Neurogenesis response of middle-aged hippocampus to acute seizure activity

Acute Seizure (AS) activity in young adult age conspicuously modifies hippocampal neurogenesis. This is epitomized by both increased addition of new neurons to the granule cell layer (GCL) by neural stem/progenitor cells (NSCs) in the dentate subgranular zone (SGZ), and greatly enhanced numbers of newly born neurons located abnormally in the dentate hilus (DH). Interestingly, AS activity in old age does not induce such changes in hippocampal neurogenesis. However, the effect of AS activity on neurogenesis in the middle-aged hippocampus is yet to be elucidated. We examined hippocampal neurogenesis in middle-aged F344 rats after a continuous AS activity for >4 hrs, induced through graded intraperitoneal injections of the kainic acid. We labeled newly born cells via daily intraperitoneal injections of the 5'-bromodeoxyuridine (BrdU) for 12 days, commencing from the day of induction of AS activity. AS activity enhanced the addition of newly born BrdU+ cells by 5.6 fold and newly born neurons (expressing both BrdU and doublecortin [DCX]) by 2.2 fold to the SGZ-GCL. Measurement of the total number of DCX+ newly born neurons also revealed a similar trend. Furthermore, AS activity increased DCX+ newly born neurons located ectopically in the DH (2.7 fold increase and 17% of total newly born neurons). This rate of ectopic migration is however considerably less than what was observed earlier for the young adult hippocampus after similar AS activity. Thus, the plasticity of hippocampal neurogenesis to AS activity in middle age is closer to its response observed in the young adult age. However, the extent of abnormal migration of newly born neurons into the DH is less than that of the young adult hippocampus after similar AS activity. These results also point out a highly divergent response of neurogenesis to AS activity between middle age and old age.     

Zinc chelation reduces traumatic brain injury-induced neurogenesis in the subgranular zone of the hippocampal dentate gyrus

Numerous studies have demonstrated that traumatic brain injury (TBI) increases hippocampal neurogenesis in the rodent brain. However, the mechanisms underlying increased neurogenesis after TBI remain unknown. Continuous neurogenesis occurs in the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG) in the adult brain. The mechanism that maintains active neurogenesis in the hippocampal area is not known. A high level of vesicular zinc is localized in the presynaptic terminals of the SGZ (mossy fiber). The mossy fiber of dentate granular cells contains high levels of chelatable zinc in their terminal vesicles, which can be released into the extracellular space during neuronal activity. Previously, our lab presented findings indicating that a possible correlation may exist between synaptic zinc localization and high rates of neurogenesis in this area after hypoglycemia or epilepsy. Using a weight drop animal model to mimic human TBI, we tested our hypothesis that zinc plays a key role in modulating hippocampal neurogenesis after TBI. Thus, we injected a zinc chelator, clioquinol (CQ, 30 mg/kg), into the intraperitoneal space to reduce brain zinc availability twice per day for 1 week. Neuronal death was evaluated with Fluoro Jade-B and NeuN staining to determine whether CQ has neuroprotective effects after TBI. The number of degenerating neurons (FJB (+)) and live neurons (NeuN (+)) was similar in vehicle and in CQ-treated rats at 1 week after TBI. Neurogenesis was evaluated using BrdU, Ki67 and doublecortin (DCX) immunostaining 1 week after TBI. The number of BrdU, Ki67 and DCX positive cell was increased after TBI. However, the number of BrdU, Ki67 and DCX positive cells was significantly decreased by CQ treatment. The present study shows that zinc chelation did not prevent neurodegeneration but did reduce TBI-induced progenitor cell proliferation and neurogenesis. Therefore, this study suggests that zinc has an essential role for modulating hippocampal neurogenesis after TBI.     

