Olfactory dysfunction correlates with amyloid-beta burden in an Alzheimer’s disease mouse model. J Neurosci. 2010;30:505-514. [PMID: 20071513 DOI: 10.1523/jneurosci.4622-09.2010]

Biomarkers in Alzheimer's disease: new frontiers with olfactory models

Alzheimer's disease (AD), the leading cause of dementia worldwide, presents a significant diagnostic challenge, as clinical diagnoses are often made at advanced stages when neurodegenerative damage is already extensive. The study of biomarkers is necessary for improving identification, prognosis, and disease monitoring. Current research has primarily focused on cerebrospinal fluid and imaging biomarkers, including amyloid-β (Aβ1-42), phosphorylated tau, and total tau. However, these methods are invasive, expensive, and not widely accessible. Emerging approaches aim to identify novel, cost-effective, and minimally invasive biomarkers, particularly from blood-based and other peripheral sources. This review explores the role of olfactory neuronal precursors (ONPs) derived from the olfactory neuroepithelium (ONE) as a promising and innovative model for biomarker discovery in AD. ONPs can be non-invasively obtained directly from patients, offering a unique resource to study AD-related pathophysiological mechanisms. These neuronal lineage cells exhibit characteristics that make them a reliable surrogate model for central nervous system studies, enabling the evaluation of established biomarkers and facilitating the identification of novel candidates. Additionally, we discuss the potential of ONPs to enhance clinical practice through their accessibility and suitability for high-throughput biomarker analysis. By integrating the study of ONPs with existing biomarker research, this review highlights new frontiers in the quest to refine diagnostic tools and advance our understanding of Alzheimer's disease, paving the way for innovative strategies in early detection and personalized management.

Olfactory receptors and human diseases

Olfaction plays a crucial role in distinguishing odors, enabling organisms to seek benefits and evade hazards. Olfactory receptors (ORs), characterized by highly variable binding pockets, facilitate the detection of diverse odorants from both external and internal environments. Nasal ORs, expressed in olfactory sensory neurons (OSNs), are critical for olfactory cognition and associated neuronal plasticity. In contrast, extra-nasal ORs, expressed in extra-olfactory tissues, detect specific chemicals and modulate cellular processes such as proliferation, migration, inflammation, and apoptosis. Aberrant OR expression or dysfunction has been implicated in numerous human diseases, including anosmia, dementia, dermatopathies, obesity, infertility, cancers, respiratory disorders, atherosclerosis and viral infections. Olfactory training, such as aromatherapy, demonstrates significant therapeutic potential for anosmia, dementia and psychological distress. Natural or synthetic odorants have been applied for promoting hair regeneration and cutaneous wound healing. Conversely, overexpression of specific ORs in cancer cells may drive tumor progression. Additionally, ORs may mediate virus-host interactions during infection, owing to their structural variability. Collectively, OR-targeted agonists and antagonists (odorants) represent promising candidates for treating OR-associated pathologies.

Olfactory deprivation promotes amyloid β deposition in a mouse model of Alzheimer's disease

Olfactory dysfunction is regarded as an early marker for Alzheimer's disease (AD). Slowly progressing AD pathology is interpreted to impair cognition and olfactory sensation independently, while olfactory deficits emerge earlier. The present experiments tested the possibility that olfactory impairment may worsen cognition or AD pathology using 3xTg AD model mice with olfactory bulbectomy (OBX). In open-field tests, OBX was shown to increase anxiety-like behavior in both wild-type (WT) and AD model mice, and hyperactivity was induced in WT mice only. Spatial memory, assessed by the Morris water maze (MWM) test, was impaired in WT but not AD mice. Object memory, assessed by the novel object recognition test, was not changed by OBX either in WT or AD mice. Densitometry of Aβ plaques stained with 6E10 and anti-Aβ42 antibodies was carried out in sections containing the hippocampal formation obtained from AD mice aged 12 and 18 months. The plaque area was larger in the OBX than in the sham group at 12 months. At 18 months, there was also difference in the plaque area. Given that Aβ plaques emerge in 3xTg mice relatively later (>9 months of age) than in other models, OBX in 3xTg mice appears to exacerbate Aβ pathology at the early phase of Aβ emergence, implying a causative link of smell loss to AD pathogenesis. The accelerated Aβ plaque formation by OBX was accompanied by microglial activation. Early intervention to smell loss may be beneficial for AD control.

ErbB4 deficiency exacerbates olfactory dysfunction in an early-stage Alzheimer's disease mouse model

Olfactory dysfunction is increasingly recognized as an early indicator of Alzheimer's disease (AD). Aberrations in GABAergic function and the excitatory/inhibitory (E/I) balance within the olfactory bulb (OB) have been implicated in olfactory impairment during the initial stages of AD. While the neuregulin 1 (NRG1)/ErbB4 signaling pathway is known to regulate GABAergic transmission in the brain and is associated with various neuropsychiatric disorders, its specific role in early AD-related olfactory impairment remains incompletely understood. This study demonstrated that olfactory dysfunction preceded cognitive decline in young adult APP/PS1 mice and was characterized by reduced levels of NRG1 and ErbB4 in the OB. Further investigation revealed that deletion of ErbB4 in parvalbumin interneurons reduced GABAergic transmission and increased hyperexcitability in mitral and tufted cells (M/Ts) in the OB, thereby accelerating olfactory dysfunction in young adult APP/PS1 mice. Additionally, ErbB4 deficiency was associated with increased accumulation of Aβ and BACE1-mediated cleavage of APP, along with enhanced CDK5 signaling in the OB. NRG1 infusion into the OB was found to enhance GABAergic transmission in M/Ts and alleviate olfactory dysfunction in young adult APP/PS1 mice. These findings underscore the critical role of NRG1/ErbB4 signaling in regulating GABAergic transmission and E/I balance within the OB, contributing to olfactory impairment in young adult APP/PS1 mice, and provide novel insights for early intervention strategies in AD. This work has shown that ErbB4 deficiency increased the burden of Aβ, impaired GABAergic transmission, and disrupted the E/I balance of mitral and tufted cells (M/Ts) in the OB, ultimately resulting in olfactory dysfunction in young adult APP/PS1 mice. NRG1 could enhance GABAergic transmission, rescue E/I imbalance in M/Ts, and alleviate olfactory dysfunction in young adult APP/PS1 mice. OB: olfactory bulb, E/I: excitation/inhibition, Pr: probability of release, PV: parvalbumin interneurons, Aβ: β-amyloid, GABA: gamma-aminobutyric acid.

Beyond anosmia: olfactory dysfunction as a common denominator in neurodegenerative and neurodevelopmental disorders

Olfactory dysfunction has emerged as a hallmark feature shared among several neurological conditions, including both neurodevelopmental and neurodegenerative disorders. While diseases of both categories have been extensively studied for decades, their association with olfaction has only recently gained attention. Olfactory deficits often manifest already during prodromal stages of these diseases, yet it remains unclear whether common pathophysiological changes along olfactory pathways cause such impairments. Here we probe into the intricate relationship between olfactory dysfunction and neurodegenerative and neurodevelopmental disorders, shedding light on their commonalities and underlying mechanisms. We begin by providing a brief overview of the olfactory circuit and its connections to higher-associated brain areas. Additionally, we discuss olfactory deficits in these disorders, focusing on potential common mechanisms that may contribute to olfactory dysfunction across both types of disorders. We further debate whether olfactory deficits contribute to the disease propagation or are simply an epiphenomenon. We conclude by emphasizing the significance of olfactory function as a potential pre-clinical diagnostic tool to identify individuals with neurological disorders that offers the opportunity for preventive intervention before other symptoms manifest.

NEGR1 Modulates Mouse Affective Discrimination by Regulating Adult Olfactory Neurogenesis

Background

Affective recognition and sensory processing are impaired in people with autism. However, no mouse model of autism comanifesting these symptoms is available, thereby limiting the exploration of the relationship between affective recognition and sensory processing in autism and the molecular mechanisms involved.

