RESUMO
Abnormal visual experience during a developmental critical period degrades cortical responsiveness. Yet how experience-dependent plasticity alters the response properties of individual neurons and composition of visual circuitry is unclear. Here, we measured with calcium imaging in alert mice how monocular deprivation (MD) during the developmental critical period affects tuning for binocularity, orientation, and spatial frequency for neurons in primary visual cortex. MD of the contralateral eye did not uniformly shift ocular dominance (OD) of neurons towards the fellow ipsilateral eye but reduced the number of monocular contralateral neurons and increased the number of monocular ipsilateral neurons. MD also impaired matching of preferred orientation for binocular neurons and reduced the percentage of neurons responsive at most spatial frequencies for the deprived contralateral eye. Tracking the tuning properties for several hundred neurons before and after MD revealed that the shift in OD is complex and dynamic, with many previously monocular neurons becoming binocular and binocular neurons becoming monocular. Binocular neurons that became monocular were more likely to lose responsiveness to the deprived contralateral eye if they were better matched for orientation prior to deprivation. In addition, the composition of visual circuitry changed as population of neurons more responsive to the deprived eye were exchanged for neurons with tuning properties more similar to the network of responsive neurons altered by MD. Thus, plasticity during the critical period adapts to recent experience by both altering the tuning of responsive neurons and recruiting neurons with matching tuning properties.
Assuntos
Córtex Visual , Camundongos , Animais , Córtex Visual/fisiologia , Neurônios/fisiologia , Privação Sensorial/fisiologia , Plasticidade Neuronal/fisiologia , Estimulação LuminosaRESUMO
Taste bud cells are constantly replaced in taste buds as old cells die and new cells migrate into the bud. The perception of taste relies on new taste bud cells integrating with existing neural circuitry, yet how these new cells connect with a taste ganglion neuron is unknown. Do taste ganglion neurons remodel to accommodate taste bud cell renewal? If so, how much of the structure of taste axons is fixed and how much remodels? Here, we measured the motility and branching of individual taste arbors (the portion of the axon innervating taste buds) in mice over time with two-photon in vivo microscopy. Terminal branches of taste arbors continuously and rapidly remodel within the taste bud. This remodeling is faster than predicted by taste bud cell renewal, with terminal branches added and lost concurrently. Surprisingly, blocking entry of new taste bud cells with chemotherapeutic agents revealed that remodeling of the terminal branches on taste arbors does not rely on the renewal of taste bud cells. Although terminal branch remodeling was fast and intrinsically controlled, no new arbors were added to taste buds, and few were lost over 100 days. Taste ganglion neurons maintain a stable number of arbors that are each capable of high-speed remodeling. We propose that terminal branch plasticity permits arbors to locate new taste bud cells, while stability of arbor number supports constancy in the degree of connectivity and function for each neuron over time.
Assuntos
Interneurônios , Paladar , Animais , Camundongos , Neurônios , Axônios , Microscopia IntravitalRESUMO
A characteristic of the developing mammalian visual system is a brief interval of plasticity, termed the "critical period," when the circuitry of primary visual cortex is most sensitive to perturbation of visual experience. Depriving one eye of vision (monocular deprivation [MD]) during the critical period alters ocular dominance (OD) by shifting the responsiveness of neurons in visual cortex to favor the nondeprived eye. A disinhibitory microcircuit involving parvalbumin-expressing (PV) interneurons initiates this OD plasticity. The gene encoding the neuronal nogo-66-receptor 1 (ngr1/rtn4r) is required to close the critical period. Here we combined mouse genetics, electrophysiology, and circuit mapping with laser-scanning photostimulation to investigate whether disinhibition is confined to the critical period by ngr1 We demonstrate that ngr1 mutant mice retain plasticity characteristic of the critical period as adults, and that ngr1 operates within PV interneurons to restrict the loss of intracortical excitatory synaptic input following MD in adult mice, and this disinhibition induces a "lower PV network configuration" in both critical-period wild-type mice and adult ngr1-/- mice. We propose that ngr1 limits disinhibition to close the critical period for OD plasticity and that a decrease in PV expression levels reports the diminished recent cumulative activity of these interneurons. SIGNIFICANCE STATEMENT: Life experience refines brain circuits throughout development during specified critical periods. Abnormal experience during these critical periods can yield enduring maladaptive changes in neural circuits that impair brain function. In the developing visual system, visual deprivation early in life can result in amblyopia (lazy-eye), a prevalent childhood disorder comprising permanent deficits in spatial vision. Here we identify that the nogo-66 receptor 1 gene restricts an early and essential step in OD plasticity to the critical period. These findings link the emerging circuit-level description of OD plasticity to the genetic regulation of the critical period. Understanding how plasticity is confined to critical periods may provide clues how to better treat amblyopia.
