RESUMO
Erythropoietin (EPO), the hypoxia-inducible hematopoietic hormone, has well-established neuroprotective/neurotrophic roles in the developing central nervous system and the therapeutic potential of EPO has been widely explored in clinical studies for the treatment of perinatal hypoxic brain lesion, as well as prematurity. Here, we reveal that both EPO and Epo receptor (EPOR) are expressed in the developing rat somatosensory cortex during radial migration and laminar positioning of granular and supragranular neurons. Experimental deregulation of EPO signaling using genetic approaches results in aberrant migration, as well as permanent neuronal misplacement leading to abnormal network activity and protracted sensory behavioral deficits. We identify ERK as the downstream effector of the EPO signaling pathway for neuronal migration. These findings reveal a crucial role for endogenous EPO signaling in neuronal migration, and offer important insights for understanding how the temporary deregulation of EPO could result in migration defects that lead to abnormal behavior in the adult.
Assuntos
Eritropoetina/metabolismo , Neocórtex/citologia , Neocórtex/metabolismo , Animais , Movimento Celular/genética , Movimento Celular/fisiologia , Eletroporação , Eritropoetina/genética , Potenciais Somatossensoriais Evocados/genética , Potenciais Somatossensoriais Evocados/fisiologia , Feminino , Células HEK293 , Humanos , Imuno-Histoquímica , Hibridização In Situ , Masculino , Gravidez , Ratos , Transdução de Sinais/genética , Transdução de Sinais/fisiologiaRESUMO
During corticogenesis, ventricular zone progenitors sequentially generate distinct subtypes of neurons, accounting for the diversity of neocortical cells and the circuits they form. While activity-dependent processes are critical for the differentiation and circuit assembly of postmitotic neurons, how bioelectrical processes affect nonexcitable cells, such as progenitors, remains largely unknown. Here, we reveal that, in the developing mouse neocortex, ventricular zone progenitors become more hyperpolarized as they generate successive subtypes of neurons. Experimental in vivo hyperpolarization shifted the transcriptional programs and division modes of these progenitors to a later developmental status, with precocious generation of intermediate progenitors and a forward shift in the laminar, molecular, morphological, and circuit features of their neuronal progeny. These effects occurred through inhibition of the Wnt-beta-catenin signaling pathway by hyperpolarization. Thus, during corticogenesis, bioelectric membrane properties are permissive for specific molecular pathways to coordinate the temporal progression of progenitor developmental programs and thus neocortical neuron diversity.
Assuntos
Potenciais da Membrana , Neocórtex/embriologia , Neurônios/metabolismo , Células-Tronco/citologia , Animais , Encéfalo/citologia , Encéfalo/embriologia , Diferenciação Celular , Progressão da Doença , Eletroporação , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Masculino , Camundongos , Neocórtex/citologia , Proteínas do Tecido Nervoso/metabolismo , Células-Tronco Neurais/citologia , Neurogênese , Canais de Potássio Corretores do Fluxo de Internalização/metabolismo , Análise de Sequência de RNA , Transdução de Sinais , Fatores de Tempo , Proteínas Wnt/metabolismo , beta Catenina/metabolismoRESUMO
Prematurely born children often develop neurodevelopmental delay that has been correlated with reduced growth and microstructural alterations in the cerebral cortex. Much research has focused on apoptotic neuronal cell death as a key neuropathological features following preterm brain injuries. How scattered apoptotic death of neurons may contribute to microstructural alterations remains unknown. The present study investigated in a rat model the effects of targeted neuronal apoptosis on cortical microstructure using in vivo MRI imaging combined with neuronal reconstruction and histological analysis. We describe that mild, targeted death of layer IV neurons in the developing rat cortex induces MRI-defined metabolic and microstructural alterations including increased cortical fractional anisotropy. Delayed architectural modifications in cortical gray matter and myelin abnormalities in the subcortical white matter such as hypomyelination and microglia activation follow the acute phase of neuronal death and axonal degeneration. These results establish the link between mild cortical apoptosis and MRI-defined microstructure changes that are reminiscent to those previously observed in preterm babies.
