Cellular and molecular neuropathology of the olfactory epithelium and central olfactory pathways in Alzheimer's disease and schizophrenia

Inflammation-related pathology in the olfactory epithelium: its impact on the olfactory system in psychotic disorders

Smell deficits and neurobiological changes in the olfactory bulb (OB) and olfactory epithelium (OE) have been observed in schizophrenia and related disorders. The OE is the most peripheral olfactory system located outside the cranium, and is connected with the brain via direct neuronal projections to the OB. Nevertheless, it is unknown whether and how a disturbance of the OE affects the OB in schizophrenia and related disorders. Addressing this gap would be the first step in studying the impact of OE pathology in the disease pathophysiology in the brain. In this cross-species study, we observed that chronic, local OE inflammation with a set of upregulated genes in an inducible olfactory inflammation (IOI) mouse model led to a volume reduction, layer structure changes, and alterations of neuron functionality in the OB. Furthermore, IOI model also displayed behavioral deficits relevant to negative symptoms (avolition) in parallel to smell deficits. In first episode psychosis (FEP) patients, we observed a significant alteration in immune/inflammation-related molecular signatures in olfactory neuronal cells (ONCs) enriched from biopsied OE and a significant reduction in the OB volume, compared with those of healthy controls (HC). The increased expression of immune/inflammation-related molecules in ONCs was significantly correlated to the OB volume reduction in FEP patients, but no correlation was found in HCs. Moreover, the increased expression of human orthologues of the IOI genes in ONCs was significantly correlated with the OB volume reduction in FEP, but not in HCs. Together, our study implies a potential mechanism of the OE-OB pathology in patients with psychotic disorders (schizophrenia and related disorders). We hope that this mechanism may have a cross-disease implication, including COVID-19-elicited mental conditions that include smell deficits.

Comparison of Oncogenes, Tumor Suppressors, and MicroRNAs Between Schizophrenia and Glioma: The Balance of Power

The risk of cancer in schizophrenia has been controversial. Confounders of the issue are cigarette smoking in schizophrenia, and antiproliferative effects of antipsychotic medications. The author has previously suggested comparison of a specific cancer like glioma to schizophrenia might help determine a more accurate relationship between cancer and schizophrenia. To accomplish this goal, the author performed three comparisons of data; the first a comparison of conventional tumor suppressors and oncogenes between schizophrenia and cancer including glioma. This comparison determined schizophrenia has both tumor-suppressive and tumor-promoting characteristics. A second, larger comparison between brain-expressed microRNAs in schizophrenia with their expression in glioma was then performed. This identified a core carcinogenic group of miRNAs in schizophrenia offset by a larger group of tumor-suppressive miRNAs. This proposed "balance of power" between oncogenes and tumor suppressors could cause neuroinflammation. This was assessed by a third comparison between schizophrenia, glioma and inflammation in asbestos-related lung cancer and mesothelioma (ALRCM). This revealed that schizophrenia shares more oncogenic similarity to ALRCM than glioma.

The miR-124-AMPAR pathway connects polygenic risks with behavioral changes shared between schizophrenia and bipolar disorder

Schizophrenia (SZ) and bipolar disorder (BP) are highly heritable major psychiatric disorders that share a substantial portion of genetic risk as well as their clinical manifestations. This raises a fundamental question of whether, and how, common neurobiological pathways translate their shared polygenic risks into shared clinical manifestations. This study shows the miR-124-3p-AMPAR pathway as a key common neurobiological mediator that connects polygenic risks with behavioral changes shared between these two psychotic disorders. We discovered the upregulation of miR-124-3p in neuronal cells and the postmortem prefrontal cortex from both SZ and BP patients. Intriguingly, the upregulation is associated with the polygenic risks shared between these two disorders. Seeking mechanistic dissection, we generated a mouse model that upregulates miR-124-3p in the medial prefrontal cortex. We demonstrated that the upregulation of miR-124-3p increases GRIA2-lacking calcium-permeable AMPARs and perturbs AMPAR-mediated excitatory synaptic transmission, leading to deficits in the behavioral dimensions shared between SZ and BP.

Peripheral and central smell regions in children with epilepsy: An MRI evaluation

OBJECTIVES

We investigated the peripheral and central olfactory regions in children with epilepsy using cranial MRI.

METHODS

In this retrospective study, cranial MRI images were obtained from 23 children with epilepsy and 23 healthy controls. Olfactory bulb (OB) volume and olfactory sulcus (OS) depth in the peripheral olfactory region and insular cortex and corpus amygdala areas in the central olfactory region were measured.

RESULTS

There was no significant difference in the OB volume and OS depth in the peripheral olfactory regions in the two groups (p > 0.05). In the central olfactory region, the insular cortex and corpus amygdala areas in the epilepsy group were significantly smaller than those in the control group (p < 0.05). In both groups, the OS depth on the right side was significantly higher than that on the left side (p < 0.05). In the epilepsy group, there were positive correlations between each of the OB volumes, OS depths, insular cortex areas, and corpus amygdala areas bilaterally (p < 0.05). In both groups, there were positive correlations between the OB volume and OS depth, OS depth and insular cortex area and insular cortex area and corpus amygdala areas (p < 0.05).

CONCLUSION

A change in the central olfactory region in epileptic patients may be related to central tissue damage due to epilepsy. This finding has important implications for epilepsy patients, with early diagnosis and treatment potentially preventing a reduction in the volumes/depths of components of the central olfactory region in the pediatric population.

Peripheric smell regions in patients with temporal and frontal lobe epilepsies: An MRI evaluation

OBJECTIVES

We investigated peripheric smell regions of olfactory bulb (OB) volume and olfactory sulcus (OS) depth in temporal and frontal lobe epilepsy patients by cranial magnetic resonance imaging (MRI).

METHODS

In this retrospective study, cranial MRI images of 150 adult patients were included. Group 1 was consisted of 50 adult patients with temporal lobe epilepsy (TLE). Group 2 was consisted of 50 adult patients with frontal lobe epilepsy (FLE). The control group (Group 3) was consisted of 50 healthy subjects without epilepsy. OB volume and OS depth were measured in all groups.

RESULTS

OB volumes of the temporal and frontal epilepsy groups were significantly lower than those of the control group (p_adjusted < 0.0175). However, OS depths were not different between groups 1-3 (p > 0.05). In the temporal and frontal epilepsy groups, there were positive correlations between OB volumes; OS depths; left OB volume and bilateral OS depths p < 0.05). There were no significant correlations between OB volume and OS depth; and age and gender of the epilepsy group (p > 0.05).