Assuntos
Período Crítico Psicológico , Rede Nervosa/fisiologia , Plasticidade Neuronal/fisiologia , Receptor Nogo 1/metabolismo , Córtex Visual/fisiologia , Percepção Visual/fisiologia , Adaptação Fisiológica/fisiologia , Envelhecimento/metabolismo , Animais , Feminino , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Receptor Nogo 1/genéticaRESUMO
The formation and stability of dendritic spines on excitatory cortical neurons are correlated with adult visual plasticity, yet how the formation, loss, and stability of postsynaptic spines register with that of presynaptic axonal varicosities is unknown. Monocular deprivation has been demonstrated to increase the rate of formation of dendritic spines in visual cortex. However, we find that monocular deprivation does not alter the dynamics of intracortical axonal boutons in visual cortex of either adult wild-type (WT) mice or adult NgR1 mutant (ngr1-/-) mice that retain critical period visual plasticity. Restoring normal vision for a week following long-term monocular deprivation (LTMD), a model of amblyopia, partially restores ocular dominance (OD) in WT and ngr1-/- mice but does not alter the formation or stability of axonal boutons. Both WT and ngr1-/- mice displayed a rapid return of normal OD within 8 days after LTMD as measured with optical imaging of intrinsic signals. In contrast, single-unit recordings revealed that ngr1-/- exhibited greater recovery of OD by 8 days post-LTMD. Our findings support a model of structural plasticity in which changes in synaptic connectivity are largely postsynaptic. In contrast, axonal boutons appear to be stable during changes in cortical circuit function.
Assuntos
Ambliopia/fisiopatologia , Dominância Ocular , Plasticidade Neuronal , Receptor Nogo 1/fisiologia , Terminações Pré-Sinápticas/fisiologia , Córtex Visual/fisiopatologia , Ambliopia/genética , Animais , Modelos Animais de Doenças , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/fisiologia , Receptor Nogo 1/genética , Privação Sensorial , Acuidade Visual/fisiologia , Córtex Visual/citologiaRESUMO
The closure of developmental critical periods consolidates neural circuitry but also limits recovery from early abnormal sensory experience. Degrading vision by one eye throughout a critical period both perturbs ocular dominance (OD) in primary visual cortex and impairs visual acuity permanently. Yet understanding how binocularity and visual acuity interrelate has proven elusive. Here we demonstrate the plasticity of binocularity and acuity are separable and differentially regulated by the neuronal nogo receptor 1 (NgR1). Mice lacking NgR1 display developmental OD plasticity as adults and their visual acuity spontaneously improves after prolonged monocular deprivation. Restricting deletion of NgR1 to either cortical interneurons or a subclass of parvalbumin (PV)-positive interneurons alters intralaminar synaptic connectivity in visual cortex and prevents closure of the critical period for OD plasticity. However, loss of NgR1 in PV neurons does not rescue deficits in acuity induced by chronic visual deprivation. Thus, NgR1 functions with PV interneurons to limit plasticity of binocularity, but its expression is required more extensively within brain circuitry to limit improvement of visual acuity following chronic deprivation.