Assuntos
Apoptose/fisiologia , Córtex Cerebral , Neurônios/ultraestrutura , Animais , Animais Recém-Nascidos , Antígenos CD/metabolismo , Antígenos de Diferenciação Mielomonocítica/metabolismo , Ácido Aspártico/análogos & derivados , Ácido Aspártico/metabolismo , Proteínas de Ligação ao Cálcio/metabolismo , Morte Celular/genética , Morte Celular/fisiologia , Córtex Cerebral/citologia , Córtex Cerebral/diagnóstico por imagem , Córtex Cerebral/crescimento & desenvolvimento , Dendritos/metabolismo , Dendritos/ultraestrutura , Toxina Diftérica/genética , Toxina Diftérica/metabolismo , Embrião de Mamíferos , Proteína Glial Fibrilar Ácida/metabolismo , Glutamato-Amônia Ligase/metabolismo , Ácido Glutâmico/metabolismo , Glutamina/metabolismo , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Proteínas dos Microfilamentos/metabolismo , Neurônios/metabolismo , Fosfopiruvato Hidratase/metabolismo , Ratos , Ratos WistarRESUMO
Perturbed neuronal migration and circuit development have been implicated in the pathogenesis of neurodevelopmental diseases; however, the direct steps linking these developmental errors to behavior alterations remain unknown. Here we demonstrate that Wnt/C-Kit signaling is a key regulator of glia-guided radial migration in rat somatosensory cortex. Transient downregulation of Wnt signaling in migrating, callosal projection neurons results in delayed positioning in layer 2/3. Delayed neurons display reduced neuronal activity with impaired afferent connectivity causing permanent deficit in callosal projections. Animals with these defects exhibit altered somatosensory function with reduced social interactions and repetitive movements. Restoring normal migration by overexpressing the Wnt-downstream effector C-Kit or selective chemogenetic activation of callosal projection neurons during a critical postnatal period prevents abnormal interhemispheric connections as well as behavioral alterations. Our findings identify a link between defective canonical Wnt signaling, delayed neuronal migration, deficient interhemispheric connectivity and abnormal social behavior analogous to autistic characteristics in humans.
Assuntos
Neurônios/metabolismo , Comportamento Social , Proteínas Wnt/metabolismo , Via de Sinalização Wnt , Animais , Comportamento Animal , Encéfalo/metabolismo , Movimento Celular , Cérebro/metabolismo , Corpo Caloso/metabolismo , Feminino , Células HEK293 , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Potenciais da Membrana , Neurogênese , Neuroglia/metabolismo , Fenótipo , Ratos , Ratos Wistar , Análise de Sequência de RNA , Córtex Somatossensorial/metabolismoRESUMO
Stimulation of endogenous neurogenesis and recruitment of neural progenitors from the subventricular zone (SVZ) neurogenic site may represent a useful strategy to improve regeneration in the ischemic cortex. Here, we tested whether transgenic overexpression of extracellular matrix metalloproteinase inducer (EMMPRIN), the regulator of matrix metalloproteinases (MMPs) expression, in endogenous neural progenitor cells (NPCs) in the subventricular zone (SVZ) could increase migration towards ischemic injury. For this purpose, we applied a lentivector-mediated gene transfer system. We found that EMMPRIN-transduced progenitors exhibited enhanced MMP-2 activity in vitro and showed improved motility in 3D collagen gel as well as in cortical slices. Using a rat model of neonatal ischemia, we showed that EMMPRIN overexpressing SVZ cells invade the injured cortical tissue more efficiently than controls. Our results suggest that EMMPRIN overexpression could be suitable approach to improve capacities of endogenous or transplanted progenitors to invade the injured cortex.
Assuntos
Basigina/biossíntese , Isquemia Encefálica/metabolismo , Movimento Celular/fisiologia , Córtex Cerebral/metabolismo , Ventrículos Laterais/metabolismo , Células-Tronco Neurais/metabolismo , Animais , Animais Recém-Nascidos , Basigina/genética , Isquemia Encefálica/patologia , Córtex Cerebral/patologia , Expressão Gênica , Ventrículos Laterais/patologia , Técnicas de Cultura de Órgãos , Ratos , Ratos Sprague-Dawley , Ratos WistarRESUMO
Neural progenitor cells (NPCs) overexpressing fibroblast growth factor 2 (FGF-2) have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment after transplantation into the cerebral cortex. Strikingly, the vascular clusters of progenitor cells give rise to immature neurons after ischemic injury, raising prospects for the formation of ectopic neurogenic niches for repair. We investigated the spatial relationship of perivascular clusters with the host vascular structures. FGF-2-GFP-transduced NPCs were transplanted into the intact somatosensory rat cortex. Confocal microscopic analysis revealed that grafted cells preferentially contacted venules at sites with aquaporin-4-positive astrocytic endfeet and avoided contacts with desmin-positive pericytes. Electron microscopic analysis confirmed that grafted cells preferentially made contact with astroglial endfeet, and only a minority of them reached the endothelial basal lamina. These results provide new insights into the fine structural and anatomical relationship between grafted FGF-2-transduced NPCs and the host vasculature.
