RESUMO
Memories are dynamic constructs whose properties change with time and experience. The biological mechanisms underpinning these dynamics remain elusive, particularly concerning how shifts in the composition of memory-encoding neuronal ensembles influence the evolution of a memory over time. By targeting developmentally distinct subpopulations of principal neurons, we discovered that memory encoding resulted in the concurrent establishment of multiple memory traces in the mouse hippocampus. Two of these traces were instantiated in subpopulations of early- and late-born neurons and followed distinct reactivation trajectories after encoding. The divergent recruitment of these subpopulations underpinned gradual reorganization of memory ensembles and modulated memory persistence and plasticity across multiple learning episodes. Thus, our findings reveal profound and intricate relationships between ensemble dynamics and the progression of memories over time.
Assuntos
Hipocampo , Memória , Neurônios , Animais , Camundongos , Neurônios/fisiologia , Hipocampo/fisiologia , Hipocampo/citologia , Memória/fisiologia , Plasticidade Neuronal , Neurogênese , Camundongos Endogâmicos C57BL , MasculinoRESUMO
Humans have the remarkable cognitive capacity to rapidly adapt to changing environments. Central to this capacity is the ability to form high-level, abstract representations that take advantage of regularities in the world to support generalization1. However, little is known about how these representations are encoded in populations of neurons, how they emerge through learning and how they relate to behaviour2,3. Here we characterized the representational geometry of populations of neurons (single units) recorded in the hippocampus, amygdala, medial frontal cortex and ventral temporal cortex of neurosurgical patients performing an inferential reasoning task. We found that only the neural representations formed in the hippocampus simultaneously encode several task variables in an abstract, or disentangled, format. This representational geometry is uniquely observed after patients learn to perform inference, and consists of disentangled directly observable and discovered latent task variables. Learning to perform inference by trial and error or through verbal instructions led to the formation of hippocampal representations with similar geometric properties. The observed relation between representational format and inference behaviour suggests that abstract and disentangled representational geometries are important for complex cognition.
Assuntos
Hipocampo , Neurônios , Humanos , Hipocampo/fisiologia , Hipocampo/citologia , Neurônios/fisiologia , Masculino , Feminino , Aprendizagem/fisiologia , Tonsila do Cerebelo/fisiologia , Tonsila do Cerebelo/citologia , Cognição/fisiologia , Adulto , Lobo Temporal/fisiologia , Lobo Temporal/citologia , Modelos Neurológicos , Pessoa de Meia-IdadeRESUMO
The morphology of dendritic spines, the postsynaptic compartment of most excitatory synapses, decisively modulates the function of neuronal circuits as also evident from human brain disorders associated with altered spine density or morphology. Actin filaments (F-actin) form the backbone of spines, and a number of actin-binding proteins (ABP) have been implicated in shaping the cytoskeleton in mature spines. Instead, only little is known about the mechanisms that control the reorganization from unbranched F-actin of immature spines to the complex, highly branched cytoskeleton of mature spines. Here, we demonstrate impaired spine maturation in hippocampal neurons upon genetic inactivation of cyclase-associated protein 1 (CAP1) and CAP2, but not of CAP1 or CAP2 alone. We found a similar spine maturation defect upon overactivation of inverted formin 2 (INF2), a nucleator of unbranched F-actin with hitherto unknown synaptic function. While INF2 overactivation failed in altering spine density or morphology in CAP-deficient neurons, INF2 inactivation largely rescued their spine defects. From our data we conclude that CAPs inhibit INF2 to induce spine maturation. Since we previously showed that CAPs promote cofilin1-mediated cytoskeletal remodeling in mature spines, we identified them as a molecular switch that control transition from filopodia-like to mature spines.
