/128091/2016 FCT fellowship.

Stroke is a complex disorder that includes several different pathophysiological entities, and therefore requires a personalized approach to therapy. Pharmacological acute stroke therapy includes fibrinolytics such as alteplase (rt-PA) or tenecteplase which has a more favorable pharmacokinetic profile. Hemorrhagic adverse events are the main risks of these therapies, and clinical, laboratorial, and genetic factors may influence the risk of severe bleeding. After the acute time window, prevention is paramount in order to avoid recurrent stroke. Antiplatelet drugs (aspirin, clopidogrel, dipyridamole) are the default secondary prevention therapies. In some patients, such as those with cardioembolic stroke, anticoagulants are the preferred preventive treatment. These include vitamin K antagonists (warfarin) and direct oral anticoagulants (dabigatran, rivaroxaban, apixaban, edoxaban). With some drugs, such as clopidogrel and warfarin, significant heterogeneity of the magnitude of effect and side effect profile exists between subjects. In addition to environmental factors and drug-drug interactions, genetic polymorphisms contribute to intersubject variability, whether through drug receptor or metabolic pathway variations. Knowledge of the precise pharmacodynamic, pharmacokinetic, and pharmacogenetic details of drugs used in stroke care enables the selection of the most appropriate option for each individual patient. Precision medicine and pharmacogenetic-guided drug algorithms may become the standard of care in the future.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)., Epilepsy is one of the most common brain diseases worldwide, having a huge burden in society. The main hallmark of epilepsy is the occurrence of spontaneous recurrent seizures, having a tremendous impact on the lives of the patients and of their relatives. Currently, the therapeutic strategies are mostly based on the use of antiepileptic drugs, and because several types of epilepsies are of unknown origin, a high percentage of patients are resistant to the available pharmacotherapy, continuing to experience seizures overtime. Therefore, the search for new drugs and therapeutic targets is highly important. One key aspect to be targeted is the aberrant adult hippocampal neurogenesis (AHN) derived from Neural Stem Cells (NSCs). Indeed, targeting seizure-induced AHN may reduce recurrent seizures and shed some light on the mechanisms of disease. The endocannabinoid system is a known modulator of AHN, and due to the known endogenous antiepileptic properties, it is an interesting candidate for the generation of new antiepileptic drugs. However, further studies and clinical trials are required to investigate the putative mechanisms by which cannabinoids can be used to treat epilepsy. In this manuscript, we will review how cannabinoid-induced modulation of NSCs may promote neural plasticity and whether these drugs can be used as putative antiepileptic treatment., This work was supported by IF/01227/2015 and UID/BIM/50005/2019, projeto financiado pela Fundação para a Ciência e a Tecnologia (FCT)/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES) através de Fundos do Orçamento de Estado. D.M.L. (PD/BD/141784/2018) and L.R.-R. (PD/BD/150344/2019) were in receipt of a fellowship from FCT. The authors are in hold of a H2020 Twinning Action from EU (EpiEpiNet).

Late-onset sporadic Alzheimers disease (AD) is the most common neurodegenerative disorder worldwide, yet present treatment options are still very limited. Modulating adult hippocampal neurogenesis (AHN) as a potential therapeutic target for AD has been explored. However, how the process is regulated in AD remains unclear, as studies show controversial results, arising mainly from models of the familial form. Hence, in the present work, aiming at characterizing AHN in a model of the initial stages of sporadic AD, male Wistar rats were intracerebroventricularly injected with an Aβ1-42 peptide solution. Behaviour tests carried out two weeks after the injection unexpectedly revealed no impact on locomotor activity (open field), anxious-related behaviour (elevated plus maze) or learning and memory performance (novel object recognition, Y-maze, Morris water maze). Assessment of neurogenic markers one month after 5-bromo-2-deoxyuridine administration showed abnormally enhanced dendritic morphology of immature neurons in the dentate gyrus, while proliferation and neuronal differentiation were preserved. As brain-derived neurotrophic factor signalling has been shown to be compromised in the presence of Aβ due to the cleavage of TrkB full-length receptors, the levels of these receptors isoforms were evaluated. No evidence of cleavage was found at 3 or 14 days post-Aβ-infusion. Consistently, the levels of Aβ1-42 species were unaltered at these timepoints, as was the number of astrocytes and microglia. Overall, although this model has been previously described as a model of sporadic AD, the expected behavioural, cellular or molecular phenotypes were not observed, further highlighting the variability of results found in the literature.

The investigation on neurotransmission function during normal and pathologic development is a pivotal component needed to understand the basic mechanisms underlying neurodevelopmental pathologies. To study these diseases, many animal models have been generated which allowed to face the limited availability of human tissues and, as a consequence, most of the electrophysiology has been performed on these models of diseases. On the other hand, the technique of membrane microtransplantation in Xenopus oocytes allows the study of human functional neurotransmitter receptors thanks to the use of tissues from autopsies or surgeries, even in quantities that would not permit other kinds of functional studies. In this short article, we intend to underline how this technique is well-fit for the study of rare diseases by characterizing the electrophysiological properties of GABAA and AMPA receptors in Rett syndrome. For our purposes, we used both tissues from Rett syndrome patients and Mecp2-null mice, a well validated murine model of the same disease, in order to strengthen the solidity of our results through the comparison of the two. Our findings retrace previous results and, in the light of this, further argue in favor of Prof. Miledi's technique of membrane microtransplantation that proves itself a very useful tool of investigation in the field of neurophysiology. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

Copyright © 2020 Sa de Almeida, Vargas, Fonseca-Gomes, Tanqueiro, Belo, Miranda-Lourenço, Sebastião, Diógenes and Pais. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms., Microglial cells have emerged as crucial players in synaptic plasticity during development and adulthood, and also in neurodegenerative and neuroinflammatory conditions. Here we found that decreased levels of Sirtuin 2 (Sirt2) deacetylase in microglia affects hippocampal synaptic plasticity under inflammatory conditions. The results show that long-term potentiation (LTP) magnitude recorded from hippocampal slices of wild type mice does not differ between those exposed to lipopolysaccharide (LPS), a pro-inflammatory stimulus, or BSA. However, LTP recorded from hippocampal slices of microglial-specific Sirt2 deficient (Sirt2-) mice was significantly impaired by LPS. Importantly, LTP values were restored by memantine, an antagonist of N-methyl-D-aspartate (NMDA) receptors. These results indicate that microglial Sirt2 prevents NMDA-mediated excitotoxicity in hippocampal slices in response to an inflammatory signal such as LPS. Overall, our data suggest a key-protective role for microglial Sirt2 in mnesic deficits associated with neuroinflammation., This study was supported by Santa Casa da Misericórdia de Lisboa (MB37-2017), GAPIC Research Program of the University of Lisbon Medical School (n° 2014002 and n° 2015028) and the following doctoral grants: PD/BD/128091/2016, SFRH/BD/118238/2016, PD/BD/114337/2016, and PD/BD/1144- 41/2016.

