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Entorhinal cortex (EC) LIII and LII glutamatergic neurons make monosynaptic connections onto distal apical dendrites of hippocampal CA1 and CA2 pyramidal neurons (PNs), respectively, through perforant path (PP) projections. We previously reported that a brief train of PP stimuli evokes strong supralinear temporal summation of excitatory postsynaptic potentials (EPSPs) in CA1 PNs that requires NMDAR activation, with relatively little summation in CA2 PNs in mice of either sex. Here we provide evidence from combined immunogold electron microscopy, cell-type specific genetic deletion and pharmacology that the NMDARs required for supralinear temporal summation of the CA1 PP EPSP are presynaptic, located in the PP terminals. Moreover, we found that the number of NMDARs in PP terminals innervating CA1 PNs is significantly greater than that found in PP terminals innervating CA2 PNs, providing a potential explanation for the difference in temporal summation in these two classes of hippocampal PNs.
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Alzheimer's disease (AD) affects both grey and white matter (WM), but considerably more is known about the former. Interestingly, WM disruption has been consistently observed and thoroughly described using imaging modalities, particularly MRI which has shown WM functional disconnections between the hippocampus and other brain regions during AD pathogenesis when early neurodegeneration and synapse loss are also evident. Nonetheless, high-resolution structural and functional analyses of WM during AD pathogenesis remain scarce. Given the importance of the myelinated axons in the WM for conveying information across brain regions, such studies will provide valuable information on the cellular drivers and consequences of WM disruption that contribute to the characteristic cognitive decline of AD. Here, we employed a multi-scale approach to investigate hippocampal WM disruption during AD pathogenesis and determine whether hippocampal WM changes accompany the well-documented grey matter losses. Our data indicate that ultrastructural myelin disruption is elevated in the alveus in human AD cases and increases with age in 5xFAD mice. Unreliable action potential propagation and changes to sodium channel expression at the node of Ranvier co-emerged with this deterioration. These findings provide important insight to the neurobiological substrates and functional consequences of decreased WM integrity and are consistent with the notion that hippocampal disconnection contributes to cognitive changes in AD.
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Potenciais de Ação , Envelhecimento , Doença de Alzheimer , Axônios , Hipocampo , Camundongos Transgênicos , Substância Branca , Animais , Doença de Alzheimer/patologia , Doença de Alzheimer/fisiopatologia , Axônios/patologia , Camundongos , Potenciais de Ação/fisiologia , Hipocampo/patologia , Hipocampo/metabolismo , Substância Branca/patologia , Envelhecimento/fisiologia , Envelhecimento/patologia , Masculino , Humanos , Feminino , Substância Cinzenta/patologia , Bainha de Mielina/patologia , Bainha de Mielina/metabolismo , Idoso , Modelos Animais de Doenças , Idoso de 80 Anos ou mais , Camundongos Endogâmicos C57BLRESUMO
Entorhinal cortex neurons make monosynaptic connections onto distal apical dendrites of CA1 and CA2 pyramidal neurons through the perforant path (PP) projection. Previous studies show that differences in dendritic properties and synaptic input density enable the PP inputs to produce a much stronger excitation of CA2 compared with CA1 pyramidal neurons. Here, using mice of both sexes, we report that the difference in PP efficacy varies substantially as a function of presynaptic firing rate. Although a single PP stimulus evokes a 5- to 6-fold greater EPSP in CA2 compared with CA1, a brief high-frequency train of PP stimuli evokes a strongly facilitating postsynaptic response in CA1, with relatively little change in CA2. Furthermore, we demonstrate that blockade of NMDARs significantly reduces strong temporal summation in CA1 but has little impact on that in CA2. As a result of the differences in the frequency- and NMDAR-dependent temporal summation, naturalistic patterns of presynaptic activity evoke CA1 and CA2 responses with distinct dynamics, differentially tuning CA1 and CA2 responses to bursts of presynaptic firing versus single presynaptic spikes, respectively.SIGNIFICANCE STATEMENT Recent studies have demonstrated that abundant entorhinal cortical innervation and efficient dendritic propagation enable hippocampal CA2 pyramidal neurons to produce robust excitation evoked by single cortical stimuli, compared with CA1. Here we uncovered, unexpectedly, that the difference in efficacy of cortical excitation varies substantially as a function of presynaptic firing rate. A burst of stimuli evokes a strongly facilitating response in CA1, but not in CA2. As a result, the postsynaptic response of CA1 and CA2 to presynaptic naturalistic firing displays contrasting temporal dynamics, which depends on the activation of NMDARs. Thus, whereas CA2 responds to single stimuli, CA1 is selectively recruited by bursts of cortical input.
