RESUMEN
The long-term response to chronic stress is variable, with some individuals developing maladaptive functioning, although other "resilient" individuals do not. Stress reduces neurogenesis in the dentate gyrus subgranular zone (SGZ), but it is unknown if stress-induced changes in neurogenesis contribute to individual vulnerability. Using a chronic social defeat stress model, we explored whether the susceptibility to stress-induced social avoidance was related to changes in SGZ proliferation and neurogenesis. Immediately after social defeat, stress-exposed mice (irrespective of whether they displayed social avoidance) had fewer proliferating SGZ cells labeled with the S-phase marker BrdU. The decrease was transient, because BrdU cell numbers were normalized 24 h later. The survival of BrdU cells labeled before defeat stress was also not altered. However, 4 weeks later, mice that displayed social avoidance had more surviving dentate gyrus neurons. Thus, dentate gyrus neurogenesis is increased after social defeat stress selectively in mice that display persistent social avoidance. Supporting a functional role for adult-generated dentate gyrus neurons, ablation of neurogenesis via cranial ray irradiation robustly inhibited social avoidance. These data show that the time window after cessation of stress is a critical period for the establishment of persistent cellular and behavioral responses to stress and that a compensatory enhancement in neurogenesis is related to the long-term individual differences in maladaptive responses to stress.
Asunto(s)
Reacción de Prevención , Hipocampo/patología , Neurogénesis , Estrés Psicológico/patología , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Bromodesoxiuridina/metabolismo , Muerte Celular , Hipocampo/metabolismo , Masculino , Ratones , Fase S , Transducción de SeñalRESUMEN
Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.
RESUMEN
The innate immune response plays a critical role in traumatic brain injury (TBI), contributing to ongoing pathogenesis and worsening long-term outcomes. Here we focus on neutrophils, one of the "first responders" to TBI. These leukocytes are recruited to the injured brain where they release a host of toxic molecules including free radicals, proteases, and pro-inflammatory cytokines, all of which promote secondary tissue damage. There is mounting evidence that the developing brain is more vulnerable to injury that the adult brain. This vulnerability to greater damage from TBI is, in part, attributed to relatively low antioxidant reserves coupled with an early robust immune response. The latter is reflected in enhanced sensitivity to cytokines and a prolonged recruitment of neutrophils into both cortical and subcortical regions. This review considers the contribution of neutrophils to early secondary pathogenesis in the injured developing brain and raises the distinct possibility that these leukocytes, which exhibit phenotypic plasticity, may also be poised to support wound healing. We provide a basic review of the development, life cycle, and granular contents of neutrophils and evaluate their potential as therapeutic targets for early neuroprotection and functional recovery after injury at early age. While neutrophils have been broadly studied in neurotrauma, we are only beginning to appreciate their diverse roles in the developing brain and the extent to which their acute manipulation may result in enduring neurological recovery when TBI is superimposed upon brain development.
Asunto(s)
Lesiones Traumáticas del Encéfalo/inmunología , Lesiones Traumáticas del Encéfalo/patología , Infiltración Neutrófila , Neutrófilos/patología , Recuperación de la Función/inmunología , Adolescente , Animales , Niño , Preescolar , Humanos , Lactante , Recién Nacido , Neutrófilos/inmunologíaRESUMEN
Understanding the fate of adult-generated neurons and the mechanisms that influence them requires consistent labeling and tracking of large numbers of stem cells. We generated a nestin-CreER(T2)/R26R-yellow fluorescent protein (YFP) mouse to inducibly label nestin-expressing stem cells and their progeny in the adult subventricular zone (SVZ) and subgranular zone (SGZ). Several findings show that the estrogen ligand tamoxifen (TAM) specifically induced recombination in stem cells and their progeny in nestin-CreER(T2)/R26R-YFP mice: 97% of SGZ stem-like cells (GFAP/Sox2 with radial glial morphology) expressed YFP; YFP+ neurospheres could be generated in vitro after recombination in vivo, and maturing YFP+ progeny were increasingly evident in the olfactory bulb (OB) and dentate gyrus (DG) granule cell layer. Revealing an unexpected regional dissimilarity in adult neurogenesis, YFP+ cells accumulated up to 100 d after TAM in the OB, but in the SGZ, YFP+ cells reached a plateau 30 d after TAM. In addition, most SVZ and SGZ YFP+ cells became neurons, underscoring a link between nestin and neuronal fate. Finally, quantification of YFP+ cells in nestin-CreER(T2)/R26R-YFP mice allowed us to estimate, for example, that stem cells and their progeny contribute to no more than 1% of the adult DG granule cell layer. In addition to revealing the dynamic contribution of nestin-expressing stem cells to adult neurogenesis, this work highlights the utility of the nestin-CreER(T2)/R26R-YFP mouse for inducible gene ablation in stem cells and their progeny in vivo in the two major regions of adult neurogenesis.