Assuntos
Interneurônios/metabolismo , Proteínas da Mielina/metabolismo , Plasticidade Neuronal/fisiologia , Receptores de Superfície Celular/metabolismo , Visão Binocular/fisiologia , Acuidade Visual/fisiologia , Animais , Proteínas Ligadas por GPI/metabolismo , Imuno-Histoquímica , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Microscopia Confocal , Neurogênese/fisiologia , Receptor Nogo 1 , Parvalbuminas/metabolismo , Técnicas de Patch-ClampRESUMO
A requisite component of nervous system development is the achievement of cellular recognition and spatial segregation through competition-based refinement mechanisms. Competition for available axon space by myelinating oligodendrocytes ensures that all relevant CNS axons are myelinated properly. To ascertain the nature of this competition, we generated a transgenic mouse with sparsely labeled oligodendrocytes and establish that individual oligodendrocytes occupying similar axon tracts can greatly vary the number and lengths of their myelin internodes. Here we show that intercellular interactions between competing oligodendroglia influence the number and length of myelin internodes, referred to as myelinogenic potential, and identify the amino-terminal region of Nogo-A, expressed by oligodendroglia, as necessary and sufficient to inhibit this process. Exuberant and expansive myelination/remyelination is detected in the absence of Nogo during development and after demyelination, suggesting that spatial segregation and myelin extent is limited by microenvironmental inhibition. We demonstrate a unique physiological role for Nogo-A in the precise myelination of the developing CNS. Maximizing the myelinogenic potential of oligodendrocytes may offer an effective strategy for repair in future therapies for demyelination.
Assuntos
Sistema Nervoso Central/patologia , Doenças Desmielinizantes/fisiopatologia , Proteínas da Mielina/metabolismo , Bainha de Mielina/fisiologia , Oligodendroglia/fisiologia , Animais , Western Blotting , Sistema Nervoso Central/citologia , Técnicas de Silenciamento de Genes , Técnicas Histológicas , Camundongos , Camundongos Transgênicos , Microscopia Eletrônica , Microesferas , Proteínas da Mielina/genética , Proteínas Nogo , Oligodendroglia/metabolismo , Oligodendroglia/ultraestrutura , Poliestirenos , RNA Interferente Pequeno/genética , UltracentrifugaçãoRESUMO
To test the hypothesized crucial role of microglia in the developmental refinement of neural circuitry, we depleted microglia from mice of both sexes with PLX5622 and examined the experience-dependent maturation of visual circuitry and function. We assessed retinal function, receptive field tuning of visual cortex neurons, acuity and experience-dependent plasticity. None of these measurements detectibly differed in the absence of microglia, challenging the role of microglia in sculpting neural circuits.
Assuntos
Microglia , Córtex Visual , Animais , Microglia/fisiologia , Camundongos , Córtex Visual/fisiologia , Córtex Visual/citologia , Masculino , Feminino , Retina/fisiologia , Vias Visuais/fisiologia , Camundongos Endogâmicos C57BL , Plasticidade Neuronal/fisiologia , Neurônios/fisiologia , Estimulação Luminosa/métodos , Camundongos Transgênicos , Compostos OrgânicosRESUMO
Microglia are proposed to be critical for the refinement of developing neural circuitry. However, evidence identifying specific roles for microglia has been limited and often indirect. Here we examined whether microglia are required for the experience-dependent refinement of visual circuitry and visual function during development. We ablated microglia by administering the colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622, and then examined the consequences for retinal function, receptive field tuning of neurons in primary visual cortex (V1), visual acuity, and experience-dependent plasticity in visual circuitry. Eradicating microglia by treating mice with PLX5622 beginning at postnatal day (P) 14 did not alter visual response properties of retinal ganglion cells examined three or more weeks later. Mice treated with PLX5622 from P14 lacked more than 95% of microglia in V1 by P18, prior to the opening of the critical period. Despite the absence of microglia, the receptive field tuning properties of neurons in V1 were normal at P32. Similarly, eradicating microglia did not affect the maturation of visual acuity. Mice treated with PLX5622 displayed typical ocular dominance plasticity in response to brief monocular deprivation. Thus, none of these principal measurements of visual circuit development and function detectibly differed in the absence of microglia. We conclude that microglia are dispensable for experience-dependent refinement of visual circuitry. These findings challenge the proposed critical role of microglia in refining neural circuitry.
