Chronic fluoxetine treatment improves ischemia-induced spatial cognitive deficits through increasing hippocampal neurogenesis after stroke

Cognitive deficits, including spatial memory impairment, are very common after ischemic stroke. Neurogenesis in the dentate gyrus (DG) contributes to forming spatial memory in the ischemic brain. Fluoxetine, a selective serotonin reuptake inhibitor, can enhance neurogenesis in the hippocampus in physiological situations and some neurological diseases. However, whether it has effects on ischemia-induced spatial cognitive impairment and hippocampal neurogenesis has not been determined. Here we report that fluoxetine treatment (10 mg kg(-1), i.p.) for 4 weeks promoted the survival of newborn cells in the ischemic hippocampus and, consequently, attenuated spatial memory impairment of mice after focal cerebral ischemia. Disrupting hippocampal neurogenesis blocked the beneficial effect of fluoxetine on ischemia-induced spatial cognitive impairment. These results suggest that chronic fluoxetine treatment benefits spatial cognitive function recovery following ischemic insult, and the improved cognitive function is associated with enhanced newborn cell survival in the hippocampus. Our results raise the possibility that fluoxetine can be used as a drug to treat poststroke spatial cognitive deficits.     

NADPH oxidase mediates β-amyloid peptide-induced activation of ERK in hippocampal organotypic cultures

Newborn neurons in the subgranular zone (SGZ) of the hippocampus incorporate into the dentate gyrus and mature. Numerous studies have focused on hippocampal neurogenesis because of its importance in learning and memory. However, it is largely unknown whether hippocampal neurogenesis is involved in memory extinction per se. Here, we sought to examine the possibility that hippocampal neurogenesis may play a critical role in the formation and extinction of hippocampus-dependent contextual fear memory. By methylazoxymethanol acetate (MAM) or gamma-ray irradiation, hippocampal neurogenesis was impaired in adult mice. Under our experimental conditions, only a severe impairment of hippocampal neurogenesis inhibited the formation of contextual fear memory. However, the extinction of contextual fear memory was not affected. These results suggest that although adult newborn neurons contribute to contextual fear memory, they may not be involved in the extinction or erasure of hippocampus-dependent contextual fear memory.     

Functional recruitment of newborn hippocampal neurons after experimental stroke

The adult brain responds to diverse pathologies such as stroke with increased generation of neurons in the dentate gyrus of the hippocampus. However, only little is known regarding the functional integration of newborn neurons into pre-existing neuronal circuits. In this study, we investigated whether newborn neurons generated after experimental stroke are recruited for different behavioral tasks. Adult mice received photochemical cortical infarcts in the sensorimotor cortex and proliferating cells were labeled using the proliferation marker, bromodeoxyuridine. Eight weeks after stroke induction, the animals were trained to perform either a spatiotemporal task or a sensorimotor task. Immediate early gene expression (c-fos, Zif268) in newborn neurons was analyzed directly after the last session. Using this approach, we demonstrate that post-stroke generated neurons are recruited within the hippocampal networks. The sensorimotor task activates significantly more newborn neurons compared to the spatiotemporal task. Further experiments employing the two well-established stimulators of neurogenesis, enriched environment and voluntary wheel running, both significantly increase post-stroke neurogenesis in the dentate gyrus but do not affect the percentage of recruited neurons compared to controls. Significantly, the spatiotemporal task leads to a higher portion of activated newborn neurons in the granule cell layer, suggesting a specific spatial activation pattern of new neurons in the dentate gyrus.     

