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Cells Sep 2022In mammals, neurogenesis occurs during both embryonic and postnatal development. In eutherians, most brain structures develop embryonically; conversely, in marsupials, a... (Review)
Review
In mammals, neurogenesis occurs during both embryonic and postnatal development. In eutherians, most brain structures develop embryonically; conversely, in marsupials, a number of brain structures develop after birth. The exception is the generation of granule cells in the dentate gyrus, olfactory bulb, and cerebellum of eutherian species. The formation of these structures starts during embryogenesis and continues postnatally. In both eutherians and marsupials, neurogenesis continues in the subventricular zone of the lateral ventricle (SVZ) and the dentate gyrus of the hippocampal formation throughout life. The majority of proliferated cells from the SVZ migrate to the olfactory bulb, whereas, in the dentate gyrus, cells reside within this structure after division and differentiation into neurons. A key aim of this review is to evaluate advances in understanding developmental neurogenesis that occurs postnatally in both marsupials and eutherians, with a particular emphasis on the generation of granule cells during the formation of the olfactory bulb, dentate gyrus, and cerebellum. We debate the significance of immature neurons in the piriform cortex of young mammals. We also synthesize the knowledge of adult neurogenesis in the olfactory bulb and the dentate gyrus of marsupials by considering whether adult-born neurons are essential for the functioning of a given area.
Topics: Animals; Dentate Gyrus; Eutheria; Mammals; Marsupialia; Neurogenesis
PubMed: 36078144
DOI: 10.3390/cells11172735 -
Biomolecules Feb 2020It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear.... (Review)
Review
It is now well established that neurogenesis occurs throughout adulthood in select brain regions, but the functional significance of adult neurogenesis remains unclear. There is considerable evidence that steroid hormones modulate various stages of adult neurogenesis, and this review provides a focused summary of the effects of testosterone on adult neurogenesis. Initial evidence came from field studies with birds and wild rodent populations. Subsequent experiments with laboratory rodents have tested the effects of testosterone and its steroid metabolites upon adult neurogenesis, as well as the functional consequences of induced changes in neurogenesis. These experiments have provided clear evidence that testosterone increases adult neurogenesis within the dentate gyrus region of the hippocampus through an androgen-dependent pathway. Most evidence indicates that androgens selectively enhance the survival of newly generated neurons, while having little effect on cell proliferation. Whether this is a result of androgens acting directly on receptors of new neurons remains unclear, and indirect routes involving brain-derived neurotrophic factor (BDNF) and glucocorticoids may be involved. In vitro experiments suggest that testosterone has broad-ranging neuroprotective effects, which will be briefly reviewed. A better understanding of the effects of testosterone upon adult neurogenesis could shed light on neurological diseases that show sex differences.
Topics: Androgens; Animals; Brain; Brain-Derived Neurotrophic Factor; Cell Proliferation; Cell Survival; Dentate Gyrus; Female; Glucocorticoids; Hippocampus; Humans; Male; Neurogenesis; Neurons; Neuroprotective Agents; Olfactory Bulb; Testosterone
PubMed: 32028656
DOI: 10.3390/biom10020225 -
Cells Apr 2023In the mammalian brain, neurogenesis is maintained throughout adulthood primarily in two typical niches, the subgranular zone (SGZ) of the dentate gyrus and the... (Review)
Review
In the mammalian brain, neurogenesis is maintained throughout adulthood primarily in two typical niches, the subgranular zone (SGZ) of the dentate gyrus and the subventricular zone (SVZ) of the lateral ventricles and in other nonclassic neurogenic areas (e.g., the amygdala and striatum). During prenatal and early postnatal development, neural stem cells (NSCs) differentiate into neurons and migrate to appropriate areas such as the olfactory bulb where they integrate into existing neural networks; these phenomena constitute the multistep process of neurogenesis. Alterations in any of these processes impair neurogenesis and may even lead to brain dysfunction, including cognitive impairment and neurodegeneration. Here, we first summarize the main properties of mammalian neurogenic niches to describe the cellular and molecular mechanisms of neurogenesis. Accumulating evidence indicates that neurogenesis plays an integral role in neuronal plasticity in the brain and cognition in the postnatal period. Given that neurogenesis can be highly modulated by a number of extrinsic and intrinsic factors, we discuss the impact of extrinsic (e.g., alcohol) and intrinsic (e.g., hormones) modulators on neurogenesis. Additionally, we provide an overview of the contribution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection to persistent neurological sequelae such as neurodegeneration, neurogenic defects and accelerated neuronal cell death. Together, our review provides a link between extrinsic/intrinsic factors and neurogenesis and explains the possible mechanisms of abnormal neurogenesis underlying neurological disorders.
