Entacapone promotes hippocampal neurogenesis in mice

Entacapone, a catechol-O-methyltransferase inhibitor, can strengthen the therapeutic effects of levodopa on the treatment of Parkinson's disease. However, few studies are reported on whether entacapone can affect hippocampal neurogenesis in mice. To investigate the effects of entacapone, a modulator of dopamine, on proliferating cells and immature neurons in the mouse hippocampal dentate gyrus, 60 mice(7 weeks old) were randomly divided into a vehicle-treated group and the groups treated with 10, 50, or 200 mg/kg entacapone. The results showed that 50 and 200 mg/kg entacapone increased the exploration time for novel object recognition. Immunohistochemical staining results revealed that after entacapone treatment, the numbers of Ki67-positive proliferating cells, doublecortin-positive immature neurons, and phosphorylated cAMP response element-binding protein(pCREB)-positive cells were significantly increased. Western blot analysis results revealed that treatment with tyrosine kinase receptor B(TrkB) receptor antagonist significantly decreased the exploration time for novel object recognition and inhibited the expression of phosphorylated TrkB and brain-derived neurotrophic factor(BDNF). Entacapone treatment antagonized the effects of TrkB receptor antagonist. These results suggest that entacapone treatment promoted hippocampal neurogenesis and improved memory function through activating the BDNF-TrkB-pCREB pathway. This study was approved by the Institutional Animal Care and Use Committee of Seoul National University(approval No. SNU-130730-1) on February 24, 2014.     

Methods to study adult hippocampal neurogenesis in humans and across the phylogeny

The hippocampus hosts the continuous addition of new neurons throughout life—a phenomenon named adult hippocampal neurogenesis (AHN). Here we revisit the occurrence of AHN in more than 110 mammalian species, including humans, and discuss the further validation of these data by single-cell RNAseq and other alternative techniques. In this regard, our recent studies have addressed the long-standing controversy in the field, namely whether cells positive for AHN markers are present in the adult human dentate gyrus (DG). Here we review how we developed a tightly controlled methodology, based on the use of high-quality brain samples (characterized by short postmortem delays and ≤24 h of fixation in freshly prepared 4% paraformaldehyde), to address human AHN. We review that the detection of AHN markers in samples fixed for 24 h required mild antigen retrieval and chemical elimination of autofluorescence. However, these steps were not necessary for samples subjected to shorter fixation periods. Moreover, the detection of labile epitopes (such as Nestin) in the human hippocampus required the use of mild detergents. The application of this strictly controlled methodology allowed reconstruction of the entire AHN process, thus revealing the presence of neural stem cells, proliferative progenitors, neuroblasts, and immature neurons at distinct stages of differentiation in the human DG. The data reviewed here demonstrate that methodology is of utmost importance when studying AHN by means of distinct techniques across the phylogenetic scale. In this regard, we summarize the major findings made by our group that emphasize that overlooking fundamental technical principles might have consequences for any given research field.     

Distemper virus encephalitis exerts detrimental effects on hippocampal neurogenesis

E.‐L. von Rüden, J. Avemary, C. Zellinger, D. Algermissen, P. Bock, A. Beineke, W. Baumgärtner, V. M. Stein, A. Tipold and H. Potschka (2012) Neuropathology and Applied Neurobiology 38, 426–442 Distemper virus encephalitis exerts detrimental effects on hippocampal neurogenesis Aims: Despite knowledge about the impact of brain inflammation on hippocampal neurogenesis, data on the influence of virus encephalitis on dentate granule cell neurogenesis are so far limited. Canine distemper is considered an interesting model of virus encephalitis, which can be associated with a chronic progressing disease course and can cause symptomatic seizures. Methods: To determine the impact of canine distemper virus (CDV) infection on hippocampal neurogenesis, we compared post‐mortem tissue from dogs with infection with and without seizures, from epileptic dogs with non‐viral aetiology and from dogs without central nervous system diseases. Results: The majority of animals with infection and with epilepsy of non‐viral aetiology exhibited neuronal progenitor numbers below the age average in controls. Virus infection with and without seizures significantly decreased the mean number of neuronal progenitor cells by 43% and 76% as compared to age‐matched controls. Ki‐67 labelling demonstrated that hippocampal cell proliferation was neither affected by infection nor by epilepsy of non‐viral aetiology. Analysis of CDV infection in cells expressing caspase‐3, doublecortin or Ki‐67 indicated that infection of neuronal progenitor cells is extremely rare and suggests that infection might damage non‐differentiated progenitor cells, hamper neuronal differentiation and promote glial differentiation. A high inter‐individual variance in the number of lectin‐reactive microglial cells was evident in dogs with distemper infection. Statistical analyses did not reveal a correlation between the number of lectin‐reactive microglia cells and neuronal progenitor cells. Conclusions: Our data demonstrate that virus encephalitis with and without seizures can exert detrimental effects on hippocampal neurogenesis, which might contribute to long‐term consequences of the disease. The lack of a significant impact of distemper virus on Ki‐67‐labelled cells indicates that the infection affected neuronal differentiation and survival of newborn cells rather than hippocampal cell proliferation.     

