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Synapse (New York, N.Y.) Aug 2019Environmental enrichment (EE) can be related to changes in the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult rodents. Exposure to EE...
BACKGROUND AND AIM
Environmental enrichment (EE) can be related to changes in the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult rodents. Exposure to EE may also induce neurogenesis in the dentate gyrus (DG). The aim of this systematic review was to analyze the current literature on the correlation between neurogenesis and BDNF expression in the hippocampal DG region resulting from exposure to EE, which is associated with changes in memory, in rodents.
METHODS
Bibliographic searches of the Medline/PubMed and ScienceDirect databases were carried out, and 334 studies were found. A predefined protocol was used and registered on PROSPERO, and 32 studies were included for qualitative synthesis. The PRISMA was used to report this systematic review.
RESULTS
Most of the included studies showed that there is little evidence in the literature demonstrating that memory changes resulting from EE are dependent on BDNF expression and that there is an induction of neurogenesis in the hippocampal DG. However, the observed increase in molecular expression levels and cell proliferation is dependent on the age, the timing and duration of exposure to EE. Regarding the methodological quality of the studies, the majority presented a risk of bias due to the high variability in the age of the animals.
CONCLUSION
There are few studies in the literature that correlate the molecular and cellular mechanisms involved in neurogenesis in the hippocampal DG with BDNF expression in this region in rodents exposed to EE; however, there are other factors that can modulate this neurogenesis.
Topics: Animals; Brain-Derived Neurotrophic Factor; Environment; Hippocampus; Neurogenesis; Neuronal Plasticity
PubMed: 31056812
DOI: 10.1002/syn.22103 -
Neuropsychopharmacology Reports Dec 2018The hippocampus is considered a key region in schizophrenia pathophysiology, but the nature of hippocampal subregion abnormalities and how they contribute to disease...
AIM
The hippocampus is considered a key region in schizophrenia pathophysiology, but the nature of hippocampal subregion abnormalities and how they contribute to disease expression remain to be fully determined. This study reviews findings from schizophrenia hippocampal subregion volumetric and physiological imaging studies published within the last decade.
METHODS
The PubMed database was searched for publications on hippocampal subregion volume and physiology abnormalities in schizophrenia and their findings were reviewed.
RESULTS
The main replicated findings include smaller CA1 volumes and CA1 hyperactivation in schizophrenia, which may be predictive of conversion in individuals at clinical high risk of psychosis, smaller CA1 and CA4/DG volumes in first-episode schizophrenia, and more widespread smaller hippocampal subregion volumes with longer duration of illness. Several studies have reported relationships between hippocampal subregion volumes and declarative memory or symptom severity.
CONCLUSIONS
Together these studies provide support for hippocampal formation circuitry models of schizophrenia. These initial findings must be taken with caution as the scientific community is actively working on hippocampal subregion method improvement and validation. Further improvements in our understanding of the nature of hippocampal formation subregion involvement in schizophrenia will require the collection of structural and physiological imaging data at submillimeter voxel resolution, standardization and agreement of atlases, adequate control for possible confounding factors, and multi-method validation of findings. Despite the need for cautionary interpretation of the initial findings, we believe that improved localization of hippocampal subregion abnormalities in schizophrenia holds promise for the identification of disease contributing mechanisms.
Topics: Hippocampus; Humans; Magnetic Resonance Imaging; Schizophrenia
PubMed: 30255629
DOI: 10.1002/npr2.12031 -
Hippocampus Sep 2017The generation of new neurons in the hippocampus of adult mammals has become a widely accepted phenomenon, but the functional significance of the adult neurogenesis in... (Meta-Analysis)
Meta-Analysis Review
The generation of new neurons in the hippocampus of adult mammals has become a widely accepted phenomenon, but the functional significance of the adult neurogenesis in the hippocampus is not fully understood. One of the main hypotheses currently investigated suggests that neurogenesis contributes to pattern separation in the dentate gyrus. Many behavioral studies were conducted aiming to test this hypothesis using rodents as animal model. In those studies, researches ablated neurogenesis in the animals and subsequently evaluate them in tests of behavioral pattern separation, that is, behaviors that are thought to rely on the computational process of pattern separation. The results of these studies are varied, with most supporting a role for neurogenesis in pattern separation, but some others not. To address this controversy we performed a systematic review and meta-analysis of studies evaluating the effect of neurogenesis ablation on behavioral pattern separation. Analysis results indicated that most of the literature in the topic is surprisingly consistent and, although there are two studies with divergent results, the bulk of the literature supports an effect of hippocampal neurogenesis on behavioral pattern separation. We discuss those findings in light of other behavioral effects of hippocampal neurogenesis ablation, limitations of behavioral data and other lines of evidence about the effect of hippocampal neurogenesis in the dentate gyrus.
