Adult hippocampal neurogenesis and its role in cognition

Resveratrol mitigates activated astrocytes and microglia preventing Alzheimer's Disease (AD) progression and facilitates neuronal communication in Amyloid-β25-35 induced rat model for AD: A special emphasis on non-neuronal involvement in AD pathophysiology

RATIONALE

Amyloid deposits initiate neuroinflammation by activating astrocytes and microglia in the hippocampus, increasing neuronal vulnerability and loss. Astrocytes, while essential for cerebral function, can contribute to neuronal dysfunction by retracting neuronal synapses, that forms a consequence of neuroinflammation, leading to cognitive deficits in Alzheimer's disease (AD). Upon Amyloid-β (Aβ) deposition, astrocytes become reactive as part of a repair mechanism, however this process can impair neurogenesis resulting in AD progression.

OBJECTIVE

The current study hypothesizes that resveratrol (RSV) can address inflammation and promote neural regeneration, mitigating cognitive decline. Our previous research highlights RSV's homeostatic effect through SIRT1 normalization, which is crucial in preventing AD progression. However, its neurogenic potential in AD remains underexplored.

METHODS

In this study, Aβ25-35-induced AD rat model was used to study the anti-inflammatory, neurogenic and cellular homeostatic effect of RSV (30 mg/kg) for four weeks.

RESULTS

Results showed increased Doublecortin expressing cells, indicating favorable neurogenesis in hippocampus. Immunofluorescence of microglia and astrocytes in the hippocampus revealed that RSV counteracted their activation by reducing the formation of engulfing microglia and elongated astrocytes. Behavioral assessments using the Morris water maze and cued radial arm maze demonstrated significant improvements in spatial and learning memory. These cognitive improvements were supported by increased choline acetyltransferase and SIRT1 levels.

CONCLUSION

These findings suggest that RSV effectively reduces neuroinflammation, promotes neurogenesis in the sub granular zone of the hippocampus, and improves learning and memory in both control and AD conditions via SIRT1. This study highlights RSV's potential as a suitable therapeutic agent for AD.

Effect of adult hippocampal neurogenesis on pattern separation and its applications

Adult hippocampal neurogenesis (AHN) is considered essential in memory formation. The dentate gyrus neural network containing newborn dentate gyrus granule cells at the critical period (4-6 weeks) have been widely discussed in neurophysiological and behavioral experiments. However, how newborn dentate gyrus granule cells at this critical period influence pattern separation of dentate gyrus remains unclear. To address this issue, we propose a biologically related dentate gyrus neural network model with AHN. By Leveraging this model, we find pattern separation is enhanced at the medium level of neurogenesis (5% of mature granule cells). This is because the sparse firing of mature granule cells is increased. We can understand this change from the following two aspects. On one hand, newborn granule cells compete with mature granule cells for inputs from the entorhinal cortex, thereby weakening the firing of mature granule cells. On the other hand, newborn granule cells effectively enhance the feedback inhibition level of the network by promoting the firing of interneurons (Mossy cells and Basket cells) and then indirectly regulating the sparse firing of mature granule cells. To verify the validity of the model for pattern separation, we apply the proposed model to a similar concept separation task and reveal that our model outperforms the original model counterparts in this task.

Altered neuronal lactate dehydrogenase A expression affects cognition in a sex- and age-dependent manner

The astrocyte-neuron lactate shuttle (ANLS) model posits that astrocyte-generated lactate is transported to neurons to fuel memory processes. However, neurons express high levels of lactate dehydrogenase A (LDHA), the rate-limiting enzyme of lactate production, suggesting a cognitive role for neuronally generated lactate. It was hypothesized that lactate metabolism in neurons is critical for learning and memory. Here transgenic mice were generated to conditionally induce or knockout (KO) the Ldha gene in CNS neurons of adult mice. High pattern separation memory was enhanced by neuronal Ldha induction in young females, and by neuronal Ldha KO in aged females. In older mice, Ldha induction caused cognitive deficits whereas Ldha KO caused cognitive improvements. Genotype-associated cognitive changes were often only observed in one sex or oppositely in males and females. Thus, neuronal-generated lactate has sex-specific cognitive effects, is largely indispensable at young age, and may be detrimental to learning and memory with aging.

Hippocampal neurodegeneration induces transient endogenous regeneration and long-term exhaustion of the neurogenic niche

The hippocampal dentate gyrus, responds to diverse pathological stimuli through neurogenesis. This phenomenon, observed following brain injury or neurodegeneration, is postulated to contribute to neuronal repair and functional recovery, thereby presenting an avenue for endogenous neuronal restoration. This study investigated the extent of regenerative response in hippocampal neurogenesis by leveraging the well-established kainic acid-induced status epilepticus model in vivo. In our study, we observed the activation and proliferation of neuronal progenitors or neural stem cell (NSC) and their subsequent migration to the injury sites following the seizure. At the injury sites, new neurons (Tuj1+BrdU+ and NeuN+BrdU+) have been generated indicating regenerative and reparative roles of the progenitor cells. We further detected whether this transient neurogenic burst, which might be a response towards an attempt to repair the brain, is associated with persistent long-term exhaustion of the dentate progenitor cells and impairment of adult neurogenesis marked by downregulation of Ki67, HoPX, and Sox2 with BrdU+ cell in the later part of life. Our studies suggest that the adult brain has the constitutive endogenous regenerative potential for brain repair to restore the damaged neurons, meanwhile, in the long term, it accelerates the depletion of the finite NSC pool in the hippocampal neurogenic niche by changing its proliferative and neurogenic capacity. A thorough understanding of the impact of modulating adult neurogenesis will eventually be required to design novel therapeutics to stimulate or assist brain repair while simultaneously preventing the adverse effects of early robust neurogenesis on the proliferative potential of endogenous neuronal progenitors.

Fluvoxamine Ameliorates the Damage to the Neuro-Behavioral Status of Rats Caused by the Administration of Valproic Acid by Preventing Cognitive Memory Deficits and Decreased Hippocampal Cellular Proliferation

Fluvoxamine is a major antidepressant of the selective serotonin-reuptake inhibitor class, previously studied as a drug that improves cognitive memory by enhancing hippocampal cell division and proliferation. Valproic acid (VPA) is a commonly used antiepileptic drug and mood stabilizer that has negative effects on cognitive memory as it inhibits cellular division and proliferation in the hippocampus. This study assessed the protective effects of fluvoxamine treatment versus the memory impairment, decreased hippocampal cellular proliferation, and weight loss produced by VPA treatment. The cognitive memory of 40 male Sprague-Dawley rats was assessed by the novel object location (NOL) test. Immunostaining by Ki67 and glutathione peroxidase 1 (GPX-1) was performed to quantify the number of dividing cells in the subgranular zone (SGZ) of the dentate gyrus and to assess the antioxidant activity of different treatments, respectively. Results showed that the VPA group had fewer Ki67-positive cells than the control group (p < 0.001), indicating reduced hippocampal proliferation. In contrast, the VPA and fluvoxamine combination group showed increased proliferation (p < 0.001) compared to VPA alone. Notably, fluvoxamine treatment significantly differed in cell counts compared to other groups (p < 0.001). Fluvoxamine also attenuated the weight loss caused by VPA (p < 0.0001). Our data suggested that fluvoxamine therapy attenuated the VPA-induced decrease in SGZ cellular proliferation, memory, and weight in rats.

Taste receptor type 1 member 3 mediates diet-induced cognitive impairment in mice

AIMS

Long-term consumption of a western diet (WD), which is characterized by high intake of saturated fats and sugary drinks, causes cognitive impairment. However, the molecular mechanism by which WD induces cognitive impairment remains unclear. Taste receptor type 1 member 3 (TAS1R3), activated by ligands of WD, is expressed in extra-oral tissues, including the brain, and particularly in the hippocampus. This study investigated whether TAS1R3 regulates WD-induced cognitive impairment in mice.

MAIN METHODS

Male C57BL/6J wild-type (WT) and Tas1r3 knock-out (KO) mice were fed either a normal diet (ND) or WD for 18 weeks. Cognitive functions were assessed using novel object recognition and Barnes maze tests. The mechanisms underlying WD-induced cognitive impairment were assessed using RNA-sequencing and bioinformatics analysis.