CONCLUSION

We concluded that temporal and frontal epilepsy maybe related to decrease in OB volume and may cause olfactory impairment. Olfactory deficit maybe related to central epileptic focus. Therefore, early diagnosis and appropriate treatment of epilepsy are important to prevent olfactory impairment.

Formaldehyde and Brain Disorders: A Meta-Analysis and Bioinformatics Approach

While there is significant investigation and investment in brain and neurodegenerative disease research, current understanding of the etiologies of illnesses like Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and brain cancer remains limited. Environmental exposure to the pollutant formaldehyde, an emerging neurotoxin widely used in industry, is suspected to play a critical role in mediating these disorders, although findings are limited and inconsistent. Focusing on highly exposed groups, we performed a meta-analysis of human epidemiological studies of formaldehyde and neurodegenerative disease (N =  19) or brain tumors (N = 12). To assess the biological plausibility of observed associations, we then conducted a bioinformatics analysis using WikiPathways and the Comparative Toxicogenomics Database and identified candidate genes and pathways that may be related to these interactions. We reported the meta-relative risk (meta-RR) of ALS following high exposures to formaldehyde was increased by 78% (meta-RR = 1.78, 95% confidence interval, CI 1.20-2.65). Similarly, the meta-RR for brain cancer was increased by 71% (meta-RR = 1.71; 95% CI 1.07-2.73) among highly exposed individuals. Multiple sensitivity analyses did not reveal sources of heterogeneity or bias. Our bioinformatics analysis revealed that the oxidative stress genes superoxide dismutase (SOD1, SOD2) and the pro-inflammatory marker tumor necrosis factor (TNF) were identified as the top relevant genes, and the folate metabolism, vitamin B12 metabolism, and the ALS pathways were highly affected by formaldehyde and related to the most brain diseases of interest. Further inquiry revealed the two metabolic pathways are also intimately tied with the formaldehyde cycle. Overall, our bioinformatics analysis supports the link of formaldehyde exposure to ALS or brain tumor reported from our meta-analysis. This new multifactorial approach enabled us to both interrogate the robustness of the epidemiological data and identify genes and pathways that may be involved in these interactions, ultimately lending strong evidence and potential biological plausibility for the association between formaldehyde exposure and brain disease.

Comparison of Noninvasive Imagery Methods to Observe Healthy and Degenerated Olfactory Epithelium in Mice for the Early Diagnosis of Neurodegenerative Diseases

Olfactory dysfunction could be an early and reliable indicator for the diagnosis of neurodegenerative disorders such as Alzheimer and Parkinson's diseases. In this paper, we compare the potential of different noninvasive medical imaging modalities (optical coherence tomography, confocal microscopy, and fluorescence endomicroscopy) to distinguish how the olfactory epithelium, both at the cellular and the structural levels, is altered. Investigations were carried out on three experimental groups: two pathological groups (mice models with deliberately altered olfactory epithelium and Alzheimer's disease transgenic mice models) were compared with healthy mice models. As histological staining, the three tested noninvasive imaging tools demonstrated the general tubular organization of the olfactory epithelium on healthy mice. Contrary to OCT, confocal microscopy, and endomicroscopy allowed visualizing the inner structure of olfactory epithelium as well as its morphological or functional changes on pathological models, alterations classically observed with histological assessment. The results could lead to relevant development of imaging tools for noninvasive and early diagnosis of neurodegenerative diseases through the in situ characterization of the olfactory epithelium.

The human olfactory system in two proteinopathies: Alzheimer's and Parkinson's diseases

Alzheimer's and Parkinson's diseases are the most prevalent neurodegenerative disorders. Their etiologies are idiopathic, and treatments are symptomatic and orientated towards cognitive or motor deficits. Neuropathologically, both are proteinopathies with pathological aggregates (plaques of amyloid-β peptide and neurofibrillary tangles of tau protein in Alzheimer's disease, and Lewy bodies mostly composed of α-synuclein in Parkinson's disease). These deposits appear in the nervous system in a predictable and accumulative sequence with six neuropathological stages. Both disorders present a long prodromal period, characterized by preclinical signs including hyposmia. Interestingly, the olfactory system, particularly the anterior olfactory nucleus, is initially and preferentially affected by the pathology. Cerebral atrophy revealed by magnetic resonance imaging must be complemented by histological analyses to ascertain whether neuronal and/or glial loss or neuropil remodeling are responsible for volumetric changes. It has been proposed that these proteinopathies could act in a prion-like manner in which a misfolded protein would be able to force native proteins into pathogenic folding (seeding), which then propagates through neurons and glia (spreading). Existing data have been examined to establish why some neuronal populations are vulnerable while others are resistant to pathology and to what extent glia prevent and/or facilitate proteinopathy spreading. Connectomic approaches reveal a number of hubs in the olfactory system (anterior olfactory nucleus, olfactory entorhinal cortex and cortical amygdala) that are key interconnectors with the main hubs (the entorhinal-hippocampal-cortical and amygdala-dorsal motor vagal nucleus) of network dysfunction in Alzheimer's and Parkinson's diseases.

Sustentacular Cell Enwrapment of Olfactory Receptor Neuronal Dendrites: An Update

The pseudostratified olfactory epithelium (OE) may histologically appear relatively simple, but the cytological relations among its cell types, especially those between olfactory receptor neurons (ORNs) and olfactory sustentacular cells (OSCs), prove more complex and variable than previously believed. Adding to the complexity is the short lifespan, persistent neurogenesis, and continuous rewiring of the ORNs. Contrary to the common belief that ORN dendrites are mostly positioned between OSCs, recent findings indicate a sustentacular cell enwrapped configuration for a majority of mature ORN dendrites at the superficial layer of the OE. After vertically sprouting out from the borderlines between OSCs, most of the immature ORN dendrites undergo a process of sideways migration and terminal maturation to become completely invaginated into and enwrapped by OSCs. Trailing the course of the dendritic sideways migration is the mesodendrite (mesentery of the enwrapped dendrite) made of closely apposed, cell junction connected plasma membrane layers of neighboring folds of the host sustentacular cell. Only a minority of the mature ORN dendrites at the OE apical surface are found at the borderlines between OSCs (unwrapped). Below I give a brief update on the cytoarchitectonic relations between the ORNs and OSCs of the OE. Emphasis is placed on the enwrapment of ORN dendrites by OSCs, on the sideways migration of immature ORN dendrites after emerging from the OE surface, and on the terminal maturation of the ORNs. Functional implications of ORN dendrite enwrapment and a comparison with myelination or Remak’s bundling of axons or axodendrites in the central and peripheral nervous system are also discussed.

