RESUMO
Subplate neurons are early-born cortical neurons that transiently form neural circuits during perinatal development and guide cortical maturation. Thereafter, most subplate neurons undergo cell death, while some survive and renew their target areas for synaptic connections. However, the functional properties of the surviving subplate neurons remain largely unknown. This study aimed to characterize the visual responses and experience-dependent functional plasticity of layer 6b (L6b) neurons, the remnants of subplate neurons, in the primary visual cortex (V1). Two-photon Ca2+ imaging was performed in V1 of awake juvenile mice. L6b neurons showed broader tunings for orientation, direction, and spatial frequency than did layer 2/3 (L2/3) and L6a neurons. In addition, L6b neurons showed lower matching of preferred orientation between the left and right eyes compared with other layers. Post hoc 3D immunohistochemistry confirmed that the majority of recorded L6b neurons expressed connective tissue growth factor (CTGF), a subplate neuron marker. Moreover, chronic two-photon imaging showed that L6b neurons exhibited ocular dominance (OD) plasticity by monocular deprivation during critical periods. The OD shift to the open eye depended on the response strength to the stimulation of the eye to be deprived before starting monocular deprivation. There were no significant differences in visual response selectivity prior to monocular deprivation between the OD changed and unchanged neuron groups, suggesting that OD plasticity can occur in L6b neurons showing any response features. In conclusion, our results provide strong evidence that surviving subplate neurons exhibit sensory responses and experience-dependent plasticity at a relatively late stage of cortical development.
Assuntos
Córtex Visual , Camundongos , Animais , Córtex Visual/fisiologia , Neurônios/fisiologia , Dominância Ocular , Olho , Plasticidade Neuronal/fisiologiaRESUMO
Monocular deprivation (MD) causes an initial decrease in synaptic responses to the deprived eye in juvenile mouse primary visual cortex (V1) through Hebbian long-term depression (LTD). This is followed by a homeostatic increase, which has been attributed either to synaptic scaling or to a slide threshold for Hebbian long-term potentiation (LTP) rather than scaling. We therefore asked in mice of all sexes whether the homeostatic increase during MD requires GluN2B-containing NMDA receptor activity, which is required to slide the plasticity threshold but not for synaptic scaling. Selective GluN2B blockade from 2-6â d after monocular lid suture prevented the homeostatic increase in miniature excitatory postsynaptic current (mEPSC) amplitude in monocular V1 of acute slices and prevented the increase in visually evoked responses in binocular V1 in vivo. The decrease in mEPSC amplitude and visually evoked responses during the first 2â d of MD also required GluN2B activity. Together, these results support the idea that GluN2B-containing NMDA receptors first play a role in LTD immediately following eye closure and then promote homeostasis during prolonged MD by sliding the plasticity threshold in favor of LTP.
Assuntos
Dominância Ocular , Potenciais Pós-Sinápticos Excitadores , Camundongos Endogâmicos C57BL , Plasticidade Neuronal , Receptores de N-Metil-D-Aspartato , Animais , Receptores de N-Metil-D-Aspartato/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/metabolismo , Camundongos , Masculino , Dominância Ocular/fisiologia , Feminino , Plasticidade Neuronal/fisiologia , Plasticidade Neuronal/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Evocados Visuais/fisiologia , Córtex Visual/fisiologia , Córtex Visual/efeitos dos fármacos , Antagonistas de Aminoácidos Excitatórios/farmacologia , Privação Sensorial/fisiologia , Potenciação de Longa Duração/fisiologia , Potenciação de Longa Duração/efeitos dos fármacos , Depressão Sináptica de Longo Prazo/fisiologia , Depressão Sináptica de Longo Prazo/efeitos dos fármacos , Estimulação Luminosa/métodosRESUMO
During developmental critical periods, circuits are sculpted by a process of activity-dependent competition. The molecular machinery involved in regulating the complex process of responding to different levels of activity is now beginning to be identified. Here, we show that the nonclassical major histocompatibility class I (MHCI) molecule Qa-1 is expressed in the healthy brain in layer 6 corticothalamic neurons. In the visual cortex, Qa-1 expression begins during the critical period for ocular dominance (OD) plasticity and is regulated by neuronal activity, suggesting a role in regulating activity-dependent competition. Indeed, in mice lacking Qa-1, OD plasticity is perturbed. Moreover, signaling through CD94/NKG2, a known cognate Qa-1 heterodimeric receptor in the immune system, is implicated: selectively targeting this interaction phenocopies the plasticity perturbation observed in Qa-1 knockouts. In the cortex, CD94/NKG2 is expressed by microglial cells, which undergo activity-dependent changes in their morphology in a Qa-1dependent manner. Our study thus reveals a neuronmicroglial interaction dependent upon a nonclassical MHCI molecule expressed in L6 neurons, which regulates plasticity in the visual cortex. These results also point to an unexpected function for the Qa-1/HLA-E (ligand) and CD94/NKG2 (receptor) interaction in the nervous system, in addition to that described in the immune system.
