RESUMEN
Epileptic seizures induce aberrant neurogenesis from resident neural stem cells (NSCs) in the dentate gyrus of the adult mouse hippocampus, which has been implicated in depletion of the NSC pool and impairment of hippocampal function. However, the mechanisms regulating neurogenesis after seizures remain unknown. Here, we demonstrate that Sonic hedgehog (Shh) from mossy cells is a major source of Shh signaling activity after seizures, by which mossy cells contribute to seizure-induced neurogenesis and maintenance of the NSC pool. Deletion of Shh from mossy cells attenuates seizure-induced neurogenesis. Moreover, in the absence of Shh from mossy cells, NSCs pool are prematurely depleted after seizure-induced proliferation, and NSCs have impaired self-renewal. Likewise, lack of Shh from mossy cells accelerates age-related decline of the NSC pool with accompanying reduction of self-renewal of NSCs outside the context of pathology such as seizures. Together, our findings indicate that Shh from mossy cells is critical to maintain NSCs and to prevent exhaustion from excessive consumption in aging and after seizures.
Asunto(s)
Proteínas Hedgehog , Fibras Musgosas del Hipocampo , Ratones , Animales , Fibras Musgosas del Hipocampo/metabolismo , Proteínas Hedgehog/metabolismo , Hipocampo/metabolismo , Neurogénesis , Envejecimiento , ConvulsionesRESUMEN
The timing and specificity of oligodendrocyte myelination during development, as well as remyelination after injury or immune attack, remain poorly understood. Recent work has shown that oligodendrocyte progenitors receive synapses from neurons, providing a potential mechanism for neuronal-glial communication. In this study, we investigated the importance of these neuroglial connections in myelination during development and during neuronal plasticity in the mouse hippocampus. We used chemogenetic tools and viral monosynaptic circuit tracing to analyze these connections and to examine oligodendrocyte progenitor cells (OPCs) proliferation, myelination, synapse formation, and neuronal-glial connectivity in vivo after increasing or decreasing neuronal activity levels. We found that increasing neuronal activity led to greater OPC activation and proliferation. Modulation of neuronal activity also altered the organization of neuronal-glial connections: while it did not impact the total number of RabV-labeled neuronal inputs, or the number of RabV-labeled inhibitory neuronal (IN) inputs, it did alter the number of RabV-labeled excitatory neuron to OPC connections. Overall, our findings support the idea that neuronal activity plays a crucial role in regulating OPC proliferation and activation as well as the types of neuronal inputs to OPCs, indicating that neuronal activity is important for OPC circuit composition and function.
Asunto(s)
Células Precursoras de Oligodendrocitos , Ratones , Animales , Neuronas/fisiología , Neuroglía , Oligodendroglía , Neurogénesis , Diferenciación CelularRESUMEN
Epileptic seizures induce aberrant neurogenesis from resident neural stem cells (NSCs) in the dentate gyrus of the adult mouse hippocampus, which has been implicated in depletion of the NSC pool and impairment of hippocampal function. However, the mechanisms regulating neurogenesis after seizures remain unknown. Here we demonstrate that Shh from mossy cells is a major source of Shh signaling activity after seizures, by which mossy cells contribute to seizure-induced neurogenesis and maintenance of the NSC pool. Deletion of Shh from mossy cells attenuates seizure-induced neurogenesis. Moreover, in the absence of Shh from mossy cells, NSCs pool are prematurely depleted after seizure-induced proliferation, and NSCs have impaired self-renewal. Likewise, lack of Shh from mossy cells accelerates age-related decline of the NSC pool with accompanying reduction of self-renewal of NSCs outside the context of pathology such as seizures. Together, our findings indicate that Shh from mossy cells is critical to maintain NSCs and to prevent exhaustion from excessive consumption in aging and after seizures.
RESUMEN
The development of neuronal circuitry required for cognition, complex motor behaviors, and sensory integration requires myelination. The role of glial cells such as astrocytes and microglia in shaping synapses and circuits have been covered in other reviews in this journal and elsewhere. This review summarizes the role of another glial cell type, oligodendrocytes, in shaping synapse formation, neuronal circuit development, and myelination in both normal development and in demyelinating disease. Oligodendrocytes ensheath and insulate neuronal axons with myelin, and this facilitates fast conduction of electrical nerve impulses via saltatory conduction. Oligodendrocytes also proliferate during postnatal development, and defects in their maturation have been linked to abnormal myelination. Myelination also regulates the timing of activity in neural circuits and is important for maintaining the health of axons and providing nutritional support. Recent studies have shown that dysfunction in oligodendrocyte development and in myelination can contribute to defects in neuronal synapse formation and circuit development. We discuss glutamatergic and GABAergic receptors and voltage gated ion channel expression and function in oligodendrocyte development and myelination. We explain the role of excitatory and inhibitory neurotransmission on oligodendrocyte proliferation, migration, differentiation, and myelination. We then focus on how our understanding of the synaptic connectivity between neurons and OPCs can inform future therapeutics in demyelinating disease, and discuss gaps in the literature that would inform new therapies for remyelination.