Age-dependent impairment of hippocampal neurogenesis in chronic cerebral hypoperfusion

Acute ischaemic brain damages, including both strokes and local ischaemia, are powerful stimulators of neurogenesis in the dentate gyrus of the hippocampus in adult rats and mice. As no data are available in chronic cerebral hypoperfusion, we investigated neurogenesis in rats after bilateral chronic occlusion of the carotid arteries (2VO). 2VO was performed in 3- and 12-month-old rats. Proliferation was investigated by bromodeoxyuridine uptake and MCM2 nuclear immunoreactivity, neurogenesis by counting doublecortin-IR cells in the subgranular area of the dentate gyrus of the hippocampus. We found increased proliferation and neurogenesis in the subgranular area of the dentate gyrus of the hippocampus in adult (3-month-old) rats 8 days after 2VO. This capability is lost in middle-aged (12-month-old) rats. Our data suggest that 2VO ligation can be a useful model for studying neurogenesis in experimental conditions mimicking long-lasting human pathologies, and also in the exploration of the uncertain relation between chronic brain hypoperfusion and age-related changes of cognitive function.     

Ablation of proliferating neural stem cells during early life is sufficient to reduce adult hippocampal neurogenesis

Environmental exposures during early life, but not during adolescence or adulthood, lead to persistent reductions in neurogenesis in the adult hippocampal dentate gyrus (DG). The mechanisms by which early life exposures lead to long‐term deficits in neurogenesis remain unclear. Here, we investigated whether targeted ablation of dividing neural stem cells during early life is sufficient to produce long‐term decreases in DG neurogenesis. Having previously found that the stem cell lineage is resistant to long‐term effects of transient ablation of dividing stem cells during adolescence or adulthood (Kirshenbaum, Lieberman, Briner, Leonardo, & Dranovsky, 2014 ), we used a similar pharmacogenetic approach to target dividing neural stem cells for elimination during early life periods sensitive to environmental insults. We then assessed the Nestin stem cell lineage in adulthood. We found that the adult neural stem cell reservoir was depleted following ablation during the first postnatal week, when stem cells were highly proliferative, but not during the third postnatal week, when stem cells were more quiescent. Remarkably, ablating proliferating stem cells during either the first or third postnatal week led to reduced adult neurogenesis out of proportion to the changes in the stem cell pool, indicating a disruption of the stem cell function or niche following stem cell ablation in early life. These results highlight the first three postnatal weeks as a series of sensitive periods during which elimination of dividing stem cells leads to lasting alterations in adult DG neurogenesis and stem cell function. These findings contribute to our understanding of the relationship between DG development and adult neurogenesis, as well as suggest a possible mechanism by which early life experiences may lead to lasting deficits in adult hippocampal neurogenesis.     

Adult neurogenesis in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of age-related dementia, characterized by progressive memory loss and cognitive disturbances. The hippocampus, where adult hippocampal neurogenesis (AHN), a relatively novel form of brain plasticity that refers to the birth of new neurons, occurs, is one of the first brain regions to be affected in AD patients. Recent studies showed that AHN persists throughout life in humans, but it drops sharply in AD patients. Next questions to consider would be whether AHN impairment is a contributing factor to learning and memory impairment in AD and whether restoring AHN could ameliorate or delay cognitive dysfunction. Here, we outline and discuss the current knowledge about the state of AHN in AD patients, AHN impairment as a potentially relevant mechanism underlying memory deficits in AD, therapeutic potential of activating AHN in AD, and the mechanisms of AHN impairment in AD.     