Topics: Animals; Databases, Bibliographic; Hippocampus; Humans; Neurogenesis; Neurons
PubMed: 28597491
DOI: 10.1002/hipo.22746 -
Pharmacological Reports : PR Apr 2016Lithium has been used in modern psychiatry for more than 65 years, constituting a cornerstone for the long-term treatment of bipolar disorder. A number of biological... (Review)
Review
Lithium has been used in modern psychiatry for more than 65 years, constituting a cornerstone for the long-term treatment of bipolar disorder. A number of biological properties of lithium have been discovered, including its hematological, antiviral and neuroprotective effects. In this article, a systematic review of the effect of lithium on hematopoietic, mesenchymal and neural stem cells is presented. The beneficial effects of lithium on the level of hematopoietic stem cells (HSC) and growth factors have been reported since 1970s. Lithium improves homing of stem cells, the ability to form colonies and HSC self-renewal. Lithium also exerts a favorable influence on the proliferation and maintenance of mesenchymal stem cells (MSC). Studies on the effect of lithium on neurogenesis have indicated an increased proliferation of progenitor cells in the dentate gyrus of the hippocampus and enhanced mitotic activity of Schwann cells. This may be connected with the neuroprotective and neurotrophic effects of lithium, reflected in an improvement in synaptic plasticity promoting cell survival and inhibiting apoptosis. In clinical studies, lithium treatment increases cerebral gray matter, mainly in the frontal lobes, hippocampus and amygdala. Recent findings also suggest that lithium may reduce the risk of dementia and exert a beneficial effect in neurodegenerative diseases. The most important mediators and signaling pathways of lithium action are the glycogen synthase kinase-3 and Wnt/β-catenin pathways. Recently, to study of bipolar disorder pathogenesis and the mechanism of lithium action, the induced pluripotent stem cells (iPSC) obtained from bipolar patients have been used.
Topics: Animals; Cell Proliferation; Hematopoietic Stem Cells; Hippocampus; Humans; Lithium; Mesenchymal Stem Cells; Neural Stem Cells; Neurogenesis
PubMed: 26922521
DOI: 10.1016/j.pharep.2015.09.005 -
Hippocampus Jun 2016To systematically review the characteristics, validity and outcome measures of tasks that have been described in the literature as assessing pattern separation and... (Review)
Review
To systematically review the characteristics, validity and outcome measures of tasks that have been described in the literature as assessing pattern separation and pattern completion in humans. Electronic databases were searched for articles. Parameters for task validity were obtained from two reviews that described optimal task design factors to evaluate pattern separation and pattern completion processes. These were that pattern separation should be tested during an encoding task using abstract, never-before-seen visual stimuli, and pattern completion during a retrieval task using partial cues; parametric alteration of the degree of interference of stimuli or degradation of cues should be used to generate a corresponding gradient in behavioral output; studies should explicitly identify the specific memory domain under investigation (sensory/perceptual, temporal, spatial, affect, response, or language) and account for the contribution of other potential attributes involved in performance of the task. A systematic, qualitative assessment of validity in relation to these parameters was performed, along with a review of general validity and task outcome measures. Sixty-two studies were included. The majority of studies investigated pattern separation and most tasks were performed on young, healthy adults. Pattern separation and pattern completion were most frequently tested during a retrieval task using familiar or recognizable visual stimuli and cues. Not all studies parametrically altered the degree of stimulus interference or cue degradation, or controlled for potential confounding factors. This review found evidence that some of the parameters for task validity have been followed in some human studies of pattern separation and pattern completion, but no study was judged to have adequately met all the parameters for task validity. The contribution of these parameters and other task design factors towards an optimal behavioral paradigm is discussed and recommendations for future research are made. © 2015 Wiley Periodicals, Inc.
Topics: Discrimination, Psychological; Hippocampus; Humans; Recognition, Psychology
PubMed: 26663362
DOI: 10.1002/hipo.22561 -
Neuropsychologia Jul 2014In this systematic review and meta-analysis, we explore how the time scale of practice affects patterns of brain activity associated with motor skill acquisition.... (Meta-Analysis)
Meta-Analysis Review
In this systematic review and meta-analysis, we explore how the time scale of practice affects patterns of brain activity associated with motor skill acquisition. Fifty-eight studies that involved skill learning with healthy participants (117 contrasts) met inclusion criteria. Two meta-contrasts were coded: decreases: peak coordinates that showed decreases in brain activity over time; increases: peak coordinates that showed increases in activity over time. Studies were grouped by practice time scale: short (≤1 h; 25 studies), medium (>1 and ≤24 h; 18 studies), and long (>24h to 5 weeks; 17 studies). Coordinates were analyzed using Activation Likelihood Estimation to show brain areas that were consistently activated for each contrast. Across time scales, consistent decreases in activity were shown in prefrontal and premotor cortex, the inferior parietal lobules, and the cerebellar cortex. Across the short and medium time scales there were consistent increases in supplementary and primary motor cortex and dentate nucleus. At the long time scale, increases were seen in posterior cingulate gyrus, primary motor cortex, putamen, and globus pallidus. Comparisons between time scales showed that increased activity in M1 at medium time scales was more spatially consistent across studies than increased activity in M1 at long time scales. Further, activity in the striatum (viz. putamen and globus pallidus) was consistently more rostral in the medium time scale and consistently more caudal in the long time scale. These data support neurophysiological models that posit that both a cortico-cerebellar system and a cortico-striatal system are active, but at different time points, during motor learning, and suggest there are associative/premotor and sensorimotor networks active within each system.
Topics: Brain; Brain Mapping; Humans; Learning; Motor Skills; Neural Pathways; Neuroimaging; Time Factors
PubMed: 24831923
DOI: 10.1016/j.neuropsychologia.2014.05.001