Several observational studies suggest that greasy fish may reduce cardiovascular risk, whose benefits have been attributed to the presence Omega-3 polyunsaturated fatty acids (OM3FA). However, there are some randomized controlled trials (RCTs) that have shown contradictory results concerning the cardiovascular benefits of OM3FA. Analyzing these RCTs we found that the use of olive oil in some RCTs could be responsible for contradictory results, since both. since both olive oil and OM3FA, in addition to reduce triglycerides, have anti-platelet and anti-inflammatory activities, considered important for the stabilization of atherosclerotic plaques. This pharmacodynamic profile may have a cardio protective effect that was confirmed by several RCTs. Therefore, olive oil seems an active substance, and its use might have reduced the differences between groups masking the efficacy of OM3FA. This inferred lack of OM3FA cardiovascular benefits due to bias induced by a “false placebo” control, raises epistemological considerations on the choice of placebos that always should be pharmacologically inert substances. More studies are necessary to clarify the real efficacy of OM3FA that is more innocuous than many medicines, but it seems useful in future RCTs the use of a truly inert substance as a placebo, as well as the outline of a semi quantitative dose-response curve suggestive of a causal nexus between active substances and their outcomes.

© 2020 Elsevier Ltd. All rights reserved., Neurotrophins are a well-known family of neurotrophic factors that play an important role both in the central and peripheral nervous systems, where they modulate neuronal survival, development, function and plasticity. Brain-derived neurotrophic factor (BDNF) possesses diverse biological functions which are mediated by the activation of two main classes of receptors, the tropomyosin-related kinase (Trk) B and the p75 neurotrophin receptor (p75NTR). The therapeutic potential of BDNF has drawn attention since dysregulation of its signalling cascades has been suggested to underlie the pathogenesis of both common and rare diseases. Multiple strategies targeting this neurotrophin have been tested; most have found obstacles that ultimately hampered their effectiveness. This review focuses on the involvement of BDNF and its receptors in the pathophysiology of Alzheimer's disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Rett Syndrome (RTT). We describe the known mechanisms leading to the impairment of BDNF/TrkB signalling in these disorders. Such mechanistic insight highlights how BDNF signalling compromise can take various shapes, nearly disease-specific. Therefore, BDNF-based therapeutic strategies must be specifically tailored and are more likely to succeed if a combination of resources is employed., The work was supported by Fundação Calouste Gulbenkian and FMUL (grant awarded to T.M.R., 20130002/PEC/BG); Santa Casa da Misericórdia de Lisboa (MB37-2017); Fundação para a Ciência e Tecnologia (FCT, AdoRett – LISBOA-01- 0145-FEDER-031929/2017); Uni-versidade de Lisboa (grant awarded to C.M.L., BD2015); the Association Française du Syndrome de Rett; Program “Educaç ̃ao pela Ciˆencia” Bolsas CHLN/FMUL – GAPIC (Project No. 20190017); Twinning action (Syn-aNet) from the EU H2020 Programme; H2020-WIDESPREAD-05-2017- Twinning (EpiEpinet) (grant agreement No. 952455); and FCT/Minis-t ́erio da Ciˆencia, Tecnologia e Ensino Superior (MCTES), through the Fundos do Orçamento de Estado (UID/BIM/50005/2019). This work was supported by Fundaç ̃ao para a Ciˆencia e a Tecnologia (FCT), Lisboa, Portugal [Fellowship numbers: C.M.L (SFRH/BD/118238/2016), L.R.R (PD/BD/150344/2019), J.F.G (PD/BD/114441/2016), S.R.T (PD/BD/ 128091/2016), R.F.B (PD/BD/114337/2016), C.B.F (PD/BD/128390/ 2017), N.R (PD/BD/113463/2015

© 2020 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/), Rett syndrome (RTT; OMIM#312750) is mainly caused by mutations in the X-linked MECP2 gene (methyl-CpG-binding protein 2 gene; OMIM*300005), which leads to impairments in the brain-derived neurotrophic factor (BDNF) signalling. The boost of BDNF mediated effects would be a significant breakthrough but it has been hampered by the difficulty to administer BDNF to the central nervous system. Adenosine, an endogenous neuromodulator, may accomplish that role since through A2AR it potentiates BDNF synaptic actions in healthy animals. We thus characterized several hallmarks of the adenosinergic and BDNF signalling in RTT and explored whether A2AR activation could boost BDNF actions. For this study, the RTT animal model, the Mecp2 knockout (Mecp2-/y) (B6.129P2 (C)-Mecp2tm1.1Bird/J) mouse was used. Whenever possible, parallel data was also obtained from post-mortem brain samples from one RTT patient. Ex vivo extracellular recordings of field excitatory post-synaptic potentials in CA1 hippocampal area were performed to evaluate synaptic transmission and long-term potentiation (LTP). RT-PCR was used to assess mRNA levels and Western Blot or radioligand binding assays were performed to evaluate protein levels. Changes in cortical and hippocampal adenosine content were assessed by liquid chromatography with diode array detection (LC/DAD). Hippocampal ex vivo experiments revealed that the facilitatory actions of BDNF upon LTP is absent in Mecp2-/y mice and that TrkB full-length (TrkB-FL) receptor levels are significantly decreased. Extracts of the hippocampus and cortex of Mecp2-/y mice revealed less adenosine amount as well as less A2AR protein levels when compared to WT littermates, which may partially explain the deficits in adenosinergic tonus in these animals. Remarkably, the lack of BDNF effect on hippocampal LTP in Mecp2-/y mice was overcome by selective activation of A2AR with CGS21680. Overall, in Mecp2-/y mice there is an impairment on adenosinergic system and BDNF signalling. These findings set the stage for adenosine-based pharmacological therapeutic strategies for RTT, highlighting A2AR as a therapeutic target in this devastating pathology., The work was supported by a joint research grant awarded to TMR from Fundação Calouste Gulbenkian and FMUL (20130002/PEC/BG); Fundação para a Ciência e Tecnologia (FCT, AdoRett – LISBOA-01-0145-FEDER-031929/2017 and FCT SFRH/BD/118238/2016 granted to CML); Universidade de Lisboa (grant awarded by CML BD2015); the Association Française du Syndrome de Rett; Program “Educação pela Ciência” Bolsas CHLN/FMUL – GAPIC (Project No. 20190017); Twinning action (SynaNet) from the EU H2020 Programme; and the UID/BIM/50005/2019, project financed by the FCT/Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), through the Fundos do Orçamento de Estado. The work performed at ICBAS/MedInUP by PCS and TMC was partially supported by FCT (FEDER funding, project UID/BIM/4308/2019 and UIDP/04308/2020).