Assuntos
Córtex Cerebral/irrigação sanguínea , Fator 2 de Crescimento de Fibroblastos/metabolismo , Células-Tronco Neurais/metabolismo , Células-Tronco Neurais/transplante , Animais , Animais Recém-Nascidos , Astrócitos/citologia , Vasos Sanguíneos/citologia , Vasos Sanguíneos/ultraestrutura , Agregação Celular , Células Cultivadas , Córtex Cerebral/citologia , Feminino , Proteínas de Fluorescência Verde/metabolismo , Masculino , Pericitos/citologia , Ratos Sprague-Dawley , Córtex Somatossensorial/citologiaRESUMO
Apoptotic cell death is the leading cause of neuronal loss after neonatal brain injury. Little is known about the intrinsic capacity of the immature cerebral cortex for replacing dead cells. Here we test the hypothesis that neuronal apoptosis is able to trigger compensatory proliferation in surrounding cells. In order to establish a "pure" apoptotic cell death model and to avoid the confounding effects of broken blood-brain barrier and inflammatory reactions, we used a diphtheria toxin (DT) and diphtheria toxin receptor (DTR) system to induce ablation of layer IV neurons in the rodent somatosensory cortex during the early postnatal period. We found that DT-triggered apoptosis is a slowly progressing event lasting about for 7 days. While dying cells expressed the morphological features of apoptosis, we could not detect immunoreactivity for activated caspase-3 in these cells. Microglia activation and proliferation represented the earliest cellular responses to apoptotic cell death. In addition, we found that induced apoptosis triggered a massive proliferation of undifferentiated progenitor cell pool including Sox2 as well as NG2 cells. The default differentiation pattern of proliferating progenitors appears to be the glial phenotype; we could not find evidence for newly generated neurons in response to apoptotic neuronal death. These results suggest that mitotically active progenitor populations are intrinsically capable to contribute to the repair process of injured cortical tissue and may represent a potential target for neuronal replacement strategies.
Assuntos
Apoptose/fisiologia , Lesões Encefálicas/fisiopatologia , Proliferação de Células/fisiologia , Córtex Cerebral/citologia , Células-Tronco Neurais/fisiologia , Neurônios/fisiologia , Animais , Animais Recém-Nascidos , Apoptose/efeitos dos fármacos , Apoptose/genética , Lesões Encefálicas/patologia , Caspase 3/metabolismo , Proliferação de Células/efeitos dos fármacos , Córtex Cerebral/crescimento & desenvolvimento , Toxina Diftérica/farmacologia , Proteínas do Olho/genética , Proteínas do Olho/metabolismo , Fator de Crescimento Semelhante a EGF de Ligação à Heparina/genética , Fator de Crescimento Semelhante a EGF de Ligação à Heparina/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Técnicas In Vitro , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Rede Nervosa/efeitos dos fármacos , Rede Nervosa/fisiologia , Proteínas do Tecido Nervoso/genética , Proteínas do Tecido Nervoso/metabolismo , Neuroglia/efeitos dos fármacos , Neuroglia/fisiologia , Neurônios/ultraestrutura , Ratos , Ratos Wistar , Fatores de Tempo , Proteína Homeobox SIX3RESUMO
The precise timing of pyramidal cell migration from the ventricular germinal zone to the cortical plate is essential for establishing cortical layers, and migration errors can lead to neurodevelopmental disorders underlying psychiatric and neurological diseases. Here, we report that Wnt canonical as well as non-canonical signaling is active in pyramidal precursors during radial migration. We demonstrate using constitutive and conditional genetic strategies that transient downregulation of canonical Wnt/ß-catenin signaling during the multipolar stage plays a critical role in polarizing and orienting cells for radial migration. In addition, we show that reduced canonical Wnt signaling is triggered cell autonomously by time-dependent expression of Wnt5A and activation of non-canonical signaling. We identify ephrin-B1 as a canonical Wnt-signaling-regulated target in control of the multipolar-to-bipolar switch. These findings highlight the critical role of Wnt signaling activity in neuronal positioning during cortical development.