KEY FINDINGS

Cognitive impairment was observed in WT mice fed WD (WT-WD) compared with WT-ND mice. Conversely, mice lacking TAS1R3 were not cognitively impaired even under long-term WD feeding. Hippocampal transcriptome analysis revealed upregulated AMP-activated protein kinase (AMPK) signaling and increased AMPK-targeted sirtuin 3 expression in KO-WD mice. Pathway enrichment analysis showed that response to oxidative stress was downregulated, whereas neurogenesis was upregulated in dentate gyrus of KO-WD mice. In vitro studies validated the findings, indicating that Tas1r3 knockdown directly upregulated decreased sirtuin 3 expression, its downstream genes-related to oxidative stress, and apoptosis induced by WD condition in hippocampal neuron cells.

SIGNIFICANCE

TAS1R3 acts as a critical mediator of WD-induced cognitive impairment in mice, thereby offering potential as a novel therapeutic target to prevent WD-induced cognitive impairment.

Brain and spinal cord trauma: what we know about the therapeutic potential of insulin growth factor 1 gene therapy

Although little attention has been paid to cognitive and emotional dysfunctions observed in patients after spinal cord injury, several reports have described impairments in cognitive abilities. Our group also has contributed significantly to the study of cognitive impairments in a rat model of spinal cord injury. These findings are very significant because they demonstrate that cognitive and mood deficits are not induced by lifestyle changes, drugs of abuse, and combined medication. They are related to changes in brain structures involved in cognition and emotion, such as the hippocampus. Chronic spinal cord injury decreases neurogenesis, enhances glial reactivity leading to hippocampal neuroinflammation, and triggers cognitive deficits. These brain distal abnormalities are recently called tertiary damage. Given that there is no treatment for Tertiary Damage, insulin growth factor 1 gene therapy emerges as a good candidate. Insulin growth factor 1 gene therapy recovers neurogenesis and induces the polarization from pro-inflammatory towards anti-inflammatory microglial phenotypes, which represents a potential strategy to treat the neuroinflammation that supports tertiary damage. Insulin growth factor 1 gene therapy can be extended to other central nervous system pathologies such as traumatic brain injury where the neuroinflammatory component is crucial. Insulin growth factor 1 gene therapy could emerge as a new therapeutic strategy for treating traumatic brain injury and spinal cord injury.

Grape seed extract effects on hippocampal neurogenesis, synaptogenesis and dark neurons production in old mice. Can this extract improve learning and memory in aged animals?

BACKGROUND

During the elderly, hippocampal neurogenesis and synaptogenesis reduce and dark neurons (DNs) increase, leading to cognitive impairment. It is believed that natural products can protect the neural cells and system by protecting from damages or promoting regeneration. Therefore, the effects of grape seed extract (GSE) on the hippocampus of aged mice were investigated in this study.

METHODS

twelve old mice were divided into two groups of control and GSE. Animals in the GSE group received 300 mg/kg of GSE for eight weeks via gavage. At the end of treatment, cognition performance was evaluated by Morris water maze (MWM) and passive avoidance tests. Hippocampal neurogenesis, synaptogenesis and DNs production were evaluated with immunohistochemistry and histological evaluations on 5-micron coronal tissue sections.

RESULTS

The hippocampal mean number of double cortin positive cells (DCX+) per unit area, as well as synaptophysin expression in the GSE group, were significantly higher than the control group (p < 0.01). The frequency of DNs in the GSE group was lower than the control group (p < 0.05). Behavioral tests showed that GSE improves memory and learning performance.

CONCLUSION

Consuming GSE in the elderly can potentially alleviate the age-related reduction of hippocampal neurogenesis and synaptogenesis. It is also able to decrease hippocampal DNs production and increase memory and learning.

Spinal Cord Injury Leads to Hippocampal Glial Alterations and Neural Stem Cell Inactivation

The hippocampus encodes spatial and contextual information involved in memory and learning. The incorporation of new neurons into hippocampal networks increases neuroplasticity and enhances hippocampal-dependent learning performances. Only few studies have described hippocampal abnormalities after spinal cord injury (SCI) although cognitive deficits related to hippocampal function have been reported in rodents and even humans. The aim of this study was to characterize in further detail hippocampal changes in the acute and chronic SCI. Our data suggested that neurogenesis reduction in the acute phase after SCI could be due to enhanced death of amplifying neural progenitors (ANPs). In addition, astrocytes became reactive and microglial cells increased their number in almost all hippocampal regions studied. Glial changes resulted in a non-inflammatory response as the mRNAs of the major pro-inflammatory cytokines (IL-1β, TNFα, IL-18) remained unaltered, but CD200R mRNA levels were downregulated. Long-term after SCI, astrocytes remained reactive but on the other hand, microglial cell density decreased. Also, glial cells induced a neuroinflammatory environment with the upregulation of IL-1β, TNFα and IL-18 mRNA expression and the decrease of CD200R mRNA. Neurogenesis reduction may be ascribed at later time points to inactivation of neural stem cells (NSCs) and inhibition of ANP proliferation. The number of granular cells and CA1 pyramidal neurons decreased only in the chronic phase. The release of pro-inflammatory cytokines at the chronic phase might involve neurogenesis reduction and neurodegeneration of hippocampal neurons. Therefore, SCI led to hippocampal changes that could be implicated in cognitive deficits observed in rodents and humans.

Chronic Administration of Thymoquinone Enhances Adult Hippocampal Neurogenesis and Improves Memory in Rats Via Regulating the BDNF Signaling Pathway

Thymoquinone is a pharmacologically active component of Nigella sativa Linn. seeds. Despite the diverse neuropharmacological attributes of TQ, limited reports related to adult neurogenesis and memory research are available. In this study, we investigated the effects of TQ on the proliferation and neural differentiation of cultured neural stem/progenitor cells (NSCs/NPCs). We also investigated the effect of TQ chronic administration on neurogenesis and memory in adult rats. Under proliferation conditions, TQ (0.05-0.3 μM) significantly increased NSCs/NPCs viability, neurosphere diameter, and cell count. TQ treatment under differentiation conditions increased the proportion of cells positive for Tuj1 (a neuronal marker). Furthermore, chronic oral administration of TQ (25 mg/kg/day for 12 weeks) to adult rats increased the number of bromodeoxyuridine (BrdU)-immunopositive cells double-stained with a mature neuronal marker, neuronal nuclei (NeuN), and a proliferation marker, doublecortin (Dcx), in the dentate gyrus of the hippocampus. TQ-administered rats showed a profound beneficial effect on avoidance-related learning ability, associated with an increase in the hippocampal mRNA and protein levels of brain-derived neurotrophic factor (BDNF), as measured by both real-time PCR and ELISA. Western blot analysis revealed that TQ stimulates the phosphorylation of cAMP-response element-binding protein (CREB), the upstream signaling molecule in the BDNF pathway. Furthermore, chronic administration of TQ decreased lipid peroxide and reactive oxygen species levels in the hippocampus. Taken together, our results suggest that TQ plays a role in memory improvement in adult rats and that the CREB/BDNF signaling pathways are involved in mediating the actions of TQ in hippocampal neurogenesis.

Short high fat diet triggers reversible and region specific effects in DCX+ hippocampal immature neurons of adolescent male mice

Adolescence represents a crucial period for maturation of brain structures involved in cognition. Early in life unhealthy dietary patterns are associated with inferior cognitive outcomes at later ages; conversely, healthy diet is associated with better cognitive results. In this study we analyzed the effects of a short period of hypercaloric diet on newborn hippocampal doublecortin⁺ (DCX) immature neurons in adolescent mice. Male mice received high fat diet (HFD) or control low fat diet (LFD) from the 5th week of age for 1 or 2 weeks, or 1 week HFD followed by 1 week LFD. After diet supply, mice were either perfused for immunohistochemical (IHC) analysis or their hippocampi were dissected for biochemical assays. Detailed morphometric analysis was performed in DCX⁺ cells that displayed features of immature neurons. We report that 1 week-HFD was sufficient to dramatically reduce dendritic tree complexity of DCX⁺ cells. This effect occurred specifically in dorsal and not ventral hippocampus and correlated with reduced BDNF expression levels in dorsal hippocampus. Both structural and biochemical changes were reversed by a return to LFD. Altogether these studies increase our current knowledge on potential consequences of hypercaloric diet on brain and in particular on dorsal hippocampal neuroplasticity.

