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Frontiers in Cellular Neuroscience 2020Neuronal migration is a fundamental brain development process that allows cells to move from their birthplaces to their sites of integration. Although neuronal migration... (Review)
Review
Neuronal migration is a fundamental brain development process that allows cells to move from their birthplaces to their sites of integration. Although neuronal migration largely ceases during embryonic and early postnatal development, neuroblasts continue to be produced and to migrate to a few regions of the adult brain such as the dentate gyrus and the subventricular zone (SVZ). In the SVZ, a large number of neuroblasts migrate into the olfactory bulb (OB) along the rostral migratory stream (RMS). Neuroblasts migrate in chains in a tightly organized micro-environment composed of astrocytes that ensheath the chains of neuroblasts and regulate their migration; the blood vessels that are used by neuroblasts as a physical scaffold and a source of molecular factors; and axons that modulate neuronal migration. In addition to diverse sets of extrinsic micro-environmental cues, long-distance neuronal migration involves a number of intrinsic mechanisms, including membrane and cytoskeleton remodeling, Ca signaling, mitochondria dynamics, energy consumption, and autophagy. All these mechanisms are required to cope with the different micro-environment signals and maintain cellular homeostasis in order to sustain the proper dynamics of migrating neuroblasts and their faithful arrival in the target regions. Neuroblasts in the postnatal brain not only migrate into the OB but may also deviate from their normal path to migrate to a site of injury induced by a stroke or by certain neurodegenerative disorders. In this review, we will focus on the intrinsic mechanisms that regulate long-distance neuroblast migration in the adult brain and on how these pathways may be modulated to control the recruitment of neuroblasts to damaged/diseased brain areas.
PubMed: 33519385
DOI: 10.3389/fncel.2020.620379 -
Basic and Clinical Neuroscience 2022Addiction is a mental disorder that has many adverse effects on brain health. It alters brain structure and deteriorates brain functionality. Impairment of brain...
INTRODUCTION
Addiction is a mental disorder that has many adverse effects on brain health. It alters brain structure and deteriorates brain functionality. Impairment of brain cognition in drug addiction is illustrated in many previous works; however, olfactory perception in addiction and, in particular, its neuronal mechanisms have rarely been studied.
METHODS
In this experiment, we recruited 20 heroin addicts and 20 normal controls of the same sex, age, handedness, and socioeconomic status and compared their brain function while perceiving non-craving odors during the functional magnetic resonance imaging (fMRI). We intended to define the default olfactory system performance in addicts compared to healthy people.
RESULTS
Our study showed an overall larger activation in addicts when processing olfactory stimuli. In particular, and when comparing the two groups, the right anterior cingulate and right superior frontal gyrus had higher activations than normal, whereas the left lingual gyrus and left cerebellum showed stronger activations in the addicts.
CONCLUSION
The result of this study can unveil the missing components in addiction brain circuitry. This information is helpful in better understanding the neural mechanisms of addiction and may be advantageous in designing programs for addiction prevention or clinical treatment.
HIGHLIGHTS
Addiction is a mental disorder with cognitive, clinical, and social adverse effects.Drugs affect the functional brain networks by altering the level of neurotransmitters or by over-exciting the brain's reward system.Addiction could be in the form of drug dependency or behaviors.
PLAIN LANGUAGE SUMMARY
Addiction is a mental disorder that has many adverse effects on brain. It alters brain structure and deteriorates brain functionality. Impairment of brain cognition in many previous works. We intended to define the default olfactory system performance in addicts compared to healthy people. Our study showed an overall larger activation in addicts when processing olfactory stimuli. In particular, and when comparing the two groups, the right anterior cingulate and right superior frontal gyrus had higher activations than normal, whereas the left lingual gyrus and left cerebellum showed stronger activations in the addicts. Addiction could be in the form of drug dependency or behaviors such as gambling or gaming. Addictive disorders is so vast that sometimes an impulse control disorder, such as pathologic gambling, could also be included.
PubMed: 36425954
DOI: 10.32598/bcn.12.6.2210.1 -
Brain and Behavior May 2021Pathological abnormalities first appear in the medial temporal regions including entorhinal cortex and parahippocampus in patients with Alzheimer's disease. Previous...