Tanshinone I Enhances Neurogenesis in the Mouse Hippocampal Dentate Gyrus via Increasing Wnt-3, Phosphorylated Glycogen Synthase Kinase-3β and β-Catenin Immunoreactivities

Tanshinone I (TsI), a lipophilic diterpene extracted from Danshan (Radix Salvia miltiorrhizae), exerts neuroprotection in cerebrovascular diseases including transient ischemic attack. In this study, we examined effects of TsI on cell proliferation and neuronal differentiation in the subgranular zone (SGZ) of the mouse dentate gyrus (DG) using Ki-67, BrdU and doublecortin (DCX) immunohistochemistry. Mice were treated with 1 and 2 mg/kg TsI for 28 days. In the 1 mg/kg TsI-treated-group, distribution patterns of BrdU, Ki-67 and DCX positive (⁺) cells in the SGZ were similar to those in the vehicle-treated-group. However, in the 2 mg/kg TsI-treated-group, double labeled BrdU⁺/NeuN⁺ cells, which are mature neurons, as well as Ki-67⁺, DCX⁺ and BrdU⁺ cells were significantly increased compared with those in the vehicle-treated-group. On the other hand, immunoreactivities and protein levels of Wnt-3, β-catenin and serine-9-glycogen synthase kinase-3β (p-GSK-3β), which are related with morphogenesis, were significantly increased in the granule cell layer of the DG only in the 2 mg/kg TsI-treated-group. Therefore, these findings indicate that TsI can promote neurogenesis in the mouse DG and that the neurogenesis is related with increases of Wnt-3, p-GSK-3β and β-catenin immunoreactivities.     

Neurogenesis and aging: FGF-2 and HB-EGF restore neurogenesis in hippocampus and subventricular zone of aged mice

Neurogenesis, which may contribute to the ability of the adult brain to function normally and adapt to disease, nevertheless declines with advancing age. Adult neurogenesis can be enhanced by administration of growth factors, but whether the aged brain remains responsive to these factors is unknown. We compared the effects of intracerebroventricular fibroblast growth factor (FGF)-2 and heparin-binding epidermal growth factor-like growth factor (HB-EGF) on neurogenesis in the hippocampal dentate subgranular zone (SGZ) and the subventricular zone (SVZ) of young adult (3-month) and aged (20-month) mice. Neurogenesis, measured by labelling with bromodeoxyuridine (BrdU) and by expression of doublecortin, was reduced by approximately 90% in SGZ and by approximately 50% in SVZ of aged mice. HB-EGF increased BrdU labelling in SGZ at 3 months by approximately 60% and at 20 months by approximately 450%, which increased the number of BrdU-labelled cells in SGZ of aged mice to approximately 25% of that in young adults. FGF-2 also stimulated BrdU labelling in SGZ, by approximately 25% at 3 months and by approximately 250% at 20 months, increasing the number of newborn neurones in older mice to approximately 20% of that in younger mice. In SVZ, HB-EGF and FGF-2 increased BrdU incorporation by approximately 140% at 3 months and approximately 170% at 20 months, so the number of BrdU-labelled cells was comparable in untreated 3-month-old and growth factor-treated 20-month-old mice. These results demonstrate that the aged brain retains the capacity to respond to exogenous growth factors with increased neurogenesis, which may have implications for the therapeutic potential of neurogenesis enhancement in age-associated neurological disorders.     

Plasticity of hippocampal stem/progenitor cells to enhance neurogenesis in response to kainate-induced injury is lost by middle age

A remarkable up-regulation of neurogenesis through increased proliferation of neural stem/progenitor cells (NSCs) is a well-known plasticity displayed by the young dentate gyrus (DG) following brain injury. To ascertain whether this plasticity is preserved during aging, we quantified DG neurogenesis in the young adult, middle-aged and aged F344 rats after kainic acid induced hippocampal injury. Measurement of new cells that are added to the dentate granule cell layer (GCL) between post-injury days 4 and 15 using 5'-bromodeoxyuridine labeling revealed an increased addition of new cells in the young DG but not in the middle-aged and aged DG. Quantification of newly born neurons using doublecortin immunostaining also demonstrated a similar trend. Furthermore, the extent of ectopic migration of new neurons into the dentate hilus was dramatically increased in the young DG but was unaltered in the middle-aged and aged DG. However, there was no change in neuronal fate-choice decision of newly born cells following injury in all age groups. Similarly, comparable fractions of new cells that are added to the GCL after injury exhibited 5-month survival and expressed the mature neuronal marker NeuN, regardless of age or injury at the time of their birth. Thus, hippocampal injury does not adequately stimulate NSCs in the middle-aged and aged DG, resulting in no changes in neurogenesis after injury. Interestingly, rates of both neuronal fate-choice decision and long-term survival of newly born cells remain stable with injury in all age groups. These results underscore that the ability of the DG to increase neurogenesis after injury is lost as early as middle age.     

