Human Adult Neurogenesis: Evidence and Remaining Questions

Potential role of tanycyte-derived neurogenesis in Alzheimer's disease

Tanycytes, specialized ependymal cells located in the hypothalamus, play a crucial role in the generation of new neurons that contribute to the neural circuits responsible for regulating the systemic energy balance. The precise coordination of the gene networks controlling neurogenesis in naive and mature tanycytes is essential for maintaining homeostasis in adulthood. However, our understanding of the molecular mechanisms and signaling pathways that govern the proliferation and differentiation of tanycytes into neurons remains limited. This article aims to review the recent advancements in research into the mechanisms and functions of tanycyte-derived neurogenesis. Studies employing lineage-tracing techniques have revealed that the neurogenesis specifically originating from tanycytes in the hypothalamus has a compensatory role in neuronal loss and helps maintain energy homeostasis during metabolic diseases. Intriguingly, metabolic disorders are considered early biomarkers of Alzheimer's disease. Furthermore, the neurogenic potential of tanycytes and the state of newborn neurons derived from tanycytes heavily depend on the maintenance of mild microenvironments, which may be disrupted in Alzheimer's disease due to the impaired blood-brain barrier function. However, the specific alterations and regulatory mechanisms governing tanycyte-derived neurogenesis in Alzheimer's disease remain unclear. Accumulating evidence suggests that tanycyte-derived neurogenesis might be impaired in Alzheimer's disease, exacerbating neurodegeneration. Confirming this hypothesis, however, poses a challenge because of the lack of long-term tracing and nucleus-specific analyses of newborn neurons in the hypothalamus of patients with Alzheimer's disease. Further research into the molecular mechanisms underlying tanycyte-derived neurogenesis holds promise for identifying small molecules capable of restoring tanycyte proliferation in neurodegenerative diseases. This line of investigation could provide valuable insights into potential therapeutic strategies for Alzheimer's disease and related conditions.

Discovery of a potent melatonin-based inhibitor of quinone reductase-2 with neuroprotective and neurogenic properties

5-Methoxy-3-(5-methoxyindolin-2-yl)-1H-indole (3), whose structure was unambiguously elucidated by X-ray analysis, was identified as a multi-target compound with potential application in neurodegenerative diseases. It is a low nanomolar inhibitor of QR2 (IC50 = 7.7 nM), with greater potency than melatonin and comparable efficacy to the most potent QR2 inhibitors described to date. Molecular docking studies revealed the potential binding mode of 3 to QR2, which explains its superior potency compared to melatonin. Furthermore, compound 3 inhibits hMAO-A, hMAO-B and hLOX-5 in the low micromolar range and is an excellent ROS scavenger. In phenotypic assays, compound 3 showed neuroprotective activity in a cellular model of oxidative stress damage, it was non-toxic, and was able to activate neurogenesis from neural stem-cell niches of adult mice. These excellent biological properties, together with its both good in silico and in vitro drug-like profile, highlight compound 3 as a promising drug candidate for neurodegenerative diseases.

Role of Agrin in tissue repair and regeneration: From mechanisms to therapeutic opportunities (Review)

Tissue regeneration is a complex process that involves the recruitment of various types of cells for healing after injury; it is mediated by numerous precise interactions. However, the identification of effective targets for improving tissue regeneration remains a challenge. As an extracellular matrix protein, Agrin plays a critical role in neuromuscular junction formation. Furthermore, recent studies have revealed the role of Agrin in regulating tissue proliferation and regeneration, which contributes to the repair process of injured tissues. An in‑depth understanding of the role of Agrin will therefore be of value. Given that repair and regeneration processes occur in various parts of the human body, the present systematic review focuses on the role of Agrin in typical tissue and highlights the potential signaling pathways that are involved in Agrin‑induced repair and regeneration. This review offers important insight into novel strategies for the future clinical applications of Agrin‑based therapies, which may represent a feasible treatment option for patients who require organ replacement or repair.

Sequential physical and cognitive training disrupts cocaine-context associations via multi-level stimulation of adult hippocampal neurogenesis

Cocaine-related contextual cues are a recurrent source of craving and relapse. Extinction of cue-driven cocaine seeking remains a clinical challenge, and the search for adjuvants is ongoing. In this regard, combining physical and cognitive training is emerging as a promising strategy that has shown synergistic benefits on brain structure and function, including enhancement of adult hippocampal neurogenesis (AHN), which has been recently linked to reduced maintenance of maladaptive drug seeking. Here, we examined whether this behavioral approach disrupts cocaine-context associations via improved AHN. To this aim, C57BL/6J mice (N = 37) developed a cocaine-induced conditioned place preference (CPP) and underwent interventions consisting of exercise and/or spatial working memory training. Bromodeoxyuridine (BrdU) was administered during early running sessions to tag a subset of new dentate granule cells (DGCs) reaching a critical window of survival during spatial learning. Once these DGCs became functionally mature (∼ 6 weeks-old), mice received extinction training before testing CPP extinction and reinstatement. We found that single and combined treatments accelerated CPP extinction and prevented reinstatement induced by a low cocaine priming (2 mg/kg). Remarkably, the dual-intervention mice showed a significant decrease of CPP after extinction relative to untreated animals. Moreover, combining the two strategies led to increased number and functional integration of BrdU+ DGCs, which in turn maximized the effect of spatial training (but not exercise) to reduce CPP persistence. Together, our findings suggests that sequencing physical and cognitive training may redound to decreased maintenance of cocaine-context associations, with multi-level stimulation of AHN as a potential underlying mechanism.

Increasing adult-born neurons protects mice from epilepsy

Neurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult-born neurons would prevent epilepsy. Adult-born neurons were selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2 Bax fl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult-born neurons exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were the more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult-born neurons also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild type females or males, which is notable because these two hilar cell types are implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult-born neurons can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.

NACC2, a molecular effector of miR-132 regulation at the interface between adult neurogenesis and Alzheimer's disease

The generation of new neurons at the hippocampal neurogenic niche, known as adult hippocampal neurogenesis (AHN), and its impairment, have been implicated in Alzheimer's disease (AD). MicroRNA-132 (miR-132), the most consistently downregulated microRNA (miRNA) in AD, was recently identified as a potent regulator of AHN, exerting multilayered proneurogenic effects in adult neural stem cells (NSCs) and their progeny. Supplementing miR-132 in AD mouse brain restores AHN and relevant memory deficits, yet the exact mechanisms involved are still unknown. Here, we identify NACC2 as a novel miR-132 target implicated in both AHN and AD. miR-132 deficiency in mouse hippocampus induces Nacc2 expression and inflammatory signaling in adult NSCs. We show that miR-132-dependent regulation of NACC2 is involved in the initial stages of human NSC differentiation towards astrocytes and neurons. Later, NACC2 function in astrocytic maturation becomes uncoupled from miR-132. We demonstrate that NACC2 is present in reactive astrocytes surrounding amyloid plaques in mouse and human AD hippocampus, and that there is an anticorrelation between miR-132 and NACC2 levels in AD and upon induction of inflammation. Unraveling the molecular mechanisms by which miR-132 regulates neurogenesis and cellular reactivity in AD, will provide valuable insights towards its possible application as a therapeutic target.

DENOISING: Dynamic enhancement and noise overcoming in multimodal neural observations via high-density CMOS-based biosensors

Large-scale multimodal neural recordings on high-density biosensing microelectrode arrays (HD-MEAs) offer unprecedented insights into the dynamic interactions and connectivity across various brain networks. However, the fidelity of these recordings is frequently compromised by pervasive noise, which obscures meaningful neural information and complicates data analysis. To address this challenge, we introduce DENOISING, a versatile data-derived computational engine engineered to adjust thresholds adaptively based on large-scale extracellular signal characteristics and noise levels. This facilitates the separation of signal and noise components without reliance on specific data transformations. Uniquely capable of handling a diverse array of noise types (electrical, mechanical, and environmental) and multidimensional neural signals, including stationary and non-stationary oscillatory local field potential (LFP) and spiking activity, DENOISING presents an adaptable solution applicable across different recording modalities and brain networks. Applying DENOISING to large-scale neural recordings from mice hippocampal and olfactory bulb networks yielded enhanced signal-to-noise ratio (SNR) of LFP and spike firing patterns compared to those computed from raw data. Comparative analysis with existing state-of-the-art denoising methods, employing SNR and root mean square noise (RMS), underscores DENOISING's performance in improving data quality and reliability. Through experimental and computational approaches, we validate that DENOISING improves signal clarity and data interpretation by effectively mitigating independent noise in spatiotemporally structured multimodal datasets, thus unlocking new dimensions in understanding neural connectivity and functional dynamics.

