Autoradiographic and histological studies of postnatal neurogenesis. IV. Cell proliferation and migration in the anterior forebrain, with special reference to persisting neurogenesis in the olfactory bulb

Biomaterials and tissue engineering in traumatic brain injury: novel perspectives on promoting neural regeneration

Traumatic brain injury is a serious medical condition that can be attributed to falls, motor vehicle accidents, sports injuries and acts of violence, causing a series of neural injuries and neuropsychiatric symptoms. However, limited accessibility to the injury sites, complicated histological and anatomical structure, intricate cellular and extracellular milieu, lack of regenerative capacity in the native cells, vast variety of damage routes, and the insufficient time available for treatment have restricted the widespread application of several therapeutic methods in cases of central nervous system injury. Tissue engineering and regenerative medicine have emerged as innovative approaches in the field of nerve regeneration. By combining biomaterials, stem cells, and growth factors, these approaches have provided a platform for developing effective treatments for neural injuries, which can offer the potential to restore neural function, improve patient outcomes, and reduce the need for drugs and invasive surgical procedures. Biomaterials have shown advantages in promoting neural development, inhibiting glial scar formation, and providing a suitable biomimetic neural microenvironment, which makes their application promising in the field of neural regeneration. For instance, bioactive scaffolds loaded with stem cells can provide a biocompatible and biodegradable milieu. Furthermore, stem cells-derived exosomes combine the advantages of stem cells, avoid the risk of immune rejection, cooperate with biomaterials to enhance their biological functions, and exert stable functions, thereby inducing angiogenesis and neural regeneration in patients with traumatic brain injury and promoting the recovery of brain function. Unfortunately, biomaterials have shown positive effects in the laboratory, but when similar materials are used in clinical studies of human central nervous system regeneration, their efficacy is unsatisfactory. Here, we review the characteristics and properties of various bioactive materials, followed by the introduction of applications based on biochemistry and cell molecules, and discuss the emerging role of biomaterials in promoting neural regeneration. Further, we summarize the adaptive biomaterials infused with exosomes produced from stem cells and stem cells themselves for the treatment of traumatic brain injury. Finally, we present the main limitations of biomaterials for the treatment of traumatic brain injury and offer insights into their future potential.

Cell type- and layer-specific plasticity of olfactory bulb interneurons following olfactory sensory neuron ablation

Lifelong neurogenesis endows the mouse olfactory system with a capacity for regeneration that is unique in the mammalian nervous system. Throughout life, olfactory sensory neurons (OSNs) are generated from olfactory epithelium (OE) stem cells in the nose, while the subventricular zone generates neuroblasts that migrate to the olfactory bulb (OB) and differentiate into multiple populations of inhibitory interneurons. Methimazole (MMZ) selectively ablates OSNs, but OE neurogenesis enables OSN repopulation and gradual recovery of OSN input to the OB within 6 weeks. However, it is not known how OB interneurons are affected by this loss and subsequent regeneration of OSN input following MMZ treatment. We found that dopaminergic neuron density was significantly reduced 7-14 days post-MMZ but recovered substantially at 35 days. The density of parvalbumin-expressing interneurons was unaffected by MMZ; however, their soma size was significantly reduced at 7-14 days post-MMZ, recovering by 35 days. Surprisingly, we found a transient increase in the density of calretinin-expressing neurons in the glomerular and external plexiform layers, but not the granule cell layer, 7 days post-MMZ. This could not be accounted for by increased neurogenesis but may result from increased calretinin expression. Together, our data demonstrate cell type- and layer-specific changes in OB interneuron density and morphology after MMZ treatment, providing new insight into the range of plasticity mechanisms employed by OB circuits during loss and regeneration of sensory input.

Stem Cell Therapy and Thiamine Deficiency-Induced Brain Damage

Wernicke's encephalopathy (WE) is a major central nervous system disorder resulting from thiamine deficiency (TD) in which a number of brain regions can develop serious damage including the thalamus and inferior colliculus. Despite decades of research into the pathophysiology of TD and potential therapeutic interventions, little progress has been made regarding effective treatment following the development of brain lesions and its associated cognitive issues. Recent developments in our understanding of stem cells suggest they are capable of repairing damage and improving function in different maladys. This article puts forward the case for the potential use of stem cell treatment as a therapeutic strategy in WE by first examining the effects of TD on brain functional integrity and its consequences. The second half of the paper will address the future benefits of treating TD with these cells by focusing on their nature and their potential to effectively treat neurodegenerative diseases that share some overlapping pathophysiological features with TD. At the same time, some of the obstacles these cells will have to overcome in order to become a viable therapeutic strategy for treating this potentially life-threatening illness in humans will be highlighted.

Neurogenesis and pesticides: news of no new neurons

New hippocampal neurons are continuously generated in the adult human brain. Several studies have demonstrated that the proliferation of hippocampal cells is strongly influenced by a variety of stimuli, including pesticides exposure. These effects are particularly important because neurogenesis dysregulation could be associated with the decline of neuronal and cognitive functions and the possible development of neuropsychiatric disorders.

Olfactory bulb anomalies in KBG syndrome mouse model and patients

ANKRD11 (ankyrin repeat domain 11) is a chromatin regulator and the only gene associated with KBG syndrome, a rare neurodevelopmental disorder. We have previously shown that Ankrd11 regulates murine embryonic cortical neurogenesis. Here, we show a novel olfactory bulb phenotype in a KBG syndrome mouse model and two diagnosed patients. Conditional knockout of Ankrd11 in murine embryonic neural stem cells leads to aberrant postnatal olfactory bulb development and reduced size due to reduction of the olfactory bulb granule cell layer. We further show that the rostral migratory stream has incomplete migration of neuroblasts, reduced cell proliferation as well as aberrant differentiation of neurons. This leads to reduced neuroblasts and neurons in the olfactory bulb granule cell layer. In vitro, Ankrd11-deficient neural stem cells from the postnatal subventricular zone display reduced migration, proliferation, and neurogenesis. Finally, we describe two clinically and molecularly confirmed KBG syndrome patients with anosmia and olfactory bulb and groove hypo-dysgenesis/agenesis. Our report provides evidence that Ankrd11 is a novel regulator of olfactory bulb development and neuroblast migration. Moreover, our study highlights a novel clinical sign of KBG syndrome linked to ANKRD11 perturbations in mice and humans.

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.

Protracted neuronal recruitment in the temporal lobes of young children

The temporal lobe of the human brain contains the entorhinal cortex (EC). This region of the brain is a highly interconnected integrative hub for sensory and spatial information; it also has a key role in episodic memory formation and is the main source of cortical hippocampal inputs1-4. The human EC continues to develop during childhood5, but neurogenesis and neuronal migration to the EC are widely considered to be complete by birth. Here we show that the human temporal lobe contains many young neurons migrating into the postnatal EC and adjacent regions, with a large tangential stream persisting until the age of around one year and radial dispersal continuing until around two to three years of age. By contrast, we found no equivalent postnatal migration in rhesus macaques (Macaca mulatta). Immunostaining and single-nucleus RNA sequencing of ganglionic eminence germinal zones, the EC stream and the postnatal EC revealed that most migrating cells in the EC stream are derived from the caudal ganglionic eminence and become LAMP5+RELN+ inhibitory interneurons. These late-arriving interneurons could continue to shape the processing of sensory and spatial information well into postnatal life, when children are actively interacting with their environment. The EC is one of the first regions of the brain to be affected in Alzheimer's disease, and previous work has linked cognitive decline to the loss of LAMP5+RELN+ cells6,7. Our investigation reveals that many of these cells arrive in the EC through a major postnatal migratory stream in early childhood.

Neural stem cells persist to generate new neurons in the hippocampus of adult and aged human brain - Fiction or accurate?