The relationship between behavior acquisition and persistence abilities: Involvement of adult hippocampal neurogenesis

The influence of the learning process on the persistence of the newly acquired behavior is relevant both for our knowledge of the learning/memory mechanisms and for the educational policy. However, it is unclear whether during an operant conditioning process with a continuous reinforcement paradigm, individual differences in acquisition are also associated to differences in persistence of the acquired behavior. In parallel, adult neurogenesis has been implicated in spatial learning and memory, but the specific role of the immature neurons born in the adult brain is not well known for this process. We have addressed both questions by analyzing the relationship between water maze task acquisition scores, the persistence of the acquired behavior, and the size of the different subpopulations of immature neurons in the adult murine hippocampus. We have found that task acquisition and persistence rates were negatively correlated: the faster the animals find the water maze platform at the end of acquisition stage, the less they persist in searching for it at the learned position in a subsequent non‐reinforced trial; accordingly, the correlation in the number of some new neurons' subpopulations and the acquisition rate is negative while with persistence in acquired behavior is positive. These findings reveal an unexpected relationship between the efficiency to learn a task and the persistence of the new behavior after a non‐reinforcement paradigm, and suggest that the immature neurons might be involved in different roles in acquisition and persistence/extinction of a learning task. © 2016 Wiley Periodicals, Inc.     

Korean red ginseng promotes hippocampal neurogenesis in mice

Neurogenesis in the adult hippocampus plays a major role in cognitive ability of animals including learning and memory.Korean red ginseng (KRG) has long been known as a medicinal herb with the potential to improve learning and memory;however,the mechanisms are still elusive.Therefore,we evaluated whether KRG can promote cognitive function and enhance neurogenesis in the hippocampus.Eight-week-old male C57BL/6 mice received 50 mg/kg of 5-bromo-2′-deoxyuridine (BrdU) intraperitoneally and 100 mg/kg of KRG or vehicle orally once a day for 14 days.Pole,Rotarod and Morris water maze tests were performed and the brains were collected after the last behavioral test.Changes in the numbers of BrdU- and BrdU/ doublecortin (DCX;a marker for neuronal precursor cells and immature neurons)-positive cells in the dentate gyrus and the gene expression of proliferating cell nuclear antigen (a marker for cell differentiation),cerebral dopamine neurotrophic factor and ciliary neurotrophic factor in the hippocampus were then investigated.KRG-treated mice came down the pole significantly faster and stood on the rotarod longer than vehicle-treated mice.The Morris water maze test showed that KRG administration enhanced the learning and memory abilities significantly.KRG also significantly increased BrdU- and BrdU/DCX-positive cells in the dentate gyrus as well as the proliferating cell nuclear antigen,cerebral dopamine neurotrophic factor and ciliary neurotrophic factor mRNA expression levels in the hippocampus compared to vehicle.Administration of KRG promotes learning and memory abilities,possibly by enhancing hippocampal neurogenesis.This study was approved by the Pusan National University Institutional Animal Care and Use Committee (approval No.PNU-2016-1071) on January 19,2016.     

Impact of pediatric traumatic brain injury on hippocampal neurogenesis

Traumatic brain injury(TBI) is a major cause of mortality and morbidity in the pediatric population. With advances in medical care, the mortality rate of pediatric TBI has declined. However, more children and adolescents are living with TBI-related cognitive and emotional impairments, which negatively affects the quality of their life. Adult hippocampal neurogenesis plays an important role in cognition and mood regulation. Alterations in adult hippocampal neurogenesis are associated with a variety of neurological and neurodegenerative diseases, including TBI. Promoting endogenous hippocampal neurogenesis after TBI merits significant attention. However, TBI affects the function of neural stem/progenitor cells in the dentate gyrus of hippocampus, which results in aberrant migration and impaired dendrite development of adult-born neurons. Therefore, a better understanding of adult hippocampal neurogenesis after TBI can facilitate a more successful neuro-restoration of damage in immature brains. Secondary injuries, such as neuroinflammation and oxidative stress, exert a significant impact on hippocampal neurogenesis. Currently, a variety of therapeutic approaches have been proposed for ameliorating secondary TBI injuries. In this review, we discuss the uniqueness of pediatric TBI, adult hippocampal neurogenesis after pediatric TBI, and current efforts that promote neuroprotection to the developing brains, which can be leveraged to facilitate neuroregeneration.     