Assuntos
Região CA1 Hipocampal/fisiologia , Região CA2 Hipocampal/fisiologia , Córtex Cerebral/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Células Piramidais/fisiologia , Sinapses/fisiologia , Animais , Região CA1 Hipocampal/efeitos dos fármacos , Região CA2 Hipocampal/efeitos dos fármacos , Córtex Cerebral/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Feminino , Antagonistas de Receptores de GABA-A/farmacologia , Antagonistas de Receptores de GABA-B/farmacologia , Masculino , Camundongos , Vias Neurais/efeitos dos fármacos , Vias Neurais/fisiologia , Técnicas de Patch-Clamp , Células Piramidais/efeitos dos fármacos , Sinapses/efeitos dos fármacosRESUMO
Cue-induced cocaine craving progressively intensifies (incubates) after withdrawal from cocaine self-administration in rats and humans. In rats, the expression of incubation ultimately depends on Ca2+-permeable AMPARs that accumulate in synapses onto medium spiny neurons (MSNs) in the NAc core. However, the delay in their accumulation (â¼1 month after drug self-administration ceases) suggests earlier waves of plasticity. This prompted us to conduct the first study of NMDAR transmission in NAc core during incubation, focusing on the GluN3 subunit, which confers atypical properties when incorporated into NMDARs, including insensitivity to Mg2+ block and Ca2+ impermeability. Whole-cell patch-clamp recordings were conducted in MSNs of adult male rats 1-68 d after discontinuing extended-access saline or cocaine self-administration. NMDAR transmission was enhanced after 5 d of cocaine withdrawal, and this persisted for at least 68 d of withdrawal. The earliest functional alterations were mediated through increased contributions of GluN2B-containing NMDARs, followed by increased contributions of GluN3-containing NMDARs. As predicted by GluN3-NMDAR incorporation, fewer MSN spines exhibited NMDAR-mediated Ca2+ entry. GluN3A knockdown in NAc core was sufficient to prevent incubation of craving, consistent with biotinylation studies showing increased GluN3A surface expression, although array tomography studies suggested that adaptations involving GluN3B also occur. Collectively, our data show that a complex cascade of NMDAR and AMPAR plasticity occurs in NAc core, potentially through a homeostatic mechanism, leading to persistent increases in cocaine cue reactivity and relapse vulnerability. This is a remarkable example of experience-dependent glutamatergic plasticity evolving over a protracted window in the adult brain.SIGNIFICANCE STATEMENT "Incubation of craving" is an animal model for the persistence of vulnerability to cue-induced relapse after prolonged drug abstinence. Incubation also occurs in human drug users. AMPAR plasticity in medium spiny neurons (MSNs) of the NAc core is critical for incubation of cocaine craving but occurs only after a delay. Here we found that AMPAR plasticity is preceded by NMDAR plasticity that is essential for incubation and involves GluN3, an atypical NMDAR subunit that markedly alters NMDAR transmission. Together with AMPAR plasticity, this represents profound remodeling of excitatory synaptic transmission onto MSNs. Given the importance of MSNs for translating motivation into action, this plasticity may explain, at least in part, the profound shifts in motivated behavior that characterize addiction.
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Cocaína/administração & dosagem , Fissura/efeitos dos fármacos , Inibidores da Captação de Dopamina/administração & dosagem , Comportamento de Procura de Droga/efeitos dos fármacos , Glicoproteínas de Membrana/metabolismo , Núcleo Accumbens/metabolismo , Animais , Cálcio/metabolismo , Comportamento de Procura de Droga/fisiologia , Masculino , Núcleo Accumbens/efeitos dos fármacos , Técnicas de Patch-Clamp , Ratos , Ratos Sprague-Dawley , AutoadministraçãoRESUMO
The hippocampus is vulnerable to deterioration in Alzheimer's disease (AD). It is, however, a heterogeneous structure, which may contribute to the differential volumetric changes along its septotemporal axis during AD progression. Here, we investigated amyloid plaque deposition along the dorsoventral axis in two strains of transgenic AD (ADTg) mouse models. We also used patch-clamp physiology in these mice to probe for functional consequences of AD pathogenesis in ventral hippocampus, which we found bears significantly higher plaque burden in the aged ADTg group compared to corresponding dorsal regions. Despite dorsoventral differences in amyloid load, ventral CA1 pyramidal neurons of aged ADTg mice exhibited subthreshold physiological changes similar to those previously reported in dorsal neurons, indicative of an HCN channelopathy, but lacked exacerbated suprathreshold accommodation. Additionally, HCN channel function could be rescued by pharmacological manipulation of the endoplasmic reticulum. These observations suggest that an AD-linked HCN channelopathy emerges in both dorsal and ventral CA1 pyramidal neurons, but that the former encounter an additional integrative obstacle in the form of reduced intrinsic excitability.
