RESUMO
p11, through unknown mechanisms, is required for behavioral and cellular responses to selective serotonin reuptake inhibitors (SSRIs). We show that SMARCA3, a chromatin-remodeling factor, is a target for the p11/annexin A2 heterotetrameric complex. Determination of the crystal structure indicates that SMARCA3 peptide binds to a hydrophobic pocket in the heterotetramer. Formation of this complex increases the DNA-binding affinity of SMARCA3 and its localization to the nuclear matrix fraction. In the dentate gyrus, both p11 and SMARCA3 are highly enriched in hilar mossy cells and basket cells. The SSRI fluoxetine induces expression of p11 in both cell types and increases the amount of the ternary complex of p11/annexin A2/SMARCA3. SSRI-induced neurogenesis and behavioral responses are abolished by constitutive knockout of SMARCA3. Our studies indicate a central role for a chromatin-remodeling factor in the SSRI/p11 signaling pathway and suggest an approach to the development of improved antidepressant therapies. PAPERCLIP:
Assuntos
Anexina A2/metabolismo , Proteínas de Ligação a DNA/metabolismo , Giro Denteado/metabolismo , Proteínas S100/metabolismo , Inibidores Seletivos de Recaptação de Serotonina/farmacologia , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Animais , Proteínas de Ligação a DNA/química , Feminino , Masculino , Modelos Moleculares , Dados de Sequência Molecular , Fibras Musgosas Hipocampais/metabolismo , Alinhamento de Sequência , Transdução de Sinais , Fatores de Transcrição/química , Difração de Raios XRESUMO
At the center of the hippocampal tri-synaptic loop are synapses formed between mossy fiber (MF) terminals from granule cells in the dentate gyrus (DG) and proximal dendrites of CA3 pyramidal neurons. However, the molecular mechanism regulating the development and function of these synapses is poorly understood. In this study, we showed that neurotrophin-3 (NT3) was expressed in nearly all mature granule cells but not CA3 cells. We selectively deleted the NT3-encoding Ntf3 gene in the DG during the first two postnatal weeks to generate a Ntf3 conditional knockout (Ntf3-cKO). Ntf3-cKO mice of both sexes had normal hippocampal cytoarchitecture but displayed impairments in contextual memory, spatial reference memory, and nest building. Furthermore, male Ntf3-cKO mice exhibited anxiety-like behaviors, whereas female Ntf3-cKO showed some mild depressive symptoms. As MF-CA3 synapses are essential for encoding of contextual memory, we examined synaptic transmission at these synapses using ex vivo electrophysiological recordings. We found that Ntf3-cKO mice had impaired basal synaptic transmission due to deficits in excitatory postsynaptic currents mediated by AMPA receptors but normal presynaptic function and intrinsic excitability of CA3 pyramidal neurons. Consistent with this selective postsynaptic deficit, Ntf3-cKO mice had fewer and smaller thorny excrescences on proximal apical dendrites of CA3 neurons and lower GluR1 levels in the stratum lucidum area where MF-CA3 synapses reside but normal MF terminals, compared with control mice. Thus, our study indicates that NT3 expressed in the dentate gyrus is crucial for the postsynaptic structure and function of MF-CA3 synapses and hippocampal-dependent memory.
Assuntos
Região CA3 Hipocampal , Giro Denteado , Camundongos Knockout , Fibras Musgosas Hipocampais , Neurotrofina 3 , Sinapses , Animais , Giro Denteado/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Sinapses/metabolismo , Camundongos , Neurotrofina 3/metabolismo , Neurotrofina 3/genética , Masculino , Feminino , Região CA3 Hipocampal/metabolismo , Células Piramidais/metabolismo , Células Piramidais/fisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Transmissão Sináptica/fisiologia , Cognição/fisiologia , Hipocampo/metabolismo , Camundongos Endogâmicos C57BL , Memória/fisiologia , Receptores de AMPA/metabolismoRESUMO
A Disintegrin And Metalloproteinase 10 (ADAM10) plays a pivotal role in shaping neuronal networks by orchestrating the activity of numerous membrane proteins through the shedding of their extracellular domains. Despite its significance in the brain, the specific cellular localization of ADAM10 remains not well understood due to a lack of appropriate tools. Here, using a specific ADAM10 antibody suitable for immunostainings, we observed that ADAM10 is localized to presynapses and especially enriched at presynaptic vesicles of mossy fiber (MF)-CA3 synapses in the hippocampus. These synapses undergo pronounced frequency facilitation of neurotransmitter release, a process that play critical roles in information transfer and neural computation. We demonstrate, that in conditional ADAM10 knockout mice the ability of MF synapses to undergo this type of synaptic plasticity is greatly reduced. The loss of facilitation depends on the cytosolic domain of ADAM10 and association with the calcium sensor synaptotagmin 7 rather than ADAM10's proteolytic activity. Our findings unveil a new role of ADAM10 in the regulation of synaptic vesicle exocytosis.