Assuntos
Proteínas do Citoesqueleto , Espinhas Dendríticas , Forminas , Hipocampo , Proteínas dos Microfilamentos , Espinhas Dendríticas/metabolismo , Animais , Camundongos , Forminas/metabolismo , Forminas/genética , Proteínas dos Microfilamentos/metabolismo , Proteínas dos Microfilamentos/genética , Proteínas do Citoesqueleto/metabolismo , Proteínas do Citoesqueleto/genética , Hipocampo/metabolismo , Hipocampo/citologia , Células Cultivadas , Neurônios/metabolismo , Actinas/metabolismo , Citoesqueleto de Actina/metabolismo , Camundongos Knockout , Humanos , Proteínas de TransporteRESUMO
Long-term synaptic plasticity is typically associated with morphological changes in synaptic connections. However, the molecular mechanisms coupling functional and structural aspects of synaptic plasticity are still poorly defined. The catalytic activity of type I phosphoinositide-3-kinase (PI3K) is required for specific forms of synaptic plasticity, such as NMDA receptor-dependent long-term potentiation (LTP) and mGluR-dependent long-term depression (LTD). On the other hand, PI3K signaling has been linked to neuronal growth and synapse formation. Consequently, PI3Ks are promising candidates to coordinate changes in synaptic strength with structural remodeling of synapses. To investigate this issue, we targeted individual regulatory subunits of type I PI3Ks in hippocampal neurons and employed a combination of electrophysiological, biochemical and imaging techniques to assess their role in synaptic plasticity. We found that a particular regulatory isoform, p85α, is selectively required for LTP. This specificity is based on its BH domain, which engages the small GTPases Rac1 and Cdc42, critical regulators of the actin cytoskeleton. Moreover, cofilin, a key regulator of actin dynamics that accumulates in dendritic spines after LTP induction, failed to do so in the absence of p85α or when its BH domain was overexpressed as a dominant negative construct. Finally, in agreement with this convergence on actin regulatory mechanisms, the presence of p85α in the PI3K complex determined the extent of actin polymerization in dendritic spines during LTP. Therefore, this study reveals a molecular mechanism linking structural and functional synaptic plasticity through the coordinate action of PI3K catalytic activity and a specific isoform of the regulatory subunits.
Assuntos
Fatores de Despolimerização de Actina , Actinas , Espinhas Dendríticas , Hipocampo , Potenciação de Longa Duração , Animais , Espinhas Dendríticas/metabolismo , Potenciação de Longa Duração/fisiologia , Actinas/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Fatores de Despolimerização de Actina/metabolismo , Ratos , Proteínas rac1 de Ligação ao GTP/metabolismo , Sinapses/metabolismo , Polimerização , Proteína cdc42 de Ligação ao GTP/metabolismo , Plasticidade Neuronal/fisiologia , Fosfatidilinositol 3-Quinases/metabolismo , Classe Ia de Fosfatidilinositol 3-Quinase/metabolismo , Classe Ia de Fosfatidilinositol 3-Quinase/genética , Neurônios/metabolismo , Transdução de Sinais , Camundongos , Células CultivadasRESUMO
Mature neurons have stable dendritic architecture, which is essential for the nervous system to operate correctly. The ability to undergo structural plasticity, required to support adaptive processes like memory formation, is still present in mature neurons. It is unclear what molecular and cellular processes control this delicate balance between dendritic structural plasticity and stabilization. Failures in the preservation of optimal dendrite structure due to atrophy or maladaptive plasticity result in abnormal connectivity and are associated with various neurological diseases. Vascular endothelial growth factor D (VEGFD) is critical for the maintenance of mature dendritic trees. Here, we describe how VEGFD affects the neuronal cytoskeleton and demonstrate that VEGFD exerts its effects on dendrite stabilization by influencing the actin cortex and reducing microtubule dynamics. Further, we found that during synaptic activity-induced structural plasticity VEGFD is downregulated. Our findings revealed that VEGFD, acting on its cognate receptor VEGFR3, opposes structural changes by negatively regulating dendrite growth in cultured hippocampal neurons and in vivo in the adult mouse hippocampus with consequences on memory formation. A phosphoproteomic screening identified several regulatory proteins of the cytoskeleton modulated by VEGFD. Among the actin cortex-associated proteins, we found that VEGFD induces dephosphorylation of ezrin at tyrosine 478 via activation of the striatal-enriched protein tyrosine phosphatase (STEP). Activity-triggered structural plasticity of dendrites was impaired by expression of a phospho-deficient mutant ezrin in vitro and in vivo. Thus, VEGFD governs the equilibrium between stabilization and plasticity of dendrites by acting as a molecular brake of structural remodeling.