INTRODUCTION
Pathological abnormalities first appear in the medial temporal regions including entorhinal cortex and parahippocampus in patients with Alzheimer's disease. Previous studies showed that olfactory decline in elderly subjects was associated with volume reductions in the left hippocampus and left parahippocampus without cognitive impairment. The aim of this study is to investigate the link between olfaction and volume reductions in the medial temporal regions including the parahippocampus, entorhinal cortex, and hippocampal subfields.
METHOD
27 elderly subjects and 27 young controls were measured olfaction acuity, cognitive function, and structural magnetic resonance imaging. Image processing and gray matter volumetric segmentation were performed with FreeSurfer. Volume data were analyzed with SPSS Statistics software.
RESULTS
Interesting results of this study were that volume reduction in the entorhinal cortex was not directly linked with declining olfactory ability. Volume reduction in the left entorhinal cortex was correlated with volume reduction in the left parahippocampus and dentate gyrus. However, left parahippocampus volume reduction had the greatest impact on olfactory decline, and the entorhinal cortex and dentate gyrus might additionally contribute to olfactory decline.
CONCLUSION
Our results indicate that olfactory decline may be directly reflected in the medial temporal regions as reduced parahippocampus volumes, rather than as morphological changes in the entorhinal cortex and hippocampus. The parahippocampus may play an important role in the association between memory retrieval and olfactory identification.
Topics: Aged; Entorhinal Cortex; Hippocampus; Humans; Image Processing, Computer-Assisted; Magnetic Resonance Imaging; Smell
PubMed: 33769719
DOI: 10.1002/brb3.2115 -
Frontiers in Neuroanatomy 2015New neurons are continually generated in the subependymal layer of the lateral ventricles and the subgranular zone of dentate gyrus during adulthood. In the...
New neurons are continually generated in the subependymal layer of the lateral ventricles and the subgranular zone of dentate gyrus during adulthood. In the subventricular zone, neuroblasts migrate a long distance to the olfactory bulb where they differentiate into granule or periglomerular interneurons. In the hippocampus, neuroblasts migrate a short distance from the subgranular zone to the granule cell layer of the dentate gyrus to become granule neurons. In addition to the short-distance inputs, bulbar interneurons receive long-distance centrifugal afferents from olfactory-recipient structures. Similarly, dentate granule cells receive differential inputs from the medial and lateral entorhinal cortices through the perforant pathway. Little is known concerning these new inputs on the adult-born cells. In this work, we have characterized afferent inputs to 21-day old newly-born neurons. Mice were intraperitoneally injected with bromodeoxyuridine. Two weeks later, rhodamine-labeled dextran-amine was injected into the anterior olfactory nucleus, olfactory tubercle, piriform cortex and lateral and medial entorhinal cortices. One week later, animals were perfused and immunofluorescences were carried out. The data show that projection neurons from the mentioned structures, establish putative synaptic contacts onto 21-day-old neurons in the olfactory bulb and dentate gyrus, in some cases even before they start to express specific subpopulation proteins. Long-distance afferents reach middle and outer one-third portions of the molecular layer of the dentate gyrus and granule and, interestingly, periglomerular layers of the olfactory bulb. In the olfactory bulb, these fibers appear to establish presumptive axo-somatic contacts onto newly-born granule and periglomerular cells.
PubMed: 25698936
DOI: 10.3389/fnana.2015.00004 -
Frontiers in Cellular Neuroscience 2023Translocator protein (TSPO), a 18 kDa protein found in the outer mitochondrial membrane, has historically been associated with the transport of cholesterol in highly... (Review)
Review
Translocator protein (TSPO), a 18 kDa protein found in the outer mitochondrial membrane, has historically been associated with the transport of cholesterol in highly steroidogenic tissues though it is found in all cells throughout the mammalian body. TSPO has also been associated with molecular transport, oxidative stress, apoptosis, and energy metabolism. TSPO levels are typically low in the central nervous system (CNS), but a significant upregulation is observed in activated microglia during neuroinflammation. However, there are also a few specific regions that have been reported to have higher TSPO levels than the rest of the brain under normal conditions. These include the dentate gyrus of the hippocampus, the olfactory bulb, the subventricular zone, the choroid plexus, and the cerebellum. These areas are also all associated with adult neurogenesis, yet there is no explanation of TSPO's function in these cells. Current studies have investigated the role of TSPO in microglia during neuron degeneration, but TSPO's role in the rest of the neuron lifecycle remains to be elucidated. This review aims to discuss the known functions of TSPO and its potential role in the lifecycle of neurons within the CNS.
