Tumour necrosis factor alpha and interleukin-5 inhibit olfactory regeneration via apoptosis of olfactory sphere cells in mice models of allergic rhinitis

BACKGROUND

Olfactory dysfunction is frequently experienced by patients with allergic rhinitis. It is thought to result from structural and functional changes occurring in the olfactory mucosa caused by inflammation. However, the current understanding of the pathophysiology of olfactory dysfunction in allergic rhinitis remains unclear.

OBJECTIVE

To investigate the mechanism by which the olfactory neural cells are damaged in allergic rhinitis.

METHODS

Olfactory sphere cells (OSCs) were established after dissociation and serial cultures of cells from the mouse olfactory mucosa. Viability and proliferation of OSCs were compared between control and allergic rhinitis mice models, and olfactory stem cell markers were analysed in vivo. To elucidate which cytokines have an inhibitory effect on OSCs, viability and apoptotic markers of OSCs were investigated.

RESULTS

Olfactory sphere cells were successfully isolated from the olfactory mucosa of mice, and these cells expressed markers of neural stem cells. To investigate the neural differentiation, we performed the immunocytochemical staining and found significantly elevated expressions of Tuji1, GFAP and O4 on OSCs. On the comparison of the characteristics of OSCs between control and allergic rhinitis model, we detected significantly fewer neurospheres, reduced clonogenic capacity and decreased expression of olfactory neural stem cell markers in allergic rhinitis model. When OSCs were treated with several major allergic cytokines were treated on OSCs, only TNF-α showed an inhibitory effect on OSCs. Interestingly, IL-5 had an inhibitory effect on the viability of OSCs in combination with TNF-α, whereas IL-5 alone does not have an effect. Moreover, TNF-α combined with IL-5 significantly increased the apoptotic expression, compared with TNF-α or IL-5 alone. Additionally, allergic rhinitis mice models showed the increased apoptotic expression.

CONCLUSION AND CLINICAL RELEVANCE

Allergic rhinitis mice models showed lower expression of OSCs, and TNF-α combined with IL-5 had an apoptotic effect on OSCs. Therefore, these cytokines may be therapeutic targets for olfactory dysfunction in patients with allergic rhinitis.

Optimal Timing to Utilize Olfactory Stimulation with Maternal Breast Milk to Improve Oral Feeding Skills in the Premature Newborn

Background: Olfactory maturation is essential for successful oral feeding. Previous studies have suggested that olfactory stimulation with maternal breast milk may expedite oral feeding skills in the premature infant; however, the optimal developmental window to utilize this intervention and sex-specific responses to stimuli are largely unknown. Objectives: To determine individual responses to olfactory stimulation with mother's own milk (MOM) on feeding outcomes in premature newborns. Materials and Methods: Infants born between 28 0/7 and 33 6/7 weeks' gestation (n = 36) were randomized to receive either MOM or water (sham) stimulus during the learning process of oral feeding. Clinical and feeding outcomes were recorded. Statistical analyses examined the effect of stimulation with MOM on feeding outcomes stratified for age and sex. Results: Overall, there was no significant difference between sham infants compared with MOM infants in mean postmenstrual age of full oral feeds (sham: 35 5/7 versus MOM 36 0/7; p = 0.37). However, when stratified by gestational age (GA), infants born <31 weeks' gestation who received MOM stimulation learned to feed sooner than controls (p = 0.06), whereas infants born ≥31 weeks' gestation learned to feed later than controls (p = 0.20) with a significant interaction (p = 0.02) between the stimulus (MOM versus sham) and dichotomized GA (<31 versus ≥31 weeks). There were no sex differences in response to olfactory stimulus. Conclusions: Infants born <31 weeks' GA who received MOM stimulation learned to feed sooner than control infants and the impact of MOM is significantly different between infants born before or after 31 weeks GA. These data suggest there may be an optimal time in development to utilize maternal breast milk to expedite oral feeding maturation in the premature newborn.