Methods

With Negr1 -/- mice, we conducted the affective state discrimination test and an odor habituation/dishabituation test. Data were analyzed using the k-means clustering method. We also employed a whole-cell patch clamp and bromodeoxyuridine incorporation assay to investigate underlying mechanisms.

Results

When encountering mice exposed to restraint stress or chronic pain, wild-type mice discriminated between them by either approaching the stressed mouse or avoiding the painful mouse, whereas Negr1 -/- mice showed unbiased social interactions with them. Next, we demonstrated that both wild-type and Negr1 -/- mice used their olfaction for social interaction in the experimental context, but Negr1 -/- mice showed aberrant olfactory habituation and dishabituation against social odors. In electrophysiological studies, inhibitory inputs to the mitral cells in the olfactory bulb were increased in Negr1 -/- mice compared with wild-type mice, and subsequently their excitability was decreased. As a potential underlying mechanism, we found that adult neurogenesis in the subventricular zone was diminished in Negr1 -/- mice, which resulted in decreased integration of newly generated inhibitory neurons in the olfactory bulb.

Conclusions

NEGR1 contributes to mouse affective recognition, possibly by regulating olfactory neurogenesis and subsequent olfactory sensory processing. We propose a novel neurobiological mechanism of autism-related behaviors based on disrupted adult olfactory neurogenesis.

The role of olfactory dysfunction in mild cognitive impairment and Alzheimer's disease: A meta-analysis

PURPOSE

This comprehensive meta-analysis investigates the association between olfactory deficits in mild cognitive impairment (MCI) and Alzheimer's disease (AD).

METHODS

A thorough search across databases identified articles analyzing olfactory status in MCI or AD patients. Methodological quality assessment followed PRISMA guidelines. Hedges' g effect size statistic computed standard mean differences and 95% confidence intervals. Moderator analysis was conducted.

RESULTS

Among the included studies (65 for MCI and 61 for AD), odor identification exhibited larger effect sizes compared to odor threshold and discrimination, in both MCI and AD samples. Moderate effect size is found in OI scores in MCI (k = 65, SE = 0.078, CI 95% = [-1.151, -0.844]). Furthermore, compared to MCI, AD had moderate to large heterogeneous effects in olfactory identification (k = 61, g = -2.062, SE = 0.125, CI 95% = [-2.308, -1.816]). Global cognitive status is positively related to olfactory identification impairment in both MCI (k = 57, Z = 2.74, p = 0.006) and AD (k = 53, Z = 5.03, p < 0.0001) samples.

CONCLUSION

Olfactory impairments exhibit a notable and substantial presence in MCI. Among these impairments, odor identification experiences the greatest decline in MCI, mirroring the primary sensory deficit observed in AD. Consequently, the incorporation of a straightforward odor identification test is advisable in the evaluation of individuals vulnerable to the onset of AD, offering a practical screening tool for early detection.

Aβ42 and ROS dual-targeted multifunctional nanocomposite for combination therapy of Alzheimer's disease

Amyloid-β (Aβ) readily misfolds into neurotoxic aggregates, generating high levels of reactive oxygen species (ROS), leading to progressive oxidative damage and ultimately cell death. Therefore, simultaneous inhibition of Aβ aggregation and scavenging of ROS may be a promising therapeutic strategy to alleviate Alzheimer's disease pathology. Based on the previously developed antibody 1F12 that targets all forms of Aβ42, we developed an Aβ42 and ROS dual-targeting nanocomposite using biodegradable mesoporous silica nanoparticles as carriers to load ultra-small cerium oxide nanocrystals (bMSNs@Ce-1F12). By modifying the brain-targeted rabies virus glycoprotein 29 (RVG29-bMSNs@Ce-1F12), this intelligent nanocomposite can efficiently target brain Aβ-rich regions. Combined with peripheral and central nervous system treatments, RVG29-bMSNs@Ce-1F12 can significantly alleviate AD symptoms by inhibiting Aβ42 misfolding, accelerating Aβ42 clearance, and scavenging ROS. Furthermore, this synergistic effect of ROS scavenging and Aβ clearance exhibited by this Aβ42 and ROS dual-targeted strategy also reduced the burden of hyperphosphorylated tau, alleviated glial cell activation, and ultimately improved cognitive function in APP/PS1 mice. Our findings indicate that RVG29-bMSNs@Ce-1F12 is a promising nanodrug that can facilitate multi-target treatment of AD.

Olfactory deficit: a potential functional marker across the Alzheimer's disease continuum

Alzheimer's disease (AD) is a prevalent form of dementia that affects an estimated 32 million individuals globally. Identifying early indicators is vital for screening at-risk populations and implementing timely interventions. At present, there is an urgent need for early and sensitive biomarkers to screen individuals at risk of AD. Among all sensory biomarkers, olfaction is currently one of the most promising indicators for AD. Olfactory dysfunction signifies a decline in the ability to detect, identify, or remember odors. Within the spectrum of AD, impairment in olfactory identification precedes detectable cognitive impairments, including mild cognitive impairment (MCI) and even the stage of subjective cognitive decline (SCD), by several years. Olfactory impairment is closely linked to the clinical symptoms and neuropathological biomarkers of AD, accompanied by significant structural and functional abnormalities in the brain. Olfactory behavior examination can subjectively evaluate the abilities of olfactory identification, threshold, and discrimination. Olfactory functional magnetic resonance imaging (fMRI) can provide a relatively objective assessment of olfactory capabilities, with the potential to become a promising tool for exploring the neural mechanisms of olfactory damage in AD. Here, we provide a timely review of recent literature on the characteristics, neuropathology, and examination of olfactory dysfunction in the AD continuum. We focus on the early changes in olfactory indicators detected by behavioral and fMRI assessments and discuss the potential of these techniques in MCI and preclinical AD. Despite the challenges and limitations of existing research, olfactory dysfunction has demonstrated its value in assessing neurodegenerative diseases and may serve as an early indicator of AD in the future.

Olfactory Dysfunction Associated with Cognitive Decline in an Elderly Population

BACKGROUND

In many neurological disorders, including Alzheimer disease, early olfactory dysfunction is observed.

OBJECTIVE

In order to determine if deficits in olfactory memory are present in the elderly and if olfactory dysfunction correlates with cognitive impairment in the aging population, olfactory testing has been done on seniors from the NuAge cohort accepting to participate in the Olfactory Response Cognition and Aging (ORCA) secondary sub-study. The t-Mini Mental Statement Examination and the Telephone Interview for Cognitive Status tests were done to assess cognition levels.

RESULTS

Overall, 94% of the ORCA cohort displayed olfactory dysfunction. Deficits in olfactory memory were also present. A correlation was observed between olfactory function and cognitive test scores. Moreover, in women who smoked, there was an association between olfactory memory and cognitive scores.

CONCLUSION

Our results suggest that olfactory dysfunction may predict impending cognitive decline and highlights the need for olfactory training in seniors to improve olfaction and overall well-being.

Serial reversal learning in an olfactory discrimination task in 3xTg-AD mice

Male and female 3xTg-AD mice between 5 and 24 mo of age and their B6129F2/J wild-type controls were tested on a series of 18 olfactory discrimination and reversal tasks in an operant olfactometer. All mice learned the odor discriminations and reversals to a criterion of 85% correct, but the 3xTg-AD mice made fewer errors than the B6129F2/J mice in the odor discriminations and in the first six reversal learning tasks. Many mice showed evidence of near errorless learning, and on the reversal tasks the 3xTg-AD mice showed more instances of near errorless learning than the B6129F2/J mice. There was no evidence of an age effect on odor discrimination, but there was a decrease in errorless reversal learning in aged B6129F2/J mice. In long-term memory tests, there was an increase in the number of errors made but no genotype difference. The high level of performance indicates that the mice were able to develop a "learning to learn" strategy. The finding that the 3xTg-AD mice outperformed their littermate controls provides an example of paradoxical functional facilitation in these mice.