Quiescent Adult Neural Stem Cells: Developmental Origin and Regulatory Mechanisms

The existence of neural stem cells (NSCs) in the adult mammalian nervous system, although small in number and restricted to the sub-ventricular zone of the lateral ventricles, the dentate gyrus of the hippocampus, and the olfactory epithelium, is a gift of evolution for the adaptive brain function which requires persistent plastic changes of these regions. It is known that most adult NSCs are latent, showing long cell cycles. In the past decade, the concept of quiescent NSCs (qNSCs) has been widely accepted by researchers in the field, and great progress has been made in the biology of qNSCs. Although the spontaneous neuronal regeneration derived from adult NSCs is not significant, understanding how the behaviors of qNSCs are regulated sheds light on stimulating endogenous NSC-based neuronal regeneration. In this review, we mainly focus on the recent progress of the developmental origin and regulatory mechanisms that maintain qNSCs under normal conditions, and that mobilize qNSCs under pathological conditions, hoping to give some insights for future study.

Exploring the parity paradox: Differential effects on neuroplasticity and inflammation by APOEe4 genotype at middle age

Female sex and Apolipoprotein E (APOE) ε4 genotype are top non-modifiable risk factors for Alzheimer's disease (AD). Although female-unique experiences like parity (pregnancy and motherhood) have positive effects on neuroplasticity at middle age, previous pregnancy may also contribute to AD risk. To explore these seemingly paradoxical long-term effects of parity, we investigated the impact of parity with APOEε4 genotype by examining behavioural and neural biomarkers of brain health in middle-aged female rats. Our findings show that primiparous (parous one time) hAPOEε4 rats display increased use of a non-spatial cognitive strategy and exhibit decreased number and recruitment of new-born neurons in the ventral dentate gyrus of the hippocampus in response to spatial working memory retrieval. Furthermore, primiparity and hAPOEε4 genotype synergistically modulate inflammatory markers in the ventral hippocampus. Collectively, these findings demonstrate that previous parity in hAPOEε4 rats confers an added risk to present with reduced activity and engagement of the hippocampus as well as elevated pro-inflammatory signaling, and underscore the importance of considering female-specific factors and genotype in health research.

The impact of adult neurogenesis on affective functions: of mice and men

In most mammals, new neurons are not only produced during embryogenesis but also after birth. Soon after adult neurogenesis was discovered, the influence of recruiting new neurons on cognitive functions, especially on memory, was documented. Likewise, the late process of neuronal production also contributes to affective functions, but this outcome was recognized with more difficulty. This review covers hypes and hopes of discovering the influence of newly-generated neurons on brain circuits devoted to affective functions. If the possibility of integrating new neurons into the adult brain is a commonly accepted faculty in the realm of mammals, the reluctance is strong when it comes to translating this concept to humans. Compiling data suggest now that new neurons are derived not only from stem cells, but also from a population of neuroblasts displaying a protracted maturation and ready to be engaged in adult brain circuits, under specific signals. Here, we discuss the significance of recruiting new neurons in the adult brain circuits, specifically in the context of affective outcomes. We also discuss the fact that adult neurogenesis could be the ultimate cellular process that integrates elements from both the internal and external environment to adjust brain functions. While we must be critical and beware of the unreal promises that Science could generate sometimes, it is important to continue exploring the potential of neural recruitment in adult primates. Reporting adult neurogenesis in humankind contributes to a new vision of humans as mammals whose brain continues to develop throughout life. This peculiar faculty could one day become the target of treatment for mental health, cognitive disorders, and elderly-associated diseases. The vision of an adult brain which never stops integrating new neurons is a real game changer for designing new therapeutic interventions to treat mental disorders associated with substantial morbidity, mortality, and social costs.

Altered hippocampal doublecortin expression in Parkinson's disease

Parkinson's disease (PD) is a complex neurodegenerative disorder characterized by motor and non-motor symptoms. Motor symptoms include bradykinesia, resting tremors, muscular rigidity, and postural instability, while non-motor symptoms include cognitive impairments, mood disturbances, sleep disturbances, autonomic dysfunction, and sensory abnormalities. Some of these symptoms may be influenced by the proper hippocampus functioning, including adult neurogenesis. Doublecortin (DCX) is a microtubule-associated protein that plays a pivotal role in the development and differentiation of migrating neurons. This study utilized postmortem human brain tissue of PD and age-matched control individuals to investigate DCX expression in the context of adult hippocampal neurogenesis. Our findings demonstrate a significant reduction in the number of DCX-expressing cells within the subgranular zone (SGZ), as well as a decrease in the nuclear area of these DCX-positive cells in postmortem brain tissue obtained from PD cases, suggesting an impairment in the adult hippocampal neurogenesis. Additionally, we found that the nuclear area of DCX-positive cells correlates with pH levels. In summary, we provide evidence supporting that the process of hippocampal adult neurogenesis is likely to be compromised in PD patients before cognitive dysfunction, shedding light on potential mechanisms contributing to the neuropsychiatric symptoms observed in affected individuals. Understanding these mechanisms may offer novel insights into the pathophysiology of PD and possible therapeutic avenues.

Dandouchi Polypeptide Alleviates Depressive-like Behavior and Promotes Hippocampal Neurogenesis by Activating the TRIM67/NF-κB Pathway in CUMS-Induced Mice

Background: Dandouchi polypeptide (DDCP) is derived from Semen Sojae Praeparatum (Dandouchi in Chinese), a fermented product of Glycine max (L.) Merr. Semen Sojae Praeparatum is widely used in the food industry for its unique flavor and nutritional value, and DDCP, as its derivative, also shows potential health benefits in food applications. However, the specific active substances responsible for Semen Sojae Praeparatum and the underlying mechanisms involved have not been fully elucidated. Methods: DDCP was extracted from Semen Sojae Praeparatum using enzymes, and its antidepressant effects were tested in chronic unpredictable mild stress (CUMS)-induced mice. Immunohistochemistry, immunofluorescence, and western blotting were used to analyze neurogenesis and the nuclear factor κB (NF-κB) pathway. Moreover, an adeno-associated virus (AAV) shRNA was used to induce tripartite motif-containing 67 (TRIM67) deficiency to examine the function of TRIM67 in the neuroprotective effects of DDCP in depressive disorders. Results: DDCP reduced depressive behaviors in CUMS mice and the expression of proinflammatory markers in the hippocampus. DDCP promoted neurogenesis and modulated the TRIM67/NF-κB pathway, with TRIM67 deficiency impairing its antidepressant effect. Conclusions: This research revealed that DDCP has a protective effect on countering depression triggered by CUMS. Notably, TRIM67 plays a crucial role in mitigating depression through DDCP, positioning DDCP as a potential therapeutic option for treating depressive disorders.

Differentiation of SH-SY5Y neuroblastoma cells using retinoic acid and BDNF: a model for neuronal and synaptic differentiation in neurodegeneration

There has been much interest in the use of cell culture models of neurones, to avoid the animal welfare and cost issues of using primary and human-induced pluripotent stem cell (hiPSC)-derived neurones respectively. The human neuroblastoma cell line, SH-SY5Y, is extensively used in laboratories as they can be readily expanded, are of low cost and can be differentiated into neuronal-like cells. However, much debate remains as to their phenotype once differentiated, and their ability to recapitulate the physiology of bona fide neurones. Here, we characterise a differentiation protocol using retinoic acid and BDNF, which results in extensive neurite outgrowth/branching within 10 days, and expression of key neuronal and synaptic markers. We propose that these differentiated SH-SY5Y cells may be a useful substitute for primary or hiPSC-derived neurones for cell biology studies, in order to reduce costs and animal usage. We further propose that this characterised differentiation timecourse could be used as an in vitro model for neuronal differentiation, for proof-of principle studies on neurogenesis, e.g. relating to neurodegenerative diseases. Finally, we demonstrate profound changes in Tau phosphorylation during differentiation of these cells, suggesting that they should not be used for neurodegeneration studies in their undifferentiated state.