Assuntos
Proteína ADAM10 , Secretases da Proteína Precursora do Amiloide , Proteínas de Membrana , Camundongos Knockout , Plasticidade Neuronal , Vesículas Sinápticas , Animais , Proteína ADAM10/metabolismo , Proteína ADAM10/genética , Plasticidade Neuronal/fisiologia , Secretases da Proteína Precursora do Amiloide/metabolismo , Secretases da Proteína Precursora do Amiloide/genética , Proteínas de Membrana/metabolismo , Proteínas de Membrana/genética , Camundongos , Vesículas Sinápticas/metabolismo , Camundongos Endogâmicos C57BL , Sinapses/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Hipocampo/metabolismo , Exocitose/fisiologia , Terminações Pré-Sinápticas/metabolismo , Transmissão Sináptica , Sinaptotagminas/metabolismo , Sinaptotagminas/genéticaRESUMO
Synaptic cell-adhesion molecules (CAMs) organize the architecture and properties of neural circuits. However, whether synaptic CAMs are involved in activity-dependent remodeling of specific neural circuits is incompletely understood. Leucine-rich repeat transmembrane protein 3 (LRRTM3) is required for the excitatory synapse development of hippocampal dentate gyrus (DG) granule neurons. Here, we report that Lrrtm3-deficient mice exhibit selective reductions in excitatory synapse density and synaptic strength in projections involving the medial entorhinal cortex (MEC) and DG granule neurons, accompanied by increased neurotransmitter release and decreased excitability of granule neurons. LRRTM3 deletion significantly reduced excitatory synaptic innervation of hippocampal mossy fibers (Mf) of DG granule neurons onto thorny excrescences in hippocampal CA3 neurons. Moreover, LRRTM3 loss in DG neurons significantly decreased mossy fiber long-term potentiation (Mf-LTP). Remarkably, silencing MEC-DG circuits protected against the decrease in the excitatory synaptic inputs onto DG and CA3 neurons, excitability of DG granule neurons, and Mf-LTP in Lrrtm3-deficient mice. These results suggest that LRRTM3 may be a critical factor in activity-dependent synchronization of the topography of MEC-DG-CA3 excitatory synaptic connections. Collectively, our data propose that LRRTM3 shapes the target-specific structural and functional properties of specific hippocampal circuits.
Assuntos
Sincronização Cortical/fisiologia , Hipocampo/fisiologia , Proteínas de Membrana/metabolismo , Rede Nervosa/fisiologia , Proteínas do Tecido Nervoso/metabolismo , Sinapses/fisiologia , Animais , Região CA3 Hipocampal/metabolismo , Giro Denteado/metabolismo , Córtex Entorrinal/metabolismo , Potenciação de Longa Duração , Proteínas de Membrana/deficiência , Camundongos Knockout , Fibras Musgosas Hipocampais/metabolismo , Proteínas do Tecido Nervoso/deficiência , Neurônios/metabolismo , Pseudópodes/metabolismo , Transmissão Sináptica/fisiologiaRESUMO
A hippocampal mossy fiber synapse implicated in learning and memory is a complex structure in which a presynaptic bouton attaches to the dendritic trunk by puncta adherentia junctions (PAJs) and wraps multiply branched spines. The postsynaptic densities (PSDs) are localized at the heads of each of these spines and faces to the presynaptic active zones. We previously showed that the scaffolding protein afadin regulates the formation of the PAJs, PSDs, and active zones in the mossy fiber synapse. Afadin has two splice variants: l-afadin and s-afadin. l-Afadin, but not s-afadin, regulates the formation of the PAJs but the roles of s-afadin in synaptogenesis remain unknown. We found here that s-afadin more preferentially bound to MAGUIN (a product of the Cnksr2 gene) than l-afadin in vivo and in vitro. MAGUIN/CNKSR2 is one of the causative genes for nonsyndromic X-linked intellectual disability accompanied by epilepsy and aphasia. Genetic ablation of MAGUIN impaired PSD-95 localization and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) receptor surface accumulation in cultured hippocampal neurons. Our electrophysiological analysis revealed that the postsynaptic response to glutamate, but not its release from the presynapse, was impaired in the MAGUIN-deficient cultured hippocampal neurons. Furthermore, disruption of MAGUIN did not increase the seizure susceptibility to flurothyl, a GABAA receptor antagonist. These results indicate that s-afadin binds to MAGUIN and regulates the PSD-95-dependent cell surface localization of the AMPA receptor and glutamatergic synaptic responses in the hippocampal neurons and that MAGUIN is not involved in the induction of epileptic seizure by flurothyl in our mouse model.