Effects of <Emphasis Type="Italic">Melissa officinalis</Emphasis> L. (Lemon Balm) Extract on Neurogenesis Associated with Serum Corticosterone and GABA in the Mouse Dentate Gyrus

Lemon balm, leaves of Melissa officinalis L., has been used for anti-anxiety and spasmolytics. We observed the extract of Melissa officinalis L. (MOE) on cell proliferation and neuroblast differentiation in the hippocampal dentate gyrus (DG) of middle-aged mice (12 months of age) using Ki67 and doublecortin (DCX), respectively. We also observed changes in corticosterone, GAD67 and GABA-transaminase (GABA-T) to check their possible mechanisms related to neurogenesis. We administered 50 or 200 mg/kg MOE to the animals once a day for 3 weeks. For labeling of newly generated cells, we also administered 5-bromodeoxyuridine (BrdU) twice a day for 3 days from the day of the first MOE treatment. Administration of 50 or 200 mg/kg MOE dose-dependently increased Ki67 positive nuclei to 244.1 and 763.9% of the vehicle-treated group, respectively. In addition, 50 or 200 mg/kg MOE significantly increased DCX positive neuroblasts with well-developed (tertiary) dendrites. Furthermore, MOE administration significantly increased BrdU/calbindin D-28 k double labeled cells (integrated neurons into granule cells in the DG) to 245.2% of the vehicle-treated group. On the other hand, administration of MOE reduced corticosterone levels in serum and decreased GABA-T levels in the DG homogenates. These results suggest that MOE increases cell proliferation, neuroblast differentiation and integration into granule cells by decreasing serum corticosterone levels as well as by increasing GABA levels in the mouse DG.     

Stroke-induced progenitor cell proliferation in adult spontaneously hypertensive rat brain: effect of exogenous IGF-1 and GDNF

Progenitor cells in the dentate gyrus of hippocampus (DG) and the subventricular zone of lateral ventricles (SVZ) generate new neurons throughout the life of mammals. Cerebral ischemia increases this basal progenitor cell proliferation. The present study evaluated the time frame of proliferation, length of survival and the phenotypes of the new cells formed after transient middle cerebral artery occlusion (MCAO) in adult spontaneously hypertensive rats. Compared to sham controls, ischemic rats showed a significantly higher number of newly proliferated cells (as defined by BrdU immunostaining) in both the DG (by fourfold, p < 0.05) and the SVZ (by twofold, p < 0.05). DG showed increased proliferation only in the first week of reperfusion and 49% of the cells formed in this period survived to the end of third week. Whereas, SVZ showed a continuous proliferation up to 3 weeks after MCAO, but the cells formed survived for less than a week. In both DG and SVZ, at the end of the first week of reperfusion, majority of the BrdU-positive (BrdU+) cells were immature neurons (DCX positive). In the DG, 28% of the cells formed in the first week after MCAO mature into neurons (NeuN positive). The ischemic cortex and striatum showed several BrdU+ cells which were ED-1 positive microglia/macrophages. At 1 week of reperfusion, MCAO-induced progenitor cell proliferation in the ipsilateral DG was significantly increased by i.c.v. infusion of IGF-1 (by 127 +/- 14%, p < 0.05) and GDNF (by 91 +/- 5%, p < 0.05), compared to vehicle. In the growth factor treated rats subjected to transient MCAO, several BrdU+ cells formed in the first week survived up to the third week.     