PubMed: 37416505
DOI: 10.3389/fncel.2023.1210205 -
Brain Sciences Apr 2023Alzheimer's disease (AD) is associated with the abnormal connection of functional networks. Olfactory impairment occurs in early AD; therefore, exploring alterations in...
Alzheimer's disease (AD) is associated with the abnormal connection of functional networks. Olfactory impairment occurs in early AD; therefore, exploring alterations in olfactory-related regions is useful for early AD diagnosis. We combined the graph theory of local brain network topology with olfactory performance to analyze the differences in AD brain network characteristics. A total of 23 patients with AD and 18 normal controls were recruited for resting-state functional magnetic resonance imaging (fMRI), clinical neuropsychological examinations and the University of Pennsylvania Smell Identification Test (UPSIT). Between-group differences in the topological properties of the local network were compared. Pearson correlations were explored based on differential brain regions and olfactory performance. Statistical analysis revealed a correlation of the degree of cognitive impairment with olfactory recognition function. Local node topological properties were significantly altered in many local brain regions in the AD group. The nodal clustering coefficients of the bilateral temporal pole: middle temporal gyrus (TPOmid), degree centrality of the left insula (INS.L), degree centrality of the right middle temporal gyrus (MTG.R), and betweenness centrality of the left middle temporal gyrus (MTG.L) were related to olfactory performance. Alterations in local topological properties combined with the olfactory impairment can allow early identification of abnormal olfactory-related regions, facilitating early AD screening.
PubMed: 37190596
DOI: 10.3390/brainsci13040631 -
Journal of Neurological Surgery. Part... Oct 2021We investigated the effects of vitamin D deficiency in the peripheral and central smell regions by magnetic resonance imaging (MRI). This retrospective study...
We investigated the effects of vitamin D deficiency in the peripheral and central smell regions by magnetic resonance imaging (MRI). This retrospective study included 29 patients (12 males, 17 females) with 25-dihydroxy vitamin D3 [25(OH) D ] deficiency (group 1) and 34 subjects without 25(OH) D deficiency (14 males, 20 females) (group 2). Using cranial MRIs, the peripheral (olfactory bulb [OB] volume and olfactory sulcus [OS] depth) and central (insular gyrus and corpus amygdala) smell regions were evaluated. The OB volume and OS depth values of the 25(OH) D3 deficiency group were significantly lower than those of the control group ( < 0.05). For the central smell regions, the insular gyrus and corpus amygdala areas of the 25(OH) D3 deficiency group were nonsignificantly lower than those in the control group ( > 0.05). There were positive correlations between OB volumes, OS depths, and insular gyrus and corpus amygdala areas bilaterally in the 25(OH) D3 deficiency group separately and in all subjects (groups 1 and 2) ( < 0.05). In the 25(OH) D3 deficiency group, as the 25(OH) D3 values became lower, the insular gyrus area values decreased bilaterally ( < 0.05). In females, the corpus amygdala area values were lower than in males ( < 0.05). Since vitamin D3 deficiency affected the peripheral and central smell regions negatively, we recommend evaluating patients' vitamin D levels as a health policy to prevent vitamin D3 deficiency-related cranial smell region problems. Moreover, sunlight exposure is very important to increase vitamin D levels, and the public should be informed about this topic.
PubMed: 34513566
DOI: 10.1055/s-0040-1722227 -
NeuroImage Apr 2021The human sense of smell is highly individual and characterized by a strong variability in the perception and evaluation of olfactory stimuli, depending on cultural...
INTRO
The human sense of smell is highly individual and characterized by a strong variability in the perception and evaluation of olfactory stimuli, depending on cultural imprint and current physiological conditions. Since this individual perspective has often been neglected in fMRI studies on olfactory hedonic coding, this study focuses on the neuronal activity and connectivity patterns resulting from subject-specific olfactory stimulation.
METHODS
Thirty-one normosmic participants took part in a fMRI block designed paradigm consisting of three olfactory stimulation sessions. The most pleasant and unpleasant odors were individually specified during a pre-test for each participant and validated in the main experiment. Mean activation and functional connectivity analysis focusing on the right and left piriform cortex were performed for the predefined olfactory regions-of-interest (ROIs) and compared between the three olfactory conditions.