RESUMO
OBJECTIVE: Several interventions promote axonal growth and functional recovery when initiated shortly after central nervous system injury, including blockade of myelin-derived inhibitors with soluble Nogo receptor (NgR1, RTN4R) decoy protein. We examined the efficacy of this intervention in the much more prevalent and refractory condition of chronic spinal cord injury. METHODS: We eliminated the NgR1 pathway genetically in mice by conditional gene targeting starting 8 weeks after spinal hemisection injury and monitored locomotion in the open field and by video kinematics over the ensuing 4 months. In a separate pharmacological experiment, intrathecal NgR1 decoy protein administration was initiated 3 months after spinal cord contusion injury. Locomotion and raphespinal axon growth were assessed during 3 months of treatment between 4 and 6 months after contusion injury. RESULTS: Conditional deletion of NgR1 in the chronic state results in gradual improvement of motor function accompanied by increased density of raphespinal axons in the caudal spinal cord. In chronic rat spinal contusion, NgR1 decoy treatment from 4 to 6 months after injury results in 29% (10 of 35) of rats recovering weight-bearing status compared to 0% (0 of 29) of control rats (p < 0.05). Open field Basso, Beattie, and Bresnahan locomotor scores showed a significant improvement in the NgR-treated group relative to the control group (p < 0.005, repeated measures analysis of variance). An increase in raphespinal axon density caudal to the injury is detected in NgR1 decoy-treated animals by immunohistology and by positron emission tomography using a serotonin reuptake ligand. INTERPRETATION: Antagonizing myelin-derived inhibitors signaling with NgR1 decoy augments recovery from chronic spinal cord injury.
Assuntos
Axônios/efeitos dos fármacos , Locomoção/efeitos dos fármacos , Atividade Motora/efeitos dos fármacos , Proteínas Recombinantes de Fusão/farmacologia , Recuperação de Função Fisiológica/efeitos dos fármacos , Traumatismos da Medula Espinal/tratamento farmacológico , Animais , Modelos Animais de Doenças , Injeções Espinhais , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas da Mielina/deficiência , Proteínas da Mielina/genética , Testes Neuropsicológicos , Proteínas Nogo , Proteínas Recombinantes de Fusão/administração & dosagem , Traumatismos da Medula Espinal/metabolismo , Fatores de Tempo , Resultado do TratamentoRESUMO
Subpopulations of neurons and associated neural circuits can be targeted in mice with genetic tools in a highly selective manner for visualization and manipulation. However, there are not well-defined Cre "driver" lines that target the expression of Cre recombinase to thalamocortical (TC) neurons. Here, we characterize three Cre driver lines for the nuclei of the dorsal thalamus: Oligodendrocyte transcription factor 3 (Olig3)-Cre, histidine decarboxylase (HDC)-Cre, and corticotropin-releasing hormone (CRH)-Cre. We examined the postnatal distribution of Cre expression for each of these lines with the Cre-dependent reporter CAG-tdTomato (Ai9). Cre-dependent expression of tdTomato reveals that Olig3-Cre expresses broadly within the thalamus, including TC neurons and interneurons, while HDC-Cre and CRH-Cre each have unique patterns of expression restricted to TC neurons within and across the sensory relay nuclei of the dorsal thalamus. Cre expression is present by the time of natural birth in all three lines, underscoring their utility for developmental studies. To demonstrate the utility of these Cre drivers for studying sensory TC circuitry, we targeted the expression of channelrhodopsin-2 to thalamus from the CAG-COP4*H134R/EYFP (Ai32) allele with either HDC-Cre or CRH-Cre. Optogenetic activation of TC afferents in primary visual cortex was sufficient to measure frequency-dependent depression. Thus, these Cre drivers provide selective Cre-dependent gene expression in thalamus suitable for both anatomical and functional studies.
