Search

Patients under cannabis-based therapies are usually chronically exposed to cannabinoids. Chronic treatment with a cannabinoid receptor agonist, WIN 55,212–2, affects brain metabolism and modifies functional connectivity between brain areas responsible for memory and learning. Therefore, it is of uttermost importance to discover strategies to mitigate the negative side-effects of cannabinoid-based therapies. Previously, we showed that a single treatment with the synthetic cannabinoid WIN 55,212-2 disrupts recognition memory, an effect mediated by cannabinoid receptor 1 (CB1R) and cancelled by concomitant administration of adenosine A2A receptor (A2AR) antagonists. We herein evaluate if memory deficits induced by chronic exposure to WIN 55,212–2 can also be reverted by A2AR antagonism, and assessed the synaptic mechanisms that could be involved in that reversal. We show that chronic administration of KW-6002 (istradefylline) (3 mg/kg/28days) reverts memory deficits (evaluated through the Novel Object Recognition Test) induced by chronic cannabinoid exposure (WIN 55,212–2, 1 mg/kg/28 days). Long Term Potentiation (LTP) of synaptic potentials recorded from the CA1 area of the hippocampus was impaired by WIN 55,212–2 (300 nM), an effect partially rescued by the A2AR antagonist, SCH 58261 (100 nM). Chronic administration of KW-6002 or WIN 55,212-2 did not affect A2AR or CB1R binding in the hippocampus and in the prefrontal cortex. These results, showing that A2AR antagonism can still revert memory deficits after chronic administration of a cannabinoid, an effect that involves mitigation of synaptic plasticity impairment, strongly indicate that adenosine A2ARs are appropriate targets to tackle side-effects of putative therapies involving the activation of cannabinoid receptors.

© 2017 Elsevier Ltd. All rights reserved., Cannabinoid-mediated memory impairment is a concern in cannabinoid-based therapies. Caffeine exacerbates cannabinoid CB1 receptor (CB1R)-induced memory deficits through an adenosine A1 receptor-mediated mechanism. We now evaluated how chronic or acute blockade of adenosine A2A receptors (A2ARs) affects long-term episodic memory deficits induced by a single injection of a selective CB1R agonist. Long-term episodic memory was assessed by the novel object recognition (NOR) test. Mice received an intraperitoneal (i.p.) injection of the CB1/CB2 receptor agonist WIN 55,212-2 (1 mg/kg) immediately after the NOR training, being tested for novelty recognition 24 h later. Anxiety levels were assessed by the Elevated Plus Maze test, immediately after the NOR. Mice were also tested for exploratory behaviour at the Open Field. For chronic A2AR blockade, KW-6002 (istradefylline) (3 mg/kg/day) was administered orally for 30 days; acute blockade of A2ARs was assessed by i.p. injection of SCH 58261 (1 mg/kg) administered either together with WIN 55,212-2 or only 30 min before the NOR test phase. The involvement of CB1Rs was assessed by using the CB1R antagonist, AM251 (3 mg/kg, i.p.). WIN 55,212-2 caused a disruption in NOR, an action absent in mice also receiving AM251, KW-6002 or SCH 58261 during the encoding/consolidation phase; SCH 58251 was ineffective if present during retrieval only. No effects were detected in the Elevated Plus maze or Open Field Test. The finding that CB1R-mediated memory disruption is prevented by antagonism of adenosine A2ARs, highlights a possibility to prevent cognitive side effects when therapeutic application of CB1R drugs is desired., Work supported by FCT (Fundação para a Ciência e Tecnologia, PTDC/DTP-FTO/3346/2014). FMM was in receipt of an FCT fellowship (SFRH/BD/89582/2012).