Genetic variation across the human olfactory receptor repertoire alters odor perception

Humans use a family of more than 400 olfactory receptors (ORs) to detect odors, but there is currently no model that can predict olfactory perception from receptor activity patterns. Genetic variation in human ORs is abundant and alters receptor function, allowing us to examine the relationship between receptor function and perception. We sequenced the OR repertoire in 332 individuals and examined how genetic variation affected 276 olfactory phenotypes, including the perceived intensity and pleasantness of 68 odorants at two concentrations, detection thresholds of three odorants, and general olfactory acuity. Genetic variation in a single OR was frequently associated with changes in odorant perception, and we validated 10 cases in which in vitro OR function correlated with in vivo odorant perception using a functional assay. In 8 of these 10 cases, reduced receptor function was associated with reduced intensity perception. In addition, we used participant genotypes to quantify genetic ancestry and found that, in combination with single OR genotype, age, and gender, we can explain between 10% and 20% of the perceptual variation in 15 olfactory phenotypes, highlighting the importance of single OR genotype, ancestry, and demographic factors in the variation of olfactory perception.

Olfactory language and abstraction across cultures

Olfaction presents a particularly interesting arena to explore abstraction in language. Like other abstract domains, such as time, odours can be difficult to conceptualize. An odour cannot be seen or held, it can be difficult to locate in space, and for most people odours are difficult to verbalize. On the other hand, odours give rise to primary sensory experiences. Every time we inhale we are using olfaction to make sense of our environment. We present new experimental data from 30 Jahai hunter-gatherers from the Malay Peninsula and 30 matched Dutch participants from the Netherlands in an odour naming experiment. Participants smelled monomolecular odorants and named odours while reaction times, odour descriptors and facial expressions were measured. We show that while Dutch speakers relied on concrete descriptors, i.e. they referred to odour sources (e.g. smells like lemon), the Jahai used abstract vocabulary to name the same odours (e.g. musty). Despite this differential linguistic categorization, analysis of facial expressions showed that the two groups, nevertheless, had the same initial emotional reactions to odours. Critically, these cross-cultural data present a challenge for how to think about abstraction in language.

This article is part of the theme issue ‘Varieties of abstract concepts: development, use and representation in the brain’.

A Functional Agonist of Insect Olfactory Receptors: Behavior, Physiology and Structure

Chemical signaling is ubiquitous and employs a variety of receptor types to detect the cacophony of molecules relevant for each living organism. Insects, our most diverse taxon, have evolved unique olfactory receptors with as little as 10% sequence identity between receptor types. We have identified a promiscuous volatile, 2-methyltetrahydro-3-furanone (coffee furanone), that elicits chemosensory and behavioral activity across multiple insect orders and receptors. In vivo and in vitro physiology showed that coffee furanone was detected by roughly 80% of the recorded neurons expressing the insect-specific olfactory receptor complex in the antenna of Drosophila melanogaster, at concentrations similar to other known, and less promiscuous, ligands. Neurons expressing specialized receptors, other chemoreceptor types, or mutants lacking the complex entirely did not respond to this compound. This indicates that coffee furanone is a promiscuous ligand for the insect olfactory receptor complex itself and did not induce non-specific cellular responses. In addition, we present homology modeling and docking studies with selected olfactory receptors that suggest conserved interaction regions for both coffee furanone and known ligands. Apart from its physiological activity, this known food additive elicits a behavioral response for several insects, including mosquitoes, flies, and cockroaches. A broad-scale behaviorally active molecule non-toxic to humans thus has significant implications for health and agriculture. Coffee furanone serves as a unique tool to unlock molecular, physiological, and behavioral relationships across this diverse receptor family and animal taxa.

Effect of Maternal Obesity and Preconceptional Weight Loss on Male and Female Offspring Metabolism and Olfactory Performance in Mice

According to the “developmental origins of health and disease” (DOHaD) concept, maternal obesity predisposes the offspring to non-communicable diseases in adulthood. While a preconceptional weight loss (WL) is recommended for obese women, its benefits on the offspring have been poorly addressed. We evaluated whether preconceptional WL was able to reverse the adverse effects of maternal obesity in a mouse model, exhibiting a modification of foetal growth and of the expression of genes encoding epigenetic modifiers in liver and placenta. We tracked metabolic and olfactory behavioural trajectories of offspring born to control, obese or WL mothers. After weaning, the offspring were either put on a control diet (CD) or a high-fat (HFD). After only few weeks of HFD, the offspring developed obesity, metabolic alterations and olfactory impairments, independently of maternal context. However, male offspring born to obese mother gained even more weight under HFD than their counterparts born to lean mothers. Preconceptional WL normalized the offspring metabolic phenotypes but had unexpected effects on olfactory performance: a reduction in olfactory sensitivity, along with a lack of fasting-induced, olfactory-based motivation. Our results confirm the benefits of maternal preconceptional WL for male offspring metabolic health but highlight some possible adverse outcomes on olfactory-based behaviours.

