RESUMO
Impulsive choice, often characterized by excessive preference for small, short-term rewards over larger, long-term rewards, is a prominent feature of substance use and other neuropsychiatric disorders. The neural mechanisms underlying impulsive choice are not well understood, but growing evidence implicates nucleus accumbens (NAc) dopamine and its actions on dopamine D2 receptors (D2Rs). Because several NAc cell types and afferents express D2Rs, it has been difficult to determine the specific neural mechanisms linking NAc D2Rs to impulsive choice. Of these cell types, cholinergic interneurons (CINs) of the NAc, which express D2Rs, have emerged as key regulators of striatal output and local dopamine release. Despite these relevant functions, whether D2Rs expressed specifically in these neurons contribute to impulsive choice behavior is unknown. Here, we show that D2R upregulation in CINs of the mouse NAc increases impulsive choice as measured in a delay discounting task without affecting reward magnitude sensitivity or interval timing. Conversely, mice lacking D2Rs in CINs showed decreased delay discounting. Furthermore, CIN D2R manipulations did not affect probabilistic discounting, which measures a different form of impulsive choice. Together, these findings suggest that CIN D2Rs regulate impulsive decision-making involving delay costs, providing new insight into the mechanisms by which NAc dopamine influences impulsive behavior.
Assuntos
Núcleo Accumbens , Receptores de Dopamina D2 , Camundongos , Animais , Núcleo Accumbens/metabolismo , Receptores de Dopamina D2/metabolismo , Dopamina/metabolismo , Comportamento Impulsivo/fisiologia , Recompensa , Colinérgicos , Interneurônios/metabolismo , Receptores de Dopamina D1/metabolismoRESUMO
Impulsive choice, often characterized by excessive preference for small, short-term rewards over larger, long-term rewards, is a prominent feature of substance use and other neuropsychiatric disorders. The neural mechanisms underlying impulsive choice are not well understood, but growing evidence implicates nucleus accumbens (NAc) dopamine and its actions on dopamine D2 receptors (D2Rs). Because several NAc cell types and afferents express D2Rs, it has been difficult to determine the specific neural mechanisms linking NAc D2Rs to impulsive choice. Of these cell types, cholinergic interneurons (CINs) of the NAc, which express D2Rs, have emerged as key regulators of striatal output and local dopamine release. Despite these relevant functions, whether D2Rs expressed specifically in these neurons contribute to impulsive choice behavior is unknown. Here, we show that D2R upregulation in CINs of the mouse NAc increases impulsive choice as measured in a delay discounting task without affecting reward magnitude sensitivity or interval timing. Conversely, mice lacking D2Rs in CINs showed decreased delay discounting. Furthermore, CIN D2R manipulations did not affect probabilistic discounting, which measures a different form of impulsive choice. Together, these findings suggest that CIN D2Rs regulate impulsive decision-making involving delay costs, providing new insight into the mechanisms by which NAc dopamine influences impulsive behavior.
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Sex differences are found in brain structure and function across species, and across brain disorders in humans1-3. The major source of brain sex differences is differential secretion of steroid hormones from the gonads across the lifespan4. Specifically, ovarian hormones oestrogens and progesterone are known to dynamically change structure and function of the adult female brain, having a major impact on psychiatric risk5-7. However, due to limited molecular studies in female rodents8, very little is still known about molecular drivers of female-specific brain and behavioural plasticity. Here we show that overexpressing Egr1, a candidate oestrous cycle-dependent transcription factor9, induces sex-specific changes in ventral hippocampal neuronal chromatin, gene expression, and synaptic plasticity, along with hippocampus-dependent behaviours. Importantly, Egr1 overexpression mimics the high-oestrogenic phase of the oestrous cycle, and affects behaviours in ovarian hormone-depleted females but not in males. We demonstrate that Egr1 opens neuronal chromatin directly across the sexes, although with limited genomic overlap. Our study not only reveals the first sex-specific chromatin regulator in the brain, but also provides functional evidence that this sex-specific gene regulation drives neuronal gene expression, synaptic plasticity, and anxiety- and depression-related behaviour. Our study exemplifies an innovative sex-based approach to studying neuronal gene regulation1 in order to understand sex-specific synaptic and behavioural plasticity and inform novel brain disease treatments.