Adult neurogenesis, comprising the generation, differentiation and integration of new neurons in the mature brain, has emerged as a dynamic area of research over decades. The discovery of adult neurogenesis was a paradigm shift to comprehend mechanisms underlying brain plasticity, cognitive function, and neurological disorders. This review deliberates significant findings from articles published over four decades on adult neurogenesis, highlighting key milestones, methodological advances, and controversies that have shaped our comprehension of the phenomenon of adult neurogenesis. Early skepticism gave way to a rich body of evidence via various reliable approaches. Studies on neurogenic niches, microenvironmental factors, molecular regulators, and functional implications have uncovered the involvement of adult neurogenesis in learning, memory, mood, and even neurological and neurodegenerative conditions. Despite significant progress, several questions still need to be answered, including the exact contributions of new neurons to brain function, their integration into existing circuits, and the impact of enhancing adult neurogenesis in the human hippocampus. While the existence of robust neurogenesis in the adult and aged human hippocampus is yet to be confirmed, this review highlights evidence from a significant number of studies supporting the persistence of hippocampal neurogenesis during adulthood and aging in humans, including in some neurological conditions, such as epilepsy and Alzheimer's disease. Nonetheless, additional large-scale studies using single cell-RNA-seq, single nucleus-RNA-seq, and spatial transcriptomics are critical to validate the presence and contribution of hippocampal neurogenesis in the pathophysiology of various neurological and neurodegenerative conditions at different stages of the disease. There is also a need to develop standardized protocols for analyzing postmortem hippocampal tissues for cellular and molecular analyses.

Bioactive Compounds and Their Influence on Postnatal Neurogenesis

Since postnatal neurogenesis was revealed to have significant implications for cognition and neurological health, researchers have been increasingly exploring the impact of natural compounds on this process, aiming to uncover strategies for enhancing brain plasticity. This review provides an overview of postnatal neurogenesis, neurogenic zones, and disorders characterized by suppressed neurogenesis and neurogenesis-stimulating bioactive compounds. Examining recent studies, this review underscores the multifaceted effects of natural compounds on postnatal neurogenesis. In essence, understanding the interplay between postnatal neurogenesis and natural compounds could bring novel insights into brain health interventions. Exploiting the therapeutic abilities of these compounds may unlock innovative approaches to enhance cognitive function, mitigate neurodegenerative diseases, and promote overall brain well-being.

Microglial depletion after brain injury prolongs inflammation and impairs brain repair, adult neurogenesis and pro-regenerative signaling

The adult zebrafish brain, unlike mammals, has a remarkable regenerative capacity. Although inflammation in part hinders regeneration in mammals, it is necessary for zebrafish brain repair. Microglia are resident brain immune cells that regulate the inflammatory response. To explore the microglial role in repair, we used liposomal clodronate or colony stimulating factor-1 receptor (csf1r) inhibitor to suppress microglia after brain injury, and also examined regeneration in two genetic mutant lines that lack microglia. We found that microglial ablation impaired telencephalic regeneration after injury. Microglial suppression attenuated cell proliferation at the intermediate progenitor cell amplification stage of neurogenesis. Notably, the loss of microglia impaired phospho-Stat3 (signal transducer and activator of transcription 3) and ß-Catenin signaling after injury. Furthermore, the ectopic activation of Stat3 and ß-Catenin rescued neurogenesis defects caused by microglial loss. Microglial suppression also prolonged the post-injury inflammatory phase characterized by neutrophil accumulation, likely hindering the resolution of inflammation. These findings reveal specific roles of microglia and inflammatory signaling during zebrafish telencephalic regeneration that should advance strategies to improve mammalian brain repair.

Depletion of transit amplifying cells in the adult brain does not affect quiescent neural stem cell pool size

Neural stem cells (NSCs) are maintained in the adult mammalian brain throughout the animal's lifespan. NSCs in the subependymal zone infrequently divide and generate transit amplifying cells, which are destined to become olfactory bulb neurons. When transit amplifying cells are depleted, they are replenished by the quiescent NSC pool. However, the cellular basis for this recovery process remains largely unknown. In this study, we traced NSCs and their progeny after transit amplifying cells were eliminated by intraventricular infusion of cytosine β-D-arabinofuranoside. We found that although the number of neurosphere-forming NSCs decreased shortly after the treatment, they were restored to normal levels 3 weeks after the cessation of treatment. More importantly, the depletion of transit amplifying cells did not induce a significant expansion of the NSC pool by symmetric divisions. Our data suggest that the size of the NSC pool is hardly affected by brain damage due to antimitotic drug treatment.

Nerve growth factor receptor (Ngfr) induces neurogenic plasticity by suppressing reactive astroglial Lcn2/Slc22a17 signaling in Alzheimer's disease

Neurogenesis, crucial for brain resilience, is reduced in Alzheimer's disease (AD) that induces astroglial reactivity at the expense of the pro-neurogenic potential, and restoring neurogenesis could counteract neurodegenerative pathology. However, the molecular mechanisms promoting pro-neurogenic astroglial fate despite AD pathology are unknown. In this study, we used APP/PS1dE9 mouse model and induced Nerve growth factor receptor (Ngfr) expression in the hippocampus. Ngfr, which promotes neurogenic fate of astroglia during the amyloid pathology-induced neuroregeneration in zebrafish brain, stimulated proliferative and neurogenic outcomes. Histological analyses of the changes in proliferation and neurogenesis, single-cell transcriptomics, spatial proteomics, and functional knockdown studies showed that the induced expression of Ngfr reduced the reactive astrocyte marker Lipocalin-2 (Lcn2), which we found was sufficient to reduce neurogenesis in astroglia. Anti-neurogenic effects of Lcn2 was mediated by Slc22a17, blockage of which recapitulated the pro-neurogenicity by Ngfr. Long-term Ngfr expression reduced amyloid plaques and Tau phosphorylation. Postmortem human AD hippocampi and 3D human astroglial cultures showed elevated LCN2 levels correlate with reactive gliosis and reduced neurogenesis. Comparing transcriptional changes in mouse, zebrafish, and human AD brains for cell intrinsic differential gene expression and weighted gene co-expression networks revealed common altered downstream effectors of NGFR signaling, such as PFKP, which can enhance proliferation and neurogenesis in vitro when blocked. Our study suggests that the reactive non-neurogenic astroglia in AD can be coaxed to a pro-neurogenic fate and AD pathology can be alleviated with Ngfr. We suggest that enhancing pro-neurogenic astroglial fate may have therapeutic ramifications in AD.

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

Animal survival depends on cognitive abilities such as learning and memory to adapt to environmental changes. Memory functions require an enhanced activity and connectivity of a particular arrangement of engram neurons, supported by the concerted action of neurons, glia, and vascular cells. The deterioration of the cholinergic system is a common occurrence in neurological conditions exacerbated by aging such as traumatic brain injury (TBI), posttraumatic stress disorder (PTSD), Alzheimer's disease (AD), and Parkinson's disease (PD). Cotinine is a cholinergic modulator with neuroprotective, antidepressant, anti-inflammatory, antioxidant, and memory-enhancing effects. Current evidence suggests Cotinine's beneficial effects on cognition results from the positive modulation of the α7-nicotinic acetylcholine receptors (nAChRs) and the inhibition of the toll-like receptors (TLRs). The α7nAChR affects brain functions by modulating the function of neurons, glia, endothelial, immune, and dendritic cells and regulates inhibitory and excitatory neurotransmission throughout the GABA interneurons. In addition, Cotinine acting on the α7 nAChRs and TLR reduces neuroinflammation by inhibiting the release of pro-inflammatory cytokines by the immune cells. Also, α7nAChRs stimulate signaling pathways supporting structural, biochemical, electrochemical, and cellular changes in the Central nervous system during the cognitive processes, including Neurogenesis. Here, the mechanisms of memory formation as well as potential mechanisms of action of Cotinine on memory preservation in aging and neurological diseases are discussed.