Aedes aegypti Mosquitoes Use Their Legs to Sense DEET on Contact

DEET (N, N-diethyl-meta-toluamide) is the most effective and widely used insect repellent, but its mechanism of action is both complex and controversial [1]. DEET acts on insect smell [2-6] and taste [7-11], and its olfactory mode of action requires the odorant co-receptor orco [2, 3, 6]. We previously observed that orco mutant female Aedes aegypti mosquitoes are strongly attracted to humans even in the presence of DEET, but they are rapidly repelled after contacting DEET-treated skin [6]. DEET inhibits food ingestion by Drosophila melanogaster flies, and this repellency is mediated by bitter taste neurons in the proboscis [9]. Similar neurons were identified in the mosquito proboscis, leading to the hypothesis that DEET repels on contact by activating an aversive bitter taste pathway [10]. To understand the basis of DEET contact chemorepellency, we carried out behavioral experiments and discovered that DEET acts by three distinct mechanisms: smell, ingestion, and contact. Like bitter tastants, DEET is a feeding deterrent when ingested, but its bitterness per se does not fully explain DEET contact chemorepellency. Mosquitoes blood fed on human arms treated with high concentrations of bitters, but rapidly avoided DEET-treated skin and did not blood feed. Insects detect tastants both through their proboscis and legs. We show that DEET contact chemorepellency is mediated exclusively by the tarsal segments of the legs and not the proboscis. This work establishes mosquito legs as the behaviorally relevant contact sensors of DEET. These results will inform the search for molecular mechanisms mediating DEET contact chemorepellency and novel contact-based insect repellents.

Competitive binding predicts nonlinear responses of olfactory receptors to complex mixtures

In color vision, the quantitative rules for mixing lights to make a target color are well understood. By contrast, the rules for mixing odorants to make a target odor remain elusive. A solution to this problem in vision relied on characterizing receptor responses to different wavelengths of light and subsequently relating these responses to perception. In olfaction, experimentally measuring receptor responses to a representative set of complex mixtures is intractable due to the vast number of possibilities. To meet this challenge, we develop a biophysical model that predicts mammalian receptor responses to complex mixtures using responses to single odorants. The dominant nonlinearity in our model is competitive binding (CB): Only one odorant molecule can attach to a receptor binding site at a time. This simple framework predicts receptor responses to mixtures of up to 12 monomolecular odorants to within 15% of experimental observations and provides a powerful method for leveraging limited experimental data. Simple extensions of our model describe phenomena such as synergy, overshadowing, and inhibition. We demonstrate that the presence of such interactions can be identified via systematic deviations from the competitive-binding model.

Purinergic Signaling in the Vertebrate Olfactory System

Adenosine 5'-triphosphate (ATP) is an ubiquitous co-transmitter in the vertebrate brain. ATP itself, as well as its breakdown products ADP and adenosine are involved in synaptic transmission and plasticity, neuron-glia communication and neural development. Although purinoceptors have been demonstrated in the vertebrate olfactory system by means of histological techniques for many years, detailed insights into physiological properties and functional significance of purinergic signaling in olfaction have been published only recently. We review the current literature on purinergic neuromodulation, neuron-glia interactions and neurogenesis in the vertebrate olfactory system.

Somatostatin Serves a Modulatory Role in the Mouse Olfactory Bulb: Neuroanatomical and Behavioral Evidence

Somatostatin (SOM) and somatostatin receptors (SSTR1-4) are present in all olfactory structures, including the olfactory bulb (OB), where SOM modulates physiological gamma rhythms and olfactory discrimination responses. In this work, histological, viral tracing and transgenic approaches were used to characterize SOM cellular targets in the murine OB. We demonstrate that SOM targets all levels of mitral dendritic processes in the OB with somatostatin receptor 2 (SSTR2) detected in the dendrites of previously uncharacterized mitral-like cells. We show that inhibitory interneurons of the glomerular layer (GL) express SSTR4 while SSTR3 is confined to the granule cell layer (GCL). Furthermore, SOM cells in the OB receive synaptic inputs from olfactory cortical afferents. Behavioral studies demonstrate that genetic deletion of SSTR4, SSTR2 or SOM differentially affects olfactory performance. SOM or SSTR4 deletion have no major effect on olfactory behavioral performances while SSTR2 deletion impacts olfactory detection and discrimination behaviors. Altogether, these results describe novel anatomical and behavioral contributions of SOM, SSTR2 and SSTR4 receptors in olfactory processing.