© 2016 Published by Elsevier Ltd., Age-dependent memory deterioration has been well documented and yet an increase in rat hippocampal LTP upon aging has been reported. This poses the question of whether the enhanced LTP is a cause or an attempt to compensate the memory deficits described in aged rats. Hippocampal slices from young, adult and aged Wistar rats were pre-incubated, with an NMDA receptor (NMDAR) antagonist, memantine (1 μM, 4 h), and hippocampal LTP was evaluated. The results show that memantine significantly decreases the larger LTP magnitude recorded in hippocampal slices from aged rats without compromising LTP recorded in slices from young and adult animals. To unveil the impact of in vivo administration of memantine, different doses (1, 5 and 10 mg/kg/day) or saline vehicle solution were intraperitoneally administered, for 15-20 days, to both young and aged animals. Memantine did not significantly affect neither the place learning of young animals, evaluated by Morris Water Maze, nor LTP recorded from hippocampal slices from the same group of animals. However, memantine (5 and 10 mg/kg/day) significantly decreased the large LTP recorded in hippocampal slices from aged animals. Moreover, aged animals treated with memantine (10 mg/kg/day) showed a significantly compromised place learning when compared to aged control animals. Overall, these results suggest that the larger LTP observed in aged animals is a compensatory phenomenon, rather than pathological. The finding that age-dependent blockade of LTP by a NMDAR antagonist leads to learning deficits, implies that the increased LTP observed upon aging may be playing an important role in the learning process., This work was supported by Bial Foundation (Grant 57/12) and the “Educação pela Ciência” Program, GAPIC/Faculty of Medicine of the University of Lisbon (201100015). LVL is an investigator FCT.

© 2014 Elsevier Ltd. All rights reserved, Brain-derived neurotrophic factor (BDNF) through the activation of its receptor (TrkB-FL) exert well-described neuroprotective effects playing a major role in hippocampal synaptic transmission and plasticity such as long-term potentiation (LTP), a molecular surrogate for learning and memory. Impairments in BDNF signalling have been associated to several neurodegenerative disorders such as Alzheimer's disease (AD). Therefore, the reestablishment of BDNF actions is considered a promising strategy for AD treatment. While, most of BDNF synaptic actions, namely on LTP, require the activation of adenosine A2A receptor (A2AR), the antagonists of A2AR have been proven to prevent AD induced deficits in different animal models. Therefore in this work we aimed to evaluate the impact of a chronic in vivo oral administration of an A2AR antagonist (KW-6002) in the BDNF actions upon hippocampal CA1 LTP. The results showed that chronic blockade of A2AR in male Wistar rats inhibits the facilitatory action of BDNF upon LTP on hippocampal CA1 area and decreases both mRNA and protein levels of the TrkB-FL receptor in hippocampus. These findings imply that BDNF signalling may be affected in chronic A2AR blocking conditions.

Hippocampal Long-Term Potentiation (LTP) is facilitated by BDNF, through the activation of tropomyosin-related kinase B (TrkB) receptors. However, an influence of BDNF upon Long-Term Depression (LTD) was also shown. The present work aimed to further evaluate the effect of BDNF and TrkB receptors upon CA1 hippocampal LTD and to elucidate whether this effect is under the upstream control of other signalling processes, such as the adenosine A(2A)Receptors (A(2A)Rs). LTD, induced by a Low-Frequency Stimulation (LFS, 900 pulses, 1 Hz) in the CA1 area of rat hippocampal slices, was significantly attenuated when these slices were exposed to BDNF (60-100 ng/mL). A lower BDNF concentration (20 ng/ml) was only effective to inhibit LTD if A(2A)Rs were activated by a selective agonist, CGS 21680 (10 nM), or if the extracellular adenosine level was increased by 5-iodotubercidin (100 nM). BDNF (100 ng/ml) effect upon LTD was prevented by K252a (200 nM), which is known to prevent TrkB transphosphorylation, hence suggesting that this action requires TrkB receptor activation. BDNF (100 ng/ml) lacked effect on an adenosine-depleted background (adenosine deaminase, 2 U/ml) or under selective A(2A)R blockade (SCH 58261, 100 nM), indicating that it relies on tonic A(2A)R activation. Forskolin (10 μM), a cell-permeable activator of adenylate cyclase, rescued BDNF (100 ng/ml) effect in slices where A(2A)Rs were blocked with SCH 58261 (100 nM), whereas a PKA inhibitor, H-89 (1 μM), prevented LTD attenuation by BDNF (100 ng/ml). We conclude that the influence of BDNF TrkB receptors upon LTD is under the strict control of A(2A)Rs activation, through a mechanism that requires the cAMP/PKA transducing system.