Connexin 43-mediated neurovascular interactions regulate neurogenesis in the adult brain subventricular zone

The subventricular zone (SVZ) is the largest neural stem cell (NSC) niche in the adult brain; herein, the blood-brain barrier is leaky, allowing direct interactions between NSCs and endothelial cells (ECs). Mechanisms by which direct NSC-EC interactions in the adult SVZ control NSC behavior are unclear. We found that Cx43 is highly expressed by SVZ NSCs and ECs, and its deletion in either leads to increased NSC proliferation and neuroblast generation, suggesting that Cx43-mediated NSC-EC interactions maintain NSC quiescence. This is further supported by single-cell RNA sequencing and in vitro studies showing that ECs control NSC proliferation by regulating expression of genes associated with NSC quiescence and/or activation in a Cx43-dependent manner. Cx43 mediates these effects in a channel-independent manner involving its cytoplasmic tail and ERK activation. Such insights inform adult NSC regulation and maintenance aimed at stem cell therapies for neurodegenerative disorders.

Programmed ageing: decline of stem cell renewal, immunosenescence, and Alzheimer's disease

The characteristic maximum lifespan varies enormously across animal species from a few hours to hundreds of years. This argues that maximum lifespan, and the ageing process that itself dictates lifespan, are to a large extent genetically determined. Although controversial, this is supported by firm evidence that semelparous species display evolutionarily programmed ageing in response to reproductive and environmental cues. Parabiosis experiments reveal that ageing is orchestrated systemically through the circulation, accompanied by programmed changes in hormone levels across a lifetime. This implies that, like the circadian and circannual clocks, there is a master 'clock of age' (circavital clock) located in the limbic brain of mammals that modulates systemic changes in growth factor and hormone secretion over the lifespan, as well as systemic alterations in gene expression as revealed by genomic methylation analysis. Studies on accelerated ageing in mice, as well as human longevity genes, converge on evolutionarily conserved fibroblast growth factors (FGFs) and their receptors, including KLOTHO, as well as insulin-like growth factors (IGFs) and steroid hormones, as key players mediating the systemic effects of ageing. Age-related changes in these and multiple other factors are inferred to cause a progressive decline in tissue maintenance through failure of stem cell replenishment. This most severely affects the immune system, which requires constant renewal from bone marrow stem cells. Age-related immune decline increases risk of infection whereas lifespan can be extended in germfree animals. This and other evidence suggests that infection is the major cause of death in higher organisms. Immune decline is also associated with age-related diseases. Taking the example of Alzheimer's disease (AD), we assess the evidence that AD is caused by immunosenescence and infection. The signature protein of AD brain, Aβ, is now known to be an antimicrobial peptide, and Aβ deposits in AD brain may be a response to infection rather than a cause of disease. Because some cognitively normal elderly individuals show extensive neuropathology, we argue that the location of the pathology is crucial - specifically, lesions to limbic brain are likely to accentuate immunosenescence, and could thus underlie a vicious cycle of accelerated immune decline and microbial proliferation that culminates in AD. This general model may extend to other age-related diseases, and we propose a general paradigm of organismal senescence in which declining stem cell proliferation leads to programmed immunosenescence and mortality.

Vesicular Zinc Modulates Cell Proliferation and Survival in the Developing Hippocampus

In the brain, vesicular zinc, which refers to a subset of zinc that is sequestered into synaptic vesicles by zinc transporter 3 (ZnT3), has extensive effects on neuronal signalling and modulation. Vesicular zinc-focused research has mainly been directed to its role in the hippocampus, particularly in adult neurogenesis. However, whether vesicular zinc is involved in modulating neurogenesis during the early postnatal period has been less studied. As a first step to understanding this, we used ZnT3 knockout (KO) mice, which lack ZnT3 and, thus, vesicular zinc, to evaluate cell proliferation at three different age points spanning postnatal development (P6, P14, and P28). The survival and the neuronal phenotype of these cells was also assessed in adulthood. We found that male ZnT3 KO mice exhibited lower rates of cell proliferation at P14, but a greater number of these cells survived to adulthood. Additionally, significantly more cells labelled on P6 survived to adulthood in male and female ZnT3 KO mice. We also found sex-dependent differences, whereby male mice showed higher levels of cell proliferation at P28, as well as higher levels of cell survival for P14-labelled cells, compared to female mice. However, female mice showed greater percentages of neuronal differentiation for P14-labelled cells. Finally, we found significant effects of age of BrdU injections on cell proliferation, survival, and neuronal differentiation. Collectively, our results suggest that the loss of vesicular zinc affects normal proliferation and survival of cells born at different age points during postnatal development and highlight prominent sex- and age-dependent differences. Our findings provide the foundation for future studies to further probe the role of vesicular zinc in the modulation of developmental neurogenesis.

Sex and Age-Dependent Olfactory Memory Dysfunction in ADHD Model Mice

ADHD is a typical neurodevelopmental disorder with a high prevalence rate. NSCs in the subventricular zone (SVZ) are closely related to neurodevelopmental disorder and can affect olfactory function by neurogenesis and migratory route. Although olfactory dysfunction is one of the symptoms of ADHD, the relevance of cells in the olfactory bulb derived from NSCs has not been studied. Therefore, we investigated olfactory memory and NSCs in Git1-deficient mice, under the ADHD model. Interestingly, only adult male G protein-coupled receptor kinase-interacting protein-1 (GIT1)-deficient (+/−, HE) mice showed impaired olfactory memory, suggesting sex and age dependence. We performed adult NSCs culture from the SVZ and observed distinct cell population in both sex and genotype. Taken together, our study suggests that the altered differentiation of NSCs in GIT1+/− mice can contribute to olfactory dysfunction in ADHD.

Promoting Endogenous Neurogenesis as a Treatment for Alzheimer's Disease

Alzheimer's disease (AD) is the most universal neurodegenerative disorder characterized by memory loss and cognitive impairment. AD is biologically defined by production and aggregation of misfolded protein including extracellular amyloid β (Aβ) peptide and intracellular microtubule-associated protein tau tangles in neurons, leading to irreversible neuronal loss. At present, regulation of endogenous neurogenesis to supplement lost neurons has been proposed as a promising strategy for treatment of AD. However, the exact underlying mechanisms of impaired neurogenesis in AD have not been fully explained and effective treatments targeting neurogenesis for AD are limited. In this review, we mainly focus on the latest research of impaired neurogenesis in AD. Then we discuss the factors affecting stages of neurogenesis and the interplay between neural stem cells (NSCs) and neurogenic niche under AD pathological conditions. This review aims to explore potential therapeutic strategies that promote endogenous neurogenesis for AD treatments.

Characterization by Gene Expression Analysis of Two Groups of Dopaminergic Cells Isolated from the Mouse Olfactory Bulb

The olfactory bulb (OB) is one of two regions of the mammalian brain which undergo continuous neuronal replacement during adulthood. A significant fraction of the cells added in adulthood to the bulbar circuitry is constituted by dopaminergic (DA) neurons. We took advantage of a peculiar property of dopaminergic neurons in transgenic mice expressing eGFP under the tyrosine hydroxylase (TH) promoter: while DA neurons located in the glomerular layer (GL) display full electrophysiological maturation, eGFP+ cells in the mitral layer (ML) show characteristics of immature cells. In addition, they also display a lower fluorescence intensity, possibly reflecting different degrees of maturation. To investigate whether this difference in maturation might be confirmed at the gene expression level, we used a fluorescence-activated cell sorting technique on enzymatically dissociated cells of the OB. The cells were divided into two groups based on their level of fluorescence, possibly corresponding to immature ML cells and fully mature DA neurons from the GL. Semiquantitative real-time PCR was performed to detect the level of expression of genes linked to the degree of maturation of DA neurons. We showed that indeed the cells expressing low eGFP fluorescence are immature neurons. Our method can be further used to explore the differences between these two groups of DA neurons.