Early tactile stimulation influences the development of Alzheimer's disease in gestationally stressed APP NL-G-F adult offspring NL-G-F/NL-G-F mice

Alzheimer's disease (AD) is associated with cerebral plaques and tangles, reduced synapse number, and shrinkage in several brain areas and these morphological effects are associated with the onset of compromised cognitive, motor, and anxiety-like behaviours. The appearance of both anatomical and behavioural symptoms is worsened by stress. The focus of this study was to examine the effect of neonatal tactile stimulation on AD-like behavioural and neurological symptoms on APP NL-G-F/NL-G-F mice, a mouse model of AD, who have been gestationally stressed. Our findings indicate that neonatal tactile stimulation improves cognition, motor skills, and anxiety-like symptoms in both gestationally stressed and non-stressed adult APP mice and that these alterations are associated with reduced Aβ plaque formation. Thus, tactile stimulation appears to be a promising non-invasive preventative strategy for slowing the onset of dementia in aging animals.

In vivo tracing of the ascending vagal projections to the brain with manganese enhanced magnetic resonance imaging

Introduction

The vagus nerve, the primary neural pathway mediating brain-body interactions, plays an essential role in transmitting bodily signals to the brain. Despite its significance, our understanding of the detailed organization and functionality of vagal afferent projections remains incomplete.

Methods

In this study, we utilized manganese-enhanced magnetic resonance imaging (MEMRI) as a non-invasive and in vivo method for tracing vagal nerve projections to the brainstem and assessing their functional dependence on cervical vagus nerve stimulation (VNS). Manganese chloride solution was injected into the nodose ganglion of rats, and T1-weighted MRI scans were performed at both 12 and 24 h after the injection.

Results

Our findings reveal that vagal afferent neurons can uptake and transport manganese ions, serving as a surrogate for calcium ions, to the nucleus tractus solitarius (NTS) in the brainstem. In the absence of VNS, we observed significant contrast enhancements of around 19-24% in the NTS ipsilateral to the injection side. Application of VNS for 4 h further promoted nerve activity, leading to greater contrast enhancements of 40-43% in the NTS.

Discussion

These results demonstrate the potential of MEMRI for high-resolution, activity-dependent tracing of vagal afferents, providing a valuable tool for the structural and functional assessment of the vagus nerve and its influence on brain activity.

Sensory processing deficits and related cortical pathological changes in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder primarily affecting cognitive functions. However, sensory deficits in AD start to draw attention due to their high prevalence and early onsets which suggest that they could potentially serve as diagnostic biomarkers and even contribute to the disease progression. This literature review examines the sensory deficits and cortical pathological changes observed in visual, auditory, olfactory, and somatosensory systems in AD patients, as well as in various AD animal models. Sensory deficits may emerge at the early stages of AD, or even precede the cognitive decline, which is accompanied by cortical pathological changes including amyloid-beta deposition, tauopathy, gliosis, and alterations in neuronal excitability, synaptic inputs, and functional plasticity. Notably, these changes are more pronounced in sensory association areas and superficial cortical layers, which may explain the relative preservation of basic sensory functions but early display of deficits of higher sensory functions. We propose that sensory impairment and the progression of AD may establish a cyclical relationship that mutually perpetuates each condition. This review highlights the significance of sensory deficits with or without cortical pathological changes in AD and emphasizes the need for further research to develop reliable early detection and intervention through sensory systems.

Olfactory function reflects episodic memory performance and atrophy in the medial temporal lobe in individuals at risk for Alzheimer's disease

We examined cognitive domains and brain regions associated with olfactory performance in cognitively unimpaired older adults (CU-OAs) and individuals with or at risk for Alzheimer's Disease (AD). We compared CU-OAs (N = 55), individuals with subjective cognitive decline (SCD, N = 55), mild cognitive impairment (MCI, N = 101), and AD (N = 45) on measures of olfactory function (Brief Smell Identification Test), cognition (episodic and semantic memory), and medial temporal lobe thickness and volume. Analyses controlled for age, sex, education, and total intracranial volume. Olfactory function decreased from SCD to MCI to AD. CU-OAs outperformed all groups except SCDs on tests of cognition and olfaction. Although these measures did not differ between the CU-OAs and SCDs, olfactory function correlated with episodic memory tests and with entorhinal cortex atrophy only in the SCD group. Olfactory function also correlated with hippocampal volume and right-hemisphere entorhinal cortex thickness in the MCI group. Olfactory dysfunction reflects medial temporal lobe integrity and memory performance in a group at risk for AD with normal cognition and olfaction.

Alzheimer's disease: using gene/protein network machine learning for molecule discovery in olive oil

Alzheimer's disease (AD) poses a profound human, social, and economic burden. Previous studies suggest that extra virgin olive oil (EVOO) may be helpful in preventing cognitive decline. Here, we present a network machine learning method for identifying bioactive phytochemicals in EVOO with the highest potential to impact the protein network linked to the development and progression of the AD. A balanced classification accuracy of 70.3 ± 2.6% was achieved in fivefold cross-validation settings for predicting late-stage experimental drugs targeting AD from other clinically approved drugs. The calibrated machine learning algorithm was then used to predict the likelihood of existing drugs and known EVOO phytochemicals to be similar in action to the drugs impacting AD protein networks. These analyses identified the following ten EVOO phytochemicals with the highest likelihood of being active against AD: quercetin, genistein, luteolin, palmitoleate, stearic acid, apigenin, epicatechin, kaempferol, squalene, and daidzein (in the order from the highest to the lowest likelihood). This in silico study presents a framework that brings together artificial intelligence, analytical chemistry, and omics studies to identify unique therapeutic agents. It provides new insights into how EVOO constituents may help treat or prevent AD and potentially provide a basis for consideration in future clinical studies.

Photobiomodulation therapy restores olfactory function impaired by photothrombosis in mouse olfactory bulb

An ischemic stroke typically accompanies numerous disorders ranging from somatosensory dysfunction to cognitive impairments, inflicting patients with various neurologic symptoms. Among pathologic outcomes, post-stroke olfactory dysfunctions are frequently observed. Despite the well-known prevalence, therapy options for such compromised olfaction are limited, likely due to the complexity of olfactory bulb architecture, which encompasses both the peripheral and central nervous systems. As photobiomodulation (PBM) emerged for treating ischemia-associated symptoms, the effectiveness of PBM on stroke-induced impairment of olfactory function was explored. Novel mouse models with olfactory dysfunctions were prepared using photothrombosis (PT) in the olfactory bulb on day 0. The post-PT PBM was performed daily from day 2 to day 7 by irradiating the olfactory bulb via an 808 nm laser with a fluence of 40 J/cm2 (325 mW/cm2 for 2 min per day). The buried food test (BFT) was used to score behavioral acuity in food-deprived mice to assess the olfactory function before PT, after PT, and after PBM. Histopathological examinations and cytokine assays were performed on the mouse brains harvested on day 8. The results from BFT were specific to an individual, with positive correlations between the baseline latency time measured before PT and its alteration at the ensuing stages for both the PT and PT + PBM groups. Also, the correlation analysis in both groups showed highly similar, significant positive relationships between the early and late latency time change independent of PBM, implicating a common recovery mechanism. Particularly, PBM treatment accelerated the recovery of impaired olfaction following PT by suppressing inflammatory cytokines and enhancing both glial and vascular factors (e.g., GFAP, IBA-1, and CD31). PBM therapy during the acute phase of ischemia improves the compromised olfactory function by modulating microenvironments and inflammation status of the affected tissue.

Signatures for viral infection and inflammation in the proximal olfactory system in familial Alzheimer's disease

Alzheimer's disease (AD) is characterized by deficits in olfaction and olfactory pathology preceding diagnosis of dementia. Here we analyzed differential gene and protein expression in the olfactory bulb (OB) and tract (OT) of familial AD (FAD) individuals carrying the autosomal dominant presenilin 1 E280A mutation. Compared to control, FAD OT had increased immunostaining for β-amyloid (Aβ) and CD68 in high and low myelinated regions, as well as increased immunostaining for Iba1 in the high myelinated region. In FAD samples, RNA sequencing showed: (1) viral infection in the OB; (2) inflammation in the OT that carries information via entorhinal cortex from the OB to hippocampus, a brain region essential for learning and memory; and (3) decreased oligodendrocyte deconvolved transcripts. Interestingly, spatial proteomic analysis confirmed altered myelination in the OT of FAD individuals, implying dysfunction of communication between the OB and hippocampus. These findings raise the possibility that viral infection and associated inflammation and dysregulation of myelination of the olfactory system may disrupt hippocampal function, contributing to acceleration of FAD progression.