Neuron-Specific Expression of Tomosyn1 in the Mouse Hippocampal Dentate Gyrus Impairs Spatial Learning and Memory

Tomosyn, a syntaxin-binding protein, is known to inhibit vesicle priming and synaptic transmission via interference with the formation of SNARE complexes. Using a lentiviral vector, we specifically overexpressed tomosyn1 in hippocampal dentate gyrus neurons in adult mice. Mice were then subjected to spatial learning and memory tasks and electrophysiological measurements from hippocampal slices. Tomosyn1-overexpression significantly impaired hippocampus-dependent spatial memory while tested in the Morris water maze. Further, tomosyn1-overexpressing mice utilize swimming strategies of lesser cognitive ability in the Morris water maze compared with control mice. Electrophysiological measurements at mossy fiber-CA3 synapses revealed impaired paired-pulse facilitation in the mossy fiber of tomosyn1-overexpressing mice. This study provides evidence for novel roles for tomosyn1 in hippocampus-dependent spatial learning and memory, potentially via decreased synaptic transmission in mossy fiber-CA3 synapses. Moreover, it provides new insight regarding the role of the hippocampal dentate gyrus and mossy fiber-CA3 synapses in swimming strategy preference, and in learning and memory.     

Enriched environment and physical activity stimulate hippocampal but not olfactory bulb neurogenesis

Exposure to an enriched environment and physical activity, such as voluntary running, increases neurogenesis of granule cells in the dentate gyrus of adult mice. These stimuli are also known to improve performance in hippocampus-dependent learning tasks, but it is unclear whether their effects on neurogenesis are exclusive to the hippocampal formation. In this study, we housed adult mice under three conditions (enriched environment, voluntary wheel running and standard housing), and analysed proliferation in the lateral ventricle wall and granule cell neurogenesis in the olfactory bulb in comparison to the dentate gyrus. Using bromodeoxyuridine to label dividing cells, we could not detect any difference in the number of newly generated cells in the ventricle wall. When giving the new cells time to migrate and differentiate in the olfactory bulb, we observed no changes in the number of adult-generated olfactory granule cells; however, voluntary running and enrichment produced a doubling in the amount of new hippocampal granule cells. The discrepancy between the olfactory bulb and the dentate gyrus suggests that these living conditions trigger locally through an as yet unidentified mechanism specific to neurogenic signals in the dentate gyrus.     

Requirement of adult-born neurons for hippocampus-dependent learning

A fundamental question in the field of adult neurogenesis relies in addressing whether neurons generated in the adult dentate gyrus are needed for hippocampal function. Increasing evidence is accumulating in support of the notion that hippocampus-dependent behaviors activate new neurons and that those neurons are highly relevant for information processing. More specifically, immature new neurons under development that have unique functional characteristics begin to emerge as a highly relevant population in the dentate gyrus network. This review focuses on how hippocampus-dependent behaviors activate adult-born neurons and how modulation and ablation of adult hippocampal neurogenesis alter spatial and associative memory. While several contradictory findings emerge when analyzing the literature, evidence in favor of a relevant role of adult-born neurons in hippocampal function is compelling.     

SREB2/GPR85, a schizophrenia risk factor, negatively regulates hippocampal adult neurogenesis and neurogenesis-dependent learning and memory

SREB2/GPR85, a member of the super-conserved receptor expressed in brain (SREB) family, is the most conserved G-protein-coupled receptor in vertebrate evolution. Previous human and mouse genetic studies have indicated a possible link between SREB2 and schizophrenia. SREB2 is robustly expressed in the hippocampal formation, especially in the dentate gyrus, a structure with an established involvement in psychiatric disorders and cognition. However, the function of SREB2 in the hippocampus remains elusive. Here we show that SREB2 regulates hippocampal adult neurogenesis, which impacts on cognitive function. Bromodeoxyuridine incorporation and immunohistochemistry were conducted in SREB2 transgenic (Tg, over-expression) and knockout (KO, null-mutant) mice to quantitatively assay adult neurogenesis and newborn neuron dendritic morphology. Cognitive responses associated with adult neurogenesis alteration were evaluated in SREB2 mutant mice. In SREB2 Tg mice, both new cell proliferation and new neuron survival were decreased in the dentate gyrus, whereas an enhancement of new neuron survival occurred in SREB2 KO mouse dentate gyrus. Doublecortin staining revealed dendritic morphology deficits of newly generated neurons in SREB2 Tg mice. In a spatial pattern separation task, SREB2 Tg mice displayed a decreased ability to discriminate spatial relationships, whereas SREB2 KO mice had enhanced abilities in this task. Additionally, SREB2 Tg and KO mice had reciprocal phenotypes in a Y-maze working memory task. Our results indicate that SREB2 is a negative regulator of adult neurogenesis and consequential cognitive functions. Inhibition of SREB2 function may be a novel approach to enhance hippocampal adult neurogenesis and cognitive abilities to ameliorate core symptoms of psychiatric patients.     