Adenosine kinase (ADK) deficiency in human patients (OMIM:614300) disrupts the methionine cycle and triggers hypermethioninemia, hepatic encephalopathy, cognitive impairment, and seizures. To identify whether this neurological phenotype is intrinsically based on ADK deficiency in the brain or if it is secondary to liver dysfunction, we generated a mouse model with a brain-wide deletion of ADK by introducing aNestin-Cretransgene into a line of conditional ADK deficient Adkfl/flmice. These AdkΔbrainmice developed a progressive stress-induced seizure phenotype associated with spontaneous convulsive seizures and profound deficits in hippocampus-dependent learning and memory. Pharmacological, biochemical, and electrophysiological studies suggest enhanced adenosine levels around synapses resulting in an enhanced adenosine A1receptor (A1R)-dependent protective tone despite lower expression levels of the receptor. Theta-burst-induced LTP was enhanced in the mutants and this was dependent on adenosine A2Areceptor (A2AR) and tropomyosin-related kinase B signaling, suggesting increased activation of these receptors in synaptic plasticity phenomena. Accordingly, reducing adenosine A2Areceptor activity in AdkΔbrainmice restored normal associative learning and contextual memory and attenuated seizure risk. We conclude that ADK deficiency in the brain triggers neuronal adaptation processes that lead to dysregulated synaptic plasticity, cognitive deficits, and increased seizure risk. Therefore, ADK mutations have an intrinsic effect on brain physiology and may present a genetic risk factor for the development of seizures and learning impairments. Furthermore, our data show that blocking A2AR activity therapeutically can attenuate neurological symptoms in ADK deficiency.SIGNIFICANCE STATEMENTA novel human genetic condition (OMIM #614300) that is based on mutations in the adenosine kinase (Adk) gene has been discovered recently. Affected patients develop hepatic encephalopathy, seizures, and severe cognitive impairment. To model and understand the neurological phenotype of the human mutation, we generated a new conditional knock-out mouse with a brain-specific deletion ofAdk(AdkΔbrain). Similar to ADK-deficient patients, AdkΔbrainmice develop seizures and cognitive deficits. We identified increased basal synaptic transmission and enhanced adenosine A2Areceptor (A2AR)-dependent synaptic plasticity as the underlying mechanisms that govern these phenotypes. Our data show that neurological phenotypes in ADK-deficient patients are intrinsic to ADK deficiency in the brain and that blocking A2AR activity therapeutically can attenuate neurological symptoms in ADK deficiency.

© 2016 – IOS Press and the authors. All rights reserved., Cocoa-related products like chocolate have taken an important place in our food habits and culture. In this work, we aim to examine the relationship between chocolate consumption and cognitive decline in an elderly cognitively healthy population. In the present longitudinal prospective study, a cohort of 531 participants aged 65 and over with normal Mini-Mental State Examination (MMSE; median 28) was selected. The median follow-up was 48 months. Dietary habits were evaluated at baseline. The MMSE was used to assess global cognitive function at baseline and at follow-up. Cognitive decline was defined by a decrease ≥ 2 points in the MMSE score between evaluations. Relative risk (RR) and 95% confidence interval (95% CI) estimates were adjusted for age, education, smoking, alcohol drinking, body mass index, hypertension, and diabetes. Chocolate intake was associated with a lower risk of cognitive decline (RR = 0.59, 95% CI 0.38-0.92). This protective effect was observed only among subjects with an average daily consumption of caffeine lower than 75 mg (69% of the participants; RR = 0.50, 95% CI 0.31-0.82). To our knowledge, this is the first prospective cohort study to show an inverse association between regular long-term chocolate consumption and cognitive decline in humans., Grants from Fundação para a Ciência e a Tecnologia (JNICT UI&D 51/94, POCI/SAU-ESP/61492/2004, POCI/SAU-ESP/61160/2004, JPND-HC/0003/2012) are gratefully acknowledged. The present work was supported by the BIOMARKAPD project, through the funding organisations under the aegis of the EU Joint Programme - NeurodegenerativeDisease Research (JPND) - www.jpnd.eu, namely Fundação para a Ciência e a Tecnologia, Portugal.

International audience; Extracellular adenosine, a key regulator of neuronal excitability, is metabolized by astrocyte-based enzyme adenosine kinase (ADK). We hypothesized that ADK might be an upstream regulator of adenosine-based homeostatic brain functions by simultaneously affecting several downstream pathways. We therefore studied the relationship between ADK expression, levels of extracellular adenosine, synaptic transmission, intrinsic excitability, and brain-derived neurotrophic factor (BDNF)-dependent synaptic actions in transgenic mice underexpressing or overexpressing ADK. We demonstrate that ADK: 1) Critically influences the basal tone of adenosine, evaluated by microelectrode adenosine biosensors, and its release following stimulation; 2) determines the degree of tonic adenosine-dependent synaptic inhibition, which correlates with differential plasticity at hippocampal synapses with low release probability; 3) modulates the age-dependent effects of BDNF on hippocampal synaptic transmission, an action dependent upon co-activation of adenosine A2A receptors; and 4) influences GABAA receptor-mediated currents in CA3 pyramidal neurons. We conclude that ADK provides important upstream regulation of adenosine-based homeostatic function of the brain and that this mechanism is necessary and permissive to synaptic actions of adenosine acting on multiple pathways. These mechanistic studies support previous therapeutic studies and implicate ADK as a promising therapeutic target for upstream control of multiple neuronal signaling pathways crucial for a variety of neurological disorders.

Adenosine neuromodulation depends on a balanced activation of inhibitory A₁ (A₁R) and facilitatory A(₂A) receptors (A(₂A) R). Both A₁ R and A(₂A) R modulate hippocampal glutamate release and NMDA-dependent long-term potentiation (LTP) but ageing affects the density of both A₁ R and A(₂A) R. We tested the effects of selective A₁ R and A(2A) R 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 A(₂A) R 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 A₁ R 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 A(₂A) R mRNA in the hippocampus and a higher number of glutamatergic nerve terminals equipped with A(2A) R in aged (67 ± 6%) compared with middle-aged (34 ± 7%) and young rats (25 ± 5%). The results show an enhanced A(₂A) R-mediated modulation of LTP in aged rats, in accordance with the age-associated increased expression and density of A(₂A) R in glutamatergic terminals. This age-associated gain of function of A(₂A) R modulating synaptic plasticity may underlie the ability of A(₂A) R antagonists to prevent memory dysfunction in aged animals.