Exogenous neuropeptide Y promotes in vivo hippocampal neurogenesis

Adult neurogenesis mainly occurs in two brain regions, the subventricular zone and the dentate gyrus (DG) of the hippocampus. Neuropeptide Y (NPY) is widely expressed throughout the brain and is known to enhance in vitro hippocampal cell proliferation. Mice lacking either NPY or the Y1 receptor display lower levels of cell proliferation, thereby suggesting a role for NPY in basal in vivo neurogenesis. Here, we investigated whether exogenous NPY stimulates DG progenitors proliferation in vivo. We show that intracerebroventricular administration of NPY increases DG cell proliferation and promotes neuronal differentiation in C57BL/6 adult mice. In these mice, the proliferative effect of NPY is mediated by the Y1 and not the Y2 receptor, as a Y1 ([Leu³¹,Pro³⁴]), but not a Y2 (NPY_3–36), receptor agonist enhanced proliferation. In addition, no NPY‐induced DG cellular proliferation is observed following NPY injection when coadministered with a Y1 antagonist or in the Y1 receptor knockout mouse. These results are in line with data obtained in Y1^?/? mice, demonstrating that NPY regulates in vivo hippocampal neurogenesis. © 2010 Wiley‐Liss, Inc.     

Long‐term antiepileptic drug administration during early life inhibits hippocampal neurogenesis in the developing brain

Certain antiepileptic drugs (AEDs) that are commonly used to treat seizures in children also affect cognition, and these effects can persist into adulthood, long after drug withdrawal. Widespread enhancement of apoptosis may be one mechanism underlying these lasting cognitive changes. Whether AEDs affect other processes in brain development during early postnatal life has not, however, been systematically analyzed. Here we determined whether chronic administration of common AEDs during early life alters cell proliferation and neurogenesis in the hippocampus. Postnatal day 7 (P7) rats received phenobarbital, clonazepam, carbamazepine, valproate, topiramate, or vehicle for 28 days. Bromodeoxyuridine was administered on P34 to label dividing cells. Cell proliferation was assessed 24 hr later, and cell survival and differentiation were assessed 28 days later. Phenobarbital and clonazepam significantly inhibited cell proliferation by 63% and 59%, respectively, and doublecortin immunoreactivity (indicator of neurogenesis) in the dorsal hippocampus was also significantly decreased by 26% and 24%, respectively. Survival of new cells steadily decreased in phenobarbital and clonazepam groups over 28 days. Reduced cell proliferation and survival resulted in fewer new neurons in the dentate gyrus, as confirmed by neuronal counting on P62. There were, however, no differences in cell distribution pattern or differentiation toward neuron and glial cells when phenobarbital and clonazepam groups were compared with controls. There were no changes in rats exposed to carbamazepine, valproate, or topiramate. Thus, inhibiting cell proliferation, survival, and neurogenesis in the developing hippocampus may be another potential mechanism underlying brain impairment associated with certain AED therapies in early life. © 2009 Wiley‐Liss, Inc.     

Toll‐like receptor 4 differentially regulates adult hippocampal neurogenesis in an age‐ and sex‐dependent manner

Toll‐like receptor 4 (TLR4) is primarily responsible for initiating an immune response following pathogen recognition. However, TLR4 is also expressed on neural progenitor cells and has been reported to regulate hippocampal neurogenesis as young male TLR4 knockout mice show increases in cell proliferation and doublecortin positive cells. Whether these effects occur in both sexes and are sustained with normal aging is currently unknown. The present study evaluated whether TLR4 deficiency alters adult hippocampal neurogenesis in young (3–4 months) and aged (18–20 months), male and female, TLR4 deficient (TLR4?/?; B6.B10ScN‐Tlr4lps‐del/JthJ) and wild type (WT) mice. Additionally, neurogenesis within the dorsal and the ventral hippocampal subdivisions was evaluated to determine if TLR4 has differential effects across the hippocampus. Bromodeoxyuridine (BrdU) was administered to quantify new cell survival as well as cell differentiation. Ki‐67 was measured to evaluate cell proliferation. Results show that young TLR4?/? females had higher rates of proliferation and neuronal differentiation in both the dorsal and ventral hippocampus relative to WT females. Young TLR4?/? males show elevated proliferation and neuronal differentiation mainly in the ventral hippocampus. While young TLR4?/? mice show enhanced neurogenesis compared to young WT mice, the increase was not apparent in the aged TLR4?/? mice. Both aged WT and TLR4?/? mice showed a decrease in proliferation, new cell survival, and neuronal differentiation compared to young WT and TLR4?/? mice. The data collectively indicate that TLR4 regulates hippocampal neurogenesis in young adults, but that these effects are region‐specific in males and that females show broader changes in neurogenesis throughout the hippocampus.     