Environmental enrichment and physical exercise revert behavioral and electrophysiological impairments caused by reduced adult neurogenesis

It is well known that adult neurogenesis occurs in two distinct regions, the subgranular zone of the dentate gyrus and the subventricular zone along the walls of the lateral ventricles. Until now, the contribution of these newly born neurons to behavior and cognition is still uncertain. The current study tested the functional impacts of diminished hippocampal neurogenesis on emotional and cognitive functions in transgenic Gfap‐tk mice. Our results showed that anxiety‐related behavior evaluated both in the elevated plus maze as well as in the open field, social interaction in the sociability test, and spatial working memory in the spontaneous alternation test were not affected. On the other hand, recognition and emotional memory in the object recognition test and contextual fear conditioning, and hippocampal long‐term potentiation were impaired in transgenic mice. Furthermore, we evaluated whether environmental enrichment together with physical exercise could improve or even restore the level of adult neurogenesis, as well as the behavioral functions. Our results clearly demonstrated that environmental enrichment together with physical exercise successfully elevated the overall number of progenitor cells and young neurons in the dentate gyrus of transgenic mice. Furthermore, it led to a significant improvement in object recognition memory and contextual fear conditioning, and reverted impairments in hippocampal long‐term potentiation. Thus, our results confirm the importance of adult neurogenesis for learning and memory processes and for hippocampal circuitry in general. Environmental enrichment and physical exercise beneficially influenced adult neurogenesis after it had been disrupted and most importantly recovered cognitive functions and long‐term potentiation. © 2016 Wiley Periodicals, Inc.     

Inhibition of adult neurogenesis by inducible and targeted deletion of ERK5 mitogen-activated protein kinase specifically in adult neurogenic regions impairs contextual fear extinction and remote fear memory

Although there is evidence suggesting that adult neurogenesis may contribute to hippocampus-dependent memory, signaling mechanisms responsible for adult hippocampal neurogenesis are not well characterized. Here we report that ERK5 mitogen-activated protein kinase is specifically expressed in the neurogenic regions of the adult mouse brain. The inducible and conditional knock-out (icKO) of erk5 specifically in neural progenitors of the adult mouse brain attenuated adult hippocampal neurogenesis. It also caused deficits in several forms of hippocampus-dependent memory, including contextual fear conditioning generated by a weak footshock. The ERK5 icKO mice were also deficient in contextual fear extinction and reversal of Morris water maze spatial learning and memory, suggesting that adult neurogenesis plays an important role in hippocampus-dependent learning flexibility. Furthermore, our data suggest a critical role for ERK5-mediated adult neurogenesis in pattern separation, a form of dentate gyrus-dependent spatial learning and memory. Moreover, ERK5 icKO mice have no memory 21 d after training in the passive avoidance test, suggesting a pivotal role for adult hippocampal neurogenesis in the expression of remote memory. Together, our results implicate ERK5 as a novel signaling molecule regulating adult neurogenesis and provide strong evidence that adult neurogenesis is critical for several forms of hippocampus-dependent memory formation, including fear extinction, and for the expression of remote memory.     

Granule cell dispersion and aberrant neurogenesis in the adult hippocampus of an LIS1 mutant mouse

Human type 1 lissencephaly is a severe brain malformation associated with cognitive dysfunction and intractable epilepsy. Mutant mice with a heterozygous deletion of LIS1 show varying degrees of hippocampal abnormality and enhanced excitability. Whether a reduction of LIS1 function affects adult hippocampal neurogenesis, and if so, whether aberrant neurogenesis contributes to the generation of a disorganized hippocampus remain unknown. Previous reports indicate the presence of multiple pyramidal cell layers and granule cell dispersion in LIS1 mutant mice. Here we observed disruption of the subgranular zone and glial fibrillary acidic protein-immunoreactive radial astrocytes in the dentate gyrus of adult LIS1 mice. Using pulse-chase bromodeoxyuridine (BrdU) labeling combined with neuronal and glial antibody staining we provide evidence for ectopic adult neurogenesis in LIS1 mice. A gradually decreased survival rate for these newborn granule cells was also demonstrated in LIS1 mice 7 days after BrdU injection. This reduced survival rate was associated with impaired neuronal differentiation 28 days after BrdU administration. Thus, LIS1 haploinsufficiency can lead to abnormal cell proliferation, migration and differentiation in the adult dentate gyrus.     