New balance capability index as a screening tool for mild cognitive impairment

BACKGROUND

Mild cognitive impairment (MCI) is not just a prodrome to dementia, but a very important intervention point to prevent dementia caused by Alzheimer's disease (AD). It has long been known that people with AD have a higher frequency of falls with some gait instability. Recent evidence suggests that vestibular impairment is disproportionately prevalent among individuals with MCI and dementia due to AD. Therefore, we hypothesized that the measurement of balance capability is helpful to identify individuals with MCI.

METHODS

First, we developed a useful method to evaluate balance capability as well as vestibular function using Nintendo Wii balance board as a stabilometer and foam rubber on it. Then, 49 healthy volunteers aged from 56 to 75 with no clinically apparent cognitive impairment were recruited and the association between their balance capability and cognitive function was examined. Cognitive functions were assessed by MoCA, MMSE, CDR, and TMT-A and -B tests.

RESULTS

The new balance capability indicator, termed visual dependency index of postural stability (VPS), was highly associated with cognitive impairment assessed by MoCA, and the area under the receiver operating characteristic (ROC) curve was more than 0.8, demonstrating high sensitivity and specificity (app. 80% and 60%, respectively).

CONCLUSIONS

Early evidence suggests that VPS measured using Nintendo Wii balance board as a stabilometer helps identify individuals with MCI at an early and preclinical stage with high sensitivity, establishing a useful method to screen MCI.

Temporal Appearance of Enhanced Innate Anxiety in Alzheimer Model Mice

The prevalence of Alzheimer's disorder (AD) is increasing worldwide, and the co-morbid anxiety is an important, albeit often neglected problem, which might appear early during disease development. Animal models can be used to study this question. Mice, as prey animals, show an innate defensive response against a predator odor, providing a valuable tool for anxiety research. Our aim was to test whether the triple-transgenic mice model of AD shows signs of innate anxiety, with specific focus on the temporal appearance of the symptoms. We compared 3xTg-AD mice bearing human mutations of amyloid precursor protein, presenilin 1, and tau with age-matched controls. First, separate age-groups (between 2 and 18 months) were tested for the avoidance of 2-methyl-2-thiazoline, a fox odor component. To test whether hypolocomotion is a general sign of innate anxiety, open-field behavior was subsequently followed monthly in both sexes. The 3xTg-AD mice showed more immobility, approached the fox odor container less often, and spent more time in the avoidance zone. This effect was detectable already in two-month-old animals irrespective of sex, not visible around six months of age, and was more pronounced in aged females than males. The 3xTg-AD animals moved generally less. They also spent less time in the center of the open-field, which was detectable mainly in females older than five months. In contrast to controls, the aged 3xTg-AD was not able to habituate to the arena during a 30-min observation period irrespective of their sex. Amyloid beta and phospho-Tau accumulated gradually in the hippocampus, amygdala, olfactory bulb, and piriform cortex. In conclusion, the early appearance of predator odor- and open space-induced innate anxiety detected already in two-month-old 3xTg-AD mice make this genetically predisposed strain a good model for testing anxiety both before the onset of AD-related symptoms as well as during the later phase. Synaptic dysfunction by protein deposits might contribute to these disturbances.

Translational potential of synaptic alterations in Alzheimer's disease patients and amyloid precursor protein knock-in mice

Synaptic dysfunction is an early event in Alzheimer's disease. Post-mortem studies suggest that alterations in synaptic proteins are associated with cognitive decline in Alzheimer's disease. We measured the concentration of three synaptic proteins, zinc transporter protein 3, dynamin1 and AMPA glutamate receptor 3 in cerebrospinal fluid of subjects with mild cognitive impairment (n = 18) and Alzheimer's disease (n = 18) and compared the levels to cognitively and neurologically healthy controls (n = 18) by using ELISA assay. In addition, we aimed to assess the translational potential of these synaptic proteins in two established amyloid precursor protein knock-in Alzheimer's disease mouse models by assessing the cerebrospinal fluid, hippocampal and cortical synaptic protein concentrations. Using ELISA, we measured in parallel these three proteins in cerebrospinal fluid and/or brain of 12- and 24-month-old App^NL-F and App^NL-G-F knock-in mice and App^Wt control mice. The regional distribution and expression of these proteins were explored upon aging of the App knock-in models by quantitative immunofluorescence microscopy. Notably, we found a significant increase in concentrations of zinc transporter protein 3 and AMPA glutamate receptor 3 in cerebrospinal fluid of both patient groups compared with cognitively healthy controls. Dynamin1 concentration was significantly higher in Alzheimer's disease patients. Remarkably, patients with mild cognitive impairment who converted to Alzheimer's disease (n = 7) within 2 years exhibited elevated baseline cerebrospinal fluid zinc transporter protein 3 concentrations compared with mild cognitive impairment patients who did not convert (n = 11). Interestingly, similar to the alterations in Alzheimer's disease subjects, cerebrospinal fluid AMPA glutamate receptor 3 concentration was significantly higher in App^NL-G-F knock-in mice when compared with wild-type controls. Furthermore, we have detected age and brain regional specific changes of the three synaptic proteins in the hippocampus and prefrontal cortex of both App^NL-F and App^NL-G-F knock-in mice. Notably, all the three cerebrospinal fluid synaptic protein concentrations correlated negatively with concentrations in hippocampal lysates. The elevated zinc transporter protein 3 concentrations in the cerebrospinal fluid of converter versus non-converter mild cognitive impairment patients suggests a prospective role of zinc transporter 3 in differentiating dementia patients of the biological continuum of Alzheimer's disease. The increased cerebrospinal fluid concentrations of synaptic proteins in both patient groups, potentially reflecting synaptic alterations in the brain, were similarly observed in the amyloid precursor protein knock-in mouse models highlighting the translational potential of these proteins as markers for synaptic alterations. These synaptic markers could potentially help reduce the current disparities between human and animal model-based studies aiding the translation of preclinical discoveries of pathophysiological changes into clinical research.

Transcriptional profiles in olfactory pathway-associated brain regions of African green monkeys: Associations with age and Alzheimer's disease neuropathology

Introduction

Olfactory impairment in older individuals is associated with an increased risk of Alzheimer's disease (AD). Characterization of age versus neuropathology-associated changes in the brain olfactory pathway may elucidate processes underlying early AD pathogenesis. Here, we report age versus AD neuropathology-associated differential transcription in four brain regions in the olfactory pathway of 10 female African green monkeys (vervet, Chlorocebus aethiops sabaeus), a well-described model of early AD-like neuropathology.

Methods

Transcriptional profiles were determined by microarray in the olfactory bulb (OB), piriform cortex (PC), temporal lobe white matter (WM), and inferior temporal cortex (ITC). Amyloid beta (Aβ) plaque load in parietal and temporal cortex was determined by immunohistochemistry, and concentrations of Aβ42, Aβ40, and norepinephrine in ITC were determined by enzyme-linked immuosorbent assay (ELISA). Transcriptional profiles were compared between middle-aged and old animals, and associations with AD-relevant neuropathological measures were determined.

Results

Transcriptional profiles varied by brain region and age group. Expression levels of TRO and RNU4-1 were significantly lower in all four regions in the older group. An additional 29 genes were differentially expressed by age in three of four regions. Analyses of a combined expression data set of all four regions identified 77 differentially expressed genes (DEGs) by age group. Among these DEGs, older subjects had elevated levels of CTSB , EBAG9, LAMTOR3, and MRPL17, and lower levels of COMMD10 and TYW1B. A subset of these DEGs was associated with neuropathology biomarkers. Notably, CTSB was positively correlated with Aβ plaque counts, Aβ42:Aβ40 ratios, and norepinephrine levels in all brain regions.