Assuntos
Dendritos , Hipocampo , Plasticidade Neuronal , Transdução de Sinais , Animais , Dendritos/metabolismo , Camundongos , Hipocampo/metabolismo , Hipocampo/citologia , Camundongos Endogâmicos C57BL , Células Cultivadas , Citoesqueleto/metabolismo , Masculino , Neurônios/metabolismo , Neurônios/citologia , Actinas/metabolismo , Fosforilação , Microtúbulos/metabolismoRESUMO
AMPA-type receptors (AMPARs) are rapidly inserted into synapses undergoing plasticity to increase synaptic transmission, but it is not fully understood if and how AMPAR-containing vesicles are selectively trafficked to these synapses. Here, we developed a strategy to label AMPAR GluA1 subunits expressed from their endogenous loci in cultured rat hippocampal neurons and characterized the motion of GluA1-containing vesicles using single-particle tracking and mathematical modeling. We find that GluA1-containing vesicles are confined and concentrated near sites of stimulation-induced structural plasticity. We show that confinement is mediated by actin polymerization, which hinders the active transport of GluA1-containing vesicles along the length of the dendritic shaft by modulating the rheological properties of the cytoplasm. Actin polymerization also facilitates myosin-mediated transport of GluA1-containing vesicles to exocytic sites. We conclude that neurons utilize F-actin to increase vesicular GluA1 reservoirs and promote exocytosis proximal to the sites of synaptic activity.
Assuntos
Actinas , Dendritos , Hipocampo , Plasticidade Neuronal , Polimerização , Receptores de AMPA , Animais , Receptores de AMPA/metabolismo , Actinas/metabolismo , Ratos , Plasticidade Neuronal/fisiologia , Dendritos/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Transporte Proteico , Neurônios/metabolismo , Células Cultivadas , ExocitoseAssuntos
Memória , Neurônios , Animais , Neurônios/fisiologia , Memória/fisiologia , Humanos , Camundongos , Hipocampo/citologia , Hipocampo/fisiologiaRESUMO
Sevoflurane (Sev) is a commonly used inhalation anaesthetic that has been shown to cause hippocampus dysfunction through multiple underlying molecular processes, including mitochondrial malfunction, oxidative stress and inflammation. Dihydromyricetin (DHM) is a 2,3-dihydroflavonoid with various biological properties, such as anti-inflammation and anti-oxidative stress. The purpose of this study was to investigate the effect of DHM on Sev-induced neuronal dysfunction. HT22 cells were incubated with 10, 20 and 30 µM of DHM for 24 h, and then stimulated with 4% Sev for 6 h. The effects and mechanism of DHM on inflammation, oxidative stress and mitochondrial dysfunction were explored in Sev-induced HT22 cells by Cell Counting Kit-8, flow cytometry, enzyme-linked immunosorbent assay, reverse transcription-quantitative polymerase chain reaction, colorimetric detections, detection of the level of reactive oxygen species (ROS), mitochondrial ROS and mitochondrial membrane potential (MMP), immunofluorescence and western blotting. Our results showed that DHM increased Sev-induced cell viability of HT22 cells. Pretreatment with DHM attenuated apoptosis, inflammation, oxidative stress and mitochondrial dysfunction in Sev-elicited HT22 cells by remedying the abnormality of the indicators involved in these progresses, including apoptosis rate, the cleaved-caspase 3 expression, as well as the level of tumour necrosis factor α, interleukin (IL)-1ß, IL-6, malondialdehyde, superoxide dismutase, catalase, ROS, mitochondrial ROS and MMP. Mechanically, pretreatment with DHM restored the Sev-induced the expression of SIRT1/FOXO3a pathway in HT22 cells. Blocking of SIRT1 counteracted the mitigatory effect of DHM on apoptosis, inflammation, oxidative stress and mitochondrial dysfunction in Sev-elicited HT22 cells. Collectively, pretreatment with DHM improved inflammation, oxidative stress and mitochondrial dysfunction via SIRT1/FOXO3a pathway in Sev-induced HT22 cells.