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Envelhecimento/metabolismo , Doença de Alzheimer/etiologia , Doença de Alzheimer/metabolismo , Região CA1 Hipocampal/citologia , Região CA1 Hipocampal/metabolismo , Placa Amiloide/metabolismo , Células Piramidais/metabolismo , Transdução de Sinais , Animais , Modelos Animais de Doenças , Progressão da Doença , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização , Camundongos Transgênicos , Tamanho do Órgão , Técnicas de Patch-ClampRESUMO
Behaviors that rely on the hippocampus are particularly susceptible to chronological aging, with many aged animals (including humans) maintaining cognition at a young adult-like level, but many others the same age showing marked impairments. It is unclear whether the ability to maintain cognition over time is attributable to brain maintenance, sufficient cognitive reserve, compensatory changes in network function, or some combination thereof. While network dysfunction within the hippocampal circuit of aged, learning-impaired animals is well-documented, its neurobiological substrates remain elusive. Here we show that the synaptic architecture of hippocampal regions CA1 and CA3 is maintained in a young adult-like state in aged rats that performed comparably to their young adult counterparts in both trace eyeblink conditioning and Morris water maze learning. In contrast, among learning-impaired, but equally aged rats, we found that a redistribution of synaptic weights amplifies the influence of autoassociational connections among CA3 pyramidal neurons, yet reduces the synaptic input onto these same neurons from the dentate gyrus. Notably, synapses within hippocampal region CA1 showed no group differences regardless of cognitive ability. Taking the data together, we find the imbalanced synaptic weights within hippocampal CA3 provide a substrate that can explain the abnormal firing characteristics of both CA3 and CA1 pyramidal neurons in aged, learning-impaired rats. Furthermore, our work provides some clarity with regard to how some animals cognitively age successfully, while others' lifespans outlast their "mindspans."
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Região CA1 Hipocampal/patologia , Região CA3 Hipocampal/patologia , Envelhecimento Cognitivo , Células Piramidais/patologia , Sinapses/patologia , Animais , Masculino , Ratos , Ratos Endogâmicos BN , Ratos Endogâmicos F344RESUMO
The development of safe and effective treatments for age-associated neurodegenerative disorders is an on-going challenge faced by the scientific field. Key to the development of such therapies is the appropriate selection of modeling systems in which to investigate disease mechanisms and to test candidate interventions. There are unique challenges in the development of representative laboratory models of neurodegenerative diseases, including the complexity of the human brain, the cumulative and variable contributions of genetic and environmental factors over the course of a lifetime, inability to culture human primary neurons, and critical central nervous system differences between small animal models and humans. While traditional rodent models have advanced our understanding of neurodegenerative disease mechanisms, key divergences such as the species-specific genetic background can limit the application of animal models in many cases. Here we review in vitro human neuronal systems that employ stem cell and reprogramming technology and their application to a range of neurodegenerative diseases. Specifically, we compare human-induced pluripotent stem cell-derived neurons to directly converted, or transdifferentiated, induced neurons, as both model systems can take advantage of patient-derived human tissue to produce neurons in culture. We present recent technical developments using these two modeling systems, as well as current limitations to these systems, with the aim of advancing investigation of neuropathogenic mechanisms using these models.
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Técnicas de Reprogramação Celular/métodos , Células-Tronco Pluripotentes Induzidas/citologia , Células-Tronco Neurais/citologia , Doenças Neurodegenerativas , Neurônios/citologia , Células Cultivadas , Reprogramação Celular , Humanos , Técnicas In VitroRESUMO
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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Ginkgolic acids (GA) are alkylphenol constituents of the leaves and fruits of Ginkgo biloba. GA has shown pleiotropic effects in vitro, including: antitumor effects through inhibition of lipogenesis; decreased expression of invasion associated proteins through AMPK activation; and potential rescue of amyloid-ß (Aß) induced synaptic impairment. GA was also reported to have activity against Escherichia coli and Staphylococcus aureus. Several mechanisms for this activity have been suggested including: SUMOylation inhibition; blocking formation of the E1-SUMO intermediate; inhibition of fatty acid synthase; non-specific SIRT inhibition; and activation of protein phosphatase type-2C. Here we report that GA inhibits Herpes simplex virus type 1 (HSV-1) by inhibition of both fusion and viral protein synthesis. Additionally, we report that GA inhibits human cytomegalovirus (HCMV) genome replication and Zika virus (ZIKV) infection of normal human astrocytes (NHA). We show a broad spectrum of fusion inhibition by GA of all three classes of fusion proteins including HIV, Ebola virus (EBOV), influenza A virus (IAV) and Epstein Barr virus (EBV). In addition, we show inhibition of a non-enveloped adenovirus. Our experiments suggest that GA inhibits virion entry by blocking the initial fusion event. Data showing inhibition of HSV-1 and CMV replication, when GA is administered post-infection, suggest a possible secondary mechanism targeting protein and DNA synthesis. Thus, in light of the strong effect of GA on viral infection, even after the infection begins, it may potentially be used to treat acute infections (e.g. Coronavirus, EBOV, ZIKV, IAV and measles), and also topically for the successful treatment of active lesions (e.g. HSV-1, HSV-2 and varicella-zoster virus (VZV)).