Assuntos
Proteínas dos Microfilamentos , Receptores de AMPA , Sinapses , Animais , Camundongos , Proteína 4 Homóloga a Disks-Large/metabolismo , Flurotila , Hipocampo/metabolismo , Proteínas dos Microfilamentos/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Receptores de AMPA/metabolismo , Sinapses/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Long-term changes in synaptic strength form the basis of learning and memory. These changes rely upon energy-demanding mechanisms, which are regulated by local Ca2+ signalling. Mitochondria are optimised for providing energy and buffering Ca2+. However, our understanding of the role of mitochondria in regulating synaptic plasticity is incomplete. Here, we have used optical and electrophysiological techniques in cultured hippocampal neurons and ex vivo hippocampal slices from mice with haploinsufficiency of the mitochondrial Ca2+ uniporter (MCU+/-) to address whether reducing mitochondrial Ca2+ uptake alters synaptic transmission and plasticity. We found that cultured MCU+/- hippocampal neurons have impaired Ca2+ clearance, and consequently enhanced synaptic vesicle fusion at presynapses occupied by mitochondria. Furthermore, long-term potentiation (LTP) at mossy fibre (MF) synapses, a process which is dependent on presynaptic Ca2+ accumulation, is enhanced in MCU+/- slices. Our results reveal a previously unrecognised role for mitochondria in regulating presynaptic plasticity of a major excitatory pathway involved in learning and memory.
Assuntos
Potenciação de Longa Duração , Fibras Musgosas Hipocampais , Camundongos , Animais , Fibras Musgosas Hipocampais/metabolismo , Potenciação de Longa Duração/fisiologia , Cálcio/metabolismo , Haploinsuficiência , Sinapses/metabolismo , Transmissão Sináptica/fisiologia , Mitocôndrias/metabolismoRESUMO
Synaptic plasticity is a cellular model for learning and memory. However, the expression mechanisms underlying presynaptic forms of plasticity are not well understood. Here, we investigate functional and structural correlates of presynaptic potentiation at large hippocampal mossy fiber boutons induced by the adenylyl cyclase activator forskolin. We performed 2-photon imaging of the genetically encoded glutamate sensor iGluu that revealed an increase in the surface area used for glutamate release at potentiated terminals. Time-gated stimulated emission depletion microscopy revealed no change in the coupling distance between P/Q-type calcium channels and release sites mapped by Munc13-1 cluster position. Finally, by high-pressure freezing and transmission electron microscopy analysis, we found a fast remodeling of synaptic ultrastructure at potentiated boutons: Synaptic vesicles dispersed in the terminal and accumulated at the active zones, while active zone density and synaptic complexity increased. We suggest that these rapid and early structural rearrangements might enable long-term increase in synaptic strength.
Assuntos
Fibras Musgosas Hipocampais/metabolismo , Terminações Pré-Sinápticas/metabolismo , Animais , Colforsina/farmacologia , Ácido Glutâmico/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Microscopia de Fluorescência por Excitação Multifotônica , Fibras Musgosas Hipocampais/efeitos dos fármacos , Fibras Musgosas Hipocampais/ultraestrutura , Neurotransmissores/metabolismo , Terminações Pré-Sinápticas/efeitos dos fármacos , Vesículas Sinápticas/efeitos dos fármacos , Vesículas Sinápticas/metabolismoRESUMO
BACKGROUND: Mossy cells comprise a large fraction of excitatory neurons in the hippocampal dentate gyrus, and their loss is one of the major hallmarks of temporal lobe epilepsy (TLE). The vulnerability of mossy cells in TLE is well known in animal models as well as in patients; however, the mechanisms leading to cellular death is unclear. RESULTS: Transient receptor potential melastatin 4 (TRPM4) is a Ca2+-activated non-selective cation channel regulating diverse physiological functions of excitable cells. Here, we identified that TRPM4 is present in hilar mossy cells and regulates their intrinsic electrophysiological properties including spontaneous activity and action potential dynamics. Furthermore, we showed that TRPM4 contributes to mossy cells death following status epilepticus and therefore modulates seizure susceptibility and epilepsy-related memory deficits. CONCLUSIONS: Our results provide evidence for the role of TRPM4 in MC excitability both in physiological and pathological conditions.
