Running increases neurogenesis without retinoic acid receptor activation in the adult mouse dentate gyrus

Both vitamin A deficiency and high doses of retinoids can result in learning and memory impairments, depression as well as decreases in cell proliferation, neurogenesis and cell survival. Physical activity enhances hippocampal neurogenesis and can also exert an antidepressant effect. Here we elucidate a putative link between running, retinoid signaling, and neurogenesis in hippocampus. Adult transgenic reporter mice designed to detect ligand-activated retinoic acid receptors (RAR) or retinoid X receptors (RXR) were used to localize the distribution of activated RAR or RXR at the single-cell level in the brain. Two months of voluntary wheel-running induced an increase in hippocampal neurogenesis as indicated by an almost two-fold increase in doublecortin-immunoreactive cells. Running activity was correlated with neurogenesis. Under basal conditions a distinct pattern of RAR-activated cells was detected in the granule cell layer of the dentate gyrus (DG), thalamus, and cerebral cortex layers 3-4 and to a lesser extent in hippocampal pyramidal cell layers CA1-CA3. Running did not change the number of RAR-activated cells in the DG. There was no correlation between running and RAR activation or between RAR activation and neurogenesis in the DG of hippocampus. Only a few scattered activated retinoid X receptors were found in the DG under basal conditions and after wheel-running, but RXR was detected in other areas such as in the hilus region of hippocampus and in layer VI of cortex cerebri. RAR agonists affect mood in humans and reduce neurogenesis, learning and memory in animal models. In our study, long-term running increased neurogenesis but did not alter RAR ligand activation in the DG in individually housed mice. Thus, our data suggest that the effects of exercise on neurogenesis and other plasticity changes in the hippocampal formation are mediated by mechanisms that do not involve retinoid receptor activation.     

Tooth loss inhibits neurogenesis in the dentate gyrus of adult mice

Tooth loss has been shown to affect learning and memory in mice and increases the risk of Alz- heimer＇s disease. The dentate gyrus is strongly associated with cognitive function. This study hypothesized that tooth loss affects neurons in the dentate gyrus. Adult male mice were randomly assigned to either the tooth loss group or normal control group. In the tooth loss group, the left maxillary and mandibular molars were extracted. Normal control mice did not receive any intervention. Immunofluorescence staining revealed that the density and absorbance of double- cortinand neuronal nuclear antigen-positive cells were lower in the tooth loss group than in the normal control group. These data suggest that tooth loss may inhibit neurogenesis in the dentate gyrus of adult mice.     

Effects of Abeta25-35 on neurogenesis in the adult mouse subventricular zone and dentate gyrus

It has been demonstrated that neuorgenesis driven by neural precursor cells persists well into the adult period. This study was to observe the effects of Amyloid-beta (25-35) peptide (Abeta(25-35)) on neurogenesis in the subventricular zone and dentate gyrus of adult mouse brain. Aggregated Abeta(25-35)(1 mg/ml, 3 microl) was injected into the lateral ventricle of adult mouse. Animals were transcardially perfused with 4% paraformaldehyde in PBS, respectively at 5, 10, 20, 30 days after the Abeta(25-35) injection. All the animals were injected with BrdU (50 mg/kg, i. p) to label the neural precursor cells 24 h before the each perfusion. NeuN immunofluorescence and BrdU immunohistology were performed. It was found that Abeta(25-35) could injure the mature neurons and decrease the number of NeuN positive neurons. It also showed that Abeta(25-35) inhibited neurogenesis and significantly decreased the number of BrdU positive cells in the dentate gyrus of hippocampus, but it had no obvious effects on neurogenesis in the subventricular zone. The present results indicated that Abeta(25-35) could impair neurogenesis in the hippocampus of adult mouse brain.     