RESUMEN
An attenuated rabies virus that expresses fluorescent protein has made it possible to analyze retrograde (presynaptic) monosynaptic connections in vivo. By combining attenuated rabies virus with a Cre-loxP based system to target cells in a subtype-specific fashion, it is possible to examine neuronal input in vivo onto any class of neuron, in development and in the mature brain. We describe here the methods to amplify deletion mutant, pseudotyped rabies virus, selectively target cells of interest using genetic and viral approaches, as well as the stereotaxic procedures required to target neuronal subtypes of interest in vivo.
Asunto(s)
Conectoma/métodos , Neuronas/fisiología , Neuronas/virología , Virus de la Rabia/fisiología , Sinapsis/fisiología , Animales , Transporte Biológico , Línea Celular , Expresión Génica , Genes Reporteros , Vectores Genéticos , Virus Helper/fisiología , Ratones , Microscopía Fluorescente , Sinapsis/virología , Tropismo Viral , Replicación ViralRESUMEN
The mammalian cerebral cortex is a dense network composed of local, subcortical, and intercortical synaptic connections. As a result, mapping cell type-specific neuronal connectivity in the cerebral cortex in vivo has long been a challenge for neurobiologists. In particular, the development of excitatory and inhibitory interneuron presynaptic input has been hard to capture. We set out to analyze the development of this connectivity in the first postnatal month using a murine model. First, we surveyed the connectivity of one of the earliest populations of neurons in the brain, the Cajal-Retzius (CR) cells in the neocortex, which are known to be critical for cortical layer formation and are hypothesized to be important in the establishment of early cortical networks. We found that CR cells receive inputs from deeper-layer excitatory neurons and inhibitory interneurons in the first postnatal week. We also found that both excitatory pyramidal neurons and inhibitory interneurons received broad inputs in the first postnatal week, including inputs from CR cells. Expanding our analysis into the more mature brain, we assessed the inputs onto inhibitory interneurons and excitatory projection neurons, labeling neuronal progenitors with Cre drivers to study discrete populations of neurons in older cortex, and found that excitatory cortical and subcortical inputs are refined by the fourth week of development, whereas local inhibitory inputs increase during this postnatal period. Cell type-specific circuit mapping is specific, reliable, and effective, and can be used on molecularly defined subtypes to determine connectivity in the cortex. SIGNIFICANCE STATEMENT: Mapping cortical connectivity in the developing mammalian brain has been an intractable problem, in part because it has not been possible to analyze connectivity with cell subtype precision. Our study systematically targets the presynaptic connections of discrete neuronal subtypes in both the mature and developing cerebral cortex. We analyzed the connections that Cajal-Retzius cells make and receive, and found that these cells receive inputs from deeper-layer excitatory neurons and inhibitory interneurons in the first postnatal week. We assessed the inputs onto inhibitory interneurons and excitatory projection neurons, the major two types of neurons in the cortex, and found that excitatory inputs are refined by the fourth week of development, whereas local inhibitory inputs increase during this postnatal period.
Asunto(s)
Corteza Cerebral/citología , Corteza Cerebral/crecimiento & desarrollo , Red Nerviosa/fisiología , Neuronas/clasificación , Neuronas/fisiología , Terminales Presinápticos/fisiología , Factores de Edad , Animales , Animales Recién Nacidos , Mapeo Encefálico , Embrión de Mamíferos , Femenino , Interneuronas/fisiología , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Masculino , Ratones , Ratones Transgénicos , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Organogénesis/fisiología , Transducción Genética , Proteínas del Envoltorio Viral/genética , Proteínas del Envoltorio Viral/metabolismoRESUMEN
During embryogenesis, the pallial-subpallial boundary (PSB) divides the two main progenitor domains in the telencephalon: the pallium, the major source of excitatory neurons, and the subpallium, the major source of inhibitory neurons. The PSB is formed at the molecular interface between the pallial (high Pax6+) and subpallial (high Gsx2+) ventricular zone (VZ) compartments. Initially, the PSB contains cells that express both Pax6 and Gsx2, but during later stages of development this boundary is largely refined into two separate compartments. In this study we examined the developmental mechanisms underlying PSB boundary formation and the postnatal consequences of conditional loss of Pax6 function at the PSB on neuronal fate in the amygdala and olfactory bulb, two targets of PSB-derived migratory populations. Our cell fate and time-lapse imaging analyses reveal that the sorting of Pax6+ and Gsx2+ progenitors during embryogenesis is the result of a combination of changes in gene expression and cell movements. Interestingly, we find that in addition to giving rise to inhibitory neurons in the amygdala and olfactory bulb, Gsx2+ progenitors generate a subpopulation of amygdala excitatory neurons. Consistent with this finding, targeted conditional ablation of Pax6 in Gsx2+ progenitors results in discrete local embryonic patterning defects that are linked to changes in the generation of subsets of postnatal excitatory and inhibitory neurons in the amygdala and inhibitory neurons in the olfactory bulb. Thus, in PSB progenitors, Pax6 plays an important role in the generation of multiple subtypes of neurons that contribute to the amygdala and olfactory bulb.