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Antivirais/farmacologia , Infecções por Vírus de DNA/metabolismo , Vírus de DNA/efeitos dos fármacos , Infecções por Vírus de RNA/metabolismo , Vírus de RNA/efeitos dos fármacos , Salicilatos/farmacologia , Proteínas do Envelope Viral/antagonistas & inibidores , Proteínas Virais de Fusão/antagonistas & inibidores , Animais , Astrócitos/metabolismo , Chlorocebus aethiops , Replicação do DNA/efeitos dos fármacos , Infecções por Vírus de DNA/virologia , Vírus de DNA/genética , DNA Viral/genética , Células HEK293 , Humanos , Infecções por Vírus de RNA/virologia , Vírus de RNA/genética , Células Vero , Proteínas do Envelope Viral/biossíntese , Proteínas Virais de Fusão/biossíntese , Vírion/efeitos dos fármacos , Internalização do Vírus/efeitos dos fármacos , Replicação Viral/efeitos dos fármacosRESUMO
BIN1, a member of the BAR adaptor protein family, is a significant late-onset Alzheimer disease risk factor. Here, we investigate BIN1 function in the brain using conditional knockout (cKO) models. Loss of neuronal Bin1 expression results in the select impairment of spatial learning and memory. Examination of hippocampal CA1 excitatory synapses reveals a deficit in presynaptic release probability and slower depletion of neurotransmitters during repetitive stimulation, suggesting altered vesicle dynamics in Bin1 cKO mice. Super-resolution and immunoelectron microscopy localizes BIN1 to presynaptic sites in excitatory synapses. Bin1 cKO significantly reduces synapse density and alters presynaptic active zone protein cluster formation. Finally, 3D electron microscopy reconstruction analysis uncovers a significant increase in docked and reserve pools of synaptic vesicles at hippocampal synapses in Bin1 cKO mice. Our results demonstrate a non-redundant role for BIN1 in presynaptic regulation, thus providing significant insights into the fundamental function of BIN1 in synaptic physiology relevant to Alzheimer disease.
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Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Consolidação da Memória , Proteínas do Tecido Nervoso/metabolismo , Neurônios/metabolismo , Neurotransmissores/metabolismo , Terminações Pré-Sinápticas/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Animais , Encéfalo/metabolismo , Potenciais Pós-Sinápticos Excitadores , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/ultraestrutura , Terminações Pré-Sinápticas/ultraestrutura , Reconhecimento Psicológico , Proteínas SNARE/metabolismo , Aprendizagem EspacialRESUMO
JC virus (JCV) can cause a lytic infection of oligodendrocytes and astrocytes in the central nervous system (CNS) leading to progressive multifocal leukoencephalopathy (PML). JCV can also infect meningeal and choroid plexus cells causing JCV meningitis (JCVM). Whether JCV also infects meningeal and choroid plexus cells in PML patients and other immunosuppressed individuals with no overt symptoms of meningitis remains unknown. We therefore analyzed archival formalin-fixed, paraffin-embedded brain samples from PML patients, and HIV-seropositive and seronegative control subjects by immunohistochemistry for the presence of JCV early regulatory T Ag and JCV VP1 late capsid protein. In meninges, we detected JCV T Ag in 11/48 (22.9%) and JCV VP1 protein in 8/48 (16.7%) PML patients. In choroid plexi, we detected JCV T Ag in 1/7 (14.2%) and JCV VP1 protein in 1/8 (12.5%) PML patients. Neither JCV T Ag nor VP1 protein could be detected in meninges or choroid plexus of HIV-seropositive and HIV-seronegative control subjects without PML. In addition, examination of underlying cerebellar cortex of PML patients revealed JCV-infected cells in the molecular layer, including GAD 67+ interneurons, but not in HIV-seropositive and HIV-seronegative control subjects without PML. Our findings suggest that productive JCV infection of meningeal cells and choroid plexus cells also occurs in PML patients without signs or symptoms of meningitis. The phenotypic characterization of JCV-infected neurons in the molecular layer deserves further study. This data provides new insight into JCV pathogenesis in the CNS.