N-methyl-D-aspartate receptor subunit 1 regulates neurogenesis in the hippocampal dentate gyrus of schizophrenia-like mice

N-methyl-D-aspartate receptor hypofunction is the basis of pathophysiology in schizophrenia. Blocking the N-methyl-D-aspartate receptor impairs learning and memory abilities and induces pathological changes in the brain. Previous studies have paid little attention to the role of the N-methyl-D-aspartate receptor subunit 1(NR1) in neurogenesis in the hippocampus of schizophrenia. A mouse model of schizophrenia was established by intraperitoneal injection of 0.6 mg/kg MK-801, once a day, for 14 days. In N-methyl-D-aspartate-treated mice, N-methyl-D-aspartate was administered by intracerebroventricular injection in schizophrenia mice on day 15. The number of NR1-,Ki67-or BrdU-immunoreactive cells in the dentate gyrus was measured by immunofluorescence staining. Our data showed the number of NR1-immunoreactive cells increased along with the decreasing numbers of BrdU-and Ki67-immunoreactive cells in the schizophrenia groups compared with the control group. N-methyl-D-aspartate could reverse the above changes. These results indicated that NR1 can regulate neurogenesis in the hippocampal dentate gyrus of schizophrenia mice, supporting NR1 as a promising therapeutic target in the treatment of schizophrenia. This study was approved by the Experimental Animal Ethics Committee of the Ningxia Medical University,China(approval No. 2014-014) on March 6, 2014.     

N-methyl-D-aspartate receptor-mediated increase of neurogenesis in adult rat dentate gyrus following stroke

Neurogenesis in the adult rat dentate gyrus was studied following focal ischemic insults produced by middle cerebral artery occlusion (MCAO). Animals were subjected to either 30 min of MCAO, which causes damage confined to the striatum, or 2 h of MCAO, which leads to both striatal and cortical infarction. When compared to sham-operated rats, MCAO-rats showed a marked increase of the number of cells double-labelled for 5-bromo-2'-deoxyuridine-5'-monophosphate (BrdU; injected during 4-6 days postischemia) and neuronal-specific antigen (NeuN; a marker of postmitotic neurons) in the ipsilateral dentate granule cell layer and subgranular zone at 5 weeks following the 2 h insult. Only a modest and variable increase of BrdU-labelled cells was found after 30 min of MCAO. The enhanced neurogenesis was not dependent on cell death in the hippocampus, and its magnitude was not correlated to the degree of cortical damage. Systemic administration of the N-methyl-D-aspartate (NMDA) receptor blocker dizocilpine maleate (MK-801) completely suppressed the elevated neurogenesis following 2 h of MCAO. Our findings indicate that stroke leads to increased neurogenesis in the adult rat dentate gyrus through glutamatergic mechanisms acting on NMDA receptors. This modulatory effect may be mediated through changes in the levels of several growth factors, which occur after stroke, and could influence various regulatory steps of neurogenesis.     

Differential neurogenesis in the adult rat dentate gyrus: an identifiable zone that consistently lacks neurogenesis

The dentate gyrus continues to produce new neurons in adult rodents. The possibility of differential regulation of neurogenesis within regions of the dentate gyrus is largely unexplored, despite several other aspects of this phenomenon being well characterized in a large number of studies. In this report, we describe an area located at the anterior pole of the dentate gyrus that consistently lacks neurogenesis. This neurogenically quiescent zone invariably lacks expression of the neuroblast marker doublecortin (DCX), bromodeoxyuridine and Ki-67, though DCX expression can be elicited in response to a combined paradigm of environmental enrichment and wheel running. We propose that this region may provide a valuable model system to discern the factors that regulate the process of neurogenesis.     