Assuntos
Córtex Cerebral/metabolismo , Neurônios/metabolismo , Via de Sinalização Wnt , Animais , Movimento Celular , Córtex Cerebral/citologia , Córtex Cerebral/patologia , Embrião de Mamíferos/citologia , Embrião de Mamíferos/metabolismo , Efrina-B1/metabolismo , Microscopia de Fluorescência , Neurônios/citologia , Neurônios/patologia , Células Piramidais/citologia , Células Piramidais/metabolismo , Interferência de RNA , RNA Interferente Pequeno/metabolismo , Ratos , Ratos Wistar , Proteínas com Domínio T/metabolismo , Imagem com Lapso de Tempo , Proteínas Wnt/antagonistas & inibidores , Proteínas Wnt/genética , Proteínas Wnt/metabolismo , Proteína Wnt-5a , beta Catenina/metabolismoRESUMO
Cortical processing of sensory stimuli typically recruits multiple areas, but how each area dynamically incorporates activity from other areas is not well understood. We investigated interactions between cortical columns of bilateral primary sensory regions (S1s) in rats by recording local field potentials and multi-unit activity simultaneously in both S1s with electrodes positioned at each cortical layer. Using dynamic connectivity analysis based on Granger-causal modeling, we found that, shortly after whisker stimulation (< 10 ms), contralateral S1 (cS1) already relays activity to granular and infragranular layers of S1 in the other hemisphere, after which cS1 shows a pattern of within-column interactions that directs activity upwards toward superficial layers. This pattern of predominant upward driving was also observed in S1 ipsilateral to stimulation, but at longer latencies. In addition, we found that interactions between the two S1s most strongly target granular and infragranular layers. Taken together, the results suggest a possible mechanism for how cortical columns integrate local and large-scale neocortical computation by relaying information from deeper layers to local processing in superficial layers.
Assuntos
Córtex Somatossensorial/fisiologia , Tato/fisiologia , Animais , Potenciais Somatossensoriais Evocados , Feminino , Masculino , Modelos Neurológicos , Estimulação Física , Ratos , Ratos Wistar , Vibrissas/fisiologiaRESUMO
Vascular endothelial growth factor (VEGF) is a critical regulator of endothelial cell differentiation and vasculogenesis during both development and tumor vascularization. VEGF-165 is a major form that is secreted from the cells via a poorly characterized pathway. Here we use green fluorescent protein- and epitope-tagged VEGF-165 and find that its early trafficking between the endoplasmic reticulum and the Golgi requires the small GTP-binding proteins Sar1 and Arf1 and that its glycosylation in the Golgi compartment is necessary for efficient post-Golgi transport and secretion from the cells. The relative temperature insensitivity of VEGF secretion and its Sar1 and Arf1 inhibitory profiles distinguish it from other cargoes using the "constitutive" secretory pathway. Prominent features of VEGF secretion are the retention of the protein on the outer surface of the plasma membrane and the stimulation of its secretion by Ca(2+) and protein kinase C. Of importance, shedding of VEGF-165 from the cell surface together with other membrane components appears to be a unique feature by which some VEGF is delivered to the surroundings to exert its known biological actions. Understanding VEGF trafficking can reveal additional means by which tumor vascularization can be inhibited by pharmacological interventions.