Lrig1 expression identifies quiescent stem cells in the ventricular-subventricular zone from postnatal development to adulthood and limits their persistent hyperproliferation

BACKGROUND

We previously identified Leucine-rich repeats and immunoglobulin-like domains 1 (Lrig1) as a marker of long-term neurogenic stem cells in the lateral wall of the adult mouse brain. The morphology of the stem cells thus identified differed from the canonical B1 type stem cells, raising a question about their cellular origin. Thus, we investigated the development of these stem cells in the postnatal and juvenile brain. Furthermore, because Lrig1 is a known regulator of quiescence, we also investigated the effect(s) of its deletion on the cellular proliferation in the lateral wall.

METHODS

To observe the development of the Lrig1-lineage stem cells, genetic inducible fate mapping studies in combination with thymidine analog administration were conducted using a previously published Lrig1^T2A-iCreERT2 mouse line. To identify the long-term consequence(s) of Lrig1 germline deletion, old Lrig1 knock-out mice were generated using two different Lrig1 null alleles in the C57BL/6J background. The lateral walls from these mice were analyzed using an optimized whole mount immunofluorescence protocol and confocal microscopy.

RESULTS

We observed the Lrig1-lineage labeled cells with morphologies consistent with neurogenic stem cell identity in postnatal, juvenile, and adult mouse brains. Interestingly, when induced at postnatal or juvenile ages, morphologically distinct cells were revealed, including cells with the canonical B1 type stem cell morphology. Almost all of the presumptive stem cells labeled were non-proliferative at these ages. In the old Lrig1 germline knock-out mice, increased proliferation was observed compared to wildtype littermates without concomitant increase in apoptosis.

CONCLUSIONS

Once set aside during embryogenesis, the Lrig1-lineage stem cells remain largely quiescent during postnatal and juvenile development until activation in adult age. The absence of premature proliferative exhaustion in the Lrig1 knock-out stem cell niche during aging is likely due to a complex cascade of effects on the adult stem cell pool. Thus, we suggest that the adult stem cell pool size may be genetically constrained via Lrig1.

Zebrafish: A Model Deciphering the Impact of Flavonoids on Neurodegenerative Disorders

Over the past century, advances in biotechnology, biochemistry, and pharmacognosy have spotlighted flavonoids, polyphenolic secondary metabolites that have the ability to modulate many pathways involved in various biological mechanisms, including those involved in neuronal plasticity, learning, and memory. Moreover, flavonoids are known to impact the biological processes involved in developing neurodegenerative diseases, namely oxidative stress, neuroinflammation, and mitochondrial dysfunction. Thus, several flavonoids could be used as adjuvants to prevent and counteract neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Zebrafish is an interesting model organism that can offer new opportunities to study the beneficial effects of flavonoids on neurodegenerative diseases. Indeed, the high genome homology of 70% to humans, the brain organization largely similar to the human brain as well as the similar neuroanatomical and neurochemical processes, and the high neurogenic activity maintained in the adult brain makes zebrafish a valuable model for the study of human neurodegenerative diseases and deciphering the impact of flavonoids on those disorders.

Spontaneous neuronal regeneration in the forebrain of the leopard gecko (Eublepharis macularius) following neurochemical lesioning

BACKGROUND

Neurogenesis is the ability to generate new neurons from resident stem/progenitor populations. Although often understood as a homeostatic process, several species of teleost fish, salamanders, and lacertid lizards are also capable of reactive neurogenesis, spontaneously replacing lost or damaged neurons. Here, we demonstrate that reactive neurogenesis also occurs in a distantly related lizard species, Eublepharis macularius, the leopard gecko.

RESULTS

To initiate reactive neurogenesis, the antimetabolite 3-acetylpyridine (3-AP) was administered. Four days following 3-AP administration there is a surge in neuronal cell death within a region of the forebrain known as the medial cortex (homolog of the mammalian hippocampal formation). Neuronal cell death is accompanied by a shift in resident microglial morphology and an increase neural stem/progenitor cell proliferation. By 30 days following 3-AP administration, the medial cortex was entirely repopulated by NeuN+ neurons. At the same time, local microglia have reverted to a resting state and cell proliferation by neural stem/progenitors has returned to levels comparable with uninjured controls.

CONCLUSIONS

Together, these data provide compelling evidence of reactive neurogenesis in leopard geckos, and indicate that the ability of lizards to spontaneously replace lost or damaged forebrain neurons is more taxonomically widespread and evolutionarily conserved than previously considered.

What has single-cell transcriptomics taught us about long non-coding RNAs in the ventricular-subventricular zone?

Long non-coding RNA (lncRNA) function is mediated by the process of transcription or through transcript-dependent associations with proteins or nucleic acids to control gene regulatory networks. Many lncRNAs are transcribed in the ventricular-subventricular zone (V-SVZ), a postnatal neural stem cell niche. lncRNAs in the V-SVZ are implicated in neurodevelopmental disorders, cancer, and brain disease, but their functions are poorly understood. V-SVZ neurogenesis capacity declines with age due to stem cell depletion and resistance to neural stem cell activation. Here we analyzed V-SVZ transcriptomics by pooling current single-cell RNA-seq data. They showed consistent lncRNA expression during stem cell activation, lineage progression, and aging. In conjunction with epigenetic and genetic data, we predicted V-SVZ lncRNAs that regulate stem cell activation and differentiation. Some of the lncRNAs validate known epigenetic mechanisms, but most remain uninvestigated. Our analysis points to several lncRNAs that likely participate in key aspects of V-SVZ stem cell activation and neurogenesis in health and disease.

The knowns and many unknowns of CNS immunity in teleost fish

Many disease agents infect the central nervous system (CNS) of teleost fish causing severe losses for the fish farming sector. Yet, neurotropic fish pathogens remain poorly documented and immune responses in the teleost CNS essentially unknown. Previously thought to be devoid of an immune system, the mammalian CNS is now recognized to be protected from infection by diverse immune cells that mostly reside in the meningeal lymphatic system. Here we review the current body of work pertaining immune responses in the teleost CNS to infection. We identify important knowledge gaps with regards to CNS immunity in fish and make recommendations for rigorous experimentation and reporting in manuscripts so that fish immunologists can advance this burgeoning field.

Reversal of idiopathic hypogonadotropic hypogonadism in a Chinese male cohort

Idiopathic hypogonadotropic hypogonadism (IHH) is a rare genetically heterogeneous disease and characterized by incomplete or absent puberty and infertility. It is worth noting that partial IHH patients could recover reproductive endocrine function following treatment, which is termed reversal. This study aimed to investigate clinical and genetic characteristics of IHH reversal patients. A total of 141 IHH male patients were enrolled and followed up regularly. Their clinical and genetic features were collected and analysed to discover something in common in reversal cases. These IHH patients with a median age of 21 years (interquartile range: 18-24) were divided into reversal group (n = 13) and non-reversal group (n = 128). IL17RD, ERBB4, DLX5, EGFR, SEMA4D, B3GNT1 and CCKAR RSVs were demonstrated in reversal cases for the first time. Pathogenic/likely pathogenic (P/LP) RSVs consisted of 3 RSVs (one each patient, including PROKR2 p.W178S, EGFR p.G630R and CCKAR p.S291del) in reversal group. Reversal of IHH could not be ignored in clinical follow-up. Patients with high levels of basal LH and T may harbour more possibility of reversal and worthy extra attention to identify whether reversal occurs or not. Relapse after reversal also needs to be monitored.