Assuntos
Córtex Cerebral , Antígenos de Histocompatibilidade Classe I , Microglia , Subfamília C de Receptores Semelhantes a Lectina de Células NK , Subfamília D de Receptores Semelhantes a Lectina de Células NK , Plasticidade Neuronal , Animais , Córtex Cerebral/metabolismo , Antígenos de Histocompatibilidade Classe I/genética , Antígenos de Histocompatibilidade Classe I/metabolismo , Camundongos , Camundongos Knockout , Microglia/metabolismo , Subfamília C de Receptores Semelhantes a Lectina de Células NK/metabolismo , Subfamília D de Receptores Semelhantes a Lectina de Células NK/metabolismo , Plasticidade Neuronal/genética , Plasticidade Neuronal/fisiologia , Neurônios/metabolismoRESUMO
Neural dynamics are altered in the primary visual cortex (V1) during critical period monocular deprivation (MD). Synchronization of neural oscillations is pertinent to physiological functioning of the brain. Previous studies have reported chronic disruption of V1 functional properties such as ocular dominance, spatial acuity, and binocular matching after long-term monocular deprivation (LTMD). However, the possible neuromodulation and neural synchrony has been less explored. Here, we investigated the difference between juvenile and adult experience-dependent plasticity in mice from intracellular calcium signals with fluorescent indicators. We also studied alterations in local field potentials power bands and phase-amplitude coupling (PAC) of specific brain oscillations. Our results showed that LTMD in juveniles causes higher neuromodulatory changes as seen by high-intensity fluorescent signals from the non-deprived eye (NDE). Meanwhile, adult mice showed a greater response from the deprived eye (DE). LTMD in juvenile mice triggered alterations in the power of delta, theta, and gamma oscillations, followed by enhancement of delta-gamma PAC in the NDE. However, LTMD in adult mice caused alterations in the power of delta oscillations and enhancement of delta-gamma PAC in the DE. These markers are intrinsic to cortical neuronal processing during LTMD and apply to a wide range of nested oscillatory markers.
Assuntos
Visão Monocular , Córtex Visual , Animais , Camundongos , Visão Monocular/fisiologia , Privação Sensorial/fisiologia , Córtex Visual/fisiologia , Dominância Ocular , Neurônios/fisiologia , Plasticidade Neuronal/fisiologiaRESUMO
Short-term monocular deprivation (MD) shifts sensory eye balance in favour of the previously deprived eye. The effect of MD on eye balance is significant but brief in adult humans. Recently, researchers and clinicians have attempted to implement MD in clinical settings for adults with impaired binocular vision. Although the effect of MD has been studied in detail in single-session protocols, what is not known is whether the effect of MD on eye balance deteriorates after repeated periods of MD (termed 'perceptual deterioration'). An answer to this question is relevant for two reasons. Firstly, the effect of MD (i.e., dose-response) should not decrease with repeated use if MD is to be used therapeutically (e.g., daily for weeks). Second, it bears upon the question of whether the neural basis of the effects of MD and contrast adaptation, a closely related phenomenon, is the same. The sensory change from contrast adaptation depends on recent experience. If the observer has recently experienced the same adaptation multiple times for consecutive days, then the adaptation effect will be smaller because contrast adaptation exhibits perceptual deterioration, so it is of interest to know if the effects of MD follow suit. This study measured the effect of 2-h MD for seven consecutive days on binocular balance of 15 normally sighted adults. We found that the shift in eye balance from MD stayed consistent, showing no signs of deterioration after subjects experienced multiple periods of MD. This finding shows no loss of effectiveness of repeated daily doses of MD if used therapeutically to rebalance binocular vision in otherwise normal individuals. Furthermore, ocular dominance plasticity, which is the basis of the effects of short-term MD, does not seem to share the property of 'perceptual deterioration' with contrast adaptation, suggesting different neural bases for these two related phenomena.