Epigenetic maintenance of adult neural stem cell quiescence in the mouse hippocampus via Setd1a

Quiescence, a hallmark of adult neural stem cells (NSCs), is required for maintaining the NSC pool to support life-long continuous neurogenesis in the adult dentate gyrus (DG). Whether long-lasting epigenetic modifications maintain NSC quiescence over the long term in the adult DG is not well-understood. Here we show that mice with haploinsufficiency of Setd1a, a schizophrenia risk gene encoding a histone H3K4 methyltransferase, develop an enlarged DG with more dentate granule cells after young adulthood. Deletion of Setd1a specifically in quiescent NSCs in the adult DG promotes their activation and neurogenesis, which is countered by inhibition of the histone demethylase LSD1. Mechanistically, RNA-sequencing and CUT & RUN analyses of cultured quiescent adult NSCs reveal Setd1a deletion-induced transcriptional changes and many Setd1a targets, among which down-regulation of Bhlhe40 promotes quiescent NSC activation in the adult DG in vivo. Together, our study reveals a Setd1a-dependent epigenetic mechanism that sustains NSC quiescence in the adult DG.

Glial-restricted precursors stimulate endogenous cytogenesis and effectively recover emotional deficits in a model of cytogenesis ablation

Adult cytogenesis, the continuous generation of newly-born neurons (neurogenesis) and glial cells (gliogenesis) throughout life, is highly impaired in several neuropsychiatric disorders, such as Major Depressive Disorder (MDD), impacting negatively on cognitive and emotional domains. Despite playing a critical role in brain homeostasis, the importance of gliogenesis has been overlooked, both in healthy and diseased states. To examine the role of newly formed glia, we transplanted Glial Restricted Precursors (GRPs) into the adult hippocampal dentate gyrus (DG), or injected their secreted factors (secretome), into a previously validated transgenic GFAP-tk rat line, in which cytogenesis is transiently compromised. We explored the long-term effects of both treatments on physiological and behavioral outcomes. Grafted GRPs reversed anxiety-like deficits and demonstrated an antidepressant-like effect, while the secretome promoted recovery of only anxiety-like behavior. Furthermore, GRPs elicited a recovery of neurogenic and gliogenic levels in the ventral DG, highlighting the unique involvement of these cells in the regulation of brain cytogenesis. Both GRPs and their secretome induced significant alterations in the DG proteome, directly influencing proteins and pathways related to cytogenesis, regulation of neural plasticity and neuronal development. With this work, we demonstrate a valuable and specific contribution of glial progenitors to normalizing gliogenic levels, rescuing neurogenesis and, importantly, promoting recovery of emotional deficits characteristic of disorders such as MDD.

Pregnancy-induced oxidative stress and inflammation are not associated with impaired maternal neuronal activity or memory function

Pregnancy is associated with neural and behavioral plasticity, systemic inflammation, and oxidative stress, yet the impact of inflammation and oxidative stress on maternal neural and behavioral plasticity during pregnancy is unclear. We hypothesized that healthy pregnancy transiently reduces learning and memory and these deficits are associated with pregnancy-induced elevations in inflammation and oxidative stress. Cognitive performance was tested with novel object recognition (recollective memory), Morris water maze (spatial memory), and open field (anxiety-like) behavior tasks in female Sprague-Dawley rats of varying reproductive states [nonpregnant (nulliparous), pregnant (near term), and 1-2 mo after pregnancy (primiparous); n = 7 or 8/group]. Plasma and CA1 proinflammatory cytokines were measured with a MILLIPLEX magnetic bead assay. Plasma oxidative stress was measured via advanced oxidation protein products (AOPP) assay. CA1 markers of oxidative stress, neuronal activity, and apoptosis were quantified via Western blot analysis. Our results demonstrate that CA1 oxidative stress-associated markers were elevated in pregnant compared with nulliparous rats (P ≤ 0.017) but there were equivalent levels in pregnant and primiparous rats. In contrast, reproductive state did not impact CA1 inflammatory cytokines, neuronal activity, or apoptosis. Likewise, there was no effect of reproductive state on recollective or spatial memory. Even so, spatial learning was impaired (P ≤ 0.007) whereas anxiety-like behavior (P ≤ 0.034) was reduced in primiparous rats. Overall, our data suggest that maternal hippocampal CA1 is protected from systemic inflammation but vulnerable to peripartum oxidative stress. Peripartum oxidative stress elevations, such as in pregnancy complications, may contribute to peripartum neural and behavioral plasticity.NEW & NOTEWORTHY Healthy pregnancy is associated with elevated maternal systemic and brain oxidative stress. During postpregnancy, brain oxidative stress remains elevated whereas systemic oxidative stress is resolved. This sustained maternal brain oxidative stress is associated with learning impairments and decreased anxiety-like behavior during the postpregnancy period.

Mapping the current trends and hotspots of adult hippocampal neurogenesis from 2004-2023: a bibliometric analysis

Objective

We utilized bibliometric and data visualization techniques to discern the primary research domains and emerging frontiers in the field of adult hippocampal neurogenesis (AHN).

Methods

We systematically searched the Web of Science database for AHN-related articles published between 2004 and 2023. The retrieved articles were filtered based on publication types (articles and reviews) and language (English). We employed CiteSpace, VOSviewer, and the online bibliometric platform (bibliometric.com) to visualize and analyze the collected data.

Results

In total, 1,590 AHN-related publications were discovered, exhibiting a steady increase in yearly publications over time. The United States emerged as the leading contributor in AHN research in terms of both publication quantity and national influence. Among all research institutions in the field of AHN, the University of California System exhibited the highest impact. Kempermann, Gerd was the most active author. The publications of the top three active authors primarily focused on the functions of AHN, and reversing hippocampal damage and cognitive impairment by improving AHN. An analysis of reference co-citation clustering revealed 8 distinct research clusters, and the notable ones included "adult hippocampal neurogenesis," "neurogenesis," "hippocampus," "dentate gyrus," "neural stem cell," and "depression." Additionally, a burst keyword detection indicated that 'anxiety' is a current research hotspot in the field of AHN.

Conclusion

This in-depth bibliographic assessment of AHN offers a deeper insight into the present research hotspots in the field. The association between AHN and cognitive diseases, such as Alzheimer's disease (AD) and anxiety, has emerged as a prominent research hotspot.

Traumatic brain injury promotes neurogenesis at the cost of astrogliogenesis in the adult hippocampus of male mice

Traumatic brain injury (TBI) can result in long-lasting changes in hippocampal function. The changes induced by TBI on the hippocampus contribute to cognitive deficits. The adult hippocampus harbors neural stem cells (NSCs) that generate neurons (neurogenesis), and astrocytes (astrogliogenesis). While deregulation of hippocampal NSCs and neurogenesis have been observed after TBI, it is not known how TBI may affect hippocampal astrogliogenesis. Using a controlled cortical impact model of TBI in male mice, single cell RNA sequencing and spatial transcriptomics, we assessed how TBI affected hippocampal NSCs and the neuronal and astroglial lineages derived from them. We observe an increase in NSC-derived neuronal cells and a concomitant decrease in NSC-derived astrocytic cells, together with changes in gene expression and cell dysplasia within the dentate gyrus. Here, we show that TBI modifies NSC fate to promote neurogenesis at the cost of astrogliogenesis and identify specific cell populations as possible targets to counteract TBI-induced cellular changes in the adult hippocampus.

Psilocybin for dementia prevention? The potential role of psilocybin to alter mechanisms associated with major depression and neurodegenerative diseases

Major depression is an established risk factor for subsequent dementia, and depression in late life may also represent a prodromal state of dementia. Considering current challenges in the clinical development of disease modifying therapies for dementia, the focus of research is shifting towards prevention and modification of risk factors to alter the neurodegenerative disease trajectory. Understanding mechanistic commonalities underlying affective symptoms and cognitive decline may reveal biomarkers to aid early identification of those at risk of progressing to dementia during the preclinical phase of disease, thus allowing for timely intervention. Adult hippocampal neurogenesis (AHN) is a phenomenon that describes the birth of new neurons in the dentate gyrus throughout life and it is associated with spatial learning, memory and mood regulation. Microglia are innate immune system macrophages in the central nervous system that carefully regulate AHN via multiple mechanisms. Disruption in AHN is associated with both dementia and major depression and microgliosis is a hallmark of several neurodegenerative diseases. Emerging evidence suggests that psychedelics promote neuroplasticity, including neurogenesis, and may also be immunomodulatory. In this context, psilocybin, a serotonergic agonist with rapid-acting antidepressant properties has the potential to ameliorate intersecting pathophysiological processes relevant for both major depression and neurodegenerative diseases. In this narrative review, we focus on the evidence base for the effects of psilocybin on adult hippocampal neurogenesis and microglial form and function; which may suggest that psilocybin has the potential to modulate multiple mechanisms of action, and may have implications in altering the progression from major depression to dementia in those at risk.