Assuntos
Membrana Celular/metabolismo , Fator A de Crescimento do Endotélio Vascular/metabolismo , Animais , Células COS , Membrana Celular/efeitos dos fármacos , Membrana Celular/ultraestrutura , Chlorocebus aethiops , Retículo Endoplasmático/efeitos dos fármacos , Retículo Endoplasmático/metabolismo , GTP Fosfo-Hidrolases/metabolismo , Glicosilação/efeitos dos fármacos , Complexo de Golgi/efeitos dos fármacos , Complexo de Golgi/metabolismo , Proteínas de Fluorescência Verde/metabolismo , Células Endoteliais da Veia Umbilical Humana/efeitos dos fármacos , Células Endoteliais da Veia Umbilical Humana/metabolismo , Humanos , Fosfatidilinositol 4,5-Difosfato/metabolismo , Multimerização Proteica/efeitos dos fármacos , Transporte Proteico/efeitos dos fármacos , Proteínas Recombinantes de Fusão/metabolismo , Sirolimo/farmacologia , Fator A de Crescimento do Endotélio Vascular/ultraestruturaRESUMO
PURPOSE OF REVIEW: The aim is to review mechanisms that are central to the formation of proper cortical circuitry and relevant to perinatal brain injury and premature birth. RECENT FINDINGS: Clinical investigations using noninvasive imaging techniques suggest that impaired connectivity of cortical circuitry is associated with perinatal adverse conditions. Recent experimental and translational studies revealed developmental mechanisms that are critical for circuit formation and potentially at risk in the perinatal period. These include existence of last wave genesis, migration and integration of gamma-aminobutyric acid (GABA) interneurons in the perinatal period; maturation of GABA interneuron networks that are central to critical period plasticity; transient connections by subplate neurons that guide thalamocortical connectivity, and a perineuronal microglia network that maintains axonal growth and neuronal survival as well as executing synaptic pruning. In addition, recent work has demonstrated that birth plays a key role in triggering the maturation cascade of cortical circuits. SUMMARY: Altered maturation of cortical circuits is an increasingly recognized aspect of perinatal injury and premature birth. Potential mechanisms are revealed but further translational studies are required to associate fine changes at the cellular and molecular level with imaging data in experimental models.
Assuntos
Lesões Encefálicas/complicações , Lesões Encefálicas/etiologia , Córtex Cerebral/patologia , Rede Nervosa/patologia , Nascimento Prematuro/patologia , Animais , Córtex Cerebral/embriologia , Córtex Cerebral/crescimento & desenvolvimento , Humanos , Interneurônios/metabolismo , Interneurônios/patologia , Ácido gama-Aminobutírico/metabolismoRESUMO
The cingulate and retrosplenial regions are major components of the dorsomedial (dm) limbic cortex and have been implicated in a range of cognitive functions such as emotion, attention, and spatial memory. While the structure and connectivity of these cortices are well characterized, little is known about their development. Notably, the timing and mode of migration that govern the appropriate positioning of late-born neurons remain unknown. Here, we analyzed migratory events during the early postnatal period from ventricular/subventricular zone (VZ/SVZ) to the cerebral cortex by transducing neuronal precursors in the VZ/SVZ of newborn rats/mice with Tomato/green fluorescent protein-encoding lentivectors. We have identified a pool of postmitotic pyramidal precursors in the dm part of the neonatal VZ/SVZ that migrate into the medial limbic cortex during the first postnatal week. Time-lapse imaging demonstrates that these cells migrate on radial glial fibers by locomotion and display morphological and behavioral changes as they travel through the white matter and enter into the cortical gray matter. In the granular retrosplenial cortex, these cells give rise to a Satb2+ pyramidal subtype and develop dendritic bundles in layer I. Our observations provide the first insight into the patterns and dynamics of cell migration into the medial limbic cortex.
Assuntos
Movimento Celular/genética , Giro do Cíngulo/citologia , Giro do Cíngulo/crescimento & desenvolvimento , Células Piramidais/fisiologia , Fatores Etários , Animais , Animais Recém-Nascidos , Bromodesoxiuridina/metabolismo , Ventrículos Cerebrais/citologia , Ventrículos Cerebrais/crescimento & desenvolvimento , Dendritos/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/genética , Vetores Genéticos/fisiologia , Glutamato Descarboxilase/genética , Proteínas de Fluorescência Verde/genética , Lentivirus/genética , Proteínas Luminescentes/genética , Proteínas de Ligação à Região de Interação com a Matriz/metabolismo , Camundongos , Camundongos Transgênicos , Microscopia Confocal , Proteínas do Tecido Nervoso/metabolismo , Células-Tronco Neurais/fisiologia , Células Piramidais/ultraestrutura , Proteínas com Domínio T/metabolismo , Fatores de Transcrição/metabolismo , Ubiquitina/genética , Proteína Vermelha FluorescenteRESUMO
Large-scale neuronal networks integrating several cortical areas mediate the complex functions of the brain such as sensorimotor integration. Little is known about the functional development of these networks and the maturational processes by which distant networks become functionally connected. We addressed this question in the postnatal rat sensorimotor system. Using epicranial multielectrode grids that span most of the cortical surface and intracortical electrodes, we show that sensory evoked cortical responses continuously maturate throughout the first 3 weeks with the strongest developmental changes occurring in a very short time around postnatal day 13 (P13). Before P13, whisker stimulation evokes slow, initially surface-negative activity restricted mostly to the lateral parietal area of the contralateral hemisphere. In a narrow time window of â¼48 h around P13, a new early, sharp surface-positive component emerges that coincides with subsequent propagation of activity to sensory and motor areas of both hemispheres. Our data show that this new component developing at the end of the second week corresponds principally to functional maturation of the supragranular cortical layers and appears to be crucial for the functional associations in the large-scale sensorimotor cortical network. It goes along with the onset of whisking behavior, as well as major synaptic and functional changes within the S1 cortex that are known to develop during this period.