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The navigation systems of autonomous aircraft rely on the readings provided by a suite of onboard sensors to estimate the aircraft state. In the case of fixed wing vehicles, the sensor suite is usually composed by triads of accelerometers, gyroscopes, and magnetometers, a Global Navigation Satellite System (GNSS) receiver, and an air data system (Pitot tube, air vanes, thermometer, and barometer), and it is often complemented by one or more digital cameras. An accurate representation of the behavior and error sources of each of these sensors, together with the images generated by the cameras, is indispensable for the design, development, and testing of inertial, visual, or visual-inertial navigation algorithms. This article presents realistic and customizable models for each of these sensors; a ready-to-use C++ implementation is released as open-source code so non-experts in the field can easily generate realistic results. The pseudo-random models provide a time-stamped series of the errors generated by each sensor based on performance values and operating frequencies obtainable from the sensor's data sheets. If in addition, the simulated true pose (position plus attitude) of the aircraft is provided, the camera model generates realistic images of the Earth's surface that resemble those taken with a real camera from the same pose.
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It was first posited, more than five decades ago, that the etiology of schizophrenia involves overstimulation of dopamine receptors. Since then, advanced clinical research methods, including brain imaging, have refined our understanding of the relationship between striatal dopamine and clinical phenotypes as well as disease trajectory. These studies point to striatal dopamine D2 receptors, the main target for all current antipsychotic medications, as being involved in both positive and negative symptoms. Simultaneously, animal models have been central to investigating causal relationships between striatal dopamine D2 receptors and behavioral phenotypes relevant to schizophrenia. We begin this article by reviewing the circuit, cell-type and subcellular locations of dopamine D2 receptors and their downstream signaling pathways. We then summarize results from several mouse models in which D2 receptor levels were altered in various brain regions, cell-types and developmental periods. Behavioral, electrophysiological and anatomical consequences of these D2 receptor perturbations are reviewed with a selective focus on striatal circuit function and alterations in motivated behavior, a core negative symptom of schizophrenia. These studies show that D2 receptors serve distinct physiological roles in different cell types and at different developmental time points, regulating motivated behaviors in sometimes opposing ways. We conclude by considering the clinical implications of this complex regulation of striatal circuit function by D2 receptors.
Assuntos
Motivação , Esquizofrenia , Animais , Corpo Estriado/metabolismo , Camundongos , Receptores de Dopamina D1/metabolismo , Receptores de Dopamina D2/metabolismo , Esquizofrenia/metabolismoRESUMO
Cholinergic interneurons (CINs) in the striatum respond to salient stimuli with a multiphasic response, including a pause, in neuronal activity. Slice-physiology experiments have shown the importance of dopamine D2 receptors (D2Rs) in regulating CIN pausing, yet the behavioral significance of the CIN pause and its regulation by dopamine in vivo is still unclear. Here, we show that D2R upregulation in CINs of the nucleus accumbens (NAc) lengthens the pause in CIN activity ex vivo and enlarges a stimulus-evoked decrease in acetylcholine (ACh) levels during behavior. This enhanced dip in ACh levels is associated with a selective deficit in the learning to inhibit responding in a Go/No-Go task. Our data demonstrate, therefore, the importance of CIN D2Rs in modulating the CIN response induced by salient stimuli and point to a role of this response in inhibitory learning. This work has important implications for brain disorders with altered striatal dopamine and ACh function, including schizophrenia and attention-deficit hyperactivity disorder (ADHD).