The excitatory action of brain-derived neurotrophic factor (BDNF) on synaptic transmission is triggered by adenosine A2A receptor activation. Since high-frequency neuronal firing, such as that inducing long-term potentiation (LTP), favours both A2A receptor activation and BDNF effects on transmission, we now evaluated the influence of adenosine on the facilitatory action of BDNF upon CA1 hippocampal LTP. theta-Burst stimulation of the pyramidal inputs induced a significant and persistent increase in field EPSP slopes, and this potentiation was augmented in the presence of BDNF (20 ng/ml), an action prevented by the inhibitor of Trk receptor autophosphorylation, K252a (200 nM). Removal of endogenous extracellular adenosine with adenosine deaminase (ADA, 1 U/ml), as well as the antagonism of adenosine A2A receptors with SCH58261 (100 nM), prevented the excitatory action of BDNF upon LTP. In an adenosine depleted background (with ADA), activation of adenosine A2A receptors (with 10nM CGS21680) restored the facilitatory effect of BDNF on LTP; this was fully prevented by the protein kinase A inhibitor, H-89 (1 microM) and mimicked by the adenylate cyclase activator, forskolin (10 microM). In similar experiments, activation of adenosine inhibitory A1 receptors (with 5 nM CPA) did not affect the facilitatory effect of BDNF. In conclusion, the facilitatory action of BDNF upon hippocampal LTP is critically dependent on the presence of extracellular adenosine and A2A receptor activation through a cAMP/PKA-dependent mechanism. Since extracellular adenosine accumulates upon high-frequency neuronal firing, the present results reveal a key process to allow the influence of BDNF upon synaptic plasticity.

We previously reported that adenosine, through A2A re- ceptor activation, potentiates synaptic actions of brain-derived neurotro- phic factor (BDNF) in the hippocampus of infant (3-4 weeks) rats. Since A2A-receptor-mediated actions are more evident in old than in young rats and since the therapeutic potential for BDNF-based strategies is greater in old subjects, we now evaluated synaptic actions of BDNF and the levels of TrkB receptors and of adenosine A2A receptors in the hip- pocampus of three groups of adult rats: young adults (10-16 weeks), old adults (36-38 weeks), and aged (70-80 weeks), as well as in one group of infant (3-4 weeks) rats. BDNF (20 ng/ml) enhances field exci- tatory postsynaptic potentials recorded from the hippocampus of young adults and aged rats, an action triggered by adenosine A2A receptor acti- vation, since it was blocked by the A2A receptor antagonist, ZM 241385. In the other groups of animals BDNF (20 ng/ml) was virtually devoid of action on synaptic transmission. Western blot analysis of re- ceptor density shows decreased amounts of TrkB receptors in old adults and aged rats, whereas A2A receptor levels assayed by ligand binding are enhanced in the hippocampus of old adults and aged rats. It is con- cluded that age-related changes in the density of TrkB receptors and of adenosine A2A receptors may be responsible for a nonmonotonous varia- tion of BDNF actions on synaptic transmission in the hippocampus. V C 2007 Wiley-Liss, Inc.

© 2015 Elsevier Ltd. All rights reserved., In the present review, we stress the importance of the purine nucleosides, adenosine and guanosine, in protecting the nervous system, both centrally and peripherally, via activation of their receptors and intracellular signalling mechanisms. A most novel part of the review focus on the mechanisms of neuronal regeneration that are targeted by nucleosides, including a recently identified action of adenosine on axonal growth and microtubule dynamics. Discussion on the role of the purine nucleosides transversally with the most established neurotrophic factors, e.g. brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), is also focused considering the intimate relationship between some adenosine receptors, as is the case of the A2A receptors, and receptors for neurotrophins. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'., The authors work has been funded by Fundação para a Ciência e Tecnologia (FCT) Portugal (EXPL/BIM-MEC/0009/2013). Filipa F Ribeiro was in receipt of a fellowship (SFRH/BD/74662/2010) from FCT

© 2015 Taylor & Francis., Brain-derived neurotrophic factor (BDNF) promotes neuronal survival through TrkB-FL activation. The activation of adenosine A2A receptors (A2AR) is essential for most of BDNF-mediated synaptic actions, such as synaptic plasticity, transmission and neurotransmitter release. We now aimed at evaluating the A2AR influence upon BDNF-mediated neuroprotection against Aβ25-35 toxicity in cultured neurons. Results showed that BDNF increases cell survival and reduces the caspase-3 and calpain activation induced by amyloid-β (Aβ) peptide, in a mechanism probably dependent on PLCγ pathway. This BDNF-mediated neuroprotection is not affected by A2AR activation or inhibition. Moreover neither activation nor inhibition of A2AR, per se, significantly influenced Aβ-induced neuronal death on calpain-mediated cleavage of TrkB induced by Aβ. In conclusion, these results suggest that, in opposition to the fast synaptic actions of BDNF, the neuroprotective actions of this neurotrophin against a strong Aβ insult do not require the activation of A2AR., The work was supported by Fundação para a Ciência e a Tecnologia (FCT) and Gabinete de Apoio à Investigação Científica, Tecnológica e Inovação (GAPIC), Faculty of Medicine of Lisbon, University of Lisbon, Portugal—16th Programme for Education and Science. AJS and RMR were supported by FCT (AJS: SFRH/BD/62828/2009; RMR: SFRH/BPD/94474/2013).

Neurotrophic factors (NTF) or drugs able to boost NTF actions have been frequently considered as promising therapies for neurodegenerative diseases namely for Parkinson’s disease (PD).