From Immunity to Neurogenesis: Toll-like Receptors as Versatile Regulators in the Nervous System

Toll-like receptors (TLRs) are among the main components of the innate immune system. They can detect conserved structures in microorganisms and molecules associated with stress and cellular damage. TLRs are expressed in resident immune cells and both neurons and glial cells of the nervous system. Increasing evidence is emerging on the participation of TLRs not only in the immune response but also in processes of the nervous system, such as neurogenesis and cognition. Below, we present a review of the literature that evaluates the expression and role of TLRs in processes such as neurodevelopment, behavior, cognition, infection, neuroinflammation, and neurodegeneration.

Adult Hippocampal Neurogenesis in the Human Brain: Updates, Challenges, and Perspectives

The existence of neurogenesis in the adult human hippocampus has been under considerable debate within the past three decades due to the diverging conclusions originating mostly from immunohistochemistry studies. While some of these reports conclude that hippocampal neurogenesis in humans occurs throughout physiologic aging, others indicate that this phenomenon ends by early childhood. More recently, some groups have adopted next-generation sequencing technologies to characterize with more acuity the extent of this phenomenon in humans. Here, we review the current state of research on adult hippocampal neurogenesis in the human brain with an emphasis on the challenges and limitations of using immunohistochemistry and next-generation sequencing technologies for its study.

Ageing, Cognitive Decline, and Effects of Physical Exercise: Complexities, and Considerations from Animal Models

In our ageing global population, the cognitive decline associated with dementia and neurodegenerative diseases represents a major healthcare problem. To date, there are no effective treatments for age-related cognitive impairment, thus preventative strategies are urgently required. Physical exercise is gaining traction as a non-pharmacological approach to promote brain health. Adult hippocampal neurogenesis (AHN), a unique form of brain plasticity which is necessary for certain cognitive functions declines with age and is enhanced in response to exercise. Accumulating evidence from research in rodents suggests that physical exercise has beneficial effects on cognition through its proneurogenic capabilities. Given ethical and technical limitations in human studies, preclinical research in rodents is crucial for a better understanding of such exercise-induced brain and behavioural changes. In this review, exercise paradigms used in preclinical research are compared. We provide an overview of the effects of different exercise paradigms on age-related cognitive decline from middle-age until older-age. We discuss the relationship between the age-related decrease in AHN and the potential impact of exercise on mitigating this decline. We highlight the emerging literature on the impact of exercise on gut microbiota during ageing and consider the role of the gut-brain axis as a future possible strategy to optimize exercise-enhanced cognitive function. Finally, we propose a guideline for designing optimal exercise protocols in rodent studies, which would inform clinical research and contribute to developing preventative strategies for age-related cognitive decline.

SAFB regulates hippocampal stem cell fate by targeting Drosha to destabilize Nfib mRNA

Neural stem cells (NSCs) are multipotent and correct fate determination is crucial to guarantee brain formation and homeostasis. How NSCs are instructed to generate neuronal or glial progeny is not well understood. Here, we addressed how murine adult hippocampal NSC fate is regulated and described how scaffold attachment factor B (SAFB) blocks oligodendrocyte production to enable neuron generation. We found that SAFB prevents NSC expression of the transcription factor nuclear factor I/B (NFIB) by binding to sequences in the Nfib mRNA and enhancing Drosha-dependent cleavage of the transcripts. We show that increasing SAFB expression prevents oligodendrocyte production by multipotent adult NSCs, and conditional deletion of Safb increases NFIB expression and oligodendrocyte formation in the adult hippocampus. Our results provide novel insights into a mechanism that controls Drosha functions for selective regulation of NSC fate by modulating the post-transcriptional destabilization of Nfib mRNA in a lineage-specific manner.

Memory circuits in dementia: The engram, hippocampal neurogenesis and Alzheimer's disease

Here, we provide an in-depth consideration of our current understanding of engrams, spanning from molecular to network levels, and hippocampal neurogenesis, in health and Alzheimer's disease (AD). This review highlights novel findings in these emerging research fields and future research directions for novel therapeutic avenues for memory failure in dementia. Engrams, memory in AD, and hippocampal neurogenesis have each been extensively studied. The integration of these topics, however, has been relatively less deliberated, and is the focus of this review. We primarily focus on the dentate gyrus (DG) of the hippocampus, which is a key area of episodic memory formation. Episodic memory is significantly impaired in AD, and is also the site of adult hippocampal neurogenesis. Advancements in technology, especially opto- and chemogenetics, have made sophisticated manipulations of engram cells possible. Furthermore, innovative methods have emerged for monitoring neurons, even specific neuronal populations, in vivo while animals engage in tasks, such as calcium imaging. In vivo calcium imaging contributes to a more comprehensive understanding of engram cells. Critically, studies of the engram in the DG using these technologies have shown the important contribution of hippocampal neurogenesis for memory in both health and AD. Together, the discussion of these topics provides a holistic perspective that motivates questions for future research.

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.

Exercise mitigates a gut microbiota-mediated reduction in adult hippocampal neurogenesis and associated behaviours in rats

Lifestyle factors, especially exercise, impact the manifestation and progression of psychiatric and neurodegenerative disorders such as depression and Alzheimer's disease, mediated by changes in hippocampal neuroplasticity. The beneficial effects of exercise may be due to its promotion of adult hippocampal neurogenesis (AHN). Gut microbiota has also been showed to be altered in a variety of brain disorders, and disturbances of the microbiota have resulted in alterations in brain and behaviour. However, whether exercise can counteract the negative effects of altered gut microbiota on brain function remains under explored. To this end, chronic disruption of the gut microbiota was achieved using an antibiotic cocktail in rats that were sedentary or allowed voluntary access to running wheels. Sedentary rats with disrupted microbiota displayed impaired performance in hippocampal neurogenesis-dependent tasks: the modified spontaneous location recognition task and the novelty suppressed feeding test. Performance in the elevated plus maze was also impaired due to antibiotics treatment. These behaviours, and an antibiotics-induced reduction in AHN were attenuated by voluntary exercise. The effects were independent of changes in the hippocampal metabolome but were paralleled by caecal metabolomic changes. Taken together these data highlight the importance of the gut microbiota in AHN-dependent behaviours and demonstrate the power of lifestyle factors such as voluntary exercise to attenuate these changes.

Enhancing Cognitive Functions and Neuronal Growth through NPY1R Agonist and Ketamine Co-Administration: Evidence for NPY1R-TrkB Heteroreceptor Complexes in Rats

This study investigates the combined effects of the neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31-Pro34]NPY at a dose of 132 µg and Ketamine at 10 mg/Kg on cognitive functions and neuronal proliferation, against a backdrop where neurodegenerative diseases present an escalating challenge to global health systems. Utilizing male Sprague-Dawley rats in a physiological model, this research employed a single-dose administration of these compounds and assessed their impact 24 h after treatment on object-in-place memory tasks, alongside cellular proliferation within the dorsal hippocampus dentate gyrus. Methods such as the in situ proximity ligation assay and immunohistochemistry for proliferating a cell nuclear antigen (PCNA) and doublecortin (DCX) were utilized. The results demonstrated that co-administration significantly enhanced memory consolidation and increased neuronal proliferation, specifically neuroblasts, without affecting quiescent neural progenitors and astrocytes. These effects were mediated by the potential formation of NPY1R-TrkB heteroreceptor complexes, as suggested by receptor co-localization studies, although further investigation is required to conclusively prove this interaction. The findings also highlighted the pivotal role of brain-derived neurotrophic factor (BDNF) in mediating these effects. In conclusion, this study presents a promising avenue for enhancing cognitive functions and neuronal proliferation through the synergistic action of the NPY1R agonist and Ketamine, potentially via NPY1R-TrkB heteroreceptor complex formation, offering new insights into therapeutic strategies for neurodegenerative diseases.