Assuntos
Epilepsia do Lobo Temporal , Animais , Potenciais de Ação , Epilepsia do Lobo Temporal/metabolismo , Epilepsia do Lobo Temporal/patologia , Fibras Musgosas Hipocampais/metabolismo , Fibras Musgosas Hipocampais/patologia , Canais de Cátion TRPM/metabolismoRESUMO
Tight regulation of neuronal Zn2+ is critical for physiological function. Multiple Zn2+ transporters are expressed in the brain, yet their spatial distribution and distinct roles are largely unknown. Here, we show developmental regulation of the expression of Zn2+ transporters ZIP1 and ZIP3 in mouse hippocampal neurons, corresponding to previously described increase in neuronal vesicular Zn2+ during the first postnatal month. Rates of Zn2+ uptake in cultured mouse hippocampal neurons, monitored using FluoZin-3 fluorescence, were higher in mature neurons, which express higher levels of ZIP1 and ZIP3. Zn2+ uptake was attenuated by â¼50% following silencing of either ZIP1 or ZIP3. Expression of both ZIP1 and ZIP3 was ubiquitous on somas and most neuronal processes in the cultured neurons. In contrast, we observed distinct localization of the transporters in adult mouse hippocampal brain, with ZIP1 predominantly expressed in the CA3 stratum pyramidale, and ZIP3 primarily localized to the stratum lucidum. Consistent with their localization, silencing of ZIP1 expression in vivo reduced Zn2+ uptake in CA3 neurons while ZIP3 silencing reduced Zn2+ influx into dentate gyrus (DG) granule cells in acute hippocampal slices. Strikingly, in vivo silencing of ZIP3, but not ZIP1, protected CA3 neurons from neurodegeneration following kainate-induced seizures. Our results indicate that distinct Zn2+ transporters control Zn2+ accumulation and toxicity in different neuronal populations in the hippocampus and suggest that selective regulation of Zn2+ transporters can prevent seizure induced brain damage.SIGNIFICANCE STATEMENT Zinc plays a major role in neuronal function and its dysregulation is associated with neurodegeneration. Multiple zinc transporters are expressed in neurons, yet little is known on their distinct roles. Here, we show that the plasma membrane ZIP1 and ZIP3 zinc transporters are expressed on distinct neuronal populations in the CA3 region of the hippocampus. We show that ZIP1 mediates zinc influx into postsynaptic cells, while ZIP3 is responsible for zinc re-uptake from this synapse into dentate granule cells. We further show that silencing of ZIP3, but not ZIP1, can rescue the postsynaptic cells from kainate-induced neurodegeneration. This suggests that neuronal zinc toxicity and degeneration can be modulated by regulation of specific zinc transporters function.
Assuntos
Ácido Caínico , Fibras Musgosas Hipocampais , Animais , Região CA3 Hipocampal/metabolismo , Proteínas de Transporte/metabolismo , Proteínas de Transporte de Cátions/metabolismo , Hipocampo/metabolismo , Ácido Caínico/toxicidade , Camundongos , Fibras Musgosas Hipocampais/metabolismoRESUMO
The CA2 pyramidal cells are mostly resistant to cell death in mesial temporal lobe epilepsy (MTLE) with hippocampal sclerosis, but they are aberrantly integrated into the epileptic hippocampal network via mossy fiber sprouting. Furthermore, they show increased excitability in vitro in hippocampal slices obtained from human MTLE specimens or animal epilepsy models. Although these changes promote CA2 to contribute to epileptic activity (EA) in vivo, the role of CA2 in the epileptic network within and beyond the sclerotic hippocampus is still unclear. We used the intrahippocampal kainate mouse model for MTLE, which recapitulates most features of the human disease including pharmacoresistant epileptic seizures and hippocampal sclerosis, with preservation of dentate gyrus (DG) granule cells and CA2 pyramidal cells. In vivo recordings with electrodes in CA2 and the DG showed that EA occurs at high coincidence between the ipsilateral DG and CA2 and current source density analysis of silicon probe recordings in dorsal ipsilateral CA2 revealed CA2 as a local source of EA. Cell-specific viral tracing in Amigo2-icreERT2 mice confirmed the preservation of the axonal projection from ipsilateral CA2 pyramidal cells to contralateral CA2 under epileptic conditions and indeed, EA propagated from ipsi- to contralateral CA2 with increasing likelihood with time after KA injection, but always at lower intensity than within the ipsilateral hippocampus. Furthermore, we show that CA2 presents with local theta oscillations and like the DG, shows a pathological reduction of theta frequency already from 2 days after KA onward. The early changes in activity might be facilitated by the loss of glutamic acid decarboxylase 67 (Gad67) mRNA-expressing interneurons directly after the initial status epilepticus in ipsi- but not contralateral CA2. Together, our data highlight CA2 as an active player in the epileptic network and with its contralateral connections as one possible router of aberrant activity.