Increased densities of white matter neurons as a cross-disease feature of neuropsychiatric disorders

While neurons of the human cerebral cortex are mainly distributed in the gray matter, the white matter (WM) also contains some excitatory and inhibitory neurons, so-called WM neurons. Studies on the cytoarchitectural alterations in the brains of patients with neuropsychiatric disorders have repeatedly reported increased densities of the WM neurons in a proportion of patients with schizophrenia and autism spectrum disorder. Although some studies have demonstrated increased densities of superficial WM neurons, others have demonstrated increased densities of deep WM neurons and increased WM neuron densities can be considered as one of the cross-disease features of neuropsychiatric disorders. Nevertheless, what actually causes the increase in the densities of the WM neurons still remains under debate, and several hypothetical mechanisms have been proposed. The WM neurons in normal brains are considered as remnants of the subplate neurons, which represent a transient cytoarchitectural zone present during development of the mammalian neocortex; it has been suggested that increased densities of the WM neurons could result from inappropriate apoptosis of the subplate neurons in the brains of patients with neuropsychiatric disorders. On the other hand, recent experimental studies have demonstrated that genetic and environmental factors that enhance the risk of development of neuropsychiatric disorders could cause altered distribution of neurons in the WM. To understand the pathophysiology underlying the increased densities of the WM neurons, it is important to investigate the cellular characteristics of the WM neurons in the brains of both normal subjects and patients with neuropsychiatric disorders.

Evaluation of the methoxy-X04 derivative BSC4090 for diagnosis of prodromal and early Alzheimer's disease from bioptic olfactory mucosa

Alzheimer's disease (AD) pathology precedes the onset of clinical symptoms by several decades. Thus, biomarkers are required to identify prodromal disease stages to allow for the early and effective treatment. The methoxy-X04-derivative BSC4090 is a fluorescent ligand which was designed to target neurofibrillary tangles in AD. BSC4090 staining was previously detected in post-mortem brains and olfactory mucosa derived from AD patients. We tested BSC4090 as a potential diagnostic marker of prodromal and early AD using olfactory mucosa biopsies from 12 individuals with AD, 13 with mild cognitive impairment (MCI), and 10 cognitively normal (CN) controls. Receiver-operating curve analysis revealed areas under the curve of 0.78 for AD versus CN and of 0.86 for MCI due to AD versus MCI of other causes. BSC4090 labeling correlated significantly with cerebrospinal fluid levels of tau protein phosphorylated at T181. Using NMR spectroscopy, we find that BSC4090 binds to fibrillar and pre-fibrillar but not to monomeric tau. Thus, BSC4090 may be an interesting candidate to detect AD at the early disease stages.

Potential Use of Exfoliated and Cultured Olfactory Neuronal Precursors for In Vivo Alzheimer's Disease Diagnosis: A Pilot Study

Histopathological hallmarks of dementia have been described postmortem in the brain of patients with Alzheimer's disease (AD). Tau, a microtubule associated protein, is abnormally arranged in neurofibrillary tangles. In living AD patients, total tau (t-tau) and hyperphosphorylated tau (p-tau) levels are increased in the cerebrospinal fluid obtained by lumbar puncture. Herein, we studied the t-tau and p-tau levels as well as the subcellular distribution of t-tau in olfactory neuronal precursors obtained by exfoliation of the nasal cavity of AD patients and control participants. Data showed that t-tau and p-tau levels were increased in cell homogenates from AD patients. Also, t-tau immunoreactivity was arranged in a punctate pattern in olfactory neuronal precursors derived from an AD participant with 5 years of evolution and in the oldest participants, either control subjects or those with Alzheimer's disease. Results support that exfoliated neuronal precursors have tau alterations demonstrated in postmortem brain and in the cerebrospinal fluid. This evidence and because the obtainment of olfactory neuronal precursors is a noninvasive procedure, detection of tau alterations shown here might be useful for an early diagnosis of AD-type dementia.

Anatomy of the olfactory mucosa

The classic notion that humans are microsmatic animals was born from comparative anatomy studies showing the reduction in the size of both the olfactory bulbs and the limbic brain relative to the whole brain. However, the human olfactory system contains a number of neurons comparable to that of most other mammals, and humans have exquisite olfactory abilities. Major advances in molecular and genetic research have resulted in the identification of extremely large gene families that express receptors for sensing odors. Such advances have led to a renaissance of studies focused on both human and nonhuman aspects of olfactory physiology and function. Evidence that olfactory dysfunction is among the earliest signs of a number of neurodegenerative and neuropsychiatric disorders has led to considerable interest in the use of olfactory epithelial biopsies for potentially identifying such disorders. Moreover, the unique features of the olfactory ensheathing cells have made the olfactory mucosa a promising and unexpected source of cells for treating spinal cord injuries and other neural injuries in which cell guidance is critical. The olfactory system of humans and other primates differs in many ways from that of other species. In this chapter we provide an overview of the anatomy of not only the human olfactory mucosa but of mucosae from a range of mammals from which more detailed information is available. Basic information regarding the general organization of the olfactory mucosa, including its receptor cells and the large number of other cell types critical for their maintenance and function, is provided. Cross-species comparisons are made when appropriate. The polemic issue of the human vomeronasal organ in both the adult and fetus is discussed, along with recent findings regarding olfactory subsystems within the nose of a number of mammals (e.g., the septal organ and Grüneberg ganglion).

Is Olfactory Epithelium Biopsy Useful for Confirming Alzheimer's Disease?

OBJECTIVES

The clinical symptoms of Alzheimer's disease (AD) are preceded by a long asymptomatic period associated with "silent" deposition of aberrant paired helical filament (PHF)-tau and amyloid-beta proteins in brain tissue. Similar depositions have been reported within the olfactory epithelium (OE), a tissue that can be biopsied in vivo. The degree to which such biopsies are useful in identifying AD is controversial. This postmortem study had 3 main goals: first, to quantify the relative densities of AD-related proteins in 3 regions of the olfactory neuroepithelium, namely, the nasal septum, middle turbinate, and superior turbinate; second, to establish whether such densities are correlated among these epithelial regions as well as with semi-quantitative ratings of general brain cortex pathology; and third, to evaluate correlations between the protein densities and measures of antemortem cognitive function.