Assuntos
Dopamina , Receptores de Dopamina D2 , Acetilcolina , Colinérgicos , Corpo Estriado , Interneurônios/fisiologia , Núcleo AccumbensRESUMO
The dopamine (DA) D2 receptor (D2R) is an important target for the treatment of neuropsychiatric disorders such as schizophrenia and Parkinson's disease. However, the development of improved therapeutic strategies has been hampered by our incomplete understanding of this receptor's downstream signaling processes in vivo and how these relate to the desired and undesired effects of drugs. D2R is a G protein-coupled receptor (GPCR) that activates G protein-dependent as well as non-canonical arrestin-dependent signaling pathways. Whether these effector pathways act alone or in concert to facilitate specific D2R-dependent behaviors is unclear. Here, we report on the development of a D2R mutant that recruits arrestin but is devoid of G protein activity. When expressed virally in "indirect pathway" medium spiny neurons (iMSNs) in the ventral striatum of D2R knockout mice, this mutant restored basal locomotor activity and cocaine-induced locomotor activity in a manner indistinguishable from wild-type D2R, indicating that arrestin recruitment can drive locomotion in the absence of D2R-mediated G protein signaling. In contrast, incentive motivation was enhanced only by wild-type D2R, signifying a dissociation in the mechanisms that underlie distinct D2R-dependent behaviors, and opening the door to more targeted therapeutics.
Assuntos
Arrestina , Locomoção , Motivação , Receptores de Dopamina D2 , Animais , Cocaína , Corpo Estriado/metabolismo , Camundongos , Camundongos Knockout , Receptores de Dopamina D2/genética , Receptores de Dopamina D2/metabolismoRESUMO
Dopamine D2 receptors (D2Rs) mediate many of the actions of dopamine in the striatum, ranging from movement to the effortful pursuit of reward. Yet despite significant advances in linking D2Rs to striatal functions with pharmacological and genetic strategies in animals, how dopamine orchestrates its myriad actions on different cell populations -each expressing D2Rs- remains unclear. Furthermore, brain imaging and genetic studies in humans have consistently associated striatal D2R alterations with various neurological and neuropsychiatric disorders, but how and which D2Rs are involved in each case is poorly understood. Therefore, a critical first step is to engage in a refined and systematic investigation of the impact of D2R function on specific striatal cells, circuits, and behaviors. Here, I will review recent efforts, primarily in animal models, aimed at unlocking the complex and heterogeneous roles of D2Rs in striatum.
Assuntos
Corpo Estriado/metabolismo , Transtornos Mentais/metabolismo , Obesidade/metabolismo , Receptores de Dopamina D2/fisiologia , Transtornos Relacionados ao Uso de Substâncias/metabolismo , Animais , Corpo Estriado/efeitos dos fármacos , Dopaminérgicos/metabolismo , Dopaminérgicos/farmacologia , Dopaminérgicos/uso terapêutico , Humanos , Transtornos Mentais/tratamento farmacológico , Rede Nervosa/efeitos dos fármacos , Rede Nervosa/metabolismo , Obesidade/tratamento farmacológico , Transtornos Relacionados ao Uso de Substâncias/tratamento farmacológicoRESUMO
Dopamine D2 receptors (D2Rs) in the nucleus accumbens (NAc) regulate motivated behavior, but the underlying neurobiological mechanisms remain unresolved. Here, we show that selective upregulation of D2Rs in the indirect pathway of the adult NAc enhances the willingness to work for food. Mechanistic studies in brain slices reveal that D2R upregulation attenuates inhibitory transmission at two main output projections of the indirect pathway, the classical long-range projections to the ventral pallidum (VP), as well as local collaterals to direct pathway medium spiny neurons. In vivo physiology confirms the reduction in indirect pathway inhibitory transmission to the VP, and inhibition of indirect pathway terminals to VP is sufficient to enhance motivation. In contrast, D2R upregulation in the indirect pathway does not disinhibit neuronal activity of the direct pathway in vivo. These data suggest that D2Rs in ventral striatal projection neurons promote motivation by weakening the canonical output to the ventral pallidum.