© Springer International Publishing Switzerland 2014, Parkinson's disease (PD) is a chronic movement disorder typically coupled to progressive degeneration of dopaminergic neurons in the substantia nigra (SN). The treatments currently available are satisfactory for symptomatic management, but the efficacy tends to decrease as neuronal loss progresses. Neurotrophic factors (NTFs) are endogenous proteins known to promote neuronal survival, even in degenerating states. Therefore, the use of these factors is regarded as a possible therapeutic approach, which would aim to prevent PD or to even restore homeostasis in neurodegenerative disorders. Intriguingly, although favorable results in in vitro and in vivo models of the disease were attained, clinical trials using these molecules have failed to demonstrate a clear therapeutic benefit. Therefore, the development of animal models that more closely reproduce the mechanisms known to underlie PD-related neurodegeneration would be a major step towards improving the capacity to predict the clinical usefulness of a given NTF-based approach in the experimental setting. Moreover, some adjustments to the design of clinical trials ought to be considered, which include recruiting patients in the initial stages of the disease, improving the efficacy of the delivery methods, and combining synergetic NTFs or adding NTF-boosting drugs to the already available pharmacological approaches. Despite the drawbacks on the road to the use of NTFs as pharmacological tools for PD, very relevant achievements have been reached. In this article, we review the current status of the potential relevance of NTFs for treating PD, taking into consideration experimental evidence, human observational studies, and data from clinical trials., This work was supported by a Fundação para a Ciência e a Tecnologia (FCT) project grant. André Jerónimo-Santos is supported by an FCT fellowship grant (SFRH/BD/62828/2009) and Tiago Fleming Outeiro is supported by the DFG Center for Nanoscale Microscopy and Molecular Physiology of the Brain.

Copyright © 2012 the authors, Parkinson's disease (PD) is the most common representative of a group of disorders known as synucleinopathies, in which misfolding and aggregation of α-synuclein (a-syn) in various brain regions is the major pathological hallmark. Indeed, the motor symptoms in PD are caused by a heterogeneous degeneration of brain neurons not only in substantia nigra pars compacta but also in other extrastriatal areas of the brain. In addition to the well known motor dysfunction in PD patients, cognitive deficits and memory impairment are also an important part of the disorder, probably due to disruption of synaptic transmission and plasticity in extrastriatal areas, including the hippocampus. Here, we investigated the impact of a-syn aggregation on AMPA and NMDA receptor-mediated rat hippocampal (CA3-CA1) synaptic transmission and long-term potentiation (LTP), the neurophysiological basis for learning and memory. Our data show that prolonged exposure to a-syn oligomers, but not monomers or fibrils, increases basal synaptic transmission through NMDA receptor activation, triggering enhanced contribution of calcium-permeable AMPA receptors. Slices treated with a-syn oligomers were unable to respond with further potentiation to theta-burst stimulation, leading to impaired LTP. Prior delivery of a low-frequency train reinstated the ability to express LTP, implying that exposure to a-syn oligomers drives the increase of glutamatergic synaptic transmission, preventing further potentiation by physiological stimuli. Our novel findings provide mechanistic insight on how a-syn oligomers may trigger neuronal dysfunction and toxicity in PD and other synucleinopathies., This research is supported by a Marie Curie International Reintegration Grant (Neurofold; T.F.O.), an EMBO Installation Grant, Fundação para a Ciência e Tecnologia (FCT), PTDC/QUI/73430/2006 Grant from FCT (A.Q), PDCT/SAU-NMC/099853/2008 from FCT (L.V.L.), PDCT/SAU-NMC/110838/2009 from FCT (A.M.S.), FCT fellowships SFRH/BD/60386/2009 (D.M.R.) and SFRH/BD/27761/2006 (R.B.D.), FCT fellowship SFRH/BPD/64702/2009 (H.V.M.), and by the University of Rome Sapienza (F.M.). We also thank Alex Kasrayan and Monica Ekberg for the production of recombinant a-syn.

In situations of hypoxia, glutamate excitotoxicity induces neuronal death. The release of extracellular adenosine is also triggered and is accompanied by an increase of the stress mediator, corticotrophin-releasing factor (CRF). Adenosine A(2A) receptors contribute to glutamate excitoxicity and their blockade is effective in stress-induced neuronal deficits, but the involvement of CRF on this effect was never explored. We now evaluated the interaction between A(2A) and CRF receptors (CRFR) function, upon glutamate insult. Primary rat cortical neuronal cultures (9 days in vitro) expressing both CRF(1)R and CRF(2)R were challenged with glutamate (20-1000 μM, 24 h). CRF(1)R was found to co-localize with neuronal markers and CRF(2)R to be present in both neuronal and glial cells. The effects of the CRF and A(2A) receptors ligands on cell viability were measured using propidium iodide and Syto-13 fluorescence staining. Glutamate decreased cell viability in a concentration-dependent manner. Urocortin (10 pM), an agonist of CRF receptors, increased cell survival in the presence of glutamate. This neuroprotective effect was abolished by blocking either CRF(1)R or CRF(2)R with antalarmin (10 nM) or anti-Sauvagine-30 (10 nM), respectively. The blockade of A(2A) receptors with a selective antagonist SCH 58261 (50 nM) improved cell viability against the glutamate insult. This effect was dependent on CRF(2)R, but not on CRF(1)R activation. Overall, these data show a protective role of CRF in cortical neurons, against glutamate-induced death. The neuroprotection achieved by A(2A) receptors blockade requires CRF(2)R activation. This interaction between the adenosine and CRF receptors can explain the beneficial effects of using A(2A) receptor antagonists against stress-induced noxious effects.

Neuronal oxidative damage and cell death by unconjugated bilirubin (UCB) showed to be mediated by overstimulation of glutamate receptors and nitric oxide (NO) production, which was abrogated by the bile acid glycoursodeoxycholic acid (GUDCA). Microglia, a crucial mediator of CNS inflammation, evidenced to react to UCB by releasing glutamate and NO before becoming senescent. Our studies demonstrated that neurite outgrowth deficits are produced in neurons exposed to UCB and that conditioned media from these UCB-treated neurons further stimulate NO production by microglia. Nevertheless, microglia protective and/or harmful effects in neonatal jaundice are poorly understood, or unrecognized. Here, we investigated the role of microglia, glutamate and NO in the impairment of neurite sprouting by UCB. Therapeutic potential of the anti-inflammatory cytokine interleukin (IL)-10 and GUDCA was also evaluated. By using MK-801 (a NMDA glutamate-subtype receptor antagonist) and L-NAME (a non-specific NO synthase inhibitor) we found that glutamate and NO are determinants in the early and enduring deficits in neurite extension and ramification induced by UCB. Both GUDCA and IL-10 prevented these effects and decreased the production of glutamate and NO. Only GUDCA was able to counteract neuronal death and synaptic changes. Data from organotypic-cultured hippocampal slices, depleted or non-depleted in microglia, supported that microglia participate in glutamate homeostasis and contribute to NO production and cell demise, which were again abrogated by GUDCA. Collectively our data suggest that microglia is a key player in UCB-induced neurotoxicity and that GUDCA might be a valuable preventive therapy in neonates at risk of UCB encephalopathy.