Discussion

These data demonstrate age differences in gene expression in olfaction-associated brain regions. Biological processes exhibiting age-related enrichment included the regulation of cell death, vascular function, mitochondrial function, and proteostasis. A subset of DEGs was specifically associated with AD phenotypes. These may represent promising targets for future mechanistic investigations and perhaps therapeutic intervention.

Mesoporous silica nanoparticle-encapsulated Bifidobacterium attenuates brain Aβ burden and improves olfactory dysfunction of APP/PS1 mice by nasal delivery

BACKGROUND

Dysbiosis or imbalance of gut microbiota in Alzheimer's disease (AD) affects the production of short-chain fatty acids (SCFAs), whereas exogenous SCFAs supplementation exacerbates brain Aβ burden in APP/PS1 mice. Bifidobacterium is the main producer of SCFAs in the gut flora, but oral administration of Bifidobacterium is ineffective due to strong acids and bile salts in the gastrointestinal tract. Therefore, regulating the levels of SCFAs in the gut is of great significance for AD treatment.

METHODS

We investigated the feasibility of intranasal delivery of MSNs-Bifidobacterium (MSNs-Bi) to the gut and their effect on behavior and brain pathology in APP/PS1 mice.

RESULTS

Mesoporous silica nanospheres (MSNs) were efficiently immobilized on the surface of Bifidobacterium. After intranasal administration, fluorescence imaging of MSNs-Bi in the abdominal cavity and gastrointestinal tract revealed that intranasally delivered MSNs-Bi could be transported through the brain to the peripheral intestine. Intranasal administration of MSNs-Bi not only inhibited intestinal inflammation and reduced brain Aβ burden but also improved olfactory sensitivity in APP/PS1 mice.

CONCLUSIONS

These findings suggested that restoring the balance of the gut microbiome contributes to ameliorating cognitive impairment in AD, and that intranasal administration of MSNs-Bi may be an effective therapeutic strategy for the prevention of AD and intestinal disease.

Use of a habituation-dishabituation test to determine canine olfactory sensitivity

The habituation-dishabituation (H-D) paradigm is an established measure of sensory perception in animals. However, it has rarely been applied to canine olfaction. It proposes that animals will lose interest in, or habituate to, a stimulus after successive exposures but will regain interest in, or dishabituate to, a novel stimulus if they can perceive it. This study assessed an H-D test's practicability to determine dogs' olfactory detection thresholds (ODTs) for a neutral odorant. A random selection of mixed-breed pet dogs (n = 26) participated in two H-D tests in a repeated-measures crossover design. They were first habituated to a carrier odor and then presented with either ascending concentrations of n-amyl acetate in the known ODT range (experimental condition) or repeated carrier odor presentations (control condition). No single odor concentration elicited dishabituation in the majority of the dogs. However, individual dogs dishabituated at differing experimental concentrations significantly more often than in the control condition (p = .012). These findings provide some tentative support for using this method in studying canine olfaction. However, further assessment and refinement are needed before it can be a viable alternative to traditional ODT measurement.

Brain alterations of regional homogeneity, degree centrality, and functional connectivity in vulnerable carotid plaque patients with neither clinical symptoms nor routine MRI lesions: A resting-state fMRI study

Aims

Based on resting-state functional MRI (fMRI), we preliminarily explored brain alterations in asymptomatic patients with vulnerable carotid plaques, but carotid stenosis was < 50%.

Methods

A total of 58 asymptomatic patients with vulnerable carotid plaques (stenosis <50%) and 38 healthy controls were recruited. Between-group differences in regional homogeneity (ReHo), degree centrality (DC), and functional connectivity (FC) were analyzed. Correlation analysis was performed between the ReHo or DC values in altered brain regions as well as voxel-wise abnormal FC and scores on neuropsychiatric scales, serum interleukin-6 (IL-6), and C-reactive protein (CRP).

Results

Both ReHo and DC values on the left superior occipital gyrus (SOG.L) of the asymptomatic vulnerable carotid plaque group reduced, regardless of plaque location (left, right, or bilateral). Functional connections weakened between the SOG.L and right lingual gyrus (LING.R)/right inferior occipital gyrus (IOG.R), right middle frontal gyrus (MFG.R)/orbital part of superior frontal gyrus (ORBsup.R)/orbital part of middle frontal gyrus (ORBmid.R), left precentral gyrus (PreCG.L)/postcentral gyrus (PoCG.L), left supplementary motor area (SMA.L), right paracentral lobule (PCL.R), left precuneus (PCUN.L), and right postcentral gyrus (PoCG.R)/PCL.R. In ReHo-altered brain regions, ReHo values were positively correlated with Hamilton Rating Scale for Depression (HAMD) scores, and the setting region of abnormal ReHo as seed points, voxel-wise FC between the SOG.L and PreCG.L was negatively correlated with CRP.

Conclusions

Cerebral alterations of neuronal synchronization, activity, and connectivity properties in the asymptomatic vulnerable carotid plaque group were independent of the laterality of vulnerable carotid plaques. Significant relation between ReHo values on the SOG.L and HAMD indicated that even when there were neither clinical symptoms nor lesions on routine MRI, brain function might have changed already at an early stage of carotid atherosclerosis. Inflammation might play a role in linking vulnerable carotid plaques and changes of resting-state functional connectivity.

Non-Invasive Nasal Discharge Fluid and Other Body Fluid Biomarkers in Alzheimer’s Disease

The key to current Alzheimer’s disease (AD) therapy is the early diagnosis for prompt intervention, since available treatments only slow the disease progression. Therefore, this lack of promising therapies has called for diagnostic screening tests to identify those likely to develop full-blown AD. Recent AD diagnosis guidelines incorporated core biomarker analyses into criteria, including amyloid-β (Aβ), total-tau (T-tau), and phosphorylated tau (P-tau). Though effective, the accessibility of screening tests involving conventional cerebrospinal fluid (CSF)- and blood-based analyses is often hindered by the invasiveness and high cost. In an attempt to overcome these shortcomings, biomarker profiling research using non-invasive body fluid has shown the potential to capture the pathological changes in the patients’ bodies. These novel non-invasive body fluid biomarkers for AD have emerged as diagnostic and pathological targets. Here, we review the potential peripheral biomarkers, including non-invasive peripheral body fluids of nasal discharge, tear, saliva, and urine for AD.

A Signal Detection Analysis of Olfactory Learning in 12-Month-Old 5xFAD Mice

Although Alzheimer’s disease is most often studied in terms of memory impairments, olfactory dysfunction begins in the early stages. We tested olfactory learning, sensitivity, and response bias using signal detection methods in 12-month-old male and female 5xFAD mice and their wildtype controls in the operant olfactometer. Odor detection was not reduced in the 5xFAD mice, but learning was, which was worse in female 5xFAD mice than in males. Female mice were more conservative in their response strategy. Signal detection analysis allows us to discriminate between cognitive and sensory deficits of male and female mouse models of AD.

Olfactory Evaluation in Alzheimer’s Disease Model Mice

Olfactory dysfunction is considered a pre-cognitive biomarker of Alzheimer’s disease (AD). Because the olfactory system is highly conserved across species, mouse models corresponding to various AD etiologies have been bred and used in numerous studies on olfactory disorders. The olfactory behavior test is a method required for early olfactory dysfunction detection in AD model mice. Here, we review the olfactory evaluation of AD model mice, focusing on traditional olfactory detection methods, olfactory behavior involving the olfactory cortex, and the results of olfactory behavior in AD model mice, aiming to provide some inspiration for further development of olfactory detection methods in AD model mice.