Asunto(s)
Encéfalo/metabolismo , Diferenciación Celular/fisiología , Linaje de la Célula/fisiología , Proteínas de Filamentos Intermediarios/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuronas/metabolismo , Células Madre/metabolismo , Animales , Encéfalo/citología , Diferenciación Celular/efectos de los fármacos , Linaje de la Célula/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Giro Dentado/citología , Giro Dentado/metabolismo , Marcación de Gen/métodos , Proteínas Luminiscentes/genética , Proteínas Luminiscentes/metabolismo , Ratones , Ratones Transgénicos , Modelos Animales , Regeneración Nerviosa/efectos de los fármacos , Regeneración Nerviosa/fisiología , Nestina , Neuroglía/citología , Neuroglía/efectos de los fármacos , Neuroglía/metabolismo , Bulbo Olfatorio/citología , Bulbo Olfatorio/metabolismo , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Recombinación Genética/efectos de los fármacos , Recombinación Genética/genética , Moduladores Selectivos de los Receptores de Estrógeno/farmacología , Células Madre/efectos de los fármacos , Tamoxifeno/farmacologíaRESUMEN
Brain-derived neurotrophic factor (BDNF) is implicated in the regulation of adult hippocampal neurogenesis, presumably via its primary receptor, TrkB. However, controversy exists about how BDNF affects neurogenesis (e.g., proliferation vs. survival/differentiation). This controversy arises, in part, due to the lack of information about whether and when TrkB is expressed on adult neural precursors in vivo. We utilized multiple methods to analyze proliferating and maturing cells in the adult mouse subgranular zone (SGZ) for TrkB protein. Using bromodeoxyuridine (BrdU) to "birthdate" cells, we found that the proportion of proliferating cells that were TrkB-immunoreactive (IR) was low and remained low for at least 1 week, but increased with further survival after BrdU labeling. Use of the nestin-GFP transgenic mouse and the immature neuron marker, doublecortin (Dcx), revealed that the likelihood of being TrkB-IR increased with presumed maturity of the cell type. Stem-like cells, which rarely divide, were likely to express TrkB protein. However, early progenitors (GFP+/Dcx-) and late progenitors (GFP+/Dcx+), both of which are still in the cell cycle, were unlikely to be TrkB-IR. Immature neuroblasts (GFP-/Dcx+) were more likely to express TrkB, especially as they presented a more mature morphology. Taken together, these findings emphasize that expression of TrkB protein is closely linked to progression toward neuronal maturity. This provides evidence that maturing, but not proliferating, cells in the adult mouse SGZ have the molecular machinery necessary to respond directly to BDNF. Furthermore, these findings lay critical groundwork for further exploration of the role of BDNF-TrkB signaling in regulation of adult hippocampal neurogenesis.
Asunto(s)
Giro Dentado/crecimiento & desarrollo , Giro Dentado/metabolismo , Neuronas/citología , Neuronas/metabolismo , Receptor trkB/biosíntesis , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Bromodesoxiuridina , Diferenciación Celular , Proliferación Celular , Proteína Doblecortina , Proteínas Fluorescentes Verdes/genética , Inmunohistoquímica , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Microscopía Confocal , Células Madre/citología , Células Madre/metabolismoRESUMEN
Abnormal subgranular zone (SGZ) neurogenesis is proposed to contribute to Alzheimer's disease (AD)-related decreases in hippocampal function. Our goal was to examine hippocampal neurogenesis in the PDAPP mouse, a model of AD with age-dependent accumulation of amyloid-beta(42) (Abeta(42))-containing plaques that is well studied with regard to AD therapies. A secondary goal was to determine whether altered neurogenesis in the PDAPP mouse is associated with abnormal maturation or number of mature cells. A tertiary goal was to provide insight into why hippocampal neurogenesis appears to be increased in AD post-mortem tissue and decreased in most AD mouse models. We report an age-dependent decrease in SGZ proliferation in homozygous PDAPP mice. At 1 year of age, PDAPP mice also had new dentate gyrus granule neurons with abnormal maturation and fewer dying cells relative to control mice. In contrast to decreased SGZ cell birth, PDAPP mice had increased birth of immature neurons in the outer portion of the granule cell layer (oGCL), providing insight into why some studies link AD with increased neurogenesis. However, these ectopic oGCL cells were still rare compared with SGZ proliferating cells, emphasizing that the primary characteristic of PDAPP mice is decreased neurogenesis. The decrease in SGZ neurogenesis was not associated with an age-dependent loss of dentate granule neurons. The altered neurogenesis in the PDAPP mouse may contribute to the age-related cognitive deficits reported in this model of AD and may be a useful adjunct target for assessing the impact of AD therapies.