Anatomical and Functional Connectivity at the Dendrodendritic Reciprocal Mitral Cell–Granule Cell Synapse: Impact on Recurrent and Lateral Inhibition

In the vertebrate olfactory bulb, reciprocal dendrodendritic interactions between its principal neurons, the mitral and tufted cells, and inhibitory interneurons in the external plexiform layer mediate both recurrent and lateral inhibition, with the most numerous of these interneurons being granule cells. Here, we used recently established anatomical parameters and functional data on unitary synaptic transmission to simulate the strength of recurrent inhibition of mitral cells specifically from the reciprocal spines of rat olfactory bulb granule cells in a quantitative manner. Our functional data allowed us to derive a unitary synaptic conductance on the order of 0.2 nS. The simulations predicted that somatic voltage deflections by even proximal individual granule cell inputs are below the detection threshold and that attenuation with distance is roughly linear, with a passive length constant of 650 μm. However, since recurrent inhibition in the wake of a mitral cell action potential will originate from hundreds of reciprocal spines, the summated recurrent IPSP will be much larger, even though there will be substantial mutual shunting across the many inputs. Next, we updated and refined a preexisting model of connectivity within the entire rat olfactory bulb, first between pairs of mitral and granule cells, to estimate the likelihood and impact of recurrent inhibition depending on the distance between cells. Moreover, to characterize the substrate of lateral inhibition, we estimated the connectivity via granule cells between any two mitral cells or all the mitral cells that belong to a functional glomerular ensemble (i.e., which receive their input from the same glomerulus), again as a function of the distance between mitral cells and/or entire glomerular mitral cell ensembles. Our results predict the extent of the three regimes of anatomical connectivity between glomerular ensembles: high connectivity within a glomerular ensemble and across the first four rings of adjacent glomeruli, substantial connectivity to up to eleven glomeruli away, and negligible connectivity beyond. Finally, in a first attempt to estimate the functional strength of granule-cell mediated lateral inhibition, we combined this anatomical estimate with our above simulation results on attenuation with distance, resulting in slightly narrowed regimes of a functional impact compared to the anatomical connectivity.

Regional Patterning of Adult Neurogenesis in the Homing Pigeon’s Brain

In the avian brain, adult neurogenesis has been reported in the telencephalon of several species, but the functional significance of this trait is still ambiguous. Homing pigeons (Columba livia f.d.) are well-known for their navigational skills. Their brains are functionally adapted to homing with, e.g., larger hippocampi. So far, no comprehensive mapping of adult neuro- and gliogenesis or studies of different developmental neuronal stages in the telencephalon of homing pigeons exists, although comprehensive analyses in various species surely will result in a higher understanding of the functional significance of adult neurogenesis. Here, adult, free flying homing pigeons were treated with 5-bromo-deoxyuridine (BrdU) to label adult newborn cells. Brains were dissected and immunohistochemically processed with several markers (GFAP, Sox2, S100ß, Tbr2, DCX, Prox1, Ki67, NeuN, Calbindin, Calretinin) to study different stages of adult neurogenesis in a quantitative and qualitative way. Therefore, immature and adult newborn neurons and glial cells were analyzed along the anterior–posterior axis. The analysis proved the existence of different neuronal maturation stages and showed that immature cells, migrating neurons and adult newborn neurons and glia were widely and regionally unequally distributed. Double- and triple-labelling with developmental markers allowed a stage classification of adult neurogenesis in the pigeon brain (1: continuity of stem cells/proliferation, 2: fate specification, 3: differentiation/maturation, 4: integration). The most adult newborn neurons and glia were found in the intercalated hyperpallium (HI) and the hippocampal formation (HF). The highest numbers of immature (DCX+) cells were detected in the nidopallium (N). Generally, the number of newborn glial cells exceeded the number of newborn neurons. Individual structures (e.g., HI, N, and HF) showed further variations along the anterior–posterior axis. Our qualitative classification and the distribution of maturing cells in the forebrain support the idea that there is a functional specialization, respectively, that there is a link between brain-structure and function, species-specific requirements and adult neurogenesis. The high number of immature neurons also suggests a high level of plasticity, which points to the ability for rapid adaption to environmental changes through additive mechanisms. Furthermore, we discuss a possible influence of adult neurogenesis on spatial cognition.

100 plus years of stem cell research-20 years of ISSCR

The International Society for Stem Cell Research (ISSCR) celebrates its 20^th anniversary in 2022. This review looks back at some of the key developments in stem cell research as well as the evolution of the ISSCR as part of that field. Important discoveries from stem cell research are described, and how the improved understanding of basic stem cell biology translates into new clinical therapies and insights into disease mechanisms is discussed. Finally, the birth and growth of ISSCR into a leading stem cell society and a respected voice for ethics, advocacy, education and policy in stem cell research are described.

Single-Cell Transcriptomics Reveals Splicing Features of Adult Neural Stem Cells in the Subventricular Zone

The central nervous system has enormously complex cellular diversity with hundreds of distinct cell types, yet alternative splicing features in single cells of important cell types at neurogenic regions are not well understood. By employing in silico analysis, we systematically identified 3,611 alternative splicing events from 1,908 genes in 28 single-cell transcriptomic data of adult mouse ependymal and subependymal regions, and found that single-cell RNA-seq has the advantage in uncovering rare splicing isoforms compared to bulk RNA-seq at the population level. We uncovered that the simultaneous presence of multiple isoforms from the same gene in a single cell is prevalent, and quiescent stem cells, activated stem cells, and neuroblast cells exhibit high heterogeneity of splicing variants. Furthermore, we also demonstrated the existence of novel bicistronic transcripts in quiescent stem cells.

Human olfactory epithelium-derived stem cells ameliorate histopathological deficits and improve behavioral functions in a rat model of cerebellar ataxia

Cell replacement therapy (CRT) is one of the most effective approaches used to alleviate symptoms of neurodegenerative syndromes such as cerebellar ataxia (CA). Human olfactory epithelium mesenchymal stem cells (OE-MSCs) have been recognized as a promising candidate for CRT, due to their distinctive features including immunomodulatory properties and ease of accessible compared to other types of MSCs. Hence, the main goal of our study was to explore the impacts of OE-MSCs transplantation on behavioral, structural, and histological deficiencies in a rat model of CA. After obtained an informed consent from volunteers, OE-MSCs were obtained from their nasal cavity. Then, OE-MSCs were characterized by the positive expression of CD73, CD90, and CD105 as MSCs as well as nestin and vimentin as primitive neuroectodermal stem cells markers. Then, the animals were randomized into three control, 3-acetylpyridine (3-AP) treated, and 3-AP + cell groups. In both experimental groups, the rats received intraperitoneal injection of 3-AP (75 mg/kg), followed by the implantation of OE-MSCs into the cerebellum of 3-AP + cell group. The impact of engrafted OE-MSCs on motor coordination and performance along with biochemical, immunohistochemical, and stereological changes in the cerebellum of the rat models of CA were investigated. According to our findings, the administration of 3-AP decreased the cerebellar GSH concentration. The injection of 3-AP also altered the morphological characteristics of the cerebellar Golgi cells. On the other hand, OE-MSCs transplantation improved motor coordination in CA. Besides, the implantation of OE-MSCs reduced caspase-3 expression and microglia proliferation in the cerebellum upon 3-AP administration. Finally, the transplant of OE-MSCs protected Purkinje cells against 3-AP toxicity. In sum, the present study revealed considerable advantages of OE-MSCs in managing CA animal model.