Age-dependent changes in the subcallosal zone neurogenesis of mice

There are several known neurogenic areas including subventricular zone and subgranular layer in the dentate gyrus of the hippocampus. Both germinal centers exhibit an age-dependent decline in cell proliferation and neurogenesis, which may be associated with age-related decline in brain function. We recently identified the subcallosal zone (SCZ) as a novel neural stem cell niche with a potential to spontaneously produce new neuroblasts. We examined whether SCZ neurogenesis is also regulated by the age of mice. The number of newly generated neuroblasts was reduced in the SCZ with age, and only marginal number of DCX-labeled neuroblasts was found in 6-month-old SCZ, which is most likely due to reduced proliferation of progenitor cells and loss of neural stem cells (NSCs). This age-dependent changes in the SCZ occurred earlier than that of other neurogenic brain regions. The neurosphere assay in vitro confirmed the depletion of NSCs within the SCZ of young adults. However, marked induction of neuroblast production in the SCZ was seen in 6-month-old mice after traumatic brain injury. Taken together, these results indicate that a rapid decline in SCZ neurogenesis in mice is due to depletion of NSCs and reduced capacity to produce neuroblasts.     

When Are New Hippocampal Neurons,Born in the Adult Brain,Integrated into the Network That Processes Spatial Information?

Adult-born neurons in the dentate gyrus (DG) functionally integrate into the behaviorally relevant hippocampal networks, showing a specific Arc-expression response to spatial exploration when mature. However, it is not clear when, during the 4- to 6-week interval that is critical for survival and maturation of these neurons, this specific response develops. Therefore, we characterized Arc expression after spatial exploration or cage control conditions in adult-born neurons from rats that were injected with BrdU on one day and were sacrificed 1, 7, 15, 30, and 45 days post-BrdU injection (PBI). Triple immunostaining for NeuN, Arc, and BrdU was analyzed through the different DG layers. Arc protein expression in BrdU-positive cells was observed from day 1 to day 15 PBI but was not related to behavioral stimulation. The specific Arc-expression response to spatial exploration was observed from day 30 and 45 in about 5% of the BrdU-positive cell population. Most of the BrdU-positive neurons expressing Arc in response to spatial exploration (～90%) were located in DG layer 1, and no Arc expression was observed in cells located in the subgranular zone (SGZ). Using the current data and that obtained previously, we propose a mathematical model suggesting that new neurons are unlikely to respond to exploration by expressing Arc after they are 301 days old, and also that in a 7-month-old rat the majority (60%) of the neurons that respond to exploration must have been born during adulthood; thus, suggesting that adult neurogenesis in the DG is highly relevant for spatial information processing.     

The pubertal-related decline in cellular proliferation and neurogenesis in the dentate gyrus of male rats is independent of the pubertal rise in gonadal hormones

Pubertal development is marked by significant decreases in cellular proliferation and neurogenesis in the dentate gyrus of the hippocampal formation. Although it is unclear what mediates these developmental changes in the dentate gyrus, gonadal hormones have been implicated in modulating many neurobiological processes during puberty and various parameters of neurogenesis in adulthood. Thus, it is possible that the gradual and sustained increase in gonadal hormones experienced during puberty plays a role in these changes in neurogenesis. In this experiments, we first quantified cellular proliferation and neurogenesis using 5-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry, respectively, in the dentate gyrus of prepubertal (30 d), midpubertal (45 d), and adult (90 d) male rats. We found the decline in BrdU and DCX cell numbers throughout these ages was coincident with increases in their plasma testosterone levels. We next tested whether exposure to the pubertal rise in gonadal hormones was necessary for this decrease in hippocampal neurogenesis to occur. Thus, we examined cellular proliferation and neurogenesis in intact 30 day (prepubertal) and 60-day-old (late-pubertal) rats, as well as 60-day-old rats that had previously been gonadectomized or sham-gonadectomized at 30 days of age. Although we again found the expected decline in BrdU and DCX cell numbers between 30 and 60 days of age in the intact groups, there were no differences among the 60-day-old animals, regardless of gonadal status. These data indicate that the pubertal-related decline in hippocampal cellular proliferation and neurogenesis is independent of the pubertal change in gonadal hormones.     