Bcl2 enhances survival of newborn neurons in the normal and ischemic hippocampus

Neuronal progenitors in the adult hippocampus continually proliferate and differentiate to the neuronal lineage, and ischemic insult promotes hippocampal neurogenesis. However, newborn neurons show a progressive reduction in numbers during the initial few weeks, therefore, enhanced survival of newborn neurons seems to be essential for therapeutic strategy. Bcl-2 is a crucial regulator of programmed cell death in CNS development and in apoptotic and necrotic cell death. Therefore, we tested whether Bcl-2 overexpression enhances survival of newborn neurons in the adult mouse hippocampus under normal and ischemic conditions. Many newborn neurons in the hippocampal dentate gyrus undergo apoptosis. Human Bcl-2 expression in NSE-bcl-2 transgenic mice began at the immature neuronal stage and remained constant in surviving mature neurons. Bcl-2 significantly increased survival of newborn neurons under both conditions, but particularly after ischemia, with decreased cell death of newborn neurons in NSE-bcl-2 transgenic mice. We also clarified the effect by Bcl-2 overexpression of enhanced survival of newborn neurons in primary hippocampal cultures with BrdU labeling. These findings suggest that Bcl-2 plays a crucial role in adult hippocampal neurogenesis under normal and ischemic conditions.     

Identification of a biphasic signaling pathway involved in ischemic resistance of the hippocampal dentate gyrus

Dentate gyrus is usually assumed to be resistant to ischemia. However, the mechanisms underlying this functional plasticity are not fully understood. Herein, we aimed at identifying a neuroprotective mechanism in the dentate gyrus of the adult rat after global ischemia. Cyclic AMP response element (CRE)-binding protein (CREB), brain-derived neurotrophic factor (BDNF) and calcium/calmodulin-dependent protein kinase IV (CaMKIV) are known to be mediators of neuronal survival and plasticity. Involvement of CaMKIV, BDNF and CREB in ischemic resistance was therefore examined using intracerebroventricular injections of pharmacological agents such as inhibitors, antibodies and consensus oligonucleotides followed by immunohistochemical and Western blot analysis. We provide evidence that ischemia triggers activation of a biphasic pathway during the resistance period of dentate neurons: (1) CaMKIV mediates the early phosphorylation of CREB which drives a prominent synthesis of BDNF; (2) this BDNF synthesis, in turn, induces a second peak of CREB phosphorylation which is required for the maintenance of BDNF synthesis. In addition, we show that: (1) impairment of these transduction signals by the pharmacological agents causes tissular damages and apoptotic deaths in the post-ischemic dentate gyrus; (2) some similar disturbances also occur beyond the resistance period in the dentate gyrus of untreated ischemic rats; (3) these disturbing effects are mainly observed in the suprapyramidal dentate subfield. Collectively, the present results suggest that activation of the CaMKIV/CREB/BDNF pathway plays principally an early protective role in the suprapyramidal subfield of the dentate gyrus.     

Modulation of adult hippocampal neurogenesis by thyroid hormones: implications in depressive-like behavior