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Astrócitos/virologia , Plexo Corióideo/virologia , Vírus JC/genética , Leucoencefalopatia Multifocal Progressiva/virologia , Meninges/virologia , Neurônios/virologia , Oligodendroglia/virologia , Antígenos Virais de Tumores/genética , Antígenos Virais de Tumores/metabolismo , Astrócitos/patologia , Autopsia , Biomarcadores/metabolismo , Proteínas do Capsídeo/genética , Proteínas do Capsídeo/metabolismo , Córtex Cerebelar/patologia , Córtex Cerebelar/virologia , Plexo Corióideo/patologia , Expressão Gênica , Glutamato Descarboxilase/genética , Glutamato Descarboxilase/metabolismo , HIV/genética , HIV/patogenicidade , Infecções por HIV/patologia , Infecções por HIV/virologia , Humanos , Imuno-Histoquímica , Vírus JC/patogenicidade , Leucoencefalopatia Multifocal Progressiva/patologia , Meninges/patologia , Neurônios/patologia , Oligodendroglia/patologiaRESUMO
Bridging integrator 1 (BIN1) is the most significant late-onset Alzheimer's disease (AD) susceptibility locus identified via genome-wide association studies. BIN1 is an adaptor protein that regulates membrane dynamics in the context of endocytosis and membrane remodeling. An increase in BIN1 expression and changes in the relative levels of alternatively spliced BIN1 isoforms have been reported in the brains of patients with AD. BIN1 can bind to Tau, and an increase in BIN1 expression correlates with Tau pathology. In contrast, the loss of BIN1 expression in cultured cells elevates Aß production and Tau propagation by insfluencing endocytosis and recycling. Here, we show that BIN1 accumulates adjacent to amyloid deposits in vivo. We found an increase in insoluble BIN1 and a striking accrual of BIN1 within and near amyloid deposits in the brains of multiple transgenic models of AD. The peri-deposit aberrant BIN1 localization was conspicuously different from the accumulation of APP and BACE1 within dystrophic neurites. Although BIN1 is highly expressed in mature oligodendrocytes, BIN1 association with amyloid deposits occurred in the absence of the accretion of other oligodendrocyte or myelin proteins. Finally, super-resolution microscopy and immunogold electron microscopy analyses highlight the presence of BIN1 in proximity to amyloid fibrils at the edges of amyloid deposits. These results reveal the aberrant accumulation of BIN1 is a feature associated with AD amyloid pathology. Our findings suggest a potential role for BIN1 in extracellular Aß deposition in vivo that is distinct from its well-characterized function as an adaptor protein in endocytosis and membrane remodeling.
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Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Doença de Alzheimer/patologia , Proteínas Nucleares/metabolismo , Placa Amiloide/patologia , Proteínas Supressoras de Tumor/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Doença de Alzheimer/metabolismo , Amiloide/metabolismo , Peptídeos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Amiloidose/patologia , Animais , Encéfalo/patologia , Modelos Animais de Doenças , Feminino , Estudo de Associação Genômica Ampla , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neurogênese/fisiologia , Proteínas Nucleares/fisiologia , Placa Amiloide/metabolismo , Transdução de Sinais , Proteínas Supressoras de Tumor/fisiologia , Proteínas tau/metabolismoRESUMO
Active coping is an adaptive stress response that improves outcomes in medical and neuropsychiatric diseases. To date, most research into coping style has focused on neurotransmitter activity and little is known about the intrinsic excitability of neurons in the associated brain regions that facilitate coping. Previous studies have shown that HCN channels regulate neuronal excitability in pyramidal cells and that HCN channel current (Ih ) in the CA1 area increases with chronic mild stress. Reduction of Ih in the CA1 area leads to antidepressant-like behavior, and this region has been implicated in the regulation of coping style. We hypothesized that the antidepressant-like behavior achieved with CA1 knockdown of Ih is accompanied by increases in active coping. In this report, we found that global loss of TRIP8b, a necessary subunit for proper HCN channel localization in pyramidal cells, led to active coping behavior in numerous assays specific to coping style. We next employed a viral strategy using a dominant negative TRIP8b isoform to alter coping behavior by reducing HCN channel expression. This approach led to a robust reduction in Ih in CA1 pyramidal neurons and an increase in active coping. Together, these results establish that changes in HCN channel function in CA1 influences coping style.