New GABAergic interneurons in the adult neocortex and striatum are generated from different precursors

Ongoing neurogenesis in the adult mammalian dentate gyrus and olfactory bulb is generally accepted, but its existence in other adult brain regions is highly controversial. We labeled newly born cells in adult rats with the S-phase marker bromodeoxyuridine (BrdU) and used neuronal markers to characterize new cells at different time points after cell division. In the neocortex and striatum, we found BrdU-labeled cells that expressed each of the eight neuronal markers. Their size as well as staining for gamma-aminobutyric acid (GABA), glutamic acid decarboxylase 67, calretinin and/or calbindin, suggest that new neurons in both regions are GABAergic interneurons. BrdU and doublecortin-immunoreactive (BrdU+/DCX+) cells were seen within the striatum, suggesting migration of immature neurons from the subventricular zone. Surprisingly, no DCX+ cells were found within the neocortex. NG2 immunoreactivity in some new neocortical neurons suggested that they may instead be generated from the NG2+ precursors that reside within the cortex itself.     

Chronic lithium enhances hippocampal long-term potentiation,but not neurogenesis,in the aged rat dentate gyrus

We investigated the hippocampal long-term potentiation (LTP), neurogenesis, and the activation of signaling molecules in the 20-month-old aged rats following chronic lithium treatment. Chronic lithium treatment produced a significant 79% increase in the numbers of BrdU(+) cells after treatment completion in the dentate gyrus (DG). Both LTP obtained from slices perfused with artificial cerebrospinal fluid (ACSF-LTP), and LTP recorded in the presence of bicuculline (bicuculline-LTP) were significantly greater in the lithium group than in the saline controls. Our results show that as with young rats, chronic lithium can substantially increase LTP and the number of BrdU(+) cells in the aged rats. However, neurogenesis, assessed by colocalization of NeuN and BrdU, was not detected in the aged rat DG subjected to chronic lithium treatment. Therefore, it is concluded that the increase in LTP and the number of BrdU(+) cells might not be associated with increases in neurogenesis in the granule cell layer of the DG. Lithium might has a beneficial effects through other signaling pathways in the aged brain.     

Ischemia-induced neurogenesis is preserved but reduced in the aged rodent brain

The adult mammalian brain retains the capacity for neurogenesis, by which new neurons may be generated to replace those lost through physiological or pathological processes. However, neurogenesis diminishes with aging, and this casts doubt on its feasibility as a therapeutic target for cell replacement therapy in stroke and neurodegenerative disorders, which disproportionately affect the aged brain. In previous studies, neurogenesis was stimulated by cerebral ischemia in young rodents, and the neurogenesis response of the aged rodent brain to physiological stimuli, such as hormonal manipulation and growth factors, was preserved. To investigate the effect of aging on ischemia-induced neurogenesis, transient (60 min) middle cerebral artery occlusion was induced in young adult (3-month) and aged (24-month) rats, who were also given bromodeoxyuridine to label newborn cells. As found in prior studies, basal neurogenesis in control, nonischemic rats was reduced with aging. Ischemia failed to stimulate neurogenesis in the dentate gyrus (DG) subgranular zone (SGZ), in contrast to results obtained previously after more prolonged (90-120 min) middle cerebral artery occlusion, but increased the number of BrdU-labeled cells in the forebrain subventricular zone (SVZ). This effect was less prominent in aged than in young adult rats, with fold-stimulation of BrdU incorporation reduced by approximately 20% and the total number of cells generated diminished by approximately 50%. BrdU-labeled cells in SVZ coexpressed neuronal lineage markers, consistent with newborn neurons. We conclude that ischemia-induced neurogenesis occurs in the aged brain, and that measures designed to augment this phenomenon might have therapeutic applications.     

Impaired adult neurogenesis in the dentate gyrus of a triple transgenic mouse model of Alzheimer's disease