Differential effects of stress on adult hippocampal cell proliferation in low and high aggressive mice

Male wild house mice selected for a long (LAL) or a short (SAL) latency to attack a male intruder generally show opposing behavioural coping responses to environmental challenges. LAL mice, unlike SAL mice, adapt to novel challenges with a highly reactive hypothalamic-pituitary-adrenal axis and show an enhanced expression of markers for hippocampal plasticity. The present study aimed to test the hypothesis that these features of the more reactive LAL mice are reflected in parameters of hippocampal cell proliferation. The data show that basal cell proliferation in the subgranular zone (SGZ) of the dentate gyrus, assessed by the endogenous proliferation marker Ki-67, is lower in LAL than in SAL mice. Furthermore, application of bromodeoxyuridine (BrdU) over 3 days showed an almost two-fold lower cell proliferation rate in the SGZ in LAL versus SAL mice. Exposure to forced swimming resulted, 24 h later, in a significant reduction in BrdU + cell numbers in LAL mice, whereas cell proliferation was unaffected by this stressor in SAL mice. Plasma corticosterone and dentate gyrus glucocorticoid receptor levels were higher in LAL than in SAL mice. However, no differences between the SAL and LAL lines were found for hippocampal NMDA receptor binding. In conclusion, the data suggest a relationship between coping responses and hippocampal cell proliferation, in which corticosterone may be one of the determinants of line differences in cell proliferation responses to environmental challenges.     

Circadian and ultradian glucocorticoid rhythmicity: Implications for the effects of glucocorticoids on neural stem cells and adult hippocampal neurogenesis

Psychosocial stress, and within the neuroendocrine reaction to stress specifically the glucocorticoid hormones, are well-characterized inhibitors of neural stem/progenitor cell proliferation in the adult hippocampus, resulting in a marked reduction in the production of new neurons in this brain area relevant for learning and memory. However, the mechanisms by which stress, and particularly glucocorticoids, inhibit neural stem/progenitor cell proliferation remain unclear and under debate.Here we review the literature on the topic and discuss the evidence for direct and indirect effects of glucocorticoids on neural stem/progenitor cell proliferation and adult neurogenesis. Further, we discuss the hypothesis that glucocorticoid rhythmicity and oscillations originating from the activity of the hypothalamus-pituitary-adrenal axis, may be crucial for the regulation of neural stem/progenitor cells in the hippocampus, as well as the implications of this hypothesis for pathophysiological conditions in which glucocorticoid oscillations are affected.     

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.     

Reduced hippocampal neurogenesis in R6/2 transgenic Huntington's disease mice

We investigated whether cell proliferation and neurogenesis are altered in R6/2 transgenic Huntington's disease mice. Using bromodeoxyuridine (BrdU), we found a progressive decrease in the number of proliferating cells in the dentate gyrus of R6/2 mice. This reduction was detected in pre-symptomatic mice, and by 11.5 weeks, R6/2 mice had 66% fewer newly born cells in the hippocampus. The results were confirmed by immunohistochemistry for the cell cycle markers Ki-67 and proliferating cell nuclear antigen (PCNA). We did not observe changes in cell proliferation in the R6/2 subventricular zone, indicating that the decrease in cell proliferation is specific for the hippocampus. This decrease corresponded to a reduction in actual hippocampal neurogenesis as assessed by double immunostaining for BrdU and the neuronal marker neuronal nuclei (NeuN) and by immunohistochemistry for the neuroblast marker doublecortin. Reduced hippocampal neurogenesis may be a novel neuropathological feature in R6/2 mice that could be assessed when evaluating potential therapies.     