Assuntos
Apoptose , Flavonóis , Hipocampo , Mitocôndrias , Estresse Oxidativo , Sevoflurano , Flavonóis/farmacologia , Animais , Camundongos , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Hipocampo/citologia , Hipocampo/patologia , Linhagem Celular , Sevoflurano/farmacologia , Estresse Oxidativo/efeitos dos fármacos , Apoptose/efeitos dos fármacos , Potencial da Membrana Mitocondrial/efeitos dos fármacos , Espécies Reativas de Oxigênio/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Sirtuína 1/metabolismo , Fármacos Neuroprotetores/farmacologiaRESUMO
The branched architecture of neuronal dendrites is a key factor in how neurons form ordered networks and discoveries continue to be made identifying proteins and protein-protein interactions that direct or execute the branching and extension of dendrites. Our prior work showed that the molecular scaffold Pdlim5 and delta-catenin, in conjunction, are two proteins that help regulate the branching and elongation of dendrites in cultured hippocampal neurons and do so through a phosphorylation-dependent mechanism triggered by upstream glutamate signaling. In this report we have focused on Pdlim5's multiple scaffolding domains and how each contributes to dendrite branching. The three identified regions within Pdlim5 are the PDZ, DUF, and a trio of LIM domains; however, unresolved is the intra-molecular conformation of Pdlim5 as well as which domains are essential to regulate dendritic branching. We address Pdlim5's structure and function by examining the role of each of the domains individually and using deletion mutants in the context of the full-length protein. Results using primary hippocampal neurons reveal that the Pdlim5 DUF domain plays a dominant role in increasing dendritic branching. Neither the PDZ domain nor the LIM domains alone support increased branching. The central role of the DUF domain was confirmed using deletion mutants in the context of full-length Pdlim5. Guided by molecular modeling, additional domain mapping studies showed that the C-terminal LIM domain forms a stable interaction with the N-terminal PDZ domain, and we identified key amino acid residues at the interface of each domain that are needed for this interaction. We posit that the central DUF domain of Pdlim5 may be subject to modulation in the context of the full-length protein by the intra-molecular interaction between the N-terminal PDZ and C-terminal LIM domains. Overall, our studies reveal a novel mechanism for the regulation of Pdlim5's function in the regulation of neuronal branching and highlight the critical role of the DUF domain in mediating these effects.
Assuntos
Dendritos , Hipocampo , Proteínas com Domínio LIM , Domínios PDZ , Dendritos/metabolismo , Animais , Hipocampo/metabolismo , Hipocampo/citologia , Proteínas com Domínio LIM/metabolismo , Proteínas com Domínio LIM/química , Proteínas com Domínio LIM/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/genética , Domínios Proteicos , Neurônios/metabolismo , Ratos , Células Cultivadas , HumanosRESUMO
Neuronal development is characterized by the unidirectional flow of signal from the axon to the dendrites via synapses. Neuronal polarization is a critical step during development that allows the specification of the different neuronal processes as a single axon and multiple dendrites both structurally and functionally, allowing the unidirectional flow of information. Along with extrinsic and intrinsic signaling, a whole network of molecular complexes involved in positive and negative feedback loops play a major role in this critical distinction of neuronal processes. As a result, neuronal morphology is drastically altered during establishment of polarity. In this chapter, we discuss how we can analyze the morphological alterations of neurons in vitro in culture to assess the development and polarity status of the neuron. We also discuss how these studies can be conducted in vivo, where polarity studies pose a greater challenge with promising results for addressing multiple pathological conditions. Our experimental model is limited to rodent hippocampal/cortical neurons in culture and cortical neurons in brain tissues, which are well-characterized model systems for understanding neuronal polarization.
Assuntos
Polaridade Celular , Hipocampo , Neurônios , Animais , Neurônios/citologia , Neurônios/fisiologia , Neurônios/metabolismo , Camundongos , Hipocampo/citologia , Células Cultivadas , Ratos , Axônios/fisiologia , Axônios/metabolismo , Dendritos/fisiologia , Dendritos/metabolismo , Córtex Cerebral/citologiaRESUMO
The highly complex structure of the brain requires an approach that can unravel its connectivity. Using volume electron microscopy and a dedicated software we can trace and measure all nerve fibers present within different samples of brain tissue. With this software tool, individual dendrites and axons are traced, obtaining a simplified "skeleton" of each fiber, which is linked to its corresponding synaptic contacts. The result is an intricate meshwork of axons and dendrites interconnected by a cloud of synaptic junctions. To test this methodology, we apply it to the stratum radiatum of the hippocampus and layers 1 and 3 of the somatosensory cortex of the mouse. We find that nerve fibers are densely packed in the neuropil, reaching up to 9 kilometers per cubic mm. We obtain the number of synapses, the number and lengths of dendrites and axons, the linear densities of synapses established by dendrites and axons, and their location on dendritic spines and shafts. The quantitative data obtained through this method enable us to identify subtle traits and differences in the synaptic organization of the samples, which might have been overlooked in a qualitative analysis.