NDRG2通过Hes1参与癫痫发作后海马齿状回的神经发生

目的 探讨N-Myc下游调节基因2(N-Myc downstream regulated gene 2,NDRG2)与癫痫发作后海马齿状回神经发生的关系。方法 C57BL/6小鼠20只,随机分为癫痫组和对照组,每组又分为癫痫造模后1和7 d两个时间点,每个时间点5只,通过蛋白免疫印迹检测癫痫后海马齿状回NDRG2蛋白相对表达水平和mRNA相对表达水平变化; 使用双皮质素(DCX)染色标记未成熟神经元,神经巢蛋白(Nestin)标记神经干细胞,神经核蛋白(NeuN)标记成熟神经元,观察NDRG2对海马齿状回神经干细胞增殖影响; 采用RT-PCR检测发状分裂相关增强子1(hairy and enhancer of split 1,Hes 1)、NDRG2 mRNA相对表达表达水平,并分析两者之间的相关性; 观察NDRG2参与癫痫发作后神经发生的可能机制。结果 癫痫组与对照组比较,DCX、Nestin、NeuN、Hes1、NDRG2蛋白相对表达水平在1和7 d这2个时间点有显著性增高,并随时间逐渐递增。结论 癫痫发作后海马NDRG2蛋白相对表达水平增高,与癫痫发作后海马齿状回的神经细胞增值时间具有一致性和相关性,NDRG2可能参与癫痫发作后海马齿状回的神经发生过程; 同时发现海马NDRG2表达增加和Hes1分子表达增加具有相关性,故推测NDRG2可能通过Hes1参与癫痫发作后海马齿状回的神经发生。     

Status epilepticus severity influences the long-term outcome of neurogenesis in the adult dentate gyrus

Status epilepticus (SE) is characterized by continual seizure activity that can vary widely in the intensity of convulsions. We induced seizures by applying continuous electrical stimulation to the hippocampus in adult rats to explore the effects of three different SE states on neurogenesis and neuronal death in the hippocampus. Rats exhibiting the most severe SE state (fully convulsive) demonstrated profound increases in cell proliferation in the dentate gyrus (DG) at 1 week post-insult, but the majority of the new neurons had died at 4 weeks. In contrast, rats exhibiting less severe SE states (ambulatory or masticatory, partial convulsive) had the same degree of cell proliferation at 1 week, but most new neurons survived at 4 weeks. As compared to partially convulsive SE rats, fully convulsive SE rats had significantly greater DG pathology. Our data indicate that SE of varying severity triggers similar short-term proliferation of neural progenitors, but that the long-term outcome of neurogenesis is influenced by the degree of insult-induced degeneration in the DG tissue environment.     

Gonadal hormone modulation of neurogenesis in the dentate gyrus of adult male and female rodents

Gonadal hormones modulate neurogenesis in the dentate gyrus differentially in male and female adult rodents. Neurogenesis is comprised of at least two components: cell proliferation (the production of new cells) and cell survival (the number of new neurons that survive to maturity). Previous studies have found sex differences in the level of cell proliferation in the dentate gyrus only when comparing females in a high estrogen state to males. This review focuses on the effects of acute and chronic levels of estrogens or androgens on hippocampal neurogenesis in the adult male and female rodent. Evidence is also reviewed for the co-localization of androgen receptors and estrogen receptors (ER) with markers for cell proliferation or immature new cell survival. Briefly, evidence suggests that acute estradiol initially enhances and subsequently suppresses cell proliferation in the dentate gyrus of adult female rodents but may have limited effects in male rodents. Both the two known ER subtypes, ER and β upregulate hippocampal neurogenesis via cell proliferation. Intriguingly, repeated exposure to estradiol modulates hippocampal neurogenesis and cell death in adult female, but not male, rodents. However short-term estradiol treatment (5 days) in male meadow voles enhances new cell survival in the dentate gyrus but only when administered during the ‘axon extension’ phase. Furthermore, evidence is also reviewed showing a difference in response to acute and chronic estradiol treatment in older female rats compared to younger female rats. Recent findings from our laboratory indicate that testosterone and dihydrotestosterone upregulate hippocampal neurogenesis (via cell survival), but not cell proliferation, in adult male rodents. Effects of endogenous fluctuations in gonadal hormones on adult neurogenesis are observed across the seasons in meadow voles and during pregnancy and lactation in the rat dam. Pregnancy and motherhood differentially regulate adult hippocampal neurogenesis in the adult female rodent, with primiparous rats displaying lower levels of hippocampal cell proliferation and survival after parturition. Few studies have compared males and females but existing research suggests a sex difference in the hormonal regulation of hippocampal neurogenesis in the adult. Clearly more work is needed to elucidate the effects of gonadal hormones on neurogenesis in the dentate gyrus of both male and female rodents across the lifespan, especially if we are to use our knowledge of how adult neurogenesis is regulated to develop strategies to repair neuron loss in neurodegenerative diseases.     