Hormonal imbalances are involved in many of the age-related pathologies, as neurodegenerative and psychiatric diseases. Specifically, thyroid state alterations in the adult are related to psychological changes and mood disorders as depression. The dentate gyrus of the hippocampal formation undergoes neurogenesis in adult mammals including humans. Recent evidence suggests that depressive disorders and their treatment are tightly related to the number of newly born neurons in the dentate gyrus. We have studied the effect of thyroid hormones (TH) on hippocampal neurogenesis in adult rats in vivo. A short period of adult-onset hypothyroidism impaired normal neurogenesis in the subgranular zone of the dentate gyrus with a 30% reduction in the number of proliferating cells. Hypothyroidism also reduced the number of newborn neuroblasts and immature neurons (doublecortin (DCX) immunopositive cells) which had a severely hypoplastic dendritic arborization. To correlate these changes with hippocampal function, we subjected the rats to the forced swimming and novel object recognition tests. Hypothyroid rats showed normal memory in object recognition, but displayed abnormal behavior in the forced swimming test, indicating a depressive-like disorder. Chronic treatment of hypothyroid rats with TH not only normalized the abnormal behavior but also restored the number of proliferative and DCX-positive cells, and induced growth of their dendritic trees. Therefore, hypothyroidism induced a reversible depressive-like disorder, which correlated to changes in neurogenesis. Our results indicate that TH are essential for adult hippocampal neurogenesis and suggest that mood disorders related to adult-onset hypothyroidism in humans could be due, in part, to impaired neurogenesis.     

Effects of CXCR7-neutralizing antibody on neurogenesis in the hippocampal dentate gyrus and cognitive function in the chronic phase of cerebral ischemia

Stromal cell-derived factor-1 and its receptor CXCR4 are essential regulators of the neurogenesis that occurs in the adult hippocampal dentate gyrus.However,the effects of CXCR7,a new atypical receptor of stromal cell-derived factor-1,on hippocampal neurogenesis after a stroke remain largely unknown.Our study is the first to investigate the effect of a CXCR7-neutralizing antibody on neurogenesis in the dentate gyrus and the associated recovery of cognitive function of rats in the chronic stage of cerebral ischemia.The rats were randomly divided into sham,sham+anti-CXCR7,ischemia and ischemia+anti-CXCR7 groups.Endothelin-1 was injected in the ipsilateral motor cortex and striatum to induce focal cerebral ischemia.Sham group rats were injected with saline instead of endothelin-1 via intracranial injection.Both sham and ischemic rats were treated with intraventricular infusions of CXCR7-neutralizing antibodies for 6 days 1 week after surgery.Immunofluorescence staining with doublecortin,a marker for neuronal precursors,was performed to assess the neurogenesis in the dentate gyrus.We found that anti-CXCR7 antibody infusion enhanced the proliferation and dendritic development of doublecortin-labeled cells in the dentate gyrus in both ischemic and sham-operated rats.Spatial learning and memory functions were assessed by Morris water maze tests 30-32 days after ischemia.CXCR7-neutralizing antibody treatment significantly reduced the escape latency of the spatial navigation trial and increased the time spent in the target quadrant of spatial probe trial in animals that received ischemic insult,but not in sham operated rats.These results suggest that CXCR7-neutralizing antibody enhances the neurogenesis in the dentate gyrus and improves the cognitive function after cerebral ischemia in rats.All animal experimental protocols and procedures were approved by the Institutional Animal Care and Use Committee of China Medical University(CMU16089 R)on December 8,2016.     

Essential role of tau phosphorylation in adult hippocampal neurogenesis

An increased hippocampal neurogenesis has been observed in Alzheimer disease (AD), the most common neurodegenerative disorder characterized with accumulation of β‐amyloid (Aβ) and hyperphosphorylated tau (p‐tau). Studies in transgenic mouse models suggest that the amyloidosis suppresses adult neurogenesis. Although emerging evidence links tau to neurodevelopment, the direct data regarding tau phosphorylation in adult neurogenesis is missing. Here, we found that the immature neurons, identified by doublecortin (DCX) and neurogenic differentiation factor (neuroD), were only immunoreactive to p‐tau but not to the non‐p‐tau in adult rat brain and human patients with AD, and the p‐tau was coexpressed temporally and spatially with DCX and neuroD in the hippocampal dentate gyrus (DG) of the rat brains during postnatal development. A correlative increase of immature neuron markers and tau phosphorylation was induced in rat hippocampal DG by upregulating glycogen synthase kinase‐3 (GSK‐3), a crucial tau kinase, and the increased neurogenesis was due to an enhanced proliferation but not survival or differentiation of the newborn neurons. The hippocampal neurogenesis was severely impaired in tau knockout mice and activation of GSK‐3 in these mice did not rescue the deficits. These results reveal an essential role of tau phosphorylation in adult hippocampal neurogenesis. It suggests that spatial/temporal manipulation of tau phosphorylation may be compensatory for the neuron loss in neurological disorders, including AD. © 2009 Wiley‐Liss, Inc.     