RESULTS
Individual unpleasant olfactory stimulation as compared to pleasant or neutral did not alter mean BOLD activation in the predefined olfactory ROIs but led to a change in connectivity pattern in the right piriform cortex.
CONCLUSION
Our data suggests that the individual pleasantness of odors is not detectable by average BOLD magnitude changes in primary or secondary olfactory brain areas, but reflected in temporal patterns of joint activation that create a network between the right piriform cortex, the left insular cortex, the orbitofrontal cortex, and the precentral gyrus. This network may serve the evolutionary defense mechanism of olfaction by preparing goal-directed action.
Topics: Adolescent; Adult; Brain; Female; Humans; Individuality; Magnetic Resonance Imaging; Male; Nerve Net; Odorants; Olfactory Perception; Oxygen Consumption; Young Adult
PubMed: 33497777
DOI: 10.1016/j.neuroimage.2021.117782 -
Neuropsychologia Nov 2022Olfaction, the sense of smell, provides important behavioral functions in many species. The hippocampus (HC) is critical for identifying odors, and hippocampal volume is...
Olfaction, the sense of smell, provides important behavioral functions in many species. The hippocampus (HC) is critical for identifying odors, and hippocampal volume is associated with odor identification ability. Impaired odor identification is often reported in old age and might provide an early marker of cognitive decline and dementia. Here, we explored cross-sectional (n = 225) and longitudinal (n = 118) associations between odor identification ability and hippocampal subfield volumes in a sample of middle-aged and older persons (25-80 years). In older participants, longitudinally decreasing volumes of the hippocampal tail, subiculum, CA4 and the dentate gyrus correlated with changes in odor identification. None of these correlations were observed in younger participants, but there was a significant correlation between longitudinal volume reduction in the tail subfield of the hippocampus and odor identification change across all participants. There were no significant cross-sectional associations between hippocampal subfields and odor identification. These exploratory results provide new information regarding precisely where and when declining HC subfield volumes might be associated with odor identification.
Topics: Middle Aged; Humans; Aged; Smell; Cross-Sectional Studies; Magnetic Resonance Imaging; Hippocampus; Organ Size
PubMed: 36210600
DOI: 10.1016/j.neuropsychologia.2022.108353 -
Frontiers in Allergy 2022Currently, clinical assessment of olfaction is largely reliant on subjective methods that require patient participation. The objective method for measuring olfaction,...
IMPORTANCE
Currently, clinical assessment of olfaction is largely reliant on subjective methods that require patient participation. The objective method for measuring olfaction, using electroencephalogram (EEG) readings, can be supplemented with the improved temporal resolution of magnetoencephalography (MEG) for olfactory measurement that can delineate cortical and peripheral olfactory loss. MEG provides high temporal and spatial resolution which can enhance our understanding of central olfactory processing compared to using EEG alone.
OBJECTIVE
To determine the feasibility of building an in-house portable olfactory stimulator paired with electrophysiological neuroimaging technique with MEG to assess olfaction in the clinical setting.
DESIGN SETTING AND PARTICIPANTS
This proof-of-concept study utilized a paired MEG-olfactometer paradigm to assess olfaction in three normosmic participants. We used a two-channel olfactory stimulator to deliver odorants according to a programmed stimulus-rest paradigm. Two synthetic odorants: 2% phenethyl alcohol (rose) and 0.5% amyl acetate (banana) were delivered in increasing increments of time followed by periods of rest. Cortical activity was measured a 306-channel MEG system.
MAIN OUTCOMES AND MEASURES
Primary outcome measure was the relative spectral power for each frequency band, which was contrasted between rest and olfactory stimulation.
RESULTS
Compared to rest, olfactory stimulation produced a 40% increase in relative alpha power within the olfactory cortex bilaterally with both odorants. A 25%-30% increase in relative alpha power occurred in the left orbitofrontal cortex and precentral gyrus with phenethyl alcohol stimulation but not amyl acetate.
CONCLUSION AND RELEVANCE
In this proof-of-concept study, we demonstrate the feasibility of olfactory measurement an olfactometer-MEG paradigm. We found that odorant-specific cortical signatures can be identified using this paradigm, setting the basis for further investigation of this system as a prognostic tool for olfactory loss.
PubMed: 36698377
DOI: 10.3389/falgy.2022.1019265