Assuntos
Epilepsia do Lobo Temporal , Epilepsia , Camundongos , Humanos , Animais , Giro Denteado/metabolismo , Hipocampo/metabolismo , Epilepsia/patologia , Epilepsia do Lobo Temporal/patologia , Convulsões/patologia , Ácido Caínico , Fibras Musgosas Hipocampais/metabolismoRESUMO
Growing evidence supports the notion that brain-derived neurotrophic factor (BDNF) and lactate are potent modulators of mammalian brain function. The modulatory actions of those biomolecules influence a wide range of neuronal responses, from the shaping of neuronal excitability to the induction and expression of structural and synaptic plasticity. The biological actions of BDNF and lactate are mediated by their cognate receptors and specific transporters located in the neuronal membrane. Canonical functions of BDNF occur via the tropomyosin-related kinase B receptor (TrkB), whereas lactate acts via monocarboxylate transporters or the hydroxycarboxylic acid receptor 1 (HCAR1). Both receptors are highly expressed in the central nervous system, and some of their physiological actions are particularly well characterized in the hippocampus, a brain structure involved in the neurophysiology of learning and memory. The multifarious neuronal circuitry between the axons of the dentate gyrus granule cells, mossy fibers (MF), and pyramidal neurons of area CA3 is of great interest given its role in specific mnemonic processes and involvement in a growing number of brain disorders. Whereas the modulation exerted by BDNF via TrkB has been extensively studied, the influence of lactate via HCAR1 on the properties of the MF-CA3 circuit is an emerging field. In this review, we discuss the role of both systems in the modulation of brain physiology, with emphasis on the hippocampal CA3 network. We complement this review with original data that suggest cross-modulation is exerted by these two independent neuromodulatory systems.
Assuntos
Fator Neurotrófico Derivado do Encéfalo , Fibras Musgosas Hipocampais , Animais , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Ácido Láctico/metabolismo , Hipocampo/metabolismo , Células Piramidais/metabolismo , Proteínas de Transporte/metabolismo , Região CA3 Hipocampal/metabolismo , Mamíferos/metabolismoRESUMO
Abnormal mossy fiber connections in the hippocampus have been implicated in schizophrenia. However, it remains unclear whether this abnormality in the patients is genetically determined and whether it contributes to the onset of schizophrenia. Here, we showed that iPSC-derived hippocampal NPCs from schizophrenia patients with the A/A allele at SNP rs16864067 exhibited abnormal NPC polarity, resulting from the downregulation of SOX11 by this high-risk allele. In the SOX11-deficient mouse brain, abnormal NPC polarity was also observed in the hippocampal dentate gyrus, and this abnormal NPC polarity led to defective hippocampal neurogenesis-specifically, irregular neuroblast distribution and disrupted granule cell morphology. As granule cell synapses, the mossy fiber pathway was disrupted, and this disruption was resistant to activity-induced mossy fiber remodeling in SOX11 mutant mice. Moreover, these mutant mice exhibited diminished PPI and schizophrenia-like behaviors. Activation of hippocampal neurogenesis in the embryonic brain, but not in the adult brain, partially alleviated disrupted mossy fiber connections and improved schizophrenia-related behaviors in mutant mice. We conclude that disrupted mossy fiber connections are genetically determined and strongly correlated with schizophrenia-like behaviors in SOX11-deficient mice. This disruption may reflect the pathological substrate of SOX11-associated schizophrenia.