Long-term functional consequences of transient occlusion of the middle cerebral artery in rats: a 1-year follow-up of the development of epileptogenesis and memory impairment in relation to sensorimotor deficits

Post-stroke seizures occur in 5-20% of patients. Modeling of stroke-induced seizures in animals provides a useful tool for investigating the molecular basis of epileptogenesis and for developing therapies for stroke patients at increased risk for epileptogenesis. The questions addressed in the study were: (1) Do rats develop spontaneous seizures after transient occlusion of the middle cerebral artery (MCAO)? (2) Is epileptogenesis associated with impaired hippocampus-dependent spatial learning and memory? (3) Are the functional abnormalities linked to axonal plasticity in the dentate gyrus? (4) Does the sensorimotor impairment induced by MCAO predict the risk of epileptogenesis? Adult male Sprague-Dawley rats were subjected to MCAO for 120 min. Development of spontaneous seizures was monitored by 1 week of continuous video-electroencephalographic (EEG) recordings at 3, 7, and 12 months after MCAO. Spontaneous seizures were not detected during 1-year follow-up in ischemic rats. Animals were, however, impaired in the spatial memory task (P<0.001), which was not associated with altered hippocampal LTP or abnormal mossy fiber sprouting (Timm staining). Animals also had a long-lasting sensorimotor deficit (P<0.05). The present study indicates that MCAO causes long-lasting sensorimotor and spatial memory impairment, but does not induce epileptogenesis or spontaneous seizures.     

Environmental enrichment enhances neurogenesis and improves functional outcome after cranial irradiation

Radiation therapy is a widely used treatment for brain tumors but it can cause delayed progressive cognitive decline and memory deficits. Previous studies suggested that this neurocognitive dysfunction might be linked to the impairment of hippocampal neurogenesis. However, little is known regarding how to reduce the cognitive impairment caused by radiation therapy. To investigate whether environmental enrichment (EE) promotes neurogenesis and cognitive function after irradiation, irradiated gerbils were housed in EE for 2 months and evaluated by neurobehavioral testing for learning and memory function, and immunohistochemical analysis for neurogenesis. Our results demonstrated that even relatively low doses (5-10 Gy) of irradiation could acutely abolish precursor cell proliferation in the dentate gyrus by more than 90%. This reduction in precursor proliferation was persistent and led to a significant decline in the granule cell population 9 months later. EE housing enhanced the number of newborn neurons and increased residual neurogenesis. EE also significantly increased the total number of immature neurons in the dentate gyrus. Furthermore, irradiated animals after EE housing showed a significant improvement in spatial learning and memory during the water-maze test and in rotorod motor learning over a 5-day training paradigm. In conclusion, EE has a positive impact on hippocampal neurogenesis and functional recovery in irradiated adult gerbils. Our data suggest that there is still a considerable amount of plasticity remaining in the hippocampal progenitor cells in adult animals after radiation injury, which can become a target of therapeutic intervention for radiation-induced cognitive dysfunction.     