Assuntos
Prosencéfalo Basal/metabolismo , Motivação/fisiologia , Núcleo Accumbens/metabolismo , Receptores de Dopamina D2/metabolismo , Animais , Feminino , Potenciais Pós-Sinápticos Inibidores , Masculino , Camundongos Endogâmicos C57BL , Neurônios/metabolismo , Regulação para CimaRESUMO
Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by developmentally inappropriate levels of inattention and hyperactivity or impulsivity. The heterogeneity of its clinical manifestations and the differential responses to treatment and varied prognoses have long suggested myriad underlying causes. Over the past decade, clinical and basic research efforts have uncovered many behavioural and neurobiological alterations associated with ADHD, from genes to higher order neural networks. Here, we review the neurobiology of ADHD by focusing on neural circuits implicated in the disorder and discuss how abnormalities in circuitry relate to symptom presentation and treatment. We summarise the literature on genetic variants that are potentially related to the development of ADHD, and how these, in turn, might affect circuit function and relevant behaviours. Whether these underlying neurobiological factors are causally related to symptom presentation remains unresolved. Therefore, we assess efforts aimed at disentangling issues of causality, and showcase the shifting research landscape towards endophenotype refinement in clinical and preclinical settings. Furthermore, we review approaches being developed to understand the neurobiological underpinnings of this complex disorder, including the use of animal models, neuromodulation, and pharmacoimaging studies.
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Transtorno do Deficit de Atenção com Hiperatividade/epidemiologia , Variação Genética , Rede Nervosa/fisiopatologia , Transtorno do Deficit de Atenção com Hiperatividade/genética , Transtorno do Deficit de Atenção com Hiperatividade/fisiopatologia , Causalidade , Humanos , NeurobiologiaRESUMO
Brain imaging studies performed in humans have associated low striatal dopamine release and D2R binding with alcohol dependence. Conversely, high striatal D2R binding has been observed in unaffected members of alcoholic families suggesting that high D2R function may protect against alcohol dependence. A possible protective role of increased D2R levels in the striatum is further supported by preclinical studies in non-human primates and rodents. Here, we determined whether there is a causal relationship between D2R levels and alcohol intake. To this end, we upregulated D2R expression levels in the nucleus accumbens of the adult mouse, but selectively restricted the upregulation to the indirect striatal output pathway, which endogenously expresses D2Rs. After overexpression was established, mice were tested in two models of free-choice alcohol drinking: the continuous and intermittent access two-bottle choice models. As anticipated, we found that D2R upregulation leads to hyperactivity in the open field. Contrary to our expectation, D2R upregulation did not reduce alcohol intake during continuous or intermittent access or when alcohol drinking was tested in the context of aversive outcomes. These data argue against a protective role of accumbal indirect pathway D2Rs in alcohol consumption but emphasize their importance in promoting locomotor activity.
Assuntos
Consumo de Bebidas Alcoólicas/genética , Álcoois/administração & dosagem , Locomoção/genética , Núcleo Accumbens/metabolismo , Receptores de Dopamina D2/metabolismo , Regulação para Cima/fisiologia , Animais , Condicionamento Operante/efeitos dos fármacos , Comportamento Exploratório/fisiologia , Locomoção/efeitos dos fármacos , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Vias Neurais/metabolismo , Neurônios/metabolismo , Núcleo Accumbens/efeitos dos fármacos , Ligação Proteica/efeitos dos fármacos , Ligação Proteica/genética , Receptores de Dopamina D2/genética , Regulação para Cima/efeitos dos fármacosRESUMO
Cyclooxygenases (COX) are prostanoid synthesizing enzymes constitutively expressed in the brain that contribute to excitotoxic neuronal cell death. While the neurotoxic role of COX-2 is well established and has been linked to prostaglandin E(2) synthesis, the role of COX-1 is not clearly understood. In a model of N-Methyl-D-aspartic acid (NMDA) induced excitotoxicity in the mouse cerebral cortex we found a distinctive temporal profile of COX-1 and COX-2 activation where COX-1, located in microglia, is responsible for the early phase of prostaglandin E(2) synthesis (10 minutes after NMDA), while both COX-1 and COX-2 contribute to the second phase (3-24 hours after NMDA). Microglial COX-1 is strongly activated by ATP but not excitatory neurotransmitters or the Toll-like receptor 4 ligand bacterial lipopolysaccharide. ATP induced microglial COX-1 dependent prostaglandin E(2) synthesis is dependent on P2X7 receptors, extracellular Ca(2+) and cytoplasmic phospholipase A2. NMDA receptor activation induces ATP release from cultured neurons leading to microglial P2X7 receptor activation and COX-1 dependent prostaglandin E(2) synthesis in mixed microglial-neuronal cultures. Pharmacological inhibition of COX-1 has no effect on the cortical lesion produced by NMDA, but counteracts the neuroprotection exerted by inhibition of COX-2 or observed in mice lacking the prostaglandin E(2) receptor type 1. Similarly, the neuroprotection exerted by the prostaglandin E(2) receptor type 2 agonist butaprost is not observed after COX-1 inhibition. P2X7 receptors contribute to NMDA induced prostaglandin E(2) production in vivo and blockage of P2X7 receptors reverses the neuroprotection offered by COX-2 inhibition. These findings suggest that purinergic signaling in microglia triggered by neuronal ATP modulates excitotoxic cortical lesion by regulating COX-1 dependent prostanoid production and unveil a previously unrecognized protective role of microglial COX-1 in excitotoxic brain injury.