Expression of Olfactory-Related Genes in the Olfactory Epithelium of an Alzheimer’s Disease Mouse Model

Using an amyloid precursor protein (App) gene knock-in (KI) mouse of Alzheimer’s disease (AD), we investigated the expression of olfactory-related genes in olfactory impairment caused by AD. We observed the change in olfactory behavior in the App-KI mice. There was no significant difference, however, in the mRNA expression levels of olfactory-related genes between the olfactory epithelia of wild-type (WT) and App-KI mice. Amyloid-β deposition was confirmed throughout the olfactory pathway in App-KI mice, but not in WT mice. These show that the change in olfactory behavior in the App-KI mice might cause by the impairment of the olfactory pathway.

Alteration of Neural Pathways and Its Implications in Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disease accompanied by cognitive and behavioral symptoms. These AD-related manifestations result from the alteration of neural circuitry by aggregated forms of amyloid-β (Aβ) and hyperphosphorylated tau, which are neurotoxic. From a neuroscience perspective, identifying neural circuits that integrate various inputs and outputs to determine behaviors can provide insight into the principles of behavior. Therefore, it is crucial to understand the alterations in the neural circuits associated with AD-related behavioral and psychological symptoms. Interestingly, it is well known that the alteration of neural circuitry is prominent in the brains of patients with AD. Here, we selected specific regions in the AD brain that are associated with AD-related behavioral and psychological symptoms, and reviewed studies of healthy and altered efferent pathways to the target regions. Moreover, we propose that specific neural circuits that are altered in the AD brain can be potential targets for AD treatment. Furthermore, we provide therapeutic implications for targeting neuronal circuits through various therapeutic approaches and the appropriate timing of treatment for AD.

Reducing local synthesis of estrogen in the tubular striatum promotes attraction to same-sex odors in female mice

Brain-derived 17β-estradiol (E2) confers rapid effects on neural activity. The tubular striatum (TuS, also called the olfactory tubercle) is both capable of local E2 synthesis due to its abundant expression of aromatase and is a critical locus for odor-guided motivated behavior and odor hedonics. TuS neurons also contain mRNA for estrogen receptors α, β, and the G protein-coupled estrogen receptor. We demonstrate here that mRNA for estrogen receptors appears to be expressed upon TuS dopamine 1 receptor-expressing neurons, suggesting that E2 may play a neuromodulatory role in circuits which are important for motivated behavior. Therefore, we reasoned that E2 in the TuS may influence attraction to urinary odors which are highly attractive. Using whole-body plethysmography, we examined odor-evoked high-frequency sniffing as a measure of odor attaction. Bilateral infusion of the aromatase inhibitor letrozole into the TuS of gonadectomized female adult mice induced a resistance to habituation over successive trials in their investigatory sniffing for female mouse urinary odors, indicative of an enhanced attraction. All males displayed resistance to habituation for female urinary odors, indicative of enhanced attraction that is independent from E2 manipulation. Letrozole's effects were not due to group differences in basal respiration, nor changes in the ability to detect or discriminate between odors (both monomolecular odorants and urinary odors). Therefore, de novo E2 synthesis in the TuS impacts females' but not males' attraction to female urinary odors, suggesting a sex-specific influence of E2 in odor hedonics.

Aging-Related Alterations of Glymphatic Transport in Rat: In vivo Magnetic Resonance Imaging and Kinetic Study

Objective

Impaired glymphatic waste clearance function during brain aging leads to the accumulation of metabolic waste and neurotoxic proteins (e.g., amyloid-β, tau) which contribute to neurological disorders. However, how the age-related glymphatic dysfunction exerts its effects on different cerebral regions and affects brain waste clearance remain unclear.

Methods

We investigated alterations of glymphatic transport in the aged rat brain using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and advanced kinetic modeling. Healthy young (3-4 months) and aged (18-20 months) male rats (n = 12/group) underwent the identical MRI protocol, including T2-weighted imaging and 3D T1-weighted imaging with intracisternal administration of contrast agent (Gd-DTPA). Model-derived parameters of infusion rate and clearance rate, characterizing the kinetics of cerebrospinal fluid (CSF) tracer transport via the glymphatic system, were evaluated in multiple representative brain regions. Changes in the CSF-filled cerebral ventricles were measured using contrast-induced time signal curves (TSCs) in conjunction with structural imaging.

Results

Compared to the young brain, an overall impairment of glymphatic transport function was detected in the aged brain, evidenced by the decrease in both infusion and clearance rates throughout the brain. Enlarged ventricles in parallel with reduced efficiency in CSF transport through the ventricular regions were present in the aged brain. While the age-related glymphatic dysfunction was widespread, our kinetic quantification demonstrated that its impact differed considerably among cerebral regions with the most severe effect found in olfactory bulb, indicating the heterogeneous and regional preferential alterations of glymphatic function.

Conclusion

The robust suppression of glymphatic activity in the olfactory bulb, which serves as one of major efflux routes for brain waste clearance, may underlie, in part, age-related neurodegenerative diseases associated with neurotoxic substance accumulation. Our data provide new insight into the cerebral regional vulnerability to brain functional change with aging.

Impact of Heat Shock Proteins in Neurodegeneration: Possible Therapeutical Targets

Human neurodegenerative diseases occur as a result of various factors. Regardless of the variety in the etiology of development, many of these diseases are characterized by the accumulation of pathological, misfolded proteins; hence, such diseases are considered as proteinopathies. While plenty of research study has been conducted in order to identify the pathophysiology of these proteinopathies, there is still a lack of understanding in terms of potential therapeutic targets. Molecular chaperones present the main workforce for cellular protection and stress response. Therefore, considering these functions, molecular chaperones present a promising target for research within the field of conformational diseases that arise from proteinopathies. Since the association between neurodegenerative disorders and their long-term consequences is well documented, the need for the development of new therapeutic strategies becomes even more critical. In this review, we summarized the molecular function of heat shock proteins and recent progress on their role, involvement, and other mechanisms related to neurodegeneration caused by different etiological factors. Based on the relevant scientific data, we will highlight the functional classification of heat shock proteins, regulatin, and their therapeutic potential for neurodegenerative disorders.

Home cage measures of Alzheimer's disease in the rTg4510 mouse model

Alzheimer's disease affects an array of activities in patients' daily lives but measures other than memory are rarely evaluated in animal models. Home cage behavior, however, may provide an opportunity to back translate a variety of measures seen in human disease progression to animal models, providing external and face validity. The aim of this study was to evaluate if home cage measures could indicate disease in the rTg4510 mouse model. We hypothesized that sleep, nesting, and smell discrimination would be altered in mutant mice. Thirty-two transgenic mice were used in a Latin square design of four genotypes x both sexes x two diets. Half the mice received a doxycycline diet to suppress tauopathy and evaluate tau severity on various measures. At 8-, 12-, and 16-weeks old, 24 h activity/sleep patterns, nest complexity, and odor discrimination were measured. After 16-weeks, tau concentration in the brain was quantified. Mutant mice had increased tau concentration in brain tissue, but it was reduced by the doxycycline diet. However, only nest complexity was different between mutant mice and controls. Overall, tauopathy in rTg4510 mice does seem to affect these commonly observed symptoms in human patients. However, while running this study, a report showed that the rTg4510 mutant phenotype is not caused by the mutation itself, but confounding factors from transgene insertion. Combined with report findings and our data, the rTg4510 model may not be an ideal model for all aspects of human Alzheimer's disease.

Ginsenoside Rd Attenuates Tau Phosphorylation in Olfactory Bulb, Spinal Cord, and Telencephalon by Regulating Glycogen Synthase Kinase 3β and Cyclin-Dependent Kinase 5

OBJECTIVE

Ginseng is a plant of the family Acanthopanaceae. It has been used for thousands of years in China. It is known as the king of hundred herbs. It was recorded first in Shennong Baicao Jing. It has been found that ginsenoside Rd is a neuroprotective agent. This article aims to explore the protective roles of ginsenoside Rd in Alzheimer's disease. Rd, a Chinese herb, may be a promising treatment drug for Alzheimer's disease (AD) and is also reported to be related to several pathological changes, including the deposition of Aβ and tau hyperphosphorylation in AD as it decreases the deposition of tau hyperphosphorylation in APP transgenic mice.