The concept of resilience to Alzheimer's Disease: current definitions and cellular and molecular mechanisms

Some individuals are able to maintain their cognitive abilities despite the presence of significant Alzheimer's Disease (AD) neuropathological changes. This discrepancy between cognition and pathology has been labeled as resilience and has evolved into a widely debated concept. External factors such as cognitive stimulation are associated with resilience to AD, but the exact cellular and molecular underpinnings are not completely understood. In this review, we discuss the current definitions used in the field, highlight the translational approaches used to investigate resilience to AD and summarize the underlying cellular and molecular substrates of resilience that have been derived from human and animal studies, which have received more and more attention in the last few years. From these studies the picture emerges that resilient individuals are different from AD patients in terms of specific pathological species and their cellular reaction to AD pathology, which possibly helps to maintain cognition up to a certain tipping point. Studying these rare resilient individuals can be of great importance as it could pave the way to novel therapeutic avenues for AD.

ErbB3 binding protein 1 contributes to adult hippocampal neurogenesis by modulating Bmp4 and Ascl1 signaling

Neural stem cells (NSCs) in the adult hippocampus divide infrequently; the endogenous molecules modulating adult hippocampal neurogenesis (AHN) remain largely unknown. Here, we show that ErbB3 binding protein 1 (Ebp1), which plays important roles in embryonic neurodevelopment, acts as an essential modulator of adult neurogenic factors. In vivo analysis of Ebp1 neuron depletion mice showed impaired AHN with a low number of hippocampal NSCs and neuroblasts. Ebp1 leads to transcriptional repression of Bmp4 and suppression of Ascl1 promoter methylation in the dentate gyrus of the adult hippocampus reflecting an unusually high level of Bmp4 and low Ascl1 level in neurons of Ebp1-deficient mice. Therefore, our findings suggests that Ebp1 could act as an endogenous modulator of the interplay between Bmp4 and Ascl1/Notch signaling, contributing to AHN. [BMB Reports 2024; 57(4): 182-187].

Versatile strategies for adult neurogenesis: avenues to repair the injured brain

Brain injuries due to trauma or stroke are major causes of adult death and disability. Unfortunately, few interventions are effective for post-injury repair of brain tissue. After a long debate on whether endogenous neurogenesis actually happens in the adult human brain, there is now substantial evidence to support its occurrence. Although neurogenesis is usually significantly stimulated by injury, the reparative potential of endogenous differentiation from neural stem/progenitor cells is usually insufficient. Alternatively, exogenous stem cell transplantation has shown promising results in animal models, but limitations such as poor long-term survival and inefficient neuronal differentiation make it still challenging for clinical use. Recently, a high focus was placed on glia-to-neuron conversion under single-factor regulation. Despite some inspiring results, the validity of this strategy is still controversial. In this review, we summarize historical findings and recent advances on neurogenesis strategies for neurorepair after brain injury. We also discuss their advantages and drawbacks, as to provide a comprehensive account of their potentials for further studies.

Contributions of Polygenic Risk and Disease Status to Gray Matter Abnormalities in Major Depression

BACKGROUND

Gray matter (GM) abnormalities in depression are potentially attributable to some combination of trait, state, and illness history factors. Here, we sought to determine the contributions of polygenic risk for depression, depressive disease status, and the interaction of these factors to these GM abnormalities.

METHODS

We conducted a cross-sectional comparison using a 2 × 3 factorial design examining effects of polygenic risk for depression (lower vs. upper quartile) and depression status (never depressed, currently depressed, or remitted depression) on regional GM concentration and GM volume. Participants were a subset of magnetic resonance imaging-scanned UK Biobank participants comprising 2682 people (876 men, 1806 women) algorithmically matched on 16 potential confounders.

RESULTS

In women but not men, we observed that elevated polygenic risk for depression was associated with reduced cerebellar GM volume. This deficit occurred in salience and dorsal attention network regions of the cerebellum and was associated with poorer performance on tests of attention and executive function but not fluid intelligence. Moreover, in women with current depression compared to both women with remitted depression and women who never had depression, we observed GM reductions in ventral and medial prefrontal, insular, and medial temporal regions. These state-related abnormalities remained when accounting for antidepressant medication status.

CONCLUSIONS

Neuroanatomical deficits attributed broadly to major depression are more likely due to an aggregation of independent factors. Polygenic risk for depression accounted for cerebellar structural abnormalities that themselves accounted for cognitive deficits observed in this disorder. Medial and ventral prefrontal, insular, and temporal cortex deficits constituted a much larger proportion of the aggregate deficit and were attributable to the depressed state.

In Situ Reprogramming of Neurons and Glia - A Risk in Altering Memory and Personality?

The recent emergence of reprogramming technologies to convert brain cell types or epigenetically alter neurons and neural progenitors in vivo and in situ hold significant promises in brain repair and neuronal aging reversal. However, given the significant epigenetic and transcriptomic changes to components of the existing neuronal cells and network, we question if these reprogramming technology might inadvertently alter or erase memory engrams, conceivably resulting in changes in narrative identity or personality. We suggest that the nature of these alterations might be less predictable compared to memory and personality changes known to be associated with diseases, drugs or brain stimulation therapies. While research in applying reprogramming technologies to neurological ailments and aging should continue, more targeted analyses should be put in place in animal experiments to gauge the severity and degree of memory alterations, and appropriate risk and benefit analyses should be conducted before these technologies move into human trials.

Astrocytes in the adult dentate gyrus-balance between adult and developmental tasks

Astrocytes, a major glial cell type in the brain, are indispensable for the integration, maintenance and survival of neurons during development and adulthood. Both life phases make specific demands on the molecular and physiological properties of astrocytes, and most research projects traditionally focus on either developmental or adult astrocyte functions. In most brain regions, the generation of brain cells and the establishment of neural circuits ends with postnatal development. However, few neurogenic niches exist in the adult brain in which new neurons and glial cells are produced lifelong, and the integration of new cells into functional circuits represent a very special form of plasticity. Consequently, in the neurogenic niche, the astrocytes must be equipped to execute both mature and developmental tasks in order to integrate newborn neurons into the circuit and yet maintain overall homeostasis without affecting the preexisting neurons. In this review, we focus on astrocytes of the hippocampal dentate gyrus (DG), and discuss specific features of the astrocytic compartment that may allow the execution of both tasks. Firstly, astrocytes of the adult DG are molecularly, morphologically and functionally diverse, and the distinct astrocytes subtypes are characterized by their localization to DG layers. This spatial separation may lead to a functional specification of astrocytes subtypes according to the neuronal structures they are embedded in, hence a division of labor. Secondly, the astrocytic compartment is not static, but steadily increasing in numbers due to lifelong astrogenesis. Interestingly, astrogenesis can adapt to environmental and behavioral stimuli, revealing an unexpected astrocyte dynamic that allows the niche to adopt to changing demands. The diversity and dynamic of astrocytes in the adult DG implicate a vital contribution to hippocampal plasticity and represent an interesting model to uncover mechanisms how astrocytes simultaneously fulfill developmental and adult tasks.

Constitutive cell proliferation and neurogenesis in the organum vasculosum lamina terminalis and subfornical organ of adult rats

Neurogenesis continues throughout adulthood in the subventricular zone, hippocampal subgranular zone, and the hypothalamic median eminence (ME) and the adjacent medio-basal hypothalamus. The ME is one of the circumventricular organs (CVO), which are specialized brain areas characterized by an incomplete blood-brain barrier and, thus, are involved in mediating communication between the central nervous system and the periphery. Additional CVOs include the organum vasculosum laminae terminalis (OVLT) and the subfornical organs (SFO). Previous studies have demonstrated that the ME contains neural stem cells (NSCs) capable of generating new neurons and glia in the adult brain. However, it remains unclear whether the OVLT and SFO also contain proliferating cells, the identity of these cells, and their ability to differentiate into mature neurons. Here we show that glial and mural subtypes exhibit NSC characteristics, expressing the endogenous mitotic maker Ki67, and incorporating the exogenous mitotic marker BrdU in the OVLT and SFO of adult rats. Glial cells constitutively proliferating in the SFO comprise NG2 glia, while in the OVLT, both NG2 glia and tanycytes appear to constitute the NSC pool. Furthermore, pericytes, which are mural cells associated with capillaries, also contribute to the pool of cells constitutively proliferating in the OVLT and SFO of adult rats. In addition to these glial and mural cells, a fraction of NSCs containing proliferation markers Ki67 and BrdU also expresses the early postmitotic neuronal marker doublecortin, suggesting that these CVOs comprise newborn neurons. Notably, these neurons can differentiate and express the mature neuronal marker NeuN. These findings establish the sensory CVOs OVLT and SFO as additional neurogenic niches, where the generation of new neurons and glia persists in the adult brain.