Assuntos
Fibras Musgosas Hipocampais/metabolismo , Neurogênese , Fatores de Transcrição SOXC/fisiologia , Esquizofrenia/metabolismo , Animais , Hipocampo/metabolismo , Hipocampo/fisiopatologia , Camundongos , Camundongos Transgênicos , Fibras Musgosas Hipocampais/fisiopatologia , Fatores de Transcrição SOXC/genética , Esquizofrenia/fisiopatologia , SinapsesRESUMO
Synapses are interneuronal junctions which form neuronal networks and play roles in a variety of functions, including learning and memory. Two types of junctions, synaptic junctions (SJs) and puncta adherentia junctions (PAJs), have been identified. SJs are found at all excitatory and inhibitory synapses whereas PAJs are found at excitatory synapses, but not inhibitory synapses, and particularly well developed at hippocampal mossy fiber giant excitatory synapses. Both SJs and PAJs are mediated by cell adhesion molecules (CAMs). Major CAMs at SJs are neuroligins-neurexins and Nectin-like molecules (Necls)/CADMs/SynCAMs whereas those at PAJs are nectins and cadherins. In addition to synaptic PAJs, extrasynaptic PAJs have been identified at contact sites between neighboring dendrites near synapses and regulate synapse formation. In addition to SJs and PAJs, a new type of cell adhesion apparatus different from these junctional apparatuses has been identified and named nectin/Necl spots. One nectin spot at contact sites between neighboring dendrites at extrasynaptic regions near synapses regulates synapse formation. Several members of nectins and Necls had been identified as viral receptors before finding their physiological functions as CAMs and evidence is accumulating that many nectins and Necls are related to onset and progression of neurological diseases. We review here nectin and Necls in synapse formation and involvement in neurological diseases.
Assuntos
Fibras Musgosas Hipocampais , Sinapses , Caderinas/metabolismo , Adesão Celular , Moléculas de Adesão Celular/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Nectinas , Sinapses/metabolismoRESUMO
In temporal lobe epilepsy, sprouting of hippocampal mossy fiber axons onto dentate granule cell dendrites creates a recurrent excitatory network. However, unlike mossy fibers projecting to CA3, sprouted mossy fiber synapses depress upon repetitive activation. Thus, despite their proximal location, relatively large presynaptic terminals, and ability to excite target neurons, the impact of sprouted mossy fiber synapses on hippocampal hyperexcitability is unclear. We find that despite their short-term depression, single episodes of sprouted mossy fiber activation in hippocampal slices initiated bursts of recurrent polysynaptic excitation. Consistent with a contribution to network hyperexcitability, optogenetic activation of sprouted mossy fibers reliably triggered action potential firing in postsynaptic dentate granule cells after single light pulses. This pattern resulted in a shift in network recruitment dynamics to an "early detonation" mode and an increased probability of release compared with mossy fiber synapses in CA3. A lack of tonic adenosine-mediated inhibition contributed to the higher probability of glutamate release, thus facilitating reverberant circuit activity.
Assuntos
Giro Denteado/fisiopatologia , Epilepsia/fisiopatologia , Fibras Musgosas Hipocampais , Adenosina/metabolismo , Adenosina/farmacologia , Animais , Região CA3 Hipocampal/fisiopatologia , Modelos Animais de Doenças , Masculino , Camundongos , Camundongos Transgênicos , Fibras Musgosas Hipocampais/efeitos dos fármacos , Fibras Musgosas Hipocampais/metabolismo , Fibras Musgosas Hipocampais/fisiopatologia , Optogenética , Sinapses/metabolismoRESUMO
Brain-derived neurotrophic factor (BDNF), a main member of the neurotrophin family that is active in the brain, supports neuronal survival and growth. Microglial BDNF affects both the structural and functional properties of neurons. In contrast, whether and how neuronal BDNF affects microglial dynamics remain largely undetermined. Here, we examined the effects of BDNF on the properties of microglia in the CA3 region of the hippocampus. We chose this site because the axonal boutons of hippocampal mossy fibers, which are mostly formed in the CA3 region, contain the highest levels of BDNF in the rodent brain. We transfected mouse dentate granule cells with an adeno-associated virus that encodes both a BDNF short hairpin RNA (shRNA) and red fluorescent protein to examine the effects of mossy fiber-derived BDNF on microglia. Based on immunohistochemistry, BDNF knockdown with an shRNA resulted in an increase in microglial density in the mossy fiber pathway and increased engulfment of mossy fiber axons by microglia. In addition, we performed time-lapse imaging of microglial processes in hippocampal slice cultures to examine the effects of BDNF on microglial motility. Time-lapse imaging revealed increases in the motility of microglial processes and the engulfment of mossy fiber synapses by microglia when BDNF signaling was pharmacologically blocked. Thus, neuronal BDNF prevents microglia from engulfing mossy fiber synapses in the hippocampus.