Assuntos
Microscopia Eletrônica , Fibras Nervosas , Sinapses , Animais , Camundongos , Microscopia Eletrônica/métodos , Fibras Nervosas/ultraestrutura , Sinapses/ultraestrutura , Axônios/ultraestrutura , Dendritos/ultraestrutura , Encéfalo/ultraestrutura , Córtex Somatossensorial/ultraestrutura , Camundongos Endogâmicos C57BL , Masculino , Software , Hipocampo/ultraestrutura , Hipocampo/citologia , Microscopia Eletrônica de VolumeRESUMO
Quiescence, a hallmark of adult neural stem cells (NSCs), is required for maintaining the NSC pool to support life-long continuous neurogenesis in the adult dentate gyrus (DG). Whether long-lasting epigenetic modifications maintain NSC quiescence over the long term in the adult DG is not well-understood. Here we show that mice with haploinsufficiency of Setd1a, a schizophrenia risk gene encoding a histone H3K4 methyltransferase, develop an enlarged DG with more dentate granule cells after young adulthood. Deletion of Setd1a specifically in quiescent NSCs in the adult DG promotes their activation and neurogenesis, which is countered by inhibition of the histone demethylase LSD1. Mechanistically, RNA-sequencing and CUT & RUN analyses of cultured quiescent adult NSCs reveal Setd1a deletion-induced transcriptional changes and many Setd1a targets, among which down-regulation of Bhlhe40 promotes quiescent NSC activation in the adult DG in vivo. Together, our study reveals a Setd1a-dependent epigenetic mechanism that sustains NSC quiescence in the adult DG.
Assuntos
Giro Denteado , Epigênese Genética , Hipocampo , Histona-Lisina N-Metiltransferase , Células-Tronco Neurais , Neurogênese , Animais , Feminino , Masculino , Camundongos , Células-Tronco Adultas/metabolismo , Células-Tronco Adultas/citologia , Giro Denteado/citologia , Giro Denteado/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Histona Desmetilases/metabolismo , Histona Desmetilases/genética , Histona-Lisina N-Metiltransferase/metabolismo , Histona-Lisina N-Metiltransferase/genética , Camundongos Endogâmicos C57BL , Camundongos Knockout , Células-Tronco Neurais/metabolismo , Células-Tronco Neurais/citologia , Neurogênese/genéticaRESUMO
A recent approach to promote central nervous system (CNS) regeneration after injury or disease is direct conversion of somatic cells to neurons. This is achieved by transduction of viral vectors that express neurogenic transcription factors. In this work we propose adult human mucosal olfactory ensheathing glia (hmOEG) as a candidate for direct reprogramming to neurons due to its accessibility and to its well-characterized neuroregenerative capacity. After induction of hmOEG with the single neurogenic transcription factor NEUROD1, the cells under study exhibited morphological and immunolabeling neuronal features, fired action potentials and expressed glutamatergic and GABAergic markers. In addition, after engraftment of transduced hmOEG cells in the mouse hippocampus, these cells showed specific neuronal labeling. Thereby, if we add to the neuroregenerative capacity of hmOEG cultures the conversion to neurons of a fraction of their population through reprogramming techniques, the engraftment of hmOEG and hmOEG-induced neurons could be a procedure to enhance neural repair after central nervous system injury.