Adult Neurogenesis of Teleost Fish Determines High Neuronal Plasticity and Regeneration

Studying the properties of neural stem progenitor cells (NSPCs) in a fish model will provide new information about the organization of neurogenic niches containing embryonic and adult neural stem cells, reflecting their development, origin cell lines and proliferative dynamics. Currently, the molecular signatures of these populations in homeostasis and repair in the vertebrate forebrain are being intensively studied. Outside the telencephalon, the regenerative plasticity of NSPCs and their biological significance have not yet been practically studied. The impressive capacity of juvenile salmon to regenerate brain suggests that most NSPCs are likely multipotent, as they are capable of replacing virtually all cell lineages lost during injury, including neuroepithelial cells, radial glia, oligodendrocytes, and neurons. However, the unique regenerative profile of individual cell phenotypes in the diverse niches of brain stem cells remains unclear. Various types of neuronal precursors, as previously shown, are contained in sufficient numbers in different parts of the brain in juvenile Pacific salmon. This review article aims to provide an update on NSPCs in the brain of common models of zebrafish and other fish species, including Pacific salmon, and the involvement of these cells in homeostatic brain growth as well as reparative processes during the postraumatic period. Additionally, new data are presented on the participation of astrocytic glia in the functioning of neural circuits and animal behavior. Thus, from a molecular aspect, zebrafish radial glia cells are seen to be similar to mammalian astrocytes, and can therefore also be referred to as astroglia. However, a question exists as to if zebrafish astroglia cells interact functionally with neurons, in a similar way to their mammalian counterparts. Future studies of this fish will complement those on rodents and provide important information about the cellular and physiological processes underlying astroglial function that modulate neural activity and behavior in animals.

Significance of the anterior cingulate cortex in neurogenesis plasticity: Connections, functions, and disorders across postnatal and adult stages

The anterior cingulate cortex (ACC) is a complex and continually evolving brain region that remains a primary focus of research due to its multifaceted functions. Various studies and analyses have significantly advanced our understanding of how the ACC participates in a wide spectrum of memory and cognitive processes. However, despite its strong connections to brain areas associated with hippocampal and olfactory neurogenesis, the functions of the ACC in regulating postnatal and adult neurogenesis in these regions are still insufficiently explored. Investigating the intricate involvement of the ACC in neurogenesis could enhance our comprehension of essential aspects of brain plasticity. This involvement stems from its complex circuitry with other relevant brain regions, thereby exerting both direct and indirect impacts on the neurogenesis process. This review sheds light on the promising significance of the ACC in orchestrating postnatal and adult neurogenesis in conditions related to memory, cognitive behavior, and associated disorders.

Cognitive Impairment in Heart Failure: A Heart Failure Society of America Scientific Statement

Cognitive impairment is common among adults with heart failure (HF), as both diseases are strongly related to advancing age and multimorbidity (including both cardiovascular and noncardiovascular conditions). Moreover, HF itself can contribute to alterations in the brain. Cognition is critical for a myriad of self-care activities that are necessary to manage HF, and it also has a major impact on prognosis; consequently, cognitive impairment has important implications for self-care, medication management, function and independence, and life expectancy. Attuned clinicians caring for patients with HF can identify clinical clues present at medical encounters that suggest cognitive impairment. When present, screening tests such as the Mini-Cog, and consideration of referral for comprehensive neurocognitive testing may be indicated. Management of cognitive impairment should focus on treatment of underlying causes of and contributors to cognitive impairment, medication management/optimization, and accommodation of deficiencies in self-care. Given its implications on care, it is important to integrate cognitive impairment into clinical decision making. Although gaps in knowledge and challenges to implementation exist, this scientific statement is intended to guide clinicians in caring for and meeting the needs of an increasingly complex and growing subpopulation of patients with HF.

Bilirubin impairs neuritogenesis and synaptogenesis in NSPCs by downregulating NMDAR-CREB-BDNF signaling

Neonatal jaundice is one of the most common disorders in the first 2 wk after birth. Unconjugated bilirubin (UCB) is neurotoxic and can cause neurological dysfunction; however, the underlying mechanisms remain unclear. Neurogenesis, neuronal growth, and synaptogenesis are exuberant in the early postnatal stage. In this study, the impact of UCB on neuritogenesis and synaptogenesis in the early postnatal stage was evaluated both in vitro and in vivo. Primary culture neuronal stem and progenitor cells (NSPCs) were treated with UCB during differentiation, and then the neurite length and synapse puncta were measured. In the bilirubin encephalopathy (BE) animal model, DCX+-marked developing neurons were used to detect apical length and dendritic arborization. According to the data, UCB significantly reduced neurite length and synapse density, as well as decreased the apical dendrite length and dendritic arborization. Furthermore, the NMDAR subunit NR2B was downregulated in NSPCs, while pCREB expression in the hippocampus progressively decreased during disease progression in the BE model. Next, we tested the expression of NR2B, pCREB, mBDNF, and p-mTOR in NSPCs in vitro, and found that UCB treatment reduced the expression of these proteins. In summary, this suggests that UCB causes chronic neurological impairment and is related to the inhibition of NMDAR-CREB-BDNF signaling in NSPCs, which is associated with reduced neuritogenesis and synaptogenesis. This finding may inspire the development of novel pharmaceuticals and treatments.

Differential effects of antiseizure medications on neurogenesis: Evidence from cells to animals

Neurogenesis, the process of generating functionally integrated neurons from neural stem and progenitor cells, is involved in brain development during embryonic stages but continues throughout life. Adult neurogenesis plays essential roles in many brain functions such as cognition, brain plasticity, and repair. Abnormalities in neurogenesis have been described in many neuropsychiatric and neurological disorders, including epilepsy. While sharing a common property of suppressing seizures, accumulating evidence has shown that some antiseizure medications (ASM) exhibit neuroprotective potential in the non-epileptic models including Parkinson's disease, Alzheimer's disease, cerebral ischemia, or traumatic brain injury. ASM are a heterogeneous group of medications with different mechanisms of actions. Therefore, it remains to be revealed whether neurogenesis is a class effect or related to them all. In this comprehensive literature study, we reviewed the literature data on the influence of ASM on the neurogenesis process during brain development and also in the adult brain under physiological or pathological conditions. Meanwhile, we discussed the underlying mechanisms associated with the neurogenic effects of ASM by linking the reported in vivo and in vitro studies. PubMed, Web of Science, and Google Scholar databases were searched until the end of February 2023. A total of 83 studies were used finally. ASM can modulate neurogenesis through the increase or decrease of proliferation, survival, and differentiation of the quiescent NSC pool. The present article indicated that the neurogenic potential of ASM depends on the administered dose, treatment period, temporal administration of the drug, and normal or disease context.

Exploring the dynamics of adult Axin2 cell lineage integration into dentate gyrus granule neurons

The Wnt pathway plays critical roles in neurogenesis. The expression of Axin2 is induced by Wnt/β-catenin signaling, making this gene a reliable indicator of canonical Wnt activity. We employed pulse-chase genetic lineage tracing with the Axin2-CreERT2 allele to follow the fate of Axin2+ lineage in the adult hippocampal formation. We found Axin2 expressed in astrocytes, neurons and endothelial cells, as well as in the choroid plexus epithelia. Simultaneously with the induction of Axin2 fate mapping by tamoxifen, we marked the dividing cells with 5-ethynyl-2'-deoxyuridine (EdU). Tamoxifen induction led to a significant increase in labeled dentate gyrus granule cells three months later. However, none of these neurons showed any EdU signal. Conversely, six months after the pulse-chase labeling with tamoxifen/EdU, we identified granule neurons that were positive for both EdU and tdTomato lineage tracer in each animal. Our data indicates that Axin2 is expressed at multiple stages of adult granule neuron differentiation. Furthermore, these findings suggest that the integration process of adult-born neurons from specific cell lineages may require more time than previously thought.