Assuntos
Fator Neurotrófico Derivado do Encéfalo , Microglia , Animais , Fator Neurotrófico Derivado do Encéfalo/genética , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Hipocampo/metabolismo , Camundongos , Microglia/metabolismo , Fibras Musgosas Hipocampais/metabolismo , RNA Interferente Pequeno/genéticaRESUMO
Adult-born granule cells (abGCs) integrate into the hippocampus and form connections with dentate gyrus parvalbumin-positive (PV+) interneurons, a circuit important for modulating plasticity. Many of these interneurons are surrounded by perineuronal nets (PNNs), extracellular matrix structures known to participate in plasticity. We compared abGC projections to PV+ interneurons with negative-to-low intensity PNNs to those with high intensity PNNs using retroviral and 3R-Tau labeling in adult mice, and found that abGC mossy fibers and boutons are more frequently located near PV+ interneurons with high intensity PNNs. These results suggest that axons of new neurons preferentially stabilize near target cells with intense PNNs. Next, we asked whether the number of abGCs influences PNN formation around PV+ interneurons, and found that near complete ablation of abGCs produced a decrease in the intensity and number of PV+ neurons with PNNs, suggesting that new neuron innervation may enhance PNN formation. Experience-driven changes in adult neurogenesis did not produce consistent effects, perhaps due to widespread effects on plasticity. Our study identifies abGC projections to PV+ interneurons with PNNs, with more presumed abGC mossy fiber boutons found near the cell body of PV+ interneurons with strong PNNs.
Assuntos
Fibras Musgosas Hipocampais , Parvalbuminas , Animais , Matriz Extracelular/metabolismo , Interneurônios/metabolismo , Camundongos , Fibras Musgosas Hipocampais/metabolismo , Neurogênese , Parvalbuminas/metabolismoRESUMO
Hindbrain precerebellar neurons arise from progenitor pools at the dorsal edge of the embryonic hindbrain: the caudal rhombic lip. These neurons follow distinct migratory routes to establish nuclei that provide climbing or mossy fiber inputs to the cerebellum. Gli3, a zinc-finger transcription factor in the Sonic hedgehog signaling pathway, is an important regulator of dorsal brain development. We demonstrate that in Gli3-null mutant mice, disrupted neuronal migratory streams lead to a disorganization of precerebellar nuclei. Precerebellar progenitors are properly established in Gli3-null embryos and, using conditional gene inactivation, we provide evidence that Gli3 does not play a cell-autonomous role in migrating precerebellar neurons. Thus, GLI3 likely regulates the development of other hindbrain structures, such as non-precerebellar nuclei or cranial ganglia and their respective projections, which may in turn influence precerebellar migration. Although the organization of non-precerebellar hindbrain nuclei appears to be largely unaffected in absence of Gli3, trigeminal ganglia and their central descending tracts are disrupted. We show that rostrally migrating precerebellar neurons are normally in close contact with these tracts, but are detached in Gli3-null embryos.
Assuntos
Movimento Celular , Cerebelo/citologia , Neurônios/citologia , Neurônios/metabolismo , Proteína Gli3 com Dedos de Zinco/metabolismo , Animais , Núcleo Celular/metabolismo , Embrião de Mamíferos/citologia , Camundongos , Fibras Musgosas Hipocampais/metabolismo , Mutação/genética , Células-Tronco Neurais/citologia , Células-Tronco Neurais/metabolismo , Receptores de Superfície Celular/metabolismo , Rombencéfalo/metabolismo , Células-Tronco/citologia , Células-Tronco/metabolismo , Nervo Trigêmeo/citologia , Nervo Trigêmeo/metabolismoRESUMO
Bmal1 is an essential component of the molecular clockwork, which drives circadian rhythms in cell function. In Bmal1-deficient (Bmal1-/-) mice, chronodisruption is associated with cognitive deficits and progressive brain pathology including astrocytosis indicated by increased expression of glial fibrillary acidic protein (GFAP). However, relatively little is known about the impact of Bmal1-deficiency on astrocyte morphology prior to astrocytosis. Therefore, in this study we analysed astrocyte morphology in young (6-8 weeks old) adult Bmal1-/- mice. At this age, overall GFAP immunoreactivity was not increased in Bmal1-deficient mice. At the ultrastructural level, we found a decrease in the volume fraction of the fine astrocytic processes that cover the hippocampal mossy fiber synapse, suggesting an impairment of perisynaptic processes and their contribution to neurotransmission. For further analyses of actin cytoskeleton, which is essential for distal process formation, we used cultured Bmal1-/- astrocytes. Bmal1-/- astrocytes showed an impaired formation of actin stress fibers. Moreover, Bmal1-/- astrocytes showed reduced levels of the actin-binding protein cortactin (CTTN). Cttn promoter region contains an E-Box like element and chromatin immunoprecipitation revealed that Cttn is a potential Bmal1 target gene. In addition, the level of GTP-bound (active) Rho-GTPase (Rho-GTP) was reduced in Bmal1-/- astrocytes. In summary, our data demonstrate that Bmal1-deficiency affects morphology of the fine astrocyte processes prior to strong upregulation of GFAP, presumably because of impaired Cttn expression and reduced Rho-GTP activation. These morphological changes might result in altered synaptic function and, thereby, relate to cognitive deficits in chronodisruption.