Topics: Animals; Humans; Adult; COVID-19; SARS-CoV-2; Neurogenesis; Neurons; Neural Stem Cells; Mammals
PubMed: 37174685
DOI: 10.3390/cells12091285 -
Behavioral and Brain Functions : BBF Dec 2023Parosmia is a qualitative olfactory dysfunction presenting as "distorted odor perception" in presence of an odor source. Aim of this study was to use resting state...
OBJECTIVE
Parosmia is a qualitative olfactory dysfunction presenting as "distorted odor perception" in presence of an odor source. Aim of this study was to use resting state functional connectivity to gain more information on the alteration of olfactory processing at the level of the central nervous system level.
METHODS
A cross sectional study was performed in 145 patients with parosmia (age range 20-76 years; 90 women). Presence and degree of parosmia was diagnosed on the basis of standardized questionnaires. Participants also received olfactory testing using the "Sniffin' Sticks". Then they underwent resting state scans using a 3 T magnetic resonance imaging scanner while fixating on a cross.
RESULTS
Whole brain analyses revealed reduced functional connectivity in salience as well as executive control networks. Region of interest-based analyses also supported reduced functional connectivity measures between primary and secondary olfactory eloquent areas (temporal pole, supramarginal gyrus and right orbitofrontal cortex; dorso-lateral pre-frontal cortex and the right piriform cortex).
CONCLUSIONS
Participants with parosmia exhibited a reduced information flow between memory, decision making centers, and primary and secondary olfactory areas.
Topics: Humans; Female; Young Adult; Adult; Middle Aged; Aged; Cross-Sectional Studies; Olfaction Disorders; Smell; Brain; Magnetic Resonance Imaging
PubMed: 38115149
DOI: 10.1186/s12993-023-00225-8 -
Annals of Clinical and Translational... Dec 2023To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior...
OBJECTIVE
To investigate structural and functional connectivity changes in brain olfactory-related structures in a longitudinal prospective cohort of isolated REM sleep behavior disorder (iRBD) and their clinical correlations, longitudinal evolution, and predictive values for phenoconversion to overt synucleinopathies, especially Lewy body diseases.
METHODS
The cohort included polysomnography-confirmed iRBD patients and controls. Participants underwent baseline assessments including olfactory tests, neuropsychological evaluations, the Movement Disorders Society-Unified Parkinson's Disease Rating Scale, 3T brain MRI, and F-FP-CIT PET scans. Voxel-based morphometry (VBM) was performed to identify regions of atrophy in iRBD, and volumes of relevant olfactory-related regions of interest (ROI) were estimated. Subgroups of patients underwent repeated volumetric MRI and resting-state functional MRI (fMRI) scans after four years.
RESULTS
A total of 51 iRBD patients were included, with 20 of them converting to synucleinopathy (mean time to conversion 3.08 years). Baseline VBM analysis revealed atrophy in the right olfactory cortex and gyrus rectus in iRBD. Subsequent ROI comparisons with controls showed atrophy in the amygdala. These olfactory-related atrophies tended to be associated with worse depression, anxiety, and urinary problems in iRBD. Amygdala F-FP-CIT uptake tended to be reduced in iRBD patients with hyposmia (nonsignificant after multiple comparison correction) and correlated with urinary problems. Resting-state fMRI of 23 patients and 32 controls revealed multiple clusters with aberrant olfactory-related functional connectivity. Hypoconnectivity between the putamen and olfactory cortex was associated with mild parkinsonian signs in iRBD. Longitudinal analysis of volumetric volumetric MRI in 22 iRBD patients demonstrated four-year progression of olfactory-related atrophy. Cox regression analysis revealed that this atrophy significantly predicted phenoconversion.
INTERPRETATION
Progressive atrophy of central olfactory structures may be a potential indicator of Lewy body disease progression in iRBD.