METHODS

Postmortem blocks of olfactory mucosa were obtained from 12 AD cadavers and 24 controls and subjected to amyloid-beta and PHF-tau immunohistochemistry.

RESULTS

We observed marked heterogeneity in the presence of the biomarkers of tau and amyloid-beta among the targeted olfactory epithelial regions. No significant difference was observed between the cadavers with AD and the controls regarding the concentration of these proteins in any of these epithelial regions. Only one correlation significant was evident, namely, that between the tau protein densities of the middle and the upper turbinate (r = .58, P = .002).

CONCLUSION

AD-related biomarker heterogeneity, which has not been previously demonstrated, makes comparisons across studies difficult and throws into question the usefulness of OE amyloid-beta and PHF-tau biopsies in detecting AD.

The olfactory bulb as the entry site for prion-like propagation in neurodegenerative diseases

Olfactory deficits are present in numerous neurodegenerative disorders and are accompanied by pathology in related brain regions. In several of these disorders, olfactory disturbances appear early and are considered as prodromal symptoms of the disease. In addition, pathological protein aggregates affect olfactory regions prior to other regions, suggesting that the olfactory system might be particularly vulnerable to neurodegenerative diseases. Exposed to the external environment, the olfactory epithelium and olfactory bulb allow pathogen and toxin penetration into the brain, a process that has been proposed to play a role in neurodegenerative diseases. Determining whether the olfactory bulb could be a starting point of pathology and of pathology spread is crucial to understanding how neurodegenerative diseases evolve. We argue that pathological changes following environmental insults contribute to the initiation of protein aggregation in the olfactory bulb, which then triggers the spread of the pathology within the brain by a templating mechanism in a prion-like manner. We review the evidence for the early involvement of olfactory structures in neurodegenerative diseases and the relationship between neuropathology and olfactory function. We discuss the vulnerability and putative underlying mechanisms by which pathology could be initiated in the olfactory bulb, from the entry of pathogens (promoted by increased permeability of the olfactory epithelium with aging or inflammation) to the sensitivity of the olfactory system to oxidative stress and inflammation. Finally, we review changes in protein expression and neural excitability triggered by pathogenic proteins that can promote pathogenesis in the olfactory bulb and beyond.

Olfactory dysfunction in the APP/PS1 transgenic mouse model of Alzheimer's disease: Morphological evaluations from the nose to the brain

Olfactory dysfunction is among the signs of Alzheimer's disease (AD) and cognitive impairment. It has been demonstrated Aβ was associated with olfactory impairment observed in both transgenic mice and in AD patients. In this study, we evaluated amyloid deposition in the olfactory circuit of APP/PS1 transgenic mouse model of AD, which showed olfactory dysfunction in olfactory behavior tests. We found amyloid depositions were widely distributed in the whole olfactory circuit. Moreover, we think these amyloid depositions contribute to neuronal atrophy, dendritic abnormalities, synapse loss and axonal degeneration. Therefore, there was a correlation between olfactory deficits and amyloid deposition. Our findings provide initial insights into the pathological basis of AD-related olfactory dysfunction.

Human neural stem/progenitor cells derived from the olfactory epithelium express the TrkB receptor and migrate in response to BDNF

Neurogenesis constitutively occurs in the olfactory epithelium of mammals, including humans. The fact that new neurons in the adult olfactory epithelium derive from resident neural stem/progenitor cells suggests a potential use for these cells in studies of neural diseases, as well as in neuronal cell replacement therapies. In this regard, some studies have proposed that the human olfactory epithelium is a source of neural stem/progenitor cells for autologous transplantation. Although these potential applications are interesting, it is important to understand the cell biology and/or whether human neural stem/progenitor cells in the olfactory epithelium sense external signals, such as brain-derived neurotrophic factor (BDNF), that is also found in other pro-neurogenic microenvironments. BDNF plays a key role in several biological processes, including cell migration. Thus, we characterized human neural stem/progenitor cells derived from the olfactory epithelium (hNS/PCs-OE) and studied their in vitro migratory response to BDNF. In the present study, we determined that hNS/PCs-OE express the protein markers Nestin, Sox2, Ki67 and βIII-tubulin. Moreover, the doubling time of hNS/PCs-OE was approximately 38h. Additionally, we found that hNS/PCs-OE express the BDNF receptor TrkB, and pharmacological approaches showed that the BDNF-induced (40ng/ml) migration of differentiated hNS/PCs-OE was affected by the compound K252a, which prevents TrkB activation. This observation was accompanied by changes in the number of vinculin adhesion contacts. Our results suggest that hNS/PCs-OE exhibit a migratory response to BDNF, accompanied by the turnover of adhesion contacts.

Different patterns of age-related central olfactory decline in men and women as quantified by olfactory fMRI

Age-related olfactory decline, or presbyosmia, is a prevalent condition with potentially devastating consequences on both quality of life and safety. Despite clear evidence for this decline, it is unknown whether presbyosmia is sex-dependent and also whether it is due to central or peripheral olfactory system deterioration. Therefore, the goals of this study were to investigate the neurofunctional substrate of olfactory decline and examine its relationship to age and sex in thirty-seven (18 women, 19 men) healthy older participants using olfactory functional MRI (fMRI). The olfactory fMRI paradigm utilized unique odor+visual and visual-only conditions to contrast peripheral-to-central and central-to-central olfactory processing, respectively. Age was negatively correlated with fMRI activation in olfactory-related regions. Significant aging effects were identifiable in male participants in all target regions. Female participants, however, showed a different pattern of functional decline. Extended unified structural equation modeling (euSEM) analysis revealed that the effective functional connectivity profile was drastically different between male and female participants, with females manifesting a top-down mechanism to offset age-related olfactory activation decline. Our results support the hypotheses that the central olfactory system is involved in age-related olfactory decline, and that resilience to age-related olfactory decline in women may be due to their profuse olfactory network effective connectivity.