Exercise mimetics: harnessing the therapeutic effects of physical activity

Exercise mimetics are a proposed class of therapeutics that specifically mimic or enhance the therapeutic effects of exercise. Increased physical activity has demonstrated positive effects in preventing and ameliorating a wide range of diseases, including brain disorders such as Alzheimer disease and dementia, cancer, diabetes and cardiovascular disease. This article discusses the molecular mechanisms and signalling pathways associated with the beneficial effects of physical activity, focusing on effects on brain function and cognitive enhancement. Emerging therapeutic targets and strategies for the development of exercise mimetics, particularly in the field of central nervous system disorders, as well as the associated opportunities and challenges, are discussed.

Characterization of substantia nigra neurogenesis in homeostasis and dopaminergic degeneration: beneficial effects of the microneurotrophin BNN-20

Background

Loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) underlines much of the pathology of Parkinson’s disease (PD), but the existence of an endogenous neurogenic system that could be targeted as a therapeutic strategy has been controversial. BNN-20 is a synthetic, BDNF-mimicking, microneurotrophin that we previously showed to exhibit a pleiotropic neuroprotective effect on the dopaminergic neurons of the SNpc in the “weaver” mouse model of PD. Here, we assessed its potential effects on neurogenesis.

Methods

We quantified total numbers of dopaminergic neurons in the SNpc of wild-type and “weaver” mice, with or without administration of BNN-20, and we employed BrdU labelling and intracerebroventricular injections of DiI to evaluate the existence of dopaminergic neurogenesis in the SNpc and to assess the origin of newborn dopaminergic neurons. The in vivo experiments were complemented by in vitro proliferation/differentiation assays of adult neural stem cells (NSCs) isolated from the substantia nigra and the subependymal zone (SEZ) stem cell niche to further characterize the effects of BNN-20.

Results

Our analysis revealed the existence of a low-rate turnover of dopaminergic neurons in the normal SNpc and showed, using three independent lines of experiments (stereologic cell counts, BrdU and DiI tracing), that the administration of BNN-20 leads to increased neurogenesis in the SNpc and to partial reversal of dopaminergic cell loss. The newly born dopaminergic neurons, that are partially originated from the SEZ, follow the typical nigral maturation pathway, expressing the transcription factor FoxA2. Importantly, the pro-cytogenic effects of BNN-20 were very strong in the SNpc, but were absent in other brain areas such as the cortex or the stem cell niche of the hippocampus. Moreover, although the in vitro assays showed that BNN-20 enhances the differentiation of NSCs towards glia and neurons, its in vivo administration stimulated only neurogenesis.

Conclusions

Our results demonstrate the existence of a neurogenic system in the SNpc that can be manipulated in order to regenerate the depleted dopaminergic cell population in the “weaver” PD mouse model. Microneurotrophin BNN-20 emerges as an excellent candidate for future PD cell replacement therapies, due to its area-specific, pro-neurogenic effects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02398-3.

Going with the grain: Fiber, cognition, and the microbiota-gut-brain-axis

Healthy dietary intake has been acknowledged for decades as one of the main contributors to health. More recently, the field of nutritional psychiatry has progressed our understanding regarding the importance of nutrition in supporting mental health and cognitive function. Thereby, individual nutrients, including omega-3 fatty acids and polyphenols, have been recognized to be key drivers in this relationship. With the progress in appreciating the influence of dietary fiber on health, increasingly research is focusing on deciphering its role in brain processes. However, while the importance of dietary fiber in gastrointestinal and metabolic health is well established, leading to the development of associated health claims, the evidence is not conclusive enough to support similar claims regarding cognitive function. Albeit the increasing knowledge of the impact of dietary fiber on mental health, only a few human studies have begun to shed light onto the underexplored connection between dietary fiber and cognition. Moreover, the microbiota-gut-brain axis has emerged as a key conduit for the effects of nutrition on the brain, especially fibers, that are acted on by specific bacteria to produce a variety of health-promoting metabolites. These metabolites (including short chain fatty acids) as well as the vagus nerve, the immune system, gut hormones, or the kynurenine pathway have been proposed as underlying mechanisms of the microbiota-brain crosstalk. In this minireview, we summarize the evidence available from human studies on the association between dietary fiber intake and cognitive function. We provide an overview of potential underlying mechanisms and discuss remaining questions that need to be answered in future studies. While this field is moving at a fast pace and holds promise for future important discoveries, especially data from human cohorts are required to further our understanding and drive the development of public health recommendations regarding dietary fiber in brain health.

Platycodon grandiflorum Root Protects against Aβ-Induced Cognitive Dysfunction and Pathology in Female Models of Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by irreversible cognitive dysfunction. Amyloid beta (Aβ) peptide is an important pathological factor that triggers the progression of AD through accumulation and aggregation, which leads to AD-related pathologies that consequently affect cognitive functions. Interestingly, several studies have reported that Platycodon grandiflorum root extract (PGE), besides exhibiting other bioactive effects, displays neuroprotective, anti-neuroinflammatory, and cognitive-enhancing effects. However, to date, it is not clear whether PGE can affect AD-related cognitive dysfunction and pathogenesis. Therefore, to investigate whether PGE influences cognitive impairment in an animal model of AD, we conducted a Y-maze test using a 5XFAD mouse model. Oral administration of PGE for 3 weeks at a daily dose of 100 mg/kg significantly ameliorated cognitive impairment in 5XFAD mice. Moreover, to elucidate the neurohistological mechanisms underlying the PGE-mediated alleviative effect on cognitive dysfunction, we performed histological analysis of hippocampal formation in these mice. Histopathological analysis showed that PGE significantly alleviated AD-related pathologies such as Aβ accumulation, neurodegeneration, oxidative stress, and neuroinflammation. In addition, we observed a neuroprotective and antioxidant effect of PGE in mouse hippocampal neurons. Our findings suggest that administration of PGE might act as one of the therapeutic agents for AD by decreasing Aβ related pathology and ameliorating Aβ induced cognitive impairment.

Hippocampal Degeneration and Behavioral Impairment During Alzheimer-Like Pathogenesis Involves Glutamate Excitotoxicity

The hallmarks of Alzheimer's disease (AD) pathology include senile plaques accumulation and neurofibrillary tangles, which is thought to underlie synaptic failure. Recent evidence however supports that synaptic failure in AD may instead be instigated by enhanced N-methyl-D-aspartate (NMDA) activity, via a reciprocal relationship between soluble amyloid-β (Aβ) accumulation and increased glutamate agonist. While previous studies have shown Aβ-mediated alterations to the glutamatergic system during AD, the underlying etiology of excitotoxic glutamate-induced changes has not been explored. Here, we investigated the acute effects of stereotaxic dentate gyrus (DG) glutamate injection on behavior and molecular expression of specific proteins and neurochemicals modulating hippocampal functions. Dependence of glutamate-mediated effects on NMDA receptor (NMDAR) hyperactivation was tested using NMDARs antagonist memantine. DG of Wistar rats (12-weeks-old) were bilaterally microinjected with glutamate (500 mM) with or without daily intraperitoneal (i.p.) memantine injection (20 mg/kg) for 14 days, while controls received either intrahippocampal/i.p. PBS or i.p. memantine. Behavioral characterization in open field and Y-maze revealed that glutamate evoked anxiogenic responses and perturbed spatial memory were inhibited by memantine. In glutamate-treated rats, increased NO expression was accompanied by marked reduction in profiles of glutathione-s-transferase and glutathione peroxidase. Similarly, glutamate-mediated increase in acetylcholinesterase expression corroborated downregulation of synaptophysin and PSD-95, coupled with initiation of reactive astrogliosis (GFAP). While neurofilament immunolocalization/immunoexpression was unperturbed, we found glutamate-mediated reduction in neurogenic markers Ki67 and PCNA immunoexpression, with a decrease in NR2B protein expression, whereas mGluR1 remains unchanged. In addition, increased expression of apoptotic regulatory proteins p53 and Bax was seen in glutamate infused rats, corroborating chromatolytic degeneration of granule neurons in the DG. Interestingly, memantine abrogated most of the degenerative changes associated with glutamate excitotoxicity in this study. Taken together, our findings causally link acute glutamate dyshomeostasis in the DG with development of AD-related behavioral impairment and molecular neurodegeneration.