Assuntos
Lesões Encefálicas/enzimologia , Ciclo-Oxigenase 1/metabolismo , Proteínas de Membrana/metabolismo , Microglia/metabolismo , Prostaglandinas/biossíntese , Receptores Purinérgicos P2X7/metabolismo , Transdução de Sinais , Trifosfato de Adenosina/farmacologia , Animais , Lesões Encefálicas/induzido quimicamente , Lesões Encefálicas/patologia , Células Cultivadas , Córtex Cerebral/efeitos dos fármacos , Córtex Cerebral/enzimologia , Córtex Cerebral/patologia , Técnicas de Cocultura , Ciclo-Oxigenase 2/metabolismo , Inibidores de Ciclo-Oxigenase/farmacologia , Dinoprostona/biossíntese , Deleção de Genes , Camundongos , Camundongos Endogâmicos C57BL , Microglia/efeitos dos fármacos , N-Metilaspartato/administração & dosagem , N-Metilaspartato/farmacologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Fármacos Neuroprotetores/farmacologia , Neurotoxinas/toxicidade , Óxido Nítrico Sintase Tipo I/metabolismo , Receptores de Prostaglandina E Subtipo EP1/metabolismo , Receptores de Prostaglandina E Subtipo EP2/metabolismo , Fatores de Tempo , Resultado do TratamentoRESUMO
Nitric oxide (NO) has emerged as a key mediator in the mechanisms of ischaemic tolerance induced by a wide variety of preconditioning stimuli. NO is involved in the brain protection that develops either early (minutes-hours) or late (days-weeks) after the preconditioning stimulus. However, the sources of NO and the mechanisms underlying the protective effects differ substantially. While in early preconditioning NO is produced by the endothelial and neuronal isoform of NO synthase, in delayed preconditioning NO is synthesized by the inducible or 'immunological' isoform of NO synthase. Furthermore, in early preconditioning, NO acts through the canonical cGMP pathway, possibly through protein kinase G and opening of mitochondrial K(ATP) channels. In late preconditioning, the protection is mediated by peroxynitrite formed by the reaction of NO with superoxide derived from the enzyme NADPH oxidase. The mechanisms by which peroxynitrite exerts its protective effect may include improvement of post-ischaemic cerebrovascular function, leading to enhancement of blood flow to the ischaemic territory, and expression of prosurvival genes resulting in cytoprotection. The evidence suggests that NO can engage highly effective and multifunctional prosurvival pathways, which could be exploited for the prevention and treatment of cerebrovascular pathologies.