Reversible effect of X-irradiation on proliferation, neurogenesis, and cell death in the dentate gyrus of adult mice

Therapeutic cranial X-irradiation causes cognitive deficits in adult and pediatric patients, in particular, when the exposed area includes the medial temporal lobes. Effects on adult neurogenesis within the hippocampus may be related to such deficits. To investigate this relation, we irradiated the brain of young adult C57Bl/6j mice with a single dose of 4 Gy at a dose-rate of 27.5 cGy/min. We observed an approximately 80% decrease in the number of cells immunoreactive for the proliferation marker Ki67, 16 and 48 h after exposure, which was restored to control values after 1 week. The number of doublecortin- and NeuroD-immunoreactive cells of neuronal lineage was reduced by 60-70% up to 1 week after irradiation, but not after 1 month. The number of pyknotic cells increased approximately 2.5 fold after 16 h, decreased to approximately 50% of control numbers after 48 h and 1 week, and was again at normal levels after 1 month. Granule cell number did not differ between different groups and time points. There was no apparent activation of microglia or astrocytes. Our findings consist of an acute and reversible effect of X-irradiation on proliferation, neurogenesis, and cell death. Transient changes of neurogenesis may play a role in transient impairments of cognitive performance of patients exposed to X-irradiation. We present an experimental approach to temporarily alter adult hippocampal neurogenesis (AhN), allowing mechanistic investigations of AhN and its relevance to cognitive performances. The work also represents a step toward optimized radiotherapy schedules.     

Deletion of lysophosphatidic acid receptor LPA1 reduces neurogenesis in the mouse dentate gyrus

Neurogenesis persists in certain regions of the adult brain including the subgranular zone of the hippocampal dentate gyrus wherein its regulation is essential, particularly in relation to learning, stress and modulation of mood. Lysophosphatidic acid (LPA) is an extracellular signaling phospholipid with important neural regulatory properties mediated by specific G protein-coupled receptors, LPA(1-5). LPA(1) is highly expressed in the developing neurogenic ventricular zone wherein it is required for normal embryonic neurogenesis, and, by extension may play a role in adult neurogenesis as well. By means of the analyses of a variant of the original LPA(1)-null mutant mouse, termed the Malaga variant or "maLPA(1)-null," which has recently been reported to have defective neurogenesis within the embryonic cerebral cortex, we report here a role for LPA(1) in adult hippocampal neurogenesis. Proliferation, differentiation and survival of newly formed neurons are defective in the absence of LPA(1) under normal conditions and following exposure to enriched environment and voluntary exercise. Furthermore, analysis of trophic factors in maLPA(1)-null mice demonstrated alterations in brain-derived neurotrophic factor and insulin growth factor 1 levels after enrichment and exercise. Morphological analyses of doublecortin positive cells revealed the anomalous prevalence of bipolar cells in the subgranular zone, supporting the operation of LPA(1) signaling pathways in normal proliferation, maturation and differentiation of neuronal precursors.     