Caffeine Compromises Proliferation of Human Hippocampal Progenitor Cells

The age-associated reduction in the proliferation of neural stem cells (NSCs) has been associated with cognitive decline. Numerous factors have been shown to modulate this process, including dietary components. Frequent consumption of caffeine has been correlated with an increased risk of cognitive decline, but further evidence of a negative effect on hippocampal progenitor proliferation is limited to animal models. Here, we used a human hippocampal progenitor cell line to investigate the effects of caffeine on hippocampal progenitor integrity and proliferation specifically. The effects of five caffeine concentrations (0 mM = control, 0.1 mM ∼ 150 mg, 0.25 mM ∼ 400 mg, 0.5 mM ∼ 750 mg, and 1.0 mM ∼ 1500 mg) were measured following acute (1 day) and repeated (3 days) exposure. Immunocytochemistry was used to quantify hippocampal progenitor integrity (i.e., SOX2- and Nestin-positive cells), proliferation (i.e., Ki67-positive cells), cell count (i.e., DAPI-positive cells), and apoptosis (i.e., CC3-positive cells). We found that progenitor integrity was significantly reduced in supraphysiological caffeine conditions (i.e., 1.0 mM ∼ 1500 mg), but relative to the lowest caffeine condition (i.e., 0.1 mM ∼ 150 mg) only. Moreover, repeated exposure to supraphysiological caffeine concentrations (i.e., 1.0 mM ∼ 1500 mg) was found to affect proliferation, significantly reducing % Ki67-positive cells relative to control and lower caffeine dose conditions (i.e., 0.1 mM ∼ 150 mg and 0.25 mM ∼ 400 mg). Caffeine treatment did not influence apoptosis and there were no significant differences in any measure between lower doses of caffeine (i.e., 0.1 mM, 0.25 mM, 0.5 mM) – representative of daily human caffeine intake – and control conditions. Our study demonstrates that dietary components such as caffeine can influence NSC integrity and proliferation and may be indicative of a mechanism by which diet affects cognitive outcomes.

Neuroregeneration: Regulation in Neurodegenerative Diseases and Aging

It had been commonly believed for a long time, that once established, degeneration of the central nervous system (CNS) is irreparable, and that adult person merely cannot restore dead or injured neurons. The existence of stem cells (SCs) in the mature brain, an organ with minimal regenerative ability, had been ignored for many years. Currently accepted that specific structures of the adult brain contain neural SCs (NSCs) that can self-renew and generate terminally differentiated brain cells, including neurons and glia. However, their contribution to the regulation of brain activity and brain regeneration in natural aging and pathology is still a subject of ongoing studies. Since the 1970s, when Fuad Lechin suggested the existence of repair mechanisms in the brain, new exhilarating data from scientists around the world have expanded our knowledge on the mechanisms implicated in the generation of various cell phenotypes supporting the brain, regulation of brain activity by these newly generated cells, and participation of SCs in brain homeostasis and regeneration. The prospects of the SC research are truthfully infinite and hitherto challenging to forecast. Once researchers resolve the issues regarding SC expansion and maintenance, the implementation of the SC-based platform could help to treat tissues and organs impaired or damaged in many devastating human diseases. Over the past 10 years, the number of studies on SCs has increased exponentially, and we have already become witnesses of crucial discoveries in SC biology. Comprehension of the mechanisms of neurogenesis regulation is essential for the development of new therapeutic approaches for currently incurable neurodegenerative diseases and neuroblastomas. In this review, we present the latest achievements in this fast-moving field and discuss essential aspects of NSC biology, including SC regulation by hormones, neurotransmitters, and transcription factors, along with the achievements of genetic and chemical reprogramming for the safe use of SCs in vitro and in vivo.

Differential Change in Hippocampal Radial Astrocytes and Neurogenesis in Shorebirds With Contrasting Migratory Routes

Little is known about environmental influences on radial glia-like (RGL) α cells (radial astrocytes) and their relation to neurogenesis. Because radial glia is involved in adult neurogenesis and astrogenesis, we investigated this association in two migratory shorebird species that complete their autumnal migration using contrasting strategies. Before their flights to South America, the birds stop over at the Bay of Fundy in Canada. From there, the semipalmated sandpiper (Calidris pusilla) crosses the Atlantic Ocean in a non-stop 5-day flight, whereas the semipalmated plover (Charadrius semipalmatus) flies primarily overland with stopovers for rest and feeding. From the hierarchical cluster analysis of multimodal morphometric features, followed by the discriminant analysis, the radial astrocytes were classified into two main morphotypes, Type I and Type II. After migration, we detected differential changes in the morphology of these cells that were more intense in Type I than in Type II in both species. We also compared the number of doublecortin (DCX)-immunolabeled neurons with morphometric features of radial glial-like α cells in the hippocampal V region between C. pusilla and C. semipalmatus before and after autumn migration. Compared to migrating birds, the convex hull surface area of radial astrocytes increased significantly in wintering individuals in both C. semipalmatus and C. pusilla. Although to a different extent we found a strong correlation between the increase in the convex hull surface area and the increase in the total number of DCX immunostained neurons in both species. Despite phylogenetic differences, it is of interest to note that the increased morphological complexity of radial astrocytes in C. semipalmatus coincides with the fact that during the migratory process over the continent, the visuospatial environment changes more intensely than that associated with migration over Atlantic. The migratory flight of the semipalmated plover, with stopovers for feeding and rest, vs. the non-stop flight of the semipalmated sandpiper may differentially affect radial astrocyte morphology and neurogenesis.

Systemic milieu and age-related deterioration

Aging is a fundamental biological process accompanied by a general decline in tissue function and an increased risk for age-related disease. The risk for cardiovascular, stroke, cancer, and neurodegenerative diseases significantly increases with aging, especially in people aged 60 years and older in the USA. Although the cellular and molecular mechanisms underlying aging and age-related disease are beginning to be unraveled, the role of the systemic milieu remains unknown. Recent studies have shown that systemic factors in young blood can revise age-related impairments and extend organismal lifespan, suggesting that the systemic milieu contains pro-aging and rejuvenating factors that play a critical role in the health and aging phenotype. In this review, we summarize the current knowledge of systemic milieu changes during the aging process and its link to age-related deterioration.

Leaf extracts from Dendropanax morbifera Léveille mitigate mercury-induced reduction of spatial memory, as well as cell proliferation, and neuroblast differentiation in rat dentate gyrus

Background

The brain is susceptible to methylmercury toxicity, which causes irreversible damage to neurons and glia and the leaf extract Dendropanax morbifera Léveille (DML) has various biological functions in the nervous system. In this study, we examined the effects of DML on mercury-induced proliferating cells and differentiated neuroblasts.

Methods

Dimethylmercury (5 μg/kg) and galantamine (5 mg/kg) was administered intraperitoneally and/or DML (100 mg/kg) was orally to 7-week-old rats every day for 36 days. One hour after the treatment, novel object recognition test was examined. In addition, spatial probe tests were conducted on the 6th day after 5 days of continuous training in the Morris swim maze. Thereafter, the rats were euthanized for immunohistochemical staining analysis with Ki67 and doublecortin and measurement for acetylcholinesterase (AChE) activity.

Results

Dimethylmercury-treated rats showed reduced discrimination index in novel object recognition test and took longer to find the platform than did control group. Compared with dimethylmercury treatment alone, supplementation with DML or galatamine significantly ameliorated the reduction of discrimination index and reduced the time spent to find the platform. In addition, the number of platform crossings was lower in the dimethylmercury-treated group than in controls, while the administration of DML or galantamine significantly increased the number of crossings than did dimethylmercury treatment alone. Proliferating cells and differentiated neuroblasts, assessed by Ki67 and doublecortin immunohistochemical staining was significantly decreased in the dimethylmercury treated group versus controls. Supplementation with DML or galantamine significantly increased the number of proliferating cells and differentiated neuroblasts in the dentate gyrus. In addition, treatment with dimethylmercury significantly increased AChE activity in hippocampal homogenates, while treatment with dimethylmercury+DML or dimethylmercury+galantamine significantly ameliorated this increase.