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Óxido Nítrico Sintase Tipo II , Óxido Nítrico , GMP Cíclico , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase/metabolismo , Óxido Nítrico Sintase Tipo II/genética , SuperóxidosRESUMO
Nitric oxide (NO) synthesized by neuronal NO synthase (nNOS) has long been implicated in brain plasticity. However, it is unclear how this short-lived mediator contributes to the long-term molecular changes underlying neuroplasticity, which typically require activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) signaling pathway and gene expression. To address this issue, we used a neuroplasticity model based on treatment of neuronal cultures with bicuculline and a model of experience-dependent plasticity in the barrel cortex. In neuronal cultures, NOS inhibition attenuated the bicuculline-induced activation of ERK and the expression of c-Fos, Egr-1, Arc, and brain-derived neurotrophic factor (BDNF), proteins essential for neuroplasticity. Furthermore, inhibition of the NO target soluble guanylyl cyclase or of the cGMP effector kinase protein kinase G (PKG) reduced both ERK activation and plasticity-related protein expression. NOS inhibition did not affect phosphorylation of cAMP response element-binding protein (CREB), a well-established ERK nuclear target, but it attenuated the nuclear accumulation of the CREB coactivator TORC1 and suppressed the activation of Elk-1, another transcription factor target of ERK. Consistent with these in vitro observations, induction of c-Fos, Egr-1, and BDNF was attenuated in the D1 cortical barrel of nNOS(-/-) mice subjected to single whisker experience. These results establish nNOS-derived NO as a key factor in the expression of proteins involved in neuroplasticity, an effect mediated through cGMP, PKG, and ERK signaling. These actions of NO do not depend on CREB phosphorylation but may involve TORC1 and Elk-1. Our data unveil a previously unrecognized link between neuronal NO and the molecular machinery responsible for the sustained synaptic changes underlying neuroplasticity.
Assuntos
Proteínas Quinases Dependentes de GMP Cíclico/metabolismo , GMP Cíclico/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Óxido Nítrico Sintase Tipo I/metabolismo , Óxido Nítrico/metabolismo , Análise de Variância , Animais , Bicuculina/farmacologia , Western Blotting , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Células Cultivadas , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Proteínas do Citoesqueleto/metabolismo , Imunofluorescência , Imuno-Histoquímica , Hibridização In Situ , Masculino , Camundongos , Proteínas do Tecido Nervoso/metabolismo , Plasticidade Neuronal/efeitos dos fármacos , Plasticidade Neuronal/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Córtex Somatossensorial/efeitos dos fármacos , Córtex Somatossensorial/fisiologia , Vibrissas/fisiologiaRESUMO
Activation of NMDA receptors during cerebral ischemia triggers signaling pathways that promote both neuronal death and survival. In this issue of Neuron, Sasaki et al. present evidence for a new endogenous survival pathway involving the kinase SIK2 and the CREB coactivator TORC1. The powerful neuroprotection conferred by this pathway has considerable translational potential for stroke therapy.
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CD36, a class B scavenger receptor present in microglia, endothelium and leukocytes, plays a key role in ischemic brain injury by promoting the expression of inflammatory genes and production of reactive oxygen species (ROS). However, it is not known whether ischemic brain damage is mediated by CD36 activation in resident brain cells, i.e., microglia, or by blood-borne cells that infiltrate the brain. To address this question, we studied oxygen-glucose deprivation (OGD) in hippocampal slice cultures, a model of ischemic injury that does not involve cells extrinsic to the brain. We found that CD36 gene knockout does not afford protection of hippocampal slices to OGD-induced cytotoxicity. In contrast, immunoactivated bone marrow-derived monocytes-macrophages (BMM) from wild type (WT) mice trigger hippocampal damage when incubated with brain slices via a mechanism that is prevented in CD36-/- BMM. The neurotoxic activity of CD36+/+ BMM was attributed to reactive oxygen species (ROS) since it was concomitant with increased ROS production and could be prevented by treatment with a selective ROS scavenger, MnTBAP, or a peroxynitrite decomposition catalyst, FeTPPS. Importantly, ROS production and accumulation 3-nitrotyrosine in hippocampal proteins (a hallmark of peroxynitrite production) was significantly dampened in immunoactivated CD36-/- BMM, whereas production of NO-derived metabolites (nitrite and nitrate) was unaltered. We conclude that CD36 signaling may not contribute to injury induced by OGD in the brain itself but is involved in the neurotoxicity mediated by activated BMM. These findings are consistent with the hypothesis that CD36 in infiltrating inflammatory cells drives peroxynitrite-mediated ischemic brain damage. Accordingly, targeting CD36 in the vascular compartment may protect against neurotoxicity in the ischemic brain.