© 2011 American College of Neuropsychopharmacology., Long-term potentiation (LTP), considered the neurophysiological basis for learning and memory, is facilitated by brain-derived neurotrophic factor (BDNF), an action more evident when LTP is evoked by weak θ-burst stimuli and dependent on co-activation of adenosine A2A receptors (A2AR), which are more expressed in aged rats. As θ-burst stimuli also favor LTP in aged animals, we hypothesized that enhanced LTP in aging could be related to changes in neuromodulation by BDNF. The magnitude of CA1 LTP induced by a weak θ-burst stimuli delivered to the Schaffer collaterals was significantly higher in hippocampal slices taken from 36 to 38 and from 70 to 80-week-old rats, when compared with LTP magnitude in slices from 4 or 10 to 15-week-old rats; this enhancement does not impact in cognitive improvement as aged rats revealed an impairment on hippocampal-dependent learning and memory performance, as assessed by the Morris water maze tests. The scavenger for BDNF, TrkB-Fc, and the inhibitor of Trk phosphorylation, K252a, attenuated LTP in slices from 70 to 80-week-old rats, but not from 10 to 15-week-old rats. When exogenously added, BDNF significantly increased LTP in slices from 4 and 10 to 15-week-old rats, but did not further increased LTP in 36 to 38 or 70 to 80-week-old rats. The effects of exogenous BDNF on LTP were prevented by the A2AR antagonist, SCH58261 (7-(2-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine). These results indicate that the higher LTP magnitude observed upon aging, which does not translate into improved spatial memory performance, is a consequence of an increase in the tonic action of endogenous BDNF., Fundação para a Ciência e Tecnologia, Fundação Calouste Gulbenkian and EU (COST B-30 concerted action)

Neurodegenerative disorders are devastating human diseases that include Parkinson's, Huntington's, Alzheimer's, amyotrophic lateral sclerosis, and the frontal temporal dementias. Although the clinical manifestations of these disorders have been known for quite some time, our understanding of the molecular underpinnings is only starting to emerge. Protein misfolding and aggregation is a common hallmark among these diseases, and produce a number of cellular and functional alterations. The loss of dopaminergic neurons in the substantia nigra justified the use of dopaminergic therapies in patients. However, these strategies do not appear to confer disease-modifying effects, and do not prevent progression. The idea that neurotrophic factors might promote cell survival is an attractive one. Existing evidence from clinical trials is currently inconclusive, but some patients display clear clinical benefits. Thus, the current challenge is to develop novel strategies that make the use of neurotrophic factors more consistent.

Objective Rett syndrome is the main cause of intellectual disability in females and is caused mainly by mutations in the X-linked MECP2 gene. In Rett syndrome, brain-derived neurotrophic factor (BDNF) signaling is impaired. BDNF regulates neuronal survival, differentiation and synaptic plasticity such as long-term potentiation, accepted as the neurophysiological basis for learning and memory. The increase of BDNF signaling would be a significant breakthrough, but has been hampered by the difficulty to administer BDNF to the central nervous system. Adenosine is a neuromodulator that acts mainly through A1 and A2A receptors. The activation of A2A receptors potentiates BDNF synaptic actions in healthy animals. Therefore, we explored whether the activation of A2AR facilitates BDNF action upon long term potentiation in a Rett Syndrome animal model. Methods MECP2 Knockout (B6.129P2 (C)-Mecp2tm1.1Bird/J) animals were used for neurophysiological and molecular assay. Results BDNF facilitatory actions upon long term potentiation are absent in the Rett Syndrome animal model. This dysfunction could be explained by a reduction in TrkB full length receptors levels, described for the first time in the present study. Additionally, we found that adenosinergic system is also compromised in the Rett syndrome model with a possible reduction on adenosine levels and a consequent decrease of inhibitory adenosinergic tonus via A1R and A2AR. When BDNF was combined with the selective A2A receptor agonist, CGS2168, the BDNF effect upon long term potentiation was restored, similar to what was observed in hippocampal slices from wild type animals with BDNF alone. Conclusion Together, our data highlight A2A receptors as new possible therapeutic targets for boosting BDNF effects in Rett syndrome.

© 2006 Elsevier, Motor nerve terminals possess adenosine A2A receptors and brain derived neurotrophic factor (BDNF) TrkB receptors. In the present work we evaluated how BDNF actions on neuromuscular transmission would be influenced by adenosine A2A receptors activation. BDNF (20–100 ng/ml)on its own was devoid of effect on evoked endplate potentials (EPPs) recorded intracellularly from rat innervated diaphragms paralysed with tubocurarine. However, when BDNF was applied 45 min after a brief (2 min) depolarizing KCl (10 mM) pulse or when the adenosine A2A receptors were activated with CGS 21680 (10 nM), BDNF (20 ng/ml) increased EPPs amplitude without influencing the resting membrane potential of the muscle fibre. The action of BDNF was prevented by the adenosine A2A receptor antagonist, ZM 241385 (50 nM) as well as by the TrkB receptor phosphorylation inhibitor, K252a (200 nM). The PKA inhibitor, H-89 (1 μM), prevented the excitatory effect of CGS 21680 (10 nM) on EPPs as well as prevented its ability to trigger a BDNF effect. The PLCγ inhibitor, U73122 (5 μM), did not prevent the excitatory action of CGS 21680 (10 nM) on neuromuscular transmission, but abolished the action of BDNF in the presence of the A2A receptor agonist. The results suggest the following sequence of events in what concerns cooperativity between A2A receptors and TrkB receptors at the neuromuscular junction: A2A receptor activates the PKA pathway, which promotes the action of BDNF through TrkB receptors coupled to PLCγ, leading to enhancement of neuromuscular transmission., Work supported by Fundação para a Ciência e Tecnologia (FCT), Portugal