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Adaptação Psicológica/fisiologia , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/metabolismo , Proteínas de Membrana/metabolismo , Peroxinas/metabolismo , Animais , Aprendizagem da Esquiva/fisiologia , Depressão/fisiopatologia , Modelos Animais de Doenças , Comportamento Exploratório , Hipocampo/citologia , Hipocampo/metabolismo , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/ultraestrutura , Masculino , Aprendizagem em Labirinto , Proteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Microscopia Eletrônica , Peroxinas/genética , Células Piramidais/metabolismo , Natação/psicologiaRESUMO
Voltage-gated ion channels are critical for neuronal integration. Some of these channels, however, are misregulated in several neurological disorders, causing both gain- and loss-of-function channelopathies in neurons. Using several transgenic mouse models of Alzheimer's disease (AD), we find that sub-threshold voltage signals strongly influenced by hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels progressively deteriorate over chronological aging in hippocampal CA1 pyramidal neurons. The degraded signaling via HCN channels in the transgenic mice is accompanied by an age-related global loss of their non-uniform dendritic expression. Both the aberrant signaling via HCN channels and their mislocalization could be restored using a variety of pharmacological agents that target the endoplasmic reticulum (ER). Our rescue of the HCN channelopathy helps provide molecular details into the favorable outcomes of ER-targeting drugs on the pathogenesis and synaptic/cognitive deficits in AD mouse models, and implies that they might have beneficial effects on neurological disorders linked to HCN channelopathies.
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Doença de Alzheimer/fisiopatologia , Região CA1 Hipocampal/fisiologia , Canalopatias/fisiopatologia , Canais Disparados por Nucleotídeos Cíclicos Ativados por Hiperpolarização/fisiologia , Plasticidade Neuronal , Células Piramidais/fisiologia , Potenciais de Ação , Envelhecimento , Animais , Região CA1 Hipocampal/ultraestrutura , Modelos Animais de Doenças , Retículo Endoplasmático/fisiologia , Feminino , Masculino , Camundongos Transgênicos , Células Piramidais/ultraestruturaRESUMO
Fragile X syndrome (FXS) is a neurodevelopmental disorder that is a leading cause of inherited intellectual disability, and the most common known cause of autism spectrum disorder. FXS is broadly characterized by sensory hypersensitivity and several developmental alterations in synaptic and circuit function have been uncovered in the sensory cortex of the mouse model of FXS (Fmr1 KO). GABA-mediated neurotransmission and fast-spiking (FS) GABAergic interneurons are central to cortical circuit development in the neonate. Here we demonstrate that there is a delay in the maturation of the intrinsic properties of FS interneurons in the sensory cortex, and a deficit in the formation of excitatory synaptic inputs on to these neurons in neonatal Fmr1 KO mice. Both these delays in neuronal and synaptic maturation were rectified by chronic administration of a TrkB receptor agonist. These results demonstrate that the maturation of the GABAergic circuit in the sensory cortex is altered during a critical developmental period due in part to a perturbation in BDNF-TrkB signaling, and could contribute to the alterations in cortical development underlying the sensory pathophysiology of FXS.SIGNIFICANCE STATEMENT Fragile X (FXS) individuals have a range of sensory related phenotypes, and there is growing evidence of alterations in neuronal circuits in the sensory cortex of the mouse model of FXS (Fmr1 KO). GABAergic interneurons are central to the correct formation of circuits during cortical critical periods. Here we demonstrate a delay in the maturation of the properties and synaptic connectivity of interneurons in Fmr1 KO mice during a critical period of cortical development. The delays both in cellular and synaptic maturation were rectified by administration of a TrkB receptor agonist, suggesting reduced BDNF-TrkB signaling as a contributing factor. These results provide evidence that the function of fast-spiking interneurons is disrupted due to a deficiency in neurotrophin signaling during early development in FXS.
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Potenciais Pós-Sinápticos Excitadores , Síndrome do Cromossomo X Frágil/metabolismo , Neurônios GABAérgicos/metabolismo , Interneurônios/metabolismo , Receptor trkB/metabolismo , Animais , Feminino , Proteína do X Frágil da Deficiência Intelectual/genética , Neurônios GABAérgicos/citologia , Neurônios GABAérgicos/fisiologia , Interneurônios/citologia , Interneurônios/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Receptor trkB/agonistas , Córtex Somatossensorial/metabolismo , Córtex Somatossensorial/fisiologiaRESUMO
The impact of a given neuronal pathway depends on the number of synapses it makes with its postsynaptic target, the strength of each individual synapse, and the integrative properties of the postsynaptic dendrites. Here we explore the cellular and synaptic mechanisms responsible for the differential excitatory drive from the entorhinal cortical pathway onto mouse CA2 compared with CA1 pyramidal neurons (PNs). Although both types of neurons receive direct input from entorhinal cortex onto their distal dendrites, these inputs produce a 5- to 6-fold larger EPSP at the soma of CA2 compared with CA1 PNs, which is sufficient to drive action potential output from CA2 but not CA1. Experimental and computational approaches reveal that dendritic propagation is more efficient in CA2 than CA1 as a result of differences in dendritic morphology and dendritic expression of the hyperpolarization-activated cation current (Ih). Furthermore, there are three times as many cortical inputs onto CA2 compared with CA1 PN distal dendrites. Using a computational model, we demonstrate that the differences in dendritic properties of CA2 compared with CA1 PNs are necessary to enable the CA2 PNs to generate their characteristically large EPSPs in response to their cortical inputs; in contrast, CA1 dendritic properties limit the size of the EPSPs they generate, even to a similar number of cortical inputs. Thus, the matching of dendritic integrative properties with the density of innervation is crucial for the differential processing of information from the direct cortical inputs by CA2 compared with CA1 PNs.SIGNIFICANCE STATEMENT Recent discoveries have shown that the long-neglected hippocampal CA2 region has distinct synaptic properties and plays a prominent role in social memory and schizophrenia. This study addresses the puzzling finding that the direct entorhinal cortical inputs to hippocampus, which target the very distal pyramidal neuron dendrites, provide an unusually strong excitatory drive at the soma of CA2 pyramidal neurons, with EPSPs that are 5-6 times larger than those in CA1 pyramidal neurons. We here elucidate synaptic and dendritic mechanisms that account quantitatively for the marked difference in EPSP size. Our findings further demonstrate the general importance of fine-tuning the integrative properties of neuronal dendrites to their density of synaptic innervation.