Valproic acid ameliorates olfactory dysfunction in APP/PS1 transgenic mice of Alzheimer's disease: Ameliorations from the olfactory epithelium to the olfactory bulb

Olfactory dysfunction is a common and early symptom of many neurodegenerative diseases, particularly of Alzheimer's disease (AD) and mild cognitive impairment, pointing to the progression to dementia. Recent studies have revealed that valproic acid (VPA) has neuroprotective effects in rodent models of AD. In this study, we investigated the effects of VPA on olfactory dysfunction of APP/PS1 double transgenic mouse models of AD. After continuous treatment with a 100mg/kg daily dose of VPA for 3 months, APP/PS1 mice showed improved olfactory performances. In agreement with the behavioral findings, VPA treatment reduced amyloid β (Aβ) burden in the olfactory epithelium (OE) of transgenic mice. And, VPA increased epithelial thickness of the olfactory mucosa through decreased cell apoptosis and increased cell proliferation. In the olfactory bulb (OB), VPA administration also reduced senile plaques and levels of soluble and insoluble Aβ42 peptides. Besides, VPA promoted the increase of mitral cells and decrease of neurofilament immunostaining. In hence, VPA treatment completely improved the olfactory performances and prevented degenerative changes of the OE and OB. Our study raises the possibility of AD diagnosis by OE biopsy. Moreover, VPA may provide a novel therapeutic strategy for the treatment of olfactory dysfunction in AD patients.

Early diagnosis of Alzheimer's disease from elevated olfactory mucosal miR-206 level

MicroRNA-206, which suppresses the expression of brain-derived neurotrophic factor, is known to be elevated in the brains of Alzheimer's disease (AD) patients. We performed intranasal biopsy of the olfactory epithelia of early dementia patients (n = 24) and cognitively healthy controls (n = 9). Patients with significant depression (n = 8) were analyzed separately, as their cognitive impairments were thought to be caused by their depression. Real-time PCR was performed on the biopsied tissues. The relative microRNA-206 level exhibited a 7.8-fold increase (P = 0.004) in the mild cognitive impairment group (CDR 0.5; n = 13) and a 41.5-fold increase (P < 0.001) in the CDR 1 group (n = 11). However, this level was not increased in the depression group, even in those with cognitive decline. Using the optimal cutoff value, the sensitivity/specificity for diagnosing CDR 0.5 and CDR 1 dementia were 87.5%/94.1% and 90.9%/93.3%, respectively. In ROC analysis, the AUCs were 0.942 and 0.976 in the CDR 0.5 and CDR 1 groups, respectively. The olfactory mucosal microRNA-206 level and cognitive assessment scores were significantly correlated in the non-depressed subjects with cognitive impairment. In conclusion, the olfactory mucosal microRNA-206 level can be easily measured, and it can be utilized as an excellent biomarker for the diagnosis of early AD, including mild cognitive impairment.

TDP-43 Pathology Progression Along the Olfactory Pathway as a Possible Substrate for Olfactory Impairment in Amyotrophic Lateral Sclerosis

Odor impairment and its relationship with TAR DNA-binding protein 43 (TDP-43) pathology in patients with amyotrophic lateral sclerosis (ALS) have not been fully elucidated. We performed the odor stick identification test for Japanese (OSIT-J) in 18 ALS patients and in 18 controls. The score was significantly decreased (6.6 ± 2.7) in the patients versus the controls (9.2 ± 2.4) (U = 77.0, p = 0.007). This decrement of the OSIT-J score paralleled the cognitive decline. We then studied samples from a series of 42 postmortem ALS cases. Quantitative analyses demonstrated that TDP-43-positive inclusions were most frequent in the hippocampus and least abundant in the olfactory bulb and were of intermediate density in the primary olfactory cortex. This centrifugal gradient suggests that TDP-43 pathology starts in the hippocampus, spreads into the primary olfactory center, and finally reaches the olfactory bulb. TDP-43, tau, and α-synuclein accumulations appeared to be independent. These observations suggest that impaired odor discrimination in ALS patients may be related to TDP-43-positive lesions affecting predominantly secondary olfactory centers (especially the hippocampus) in contrast to decreased odor sensitivity in Parkinson disease in which α-synuclein pathology mainly involves the peripheral region (i.e., olfactory bulb). We suggest that detectable odor impairments in ALS patients are useful for predicting the presence of TDP-43 pathology in the extramotor system.

Translational potential of olfactory mucosa for the study of neuropsychiatric illness

The olfactory mucosa (OM) is a unique source of regenerative neural tissue that is readily obtainable from living human subjects and thus affords opportunities for the study of psychiatric illnesses. OM tissues can be used, either as ex vivo OM tissue or in vitro OM-derived neural cells, to explore parameters that have been difficult to assess in the brain of living individuals with psychiatric illness. As OM tissues are distinct from brain tissues, an understanding of the neurobiology of the OM is needed to relate findings in these tissues to those of the brain as well as to design and interpret ex vivo or in vitro OM studies. To that end, we discuss the molecular, cellular and functional characteristics of cell types within the olfactory mucosa, describe the organization of the OM and highlight its role in the olfactory neurocircuitry. In addition, we discuss various approaches to in vitro culture of OM-derived cells and their characterization, focusing on the extent to which they reflect the in vivo neurobiology of the OM. Finally, we review studies of ex vivo OM tissues and in vitro OM-derived cells from individuals with psychiatric, neurodegenerative and neurodevelopmental disorders. In particular, we discuss the concordance of this work with postmortem brain studies and highlight possible future approaches, which may offer distinct strengths in comparison to in vitro paradigms based on genomic reprogramming.

Altered subcellular distribution of the 75-kDa DISC1 isoform, cAMP accumulation, and decreased neuronal migration in schizophrenia and bipolar disorder: implications for neurodevelopment

BACKGROUND

DISC1 (Disrupted-In-Schizophrenia-1) is considered a genetic risk factor for schizophrenia (SZ) and bipolar disorder (BD). DISC1 regulates microtubule stability, migration, and cAMP signaling in mammalian cell lines and mouse brain tissue. cAMP is a regulator of microtubule organization and migration in neurons. Aberrant microtubule organization has been observed in olfactory neuronal precursors (ONP) derived from patients with SZ and BD, which suggests involvement of DISC1 and cAMP. However, the biology of DISC1 in the physiopathology of psychiatric conditions remains elusive.

AIMS

Herein, utilizing ONP obtained from SZ, BD patients and healthy subjects, we have studied DISC1 expression, protein levels, and subcellular distribution by qRT-PCR, immunoblotting, subcellular fractionation, and confocal microscopy. Cell migration and cAMP accumulation were assessed by Transwell and PKA competition assays.

RESULTS

We found increased levels of the 75-kDa DISC1 isoform in total cell extracts of ONP from patients with SZ and BD compared with controls. Subcellular distribution showed a significant decrease of cytoplasmic DISC1 concomitant with its augmented levels in transcription sites. Moreover, significant cAMP accumulation and diminished migration were also observed in patients' cells.