Impact of Two Neuronal Sigma-1 Receptor Modulators, PRE084 and DMT, on Neurogenesis and Neuroinflammation in an Aβ1-42-Injected, Wild-Type Mouse Model of AD

Alzheimer's disease (AD) is the most common form of dementia characterized by cognitive dysfunctions. Pharmacological interventions to slow the progression of AD are intensively studied. A potential direction targets neuronal sigma-1 receptors (S1Rs). S1R ligands are recognized as promising therapeutic agents that may alleviate symptom severity of AD, possibly via preventing amyloid-β-(Aβ-) induced neurotoxicity on the endoplasmic reticulum stress-associated pathways. Furthermore, S1Rs may also modulate adult neurogenesis, and the impairment of this process is reported to be associated with AD. We aimed to investigate the effects of two S1R agonists, dimethyltryptamine (DMT) and PRE084, in an Aβ-induced in vivo mouse model characterizing neurogenic and anti-neuroinflammatory symptoms of AD, and the modulatory effects of S1R agonists were analyzed by immunohistochemical methods and western blotting. DMT, binding moderately to S1R but with high affinity to 5-HT receptors, negatively influenced neurogenesis, possibly as a result of activating both receptors differently. In contrast, the highly selective S1R agonist PRE084 stimulated hippocampal cell proliferation and differentiation. Regarding neuroinflammation, DMT and PRE084 significantly reduced Aβ1-42-induced astrogliosis, but neither had remarkable effects on microglial activation. In summary, the highly selective S1R agonist PRE084 may be a promising therapeutic agent for AD. Further studies are required to clarify the multifaceted neurogenic and anti-neuroinflammatory roles of these agonists.

mdka Expression Is Associated with Quiescent Neural Stem Cells during Constitutive and Reactive Neurogenesis in the Adult Zebrafish Telencephalon

In contrast to mammals, adult zebrafish display an extraordinary capacity to heal injuries and repair damage in the central nervous system. Pivotal for the regenerative capacity of the zebrafish brain at adult stages is the precise control of neural stem cell (NSC) behavior and the maintenance of the stem cell pool. The gene mdka, a member of a small family of heparin binding growth factors, was previously shown to be involved in regeneration in the zebrafish retina, heart, and fin. Here, we investigated the expression pattern of the gene mdka and its paralogue mdkb in the zebrafish adult telencephalon under constitutive and regenerative conditions. Our findings show that only mdka expression is specifically restricted to the telencephalic ventricle, a stem cell niche of the zebrafish telencephalon. In this brain region, mdka is particularly expressed in the quiescent stem cells. Interestingly, after brain injury, mdka expression remains restricted to the resting stem cell, which might suggest a role of mdka in regulating stem cell quiescence.

Intravital Imaging of the Murine Subventricular Zone with Three Photon Microscopy

The mouse subventricular zone (SVZ) produces neurons throughout life. It is useful for mechanism discovery and is relevant for regeneration. However, the SVZ is deep, significantly restricting live imaging since current methods do not extend beyond a few hundred microns. We developed and adapted three-photon microscopy (3PM) for non-invasive deep brain imaging in live mice, but its utility in imaging the SVZ niche was unknown. Here, with fluorescent dyes and genetic labeling, we show successful 3PM imaging in the whole SVZ, extending to a maximum depth of 1.5 mm ventral to the dura mater. 3PM imaging distinguished multiple SVZ cell types in postnatal and juvenile mice. We also detected fine processes on neural stem cells interacting with the vasculature. Previous live imaging removed overlying cortical tissue or lowered lenses into the brain, which could cause inflammation and alter neurogenesis. We found that neither astrocytes nor microglia become activated in the SVZ, suggesting 3PM does not induce major damage in the niche. Thus, we show for the first time 3PM imaging of the SVZ in live mice. This strategy could be useful for intravital visualization of cell dynamics, molecular, and pathological perturbation and regenerative events.

Neurogenesis in the Maternal Rodent Brain: Impacts of Gestation-Related Hormonal Regulation, Stress, and Obesity

In order to maintain maternal behavior, it is important that the maternal rodent brain promotes neurogenesis. Maternal neurogenesis is altered by the dynamic shifts in reproductive hormone levels during pregnancy. Thus, lifestyle events such as gestational stress and obesity that can affect hormone production will affect neuroendocrine control of maternal neurogenesis. However, there is a lack of information about the regulation of maternal neurogenesis by placental hormones, which are key components of the reproductive hormonal profile during pregnancy. There is also little known about how maternal neurogenesis can be affected by health concerns such as gestational stress and obesity, and its relationship to peripartum mental health disorders. This review summarizes the changing levels of neurogenesis in mice and rats during gestation and postpartum as well as regulation of neurogenesis by pregnancy-related hormones. The influence of neurogenesis on maternal behavior is also discussed while bringing attention to the effect of health-related concerns during gestation, such as stress and obesity on neuroendocrine control of maternal neurogenesis. In doing so, this review identifies the gaps in the literature and specifically emphasizes the importance of further research on maternal brain physiology to address them.

Monitoring Autophagy in Neural Stem and Progenitor Cells

Autophagy is a critical cellular program that is necessary for cellular survival and adaptation to nutrient and metabolic stress. In addition to homeostatic maintenance and adaptive response functions, autophagy also plays an active role during development and tissue regeneration. Within the neural system, autophagy is important for stem cell maintenance and the ability of neural stem cells to undergo self-renewal. Autophagy also contributes toward neurogenesis and provides neural progenitor cells with sufficient energy to mediate cytoskeleton remodeling during the differentiation process. In differentiated neural cells, autophagy maintains neuronal homeostasis and viability by preventing the accumulation of toxic and pathological intracellular aggregates. However, prolonged autophagy or dysregulated upregulation of autophagy can result in autophagic cell death. Moreover, mutations or defects in autophagy that result in neural stem cell instability and cell death underlie many neurodegenerative disorders, such as Parkinson's disease. Thus, autophagy plays a multi-faceted role during neurogenesis from the stem cell to the differentiated neural cell. In this chapter, we describe methods to monitor autophagy at the protein and transcript level to evaluate alterations within the autophagy program in neural stem and progenitor cells. We describe immunoblotting and immunocytochemistry approaches for evaluating autophagy-dependent protein modifications, as well as quantitative real-time PCR to assess transcript levels of autophagy genes. As autophagy is a dynamic process, we highlight the importance of using late-stage inhibitors to be able to assess autophagic flux and quantify the level of autophagy occurring within cells.

Peripheric smell regions in patients with semicircular canal dehiscence: An MRI evaluation

OBJECTIVES

We investigated the peripheric smell regions in patients with semicircular canal dehiscence (SCD) by cranial MRI.

METHODS

In this retrospective study, cranial MRI images of 186 adult patients were included. Group 1 consisted of 83 adult patients with SCD. The control group (Group 2) consisted of 83 healthy subjects without central vertigo. Olfactory bulb (OB) volume and olfactory sulcus (OS) depth were measured in all groups.

RESULTS

In group 1, SCD was detected on the right (33.7%), left (26.5%) sides and bilateral (39.8%). Localization of dehiscence was at superior SC (75.9%), posterior SC (21.7%), lateral SC (1.2%), and posterior + superior SCs (1.2%). OB volumes of the SCD group were significantly lower than the control group bilaterally (p < 0.05). There were no significant differences between OS depths of groups 1 and 2 (p > 0.05). In SCD group, there were positive correlations between OB volumes; OS depths; and OB volumes and OS depths (p < 0.05). In older patients, bilateral OS depth values got lower (p < 0.05). In females, left OB volume values were lower than males (p < 0.05). In right SCD (+) patients, left OS depth values got lower (p < 0.05).

CONCLUSION

We concluded that possible changes in CSF dynamics may cause the development of SCD at thin bone segments; and a decrease in the OB volume. CSF leaks into the perineural sheet of the olfactory bulb (OB) maybe responsible for the decrease in the OB volume. In addition, minor trauma, infection, and inflammation may also be responsible for both coexistences of SCD development and OB volume decrease.