Assuntos
Encéfalo/fisiologia , Potenciais Somatossensoriais Evocados/fisiologia , Rede Nervosa/fisiologia , Análise de Variância , Animais , Encéfalo/crescimento & desenvolvimento , Mapeamento Encefálico , Eletrodos Implantados , Eletrofisiologia , Feminino , Masculino , Rede Nervosa/crescimento & desenvolvimento , Vias Neurais/fisiologia , Estimulação Física , Ratos , Ratos Wistar , Vibrissas/fisiologiaRESUMO
The rodent somatosensory barrel cortex is an ideal model for studying the impact of sensory experience on developing brain circuitry. To examine whether and how interference with sensory perception in the early postnatal period can affect the development of synaptic networks in this system, we took advantage of a transgenic mouse strain expressing the yellow fluorescent protein in layer 5B pyramidal neurons of the somatosensory cortex. By using ex vivo confocal imaging, we first demonstrate a cortical-layer-specific increase in the number of dendritic spines during postnatal development on apical dendritic shafts of these cells extending up to cortical layer 1. Next, by performing bilateral whisker trimming at distinct developmental stages, we show that disruption of sensory perception before postnatal day 20 impairs dendritic spine development in apical dendritic segments within layers 1 and 2/3 but not in layer 4. The whisker trimming-induced decrease in dendritic spine density during this period is accompanied by a highly significant decrease in dendritic spine head diameter. Finally, we also show that these whisker trimming-induced morphological alterations of dendritic spines during the early postnatal period are no longer detectable in adult animals. Altogether, these findings further emphasize the important role of sensory activity in synaptic network assembly in the developing barrel cortex. They also support an as yet unidentified structural mechanism that might contribute to the layer- and cell-type-specific physiological effects of whisker trimming during the early postnatal period.
Assuntos
Espinhas Dendríticas , Privação Sensorial/fisiologia , Córtex Somatossensorial , Vibrissas/patologia , Fatores Etários , Animais , Comportamento Animal/fisiologia , Espinhas Dendríticas/fisiologia , Espinhas Dendríticas/ultraestrutura , Proteínas Luminescentes/metabolismo , Camundongos , Camundongos Transgênicos , Rede Nervosa/anatomia & histologia , Rede Nervosa/fisiologia , Células Piramidais/metabolismo , Células Piramidais/ultraestrutura , Córtex Somatossensorial/citologia , Córtex Somatossensorial/crescimento & desenvolvimento , Vibrissas/crescimento & desenvolvimentoRESUMO
Neonatal hypoxia-ischemia (HI) is the most important cause of brain injury in the newborn. Here we studied structural alterations and functional perturbations of developing large-scale sensorimotor cortical networks in a rat model of moderate HI at postnatal day 3 (P3). At the morphological level, HI led to a disorganized barrel pattern in the somatosensory cortex without detectable histological changes in the motor cortex. Functional effects were addressed by means of epicranial mapping of somatosensory-evoked potentials (SEPs) during the postischemic recovery period. At P10, SEPs were immature and evoked activity was almost restricted to the somatosensory and motor cortices of the contralateral hemisphere. Peak and topographic analyses of epicranial potentials revealed that responses were profoundly depressed in both sensory and motor areas of HI-lesioned animals. At the end of the postnatal period at P21, responses involved networks in both hemispheres. SEP amplitude was still depressed in the injured sensory region, but it completely recovered in the motor area. These results suggest a process of large-scale network plasticity in sensorimotor circuits after perinatal ischemic injury. The model provides new perspectives for investigating the temporal and spatial characteristics of the recovery process following HI and eventually developing therapeutic interventions.