It has become generally accepted that new neurones are added and integrated mainly in two areas of the mammalian CNS, the subventricular zone and the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus, which is of central importance in learning and memory. The newly generated cells display neuronal morphology, are able to generate action potentials and receive functional synaptic inputs, i.e. their properties are similar to those found in mature neurones. Alzheimer's disease (AD) is the primary and widespread cause of dementia and is an age-related, progressive and irreversible neurodegenerative disease that deteriorates cognitive functions. Here, we have used male and female triple transgenic mice (3xTg-AD) harbouring three mutant genes (beta-amyloid precursor protein, presenilin-1 and tau) and their respective non-transgenic (non-Tg) controls at 2, 3, 4, 6, 9 and 12 months of age to establish the link between AD and neurogenesis. Using immunohistochemistry we determined the area density of proliferating cells within the SGZ of the DG, measured by the presence of phosphorylated Histone H3 (HH3), and their possible co-localisation with GFAP to exclude a glial phenotype. Less than 1% of the HH3 labeled cells co-localised with GFAP. Both non-Tg and 3xTg-AD showed an age-dependent decrease in neurogenesis. However, male 3xTg-AD mice demonstrated a further reduction in the production of new neurones from 9 months of age (73% decrease) and a complete depletion at 12 months, when compared to controls. In addition, female 3xTg-AD mice showed an earlier but equivalent decrease in neurogenesis at 4 months (reduction of 63%) with an almost inexistent rate at 12 months (88% decrease) compared to controls. This reduction in neurogenesis was directly associated with the presence of beta-amyloid plaques and an increase in the number of beta-amyloid containing neurones in the hippocampus; which in the case of 3xgTg females was directly correlated. These results suggest that 3xTg-AD mice have an impaired ability to generate new neurones in the DG of the hippocampus, the severity of which increases with age and might be directly associated with the known cognitive impairment observed from 6 months of age onwards . The earlier reduction of neurogenesis in females, from 4 months, is in agreement with the higher prevalence of AD in women than in men. Thus it is conceivable to speculate that a recovery in neurogenesis rates in AD could help to rescue cognitive impairment.     

Three-dimensional ultrastructural and immunohistochemical study of immature neurons in the subgranular zone of the rat dentate gyrus

The present study is devoted to three-dimensional ultrastructural organization of mitotically dividing immature neurons in dentate gyrus using biophysical approaches. In adult vertebrate brain, cell proliferation persists throughout life mainly in dentate gyrus of the hippocampus (DG) and olfactory bulb. Neurogenesis has been demonstrated using tagged thymidine analogues incorporated into the S phase of the cell cycle, but these may also detect repaired DNA in postmitotic neurons. Recent retroviral labelling has shown that neuronal progenitors/neuroblasts divide and produce functional neurons. Providing ultrastructural evidence of mitotically active cells has proven problematical, not only because of technical issues of identifying dividing cells at electron microscope level, but also because it is difficult to demonstrate unequivocally that neurons identified in the electron microscope are really post mitotic. However by characterising post mitotic cells labelled with BrdU and doublecortin and comparing these with post mitotic cells reconstructed in 3-dimensions from ultrathin serial sections, we have been able to illustrate individual mitotic elements and phases of cells within the GC layer of adult rat dentate gyrus. Here we show dividing cells in metaphase within clusters of immature GCs in subgranular zone (SGZ). These reconstructions provide ultrastructural confirmation that cells expressing doublecortin (DCX), a microtubule-associated protein expressed in migrating neurons, localize as clusters in the subgranular zone (SGZ) of dentate gyrus (DG) in the hippocampus during all animal life. Such DG cells with clear synaptic specializations, somatic spines and basal dendrites are exclusive to immature GC that appear to re-enter the cell cycle, suggesting the possibility that newly generated neurons within the DG might arise not only from precursors, but also from clusters of immature GC.     

Comparison of Neurogenesis in the Dentate Gyrus Between the Adult and Aged Gerbil Following Transient Global Cerebral Ischemia

In the present study, we compared differences in cell proliferation, neuroblast differentiation and neuronal maturation in the hippocampal dentate gyrus (DG) between the adult and aged gerbil induced by 5 min of transient global cerebral ischemia using Ki-67 and BrdU (markers for cell proliferation), doublecortin (DCX, a marker for neuroblast differentiation) and neuronal nuclei (NeuN, a marker for mature neuron). The number of Ki-67-immunoreactive (⁺) cells in the DG of both the groups peaked 7 days after ischemia/reperfusion (I/R). However, the number in the aged DG was 40.6 ± 1.8% of that in the adult DG. Thereafter, the number decreased with time. After ischemic damage, DCX immunoreactivity and its protein level in the adult and aged DG peaked at 10 and 15 days post-ischemia, respectively. However, DCX immunoreactivity and its protein levels in the aged DG were much lower than those in the adult. DCX immunoreactivity and its protein level in the aged DG were 11.1 ± 0.6% and 34.4 ± 2.1% of the adult DG, respectively. In addition, the number of Ki-67⁺ cells and DCX immunoreactivity in both groups were similar to those in the sham at 60 days postischemia. At 30 days post-ischemia, the number of BrdU⁺ cells and BrdU⁺/NeuN⁺ cells in the adult-group were much higher (281.2 ± 23.4% and 126.4 ± 7.4%, respectively) than the aged-group (35.6 ± 6.8% and 79.5 ± 6.1%, respectively). These results suggest that the ability of neurogenesis in the ischemic aged DG is much lower than that in the ischemic adult DG.     