Investigation of Neurogenesis in Kindled Wistar and Genetic Absence Epilepsy Rats

Objective: The most common type of epilepsy affecting about 50 million people worldwide is temporal lobe epilepsy (TLE). Chemical and electrical kindling methods in animals can be used to form TLE model. In the present study, it was aimed to investigate neurogenesis in the hippocampus of adult kindled Wistar rats and genetic absence epilepsy rats from Strasbourg (GAERS) rats by immunofluorescence methods. Methods: Adult Wistar and GAERS albino rats weighing 250-300 gr were injected pentylenetetrazole (PTZ) (35 mg/kg, s.c.) every other day to produce chemical kindling. Animals having 5 times grade 5 seizures were considered to be kindled. Intracardiac perfusion was performed under deep anesthesia on the 7th and 14th days after the last grade 5 seizure. Immunofluorescence methods were used to demonstrate newly formed neurons, astroglial cells, and mature neurons, by using anti-doublecortin (DCX), anti-glial fibrillary acidic protein (GFAP), and anti- neuronal nuclear antigen (NeuN) primary antibodies, respectively. Sections were then examined under a fluorescence microscope. Results: DCX (+) cells were found to be increased in GAERS control groups compared to the Wistar control groups; and in Wistar PTZ groups compared to the Wistar control groups. DCX (+) cells were decreased in GAERS PTZ groups compared to their controls and to Wistar PTZ groups. Conclusion: The findings of the present study suggest that the resistance to electrical kindling of GAERS reported in previous studies might be related to the increased neurogenesis in this strain.

Novel Galectin-3 Roles in Neurogenesis, Inflammation and Neurological Diseases

Galectin-3 (Gal-3) is an evolutionarily conserved and multifunctional protein that drives inflammation in disease. Gal-3's role in the central nervous system has been less studied than in the immune system. However, recent studies show it exacerbates Alzheimer's disease and is upregulated in a large variety of brain injuries, while loss of Gal-3 function can diminish symptoms of neurodegenerative diseases such as Alzheimer's. Several novel molecular pathways for Gal-3 were recently uncovered. It is a natural ligand for TREM2 (triggering receptor expressed on myeloid cells), TLR4 (Toll-like receptor 4), and IR (insulin receptor). Gal-3 regulates a number of pathways including stimulation of bone morphogenetic protein (BMP) signaling and modulating Wnt signalling in a context-dependent manner. Gal-3 typically acts in pathology but is now known to affect subventricular zone (SVZ) neurogenesis and gliogenesis in the healthy brain. Despite its myriad interactors, Gal-3 has surprisingly specific and important functions in regulating SVZ neurogenesis in disease. Gal-1, a similar lectin often co-expressed with Gal-3, also has profound effects on brain pathology and adult neurogenesis. Remarkably, Gal-3's carbohydrate recognition domain bears structural similarity to the SARS-CoV-2 virus spike protein necessary for cell entry. Gal-3 can be targeted pharmacologically and is a valid target for several diseases involving brain inflammation. The wealth of molecular pathways now known further suggest its modulation could be therapeutically useful.

The First 50 Years of Postnatal Neurogenesis in the Cerebellum: a Long Journey Across Phenomena, Mechanisms, and Human Disease

The discovery by Altman and coworkers of adult-born microneurons in the olfactory bulb and dentate gyrus has triggered a long stream of studies and many attempts to harness adult neurogenesis, promote regeneration after injury, and contrast cognitive decline in the elderly. Likewise, the discovery of postnatal neurogenesis in the cerebellum has provided the framework for many subsequent molecular studies, including investigations of developmental processes and the assessment of GC progenitor (GCP) clonal expansion in the context of human disease. Here, I will briefly discuss some of the discoveries made in the field of cerebellar development over the years building upon the findings of Altman and his colleagues, touching upon signaling pathways that regulate granule cell neurogenesis and their involvement in developmental and neoplastic disorders of the cerebellum.

Unraveling the Role of Dopaminergic and Calretinin Interneurons in the Olfactory Bulb

The perception and discriminating of odors are sensory activities that are an integral part of our daily life. The first brain region where odors are processed is the olfactory bulb (OB). Among the different cell populations that make up this brain area, interneurons play an essential role in this sensory activity. Moreover, probably because of their activity, they represent an exception compared to other parts of the brain, since OB interneurons are continuously generated in the postnatal and adult period. In this review, we will focus on periglomerular (PG) cells which are a class of interneurons found in the glomerular layer of the OB. These interneurons can be classified into distinct subtypes based on their neurochemical nature, based on the neurotransmitter and calcium-binding proteins expressed by these cells. Dopaminergic (DA) periglomerular cells and calretinin (CR) cells are among the newly generated interneurons and play an important role in the physiology of OB. In the OB, DA cells are involved in the processing of odors and the adaptation of the bulbar network to external conditions. The main role of DA cells in OB appears to be the inhibition of glutamate release from olfactory sensory fibers. Calretinin cells are probably the best morphologically characterized interneurons among PG cells in OB, but little is known about their function except for their inhibitory effect on noisy random excitatory signals arriving at the main neurons. In this review, we will mainly describe the electrophysiological properties related to the excitability profiles of DA and CR cells, with a particular view on the differences that characterize DA mature interneurons from cells in different stages of adult neurogenesis.

The PSA-NCAM-Positive "Immature" Neurons: An Old Discovery Providing New Vistas on Brain Structural Plasticity

Studies on brain plasticity have undertaken different roads, tackling a wide range of biological processes: from small synaptic changes affecting the contacts among neurons at the very tip of their processes, to birth, differentiation, and integration of new neurons (adult neurogenesis). Stem cell-driven adult neurogenesis is an exception in the substantially static mammalian brain, yet, it has dominated the research in neurodevelopmental biology during the last thirty years. Studies of comparative neuroplasticity have revealed that neurogenic processes are reduced in large-brained mammals, including humans. On the other hand, large-brained mammals, with respect to rodents, host large populations of special "immature" neurons that are generated prenatally but express immature markers in adulthood. The history of these "immature" neurons started from studies on adhesion molecules carried out at the beginning of the nineties. The identity of these neurons as "stand by" cells "frozen" in a state of immaturity remained un-detected for long time, because of their ill-defined features and because clouded by research ef-forts focused on adult neurogenesis. In this review article, the history of these cells will be reconstructed, and a series of nuances and confounding factors that have hindered the distinction between newly generated and "immature" neurons will be addressed.

Adult brain cytogenesis in the context of mood disorders: From neurogenesis to the emergent role of gliogenesis

Psychiatric disorders severely impact patients' lives. Motivational, cognitive and emotional deficits are the most common symptoms observed in these patients and no effective treatment is still available, either due to the adverse side effects or the low rate of efficacy of currently available drugs. Neurogenesis recovery has been one important focus in the treatment of psychiatric disorders, which undeniably contributes to the therapeutic action of antidepressants. However, glial plasticity is emerging as a new strategy to explore the deficits observed in mood disorders and the efficacy of therapeutic interventions. Thus, it is crucial to understand the mechanisms behind glio- and neurogenesis to better define treatments and preventive therapies, once adult cytogenesis is of pivotal importance to cognitive and emotional components of behavior, both in healthy and pathological contexts, including in psychiatric disorders. Here, we review the concepts and history of neuro- and gliogenesis, providing as well a reflection on the functional importance of cytogenesis in the context of disease.