Increased granule cell neurogenesis in the adult dentate gyrus following mossy fiber stimulation sufficient to induce long-term potentiation

Neurons are continually added at a low rate to the granule cell layer of the dentate gyrus during adulthood in rats. The functional significance of this unusual feature is not completely understood, although recent studies suggest continued granule cell neurogenesis is essential for normal learning and memory. We report here that, in the adult rat, stimulation of the granule cell mossy fibers sufficient to induce long-term potentiation (LTP) increases the number of newly formed granule cells in the dentate gyrus, indicating that granule cell neurogenesis is regulated by efferent activity and, possibly, the induction of LTP.     

Brain-derived neurotropic factor and neurogenesis in the adult rat dentate gyrus: interactions with corticosterone

Flattening the diurnal corticosterone rhythm prevented the stimulating action of l -NAME (a nitric oxide synthase, NOS, inhibitor) on progenitor cell proliferation in the dentate gyrus in Lister-Hooded adult male rats. The increased expression of brain-derived neurotrophic factor (BDNF) and trkB mRNA in the dentate gyrus which otherwise occurred after l- NAME was also prevented by clamping the corticoid rhythm in adrenalectomized rats, but was restored by daily additional injections of corticosterone (which replicates the diurnal rhythm). Unilateral infusions of BDNF into the lateral ventricle increased proliferation in the dentate gyrus on the side of the infusion, but this was not observed following implantation of subcutaneous corticosterone, which flattened the diurnal corticosterone rhythm. 5HT1A mRNA in the dentate gyrus was increased on both sides of the brain by unilateral BDNF infusions, but this was also prevented by subcutaneous corticosterone pellets. These results show that the diurnal rhythm of corticosterone regulates the stimulating action of NOS inhibitors on BDNF as well as on neurogenesis in the dentate gyrus, and that BDNF becomes ineffective on both proliferation rates and 5HT1A expression in the absence of a rhythm in corticosterone. This, together with our previous findings, suggests that corticoid rhythms permit both serotonin and NO access to BDNF, and the latter to regulate progenitor cell activity.     

Long-term gonadal hormone treatment and endogenous neurogenesis in the dentate gyrus of the adult female monkey

Neurogenesis occurs continually throughout life in all mammals and the extent of neurogenesis is influenced by many factors including gonadal hormones. Most research regarding hormones and neurogenesis has been performed on non-primate species. To determine whether gonadal hormones can modulate endogenous neurogenesis in the dentate gyrus (DG) of the hippocampus in non-human primates, ovariectomized (OVX) female rhesus monkeys received continuous, unopposed β-estradiol (OVX-E-Con), cyclic unopposed β-estradiol (OVX-E-Cyc), continuous β-estradiol + cyclic progesterone (OVX-E-Con + P-Cyc), or control (OVX-Veh) treatments. At week 29, all monkeys received BrdU injections for 4 consecutive days, in addition to the ongoing treatment. Twenty days after the last BrdU injection, all animals were sacrificed for tissue collection. In DG of hippocampus, scattered BrdU-ir cells were observed mainly in the subgranular zone (SGZ) and in the granule cell layer and occasionally these BrdU-ir cells in the SGZ formed clusters containing between 2 and 5 cells. In the granule cell layer and SGZ, virtually none of the BrdU-ir cells were either Dcx, a marker of immature neurons, or GFAP positive. However, an occasional BrdU-ir cell was positive for both neuronal marker NeuN or β III-tubulin. Unbiased stereological analysis of BrdU-ir cells within the SGZ and the granule cell layer of DG revealed that among the experimental groups, there was no significant difference in number of BrdU-ir cells within the SGZ and the granule cell layer of the DG: OVX-E-Con (1801 ± 218.7), OVX-E-Cyc (1783 ± 415.6), OVX-E-Con ± P-Cyc (1721 ± 229.6), and OVX-Veh (1263 ± 106.3), but a trend towards increased BrdU-ir cells was observed in all the experimental groups.     