Assuntos
Região CA1 Hipocampal/fisiologia , Região CA2 Hipocampal/fisiologia , Córtex Cerebral/fisiologia , Dendritos/fisiologia , Rede Nervosa/fisiologia , Células Piramidais/fisiologia , Animais , Células Cultivadas , Córtex Cerebral/citologia , Dendritos/ultraestrutura , Hipocampo/citologia , Hipocampo/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Vias Neurais/fisiologia , Células Piramidais/citologia , Transmissão Sináptica/fisiologiaRESUMO
OBJECTIVE: The main goal of dopamine cell replacement therapy in Parkinson disease (PD) is to provide clinical benefit mediated by graft survival with nigrostriatal reinnervation. We report a dichotomy between graft structure and clinical function in a patient dying 16 years following fetal nigral grafting. METHODS: A 55-year-old levodopa-responsive woman with PD received bilateral putaminal fetal mesencephalic grafts as part of an NIH-sponsored double-blind sham-controlled trial. The patient never experienced clinical benefit, and her course was complicated by the development of graft-related dyskinesias. Fluorodopa positron emission tomography demonstrated significant increases postgrafting bilaterally. She experienced worsening of parkinsonism with severe dyskinesias, and underwent subthalamic nucleus deep brain stimulation 8 years after grafting. She died 16 years after transplantation. RESULTS: Postmortem analyses confirmed the diagnosis of PD and demonstrated >300,000 tyrosine hydroxylase (TH)-positive grafted cells per side with normalized striatal TH-immunoreactive fiber innervation and bidirectional synaptic connectivity. Twenty-seven percent and 17% of grafted neurons were serine 129-phosphorylated α-synuclein positive in the left and right putamen, respectively. INTERPRETATION: These findings represent the largest number of surviving dopamine neurons and the densest and most widespread graft-mediated striatal dopamine reinnervation following a transplant procedure reported to date. Despite this, clinical recovery was not observed. Furthermore, the grafts were associated with a form of dyskinesias that resembled diphasic dyskinesia and persisted in the off-medication state. We hypothesize that the grafted cells produced a low level of dopamine sufficient to cause a levodopa-independent continuous form of diphasic dyskinesias, but insufficient to provide an antiparkinsonian benefit. ANN NEUROL 2017;81:46-57.
Assuntos
Neurônios Dopaminérgicos/metabolismo , Sobrevivência de Enxerto , Mesencéfalo/transplante , Doença de Parkinson/cirurgia , Transplante de Tecido Encefálico , Neurônios Dopaminérgicos/ultraestrutura , Feminino , Humanos , Pessoa de Meia-Idade , Tirosina 3-Mono-Oxigenase/metabolismo , alfa-Sinucleína/metabolismoRESUMO
Parkinson's disease is the second most common neurodegenerative disorder without effective treatment. It is generally sporadic with unknown etiology. However, genetic studies of rare familial forms have led to the identification of mutations in several genes, which are linked to typical Parkinson's disease or parkinsonian disorders. The pathogenesis of Parkinson's disease remains largely elusive. Here we report a locus for autosomal dominant, clinically typical and Lewy body-confirmed Parkinson's disease on the short arm of chromosome 20 (20pter-p12) and identify TMEM230 as the disease-causing gene. We show that TMEM230 encodes a transmembrane protein of secretory/recycling vesicles, including synaptic vesicles in neurons. Disease-linked TMEM230 mutants impair synaptic vesicle trafficking. Our data provide genetic evidence that a mutant transmembrane protein of synaptic vesicles in neurons is etiologically linked to Parkinson's disease, with implications for understanding the pathogenic mechanism of Parkinson's disease and for developing rational therapies.