CONCLUSION

Alterations of DISC1 levels and its cellular distribution, which negatively modify cAMP homeostasis, microtubule organization, and cell migration, in ONP from patients with SZ and BD, suggest that their presence in early stages of brain development may impact brain maturation and function.

The olfactory system in Alzheimer’s disease: Pathology, pathophysiology and pathway for therapy

Olfaction is frequently mentioned as a “neglected sense”, although the olfactory system has several interesting and unique anatomical and physiological features. Olfactory involvement is present in several degenerative disorders, especially in Alzheimer’s disease (AD). The peripheral and central parts of the olfactory system are damaged even in the early stages of AD, manifesting in profound olfactory deficits. Besides the early pathology, the olfactory system may be involved in the pathogenesis of AD by providing a route of entry for pathological agents still unknown. In contrast to this olfactory vector hypothesis, the olfactory system can be used to deliver therapeutic agents in AD, such as nerve growth factor and insulin, by decreasing the side-effects of the therapy or providing a non-invasive method of delivery.

Olfactory discrimination predicts cognitive decline among community-dwelling older adults

The presence of olfactory dysfunction in individuals at higher risk of Alzheimer's disease has significant diagnostic and screening implications for preventive and ameliorative drug trials. Olfactory threshold, discrimination and identification can be reliably recorded in the early stages of neurodegenerative diseases. The current study has examined the ability of various olfactory functions in predicting cognitive decline in a community-dwelling sample. A group of 308 participants, aged 46-86 years old, were recruited for this study. After 3 years of follow-up, participants were divided into cognitively declined and non-declined groups based on their performance on a neuropsychological battery. Assessment of olfactory functions using the Sniffin' Sticks battery indicated that, contrary to previous findings, olfactory discrimination, but not olfactory identification, significantly predicted subsequent cognitive decline (odds ratio = 0.869; P<0.05; 95% confidence interval = 0.764-0.988). The current study findings confirm previously reported associations between olfactory and cognitive functions, and indicate that impairment in olfactory discrimination can predict future cognitive decline. These findings further our current understanding of the association between cognition and olfaction, and support olfactory assessment in screening those at higher risk of dementia.

The human brain representation of odor identification

Odor identification (OI) tests are increasingly used clinically as biomarkers for Alzheimer's disease and schizophrenia. The aim of this study was to directly compare the neuronal correlates to identified odors vs. nonidentified odors. Seventeen females with normal olfactory function underwent a functional magnetic resonance imaging (fMRI) experiment with postscanning assessment of spontaneous uncued OI. An event-related analysis was performed to compare within-subject activity to spontaneously identified vs. nonidentified odors at the whole brain level, and in anatomic and functional regions of interest (ROIs) in the medial temporal lobe (MTL). Parameter estimate values and blood oxygenated level-dependent (BOLD) signal curves for correctly identified and nonidentified odors were derived from functional ROIs in hippocampus, entorhinal, piriform, and orbitofrontal cortices. Number of activated voxels and max parameter estimate values were obtained from anatomic ROIs in the hippocampus and the entorhinal cortex. At the whole brain level the correct OI gave rise to increased activity in the left entorhinal cortex and secondary olfactory structures, including the orbitofrontal cortex. Increased activation was also observed in fusiform, primary visual, and auditory cortices, inferior frontal plus inferior temporal gyri. The anatomic MTL ROI analysis showed increased activation in the left entorhinal cortex, right hippocampus, and posterior parahippocampal gyri in correct OI. In the entorhinal cortex and hippocampus the BOLD signal increased specifically in response to identified odors and decreased for nonidentified odors. In orbitofrontal and piriform cortices both identified and nonidentified odors gave rise to an increased BOLD signal, but the response to identified odors was significantly greater than that for nonidentified odors. These results support a specific role for entorhinal cortex and hippocampus in OI, whereas piriform and orbitofrontal cortices are active in both smelling and OI. Moreover, episodic as well as semantic memory systems appeared to support OI.

Inducible dopaminergic glutathione depletion in an α-synuclein transgenic mouse model results in age-related olfactory dysfunction

Parkinson's disease (PD) involves both motor and non-motor disturbances. Non-motor features include alterations in sensory olfactory function which may constitute a viable biomarker for the disorder. It is not clear what causes olfactory dysfunction but it appears to coincide with the development of synucleopathy within the olfactory bulb (OB). Elevation in alpha-synuclein (a-syn) is indeed a risk factor for development of the sporadic disorder. The multifactorial nature of the idiopathic disease combined with variability in its presentation suggests that it is likely to be influenced by several factors and that in vivo models that explore the synergistic effect of alpha-synuclein elevation with other potential contributing factors are likely to be of importance in understanding the disease etiology. Using a dual transgenic (DTg) mouse model of dopaminergic alpha-synuclein overexpression coupled with doxycycline (Dox)-inducible glutathione (GSH) depletion in these same cells, we demonstrate an age-related loss in behavioral olfactory function coupled with a significant neurodegeneration of glomerular dopaminergic neurons. This is accompanied by increase in alpha-synuclein levels in non-dopaminergic cells in the granule cell layer (GCL). In addition, isolated olfactory bulb synaptosomes from dual transgenic lines with Dox consistently showed a slight but significant reduction in maximum mitochondrial respiration compared to controls. These results suggest that in the presence of increased oxidative stress, increased alpha-synuclein expression within dopaminergic OB neurons results in neurodegeneration in the glomerular layer (GL) and increased alpha-synuclein levels in the granular cell layer which coincide with olfactory dysfunction.

Negative symptoms of schizophrenia correlate with impairment on the University of Pennsylvania smell identification test

Deficits in odor identification have been most frequently described in schizophrenia (SZ). A relationship between dysfunction in odor identification and negative symptoms of SZ has also been reported. Furthermore, deficit SZ (a subtype of the illness with primary, enduring negative symptoms) has been found to be associated with a particularly poor performance on odor identification tests indicating that deficits in smell identification could be differentially expressed in some subtypes of SZ. We describe correlations of performance on smell identification with positive and negative symptoms of SZ. Patients with SZ (n=15) and normal controls (n=19) were tested by the University of Pennsylvania Smell Identification Test (UPSIT). Psychopathology was assessed with the Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS). SZ patients performed more poorly on the UPSIT test than did normal controls. Consistent with previous findings, we observed a correlation of SANS with UPSIT performance. In particular, specific subdomains of SANS, such as blunted affect, apathy and anhedonia, were associated with odor identification deficits. Furthermore, UPSIT score predicts these subdomains of negative symptoms. No correlation was observed between positive symptom and odor identification deficits. Our study further reinforces a relation between olfactory identification deficit and negative symptoms in SZ and suggests that smell identification could be a candidate endophenotype relevant to negative symptoms of SZ.