Assuntos
Córtex Visual , Adulto , Humanos , Córtex Visual/fisiologia , Privação Sensorial/fisiologia , Visão Ocular , Visão Binocular/fisiologia , Dominância Ocular , Visão Monocular/fisiologiaRESUMO
A fundamental regulator of neuronal network development and plasticity is the extracellular matrix (ECM) of the brain. The ECM provides a scaffold stabilizing synaptic circuits, while the proteolytic cleavage of its components and cell surface proteins are thought to have permissive roles in the regulation of plasticity. The enzymatic proteolysis is thought to be crucial for homeostasis between stability and reorganizational plasticity and facilitated largely by a family of proteinases named matrix metalloproteinases (MMPs). Here, we investigated whether MMP2 and MMP9 play a role in mediating adult primary visual cortex (V1) plasticity as well as stroke-induced impairments of visual cortex plasticity in mice. In healthy adult mice, selective inhibition of MMP2/9 for 7 d suppressed ocular dominance plasticity. In contrast, brief inhibition of MMP2/9 after a cortical stroke rescued compromised plasticity. Our data indicate that the proteolytic activity of MMP2 and MMP9 is critical and required to be within a narrow range to allow adult visual plasticity.SIGNIFICANCE STATEMENT Learning and recovery from injuries depend on the plasticity of neuronal connections. The brain's extracellular matrix (ECM) provides a scaffold for stabilizing synaptic circuits, while its enzymatic proteolysis is hypothesized to regulate homeostasis between stability and reorganizational plasticity. ECM digestion is facilitated by a family of matrix metalloproteinases (MMPs). Here, we show that treatments that inhibit MMP2/9 can either inhibit or rescue cortical plasticity depending on cortical state: in the visual cortex of healthy adult mice, inhibition of MMP2/9 suppressed cortical plasticity. In contrast, brief inhibition of MMP2/9 after a stroke rescued compromised plasticity. Our data provide strong evidence that an optimal level of MMP2/9 proteolytic activity is crucial for adult visual plasticity.
Assuntos
Metaloproteinase 2 da Matriz/metabolismo , Metaloproteinase 9 da Matriz/metabolismo , Plasticidade Neuronal/fisiologia , Córtex Visual Primário/enzimologia , Acidente Vascular Cerebral/fisiopatologia , Animais , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Acidente Vascular Cerebral/enzimologiaRESUMO
Long term monocular deprivation is considered to be necessary for the induction of significant ocular dominance plasticity in the adult visual cortex. In this study, we subjected adult mice to monocular deprivation for various durations and screened for changes in ocular dominance using dual-wavelength intrinsic signal optical imaging. We found that short-term deprivation was sufficient to cause a shift in ocular dominance and that these early-stage changes were detected only by near-infrared illumination. In addition, single-unit recordings showed that these early-stage changes primarily occurred in deep cortical layers. This early-stage ocular dominance shift was abolished by the blockade of NMDA receptors. In summary, our findings reveal an early phase of adult ocular dominance plasticity and provide the dynamics of adult plasticity.
Assuntos
Dominância Ocular , Córtex Visual , Camundongos , Animais , Plasticidade Neuronal , Visão Ocular , Córtex Visual/diagnóstico por imagem , Imagem Óptica , Privação SensorialRESUMO
Ketamine has been described as a fast-acting antidepressant, exerting effects in depressed patients and in preclinical models with a rapid onset of action. The typical antidepressant fluoxetine is known to induce plasticity in the adult rodent visual cortex, as assessed by a shift in ocular dominance, a classical model of brain plasticity, and a similar effect has been described for ketamine and its metabolite 2R,6R-hydroxynorketamine (R,R-HNK). Here, we demonstrate that ketamine (at 3 or 20 mg/kg) and R,R-HNK facilitated the shift in ocular dominance in monocularly deprived mice, after three injections, throughout the 7-day monocular deprivation regimen. Notably, the comparison between the treatments indicates a higher effect size of R,R-HNK compared with ketamine. Treatment with ketamine or R,R-HNK failed to influence the levels of perineuronal nets (PNNs) surrounding parvalbumin-positive interneurons. However, we observed in vitro that both ketamine and R,R-HNK are able to disrupt the tropomyosin-related kinase B (TRKB) interaction with the protein tyrosine phosphatase sigma (PTPσ), which upon binding to PNNs dephosphorylates TRKB. These results support a model where diverse drugs promote the reinstatement of juvenile-like plasticity by directly binding TRKB and releasing it from PTPσ regulation, without necessarily reducing PNNs deposits.