Assuntos
Predisposição Genética para Doença , Proteínas de Membrana/genética , Mutação/genética , Neurônios/patologia , Doença de Parkinson/genética , Vesículas Sinápticas/patologia , Idade de Início , Idoso , Idoso de 80 Anos ou mais , Sequência de Aminoácidos , Células Cultivadas , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Neurônios/metabolismo , Linhagem , Transporte Proteico/genética , Homologia de Sequência de Aminoácidos , Vesículas Sinápticas/metabolismoRESUMO
Alzheimer's disease (AD) is characterized by amyloid plaques composed of the ß-amyloid (Aß) peptide surrounded by swollen presynaptic dystrophic neurites consisting of dysfunctional axons and terminals that accumulate the ß-site amyloid precursor protein (APP) cleaving enzyme (BACE1) required for Aß generation. The cellular and molecular mechanisms that govern presynaptic dystrophic neurite formation are unclear, and elucidating these processes may lead to novel AD therapeutic strategies. Previous studies suggest Aß may disrupt microtubules, which we hypothesize have a critical role in the development of presynaptic dystrophies. To investigate this further, here we have assessed the effects of Aß, particularly neurotoxic Aß42, on microtubules during the formation of presynaptic dystrophic neurites in vitro and in vivo. Live-cell imaging of primary neurons revealed that exposure to Aß42 oligomers caused varicose and beaded neurites with extensive microtubule disruption, and inhibited anterograde and retrograde trafficking. In brain sections from AD patients and the 5XFAD transgenic mouse model of amyloid pathology, dystrophic neurite halos with BACE1 elevation around amyloid plaques exhibited aberrant tubulin accumulations or voids. At the ultrastructural level, peri-plaque dystrophies were strikingly devoid of microtubules and replete with multi-lamellar vesicles resembling autophagic intermediates. Proteins of the microtubule motors, kinesin and dynein, and other neuronal proteins were aberrantly localized in peri-plaque dystrophies. Inactive pro-cathepsin D also accumulated in peri-plaque dystrophies, indicating reduced lysosomal function. Most importantly, BACE1 accumulation in peri-plaque dystrophies caused increased BACE1 cleavage of APP and Aß generation. Our study supports the hypothesis that Aß induces microtubule disruption in presynaptic dystrophic neurites that surround plaques, thus impairing axonal transport and leading to accumulation of BACE1 and exacerbation of amyloid pathology in AD.
Assuntos
Doença de Alzheimer/patologia , Secretases da Proteína Precursora do Amiloide/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Ácido Aspártico Endopeptidases/metabolismo , Neuritos/patologia , Terminações Pré-Sinápticas/metabolismo , Secretases da Proteína Precursora do Amiloide/genética , Peptídeos beta-Amiloides/metabolismo , Animais , Ácido Aspártico Endopeptidases/genética , Axônios/patologia , Modelos Animais de Doenças , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Placa Amiloide/patologiaRESUMO
Aging-related impairments in hippocampus-dependent cognition have been attributed to maladaptive changes in the functional properties of pyramidal neurons within the hippocampal subregions. Much evidence has come from work on CA1 pyramidal neurons, with CA3 pyramidal neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing in the hippocampal circuit. Here, we use whole-cell current-clamp to demonstrate that aged rat (29-32 months) CA3 pyramidal neurons fire significantly more action potentials (APs) during theta-burst frequency stimulation and that this is associated with faster AP repolarization (i.e., narrower AP half-widths and enlarged fast afterhyperpolarization). Using a combination of patch-clamp physiology, pharmacology, Western blot analyses, immunohistochemistry, and array tomography, we demonstrate that these faster AP kinetics are mediated by enhanced function and expression of Kv4.2/Kv4.3 A-type K(+) channels, particularly within the perisomatic compartment, of CA3 pyramidal neurons. Thus, our study indicates that inhibition of these A-type K(+) channels can restore the intrinsic excitability properties of aged CA3 pyramidal neurons to a young-like state. Significance statement: Age-related learning deficits have been attributed, in part, to altered hippocampal pyramidal neuronal function with normal aging. Much evidence has come from work on CA1 neurons, with CA3 neurons receiving comparatively less attention despite its age-related hyperactivation being postulated to interfere with spatial processing. Hence, we conducted a series of experiments to identify the cellular mechanisms that underlie the hyperexcitability reported in the CA3 region. Contrary to CA1 neurons, we demonstrate that postburst afterhyperpolarization is not altered with aging and that aged CA3 pyramidal neurons are able to fire significantly more action potentials and that this is associated with faster action potential repolarization through enhanced expression of Kv4.2/Kv4.3 A-type K(+) channels, particularly within the cell bodies of CA3 pyramidal neurons.