Assuntos
Neuroglia , Neurônios , Humanos , Animais , Neuroglia/metabolismo , Neuroglia/citologia , Neurônios/metabolismo , Neurônios/citologia , Camundongos , Adulto , Mucosa Olfatória/citologia , Mucosa Olfatória/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/metabolismo , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Linhagem da Célula , Hipocampo/citologia , Hipocampo/metabolismo , Bulbo Olfatório/citologia , Bulbo Olfatório/metabolismo , Células CultivadasRESUMO
A single dose of psilocybin, a psychedelic that acutely causes distortions of space-time perception and ego dissolution, produces rapid and persistent therapeutic effects in human clinical trials1-4. In animal models, psilocybin induces neuroplasticity in cortex and hippocampus5-8. It remains unclear how human brain network changes relate to subjective and lasting effects of psychedelics. Here we tracked individual-specific brain changes with longitudinal precision functional mapping (roughly 18 magnetic resonance imaging visits per participant). Healthy adults were tracked before, during and for 3 weeks after high-dose psilocybin (25 mg) and methylphenidate (40 mg), and brought back for an additional psilocybin dose 6-12 months later. Psilocybin massively disrupted functional connectivity (FC) in cortex and subcortex, acutely causing more than threefold greater change than methylphenidate. These FC changes were driven by brain desynchronization across spatial scales (areal, global), which dissolved network distinctions by reducing correlations within and anticorrelations between networks. Psilocybin-driven FC changes were strongest in the default mode network, which is connected to the anterior hippocampus and is thought to create our sense of space, time and self. Individual differences in FC changes were strongly linked to the subjective psychedelic experience. Performing a perceptual task reduced psilocybin-driven FC changes. Psilocybin caused persistent decrease in FC between the anterior hippocampus and default mode network, lasting for weeks. Persistent reduction of hippocampal-default mode network connectivity may represent a neuroanatomical and mechanistic correlate of the proplasticity and therapeutic effects of psychedelics.
Assuntos
Encéfalo , Alucinógenos , Rede Nervosa , Psilocibina , Adolescente , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Adulto Jovem , Encéfalo/citologia , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Encéfalo/fisiologia , Mapeamento Encefálico , Rede de Modo Padrão/citologia , Rede de Modo Padrão/diagnóstico por imagem , Rede de Modo Padrão/efeitos dos fármacos , Rede de Modo Padrão/fisiologia , Alucinógenos/farmacologia , Alucinógenos/administração & dosagem , Voluntários Saudáveis , Hipocampo/citologia , Hipocampo/diagnóstico por imagem , Hipocampo/efeitos dos fármacos , Hipocampo/fisiologia , Imageamento por Ressonância Magnética , Metilfenidato/farmacologia , Metilfenidato/administração & dosagem , Rede Nervosa/citologia , Rede Nervosa/diagnóstico por imagem , Rede Nervosa/efeitos dos fármacos , Rede Nervosa/fisiologia , Psilocibina/farmacologia , Psilocibina/administração & dosagem , Percepção Espacial/efeitos dos fármacos , Percepção do Tempo/efeitos dos fármacos , EgoRESUMO
Brain computation performed by billions of nerve cells relies on a sufficient and uninterrupted nutrient and oxygen supply1,2. Astrocytes, the ubiquitous glial neighbours of neurons, govern brain glucose uptake and metabolism3,4, but the exact mechanisms of metabolic coupling between neurons and astrocytes that ensure on-demand support of neuronal energy needs are not fully understood5,6. Here we show, using experimental in vitro and in vivo animal models, that neuronal activity-dependent metabolic activation of astrocytes is mediated by neuromodulator adenosine acting on astrocytic A2B receptors. Stimulation of A2B receptors recruits the canonical cyclic adenosine 3',5'-monophosphate-protein kinase A signalling pathway, leading to rapid activation of astrocyte glucose metabolism and the release of lactate, which supplements the extracellular pool of readily available energy substrates. Experimental mouse models involving conditional deletion of the gene encoding A2B receptors in astrocytes showed that adenosine-mediated metabolic signalling is essential for maintaining synaptic function, especially under conditions of high energy demand or reduced energy supply. Knockdown of A2B receptor expression in astrocytes led to a major reprogramming of brain energy metabolism, prevented synaptic plasticity in the hippocampus, severely impaired recognition memory and disrupted sleep. These data identify the adenosine A2B receptor as an astrocytic sensor of neuronal activity and show that cAMP signalling in astrocytes tunes brain energy metabolism to support its fundamental functions such as sleep and memory.