Conclusions

These results suggest that DML may be a functional food that improves dimethylmercury-induced memory impairment and ameliorates dimethylmercury-induced reduction in proliferating cells and differentiated neuroblasts, and demonstrates corresponding activation of AChE activity in the dentate gyrus.

Pregnancy Promotes Maternal Hippocampal Neurogenesis in Guinea Pigs

Adult neurogenesis in the hippocampal dentate gyrus (DG) modulates cognition and behavior in mammals, while motherhood is associated with cognitive and behavioral changes essential for the care of the young. In mice and rats, hippocampal neurogenesis is reported to be reduced or unchanged during pregnancy, with few data available from other species. In guinea pigs, pregnancy lasts ~9 weeks; we set to explore if hippocampal neurogenesis is altered in these animals, relative to gestational stages. Time-pregnant primigravidas (3-5 months old) and age-matched nonpregnant females were examined, with neurogenic potential evaluated via immunolabeling of Ki67, Sp8, doublecortin (DCX), and neuron-specific nuclear antigen (NeuN) combined with bromodeoxyuridine (BrdU) birth-dating. Relative to control, subgranular Ki67, Sp8, and DCX-immunoreactive (+) cells tended to increase from early gestation to postpartum and peaked at the late gestational stage. In BrdU pulse-chasing experiments in nonpregnant females surviving for different time points (2-120 days), BrdU+ cells in the DG colocalized with DCX partially from 2 to 42 days (most frequently at 14-30 days) and with NeuN increasingly from 14 to 120 days. In pregnant females that received BrdU at early, middle, and late gestational stages and survived for 42 days, the density of BrdU+ cells in the DG was mostly high in the late gestational group. The rates of BrdU/DCX and BrdU/NeuN colocalization were similar among these groups and comparable to those among the corresponding control group. Together, the findings suggest that pregnancy promotes maternal hippocampal neurogenesis in guinea pigs, at least among primigravidas.

Whole-Body 12C Irradiation Transiently Decreases Mouse Hippocampal Dentate Gyrus Proliferation and Immature Neuron Number, but Does Not Change New Neuron Survival Rate

High-charge and -energy (HZE) particles comprise space radiation and they pose a challenge to astronauts on deep space missions. While exposure to most HZE particles decreases neurogenesis in the hippocampus—a brain structure important in memory—prior work suggests that ¹²C does not. However, much about ¹²C’s influence on neurogenesis remains unknown, including the time course of its impact on neurogenesis. To address this knowledge gap, male mice (9–11 weeks of age) were exposed to whole-body ¹²C irradiation 100 cGy (IRR; 1000 MeV/n; 8 kEV/µm) or Sham treatment. To birthdate dividing cells, mice received BrdU i.p. 22 h post-irradiation and brains were harvested 2 h (Short-Term) or three months (Long-Term) later for stereological analysis indices of dentate gyrus neurogenesis. For the Short-Term time point, IRR mice had fewer Ki67, BrdU, and doublecortin (DCX) immunoreactive (+) cells versus Sham mice, indicating decreased proliferation (Ki67, BrdU) and immature neurons (DCX). For the Long-Term time point, IRR and Sham mice had similar Ki67+ and DCX+ cell numbers, suggesting restoration of proliferation and immature neurons 3 months post-¹²C irradiation. IRR mice had fewer surviving BrdU+ cells versus Sham mice, suggesting decreased cell survival, but there was no difference in BrdU+ cell survival rate when compared within treatment and across time point. These data underscore the ability of neurogenesis in the mouse brain to recover from the detrimental effect of ¹²C exposure.

The Effects of Moderate Physical Exercise on Adult Cognition: A Systematic Review

Background: Physical exercise is a systematic sequence of movements executed with a predefined purpose. This muscular activity impacts not only on circulatory adaptations, but also neuronal integration with the potential to influence cognition. The aim of this review was to determine whether the literature supports the idea that physical exercise promotes cognitive benefits in healthy adults.

Methods: A systematic search for relevant articles was performed according to the Preferred Reporting Items for Systematic Review and Meta-Analysis criteria using available databases (PubMed, LILACS, Scopus, Web of Science, The Cochrane Library, OpenGrey, Google Scholar and CENTRAL). The search terms included “humans” or “adults” or “cognition” or “awareness” or “cognitive dissonance” or “cognitive reserve” or “comprehension” or “consciousness” and “motor activity” or “exercise” or “physical fitness,” and not “aged” or “nervous system diseases,” with the purpose of finding associations between moderate physical exercise and cognition. A methodological quality and risk of bias unit assessed the eligibility of articles.

Results: A total of 7179 articles were identified. Following review and quality assessment, three articles were identified to fulfill the inclusion criteria. An association between moderate physical exercise and cognition was observed. Improvements in cognitive parameters such as reduced simple reaction time, improved response precision and working memory were identified among the included articles.

Conclusion: This systematic review found that moderate physical exercise improves cognition.

A Role for Nrf2 Expression in Defining the Aging of Hippocampal Neural Stem Cells

Redox mechanisms are emerging as essential to stem cell function given their capacity to influence a number of important signaling pathways governing stem cell survival and regenerative activity. In this context, our recent work identified the reduced expression of nuclear factor (erythroid-derived 2)-like 2, or Nrf2, in mediating the decline in subventricular zone neural stem progenitor cell (NSPC) regeneration during aging. Since Nrf2 is a major transcription factor at the heart of cellular redox regulation and homeostasis, the current study investigates the role that it may play in the aging of NSPCs that reside within the other major mammalian germinal niche located in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus. Using rats from multiple aging stages ranging from newborn to old age, and aging Nrf2 knockout mice, we first determined that, in contrast with subventricular zone (SVZ) NSPCs, Nrf2 expression does not significantly affect overall DG NSPC viability with age. However, DG NSPCs resembled SVZ stem cells, in that Nrf2 expression controlled their proliferation and the balance of neuronal versus glial differentiation particularly in relation to a specific critical period during middle age. Also, importantly, this Nrf2-based control of NSPC regeneration was found to impact functional neurogenesis-related hippocampal behaviors, particularly in the Morris water maze and in pattern separation tasks. Furthermore, the enrichment of the hippocampal environment via the transplantation of Nrf2-overexpressing NSPCs was able to mitigate the age-related decline in DG stem cell regeneration during the critical middle-age period, and significantly improved pattern separation abilities. In summary, these results emphasize the importance of Nrf2 in DG NSPC regeneration, and support Nrf2 upregulation as a potential approach to advantageously modulate DG NSPC activity with age.

Brain plasticity, cognitive functions and neural stem cells: a pivotal role for the brain-specific neural master gene |-SRGAP2-FAM72-|

Due to an aging society with an increased dementia-induced threat to higher cognitive functions, it has become imperative to understand the molecular and cellular events controlling the memory and learning processes in the brain. Here, we suggest that the novel master gene pair |-SRGAP2-FAM72-| (SLIT-ROBO Rho GTPase activating the protein 2, family with sequence similarity to 72) reveals a new dogma for the regulation of neural stem cell (NSC) gene expression and is a distinctive player in the control of human brain plasticity. Insight into the specific regulation of the brain-specific neural master gene |-SRGAP2-FAM72-| may essentially contribute to novel therapeutic approaches to restore or improve higher cognitive functions.

Food for thought: how nutrition impacts cognition and emotion

More than one-third of American adults are obese and statistics are similar worldwide. Caloric intake and diet composition have large and lasting effects on cognition and emotion, especially during critical periods in development, but the neural mechanisms for these effects are not well understood. A clear understanding of the cognitive-emotional processes underpinning desires to over-consume foods can assist more effective prevention and treatments of obesity. This review addresses recent work linking dietary fat intake and omega-3 polyunsaturated fatty acid dietary imbalance with inflammation in developing, adult, and aged brains. Thus, early-life diet and exposure to stress can lead to cognitive dysfunction throughout life and there is potential for early nutritional interventions (e.g., with essential micronutrients) for preventing these deficits. Likewise, acute consumption of a high-fat diet primes the hippocampus to produce a potentiated neuroinflammatory response to a mild immune challenge, causing memory deficits. Low dietary intake of omega-3 polyunsaturated fatty acids can also contribute to depression through its effects on endocannabinoid and inflammatory pathways in specific brain regions leading to synaptic phagocytosis by microglia in the hippocampus, contributing to memory loss. However, encouragingly, consumption of fruits and vegetables high in polyphenolics can prevent and even reverse age-related cognitive deficits by lowering oxidative stress and inflammation. Understanding relationships between diet, cognition, and emotion is necessary to uncover mechanisms involved in and strategies to prevent or attenuate comorbid neurological conditions in obese individuals.