Assuntos
Medula Óssea/metabolismo , Antígenos CD36/metabolismo , Hipocampo/metabolismo , Monócitos/metabolismo , Ácido Peroxinitroso/biossíntese , Análise de Variância , Animais , Antígenos CD36/genética , Citometria de Fluxo , Glucose/deficiência , Hipóxia/metabolismo , Camundongos , Camundongos Knockout , Espécies Reativas de Oxigênio/metabolismoRESUMO
A central question in Alzheimer's disease research is what role synaptic activity plays in the disease process. Synaptic activity has been shown to induce beta-amyloid peptide release into the extracellular space, and extracellular beta-amyloid has been shown to be toxic to synapses. We now provide evidence that the well established synaptotoxicity of extracellular beta-amyloid requires gamma-secretase processing of amyloid precursor protein. Recent evidence supports an important role for intraneuronal beta-amyloid in the pathogenesis of Alzheimer's disease. We show that synaptic activity reduces intraneuronal beta-amyloid and protects against beta-amyloid-related synaptic alterations. We demonstrate that synaptic activity promotes the transport of the amyloid precursor protein to synapses using live cell imaging, and that the protease neprilysin is involved in reduction of intraneuronal beta-amyloid with synaptic activity.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Interneurônios/fisiologia , Plasticidade Neuronal/fisiologia , Receptores de Superfície Celular/metabolismo , Sinapses/fisiologia , Transmissão Sináptica/fisiologia , Secretases da Proteína Precursora do Amiloide/metabolismo , Animais , Transporte Biológico Ativo/fisiologia , Células Cultivadas , Proteína 4 Homóloga a Disks-Large , Espaço Extracelular/metabolismo , Guanilato Quinases , Hipocampo/fisiologia , Humanos , Técnicas In Vitro , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Potenciação de Longa Duração/fisiologia , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Transgênicos , Neprilisina/metabolismo , Fragmentos de Peptídeos/metabolismo , Nexinas de ProteasesRESUMO
Reactive oxygen species (ROS) and nitric oxide (NO) participate in NMDA receptor signaling. However, the source(s) of the ROS and their role in the increase in cerebral blood flow (CBF) induced by NMDA receptor activation have not been firmly established. NADPH oxidase generates ROS in neurons, but there is no direct evidence that this enzyme is present in neurons containing NMDA receptors, or that is involved in NMDA receptor-dependent ROS production and CBF increase. We addressed these questions using a combination of in vivo and in vitro approaches. We found that the CBF and ROS increases elicited by topical application of NMDA to the mouse neocortex were both dependent on neuronal NO synthase (nNOS), cGMP, and the cGMP effector kinase protein kinase G (PKG). In mice lacking the NADPH oxidase subunit NOX2, the ROS increase was not observed, but the CBF increase was still present. Electron microscopy of the neocortex revealed NOX2 immunolabeling in postsynaptic somata and dendrites that also expressed the NMDA receptor NR1 subunit and nNOS. In neuronal cultures, the NMDA-induced increase in ROS was mediated by NADPH oxidase through NO, cGMP and PKG. We conclude that NADPH oxidase in postsynaptic neurons generates ROS during NMDA receptor activation. However, NMDA receptor-derived ROS do not contribute to the CBF increase. The findings establish a NOX2-containing NADPH oxidase as a major source of ROS produced by NMDA receptor activation, and identify NO as the critical link between NMDA receptor activity and NOX2-dependent ROS production.