Assuntos
Ketamina , Animais , Camundongos , Antidepressivos/farmacologia , Depressão/metabolismo , Dominância Ocular , Interneurônios/metabolismo , Ketamina/farmacologia , Parvalbuminas , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores , TropomiosinaRESUMO
Brain plasticity and function is impaired in conditions of metabolic dysregulation, such as obesity. Less is known on whether brain function is also affected by transient and physiological metabolic changes, such as the alternation between fasting and fed state. Here we asked whether these changes affect the transient shift of ocular dominance that follows short-term monocular deprivation, a form of homeostatic plasticity. We further asked whether variations in three of the main metabolic and hormonal pathways affected in obesity (glucose metabolism, leptin signalling and fatty acid metabolism) correlate with plasticity changes. We measured the effects of 2 h monocular deprivation in three conditions: post-absorptive state (fasting), after ingestion of a standardised meal and during infusion of glucagon-like peptide-1 (GLP-1), an incretin physiologically released upon meal ingestion that plays a key role in glucose metabolism. We found that short-term plasticity was less manifest in fasting than in fed state, whereas GLP-1 infusion did not elicit reliable changes compared to fasting. Although we confirmed a positive association between plasticity and supraphysiological GLP-1 levels, achieved by GLP-1 infusion, we found that none of the parameters linked to glucose metabolism could predict the plasticity reduction in the fasting versus fed state. Instead, this was selectively associated with the increase in plasma beta-hydroxybutyrate (B-OH) levels during fasting, which suggests a link between neural function and energy substrates alternative to glucose. These results reveal a previously unexplored link between homeostatic brain plasticity and the physiological changes associated with the daily fast-fed cycle.
Assuntos
Peptídeo 1 Semelhante ao Glucagon , Glucose , Humanos , Adulto , Glucose/metabolismo , Obesidade , Jejum , InsulinaRESUMO
Assessing the molecular mechanism of synaptic plasticity in the cortex is vital for identifying potential targets in conditions marked by defective plasticity. In plasticity research, the visual cortex represents a target model for intense investigation, partly due to the availability of different in vivo plasticity-induction protocols. Here, we review two major protocols: ocular-dominance (OD) and cross-modal (CM) plasticity in rodents, highlighting the molecular signaling pathways involved. Each plasticity paradigm has also revealed the contribution of different populations of inhibitory and excitatory neurons at different time points. Since defective synaptic plasticity is common to various neurodevelopmental disorders, the potentially disrupted molecular and circuit alterations are discussed. Finally, new plasticity paradigms are presented, based on recent evidence. Stimulus-selective response potentiation (SRP) is one of the paradigms addressed. These options may provide answers to unsolved neurodevelopmental questions and offer tools to repair plasticity defects.
Assuntos
Roedores , Córtex Visual , Animais , Plasticidade Neuronal/fisiologia , Córtex Visual/fisiologia , Neurônios , Dominância OcularRESUMO
The mammalian visual cortex contains multiple retinotopically defined areas that process distinct features of the visual scene. Little is known about what guides the functional differentiation of visual cortical areas during development. Recent studies in mice have revealed that visual input from the two eyes provides spatiotemporally distinct signals to primary visual cortex (V1), such that contralateral eye-dominated V1 neurons respond to higher spatial frequencies than ipsilateral eye-dominated neurons. To test whether binocular visual input drives the differentiation of visual cortical areas, we used two-photon calcium imaging to characterize the effects of juvenile monocular deprivation (MD) on the responses of neurons in V1 and two higher visual areas, LM (lateromedial) and PM (posteromedial). In adult mice of either sex, we find that MD prevents the emergence of distinct spatiotemporal tuning in V1, LM, and PM. We also find that, within each of these areas, MD reorganizes the distinct spatiotemporal tuning properties driven by the two eyes. Moreover, we find a relationship between speed tuning and ocular dominance in all three areas that MD preferentially disrupts in V1, but not in LM or PM. Together, these results reveal that balanced binocular vision during development is essential for driving the functional differentiation of visual cortical areas. The higher visual areas of mouse visual cortex may provide a useful platform for investigating the experience-dependent mechanisms that set up the specialized processing within neocortical areas during postnatal development.SIGNIFICANCE STATEMENT Little is known about the factors guiding the emergence of functionally distinct areas in the brain. Using in vivo Ca2+ imaging, we recorded visually evoked activity from cells in V1 and higher visual areas LM (lateromedial) and PM (posteromedial) of mice. Neurons in these areas normally display distinct spatiotemporal tuning properties. We found that depriving one eye of normal input during development prevents the functional differentiation of visual areas. Deprivation did not disrupt the degree of speed tuning, a property thought to emerge in higher visual areas. Thus, some properties of visual cortical neurons are shaped by binocular experience, while others are resistant. Our study uncovers the fundamental role of binocular experience in the formation of distinct areas in visual cortex.