N-glycosylation and expression in human tissues of the orphan GPR61 receptor

A number of members of the G protein-coupled receptor class of cell surface receptors are 'orphans' with no known endogenous ligand. One of these orphan receptors is GPR61; there are little data about its expression in human cells and tissues. In this study, we investigated the post-translational modification of GPR61 by N-glycosylation at an identified consensus N-glycosylation site (N12) and the impact of this modification upon the subcellular expression of the protein. The N-glycosylation inhibitor tunicamycin reduced the apparent molecular weight of immunoreactivity associated with myc-tagged GPR61 by 1-2 kDa, which was comparable to the evident molecular weight of the myc-tagged N12S GPR61 mutant with disrupted consensus N-glycosylation site. Analysis of GPR61 expression demonstrated that tunicamycin treatment reduced considerably heterologous expression of GPR61 in the cell membrane despite the N12S GPR61 mutant being readily expressed at the cell surface. These results demonstrate that GPR61 is subject to N-glycosylation but suggest this is not a prerequisite for cell surface expression, although N-glycosylation of other proteins may be important for cell membrane expression of GPR61. Expression of GPR61 protein was demonstrated at the cellular level in human hippocampus and human peripheral blood mononuclear cells. In the latter, there was a significantly higher expression of GPR61 in the Th17 cell subset in comparison with resting CD4+ cells, which may point toward a potential role for the GPR61 receptor in autoimmune diseases. This is the first report that GPR61 protein is subject to post-translational modification and is expressed in immune cell subsets and the hippocampus. These findings will help guide studies to investigate the function of GPR61.

Whole-Body Exposure to 28Si-Radiation Dose-Dependently Disrupts Dentate Gyrus Neurogenesis and Proliferation in the Short Term and New Neuron Survival and Contextual Fear Conditioning in the Long Term

Astronauts traveling to Mars will be exposed to chronic low doses of galactic cosmic space radiation, which contains highly charged, high-energy (HZE) particles. 56Fe-HZE-particle exposure decreases hippocampal dentate gyrus (DG) neurogenesis and disrupts hippocampal function in young adult rodents, raising the possibility of impaired astronaut cognition and risk of mission failure. However, far less is known about how exposure to other HZE particles, such as 28Si, influences hippocampal neurogenesis and function. To compare the influence of 28Si exposure on indices of neurogenesis and hippocampal function with previous studies on 56Fe exposure, 9-week-old C57BL/6J and Nestin-GFP mice (NGFP; made and maintained for 10 or more generations on a C57BL/6J background) received whole-body 28Si-particle-radiation exposure (0, 0.2 and 1 Gy, 300 MeV/n, LET 67 KeV/μ, dose rate 1 Gy/min). For neurogenesis assessment, the NGFP mice were injected with the mitotic marker BrdU at 22 h postirradiation and brains were examined for indices of hippocampal proliferation and neurogenesis, including Ki67+, BrdU+, BrdU+NeuN+ and DCX+ cell numbers at short- and long-term time points (24 h and 3 months postirradiation, respectively). In the short-term group, stereology revealed fewer Ki67+, BrdU+ and DCX+ cells in 1-Gy-irradiated group relative to nonirradiated control mice, fewer Ki67+ and DCX+ cells in 0.2 Gy group relative to control group and fewer BrdU+ and DCX+ cells in 1 Gy group relative to 0.2 Gy group. In contrast to the clearly observed radiation-induced, dose-dependent reductions in the short-term group across all markers, only a few neurogenesis indices were changed in the long-term irradiated groups. Notably, there were fewer surviving BrdU+ cells in the 1 Gy group relative to 0- and 0.2-Gy-irradiated mice in the long-term group. When the short- and long-term groups were analyzed by sex, exposure to radiation had a similar effect on neurogenesis indices in male and female mice, although only male mice showed fewer surviving BrdU+ cells in the long-term group. Fluorescent immunolabeling and confocal phenotypic analysis revealed that most surviving BrdU+ cells in the long-term group expressed the neuronal marker NeuN, definitively confirming that exposure to 1 Gy 28Si radiation decreased the number of surviving adult-generated neurons in male mice relative to both 0- and 0.2-Gy-irradiated mice. For hippocampal function assessment, 9-week-old male C57BL/6J mice received whole-body 28Si-particle exposure and were then assessed long-term for performance on contextual and cued fear conditioning. In the context test the animals that received 0.2 Gy froze less relative to control animals, suggesting decreased hippocampal-dependent function. However, in the cued fear conditioning test, animals that received 1 Gy froze more during the pretone portion of the test, relative to controls and 0.2-Gy-irradiated mice, suggesting enhanced anxiety. Compared to previously reported studies, these data suggest that 28Si-radiation exposure damages neurogenesis, but to a lesser extent than 56Fe radiation and that low-dose 28Si exposure induces abnormalities in hippocampal function, disrupting fear memory but also inducing anxiety-like behavior. Furthermore, exposure to 28Si radiation decreased new neuron survival in long-term male groups but not females suggests that sex may be an important factor when performing brain health risk assessment for astronauts traveling in space.

Hippocampal neurogenesis and volume in migrating and wintering semipalmated sandpipers (Calidris pusilla)

Long distance migratory birds find their way by sensing and integrating information from a large number of cues in their environment. These cues are essential to navigate over thousands of kilometers and reach the same breeding, stopover, and wintering sites every year. The semipalmated sandpiper (Calidris pusilla) is a long-distance migrant that breeds in the arctic tundra of Canada and Alaska and winters on the northeast coast of South America. Its fall migration includes a 5,300-kilometer nonstop flight over the Atlantic Ocean. The avian hippocampus has been proposed to play a central role in the integration of multisensory spatial information for navigation. Hippocampal neurogenesis may contribute to hippocampal function and a variety of factors including cognitive activity, exercise, enrichment, diet and stress influence neurogenesis in the hippocampus. We quantified hippocampal neurogenesis and volume in adult migrating and wintering semipalmated sandpipers using stereological counts of doublecortin (DCX) immunolabeled immature neurons. We found that birds captured in the coastal region of Bragança, Brazil during the wintering period had more DCX positive neurons and larger volume in the hippocampus than individuals captured in the Bay of Fundy, Canada during fall migration. We also estimate the number of NeuN immunolabeled cells in migrating and wintering birds and found no significant differences between them. These findings suggest that, at this time window, neurogenesis just replaced neurons that might be lost during the transatlantic flight. Our findings also show that in active fall migrating birds, a lower level of adult hippocampal neurogenesis is associated with a smaller hippocampal formation. High levels of adult hippocampal neurogenesis and a larger hippocampal formation found in wintering birds may be late occurring effects of long distance migratory flight or the result of conditions the birds experienced while wintering.

Early-life stress diminishes the increase in neurogenesis after exercise in adult female mice

Exposure to early-life stress (ES) has long-lasting consequences for later cognition and hippocampal plasticity, including adult hippocampal neurogenesis (AHN), i.e., the generation of new neurons from stem/progenitor cells in the adult hippocampal dentate gyrus. We had previously demonstrated a sex-specific vulnerability to ES exposure; female mice exposed to ES from P2-P9 exhibited only very mild cognitive changes and no reductions in AHN as adult, whereas ES-exposed male mice showed impaired cognition closely associated with reductions in AHN. Given the apparent resilience of AHN to ES in females, we here questioned whether ES has also altered the capacity to respond to positive stimuli for neurogenesis. We therefore investigated whether exercise, known for its strong pro-neurogenic effects, can still stimulate AHN in adult female mice that had been earlier exposed to ES. We confirm a strong pro-neurogenic effect of exercise in the dorsal hippocampus of 8-month-old control female mice, but this positive neurogenic response is less apparent in female ES mice. These data provide novel insights in the lasting consequences of ES on hippocampal plasticity in females and also indicate that ES might lastingly reduce the responsiveness of the hippocampal stem cell pool, to exercise, in female mice.