Assuntos
Hormônio Liberador da Corticotropina , Integrases , Animais , Hormônio Liberador da Corticotropina/metabolismo , Integrases/genética , Integrases/metabolismo , Camundongos , Camundongos Transgênicos , Neurônios/metabolismoRESUMO
In mice and other mammals, forebrain neurons integrate right and left eye information to generate a three-dimensional representation of the visual environment. Neurons in the visual cortex of mice are sensitive to binocular disparity,1-3 yet it is unclear whether that sensitivity is linked to the perception of depth.4-8 We developed a natural task based on the classic visual cliff and pole descent tasks to estimate the psychophysical range of mouse depth discrimination.5,9 Mice with binocular vision descended to a near (shallow) surface more often when surrounding far (deep) surfaces were progressively more distant. Occlusion of one eye severely impaired their ability to target the near surface. We quantified the distance at which animals make their decisions to estimate the binocular image displacement of the checkerboard pattern on the near and far surfaces. Then, we assayed the disparity sensitivity of large populations of binocular neurons in primary visual cortex (V1) using two-photon microscopy2 and quantitatively compared this information available in V1 to their behavioral sensitivity. Disparity information in V1 matches the behavioral performance over the range of depths examined and was resistant to changes in binocular alignment. These findings reveal that mice naturally use stereoscopic cues to guide their behavior and indicate a neural basis for this depth discrimination task.
Assuntos
Percepção de Profundidade , Córtex Visual Primário , Visão Binocular , Animais , Camundongos , Neurônios , Córtex Visual Primário/fisiologia , Disparidade VisualRESUMO
Loss of function after neurological injury frequently occurs through the interruption of axonal connectivity, rather than through cell loss. Functional deficits persist because a multitude of inhibitory factors in degenerating myelin and astroglial scar prevent axonal growth in the adult brain and spinal cord. Given the high clinical significance of achieving functional recovery through axonal growth, substantial research effort has been, and will be, devoted toward this desirable goal. Unfortunately, the labels commonly used in the literature to categorize post-injury axonal anatomy might hinder advancement. In this article, we present an argument for the importance of developing precise terms that describe axonal growth in terms of the inciting event, the distance of axonal extension and the timing of axonal growth. The phenotypes produced by molecular interventions that overcome astroglial scar or myelin-associated inhibitors are reframed and discussed in this context.
Assuntos
Axônios/fisiologia , Regeneração Nervosa/fisiologia , Plasticidade Neuronal/fisiologia , Animais , Astrócitos/citologia , Astrócitos/metabolismo , Axônios/patologia , Proteoglicanas de Sulfatos de Condroitina/metabolismo , Bainha de Mielina/metabolismo , Transdução de Sinais/fisiologiaRESUMO
Disrupting binocular vision during a developmental critical period can yield enduring changes to ocular dominance (OD) in primary visual cortex (V1). Here we investigated how this experience-dependent plasticity is coordinated within the laminar circuitry of V1 by deleting separately in each cortical layer (L) a gene required to close the critical period, nogo-66 receptor (ngr1). Deleting ngr1 in excitatory neurons in L4, but not in L2/3, L5, or L6, prevented closure of the critical period, and adult mice remained sensitive to brief monocular deprivation. Intracortical disinhibition, but not thalamocortical disinhibition, accompanied this OD plasticity. Both juvenile wild-type mice and adult mice lacking ngr1 in L4 displayed OD plasticity that advanced more rapidly L4 than L2/3 or L5. Interestingly, blocking OD plasticity in L2/3 with the drug AM-251 did not impair OD plasticity in L5. We propose that L4 restricts disinhibition and gates OD plasticity independent of a canonical cortical microcircuit.
Assuntos
Plasticidade Neuronal/fisiologia , Receptor Nogo 1/genética , Receptor Nogo 1/fisiologia , Células Receptoras Sensoriais/fisiologia , Córtex Visual/fisiologia , Animais , Dominância Ocular , Deleção de Genes , Camundongos , Visão Binocular/fisiologiaRESUMO
In schizophrenia, genetic predisposition has been linked to chromosome 22q11 and myelin-specific genes are misexpressed in schizophrenia. Nogo-66 receptor 1 (NGR or RTN4R) has been considered to be a 22q11 candidate gene for schizophrenia susceptibility because it encodes an axonal protein that mediates myelin inhibition of axonal sprouting. Confirming previous studies, we found that variation at the NGR locus is associated with schizophrenia in a Caucasian case-control analysis, and this association is not attributed to population stratification. Within a limited set of schizophrenia-derived DNA samples, we identified several rare NGR nonconservative coding sequence variants. Neuronal cultures demonstrate that four different schizophrenia-derived NgR1 variants fail to transduce myelin signals into axon inhibition, and function as dominant negatives to disrupt endogenous NgR1. This provides the first evidence that certain disease-derived human NgR1 variants are dysfunctional proteins in vitro. Mice lacking NgR1 protein exhibit reduced working memory function, consistent with a potential endophenotype of schizophrenia. For a restricted subset of individuals diagnosed with schizophrenia, the expression of dysfunctional NGR variants may contribute to increased disease risk.