Assuntos
Adenosina , Astrócitos , Encéfalo , Metabolismo Energético , Neurônios , Transdução de Sinais , Animais , Feminino , Masculino , Camundongos , Ratos , Adenosina/metabolismo , Astrócitos/metabolismo , Encéfalo/metabolismo , Encéfalo/citologia , AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Glucose/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Ácido Láctico/metabolismo , Camundongos Endogâmicos C57BL , Plasticidade Neuronal , Neurônios/metabolismo , Receptor A2B de Adenosina/deficiência , Receptor A2B de Adenosina/efeitos dos fármacos , Receptor A2B de Adenosina/genética , Receptor A2B de Adenosina/metabolismo , Reconhecimento Psicológico/fisiologia , Sono/genética , Sono/fisiologia , Sinapses/metabolismoRESUMO
Postnatal hippocampal neurogenesis is essential for learning and memory. Hippocampal neural precursor cells (NPCs) can be induced to proliferate and differentiate into either glial cells or dentate granule cells. Notably, hippocampal neurogenesis decreases dramatically with age, partly due to a reduction in the NPC pool and a decrease in their proliferative activity. Alpha-melanocyte-stimulating hormone (α-MSH) improves learning, memory, neuronal survival and plasticity. Here, we used postnatally-isolated hippocampal NPCs from Wistar rat pups (male and female combined) to determine the role of the melanocortin analog [Nle4, D-Phe7]-α-MSH (NDP-MSH) in proliferation and fate acquisition of NPCs. Incubation of growth-factor deprived NPCs with 10 nM NDP-MSH for 6 days increased the proportion of Ki-67- and 5-bromo-2'-deoxyuridine (BrdU)-positive cells, compared to the control group, and these effects were blocked by the MC4R antagonist JKC-363. NDP-MSH also increased the proportion of glial fibrillar acidic protein (GFAP)/Ki-67, GFAP/sex-determining region Y-box2 (SOX2) and neuroepithelial stem cell protein (NESTIN)/Ki-67-double positive cells (type-1 and type-2 precursors). Finally, NDP-MSH induced peroxisome proliferator-activated receptor (PPAR)-γ protein expression, and co-incubation with the PPAR-γ inhibitor GW9662 prevented the effect of NDP-MSH on NPC proliferation and differentiation. Our results indicate that in vitro activation of MC4R in growth-factor-deprived postnatal hippocampal NPCs induces proliferation and promotes the relative expansion of the type-1 and type-2 NPC pool through a PPAR-γ-dependent mechanism. These results shed new light on the mechanisms underlying the beneficial effects of melanocortins in hippocampal plasticity and provide evidence linking the MC4R and PPAR-γ pathways in modulation of hippocampal NPC proliferation and differentiation.
Assuntos
Diferenciação Celular , Proliferação de Células , Hipocampo , Células-Tronco Neurais , Neurogênese , Ratos Wistar , Receptor Tipo 4 de Melanocortina , alfa-MSH , Animais , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Hipocampo/citologia , Células-Tronco Neurais/efeitos dos fármacos , Células-Tronco Neurais/metabolismo , Células-Tronco Neurais/fisiologia , Proliferação de Células/efeitos dos fármacos , Proliferação de Células/fisiologia , Receptor Tipo 4 de Melanocortina/metabolismo , alfa-MSH/farmacologia , alfa-MSH/análogos & derivados , Feminino , Diferenciação Celular/efeitos dos fármacos , Diferenciação Celular/fisiologia , Masculino , Neurogênese/efeitos dos fármacos , Neurogênese/fisiologia , Ratos , Células Cultivadas , Fatores de Transcrição SOXB1/metabolismo , Animais Recém-Nascidos , Proteína Glial Fibrilar Ácida/metabolismo , PPAR gama/metabolismoRESUMO
Adult neurogenesis is a unique form of neuronal plasticity in which newly generated neurons are integrated into the adult dentate gyrus in a process that is modulated by environmental stimuli. Adult-born neurons can contribute to spatial memory, but it is unknown whether they alter neural representations of space in the hippocampus. Using in vivo two-photon calcium imaging, we find that male and female mice previously housed in an enriched environment, which triggers an increase in neurogenesis, have increased spatial information encoding in the dentate gyrus. Ablating adult neurogenesis blocks the effect of enrichment and lowers spatial information, as does the chemogenetic silencing of adult-born neurons. Both ablating neurogenesis and silencing adult-born neurons decreases the calcium activity of dentate gyrus neurons, resulting in a decreased amplitude of place-specific responses. These findings are in contrast with previous studies that suggested a predominantly inhibitory action for adult-born neurons. We propose that adult neurogenesis improves representations of space by increasing the gain of dentate gyrus neurons and thereby improving their ability to tune to spatial features. This mechanism may mediate the beneficial effects of environmental enrichment on spatial learning and memory.