METHODS

In this study, APP transgenic mice were pretreated with 10 mg/kg Rd for six months, and the effect of Rd on neuropathological deficits in the olfactory bulb, spinal cord, and telencephalon of APP transgenic mice was investigated. The phosphorylation levels of tau (S199/202, S396, S404, and Tau5) and the activities of the proteins glycogen synthase kinase 3β (Tyr216) and cyclin-dependent kinase 5 (P25/P35) were measured.

RESULTS

The pretreatment of Rd effectively decreased the production and deposition of hyperphosphorylated tau (S199/202, S396, and S404) protein by depressing the expression of glycogen synthase kinase 3β (GSK-3β/Tyr216) and cyclin-dependent kinase 5 (CDK5/P25).

CONCLUSION

These findings suggest that ginsenoside Rd could improve the pathological changes of AD in the olfactory bulb, spinal cord, and telencephalon, which further demonstrated the potential therapeutic effect of Rd in early AD.

Adult Neural Stem Cell Migration Is Impaired in a Mouse Model of Alzheimer's Disease

Neurogenesis in the adult brain takes place in two neurogenic niches: the ventricular-subventricular zone (V-SVZ) and the subgranular zone. After differentiation, neural precursor cells (neuroblasts) have to move to an adequate position, a process known as neuronal migration. Some studies show that in Alzheimer’s disease, the adult neurogenesis is impaired. Our main aim was to investigate some proteins involved both in the physiopathology of Alzheimer’s disease and in the neuronal migration process using the APP/PS1 Alzheimer’s mouse model. Progenitor migrating cells are accumulated in the V-SVZ of the APP/PS1 mice. Furthermore, we find an increase of Cdh1 levels and a decrease of Cdk5/p35 and cyclin B1, indicating that these cells have an alteration of the cell cycle, which triggers a senescence state. We find less cells in the rostral migratory stream and less mature neurons in the olfactory bulbs from APP/PS1 mice, leading to an impaired odour discriminatory ability compared with WT mice. Alzheimer’s disease mice present a deficit in cell migration from V-SVZ due to a senescent phenotype. Therefore, these results can contribute to a new approach of Alzheimer’s based on senolytic compounds or pro-neurogenic factors.

The Correlation Between Olfactory Test and Hippocampal Volume in Alzheimer's Disease and Mild Cognitive Impairment Patients: A Meta-Analysis

Background: Previous studies have reported that olfactory identification deficits may be the earliest clinical features of Alzheimer's disease (AD). However, the association between odor identification and hippocampal atrophy remains unclear.

Objective: This meta-analysis quantified the correlation between odor identification test scores and hippocampal volume in AD.

Method: A search of the PUBMED, EMBASE, and WEB OF SCIENCE databases was conducted from January 2003 to June 2020 on studies with reported correlation coefficients between olfactory identification score and hippocampal volume in patients with amnestic AD or mild cognitive impairment (MCI). The quality of the studies was assessed using the Newcastle-Ottawa quality assessment scale (NOS). Pooled r-values were combined and computed in R studio.

Results: Seven of 627 original studies on AD/MCI using an olfactory identification test (n = 902) were included. A positive correlation was found between hippocampal volume and olfactory test scores (r = 0.3392, 95% CI: 0.2335–0.4370). Moderator analysis showed that AD and MCI patients were more profoundly correlated than normal controls (AD: r = 0.3959, 95% CI: 0.2605–0.5160; MCI: r = 0.3691, 95% CI: 0.1841–0.5288; NC: r = 0.1305, 95% CI: −0.0447–0.2980). Age difference and patient type were the main sources of heterogeneity in this analysis.

Conclusion: The correlation appears to be more predominant in the cognitive disorder group (including MCI and AD) than in the non-cognitive disorder group. Age is an independent factor that affects the severity of the correlation during disease progression. The mildness of the correlation suggests that olfactory tests may be more accurate when combined with other non-invasive examinations for early detection.

Systematic Review Registration:https://inplasy.com/, identifier INPLASY202140088.

GABAA receptor agonist muscimol rescues inhibitory microcircuit defects in the olfactory bulb and improves olfactory function in APP/PS1 transgenic mice

Olfactory damage develops at the early stages of Alzheimer's disease (AD). While amyloid-β (Aβ) oligomers are shown to impair inhibitory circuits in the olfactory bulb (OB), its underlying mechanisms remain unclear. Here, we investigated the olfactory dysfunction due to impaired inhibitory transmission to mitral cells (MCs) of the OB in APP/PS1 mice. Using electrophysiological studies, we found that MCs exhibited increased spontaneous firing rates as early as 3 months, much before development of Aβ deposits in the brain. Furthermore, the frequencies but not amplitudes of MC inhibitory postsynaptic currents decreased markedly, suggesting that presynaptic GABA release is impaired while postsynaptic GABA_A receptor responses remain intact. Notably, muscimol, a GABA_A receptor agonist, improved odor identification and discrimination behaviors in APP/PS1 mice, reduced MC basal firing activity, and rescued inhibitory circuits along with reducing the Aβ burden in the OB. Our study links the presynaptic deficits of GABAergic transmission to olfactory dysfunction and subsequent AD development and implicates the therapeutic potential of maintaining local inhibitory microcircuits against early AD progression.

Volumetry of Olfactory Structures in Mild Cognitive Impairment and Alzheimer's Disease: A Systematic Review and a Meta-Analysis

Olfactory decline is an early symptom of Alzheimer's disease (AD) and is a predictor of conversion from mild cognitive impairment (MCI) to AD. Olfactory decline could reflect AD-related atrophy of structures related to the sense of smell. The aim of this study was to verify whether the presence of a clinical diagnosis of AD or MCI is associated with a volumetric decrease in the olfactory bulbs (OB) and the primary olfactory cortex (POC). We conducted two systematic reviews, one for each region and a meta-analysis. We collected articles from PsychNet, PubMed, Ebsco, and ProQuest databases. Results showed large and heterogeneous effects indicating smaller OB volumes in patients with AD (k = 6, g = -1.21, 95% CI [-2.19, -0.44]) and in patients with MCI compared to controls. There is also a trend for smaller POC in patients with AD or MCI compared to controls. Neuroanatomical structures involved in olfactory processing are smaller in AD and these volumetric reductions could be measured as early as the MCI stage.

A novel olfactory threshold test for screening cognitive decline among elderly people

Olfactory impairment is associated with dementia and is a potential early biomarker of cognitive decline. We developed a novel olfactory threshold test called Sniff Bubble using rose odor-containing beads made with 2-phenylethyl alcohol. We aimed to define cut-off scores for this tool to help identify cognitive decline among elderly people. In total, 162 elderly people (mean age ± SD: 73.04 ± 8.73 years) were administered olfactory threshold and neurocognitive tests. For analyses, we divided the participants into two groups based on cognitive functioning, namely cognitive decline (n = 44) and normal cognition (n = 118) groups. The Sniff Bubble and YSK olfactory function test for olfactory threshold and the Structured Clinical Interview for DSM-5 Disorders-Clinician Version and Korean version of the Consortium to Establish a Registry for Alzheimer’s Disease assessment packet for neurocognitive functioning were used. We used K-means cluster analyses and receiver operating characteristic (ROC) analyses to identify the most appropriate cut-off value. We established a positive correlation between the Sniff Bubble and neurocognitive function test scores (r = 0.431, p < 0.001). We defined the cut-off score, using the ROC curve analyses for Sniff Bubble scores, at 3 and higher with an area under the curve of 0.759 (p < 0.001). The Sniff Bubble test can adequately detect cognitive decline in elderly people and may be used clinically as the first step in the screening process.