Topics: Humans; REM Sleep Behavior Disorder; Prospective Studies; Tropanes; Brain; Lewy Body Disease; Synucleinopathies
PubMed: 37743764
DOI: 10.1002/acn3.51905 -
Handbook of Clinical Neurology 2021Cerebrospinal fluid (CSF) disorders are challenging conditions in neurosurgical practice. The majority of CSF is contained in the basal cisterns of the brain, which are... (Review)
Review
Cerebrospinal fluid (CSF) disorders are challenging conditions in neurosurgical practice. The majority of CSF is contained in the basal cisterns of the brain, which are subarachnoid compartments that communicate with each other, and contribute to the circulation of CSF. Yaşargil et al. (1976) was the first to provide the systematic classification and naming of the basal cisterns. The lamina terminalis (LT) starts from the gyrus rectus and descends to the lateral aspect of the optic chiasm. It is a thick arachnoidal membrane delineating the anterior wall of the third ventricle that borders the LT cistern. With the introduction of the operating microscope and the progressive development of modern neurosurgery, the arachnoid and basal cisterns have been used as surgical corridors in order to reach deep areas of the brain and to release CSF for brain relaxation. In this way, the LT is used as a surgical corridor for the treatment of several conditions such as obstructive hydrocephalus and diencephalic tumors. In this chapter, we will describe the anatomy of the LT, possible conditions treated by opening the LT, the different surgical approaches to opening the LT, along with their advantages and disadvantages.
Topics: Humans; Hydrocephalus; Hypothalamus; Neurosurgical Procedures; Subarachnoid Space; Third Ventricle
PubMed: 34225931
DOI: 10.1016/B978-0-12-820107-7.00014-8 -
Cold Spring Harbor Perspectives in... Apr 2015Adult neurogenesis is limited to specific brain regions in the mammalian brain, such as the hippocampal dentate gyrus and the subventricular zone/olfactory bulb system.... (Review)
Review
Adult neurogenesis is limited to specific brain regions in the mammalian brain, such as the hippocampal dentate gyrus and the subventricular zone/olfactory bulb system. Alterations in adult neurogenesis appear to be a common hallmark in different neurodegenerative diseases including Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). This is remarkable, because the distinct pathological proteins responsible for the different diseases induce the loss of different neural populations. Impaired adult neurogenesis was shown in numerous animal models of neurodegenerative diseases; however, only few postmortem studies have been performed. We will review concepts related to the interplay between cellular plasticity in regions of adult neurogenesis with a specific focus on cell-autonomous and non-cell-autonomous factors. Furthermore, various strategies aimed to stimulate neuronal plasticity will be discussed within the context of a potential translation into therapeutic approaches for neuropsychiatric symptoms associated with PD, HD, and AD.
Topics: Animals; Humans; Neurodegenerative Diseases; Neurogenesis
PubMed: 25833845
DOI: 10.1101/cshperspect.a021287 -
Scientific Reports Jun 2023Although the combination antiretroviral treatment (cART) has considerably lowered the risk of HIV associated dementia (HAD), the incidence of neurocognitive...
Although the combination antiretroviral treatment (cART) has considerably lowered the risk of HIV associated dementia (HAD), the incidence of neurocognitive impairments (NCI) has not decreased likely due to the insidious and slow progressive nature of HIV infection. Recent studies showed that the resting-state functional magnetic resonance imaging (rs-fMRI) is a prominent technique in helping the non-invasive analysis of neucognitive impairment. Our study is to explore the neuroimaging characteristics among people living with HIV (PLWH) with or without NCI in terms of cerebral regional and neural network by rs-fMRI, based on the hypothesis that HIV patients with and without NCI have independent brain imaging characteristics. 33 PLWH with NCI and 33 PLWH without NCI, recruited from the Cohort of HIV-infected associated Chronic Diseases and Health Outcomes, Shanghai, China (CHCDO) which was established in 2018, were categorized into the HIV-NCI and HIV-control groups, respectively, based on Mini-Mental State Examination (MMSE) results. The two groups were matched in terms of sex, education and age. Resting-state fMRI data were collected from all participants to analyze the fraction amplitude of low-frequency fluctuation (fALFF) and functional connectivity (FC) to assess regional and neural network alterations in the brain. Correlations between fALFF/FC values in specific brain regions and clinical characteristics were also examined. The results showed increased fALFF values in the bilateral calcarine gyrus, bilateral superior occipital gyrus, left middle occipital gyrus, and left cuneus in the HIV-NCI group compared to the HIV-control group. Additionally, increased FC values were observed between the right superior occipital gyrus and right olfactory cortex, bilateral gyrus rectus, and right orbital part of the middle frontal gyrus in the HIV-NCI group. Conversely, decreased FC values were found between the left hippocampus and bilateral medial prefrontal gyrus, as well as bilateral superior frontal gyrus. The study concluded that abnormal spontaneous activity in PLWH with NCI primarily occurred in the occipital cortex, while defects in brain networks were mostly associated with the prefrontal cortex. The observed changes in fALFF and FC in specific brain regions provide visual evidence to enhance our understanding of the central mechanisms underlying the development of cognitive impairment in HIV patients.