Glyphosate: Impact on the microbiota-gut-brain axis and the immune-nervous system, and clinical cases of multiorgan toxicity

Glyphosate (GLP) and GLP-based herbicides (GBHs), such as polyethoxylated tallow amine-based GLP surfactants (GLP-SH), developed in the late 70', have become the most popular and controversial agrochemicals ever produced. Nowadays, GBHs have reached 350 million hectares of crops in over 140 countries, with an annual turnover of 5 billion and 11 billion USD in the U.S.A. and worldwide, respectively. Because of the highly efficient inhibitory activity of GLP targeted to the 5-enolpyruvylshikimate-3-phosphate synthase pathway, present in plants and several bacterial strains, the GLP-resistant crop-based genetic agricultural revolution has decreased famine and improved the costs and quality of living in developing countries. However, this progress has come at the cost of the 50-year GBH overuse, leading to environmental pollution, animal intoxication, bacterial resistance, and sustained occupational exposure of the herbicide farm and companies' workers. According to preclinical and clinical studies covered in the present review, poisoning with GLP, GLP-SH, and GBHs devastatingly affects gut microbiota and the microbiota-gut-brain (MGB) axis, leading to dysbiosis and gastrointestinal (GI) ailments, as well as immunosuppression and inappropriate immunostimulation, cholinergic neurotransmission dysregulation, neuroendocrinal system disarray, and neurodevelopmental and neurobehavioral alterations. Herein, we mainly focus on the contribution of gut microbiota (GM) to neurological impairments, e.g., stroke and neurodegenerative and neuropsychiatric disorders. The current review provides a comprehensive introduction to GLP's microbiological and neurochemical activities, including deviation of the intestinal Firmicutes-to-Bacteroidetes ratio, acetylcholinesterase inhibition, excitotoxicity, and mind-altering processes. Besides, it summarizes and critically discusses recent preclinical studies and clinical case reports concerning the harmful impacts of GBHs on the GI tract, MGB axis, and nervous system. Finally, an insightful comparison of toxic effects caused by GLP, GBH-SH, and GBHs is presented. To this end, we propose a first-to-date survey of clinical case reports on intoxications with these herbicides.

Gut microbiome promotes mice recovery from stress-induced depression by rescuing hippocampal neurogenesis

Studies from rodents to primates and humans indicate that individuals vary in how resilient they are to stress, and understanding the basis of these variations may help improve treatments for depression. Here we explored the potential contribution of the gut microbiome to such variation. Mice were exposed to chronic unpredictable mild stress (CUMS) for 4 weeks then allowed to recover for 3 weeks, after which they were subjected to behavioral tests and categorized as showing low or high stress resilience. The two types of mouse were compared in terms of hippocampal gene expression using RNA sequencing, fecal microbiomes using 16S RNA sequencing, and extent of neurogenesis in the hippocampus using immunostaining of brain sections. Fecal microbiota were transplanted from either type of mouse into previously stress-exposed and stress-naïve animals, and the effects of the transplantation on stress-induced behaviors and neurogenesis in the hippocampus were examined. Finally, we blocked neurogenesis using temozolomide to explore the role of neurogenesis promoted by fecal microbiota transplantation in enhancing resilience to stress. Results showed that highly stress-resilient mice, but not those with low resilience, improved significantly on measures of anhedonia, behavioral despair, and anxiety after 3-week recovery from CUMS. Their feces showed greater abundance of Lactobacillus, Bifidobacterium and Romboutsia than feces from mice with low stress resilience, as well as lower abundance of Staphylococcus, Psychrobacter and Corynebacterium. Similarly, highly stress-resilient mice showed greater neurogenesis in hippocampus than animals with low stress resilience. Transplanting fecal microbiota from mice with high stress resilience into previously CUMS-exposed recipients rescued neurogenesis in hippocampus, facilitating recovery from stress-induced depression and cognitive decline. Blockade of neurogenesis with temozolomide abolished recovery of recipients from CUMS-induced depression and cognitive decline in mice transplanted with fecal microbiota from mice with high stress resilience. In conclusion, our results suggested that remodeling of the gut microbiome after stress may reverse stress-induced impairment of hippocampal neurogenesis and thereby promote recovery from stress-induced depression.

Effect of exercise on sleep quality in Parkinson's disease: a mini review

The growing incidence of Parkinson's Disease (PD) is a major burden on the healthcare system. PD is caused by the degeneration of dopaminergic neurons and is known for its effects on motor function and sleep. Sleep is vital for maintaining proper homeostasis and clearing the brain of metabolic waste. Adequate time spent in each sleep stage can help maintain homeostatic function; however, patients with PD appear to exhibit sleep impairments. Although medications enhance the function of remaining dopaminergic neurons and reduce motor symptoms, their potential to improve sleep is still under question. Recently, research has shifted towards exercise protocols to help improve sleep in patients with PD. This review aims to provide an overview of how sleep is impaired in patients with PD, such as experiencing a reduction in time spent in slow-wave sleep, and how exercise can help restore normal sleep function. A PubMed search summarized the relevant research on the effects of aerobic and resistance exercise on sleep in patients with PD. Both high and low-intensity aerobic and resistance exercises, along with exercises related to balance and coordination, have been shown to improve some aspects of sleep. Neurochemically, sleeping leads to an increase in toxin clearance, including α-synuclein. Furthermore, exercise appears to enhance the concentration of brain-derived neurotrophic factors, which has preliminary evidence to suggest correlations to time spent in slow-wave sleep. More research is needed to further elucidate the physiological mechanism pertaining to sleep and exercise in patients with PD.

Pregnancy-associated oxidative stress and inflammation are not associated with impaired maternal neuronal activity or memory function

Pregnancy is associated with neural and behavioral plasticity, systemic inflammation, and oxidative stress. Yet, the impact of systemic inflammation and oxidative stress on maternal neural and behavioral plasticity during pregnancy are unclear. We hypothesized that the maternal hippocampal CA1, a brain region associated with cognition, would be protected from pregnancy-associated systemic elevations in inflammation and oxidative stress, mediating stable peripartum cognitive performance. Cognitive performance was tested using novel object recognition (recollective memory), Morris water maze (spatial memory), and open field (anxiety-like) behavior tasks in female Sprague-Dawley rats of varying reproductive states [non-pregnant (nulliparous), pregnant (near term), and two months post-pregnancy (primiparous); n = 7-8/group]. Plasma and CA1 proinflammatory cytokines were measured using a MILLIPLEX® magnetic bead assay. Plasma oxidative stress was measured via advanced oxidation protein products (AOPP) assay. CA1 markers of oxidative stress, neuronal activity, and apoptosis were quantified via western blotting. Our results demonstrate CA1 oxidative stress-associated markers were elevated in pregnant compared to nulliparous rats ( p ≤ 0.017) but were equivalent levels in pregnant and primiparous rats. In contrast, reproductive state did not impact CA1 inflammatory cytokines, neuronal activity, or apoptosis. Likewise, there was no effect of reproductive state on recollective or spatial memory. Even so, spatial learning was impaired ( p ≤ 0.007) while anxiety-like behavior ( p ≤ 0.034) was reduced in primiparous rats. Overall, our data suggest maternal hippocampal CA1 is protected from systemic inflammation but vulnerable to peripartum oxidative stress. Thus, peripartum oxidative stress elevations, such as in pregnancy complications, may contribute to peripartum neural and behavioral plasticity.

Altered in vivo early neurogenesis traits in patients with depression: Evidence from neuron-derived extracellular vesicles and electroconvulsive therapy

BACKGROUND

The neurogenesis hypothesis is a promising candidate etiologic hypothesis for depression, and it is associated with electroconvulsive therapy (ECT). However, human in vivo molecular-level evidence is lacking.

OBJECTIVE

We used neuron-derived extracellular vesicles (NDEVs) as a "window to the neurons" to explore the in vivo neurogenesis status associated with ECT in patients with treatment-resistant depression (TRD).

METHODS

In this study, we enrolled 40 patients with TRD and 35 healthy controls (HCs). We isolated NDEVs from the plasma of each participant to test the levels of doublecortin (DCX), a marker of neurogenesis, and cluster of differentiation (CD) 81, a marker of EVs. We also assessed the plasma levels of brain-derived neurotrophic factor (BDNF), a protein that is known to be associated with ECT and neuroplastic processes.