Both brain-derived neurotrophic factor (BDNF) and adenosine influence neuronal plasticity. We now investigated how adenosine influences the action of BDNF on synaptic transmission in the CA1 area of the rat hippocampal slices. Alone, BDNF (20–100 ng/ml) did not significantly affect field EPSPs (fEPSPs). However, a 2 min pulse of high-K+(10 mm) 46 min before the application of BDNF (20 ng/ml) triggered an excitatory action, an effect blocked by the TrkB receptor inhibitor K252a (200 nm), by the adenosine A2Areceptor antagonist ZM 241385 (50 nm), and by the protein kinase A inhibitor H-89 (1 μm). Presynaptic, rather than postsynaptic depolarization was required to trigger the BDNF action because after K+depolarization BDNF also increased EPSCs recorded from pyramidal neurons voltage-clamped at –60 mV, and transient postsynaptic depolarization was unable to unmask the BDNF action. A weak theta burst stimulation of the afferents could elicit potentiation of synaptic transmission only when applied in the presence of BDNF. Activation of adenosine A2Areceptors with CGS 21680 (10 nm), or the increase in extracellular adenosine levels induced by 5-iodotubercidin (100 nm) triggered the excitatory action of BDNF, a process prevented by ZM 241385 and by H-89. In the presence of dibutyryl-cAMP (0.5 mm), BDNF also increased fEPSPs but postsynaptic cAMP (0.5 mm) was unable to trigger the BDNF action.It is concluded that presynaptic activity-dependent release of adenosine, through activation of A2Areceptors, facilitates BDNF modulation of synaptic transmission at hippocampal synapses.

The pathogenesis of cholestasis, bilirubin encephalopathy, and Alzheimer's disease appears to result from accumulation of diverse cytotoxic agents, which in turn may cause apoptotic cell death. In addition, mitochondria has lately been considered as a central executioner of programmed cell death, through the release of caspase activating factors. The aims of this study were to: (a) investigate mitochondrial perturbation during incubation of isolated mitochondria with unconjugated bilirubin (Bb), amyloid beta-peptide (A beta), and glycochenodeoxycholate (GCDC); (b) characterize membrane perturbation in isolated mitochondria induced by each toxic agent, and determine whether the mitochondrial permeabilization is required for cytochrome c redistribution. Mitochondria were isolated from rat liver and brain. Swelling and cytochrome c release were evaluated by spectrophotometry and western blot, respectively. The results showed that Bb as well as A beta and GCDC act directly at the mitochondrial level causing increased organelle volume, permeabilization, as well as cytochrome c release from the intermembrane space in a dose-dependent manner (P0.01). Moreover, cyclosporine A inhibited mitochondrial permeability, particularly after Bb- and GCDC-induced swelling (P0.01). Cytochrome c efflux was invariably prevented by cyclosporine A (P0.05). In conclusion, the results indicate that Bb-, A beta-, and GCDC-induced toxicity, culminating in apoptosis, may result from enhanced mitochondrial permeability, followed by cytochrome c efflux, which can be explained at least in part by the megapore opening.

International audience; Brain-derived neurotrophic factor (BDNF) plays an important role in neuronal plasticity, learning, and memory. Levels of BDNF and its main receptor TrkB (TrkB.TK) have been reported to be decreased while the levels of the truncated TrkB (TrkB.T1) are increased in Alzheimer's disease. We show here that incubation with amyloid-β increased TrkB.T1 receptor levels and decreased TrkB.TK levels in primary neurons. In vivo, APPswe/PS1dE9 transgenic mice (APdE9) showed an age-dependent relative increase in cortical but not hippocampal TrkB.T1 receptor levels compared with TrkB.TK. To investigate the role of TrkB isoforms in Alzheimer's disease, we crossed AP mice with mice overexpressing the truncated TrkB.T1 receptor (T1) or the full-length TrkB.TK isoform. Overexpression of TrkB.T1 in APdE9 mice exacerbated their spatial memory impairment while the overexpression of TrkB.TK alleviated it. These data suggest that amyloid-β changes the ratio between TrkB isoforms in favor of the dominant-negative TrkB.T1 isoform both in vitro and in vivo and supports the role of BDNF signaling through TrkB in the pathophysiology and cognitive deficits of Alzheimer's disease.

© The Author 2014. Published by Oxford University Press. All rights reserved., Brain-derived neurotrophic factor (BDNF) and its high-affinity full-length (FL) receptor, TrkB-FL, play a central role in the nervous system by providing trophic support to neurons and regulating synaptic plasticity and memory. TrkB and BDNF signaling are impaired in Alzheimer's disease (AD), a neurodegenerative disease involving accumulation of amyloid-β (Aβ) peptide. We recently showed that Aβ leads to a decrease of TrkB-FL receptor and to an increase of truncated TrkB receptors by an unknown mechanism. In the present study, we found that (1) Aβ selectively increases mRNA levels for the truncated TrkB isoforms without affecting TrkB-FL mRNA levels, (2) Aβ induces a calpain-mediated cleavage on TrkB-FL receptors, downstream of Shc-binding site, originating a new truncated TrkB receptor (TrkB-T') and an intracellular fragment (TrkB-ICD), which is also detected in postmortem human brain samples, (3) Aβ impairs BDNF function in a calpain-dependent way, as assessed by the inability of BDNF to modulate neurotransmitter (GABA and glutamate) release from hippocampal nerve terminals, and long-term potentiation in hippocampal slices. It is concluded that Aβ-induced calpain activation leads to TrkB cleavage and impairment of BDNF neuromodulatory actions., This work was supported by Fundação para a Ciência e a Tecnologia (FCT) Grants SFRH/BD/62828/2009 (to A.J.S.) and SFRH/BPD/81627/2011 (to S.H.V.), EU (COST B-30 concerted action), Gabinete de Apoio à Investigação Científica, Tecnológica e Inovação (GAPIC)—15th Programme for Education and Science (to S.P and S.L), and Bayer grant (to A.P.C). D.B. and V.B.S. are supported by the LabEx (excellence laboratory) DISTALZ (Development of Innovative Strategies for a Transdisciplinary approach to Alzheimer's disease), Inserm, CNRS, DN2M, FEDER, France Alzheimer, Région Nord/Pas-de-Calais, LECMA, ANR (ADORATAU), and FUI MEDIALZ. E.C are supported by ERC AdG 322742-iPlasticity, Academy of Finland CoE Program and Sigrid Jusus foundation.