Asunto(s)
Proteínas del Ojo/metabolismo , Regulación del Desarrollo de la Expresión Génica/fisiología , Proteínas de Homeodominio/metabolismo , Sistema Límbico/citología , Sistema Límbico/crecimiento & desarrollo , Proteínas del Tejido Nervioso/genética , Neuronas/metabolismo , Factores de Transcripción Paired Box/metabolismo , Proteínas Represoras/metabolismo , Animales , Animales Recién Nacidos , Proteínas Bacterianas/genética , Embrión de Mamíferos , Proteínas del Ojo/genética , Regulación del Desarrollo de la Expresión Génica/genética , Proteínas de Homeodominio/genética , Proteínas Luminiscentes/genética , Proteínas de la Membrana/metabolismo , Ratones , Ratones Transgénicos , Proteínas del Tejido Nervioso/metabolismo , Vías Nerviosas , Neuronas/clasificación , Factor de Transcripción PAX6 , Factores de Transcripción Paired Box/genética , Técnicas de Placa-Clamp , Proteínas Represoras/genética , Telencéfalo , Imagen de Lapso de Tiempo/métodos , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
In the developing mammalian basal telencephalon, neural progenitors from the subpallium generate the majority of inhibitory medium spiny neurons (MSNs) in the striatum, while both pallial- and subpallial-derived progenitors contribute to excitatory and inhibitory neuronal diversity in the amygdala. Using a combination of approaches, including genetic fate mapping, cell birth dating, cell migration assays, and electrophysiology, we find that cells derived from the Emx1 lineage contribute to two distinct neuronal populations in the mature basal forebrain: inhibitory MSNs in the striatum and functionally distinct subclasses of excitatory neurons in the amygdala. Our cell birth-dating studies reveal that these two populations are born at different times during early neurogenesis, with the amygdala population born before the MSNs. In the striatum, Emx1-lineage neurons represent a unique subpopulation of MSNs: they are disproportionately localized to the dorsal striatum, are found in dopamine receiving, reelin-positive patches, and are born throughout striatal neurogenesis. In addition, our data suggest that a subpopulation of these Emx1-lineage cells originate in the pallium and subsequently migrate to the developing striatum and amygdala. Our intersectional fate-mapping analysis further reveals that Emx1-lineage cells that coexpress Dlx exclusively generate MSNs but do not contribute to the excitatory neurons in the amygdala. Thus, both the timing of neurogenesis and differential combinatorial gene expression appear to be key determinants of striatal versus amygdala fate decisions of Emx1-lineage cells.
Asunto(s)
Amígdala del Cerebelo/fisiología , Diferenciación Celular/fisiología , Linaje de la Célula/fisiología , Cuerpo Estriado/fisiología , Proteínas de Homeodominio/fisiología , Células Madre/fisiología , Factores de Transcripción/fisiología , Amígdala del Cerebelo/citología , Amígdala del Cerebelo/embriología , Animales , Diferenciación Celular/genética , Linaje de la Célula/genética , Cuerpo Estriado/citología , Cuerpo Estriado/embriología , Femenino , Proteínas de Homeodominio/biosíntesis , Proteínas de Homeodominio/genética , Ratones , Ratones Endogámicos C57BL , Neurogénesis/genética , Neurogénesis/fisiología , Neuronas/clasificación , Neuronas/citología , Neuronas/fisiología , Embarazo , Proteína Reelina , Células Madre/clasificación , Células Madre/citología , Factores de Transcripción/biosíntesis , Factores de Transcripción/genéticaRESUMEN
The development of the amygdala, a central structure of the limbic system, remains poorly understood. We found that two spatially distinct and early-specified telencephalic progenitor pools marked by the homeodomain transcription factor Dbx1 are major sources of neuronal cell diversity in the mature mouse amygdala. We found that Dbx1-positive cells of the ventral pallium generate the excitatory neurons of the basolateral complex and cortical amygdala nuclei. Moreover, Dbx1-derived cells comprise a previously unknown migratory stream that emanates from the preoptic area (POA), a ventral telencephalic domain adjacent to the diencephalic border. The Dbx1-positive, POA-derived population migrated specifically to the amygdala and, as defined by both immunochemical and electrophysiological criteria, generated a unique subclass of inhibitory neurons in the medial amygdala nucleus. Thus, this POA-derived population represents a previously unknown progenitor pool dedicated to the limbic system.