Overexpression of Mineralocorticoid Receptors in the Mouse Forebrain Partly Alleviates the Effects of Chronic Early Life Stress on Spatial Memory, Neurogenesis and Synaptic Function in the Dentate Gyrus

Evidence from human studies suggests that high expression of brain mineralocorticoid receptors (MR) may promote resilience against negative consequences of stress exposure, including childhood trauma. We examined, in mice, whether brain MR overexpression can alleviate the effects of chronic early life stress (ELS) on contextual memory formation under low and high stress conditions, and neurogenesis and synaptic function of dentate gyrus granular cells. Male mice were exposed to ELS by housing the dam with limited nesting and bedding material from postnatal day (PND) 2 to 9. We investigated the moderating role of MRs by using forebrain-specific transgenic MR overexpression (MR-tg) mice. Low-stress contextual (i.e., object relocation) memory formation was hampered by ELS in wildtype but not MR-tg mice. Anxiety like behavior and high-stress contextual (i.e., fear) memory formation were unaffected by ELS and/or MR expression level. At the cellular level, an interaction effect was observed between ELS and MR overexpression on the number of doublecortin-positive cells, with a significant difference between the wildtype ELS and MR-tg ELS groups. No interaction was found regarding Ki-67 and BrdU staining. A significant interaction between ELS and MR expression was further observed with regard to mEPSCs and mIPSC frequency. The ratio of evoked EPSC/IPSC or NMDA/AMPA responses was unaffected. Overall, these results suggest that ELS affects contextual memory formation under low stress conditions as well as neurogenesis and synaptic transmission in dentate granule cells, an effect that can be alleviated by MR-overexpression.

Sleep and hippocampal neurogenesis: Implications for Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and currently there are no effective disease-modifying treatments available. Hallmark symptoms of AD include impaired hippocampus-dependent episodic memory and disrupted sleep and circadian rhythms. The pathways connecting these symptoms are of particular interest because it is well established that sleep and circadian disruption can impair hippocampus-dependent learning and memory. In rodents, these procedures also markedly suppress adult hippocampal neurogenesis, a form of brain plasticity that is believed to play an important role in pattern separation, and thus episodic memory. A causal role for sleep disruptions in AD pathophysiology is suggested by evidence for sleep-dependent glymphatic clearance of metabolic waste products from the brain. This review explores a complementary hypothesis that sleep and circadian disruptions in AD contribute to cognitive decline by activating neuroendocrine and neuroinflammatory signaling pathways that suppress hippocampal neurogenesis. Evidence for this hypothesis underscores the promise of sleep, circadian rhythms, and neurogenesis as therapeutic targets for remediation of memory impairment in AD.

Synucleinopathies: common features and hippocampal manifestations

Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA) are three major synucleinopathies characterized by α-synuclein-containing inclusions in the brains of patients. Because the cell types and brain structures that are affected vary markedly between the disorders, the patients have different clinical manifestations in addition to some overlapping symptoms, which are the basis for differential diagnosis. Cognitive impairment and depression associated with hippocampal dysfunction are frequently observed in these disorders. While various α-synuclein-containing inclusions are found in the hippocampal formation, increasing evidence supports that small α-synuclein aggregates or oligomers may be the real culprit, causing deficits in neurotransmission and neurogenesis in the hippocampus and related brain regions, which constitute the major mechanism for the hippocampal dysfunctions and associated neuropsychiatric manifestations in synucleinopathies.

Separation or binding? Role of the dentate gyrus in hippocampal mnemonic processing

As a major component of the hippocampal trisynaptic circuit, the dentate gyrus (DG) relays inputs from the entorhinal cortex to the CA3 subregion. Although the anatomy of the DG is well characterized, its contribution to hippocampal mnemonic processing is still unclear. A currently popular theory proposes that the primary function of the DG is to orthogonalize incoming input patterns into non-overlapping patterns (pattern separation). We critically review the available data and conclude that the theoretical support and empirical evidence for this theory are not strong. We then review an alternative theory that posits a role for the DG in binding together different types of incoming sensory information. We conclude that 'binding' better captures the contribution of the DG to memory encoding than 'pattern separation'.

Adult neurogenesis and neurodegenerative diseases: A systems biology perspective

New neurons are generated throughout adulthood in two regions of the brain, the olfactory bulb and dentate gyrus of the hippocampus, and are incorporated into the hippocampal network circuitry; disruption of this process has been postulated to contribute to neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Known modulators of adult neurogenesis include signal transduction pathways, the vascular and immune systems, metabolic factors, and epigenetic regulation. Multiple intrinsic and extrinsic factors such as neurotrophic factors, transcription factors, and cell cycle regulators control neural stem cell proliferation, maintenance in the adult neurogenic niche, and differentiation into mature neurons; these factors act in networks of signaling molecules that influence each other during construction and maintenance of neural circuits, and in turn contribute to learning and memory. The immune system and vascular system are necessary for neuronal formation and neural stem cell fate determination. Inflammatory cytokines regulate adult neurogenesis in response to immune system activation, whereas the vasculature regulates the neural stem cell niche. Vasculature, immune/support cell populations (microglia/astrocytes), adhesion molecules, growth factors, and the extracellular matrix also provide a homing environment for neural stem cells. Epigenetic changes during hippocampal neurogenesis also impact memory and learning. Some genetic variations in neurogenesis related genes may play important roles in the alteration of neural stem cells differentiation into new born neurons during adult neurogenesis, with important therapeutic implications. In this review, we discuss mechanisms of and interactions between these modulators of adult neurogenesis, as well as implications for neurodegenerative disease and current therapeutic research. © 2016 Wiley Periodicals, Inc.

Neurogenic Effects of Low-Dose Whole-Body HZE (Fe) Ion and Gamma Irradiation

Understanding the dose-toxicity profile of radiation is critical when evaluating potential health risks associated with natural and man-made sources in our environment. The purpose of this study was to evaluate the effects of low-dose whole-body high-energy charged (HZE) iron (Fe) ions and low-energy gamma exposure on proliferation and differentiation of adult-born neurons within the dentate gyrus of the hippocampus, cells deemed to play a critical role in memory regulation. To determine the dose-response characteristics of the brain to whole-body Fe-ion vs. gamma-radiation exposure, C57BL/6J mice were irradiated with 1 GeV/n Fe ions or a static ¹³⁷Cs source (0.662 MeV) at doses ranging from 0 to 300 cGy. The neurogenesis was analyzed at 48 h and one month postirradiation. These experiments revealed that whole-body exposure to either Fe ions or gamma radiation leads to: 1. An acute decrease in cell division within the dentate gyrus of the hippocampus, detected at doses as low as 30 and 100 cGy for Fe ions and gamma radiation, respectively; and 2. A reduction in newly differentiated neurons (DCX immunoreactivity) at one month postirradiation, with significant decreases detected at doses as low as 100 cGy for both Fe ions and gamma rays. The data presented here contribute to our understanding of brain responses to whole-body Fe ions and gamma rays and may help inform health-risk evaluations related to systemic exposure during a medical or radiologic/nuclear event or as a result of prolonged space travel.

Regulation of behaviour by the nuclear receptor TLX

The orphan nuclear receptor Tlx (Nr2e1) is a key regulator of both embryonic and adult hippocampal neurogenesis. Several different mouse models have been developed which target Tlx in vivo including spontaneous deletion models (from birth) and targeted and conditional knockouts. Although some conflicting findings have been reported, for the most part studies have demonstrated that Tlx is important in regulating processes that underlie neurogenesis, spatial learning, anxiety-like behaviour and interestingly, aggression. More recent data have demonstrated that disrupting Tlx during early life induces hyperactivity and that Tlx plays a role in emotional regulation. Moreover, there are sex- and age-related differences in some behaviours in Tlx knockout mice during adolescence and adulthood. Here, we discuss the role of Tlx in motor-, cognitive-, aggressive- and anxiety-related behaviours during adolescence and adulthood. We examine current evidence which provides insight into Tlx during neurodevelopment, and offer our thoughts on the function of Tlx in brain and behaviour. We further hypothesize that Tlx is a key target in understanding the emergence of neurobiological disorders during adolescence and early adulthood.