Assuntos
Diferenciação Celular/fisiologia , Visão Binocular/fisiologia , Córtex Visual/crescimento & desenvolvimento , Córtex Visual/fisiologia , Algoritmos , Animais , Mapeamento Encefálico , Dominância Ocular/fisiologia , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Neocórtex/crescimento & desenvolvimento , Neocórtex/fisiologia , Plasticidade Neuronal , Estimulação Luminosa , Privação Sensorial , Percepção Espacial/fisiologia , Visão Monocular/fisiologia , Campos VisuaisRESUMO
Visual cortical circuits show profound plasticity during early life and are later stabilized by molecular "brakes" limiting excessive rewiring beyond a critical period. The mechanisms coordinating the expression of these factors during the transition from development to adulthood remain unknown. We found that miR-29a expression in the visual cortex dramatically increases with age, but it is not experience-dependent. Precocious high levels of miR-29a blocked ocular dominance plasticity and caused an early appearance of perineuronal nets. Conversely, inhibition of miR-29a in adult mice using LNA antagomirs activated ocular dominance plasticity, reduced perineuronal nets, and restored their juvenile chemical composition. Activated adult plasticity had the typical functional and proteomic signature of critical period plasticity. Transcriptomic and proteomic studies indicated that miR-29a manipulation regulates the expression of plasticity brakes in specific cortical circuits. These data indicate that miR-29a is a regulator of the plasticity brakes promoting age-dependent stabilization of visual cortical connections.
Assuntos
MicroRNAs , Córtex Visual , Animais , Dominância Ocular/genética , Camundongos , Camundongos Endogâmicos C57BL , MicroRNAs/genética , Plasticidade Neuronal/genética , ProteômicaRESUMO
C1q, the initiator of the classical complement cascade, mediates synapse elimination in the postnatal mouse dorsolateral geniculate nucleus of the thalamus and sensorimotor cortex. Here, we asked whether C1q plays a role in experience-dependent synaptic refinement in the visual system at later stages of development. The binocular zone of primary visual cortex (V1b) undergoes spine loss and changes in neuronal responsiveness following the closure of one eye during a defined critical period [a process referred to as ocular dominance plasticity (ODP)]. We therefore hypothesized that ODP would be impaired in the absence of C1q, and that V1b development would also be abnormal without C1q-mediated synapse elimination. However, when we examined several features of V1b development in mice lacking C1q, we found that the densities of most spine populations on basal and proximal apical dendrites, as well as firing rates and ocular dominance, were normal. C1q was only transiently required for the development of spines on apical, but not basal, secondary dendrites. Dendritic morphologies were also unaffected. Although we did not observe the previously described spine loss during ODP in either genotype, our results reveal that the animals lacking C1q had normal shifts in neuronal responsiveness following eye closure. Experiments were performed in both male and female mice. These results suggest that the development and plasticity of the mouse V1b is grossly normal in the absence of C1q.SIGNIFICANCE STATEMENT These findings illustrate that the development and experience-dependent plasticity of V1b is mostly normal in the absence of C1q, even though C1q has previously been shown to be required for developmental synapse elimination in the mouse visual thalamus as well as sensorimotor cortex. The V1b phenotypes in mice lacking C1q are more similar to the mild defects previously observed in the hippocampus of these mice, emphasizing that the contribution of C1q to synapse elimination appears to be dependent on context.
Assuntos
Complemento C1q/metabolismo , Dominância Ocular/fisiologia , Plasticidade Neuronal/fisiologia , Neurônios/metabolismo , Córtex Visual/metabolismo , Animais , Complemento C1q/genética , Dendritos/metabolismo , Espinhas Dendríticas/metabolismo , Camundongos , Camundongos Knockout , Sinapses/metabolismoRESUMO
Volumetric magnetic resonance imaging studies have shown that intense learning can be associated with grey matter volume increases in the adult brain. The underlying mechanisms are poorly understood. Here we used monocular deprivation in rats to analyze the mechanisms underlying use-dependent grey matter increases. Optometry for quantification of visual acuity was combined with volumetric magnetic resonance imaging and microscopic techniques in longitudinal and cross-sectional studies. We found an increased spatial vision of the open eye which was associated with a transient increase in the volumes of the contralateral visual and lateral entorhinal cortex. In these brain areas dendrites of neurons elongated, and there was a strong increase in the number of spines, the targets of synapses, which was followed by spine maturation and partial pruning. Astrocytes displayed a transient pronounced swelling and underwent a reorganization of their processes. The use-dependent increase in grey matter corresponded predominantly to the swelling of the astrocytes. Experience-dependent increase in brain grey matter volume indicates a gain of structure plasticity with both synaptic and astrocyte remodeling.