Asunto(s)
Amígdala del Cerebelo/citología , Amígdala del Cerebelo/embriología , Proteínas de Homeodominio/metabolismo , Neuronas/citología , Nicho de Células Madre/citología , Células Madre/citología , Amígdala del Cerebelo/fisiología , Animales , Movimiento Celular/fisiología , Femenino , Técnicas de Sustitución del Gen , Proteínas de Homeodominio/genética , Integrasas/genética , Operón Lac , Masculino , Potenciales de la Membrana/fisiología , Ratones , Ratones Mutantes , Ratones Transgénicos , Inhibición Neural/fisiología , Técnicas de Placa-Clamp , Embarazo , Área Preóptica/citología , Área Preóptica/embriología , Área Preóptica/fisiología , Nicho de Células Madre/fisiología , Células Madre/fisiologíaRESUMEN
In the embryonic telencephalon, the pallial-subpallial boundary (PSB) separates the dorsal Pax6+ pallium from the ventral Gsh2+ subpallium. Previous studies have revealed that this region is a source of cells that will populate both the olfactory bulb and basal telencephalic limbic system. However, the level of progenitor cell heterogeneity and developmental genetic regulation of this progenitor region remains to be fully elucidated. In this study we carried out a comprehensive analysis of gene expression patterns at the PSB, in addition to an examination of the combinatorial function of Pax6 and Gsh2 in the specification of the PSB. First, we reveal that the PSB is comprised of a complex mix of molecularly distinct progenitor pools. In addition, by analysis of single Sey, Gsh2, and Sey/Gsh2 double mutant mice, we demonstrate that both Pax6 and Gsh2 are directly required for major aspects of PSB progenitor specification. Our analysis also reveals that the establishment of the epidermal growth factor receptor positive lateral cortical stream migratory route to the basal telencephalon is Pax6 dependent. Thus, in addition to their well-characterized cross-repressive roles in dorsal/ventral patterning our analyses reveal important novel functions of Gsh2 and Pax6 in the regulation of PSB progenitor pool specification and patterning.
Asunto(s)
Tipificación del Cuerpo/fisiología , Movimiento Celular/fisiología , Proteínas del Ojo/fisiología , Globo Pálido/fisiología , Proteínas de Homeodominio/fisiología , Factores de Transcripción Paired Box/fisiología , Proteínas Represoras/fisiología , Telencéfalo/fisiología , Animales , Receptores ErbB/fisiología , Femenino , Globo Pálido/citología , Globo Pálido/embriología , Masculino , Ratones , Ratones Noqueados , Ratones Transgénicos , Neuronas/citología , Neuronas/metabolismo , Neuronas/fisiología , Factor de Transcripción PAX6 , Embarazo , Células Madre/citología , Células Madre/metabolismo , Células Madre/fisiología , Telencéfalo/citología , Telencéfalo/embriologíaRESUMEN
Two studies of 5-month-old infants explored whether a phenomenon reported by K. Wynn (1992) reflects a familiarity preference instead of a mathematical competence. Experiment 1 was a conceptual replication of Wynn's study. When data were analyzed with the relatively liberal statistical approach used by Wynn, the original phenomenon was replicated. However, an analysis of variance revealed that girls and boys behaved in different ways, and that boys did not behave as Wynn would have predicted. Experiment 2 was identical to Experiment 1, with one exception that should not have influenced computation: Infants in this study were completely familiarized with the test displays before testing. Again, the data revealed an interaction involving sex: Boys tended to be influenced by their familiarity with the test displays, whereas girls tended to behave as Wynn would have predicted. These findings are discussed with reference to the literature on sex differences--specifically the finding that male infants are typically immature relative to their female peers--as well as to articles that have been critical or supportive of Wynn's conclusions.