MORPHOLOGICAL RECOVERY OF THE GRANULE CELLS FROM THE OLFACTORY BULB AFTER THE CESSATION OF ACUTE OZONE EXPOSURE

The purpose of this study was to analyze the possible morphological recovery of the granule cells in the olfactory bulb as a consequence of oxidative stress after an acute ozone exposure. Rats were divided in two groups: Control (air exposed) and experimental group, exposed 4 h, to 1 ppm ozone and divided into 4 subgroups, which were sacrificed at 2 and 24 h, 10 and 15 days, respectively. Olfactory bulbs were processed with the rapid Golgi method and for transmission electron microscopy. The granule cells of the olfactory bulb disclosed less dendritic spine density at 2, 24 h, and 10 days after the exposure compared with controls. At 15 days, the number of spines increased to values similar to those found in controls. The granule cells ultrastructure demonstrated an increment in lipofucsin granules, as well as swollen organelles, changes that decreased overtime. This change decline might be related to a partial recovery of the associative granule cells function.

Screening for Alzheimer's dementia at age 78 with short psychometric instruments

BACKGROUND

To date, no single instrument has proved to be adequate for screening for Alzheimer's dementia (AD). The aim of this study was to identify a combination of instruments which were highly sensitive for screening late onset AD.

METHODS

Subjects were drawn from the Vienna TransDanube Aging (VITA) study. This is an interdisciplinary, longitudinal community-based cohort study of the 21st and 22nd district of Vienna (Austria). Data refer to the cohort of 478 individuals at age 78 who took part in the first follow-up investigation of the VITA study. The psychometric instruments which were investigated were: the Ten-Point Clock Test, the Human-Figure Drawing Test, a Delayed Selective Reminding Test, Naming, the Trail Making Test-B, and Verbal Fluency. Further instruments were the Pocket Smell Test, and Subjective Memory Complaints. Data were analyzed using logistic regression analyses and cross validation.

RESULTS

A combination of the Delayed Selective Reminding Test and Verbal Fluency was best for screening AD (R2 = 0.38, main model). An area under the ROC curve of 0.829 was reached. This model discriminated between subjects with incident AD and subjects who did not have incident AD with a sensitivity of 91% and a specificity of 56%.

CONCLUSION

The combination of an episodic memory test and a test of verbal fluency was an effective way of screening for AD.

Specific mechanism for blood inflow stimulation in brain area prone to Alzheimer's disease lesions

The present study describes the specific two-stage mechanism that intensifies blood supply to the brain area comprising amygdala, hippocampus, olfactory bulb, entorhinal cortex, and neocortex (AHBC). Cholinergic neurons from the nuclei of basal forebrain induce vasodilatory effect through release of acetylcholine. In physiological aging the efficacy of this neuronal system declines, while intensive formation of amyloidogenic peptides starts. These peptides at low, picomolar concentrations activate alpha7 nicotinic acetylcholine receptors, thus enhancing angiogenesis and in so doing restoring blood supply to the AHBC area.

Neurodevelopmental involvement in schizophrenia: the olfactory epithelium as an alternative model for research

It has been suggested that disturbances during neurodevelopment may play a crucial role in the etiology of schizophrenia (SZ). This premise is supported by brain imaging, epidemiological, and pathological studies as well as the discovery of susceptibility genes for SZ that appear to be implicated in development of the central nervous system. Here, we discuss the limitations of the current methods and models for studying the neurodevelopmental implications in SZ. We agree with the proposal that the olfactory epithelium, in which neurodevelopment continues throughout life, might represent an alternative model for understanding the pathophysiology of the disorder.

A speculative essay on retinoic acid regulation of neural stem cells in the developing and aging olfactory system

Circulating signals like the acidic derivative of vitamin A: retinoic acid (RA) may regulate resident stem cells in the adult nervous system, particularly in the olfactory pathway. RA is an essential factor for inducing neural stem or precursor cells that give rise to olfactory receptor neurons (ORNs) and olfactory bulb (OB) interneurons (OBINs) during embryonic development. Similar precursors in the adult brain constantly generate new ORNs and OBINs, and embryonic signaling pathways, like that via RA, may be retained or reactivated for this purpose. We have shown that RA regulates neural precursors in the embryonic and adult olfactory pathway. Moreover, RA administration after olfactory system damage stimulates an immune response and yields a more rapid recovery of olfactory-guided behavior. We suggest that olfactory integrity may be maintained by RA-mediated regulation of neurogenesis as well as local immune responses, and that aging compromises these mechanisms. The chemical senses, particularly olfaction, decline in aged individuals, and RA (via vitamin A) levels may also decline, perhaps due to changes in appetite and food intake. This synergy may result in a high prevalence of olfactory pathology in aged individuals.

Olfactory bulb volumes in patients with idiopathic Parkinson's disease a pilot study

Olfactory loss is among early signs of idiopathic Parkinson's disease (IPD). The present pilot study aimed to investigate whether this loss would be reflected in a decreased volume of the olfactory bulb (OB) established through magnetic resonance imaging. Eleven consecutive IPD patients were compared to 9 healthy, age-matched controls. Results indicated that there is little or no difference between IPD patients and healthy controls in terms of OB volume. Based upon the relation between loss of olfactory input to the olfactory bulb and consecutive decrease in volume, these data support the idea that olfactory loss in IPD is not a primary consequence of damage to the olfactory epithelium but rather results from central-nervous changes.

Heme oxygenase-1 and heme oxygenase-2 have distinct roles in the proliferation and survival of olfactory receptor neurons mediated by cGMP and bilirubin, respectively

Heme oxygenase (HO) is implicated in protection against oxidative stress, proliferation and apoptosis in many cell types, including neurons. We utilized olfactory receptor neurons (ORNs) as a model to define the roles of HO-1 and HO-2 in neuronal development and survival, and to determine the mediators of these effects. The olfactory system is a useful model as ORNs display neurogenesis post-natally and do not contain nitric oxide synthase (NOS) activity, which could confound results. HO isoforms were expressed in ORNs during embryogenesis and post-natally. Mice null for either HO-1 or HO-2 displayed decreased proliferation of neuronal precursors. However, apoptosis was increased only in HO-2 null mice. Cyclic GMP immunostaining was reduced in ORNs in both genotypes, providing direct evidence that HO mediates cGMP production in vivo. Bilirubin immunostaining was reduced only in HO-2 null mice. These roles for HO-1 and HO-2 were confirmed using detergent ablation of the epithelium to observe increased neurogenesis of ORNs after target disruption in HO null mice. Primary cultures of ORNs revealed that proliferative and survival effects of HO were mediated through cGMP and bilirubin, respectively. These results support a role for HO, the CO-cGMP signaling system and bilirubin in neurodevelopment and in response to injury.