RESULTS

Our findings indicated that both the levels of DCX in NDEVs and BDNF in plasma were significantly lower in TRD patients compared to HCs at baseline, but increased following ECTs. Conversely, levels of CD81 in NDEVs were found higher in TRD patients at baseline, but did not change after the ECT treatments. Exploratory analyses revealed that lower levels of BDNF in plasma and DCX in NDEVs, along with higher CD81 levels in NDEVs, were associated with more severe depressive symptoms and reduced cognitive function at baseline. Furthermore, higher baseline CD81 concentrations in NDEVs were correlated with greater decreases in depression symptoms.

CONCLUSIONS

We first present human in vivo evidence of early neurogenesis using DCX through NDEVs: decreased in TRD patients, increased after ECTs.

Dentate Gyrus Microstructure Is Associated With Resilience After Exposure to Maternal Stress Across Two Human Cohorts

BACKGROUND

Maternal stress (MS) is a well-documented risk factor for impaired emotional development in offspring. Rodent models implicate the dentate gyrus (DG) of the hippocampus in the effects of MS on offspring depressive-like behaviors, but mechanisms in humans remain unclear. Here, we tested whether MS was associated with depressive symptoms and DG micro- and macrostructural alterations in offspring across 2 independent cohorts.

METHODS

We analyzed DG diffusion tensor imaging-derived mean diffusivity (DG-MD) and volume in a three-generation family risk for depression study (TGS; n = 69, mean age = 35.0 years) and in the Adolescent Brain Cognitive Development (ABCD) Study (n = 5196, mean age = 9.9 years) using generalized estimating equation models and mediation analysis. MS was assessed by the Parenting Stress Index (TGS) and a measure compiled from the Adult Response Survey from the ABCD Study. The Patient Health Questionnaire-9 and rumination scales (TGS) and the Child Behavior Checklist (ABCD Study) measured offspring depressive symptoms at follow-up. The Schedule for Affective Disorders and Schizophrenia-Lifetime interview was used to assign depression diagnoses.

RESULTS

Across cohorts, MS was associated with future symptoms and higher DG-MD (indicating disrupted microstructure) in offspring. Higher DG-MD was associated with higher symptom scores measured 5 years (in the TGS) and 1 year (in the ABCD Study) after magnetic resonance imaging. In the ABCD Study, DG-MD was increased in high-MS offspring who had depressive symptoms at follow-up, but not in offspring who remained resilient or whose mother had low MS.

CONCLUSIONS

Converging results across 2 independent samples extend previous rodent studies and suggest a role for the DG in exposure to MS and offspring depression.

Towards a Unitary Hypothesis of Alzheimer's Disease Pathogenesis

The "amyloid cascade" hypothesis of Alzheimer's disease (AD) pathogenesis invokes the accumulation in the brain of plaques (containing the amyloid-β protein precursor [AβPP] cleavage product amyloid-β [Aβ]) and tangles (containing hyperphosphorylated tau) as drivers of pathogenesis. However, the poor track record of clinical trials based on this hypothesis suggests that the accumulation of these peptides is not the only cause of AD. Here, an alternative hypothesis is proposed in which the AβPP cleavage product C99, not Aβ, is the main culprit, via its role as a regulator of cholesterol metabolism. C99, which is a cholesterol sensor, promotes the formation of mitochondria-associated endoplasmic reticulum (ER) membranes (MAM), a cholesterol-rich lipid raft-like subdomain of the ER that communicates, both physically and biochemically, with mitochondria. We propose that in early-onset AD (EOAD), MAM-localized C99 is elevated above normal levels, resulting in increased transport of cholesterol from the plasma membrane to membranes of intracellular organelles, such as ER/endosomes, thereby upregulating MAM function and driving pathology. By the same token, late-onset AD (LOAD) is triggered by any genetic variant that increases the accumulation of intracellular cholesterol that, in turn, boosts the levels of C99 and again upregulates MAM function. Thus, the functional cause of AD is upregulated MAM function that, in turn, causes the hallmark disease phenotypes, including the plaques and tangles. Accordingly, the MAM hypothesis invokes two key interrelated elements, C99 and cholesterol, that converge at the MAM to drive AD pathogenesis. From this perspective, AD is, at bottom, a lipid disorder.

Adult neurogenesis: a real hope or a delusion?

Adult neurogenesis, the process of creating new neurons, involves the coordinated division, migration, and differentiation of neural stem cells. This process is restricted to neurogenic niches located in two distinct areas of the brain: the subgranular zone of the dentate gyrus of the hippocampus and the subventricular zone of the lateral ventricle, where new neurons are generated and then migrate to the olfactory bulb. Neurogenesis has been thought to occur only during the embryonic and early postnatal stages and to decline with age due to a continuous depletion of neural stem cells. Interestingly, recent years have seen tremendous progress in our understanding of adult brain neurogenesis, bridging the knowledge gap between embryonic and adult neurogenesis. Here, we discuss the current status of adult brain neurogenesis in light of what we know about neural stem cells. In this notion, we talk about the importance of intracellular signaling molecules in mobilizing endogenous neural stem cell proliferation. Based on the current understanding, we can declare that these molecules play a role in targeting neurogenesis in the mature brain. However, to achieve this goal, we need to avoid the undesired proliferation of neural stem cells by controlling the necessary checkpoints, which can lead to tumorigenesis and prove to be a curse instead of a blessing or hope.

Adult Neurogenesis, Learning and Memory

Neural plasticity can be defined as the ability of neural circuits to be shaped by external and internal factors. It provides the brain with a capacity for functional and morphological remodelling, with many lines of evidence indicating that these changes are vital for learning and memory formation. The basis of this brain plasticity resides in activity- and experience-driven modifications of synaptic strength, including synaptic formation, elimination or weakening, as well as of modulation of neuronal population, which drive the structural reorganization of neural networks. Recent evidence indicates that brain-resident glial cells actively participate in these processes, suggesting that mechanisms underlying plasticity in the brain are multifaceted. Establishing the 'tripartite' synapse, the role of astrocytes in modulating synaptic transmission in response to neuronal activity was recognized first. Further redefinition of the synapse as 'quad-partite' followed to acknowledge the contribution of microglia which were revealed to affect numerous brain functions via dynamic interactions with synapses, acting as 'synaptic sensors' that respond to neuronal activity and neurotransmitter release, as well as crosstalk with astrocytes. Early studies identified microglial ability to dynamically survey their local brain environment and established their integral role in the active interfacing of environmental stimuli (both internal and external), with brain plasticity and remodelling. Following the introduction to neurogenesis, this chapter details the role that microglia play in regulating neurogenesis in adulthood, specifically as it relates to learning and memory, as well as factors involved in modulation of microglia. Further, a microglial perspective is introduced for the context of environmental enrichment impact on neurogenesis, learning and memory across states of stress, ageing, disease and injury.

More than a small adult brain: Lessons from chemotherapy-induced cognitive impairment for modelling paediatric brain disorders

Childhood is recognised as a period of immense physical and emotional development, and this, in part, is driven by underlying neurophysiological transformations. These neurodevelopmental processes are unique to the paediatric brain and are facilitated by augmented rates of neuroplasticity and expanded neural stem cell populations within neurogenic niches. However, given the immaturity of the developing central nervous system, innate protective mechanisms such as neuroimmune and antioxidant responses are functionally naïve which results in periods of heightened sensitivity to neurotoxic insult. This is highly relevant in the context of paediatric cancer, and in particular, the neurocognitive symptoms associated with treatment, such as surgery, radio- and chemotherapy. The vulnerability of the developing brain may increase susceptibility to damage and persistent symptomology, aligning with reports of more severe neurocognitive dysfunction in children compared to adults. It is therefore surprising, given this intensified neurocognitive burden, that most of the pre-clinical, mechanistic research focuses exclusively on adult populations and extrapolates findings to paediatric cohorts. Given this dearth of age-specific research, throughout this review we will draw comparisons with neurodevelopmental disorders which share comparable pathways to cancer treatment related side-effects. Furthermore, we will examine the unique nuances of the paediatric brain along with the somatic systems which influence neurological function. In doing so, we will highlight the importance of developing in vitro and in vivo paediatric disease models to produce age-specific discovery and clinically translatable research.