Forebrain neurogenesis after focal Ischemic and traumatic brain injury

Neural stem cells persist in the adult mammalian forebrain and are a potential source of neurons for repair after brain injury. The two main areas of persistent neurogenesis, the subventricular zone (SVZ)-olfactory bulb pathway and hippocampal dentate gyrus, are stimulated by brain insults such as stroke or trauma. Here we focus on the effects of focal cerebral ischemia on SVZ neural progenitor cells in experimental stroke, and the influence of mechanical injury on adult hippocampal neurogenesis in models of traumatic brain injury (TBI). Stroke potently stimulates forebrain SVZ cell proliferation and neurogenesis. SVZ neuroblasts are induced to migrate to the injured striatum, and to a lesser extent to the peri-infarct cortex. Controversy exists as to the types of neurons that are generated in the injured striatum, and whether adult-born neurons contribute to functional restoration remains uncertain. Advances in understanding the regulation of SVZ neurogenesis in general, and stroke-induced neurogenesis in particular, may lead to improved integration and survival of adult-born neurons at sites of injury. Dentate gyrus cell proliferation and neurogenesis similarly increase after experimental TBI. However, pre-existing neuroblasts in the dentate gyrus are vulnerable to traumatic insults, which appear to stimulate neural stem cells in the SGZ to proliferate and replace them, leading to increased numbers of new granule cells. Interventions that stimulate hippocampal neurogenesis appear to improve cognitive recovery after experimental TBI. Transgenic methods to conditionally label or ablate neural stem cells are beginning to further address critical questions regarding underlying mechanisms and functional significance of neurogenesis after stroke or TBI. Future therapies should be aimed at directing appropriate neuronal replacement after ischemic or traumatic injury while suppressing aberrant integration that may contribute to co-morbidities such as epilepsy or cognitive impairment.     

Neurosteroid PREGS protects neurite growth and survival of newborn neurons in the hippocampal dentate gyrus of APPswe/PS1dE9 mice

Neurosteroids pregnenolone-sulfate (PREGS) and dehydroepiandrosterone (DHEA) have been shown to enhance neurogenesis in the hippocampal dentate gyrus (DG) of adult rodents. In Alzheimer's disease (AD) brain, the levels of these neurosteroids are known to be altered compared to age-matched non-demented controls. The aim of this study was to examine the effects of PREGS and DHEA on the hippocampal neurogenesis in 8-month-old male APPswe/PS1dE9 transgenic (APP/PS1) mice that show amyloid plaques and impaired spatial cognitive performance. In the DG of APP/PS1 mice the proliferation of progenitor cells was increased, while the neurite growth and survival of newborn neuronal cells were markedly impaired. Treatment with PREGS or DHEA rescued perfectly the hypoplastic neurite of newborn neurons in APP/PS1 mice, while neither of them affected the over-proliferation of progenitor cells. Notably, the administration of PREGS, but not DHEA, to APP/PS1 mice could protect the survival and maturation of newborn neuronal cells, which was accompanied by the improvement of spatial cognitive performance. The results indicate that treatment of AD like brains of APP/PS1 mice with PREGS might protect the hippocampal neurogenesis, leading to the improved spatial cognitive performance.     

Fibroblast growth factor receptor-1 is required for long-term potentiation, memory consolidation, and neurogenesis.

BACKGROUND: Although substantial evidence supports the view that adult neurogenesis is involved in learning and memory, how newly generated neurons contribute to the cognitive process remains unknown. Fibroblast growth factor 2 (FGF-2) is known to stimulate the proliferation of neuronal progenitor cells (NPCs) in adult brain. Using conditional knockout mice that lack brain expression of FGFR1, a major receptor for FGF-2, we have investigated the role of adult neurogenesis in hippocampal synaptic plasticity and learning and memory. METHODS: The Fgfr1 conditional knockout mice were generated by crossing the Fgfr1-null line, the Fgfr1-flox line, and the Nestin-Cre transgenic mice. Bromodeoxyuridine (BrdU) labeling, slice electrophysiology, and Morris Water Maze experiments were performed with the Fgfr1 conditional mutant mice. RESULTS: Bromodeoxyuridine labeling experiments demonstrate that FGFR1 is required for the proliferation of NPCs as well as generation of new neurons in the adult dentate gyrus (DG). Moreover, deficits in neurogenesis in Fgfr1 mutant mice are accompanied by a severe impairment of long-term potentiation (LTP) at the medial perforant path (MPP)-granule neuron synapses in the hippocampal dentate. Moreover, the Fgfr1 mutant mice exhibit significant deficits in memory consolidation but not spatial learning. CONCLUSIONS: Our study suggests a critical role of FGFR1 in adult neurogenesis in vivo, provides a potential link between proliferative neurogenesis and dentate LTP, and raises the possibility that adult neurogenesis might contribute to memory consolidation.