Postnatal neurogenesis in the dentate gyrus of the guinea pig

In all species examined, the dentate gyrus develops over an extended period that begins during gestation and continues up to adulthood. The aim of this study was to investigate the pattern of postnatal cell production in the dentate gyrus of the guinea pig, a rodent whose brain development has features more closely resembling the human condition than the most commonly used rodents (rat and mouse). Animals of different postnatal (P) ages received one or multiple injections of bromodeoxyuridine (BrdU), and the number of labeled cells in the dentate gyrus was counted after time intervals of 24 h or longer. The total granule cell number and the volume of the granule cell layer were evaluated in Nissl-stained brain sections from P1 and P30 animals. P1-P5 animals were treated with MK-801 to analyze the effect of NMDA receptor blockade on cell proliferation. Cell production occurred at a high rate (9,000-13,000 labeled cells 24 h after one injection) from P1 to P20, with a peak at 3-6 days of age, and then slowly declined from P20 to P30. The production of new cells continued in adult animals, although at a much-reduced rate (400 cells 24 h after one injection). About 20% of the labeled cells survived after a 17-day period and most (60%) of these cells had a neuronal phenotype. The total number of granule cells increased over the first postnatal month; in 30-day-old animals, it was 20% greater than in 1-day-old animals. Administration of MK-801 to P1-P5 animals caused an increase in cell proliferation restricted to the dorsal dentate gyrus. The present data show that, although the guinea pig dentate gyrus develops largely before birth, the production of new neurons continues at a high rate during the first postnatal month, leading to a considerable increase in cell number. This developmental pattern, resembling the human and nonhuman primate condition, may make the guinea pig a useful rodent model in developmental studies on dentate gyrus neurogenesis.     

Estimation of the density of neural,glial, and endothelial lineage cells in the adult mouse dentate gyrus

The dentate gyrus subregion of the mammalian hippocampus is an adult neural stem cell niche and site of lifelong neurogenesis.Hypotheses regarding the role of adult-born neuron synaptic integration in hippocampal circuit function are framed by robust estimations of adultborn versus pre/perinatally-born neuron number.In contrast,the non-neurogenic functions of adult neural stem cells and their immediate progeny,such as secretion of bioactive growth factors and expression of extracellular matrix-modifying proteins,lack similar framing due to few estimates of their number versus other prominent secretory cells.Here,we apply immunohistochemical methods to estimate cell density of neural stem/progenitor cells versus other major classes of glial and endothelial cell types that are potentially secretory in the dentate gyrus of adult mice.Of the cell types quantified,we found that GFAP⁺SOX2⁺stellate astrocytes were the most numerous,followed by CD31⁺endothelia,GFAP-SOX2⁺intermediate progenitors,Olig2⁺oligodendrocytes,Iba1+microglia,and GFAP⁺SOX2⁺radial glia-like neural stem cells.We did not observe any significant sex differences in density of any cell population.Notably,neural stem/progenitor cells were present at a similar density as several cell types known to have potent functional roles via their secretome.These findings may be useful for refining hypotheses regarding the contributions of these cell types to regulating hippocampal function and their potential therapeutic uses.All experimental protocols were approved by the Ohio State University Institutional Animal Care and Use Committee(protocol#2016A00000068)on July 14,2016.     

Adult neurogenesis and the plasticity of the dentate gyrus network

The granule cell layer (GCL) of the dentate gyrus contains neurons generated during embryonic, early postnatal and adult life. During adulthood there is a continuous production of neuronal cohorts that develop and functionally integrate in the preexisting circuits. This morphogenic process generates a stratified GCL, with the outermost layers containing dentate granule cells (DGCs) generated during perinatal life, and the innermost layers containing adult-born DGCs. In this review we analyse the functional profile of the different neuronal populations of the GCL, with an emphasis on adult-born neurons as they develop, mature and integrate in the dentate gyrus network. We focus on the contribution of adult-born neurons to activity-dependent synaptic modification in the dentate gyrus and, in turn, discuss how network activity modulates integration and survival of new neurons.