Atypical neuroleptics stimulate neurogenesis in adult rat brain

Schizophrenia has been treated effectively with atypical neuroleptics without serious side effects. We have shown previously that long-term treatment with atypical neuroleptics is correlated with an improvement of cognition in adult rats. We report here that atypical neuroleptics stimulate a 2- to 3-fold increase in newly divided cells in the subventricular zone in the rat and that some of these new cells in the subventricular zone and hippocampus also express a neuronal marker. We used bromodeoxyuridine (BrdU) to identify newly divided cells and confirmed the observation with antibody to a cell-cycle-specific, endogenous proliferating cell nuclear antigen (PCNA). Identification of BrdU-positive cells in the anterior subventricular zone (SVZa) particularly in rats treated with the atypical neuroleptics but not in those in the haloperidol-treated and control rats, suggests increased rostral migratory stream (RMS) cell traffic to replenish neurons in the olfactory bulb. Expression of a neuronal marker, NeuN, in BrdU-positive cells in rats treated with atypical neuroleptics, also suggests that these compounds may modulate in vivo differentiation of neuronal progenitor cells even within a day of BrdU injection. Our results indicate that atypical neuroleptics have a mechanism of action other than the previously proposed mechanisms, which might explain their role in improved cognition in animal and in schizophrenic patients. If substantiated by future studies, our findings may lead to an expanded use of atypical neuroleptics in other neurodegenerative diseases to stimulate neuronal replacement and repair.

Preferential alterations in the mesolimbic dopamine pathway of heterozygous reeler mice: an emerging animal-based model of schizophrenia

Based on a number of neuroanatomical and behavioural similarities, recent evidence suggests that heterozygous reeler mice, haploinsufficient for reelin expression, represent a useful model of psychosis vulnerability. As brain mesolimbic dopamine pathways have been proposed to be associated with the pathophysiology of psychotic disorders, we thought it would be of interest to examine whether these animals present disturbances in the mesolimbic dopamine system. To this end we studied by immunocytochemical, in situ hybridization procedures and receptor autoradiography, several markers of the mesotelencephalic dopamine pathway in heterozygous reeler mice and controls. We report that heterozygous reeler mice exhibit a reduction in the number of tyrosine hydroxylase-immunoreactive cell bodies and tyrosine hydroxylase mRNA levels in the ventral tegmental area, as well as a reduction of tyrosine hydroxylase and dopamine transporter immunoreactivity in the dopamine terminal fields of the limbic striatum. In these areas we also observed a reduction of dopamine D2 receptor mRNA. Finally, a marked increase in D3 receptor mRNA levels was observed concomitant with a significant increase in D3 binding sites. On the contrary, the nigrostriatal pathway did not show any significant alteration in heterozygous reeler mice with regards to the dopaminergic markers examined in substantia nigra cell bodies and dorsal striatum dopamine terminal fields. These results suggest a specific link between reelin-related neuronal pathology and dopamine involvement in the pathophysiology of psychotic disorders.

Neuropathological characterization of mutant amyloid precursor protein yeast artificial chromosome transgenic mice

Mutations in the amyloid precursor protein (APP) gene result in elevated production and deposition of the 42 amino acid beta-amyloid (Abeta1-42) peptide and early-onset Alzheimer's disease (AD). To accurately examine the effect of the APP FAD mutations in vivo, we introduced yeast artificial chromosomes (YACs) containing the entire genomic copy of human APP harboring FAD mutations into transgenic mice. Our current results demonstrate that mutant APP YAC transgenic mice exhibit many features characteristic of human AD, including regional deposition of Abeta with preferential deposition of Abeta1-42, extensive neuritic abnormalities as evidenced by staining with APP, ubiquitin, neurofilament, and hyperphosphorylated tau antibodies, increased markers of inflammation, and the overlapping deposition of Abeta with apolipoproteins E and J. Our results also suggest that APP YAC transgenic mice possess unique pathological attributes when compared to other transgenic mouse models of AD that may reflect the experimental design of each model.

Preventing schizophrenia and Alzheimer disease: comparative ethics

Schizophrenia and Alzheimer disease are both diseases of the brain that involve genetic susceptibility factors and for which the prevention or delay of symptom onset are important research goals. This paper provides some comparisons between current preventive efforts in schizophrenia and Alzheimer disease, focusing on certain ethical features of these endeavors such as potential discrimination, misdiagnosis, and stigma.

Characteristics of odorant elicited calcium changes in cultured human olfactory neurons

An important step in establishing and utilizing a cell culture system for the in vitro study of olfaction is assessing whether the cultured cells possess physiological properties similar to those of mature olfactory neurons. Various investigators have successfully established proliferating cell lines from olfactory tissue, but few have demonstrated the characteristics of odor sensitivity of these cells. We successfully established cultured cell lines from adult human olfactory tissue obtained using an olfactory biopsy procedure and measured their ability to respond to odor stimulation using calcium imaging techniques. A subset of the human olfactory cells in culture displayed a distinct morphology and specifically expressed immunocytochemical markers characteristic of mature human olfactory neurons such as OMP, G(olf), NCAM and NST. Under defined growth conditions, these cultured cells responded to odorant mixes that have been previously shown to elicit intracellular calcium changes in acutely-isolated human olfactory neurons. These odorant-elicited calcium responses displayed characteristics similar to those found in mature human olfactory neurons. First, cultured cells responded with either increases or decreases in intracellular calcium. Second, increases in calcium were abolished by removal of extracellular calcium. Third, inhibitors of the olfactory signal transduction cascades reversibly blocked these odorant-elicited intracellular calcium changes. Our results demonstrate that cultures of adult human olfactory cells established from olfactory biopsies retain some of the in vivo odorant response characteristics of acutely isolated cells from the adult olfactory epithelium. This work has important ramifications for investigation of olfactory function and dysfunction using biopsy procedures and in vitro assays of odor sensitivity.