Assuntos
Astrócitos/citologia , Encéfalo/diagnóstico por imagem , Espinhas Dendríticas , Dominância Ocular , Substância Cinzenta/diagnóstico por imagem , Aprendizagem/fisiologia , Privação Sensorial , Visão Monocular , Animais , Encéfalo/crescimento & desenvolvimento , Tamanho Celular , Dendritos , Substância Cinzenta/crescimento & desenvolvimento , Imageamento por Ressonância Magnética , Plasticidade Neuronal/fisiologia , Tamanho do Órgão , RatosRESUMO
INTRODUCTION: A variety of transgenic and knock-in mice that express mutant alleles of Amyloid precursor protein (APP) have been used to model the effects of amyloid-beta (Aß) on circuit function in Alzheimer's disease (AD); however phenotypes described in these mice may be affected by expression of mutant APP or proteolytic cleavage products independent of Aß. In addition, the effects of mutant APP expression are attributed to elevated expression of the amyloidogenic, 42-amino acid-long species of Aß (Aß42) associated with amyloid plaque accumulation in AD, though elevated concentrations of Aß40, an Aß species produced with normal synaptic activity, may also affect neural function. METHODS: To explore the effects of elevated expression of Aß on synaptic function in vivo, we assessed visual system plasticity in transgenic mice that express and secrete Aß throughout the brain in the absence of APP overexpression. Transgenic mice that express either Aß40 or Aß42 were assayed for their ability to appropriately demonstrate ocular dominance plasticity following monocular deprivation. RESULTS: Using two complementary approaches to measure the plastic response to monocular deprivation, we find that male and female mice that express either 40- or 42-amino acid-long Aß species demonstrate a plasticity defect comparable to that elicited in transgenic mice that express mutant alleles of APP and Presenilin 1 (APP/PS1 mice). CONCLUSIONS: These data support the hypothesis that mutant APP-driven plasticity impairment in mouse models of AD is mediated by production and accumulation of Aß. Moreover, these findings suggest that soluble species of Aß are capable of modulating synaptic plasticity, likely independent of any aggregation. These findings may have implications for the role of soluble species of Aß in both development and disease settings.
Assuntos
Peptídeos beta-Amiloides/biossíntese , Dominância Ocular/fisiologia , Plasticidade Neuronal/fisiologia , Fragmentos de Peptídeos/biossíntese , Córtex Visual/metabolismo , Peptídeos beta-Amiloides/genética , Animais , Feminino , Masculino , Camundongos , Camundongos Transgênicos , Fragmentos de Peptídeos/genéticaRESUMO
Primary visual cortex (V1) is the locus of numerous forms of experience-dependent plasticity. Restricting visual stimulation to one eye at a time has revealed that many such forms of plasticity are eye-specific, indicating that synaptic modification occurs prior to binocular integration of thalamocortical inputs. A common feature of these forms of plasticity is the requirement for NMDA receptor (NMDAR) activation in V1. We therefore hypothesized that NMDARs in cortical layer 4 (L4), which receives the densest thalamocortical input, would be necessary for all forms of NMDAR-dependent and input-specific V1 plasticity. We tested this hypothesis in awake mice using a genetic approach to selectively delete NMDARs from L4 principal cells. We found, unexpectedly, that both stimulus-selective response potentiation and potentiation of open-eye responses following monocular deprivation (MD) persist in the absence of L4 NMDARs. In contrast, MD-driven depression of deprived-eye responses was impaired in mice lacking L4 NMDARs, as was L4 long-term depression in V1 slices. Our findings reveal a crucial requirement for L4 NMDARs in visual cortical synaptic depression, and a surprisingly negligible role for them in cortical response potentiation. These results demonstrate that NMDARs within distinct cellular subpopulations support different forms of experience-dependent plasticity.