Protection of hippocampal neurogenesis by TAT-Bcl-xL after cerebral ischemia in mice

Endogenous neurogenesis persists in the subgranular zone (SGZ) of the adult rodent brain. Cerebral ischemia stimulates endogenous neurogenesis involving proliferation, migration and differentiation of SGZ-derived neural precursor cells (NPC). However, the biological meaning of this phenomenon is limited by poor survival of NPC. In order to study the effects of an acute neuroprotective treatment on hippocampal endogenous neurogenesis after transient cerebral ischemia in mice, we applied a fusion protein consisting of the TAT domain of the HI virus with the anti-apoptotic Bcl-x_L. Intravenous injection of TAT-Bcl-x_L resulted in reduced hippocampal cell injury for up to 4 weeks after stroke as assessed by TUNEL and NeuN staining. This was in line with a TAT-Bcl-x_L-mediated reduced postischemic microglia activation. Analysis of endogenous hippocampal cell proliferation revealed an increased number of BrdU⁺ cells in the TAT-Bcl-x_L group 4 weeks after stroke compared to animals treated with saline and TAT-HA (negative control). Cell proliferation in non-ischemic sham operated animals was not affected by TAT-Bcl-x_L. Twenty-eight days after stroke co-expression of BrdU⁺ cells with the immature neuronal marker doublecortin was significantly increased in TAT-Bcl-x_L animals. Although TAT-Bcl-x_L treatment also resulted in an increased number of BrdU⁺ cells expressing the mature neuronal marker NeuN, the total amount of these cells was low. These data show that TAT-Bcl-x_L treatment yields both postischemic sustained hippocampal neuroprotection and increased survival of NPC rather than an induction of endogenous neurogenesis itself.     

Impairment of hippocampal neurogenesis in streptozotocin-treated diabetic rats

Objectives –  Adult neurogenesis in dentate gyrus (DG) is an evolutionarily preserved trait in most mammals examined thus far. Neuronal proliferation and subsequent integration of new neurons into the hippocampal circuit are regulated processes that can have profound effects on an animal's behaviour. A streptozotocin model of type I diabetes, characterized by low insulin and high plasma glucose levels, affects not only body's overall metabolism but also brain activity.
Materials and methods –  Neurogenesis was measured within the DG of the hippocampus using immunohistochemical markers Ki67, Doublecortin, Calbindin (CaBP) and bromodeoxyuridine (BrdU).
Results –  Cell proliferation, measured with the endogenous marker Ki67, was reduced by 45%, and cell survival, measured with BrdU, was reduced by 64% of the control. Combined effects on proliferation and survival produced dramatically lower neuronal production. Among the surviving cells only 33% matured normally as judged by the co-labelling of BrdU and CaBP.
Conclusion –  Such a reduction lowered the number of surviving cells with neuronal phenotype by over 80% of the control values and this is expected to cause a significant functional impairment of learning and memory in diabetic animals. These results may shed light on causes of diabetic neuropathology and provide an explanation for the memory deficiencies seen in some diabetic patients.     

Fibroblast growth factor-2 deficiency causes defects in adult hippocampal neurogenesis, which are not rescued by exogenous fibroblast growth factor-2

Neurogenesis within the adult brain is restricted to selected areas, one of which is the dentate gyrus (DG). Several growth factors have been reported to affect neurogenesis in the adult DG. However, a role of fibroblast growth factor-2 (FGF-2) in adult hippocampal neurogenesis has not been firmly established. We have analyzed neurogenesis in the DG using in vivo and in vitro approaches. FGF-2(-/-) mice revealed no alterations in the number of proliferating cells but a significant decrease in the numbers of newly generated neurons. Moreover, FGF-2 added to hippocampal slice cultures from FGF-2(-/-) mice was unable to rescue the phenotype. Although an increase in death of neurogenic cells in the FGF-2-deficient DG could not be specifically demonstrated, there was a massive increase in global cell death in FGF-2(-/-) hippocampal slice cultures compared with slices from wild-type mice. Cell death could not be prevented by addition of FGF-2. Neutralization of endogenous FGF-2 in hippocampal slices did not interfere with neurogenesis in a short-term paradigm. Together, our data suggest that FGF-2 is essentially required for maturation of new neurons in adult hippocampal neurogenesis but is likely to operate synergistically in combination with other mechanisms/growth factors.