Elevated Testosterone Level and Urine Scent Marking in Male 5xFAD Alzheimer Model Mice

BACKGROUND

Function of the Amyloid Precursor Protein (AβPP) and its various cleavage products still is not unraveled down to the last detail. While its role as a source of the neurotoxic Amyloid beta (Aβ) peptides in Alzheimer's Disease (AD) is undisputed and its property as a cell attachment protein is intriguing, while functions outside the neuronal context are scarcely investigated. This is particularly noteworthy because AβPP has a ubiquitous expression profile and its longer isoforms, AβPP750 and 770, are found in various tissues outside the brain and in non-neuronal cells.

OBJECTIVE

Here, we aimed at analyzing the 5xFAD Alzheimer's disease mouse model in regard to male sexual function. The transgenes of this mouse model are regulated by Thy1 promoter activity and Thy1 is expressed in testes, e.g. by Sertoli cells. This allows speculation about an influence on sexual behavior.

METHODS

We analyzed morphological as well as biochemical properties of testicular tissue from 5xFAD mice and wild type littermates and testosterone levels in serum, testes and the brain. Sexual behavior was assessed by a urine scent marking test at different ages for both groups.

RESULTS

While sperm number, testes weight and morphological phenotypes of sperms were nearly indistinguishable from those of wild type littermates, testicular testosterone levels were significantly increased in the AD model mice. This was accompanied by elevated and prolonged sexual interest as displayed within the urine scent marking test.

CONCLUSION

We suggest that overexpression of AβPP, which mostly is used to mimic AD in model mice, also affects male sexual behavior as assessed additional by the Urine Scent Marking (USM) test. The elevated testosterone levels might have an additional impact on central nervous system androgen receptors and also have to be considered when assessing learning and memory capabilities.

Olfactory dysfunction in the 3xTg-AD model of Alzheimer's disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease in which the risk of development increases with age. People with AD are plagued with deficits in their cognition, memory, and basic social skills. Many of these deficits are believed to be caused by the formation of amyloid-β plaques and neurofibrillary tangles in regions of the brain associated with memory, such as the hippocampus. However, one of the early, preclinical symptoms of AD is the loss of olfactory detection and discrimination. To determine if a mouse model of AD expresses the same olfactory dysfunction seen in human AD, 3xTg-AD mice were given a buried food test and, unlike previous studies, compared to their background and parental strains. Results showed that over 52 weeks, the 3xTg-AD mice took significantly longer to find the buried food than the control strains. The olfactory bulbs of the 3xTg-AD mice were removed, sliced, and stained using Congo red for histological analysis. Amyloid deposits were observed predominantly in the granule layer of the olfactory bulb beginning at 13 weeks of age in 3xTg-AD mice, but not in the control strains of mice. Further examination of the buried food test data revealed that 3xTg-AD females had a significantly longer latency to detect the buried food than males beginning at 26 weeks of age. Overall, this study provides further validation of the 3xTg-AD mouse model of AD and supports the idea that simple olfactory testing could be part of the diagnostic process for human AD.

Olfactory neuropathology in Alzheimer's disease: a sign of ongoing neurodegeneration

Olfactory neuropathology is a cause of olfactory loss in Alzheimer's disease (AD). Olfactory dysfunction is also associated with memory and cognitive dysfunction and is an incidental finding of AD dementia. Here we review neuropathological research on the olfactory system in AD, considering both structural and functional evidence. Experimental and clinical findings identify olfactory dysfunction as an early indicator of AD. In keeping with this, amyloid-β production and neuroinflammation are related to underlying causes of impaired olfaction. Notably, physiological features of the spatial map in the olfactory system suggest the evidence of ongoing neurodegeneration. Our aim in this review is to examine olfactory pathology findings essential to identifying mechanisms of olfactory dysfunction in the development of AD in hopes of supporting investigations leading towards revealing potential diagnostic methods and causes of early pathogenesis in the olfactory system. [BMB Reports 2021; 54(6): 295-304].

Olfactory impairment in men and mice related to aging and amyloid-induced pathology

Olfaction, or the sense of smell, is one of the most ancient senses in men and mice, important for a large variety of innate and acquired behaviors. Clinical data reveal an early impairment of olfaction during normal aging and in the course of neurodegenerative diseases, but the underlying cellular/molecular mechanisms remain obscure. In the current review, we compare different aspects of the aging- and Alzheimer's disease related impairment of olfaction in men and mice, aiming at the identification of common morbidities and biomarkers, which can be analyzed in detail in the appropriate mouse models. We also identify common, often interdependent (patho)physiological pathways, including but not limited to extracellular amyloid depositions, neuroinflammation, ɛ4 allele of the apolipoprotein E, CNS insulin resistance, and the impairment of adult neurogenesis, to be targeted by basic and clinical research.

Olfactory dysfunction predicts the development of dementia in older patients with type 2 diabetes

AIMS

Olfactory dysfunction is associated with the transition from normal cognition to dementia in persons without type 2 diabetes. This study aimed to investigate whether olfactory dysfunction could be an early marker of future dementia in older patients with type 2 diabetes.

METHODS

This exploratory study included 151 older Japanese outpatients with type 2 diabetes who did not have a diagnosis of probable dementia at baseline. A multivariate logistic regression model was used to determine whether Open Essence (OE) test score at baseline is associated with the development of probable dementia.

RESULTS

Over 3 years, approximately 9% of the study subjects developed probable dementia. Subjects with olfactory dysfunction at baseline developed probable dementia more frequently than those without. Multivariate logistic regression showed that lower OE test score, higher age, lower Mini-Mental State Examination (MMSE) score, higher total protein concentration, and more frequent use of a sulfonylurea are significantly associated with the development of probable dementia. Stepwise multivariate regression analysis demonstrated that change in OE test score over 3 years is significantly associated with change in MMSE score.

CONCLUSIONS

Our study suggested that olfactory dysfunction precedes the development of probable dementia in older patients with type 2 diabetes.

Enhancing GABAergic signaling ameliorates aberrant gamma oscillations of olfactory bulb in AD mouse models

Background

Before the deposition of amyloid-beta plaques and the onset of learning memory deficits, patients with Alzheimer’s disease (AD) experience olfactory dysfunction, typified by a reduced ability to detect, discriminate, and identify odors. Rodent models of AD, such as the Tg2576 and APP/PS1 mice, also display impaired olfaction, accompanied by aberrant in vivo or in vitro gamma rhythms in the olfactory pathway. However, the mechanistic relationships between the electrophysiological, biochemical and behavioral phenomena remain unclear.

Methods

To address the above issues in AD models, we conducted in vivo measurement of local field potential (LFP) with a combination of in vitro electro-olfactogram (EOG), whole-cell patch and field recordings to evaluate oscillatory and synaptic function and pharmacological regulation in the olfactory pathway, particularly in the olfactory bulb (OB). Levels of protein involved in excitation and inhibition of the OB were investigated by western blotting and fluorescence staining, while behavioral studies assessed olfaction and memory function.

Results

LFP measurements demonstrated an increase in gamma oscillations in the OB accompanied by altered olfactory behavior in both APP/PS1 and 3xTg mice at 3–5 months old, i.e. an age before the onset of plaque formation. Fewer olfactory sensory neurons (OSNs) and a reduced EOG contributed to a decrease in the excitatory responses of M/T cells, suggesting a decreased ability of M/T cells to trigger interneuron GABA release indicated by altered paired-pulse ratio (PPR), a presynaptic parameter. Postsynaptically, there was a compensatory increase in levels of GABA_AR α1 and β3 subunits and subsequent higher amplitude of inhibitory responses. Strikingly, the GABA uptake inhibitor tiagabine (TGB) ameliorated abnormal gamma oscillations and levels of GABA_AR subunits, suggesting a potential therapeutic strategy for early AD symptoms. These findings reveal increased gamma oscillations in the OB as a core indicator prior to onset of AD and uncover mechanisms underlying aberrant gamma activity in the OB.

Conclusions

This study suggests that the concomitant dysfunction of both olfactory behavior and gamma oscillations have important implications for early AD diagnosis: in particular, awareness of aberrant GABAergic signaling mechanisms might both aid diagnosis and suggest therapeutic strategies for olfactory damage in AD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13024-021-00434-7.