In Vitro Culturing of Adult Stem Cells: The Importance of Serum and Atmospheric Oxygen

Adult stem cells are undifferentiated cells found in many different tissues in the adult human and animal body and are thought to be important for replacing damaged and dead cells during life. Due to their differentiation abilities, they have significant potential for regeneration and consequently therapeutic potential in various medical conditions. Studies on in vitro cultivation of different types of adult stem cells have shown that they have specific requirements for optimal proliferation and stemness maintenance as well as induced differentiation. The main factors affecting the success of stem cell cultivation are the composition of the growth medium, including the presence of serum, temperature, humidity, and contact with other cells and the composition of the atmosphere in which the cells grow. In this chapter, we review the literature and describe our own experience regarding the influence of the presence of fetal bovine serum in the medium and the oxygen concentration in the atmosphere on the stemness maintenance and survival of adult stem cells from various tissue sources such as adipose tissue, muscle, brain, and testicular tissue.

Positive Controls in Adults and Children Support That Very Few, If Any, New Neurons Are Born in the Adult Human Hippocampus

Adult hippocampal neurogenesis was originally discovered in rodents. Subsequent studies identified the adult neural stem cells and found important links between adult neurogenesis and plasticity, behavior, and disease. However, whether new neurons are produced in the human dentate gyrus (DG) during healthy aging is still debated. We and others readily observe proliferating neural progenitors in the infant hippocampus near immature cells expressing doublecortin (DCX), but the number of such cells decreases in children and few, if any, are present in adults. Recent investigations using dual antigen retrieval find many cells stained by DCX antibodies in adult human DG. This has been interpreted as evidence for high rates of adult neurogenesis, even at older ages. However, most of these DCX-labeled cells have mature morphology. Furthermore, studies in the adult human DG have not found a germinal region containing dividing progenitor cells. In this Dual Perspectives article, we show that dual antigen retrieval is not required for the detection of DCX in multiple human brain regions of infants or adults. We review prior studies and present new data showing that DCX is not uniquely expressed by newly born neurons: DCX is present in adult amygdala, entorhinal and parahippocampal cortex neurons despite being absent in the neighboring DG. Analysis of available RNA-sequencing datasets supports the view that DG neurogenesis is rare or absent in the adult human brain. To resolve the conflicting interpretations in humans, it is necessary to identify and visualize dividing neuronal precursors or develop new methods to evaluate the age of a neuron at the single-cell level.

In vivo live imaging of postnatal neural stem cells

Neural stem cells (NSCs) are maintained in specific regions of the postnatal brain and contribute to its structural and functional plasticity. However, the long-term renewal potential of NSCs and their mode of division remain elusive. The use of advanced in vivo live imaging approaches may expand our knowledge of NSC physiology and provide new information for cell replacement therapies. In this Review, we discuss the in vivo imaging methods used to study NSC dynamics and recent live-imaging results with respect to specific intracellular pathways that allow NSCs to integrate and decode different micro-environmental signals. Lastly, we discuss future directions that may provide answers to unresolved questions regarding NSC physiology.

Role of Adult-Born Versus Preexisting Neurons Born at P0 in Olfactory Perception in a Complex Olfactory Environment in Mice

Olfactory perceptual learning is defined as an improvement in the discrimination of perceptually close odorants after passive exposure to these odorants. In mice, simple olfactory perceptual learning involving the discrimination of two odorants depends on an increased number of adult-born neurons in the olfactory bulb, which refines the bulbar output. However, the olfactory environment is complex, raising the question of the adjustment of the bulbar network to multiple discrimination challenges. Perceptual learning of 1 to 6 pairs of similar odorants led to discrimination of all learned odor pairs. Increasing complexity did not increase adult-born neuron survival but enhanced the number of adult-born neurons responding to learned odorants and their spine density. Moreover, only complex learning induced morphological changes in neurons of the granule cell layer born during the first day of life (P0). Selective optogenetic inactivation of either population confirmed functional involvement of adult-born neurons regardless of the enrichment complexity, while preexisting neurons were required for complex discrimination only.

Role of Calpain-1 in Neurogenesis

While calpains have been implicated in neurogenesis for a long time, there is still little information regarding the specific contributions of various isoforms in this process. We took advantage of the availability of mutant mice with complete deletion of calpain-1 to analyze its contribution to neurogenesis. We first used the incorporation of BrdU in newly-generated cells in the subgranular zone of the dentate gyrus to determine the role of calpain-1 deletion in neuronal proliferation. Our results showed that the lack of calpain-1 decreased the rate of cell proliferation in adult hippocampus. As previously shown, it also decreased the long-term survival of newly-generated neurons. We also used data from previously reported RNA and miRNA sequencing analyses to identify differentially expressed genes in brain of calpain-1 knock-out mice related to cell division, cell migration, cell proliferation and cell survival. A number of differentially expressed genes were identified, which could play a significant role in the changes in neurogenesis in calpain-1 knock out mice. The results provide new information regarding the role of calpain-1 in neurogenesis and have implications for better understanding the pathologies associated with calpain-1 mutations in humans.

Neurogenesis in the adult Drosophila brain

Neurodegenerative diseases such as Alzheimer's and Parkinson's currently affect ∼25 million people worldwide (Erkkinen et al. 2018). The global incidence of traumatic brain injury (TBI) is estimated at ∼70 million/year (Dewan et al. 2018). Both neurodegenerative diseases and TBI remain without effective treatments. We are utilizing adult Drosophila melanogaster to investigate the mechanisms of brain regeneration with the long term goal of identifying targets for neural regenerative therapies. We specifically focused on neurogenesis, i.e. the generation of new cells, as opposed to the regrowth of specific subcellular structures such as axons. Like mammals, Drosophila have few proliferating cells in the adult brain. Nonetheless, within 24 hours of a Penetrating Traumatic Brain Injury (PTBI) to the central brain, there is a significant increase in the number of proliferating cells. We subsequently detect both new glia and new neurons and the formation of new axon tracts that target appropriate brain regions. Glial cells divide rapidly upon injury to give rise to new glial cells. Other cells near the injury site upregulate neural progenitor genes including asense and deadpan and later give rise to the new neurons. Locomotor abnormalities observed after PTBI are reversed within two weeks of injury, supporting the idea that there is functional recovery. Together, these data indicate that adult Drosophila brains are capable of neuronal repair. We anticipate that this paradigm will facilitate the dissection of the mechanisms of neural regeneration and that these processes will be relevant to human brain repair.

Olfactory bulb volume in patients with normal-pressure hydrocephalus: an MRI evaluation

AIM

To investigate changes in olfactory bulb (OB) volume in patients with idiopathic normal-pressure hydrocephalus (NPH).

MATERIALS AND METHODS

This multicentric retrospective study included a test group of 23 patients with NPH (10 male and 13 female patients) and a control group of 27 healthy participants without hydrocephalus. The OB volume in all participants had been measured using cranial magnetic resonance imaging (MRI). In the NPH group, positivity for disproportionately enlarged subarachnoid space hydrocephalus (DESH) was also evaluated.

RESULTS

The OB volumes of the NPH group (R 38.29 ± 9.34 mm³ and L37.52 ± 9.59 mm³) were significantly lower than those of the control group (R 45.87 ± 7.33 mm³ and L48.41 ± 7.62 mm³) bilaterally. There were no significant differences between right and left OB volumes in the NPH group. Nine of the 23 patients were DESH positive and 14 were DESH negative. There were no significant differences between OB volumes of the DESH positive and DESH vpatients in the NPH group. In both groups, there was a positive correlation between right and left OB volumes. There were no significant correlations between OB volumes and age or gender. In the NPH group, there were no significant correlations between DESH positivity and OB volumes.

CONCLUSION

OB volume decrease and olfactory problems should be taken into account in idiopathic NPH patients. When expanded ventricles and decreased OB volume are observed at cranial MRI, a diagnosis of idiopathic NPH should be considered.