Assuntos
Fatores de Transcrição ARNTL/metabolismo , Citoesqueleto de Actina/metabolismo , Astrócitos/metabolismo , Fibras Musgosas Hipocampais/metabolismo , Sinapses/metabolismo , Fatores de Transcrição ARNTL/genética , Animais , Cortactina/genética , Cortactina/metabolismo , Proteína Glial Fibrilar Ácida/metabolismo , Masculino , Camundongos , Camundongos Knockout , Transmissão Sináptica/fisiologiaRESUMO
Brain-derived neurotrophic factor (BDNF) is an essential product of protein synthesis with a prominent impact on brain signaling and synaptic plasticity. Exogenous application of this neurotrophin is able to induce long-term potentiation (LTP) in several brain structures such as the hippocampus along with increases in gene transcription and translation of proteins involved in functional and structural plasticity. In this regard, our previous studies have demonstrated that acute intrahippocampal administration of BDNF induces long-lasting enhancement of synaptic transmission at the mossy fibers projection (MF) accompanied by a structural reorganization at the CA3 hippocampus area. Thus, considering the non-canonical molecular mechanisms underlying MF-CA3-LTP and the high expression of this neurotrophin in the CA3 area, we wonder whether transcriptional and translational inhibition interferes with the persistence of the MF functional and structural synaptic plasticity elicited by BDNF in adult rats in vivo. Our results show that BDNF is able to induce a lasting potentiation of synaptic efficacy at the MF projection accompanied by a structural reorganization at the CA3 area in an mRNA synthesis and protein translation-independent manner. The present findings support the idea that BDNF is an essential plasticity related product, which is necessary and sufficient to induce and maintain functional and structural synaptic plasticity at the MF-CA3 pathway.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/metabolismo , Região CA3 Hipocampal/metabolismo , Potenciação de Longa Duração , Fibras Musgosas Hipocampais/metabolismo , Transmissão Sináptica , Animais , Fator Neurotrófico Derivado do Encéfalo/administração & dosagem , Região CA3 Hipocampal/fisiologia , Expressão Gênica , Masculino , RNA Mensageiro/metabolismo , Ratos WistarRESUMO
Action potentials trigger two modes of neurotransmitter release, with a fast synchronous component and a temporally delayed asynchronous release. Asynchronous release contributes to information transfer at synapses, including at the hippocampal mossy fiber (MF) to CA3 pyramidal cell synapse where it controls the timing of postsynaptic CA3 pyramidal neuron firing. Here, we identified and characterized the main determinants of asynchronous release at the MF-CA3 synapse. We found that asynchronous release at MF-CA3 synapses can last on the order of seconds following repetitive MF stimulation. Elevating the stimulation frequency or the external Ca2+ concentration increased the rate of asynchronous release, thus, arguing that presynaptic Ca2+ dynamics is the major determinant of asynchronous release rate. Direct MF bouton Ca2+ imaging revealed slow Ca2+ decay kinetics of action potential (AP) burst-evoked Ca2+ transients. Finally, we observed that asynchronous release was preferentially mediated by Ca2+ influx through P/Q-type voltage-gated Ca2+ channels, while the contribution of N-type VGCCs was limited. Overall, our results uncover the determinants of long-lasting asynchronous release from MF terminals and suggest that asynchronous release could influence CA3 pyramidal cell firing up to seconds following termination of granule cell bursting.