Assuntos
Potenciais Evocados Visuais/fisiologia , Plasticidade Neuronal/fisiologia , Estimulação Luminosa/métodos , Receptores de N-Metil-D-Aspartato/deficiência , Privação Sensorial/fisiologia , Córtex Visual/fisiologia , Animais , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Receptores de N-Metil-D-Aspartato/genéticaRESUMO
Cyclin-dependent kinase 5 (Cdk5) has been shown to play a critical role in brain development, learning, memory and neural processing in general. Cdk5 is widely distributed in many neuron types in the central nervous system, while its cell-specific role is largely unknown. Our previous study showed that Cdk5 inhibition restored ocular dominance (OD) plasticity in adulthood. In this study, we specifically knocked down Cdk5 in different types of neurons in the visual cortex and examined OD plasticity by optical imaging of intrinsic signals. Downregulation of Cdk5 in parvalbumin-expressing (PV) inhibitory neurons, but not other neurons, reactivated adult mouse visual cortical plasticity. Cdk5 knockdown in PV neurons reduced the evoked firing rate, which was accompanied by an increment in the threshold current for the generation of a single action potential (AP) and hyperpolarization of the resting membrane potential. Moreover, chemogenetic activation of PV neurons in the visual cortex can attenuate the restoration of OD plasticity by Cdk5 inhibition. Taken together, our results suggest that Cdk5 in PV interneurons may play a role in modulating the excitation and inhibition balance to control the plasticity of the visual cortex.
Assuntos
Quinase 5 Dependente de Ciclina/fisiologia , Dominância Ocular , Plasticidade Neuronal , Neurônios/metabolismo , Córtex Visual/enzimologia , Animais , Quinase 5 Dependente de Ciclina/genética , Quinase 5 Dependente de Ciclina/metabolismo , Técnicas de Silenciamento de Genes , Masculino , Camundongos , Neurônios/fisiologia , Córtex Visual/fisiologiaRESUMO
By virtue of their extensive axonal arborization and perisomatic synaptic targeting, cortical inhibitory parvalbumin (PV) cells strongly regulate principal cell output and plasticity and modulate experience-dependent refinement of cortical circuits during development. An interesting aspect of PV cell connectivity is its prolonged maturation time course, which is completed only by end of adolescence. The p75 neurotrophin receptor (p75NTR) regulates numerous cellular functions; however, its role on cortical circuit development and plasticity remains elusive, mainly because localizing p75NTR expression with cellular and temporal resolution has been challenging. By using RNAscope and a modified version of the proximity ligation assay, we found that p75NTR expression in PV cells decreases between the second and fourth postnatal week, at a time when PV cell synapse numbers increase dramatically. Conditional knockout of p75NTR in single PV neurons in vitro and in PV cell networks in vivo causes precocious formation of PV cell perisomatic innervation and perineural nets around PV cell somata, therefore suggesting that p75NTR expression modulates the timing of maturation of PV cell connectivity in the adolescent cortex. Remarkably, we found that PV cells still express p75NTR in adult mouse cortex of both sexes and that its activation is sufficient to destabilize PV cell connectivity and to restore cortical plasticity following monocular deprivation in vivo Together, our results show that p75NTR activation dynamically regulates PV cell connectivity, and represent a novel tool to foster brain plasticity in adults.SIGNIFICANCE STATEMENT In the cortex, inhibitory, GABA-releasing neurons control the output and plasticity of excitatory neurons. Within this diverse group, parvalbumin-expressing (PV) cells form the larger inhibitory system. PV cell connectivity develops slowly, reaching maturity only at the end of adolescence; however, the mechanisms controlling the timing of its maturation are not well understood. We discovered that the expression of the neurotrophin receptor p75NTR in PV cells inhibits the maturation of their connectivity in a cell-autonomous fashion, both in vitro and in vivo, and that p75NTR activation in adult PV cells promotes their remodeling and restores cortical plasticity. These results reveal a new p75NTR function in the regulation of the time course of PV cell maturation and in limiting cortical plasticity.