Assuntos
Cones de Crescimento/metabolismo , Inibidores do Crescimento/genética , Proteínas da Mielina/genética , Fibras Nervosas Mielinizadas/metabolismo , Receptores de Superfície Celular/genética , Esquizofrenia/genética , Esquizofrenia/metabolismo , Animais , Encéfalo/metabolismo , Encéfalo/fisiopatologia , Células COS , Embrião de Galinha , Chlorocebus aethiops , Mapeamento Cromossômico , Códon/genética , Feminino , Proteínas Ligadas por GPI , Predisposição Genética para Doença/genética , Cones de Crescimento/ultraestrutura , Inibidores do Crescimento/metabolismo , Humanos , Masculino , Camundongos , Camundongos Knockout , Mutação/genética , Proteínas da Mielina/metabolismo , Neurogênese/genética , Plasticidade Neuronal/genética , Receptor Nogo 1 , Técnicas de Cultura de Órgãos , Ratos , Receptores de Superfície Celular/metabolismo , Esquizofrenia/fisiopatologiaRESUMO
beta subunits of voltage-gated calcium channels (VGCCs) regulate channel trafficking and function, thereby shaping the intensity and duration of intracellular changes in calcium. beta subunits share limited sequence homology with the Src homology 3-guanylate kinase (SH3-GK) module of membrane-associated guanylate kinases (MAGUKs). Here, we show biochemical similarities between beta subunits and MAGUKs, revealing important aspects of beta subunit structure and function. Similar to MAGUKs, an SH3-GK interaction within beta subunits can occur both intramolecularly and intermolecularly. Mutations that disrupt the SH3-GK interaction in beta subunits alter channel inactivation and can inhibit binding between the alpha(1) and beta subunits. Coexpression of beta subunits with complementary mutations in their SH3 and GK domains rescues these deficits through intermolecular beta subunit assembly. In MAGUKs, the SH3-GK module controls protein scaffolding. In beta subunits, this module regulates the inactivation of VGCCs and provides an additional mechanism for tuning calcium responsiveness.
Assuntos
Canais de Cálcio/fisiologia , Fatores de Troca do Nucleotídeo Guanina/fisiologia , Subunidades Proteicas/fisiologia , Animais , Canais de Cálcio/química , Condutividade Elétrica , Eletrofisiologia , Expressão Gênica , Fatores de Troca do Nucleotídeo Guanina/química , Guanilato Quinases , Humanos , Cinética , Potenciais da Membrana , Modelos Moleculares , Mutação , Proteínas do Tecido Nervoso/química , Proteínas do Tecido Nervoso/genética , Inibição Neural , Núcleosídeo-Fosfato Quinase/fisiologia , Oócitos , Ligação Proteica/fisiologia , Estrutura Terciária de Proteína , Subunidades Proteicas/química , Coelhos , Ratos , Homologia de Sequência de Aminoácidos , Técnicas do Sistema de Duplo-Híbrido , Xenopus , LevedurasRESUMO
A variety of conditions ranging from glaucoma to blunt force trauma lead to optic nerve atrophy. Identifying signaling pathways for stimulating axon growth in the optic nerve may lead to treatments for these pathologies. Inhibiting signaling by the nogo-66 receptor 1 (NgR1) promotes the re-extension of axons following a crush injury to the optic nerve, and while NgR1 mRNA and protein expression are observed in the retinal ganglion cell (RGC) layer and inner nuclear layer, which retinal cell types express NgR1 remains unknown. Here we determine the expression pattern of NgR1 in the mouse retina by co-labeling neurons with characterized markers of specific retinal neurons together with antibodies specific for NgR1 or Green Fluorescent Protein expressed under control of the ngr1 promoter. We demonstrate that more than 99% of RGCs express NgR1. Thus, inhibiting NgR1 function may ubiquitously promote the regeneration of axons by RGCs. These results provide additional support for the therapeutic potential of NgR1 signaling in reversing optic nerve atrophy.