Amyotrophic Lateral Sclerosis (ALS) mostly affects motor neurons, but non-motor neural and cognitive alterations have been reported in ALS mouse models and patients. Here, we evaluated if time-dependent biphasic changes in synaptic transmission and plasticity occur in hippocampal synapses of ALS SOD1

Patients under cannabis-based therapies are usually chronically exposed to cannabinoids. Chronic treatment with a cannabinoid receptor agonist, WIN 55,212-2, affects brain metabolism and modifies functional connectivity between brain areas responsible for memory and learning. Therefore, it is of uttermost importance to discover strategies to mitigate the negative side-effects of cannabinoid-based therapies. Previously, we showed that a single treatment with the synthetic cannabinoid WIN 55,212-2 disrupts recognition memory, an effect mediated by cannabinoid receptor 1 (CB

Amyotrophic Lateral Sclerosis (ALS) mostly affects motor neurons, but non-motor neural and cognitive alterations have been reported in ALS mouse models and patients. Here, we evaluated if time-dependent biphasic changes in synaptic transmission and plasticity occur in hippocampal synapses of ALS SOD1G93A mice. Recordings were performed in hippocampal slices of SOD1G93A and age-matched WT mice, in the pre-symptomatic and symptomatic stages. We found an enhancement of pre-synaptic function and increased adenosine A2A receptor levels in the hippocampus of pre-symptomatic mice. In contrast, in symptomatic mice, there was an impairment of long-term potentiation (LTP) and a decrease in NMDA receptor-mediated synaptic currents, with A2AR levels also being increased. Chronic treatment with the A2AR antagonist KW-6002, rescued LTP and A2AR values. Altogether, these findings suggest an increase in synaptic function during the pre-symptomatic stage, followed by a decrease in synaptic plasticity in the symptomatic stage, which involves over-activation of A2AR from early disease stages.

© 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.

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.

© 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

Long lasting enhancement of synaptic transmission can be triggered by brief bursts of afferent stimulation, underlying long-term potentiation (LTP), and also by brief ischemia in a process known as i-LTP. The extent to which LTP and i-LTP rely on comparable cellular mechanisms remains unclear. Under physiological conditions, LTP induction drives transient expression of calcium-permeable AMPARs (CP-AMPARs) at synapses, whose ability to undergo plasticity is primed by endogenous activation of adenosine A(2A) receptors (A(2A)Rs). The present work thus addressed the contribution of CP-AMPARs and A(2A)Rs to i-LTP, which was induced in rat hippocampal slices by brief (10 min) oxygen/glucose deprivation (OGD). The amplitude of afferent-evoked excitatory postsynaptic currents (EPSCs) recorded from CA1 pyramidal neurons was decreased during OGD but gradually recovered toward values significantly above (157 ± 17%) the baseline (100%) 40-50 min after re-oxygenation. This i-LTP was precluded by CP-AMPAR blockade (internal spermine (500 μM) or extracellular NASPM (20 μM) application) as well as by A(2A)R blockade with a selective antagonist (SCH 58261, 100 nM). OGD prompted sustained (>70 min) facilitation of mEPSC amplitude and frequency, and decreased mEPSC decay time, all of which were prevented by SCH 58261 (100 nM). The ability of NASPM (20 μM) to acutely inhibit EPSCs 1 h after OGD, but not in control conditions nor in OGD-challenged slices when in the presence of SCH 58261 (100 nM), further supports sustained CP-AMPAR recruitment by i-LTP in an A(2A)R-dependent way. We propose that although i-LTP may initially mimic LTP, failure of auto-regulated CP-AMPAR removal from synapses could constitute an early divergent event between these forms of plasticity.

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.

The synapse is a crowded area. In the last years, the concept that proteins can be organized in different membrane domains according to their structure has emerged. Cholesterol-rich membrane domains, or lipid rafts, form an organized portion of the membrane that is thought to concentrate signaling molecules. Accumulating evidence has shown that both the pre-synaptic and post-synaptic sites are highly enriched in lipid rafts, which are likely to organize and maintain synaptic proteins in their precise localization. Here we review recent studies highlighting the importance of lipid rafts for synaptic function and plasticity, as well as their relevance for age or disease-related cognitive impairment. This article is part of a Special Issue entitled ‘Cognitive Enhancers’.