Assuntos
Envelhecimento/fisiologia , Interneurônios/fisiologia , Plasticidade Neuronal/fisiologia , Receptores de Fator de Crescimento Neural/fisiologia , Maturidade Sexual/fisiologia , Córtex Visual/crescimento & desenvolvimento , Animais , Fator Neurotrófico Derivado do Encéfalo/farmacologia , Conectoma , Potenciais Evocados Visuais , Feminino , Neurônios GABAérgicos/citologia , Regulação da Expressão Gênica no Desenvolvimento , Interneurônios/química , Interneurônios/ultraestrutura , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Técnicas de Cultura de Órgãos , Parvalbuminas/análise , Precursores de Proteínas/farmacologia , Distribuição Aleatória , Receptores de Fator de Crescimento Neural/biossíntese , Receptores de Fator de Crescimento Neural/genética , Proteínas Recombinantes/metabolismo , Proteínas Recombinantes/farmacologia , Sinapses/fisiologia , Visão Monocular/fisiologia , Córtex Visual/citologia , Córtex Visual/metabolismoRESUMO
Optic nerve (ON) injury is an established model of axonal injury which results in retrograde degeneration and death of retinal ganglion cells as well anterograde loss of transmission and Wallerian degeneration of the injured axons. While the local impact of ON crush has been extensively documented we know comparatively little about the functional changes that occur in higher visual structures such as primary visual cortex (V1). We explored the extent of adult cortical plasticity using ON crush in aged mice. V1 function of the contralateral hemisphere was assessed longitudinally by intrinsic signal imaging and 2-photon calcium imaging before and after ON crush. Functional imaging demonstrated an immediate shift in V1 ocular dominance towards the ipsilateral, intact eye, due to the expected almost complete loss of responses to contralateral eye stimulation. Surprisingly, within 2 weeks we observed a delayed increase in ipsilateral eye responses. Additionally, spontaneous activity in V1 was reduced, similar to the lesion projection zone after retinal lesions. The observed changes in V1 activity indicate that severe ON injury in adulthood evokes cortical plasticity not only cross-modally but also within the visual cortex; this plasticity may be best compared with that seen after retinal lesions.
Assuntos
Plasticidade Neuronal , Traumatismos do Nervo Óptico/fisiopatologia , Córtex Visual/fisiopatologia , Envelhecimento/fisiologia , Animais , Cálcio/metabolismo , Dominância Ocular/fisiologia , Potenciais Evocados Visuais/fisiologia , Feminino , Estudos Longitudinais , Masculino , Camundongos Endogâmicos C57BL , Neurônios/patologia , Neurônios/fisiologia , Traumatismos do Nervo Óptico/patologia , Imagem Óptica , Retina/patologia , Retina/fisiopatologiaRESUMO
Microdeletion of a region in chromosome 16p11.2 increases susceptibility to autism. Although this region contains exons of 29 genes, disrupting only a small segment of the region, which spans five genes, is sufficient to cause autistic traits. One candidate gene in this critical segment is MVP, which encodes for the major vault protein (MVP) that has been implicated in regulation of cellular transport mechanisms. MVP expression levels in MVP+/- mice closely phenocopy those of 16p11.2 mutant mice, suggesting that MVP+/- mice may serve as a model of MVP function in 16p11.2 microdeletion. Here we show that MVP regulates the homeostatic component of ocular dominance (OD) plasticity in primary visual cortex. MVP+/- mice of both sexes show impairment in strengthening of open-eye responses after several days of monocular deprivation (MD), whereas closed-eye responses are weakened as normal, resulting in reduced overall OD plasticity. The frequency of miniature EPSCs (mEPSCs) in pyramidal neurons is decreased in MVP+/- mice after extended MD, suggesting a reduction of functional synapses. Correspondingly, upregulation of surface GluA1 AMPA receptors is reduced in MVP+/- mice after extended MD, and is accompanied by altered expression of STAT1 and phosphorylated ERK, which have been previously implicated in OD plasticity. Normalization of STAT1 levels by introducing STAT1 shRNA rescues surface GluA1 and open-eye responses, implicating STAT1 as a downstream effector of MVP. These findings demonstrate a specific role for MVP as a key molecule influencing the homeostatic component of activity-dependent synaptic plasticity, and potentially the corresponding phenotypes of 16p11.2 microdeletion syndrome.SIGNIFICANCE STATEMENT Major vault protein (MVP), a candidate gene in 16p11.2 microdeletion syndrome, has been implicated in the regulation of several cellular processes including transport mechanisms and scaffold signaling. However, its role in brain function and plasticity remains unknown. In this study, we identified MVP as an important regulator of the homeostatic component of experience-dependent plasticity, via regulation of STAT1 and ERK signaling. This study helps reveal a new mechanism for an autism-related gene in brain function, and suggests a broader role for neuro-immune interactions in circuit level plasticity. Importantly, our findings might explain specific components of the pathophysiology of 16p11.2 microdeletion syndrome.