Stress-Induced Anxiety- and Depressive-Like Phenotype Associated with Transient Reduction in Neurogenesis in Adult Nestin-CreERT2/Diphtheria Toxin Fragment A Transgenic Mice

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-CreER^T2/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.     

In vivo fate analysis reveals the multipotent and self-renewal capacities of Sox2+ neural stem cells in the adult hippocampus

To characterize the properties of adult neural stem cells (NSCs), we generated and analyzed Sox2-GFP transgenic mice. Sox2-GFP cells in the subgranular zone (SGZ) express markers specific for progenitors, but they represent two morphologically distinct populations that differ in proliferation levels. Lentivirus- and retrovirus-mediated fate-tracing studies showed that Sox2+ cells in the SGZ have potential to give rise to neurons and astrocytes, revealing their multipotency at the population as well as at a single-cell level. A subpopulation of Sox2+ cells gives rise to cells that retain Sox2, highlighting Sox2+ cells as a primary source for adult NSCs. In response to mitotic signals, increased proliferation of Sox2+ cells is coupled with the generation of Sox2+ NSCs as well as neuronal precursors. An asymmetric contribution of Sox2+ NSCs may play an important role in maintaining the constant size of the NSC pool and producing newly born neurons during adult neurogenesis.     

海马齿状回神经再生对WKY大鼠抑郁样行为的影响*

目的:观察海马齿状回(DG)神经再生对成年Wistar Kyoto(WKY)大鼠抑郁样行为的影响。方法:实验共分三个组(n = 10):①正常对照(Wistar)组:选取 9 周龄Wistar大鼠,给予生理盐水 3 周(10 mg/kg, 灌胃);②抑郁模型(WKY)组:选取同龄WKY大鼠并经行为学测定后筛选出抑郁大鼠作为抑郁模型组,给予生理盐水 3 周(10 mg/kg, 灌胃);③阳性对照(AMI+WKY)组:选取同龄WKY抑郁大鼠,给予阿米替林(AMI) 3 周(10 mg/kg, 灌胃)。选用免疫荧光染色细胞增殖标记物Ki67、未成熟神经元标志物DCX检测大鼠的海马神经再生水平;应用糖水偏好实验(SPT)、旷场实验(OFT)和强迫游泳实验(FST)检测各组大鼠的抑郁样行为学变化。结果:①WKY抑郁大鼠海马DG区细胞增殖标志物Ki67⁺细胞数和未成熟神经元标志物DCX⁺细胞数较Wistar大鼠分别降低了 33.0%(P＜0.01)和39.2%(P＜0.01);阿米替林给药后使抑郁大鼠海马DG区Ki67⁺细胞数和DCX⁺细胞数分别增加了43.8%(P＜0.01)和46.7%(P＜0.01)。②与Wistar大鼠相比,WKY抑郁大鼠糖水偏好程度明显降低(P＜ 0.01),旷场实验中运动总距离显著缩短(P＜0.01)和中心停留时间显著减少(P＜0.01),强迫游泳实验中不动时间明显延长(P＜ 0.01);阿米替林治疗可显著改善WKY大鼠的上述抑郁样行为。结论:①成年WKY抑郁大鼠的海马神经干细胞的增殖和分化能力较正常对照组显著降低,提示成年WKY抑郁大鼠的神经再生受损;②改善海马受损的神经再生可以部分逆转成年WKY大鼠的抑郁样行为。