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Envejecimiento/patología , Enfermedad de Alzheimer/fisiopatología , Péptidos beta-Amiloides/metabolismo , Precursor de Proteína beta-Amiloide/metabolismo , Proliferación Celular , Giro Dentado/fisiopatología , Plasticidad Neuronal/genética , Fragmentos de Péptidos/metabolismo , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/metabolismo , Animales , Apoptosis/genética , Diferenciación Celular/genética , División Celular/genética , Supervivencia Celular/genética , Modelos Animales de Enfermedad , Femenino , Predisposición Genética a la Enfermedad/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos DBA , Ratones Mutantes Neurológicos , Ratones Transgénicos , Mutación/genética , Placa Amiloide/genética , Placa Amiloide/metabolismo , Placa Amiloide/patologíaRESUMEN
Depression and anxiety involve hippocampal dysfunction, but the specific relationship between these mood disorders and adult hippocampal dentate gyrus neurogenesis remains unclear. In both humans with MDD and rodent models of depression, administration of antidepressants increases DG progenitor and granule cell number, yet rodents with induced ablation of DG neurogenesis typically do not demonstrate depressive- or anxiety-like behaviors. The conflicting data may be explained by the varied duration and degree to which adult neurogenesis is reduced in different rodent neurogenesis ablation models. In order to test this hypothesis we examined how a transient-rather than permanent-inducible reduction in neurogenesis would alter depressive- and anxiety-like behaviors. Transgenic Nestin-CreERT2/floxed diphtheria toxin fragment A (DTA) mice (Cre+DTA+) and littermates (Cre+DTA-; control) were given tamoxifen (TAM) to induce recombination and decrease nestin-expressing stem cells and their progeny. The decreased neurogenesis was transient: 12 days post-TAM Cre+DTA+ mice had fewer DG proliferating Ki67+ cells and fewer DCX+ neuroblasts/immature neurons relative to control, but 30 days post-TAM Cre+DTA+ mice had the same DCX+ cell number as control. This ability of DG neurogenesis to recover after partial ablation also correlated with changes in behavior. Relative to control, Cre+DTA+ mice tested between 12-30 days post-TAM displayed indices of a stress-induced anxiety phenotype-longer latency to consume highly palatable food in the unfamiliar cage in the novelty-induced hypophagia test, and a depression phenotype-longer time of immobility in the tail suspension test, but Cre+DTA+ mice tested after 30 days post-TAM did not. These findings suggest a functional association between adult neurogenesis and stress induced anxiety- and depressive-like behaviors, where induced reduction in DCX+ cells at the time of behavioral testing is coupled with stress-induced anxiety and a depressive phenotype, and recovery of DCX+ cell number corresponds to normalization of these behaviors.
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Trastornos de Ansiedad/etiología , Depresión/etiología , Toxina Diftérica/genética , Hipocampo/patología , Nestina/fisiología , Neurogénesis , Neuronas/patología , Fragmentos de Péptidos/genética , Estrés Fisiológico , Animales , Conducta Animal , Proteína Doblecortina , Femenino , Hipocampo/metabolismo , Integrasas/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/metabolismo , FenotipoRESUMEN
Maintenance of energy balance requires regulation of the amount and timing of food intake. Decades of experiments utilizing pharmacological and later genetic manipulations have demonstrated the importance of serotonin signaling in this regulation. Much progress has been made in recent years in understanding how central nervous system (CNS) serotonin systems acting through a diverse array of serotonin receptors impact feeding behavior and metabolism. Particular attention has been paid to mechanisms through which serotonin impacts energy balance pathways within the hypothalamus. How upstream factors relevant to energy balance regulate the release of hypothalamic serotonin is less clear, but work addressing this issue is underway. Generally, investigation into the central serotonergic regulation of energy balance has had a predominantly "hypothalamocentric" focus, yet non-hypothalamic structures that have been implicated in energy balance regulation also receive serotonergic innervation and express multiple subtypes of serotonin receptors. Moreover, there is a growing appreciation of the diverse mechanisms through which peripheral serotonin impacts energy balance regulation. Clearly, the serotonergic regulation of energy balance is a field characterized by both rapid advances and by an extensive and diverse set of central and peripheral mechanisms yet to be delineated.