Assuntos
Receptor Nogo 1/genética , Receptor Nogo 1/metabolismo , Células Ganglionares da Retina/metabolismo , Animais , Axônios/metabolismo , Expressão Gênica , Proteínas de Fluorescência Verde/metabolismo , Imuno-Histoquímica , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Regeneração Nervosa/genética , Regeneração Nervosa/fisiologia , Receptor Nogo 1/deficiência , Nervo Óptico/metabolismo , Nervo Óptico/fisiologia , Traumatismos do Nervo Óptico/genética , Traumatismos do Nervo Óptico/metabolismo , Traumatismos do Nervo Óptico/patologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Células Ganglionares da Retina/patologia , Transdução de SinaisRESUMO
Degrading vision by one eye during a developmental critical period yields enduring deficits in both eye dominance and visual acuity. A predominant model is that "reactivating" ocular dominance (OD) plasticity after the critical period is required to improve acuity in amblyopic adults. However, here we demonstrate that plasticity of eye dominance and acuity are independent and restricted by the nogo-66 receptor (ngr1) in distinct neuronal populations. Ngr1 mutant mice display greater excitatory synaptic input onto both inhibitory and excitatory neurons with restoration of normal vision. Deleting ngr1 in excitatory cortical neurons permits recovery of eye dominance but not acuity. Reciprocally, deleting ngr1 in thalamus is insufficient to rectify eye dominance but yields improvement of acuity to normal. Abolishing ngr1 expression in adult mice also promotes recovery of acuity. Together, these findings challenge the notion that mechanisms for OD plasticity contribute to the alterations in circuitry that restore acuity in amblyopia.
Assuntos
Ambliopia/fisiopatologia , Dominância Ocular/fisiologia , Neurônios/metabolismo , Acuidade Visual/fisiologia , Ambliopia/genética , Animais , Dominância Ocular/genética , Feminino , Masculino , Camundongos , Receptor Nogo 1/genética , Receptor Nogo 1/metabolismo , Acuidade Visual/genéticaRESUMO
CNS myelin inhibits axonal outgrowth in vitro and is one of several obstacles to functional recovery following spinal cord injury. Central to our current understanding of myelin-mediated inhibition are the membrane protein Nogo and the Nogo-66 receptor (NgR). New findings implicate NgR as a point of convergence in signal transduction for several myelin-associated inhibitors. Additional studies have identified a potential coreceptor for NgR as p75(NTR), and a second-messenger pathway involving RhoA that inhibits neurite elongation. Although these findings expand our understanding of the molecular determinants of adult CNS axonal regrowth, the physiological roles of myelin-associated inhibitors in the intact adult CNS remain ill-defined.
Assuntos
Axônios/fisiologia , Proteínas da Mielina/fisiologia , Bainha de Mielina/fisiologia , Regeneração Nervosa/fisiologia , Inibição Neural/fisiologia , Receptores de Superfície Celular/fisiologia , Proteínas de Fase Aguda/metabolismo , Animais , Células Cultivadas , Proteínas Ligadas por GPI , Humanos , Técnicas In Vitro , Camundongos , Proteínas da Mielina/classificação , Proteínas da Mielina/metabolismo , Glicoproteína Associada a Mielina/metabolismo , Glicoproteína Mielina-Oligodendrócito , Plasticidade Neuronal , Proteínas Nogo , Receptor Nogo 1 , Ratos , Receptor de Fator de Crescimento Neural , Receptores de Fator de Crescimento Neural/metabolismo , Transdução de Sinais/fisiologiaRESUMO
Glutamate mediates most excitatory synaptic transmission in the brain. Synaptic strength at glutamatergic synapses shows a remarkable degree of use-dependent plasticity and such modifications may represent a physiological correlate to learning and memory. Glutamate receptors and downstream enzymes are organized at synapses by cytoskeletal proteins containing multiple protein-interacting domains. Recent studies demonstrate that these 'scaffolding' proteins within the postsynaptic specialization have the capacity to promote synaptic maturation, influence synapse size, and modulate glutamate receptor function.