Assuntos
Hipóxia-Isquemia Encefálica/fisiopatologia , Rede Nervosa/crescimento & desenvolvimento , Rede Nervosa/fisiopatologia , Recuperação de Função Fisiológica/fisiologia , Córtex Somatossensorial/crescimento & desenvolvimento , Córtex Somatossensorial/fisiopatologia , Animais , Animais Recém-Nascidos , Modelos Animais de Doenças , Potenciais Somatossensoriais Evocados/fisiologia , Humanos , Hipóxia-Isquemia Encefálica/patologia , Recém-Nascido , Córtex Motor/crescimento & desenvolvimento , Córtex Motor/patologia , Córtex Motor/fisiopatologia , Rede Nervosa/patologia , Ratos , Ratos Wistar , Córtex Somatossensorial/patologiaRESUMO
Experience-driven activity plays an essential role in the development of brain circuitry during critical periods of early postnatal life, a process that depends upon a dynamic balance between excitatory and inhibitory signals. Since general anesthetics are powerful pharmacological modulators of neuronal activity, an important question is whether and how these drugs can affect the development of synaptic networks. To address this issue, we examined here the impact of anesthetics on synapse growth and dynamics. We show that exposure of young rodents to anesthetics that either enhance GABAergic inhibition or block NMDA receptors rapidly induce a significant increase in dendritic spine density in the somatosensory cortex and hippocampus. This effect is developmentally regulated; it is transient but lasts for several days and is also reproduced by selective antagonists of excitatory receptors. Analyses of spine dynamics in hippocampal slice cultures reveals that this effect is mediated through an increased rate of protrusions formation, a better stabilization of newly formed spines, and leads to the formation of functional synapses. Altogether, these findings point to anesthesia as an important modulator of spine dynamics in the developing brain and suggest the existence of a homeostatic process regulating spine formation as a function of neural activity. Importantly, they also raise concern about the potential impact of these drugs on human practice, when applied during critical periods of development in infants.
Assuntos
Anestésicos/farmacologia , Encéfalo/efeitos dos fármacos , Encéfalo/crescimento & desenvolvimento , Sistema Nervoso/crescimento & desenvolvimento , Anestesia Geral , Animais , Espinhas Dendríticas/efeitos dos fármacos , Espinhas Dendríticas/metabolismo , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Camundongos , Microscopia Confocal/métodos , Fenômenos Fisiológicos do Sistema Nervoso , Córtex Somatossensorial/efeitos dos fármacos , Córtex Somatossensorial/metabolismo , Sinapses/metabolismoRESUMO
Stem/progenitor cell-based therapies hold promises for repairing the damaged nervous system. However, the efficiency of these approaches for neuronal replacement remains very limited. A major challenge is to develop pretransplant cell manipulations that may promote the survival, engraftment, and differentiation of transplanted cells. Here, we investigated whether overexpression of fibroblast growth factor-2 (FGF-2) in grafted neural progenitors could improve their integration in the host tissue. We show that FGF-2-transduced progenitors grafted in the early postnatal rat cortex have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment. The contact with vessels appears to be critical for maintaining progenitor cells in an undifferentiated and proliferative phenotype in the intact cortex. Strikingly, perivascular clusters of FGF-2 expressing cells seem to supply immature neurons in an ischemic environment. Our data provide evidence that engineering neural progenitors to overexpress FGF-2 may be a suitable strategy to improve the integration of grafted neural progenitor cells with the host vasculature thereby generating neurovascular clusters with a neurogenic potential for brain repair.
Assuntos
Fator 2 de Crescimento de Fibroblastos/biossíntese , Hipóxia-Isquemia Encefálica/cirurgia , Neurônios/metabolismo , Transplante de Células-Tronco/métodos , Células-Tronco/metabolismo , Animais , Vasos Sanguíneos , Diferenciação Celular/fisiologia , Fator 2 de Crescimento de Fibroblastos/genética , Imuno-Histoquímica , Neurônios/citologia , Ratos , Ratos Wistar , Células-Tronco/citologiaRESUMO
Mice actively explore their environment by rhythmically sweeping their whiskers. As a consequence, neuronal activity in somatosensory pathways is modulated by the frequency of whisker movement. The potential role of rhythmic neuronal activity for the integration and consolidation of sensory signals, however, remains unexplored. Here, we show that a brief period of rhythmic whisker stimulation in anesthetized mice resulted in a frequency-specific long-lasting increase in the amplitude of somatosensory-evoked potentials in the contralateral primary somatosensory (barrel) cortex. Mapping of evoked potentials and intracortical recordings revealed that, in addition to potentiation in layers IV and II/III of the barrel cortex, rhythmic whisker stimulation induced a decrease of somatosensory-evoked responses in the supragranular layers of the motor cortex. To assess whether rhythmic sensory input-based plasticity might arise in natural settings, we exposed mice to environmental enrichment. We found that it resulted in somatosensory-evoked responses of increased amplitude, highlighting the influence of previous sensory experience in shaping sensory responses. Importantly, environmental enrichment-induced plasticity occluded further potentiation by rhythmic stimulation, indicating that both phenomena share common mechanisms. Overall, our results suggest that natural, rhythmic patterns of whisker activity can modify the cerebral processing of sensory information, providing a possible mechanism for learning during sensory perception.