Assuntos
Giro Denteado , Hipocampo , Neurogênese , Neurônios , Memória Espacial , Animais , Neurogênese/fisiologia , Masculino , Feminino , Giro Denteado/fisiologia , Giro Denteado/citologia , Camundongos , Neurônios/fisiologia , Neurônios/metabolismo , Hipocampo/fisiologia , Hipocampo/citologia , Hipocampo/metabolismo , Memória Espacial/fisiologia , Camundongos Endogâmicos C57BL , Plasticidade Neuronal/fisiologia , Cálcio/metabolismo , Aprendizagem Espacial/fisiologiaRESUMO
Hippocampal place cells in freely moving rodents display both theta phase precession and procession, which is thought to play important roles in cognition, but the neural mechanism for producing theta phase shift remains largely unknown. Here, we show that firing rate adaptation within a continuous attractor neural network causes the neural activity bump to oscillate around the external input, resembling theta sweeps of decoded position during locomotion. These forward and backward sweeps naturally account for theta phase precession and procession of individual neurons, respectively. By tuning the adaptation strength, our model explains the difference between 'bimodal cells' showing interleaved phase precession and procession, and 'unimodal cells' in which phase precession predominates. Our model also explains the constant cycling of theta sweeps along different arms in a T-maze environment, the speed modulation of place cells' firing frequency, and the continued phase shift after transient silencing of the hippocampus. We hope that this study will aid an understanding of the neural mechanism supporting theta phase coding in the brain.
Assuntos
Potenciais de Ação , Células de Lugar , Ritmo Teta , Animais , Ritmo Teta/fisiologia , Células de Lugar/fisiologia , Potenciais de Ação/fisiologia , Modelos Neurológicos , Hipocampo/fisiologia , Hipocampo/citologia , Adaptação Fisiológica , RatosRESUMO
Dendritic spines are the postsynaptic compartments of excitatory synapses, however, a substantial subset of spines additionally receives inhibitory input. In such dually innervated spines (DiSs), excitatory long-term potentiation (LTP) mechanisms are suppressed, but can be enabled by blocking tonic inhibitory GABAB receptor signaling. Here we show that LTP mechanisms at DiSs are also enabled by two other excitatory LTP stimuli. In hippocampal neurons, these chemical LTP (cLTP) stimuli induced robust movement of the Ca2+/calmodulin-dependent protein kinase II (CaMKII) to DiSs. Such synaptic CaMKII accumulation is an essential LTP mechanism at singly innervated spines (SiSs). Indeed, CaMKII accumulation at DiSs was also accompanied by other readouts for successful LTP induction: spine growth and surface insertion of GluA1. Thus, DiSs are capable of the same LTP mechanisms as SiSs, although induction of these mechanism additionally requires either reduced inhibitory signaling or increased excitatory stimulation. This additional regulation may provide further computational control.
Assuntos
Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina , Espinhas Dendríticas , Potenciação de Longa Duração , Espinhas Dendríticas/metabolismo , Espinhas Dendríticas/fisiologia , Animais , Proteína Quinase Tipo 2 Dependente de Cálcio-Calmodulina/metabolismo , Hipocampo/metabolismo , Hipocampo/citologia , Hipocampo/fisiologia , Sinapses/fisiologia , Sinapses/metabolismo , Receptores de AMPA/metabolismo , Ratos , Neurônios/metabolismo , Neurônios/fisiologiaRESUMO
We applied the patch-seq technique to harvest transcripts from individual microglial cells from cortex, hippocampus and corpus callosum of acute brain slices from adult mice. After recording membrane currents with the patch-clamp technique, the cytoplasm was collected via the pipette and underwent adapted SMART-seq2 preparation with subsequent sequencing. On average, 4138 genes were detected in 113 cells from hippocampus, corpus callosum and cortex, including microglia markers such as Tmem119, P2ry12 and Siglec-H. Comparing our dataset to previously published single cell mRNA sequencing data from FACS-isolated microglia indicated that two clusters of cells were absent in our patch-seq dataset. Pathway analysis of marker genes in FACS-specific clusters revealed association with microglial activation and stress response. This indicates that under normal conditions microglia in situ lack transcripts associated with a stress-response, and that the microglia-isolation procedure by mechanical dissociation and FACS triggers the expression of genes related to activation and stress.