Assuntos
Circulação Cerebrovascular/fisiologia , Glicoproteínas de Membrana/metabolismo , NADPH Oxidases/metabolismo , Óxido Nítrico/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Receptores de N-Metil-D-Aspartato/fisiologia , Transdução de Sinais/fisiologia , Análise de Variância , Animais , Encéfalo/citologia , Células Cultivadas , Circulação Cerebrovascular/efeitos dos fármacos , Circulação Cerebrovascular/genética , GMP Cíclico/farmacologia , Proteínas Quinases Dependentes de GMP Cíclico/farmacologia , Maleato de Dizocilpina/farmacologia , Embrião de Mamíferos , Inibidores Enzimáticos/farmacologia , Fármacos Atuantes sobre Aminoácidos Excitatórios/farmacologia , Glicoproteínas de Membrana/deficiência , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia Imunoeletrônica/métodos , N-Metilaspartato/farmacologia , NADPH Oxidase 2 , NADPH Oxidases/deficiência , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurônios/ultraestrutura , Óxido Nítrico Sintase Tipo I/deficiência , Transdução de Sinais/efeitos dos fármacos , Sinapses/metabolismo , Sinapses/ultraestruturaRESUMO
The increase in blood flow evoked by synaptic activity is essential for normal brain function and underlies functional brain imaging signals. Nitric oxide, a vasodilator released by NMDA receptor activation, is critical for the flow increase, but the factors linking NMDA receptor activity to nitric oxide-dependent hyperemia are poorly understood. Here, we show that tissue plasminogen activator (tPA), a serine protease implicated in NMDA receptor signaling, is required for the flow increase evoked by somatosensory stimulation. tPA acts by facilitating neuronal nitric oxide release, but this effect does not involve enhancement of NMDA currents or the associated intracellular Ca(2+) rise. Rather, the evidence suggests that tPA controls NMDA-dependent nitric oxide synthesis by influencing the phosphorylation state of neuronal nitric oxide synthase. These findings unveil a previously unrecognized role of tPA in vital homeostatic mechanisms coupling NMDA receptor signaling with nitric oxide synthesis and local cerebral perfusion.
Assuntos
Neurônios/metabolismo , Ativador de Plasminogênio Tecidual/metabolismo , Animais , Cálcio/metabolismo , Eletrofisiologia , Hiperemia/induzido quimicamente , Hiperemia/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , N-Metilaspartato/farmacologia , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase Tipo I/metabolismo , Técnicas de Patch-Clamp , Fosforilação , Receptores de N-Metil-D-Aspartato/metabolismo , Fluxo Sanguíneo Regional , Ativador de Plasminogênio Tecidual/deficiência , Ativador de Plasminogênio Tecidual/genéticaRESUMO
Cerebral ischemic preconditioning or tolerance is a powerful neuroprotective phenomenon by which a sublethal injurious stimulus renders the brain resistant to a subsequent damaging ischemic insult. We used lipopolysaccharide (LPS) as a preconditioning stimulus in a mouse model of middle cerebral artery occlusion (MCAO) to examine whether improvements in cerebrovascular function contribute to the protective effect. Administration of LPS 24 h before MCAO reduced the infarct by 68% and improved ischemic cerebral blood flow (CBF) by 114% in brain areas spared from infarction. In addition, LPS prevented the dysfunction in cerebrovascular regulation induced by MCAO, as demonstrated by normalization of the increase in CBF produced by neural activity, hypercapnia, or by the endothelium-dependent vasodilator acetylcholine. These beneficial effects of LPS were not observed in mice lacking inducible nitric oxide synthase (iNOS) or the nox2 subunit of the superoxide-producing enzyme NADPH oxidase. LPS increased reactive oxygen species and the peroxynitrite marker 3-nitrotyrosine in wild-type mice but not in nox2 nulls. The peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) attenuated LPS-induced nitration and counteracted the beneficial effects of LPS on infarct volume, ischemic CBF, and vascular reactivity. Thus, LPS preserves neurovascular function and ameliorates CBF in regions of the ischemic territory at risk for infarction. This effect is mediated by peroxynitrite formed from iNOS-derived NO and nox2-derived superoxide. The data indicate that preservation of cerebrovascular function is an essential component of ischemic tolerance and suggest that combining neuroprotection and vasoprotection may be a valuable strategy for treating ischemic brain injury.