Assuntos
Córtex Motor/fisiologia , Rede Nervosa/fisiologia , Plasticidade Neuronal/fisiologia , Córtex Somatossensorial/fisiologia , Vibrissas/fisiologia , Animais , Potenciais Somatossensoriais Evocados/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Estimulação Física/métodosRESUMO
Human functional imaging studies are increasingly focusing on the identification of large-scale neuronal networks, their temporal properties, their development, and their plasticity and recovery after brain lesions. A method targeting large-scale networks in rodents would open the possibility to investigate their neuronal and molecular basis in detail. We here present a method to study such networks in mice with minimal invasiveness, based on the simultaneous recording of epicranial EEG from 32 electrodes regularly distributed over the head surface. Spatiotemporal analysis of the electrical potential maps similar to human EEG imaging studies allows quantifying the dynamics of the global neuronal activation with sub-millisecond resolution. We tested the feasibility, stability and reproducibility of the method by recording the electrical activity evoked by mechanical stimulation of the mystacial vibrissae. We found a series of potential maps with different spatial configurations that suggested the activation of a large-scale network with generators in several somatosensory and motor areas of both hemispheres. The spatiotemporal activation pattern was stable both across mice and in the same mouse across time. We also performed 16-channel intracortical recordings of the local field potential across cortical layers in different brain areas and found tight spatiotemporal concordance with the generators estimated from the epicranial maps. Epicranial EEG mapping thus allows assessing sensory processing by large-scale neuronal networks in living mice with minimal invasiveness, complementing existing approaches to study the neurophysiological mechanisms of interaction within the network in detail and to characterize their developmental, experience-dependent and lesion-induced plasticity in normal and transgenic animals.
Assuntos
Mapeamento Encefálico/métodos , Encéfalo/fisiologia , Eletroencefalografia/métodos , Potenciais Somatossensoriais Evocados/fisiologia , Modelos Animais , Rede Nervosa/fisiologia , Tato/fisiologia , Animais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Estimulação Física/métodosRESUMO
BACKGROUND: An increasing number of clinical observations suggest adverse neurologic outcome after methylene blue (MB) infusion in the setting of parathyroid surgery. Hence, the aim of the current study was to investigate the potentially neurotoxic effects of MB using a combination of in vivo and in vitro experimental approaches. METHODS: Isoflurane-anesthetized adult rats were used to evaluate the impact of a single bolus intravascular administration of MB on systemic hemodynamic responses and on the minimum alveolar concentration (MAC) of isoflurane using the tail clamp test. In vivo, MB-induced cell death was evaluated 24 h after MB administration using Fluoro-Jade B staining and activated caspase-3 immunohistochemistry. In vitro, neurotoxic effects of MB were examined in hippocampal slice cultures by measuring excitatory field potentials as well as propidium iodide incorporation after MB exposure. The impact of MB on dendritic arbor was evaluated in differentiated single cell neuronal cultures. RESULTS: Bolus injections of MB significantly reduced isoflurane MAC and initiated widespread neuronal apoptosis. Electrophysiologic recordings in hippocampal slices revealed a rapid suppression of evoked excitatory field potentials by MB, and this was associated with a dose-dependent effect of this drug on cell death. Dose-response experiments in single cell neuronal cultures revealed that a 2-h-long exposure to MB at non-cell-death-inducing concentrations could still induce significant retraction of dendritic arbor. CONCLUSIONS: These results suggest that MB exerts neurotoxic effects on the central nervous system and raise questions regarding the safety of using this drug at high doses during parathyroid gland surgery.