Pathological changes of the hippocampus and cognitive dysfunction following frontal lobe surgery in a rat model

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a known complication after intracranial surgery. Impaired hippocampal neurogenesis has been associated with cognitive dysfunction in animal models.

METHODS

In order to assess hippocampal changes after brain surgery, a frontal lobe corticectomy was performed in ten adult Wistar rats (group 4). Three different control groups (n = 10 each) included no treatment (G1), general anesthesia alone (G2), and craniectomy without dural opening (G3). Twenty-four hours after surgery, half of the animals were killed, and the mRNA levels for IL-6, TNF-α, and brain-derived growth factor (BDNF) in the contralateral hippocampus were assessed by qPCR. Seven days later, the remaining animals underwent anxiety and memory testing. Afterwards, the number of immature neurons in the hippocampal cortex was measured by doublecortin (DCX) staining.

RESULTS

Twenty-four hours after surgery, mRNA levels of IL-6 and TNF-α increased and BDNF decreased in both surgical groups G3 and G4 (p = 0.012). Cognitive tests demonstrated an increase in anxiety levels and memory impairment in surgical groups compared with non-surgical animals. These changes correlated with an inhibition of hippocampal neurogenesis evidenced by a decreased number of new neurons (mean ± SD for G1-4: 66.4 ± 24; 57.6 ± 22.2; 21.3 ± 3.78; 5.7 ± 1.05, p < 0.001, non-parametric ANOVA).

CONCLUSIONS

Intracranial surgery was demonstrated to induce an inflammatory reaction within the hippocampus that compromised neurogenesis and impaired normal cognitive processing. Corticectomy had a greater effect than craniotomy alone, indicating a central trigger for hippocampal inflammatory changes. POCD after craniotomy may originate from a central inflammatory response resulting from surgical trauma to the brain parenchyma.

Effects of Neurotrophic Support and Amyloid-Targeted Combined Therapy on Adult Hippocampal Neurogenesis in a Transgenic Model of Alzheimer's Disease

Although it is recognized that multi-drug therapies may be necessary to combat AD, there is a paucity of preclinical proof of concept studies. We present a combination treatment paradigm, which temporally affects different aspects of Alzheimer's disease (AD)-like pathology, specifically Aβ-toxicity and neurogenesis. At early stages of AD-like pathology, in TgCRND8 mice, we found that combating Aβ pathology with scyllo-inositol ameliorated deficits in neurogenesis. Older TgCRND8 mice with established amyloid load had decreased progenitor cell proliferation and survival compared to non-transgenic mice, regardless of scyllo-inositol treatment. The prolonged exposure to Aβ-pathology leads to deficits in the neurogenic niche, thus targeting Aβ alone is insufficient to rescue neurogenesis. To support the neurogenic niche, we combined scyllo-inositol treatment with leteprinim potassium (neotrofin), the latter of which stimulates neurotrophin expression. We show that the combination treatment of scyllo-inositol and neotrofin enhances neuronal survival and differentiation. We propose this proof of concept combination therapy of targeting Aβ-pathology and neurotrophin deficits as a potential treatment for AD.

Neuronal Splicing Regulator RBFOX3 (NeuN) Regulates Adult Hippocampal Neurogenesis and Synaptogenesis

Dysfunction of RBFOX3 has been identified in neurodevelopmental disorders such as autism spectrum disorder, cognitive impairments and epilepsy and a causal relationship with these diseases has been previously demonstrated with Rbfox3 homozygous knockout mice. Despite the importance of RBFOX3 during neurodevelopment, the function of RBFOX3 regarding neurogenesis and synaptogenesis remains unclear. To address this critical question, we profiled the developmental expression pattern of Rbfox3 in the brain of wild-type mice and analyzed brain volume, disease-relevant behaviors, neurogenesis, synaptic plasticity, and synaptogenesis in Rbfox3 homozygous knockout mice and their corresponding wild-type counterparts. Here we report that expression of Rbfox3 differs developmentally for distinct brain regions. Moreover, Rbfox3 homozygous knockout mice exhibited cold hyperalgesia and impaired cognitive abilities. Focusing on hippocampal phenotypes, we found Rbfox3 homozygous knockout mice displayed deficits in neurogenesis, which was correlated with cognitive impairments. Furthermore, RBFOX3 regulates the exons of genes with synapse-related function. Synaptic plasticity and density, which are related to cognitive behaviors, were altered in the hippocampal dentate gyrus of Rbfox3 homozygous knockout mice; synaptic plasticity decreased and the density of synapses increased. Taken together, our results demonstrate the important role of RBFOX3 during neural development and maturation. In addition, abnormalities in synaptic structure and function occur in Rbfox3 homozygous knockout mice. Our findings may offer mechanistic explanations for human brain diseases associated with dysfunctional RBFOX3.

Fluoxetine prevents the memory deficits and reduction in hippocampal cell proliferation caused by valproic acid

Valproic acid (VPA), a commonly used antiepileptic drug, has been reported to cause cognitive impairments in patients. In a previous study, using a rodent model, we showed that VPA treatment impaired cognition which was associated with a reduction in the cell proliferation required for hippocampal neurogenesis. The antidepressant fluoxetine has been shown to increase hippocampal neurogenesis and to reverse the memory deficits found in a number of pathological conditions. In the present study we investigated the protective effects of fluoxetine treatment against the impairments in memory and hippocampal cell proliferation produced by VPA. Male Sprague Dawley rats received daily treatment with fluoxetine (10mg/kg) by oral gavage for 21days. Some rats were co-administered with VPA (300mg/kg, twice daily i.p. injections) for 14days from day 8 to day 21 of the fluoxetine treatment. Spatial memory was tested using the novel object location (NOL) test. The number of proliferating cells present in the sub granular zone of the dentate gyrus was quantified using Ki67 immunohistochemistry at the end of the experiment. Levels of the receptor Notch1, the neurotrophic factor BDNF and the neural differentiation marker DCX were determined by Western blotting. VPA-treated rats showed memory deficits, a decrease in the number of proliferating cells in the sub granular zone and decreases in the levels of Notch1 and BDNF but not DCX compared to control animals. These changes in behavior, cell proliferation and Notch1 and BDNF were prevented in animals which had received both VPA and fluoxetine. Rats receiving fluoxetine alone did not show a significant difference in the number of proliferating cells or behavior compared to controls. These results demonstrated that the spatial memory deficits and reduction of cell proliferation produced by VPA can be ameliorated by the simultaneous administration of the antidepressant fluoxetine.

Treadmill exercise ameliorates Alzheimer disease-associated memory loss through the Wnt signaling pathway in the streptozotocin-induced diabetic rats

Diabetes mellitus is considered as a risk factor for Alzheimer disease. The aim of the present study was to evaluate the possibility whether treadmill exercise ameliorates Alzheimer disease-associated memory loss in the diabetes mellitus. For this study, the effects of treadmill exercise on short-term memory and spatial learning ability in relation with Wnt signaling pathway were evaluated using the streptozotocin (STZ)-induced diabetic rats. Diabetes was induced by intraperitoneal injection of STZ. Step-down avoidance task and 8-arm radial maze test were performed for the memory function. Immunohistochemistry for 5-bro-mo-2′-deoxyridine (BrdU) and doublecortin (DCX) and Western blot for Wnt3 and glycogen synthase kinase-3β (GSK-3β) were conducted. The rats in the exercise groups were made to run on the treadmill for 30 min per one day, 5 times a week, during 12 weeks. In the present results, short-term memory and spatial learning ability were deteriorated by induction of diabetes. Treadmill exercise improved short-term memory and spatial learning ability in the diabetic rats. The numbers of BrdU-positive and DCX-positive cells in the hippocampal dentate gyrus were decreased by induction of diabetes. Treadmill exercise increased these numbers in the diabetic rats. Wnt3 expression in the hippocampus was decreased and GSK-3β expression in the hippocampus was increased by induction of diabetes. Treadmill exercise increased Wnt3 expression and suppressed GSK-3β expression in the diabetic rats. The present study suggests that treadmill exercise alleviates Alzheimer disease-associated memory loss by increasing neurogenesis through activating Wnt signaling pathway in the diabetic rats.