Topics: Humans; Magnetic Resonance Imaging; HIV Infections; Brain Mapping; China; Brain; AIDS Dementia Complex
PubMed: 37365237
DOI: 10.1038/s41598-023-37493-3 -
Journal of Clinical Neuroscience :... Nov 2022Endogenous neural stem cells are thought to continue to generate new neurons throughout life in the human brain. Endogenous neurogenesis has been proposed to contribute...
Endogenous neural stem cells are thought to continue to generate new neurons throughout life in the human brain. Endogenous neurogenesis has been proposed to contribute to physiological roles in maintaining and regenerating olfaction, as well as promoting normal cognition, learning and memory. Specific impairments in these processes in COVID-19 - impaired olfaction and cognition - may implicate the SARS-CoV-2 virus in attenuating neurogenesis. Furthermore, neurogenesis has been linked with neuroregeneration; and impaired neuroregeneration has previously been linked with neurodegenerative diseases. Emerging evidence supports an association between COVID-19 infection and accelerated neurodegeneration. Also, structural changes indicating global reduction in brain size and specific reduction in the size of limbic structures - including orbitofrontal cortex, olfactory cortex and parahippocampal gyrus - as a result of SARS-CoV-2 infection have been demonstrated. This paper proposes the hypothesis that SARS-CoV-2 infection may impair endogenous neural stem cell activity. An attenuation of neurogenesis may contribute to reduction in brain size and/or neurodegenerative processes following SARS-CoV-2 infection. Furthermore, as neural stem cells are thought to be the cell of origin in glioma, better understanding of SARS-CoV-2 interaction with tumorigenic stem cells is indicated, with a view to informing therapeutic modulation. The subacute and chronic implications of attenuated endogenous neurogenesis are explored in the context of long COVID. Modulating endogenous neurogenesis may be a novel therapeutic strategy to address specific neurological manifestations of COVID-19 and potential applicability in tumour virotherapy.
Topics: COVID-19; Humans; Neurodegenerative Diseases; Neurogenesis; SARS-CoV-2; Post-Acute COVID-19 Syndrome
PubMed: 36113246
DOI: 10.1016/j.jocn.2022.09.006 -
Chemical Senses Jan 2023Little is known about the neural basis of lower- and higher-order olfactory functions such as odor memory, compared with other sensory systems. The aim of this study was...
Little is known about the neural basis of lower- and higher-order olfactory functions such as odor memory, compared with other sensory systems. The aim of this study was to explore neural networks and correlates associated with 3 functions: passive smelling (PS), odor encoding (OE), and in particular odor recognition memory (ORM). Twenty-six healthy participants were examined using functional magnetic resonance imaging conducted across 3 sessions, one for each function. Independent component analysis revealed a difference between sessions where a distinct ORM component incorporating hippocampus and posterior cingulate showed delayed triggering dissociated from odor stimulation and recognition. By contrasting Hit for ORM (target odors correctly recognized as old) and a combination of PS and detected odors from OE, we found significantly lower activations in amygdala, piriform cortex, insula, thalamus, and the inferior parietal lobule. Region of interest analysis including anterior insula, posterior cingulate gyrus, dentate gyrus, left middle frontal gyrus, amygdala, and piriform cortex demonstrated that Hit were associated with lower activations compared with other memory responses. In summary, our findings suggest that successful recognition of familiar odors (odor familiarity) is associated with neural suppression in the abovementioned regions of interest. Additionally, network including the hippocampus and posterior cingulate is engaged in a postrecognition process. This process may be related to incidental encoding of less familiar and more novel odors (odor novelty) and should be subject for future research.
Topics: Humans; Odorants; Smell; Recognition, Psychology; Hippocampus; Amygdala; Magnetic Resonance Imaging; Brain; Brain Mapping
PubMed: 36715106
DOI: 10.1093/chemse/bjad001