Chemosensory Event-Related Potentials in Response to Nasal Propylene Glycol Stimulation

Propylene glycol, also denoted as 1.2 propanediol (C₃H₈O₂), often serves as a solvent for dilution of olfactory stimuli. It is supposed to serve as a neutral substance and has been used in many behavioral and electrophysiological studies to dilute pure olfactory stimuli. However, the effect of propylene glycol on perception and on neuronal responses has hitherto never been studied. In this study we tested by means of a threshold test, whether a nasal propylene glycol stimulation is recognizable by humans. Participants were able to recognize propylene glycol at a threshold of 42% concentration and reported a slight cooling effect. In addition to the threshold test, we recorded electroencephalography (EEG) during nasal propylene glycol stimulation to study the neuronal processing of the stimulus. We used a flow olfactometer and stimulated 15 volunteers with three different concentrations of propylene glycol (40 trials each) and water as a control condition (40 trials). To evaluate the neuronal response, we analyzed the event-related potentials (ERPs) and power modulations. The task of the volunteers was to identify a change (olfactory, thermal, or tactile) in the continuous air flow generated by the flow olfactometer. The analysis of the ERPs showed that propylene glycol generates a clear P2 component, which was also visible in the frequency domain as an evoked power response in the theta-band. The source analysis of the P2 revealed a widespread involvement of brain regions, including the postcentral gyrus, the insula and adjacent operculum, the thalamus, and the cerebellum. Thus, it is possible that trigeminal stimulation can at least partly account for sensations and brain responses elicited by propylene glycol. Based on these results, we conclude that the use of high propylene glycol concentrations to dilute fragrances complicates the interpretation of presumed purely olfactory effects.

Dysfunction of the to in Anorexia and Bulimia Nervosa: A fMRI

Brain reward dysfunction in eating disorders has been widely reported. However, whether the neural correlates of hedonic and motivational experiences related to food cues are differentially affected in anorexia nervosa of restrictive type (ANr), bulimia nervosa (BN), and healthy control (HC) participants remains unknown. Here, 39 women (14 ANr, 13 BN, and 12 HC) underwent fMRI while smelling food or non-food odors in hunger and satiety states during liking and wanting tasks. ANr and BN patients reported less desire to eat odor-cued food and odor-cued high energy-density food (EDF), respectively. ANr patients exhibited lower ventral tegmental area (VTA) activation than BN patients to food odors when rating their desire to eat, suggesting altered incentive salience attribution to food odors. Compared with HC participants, BN patients exhibited decreased activation of the caudate nucleus to food odors in the hunger state during the wanting task. Both patient groups also showed reduced activation of the anterior ventral pallidum and insula in response to high EDF odors in the hunger state during the wanting task. These findings indicate that brain activation within the food reward-regulating circuit differentiates the three groups. ANr patients further exhibited lower activation of the precuneus than other participants, suggesting a possible role of body image distortion in ANr. Our study highlights that food odors are relevant sensory probes to gain better insight into the dysfunction of the mesolimbic and striatal circuitry involved in food reward processing in patients with EDs.

Identification of odors, faces, cities and naming of objects in patients with subjective cognitive decline, mild cognitive impairment and Alzheimer´s disease: a longitudinal study

ABSTRACTObjective:Recent studies have tried to find a reliable way of predicting the development of Alzheimer´s Disease (AD) among patients with mild cognitive impairment (MCI), often focusing on olfactory dysfunction or semantic memory. Our study aimed to validate these findings while also comparing the predictive accuracy of olfactory and semantic assessments for this purpose.

METHOD

Six hundred fifty patients (median age 68, 58% females) including controls, SCD (subjective cognitive decline), non-amnestic MCI (naMCI), amnestic MCI (aMCI), and AD patients were tested for olfactory dysfunction by means of odor identification testing and semantic memory. Of those 650 patients, 120 participants with SCD, naMCI, or aMCI at baseline underwent a follow-up examination after two years on average. Of these 120 patients, 12% had developed AD at follow-up (converters), while 88% did not develop AD at follow-up (non-converters).

RESULTS

Analysis showed a significant difference only for initial olfactory identification between converters and non-converters. Sensitivity of impairment of olfactory identification for AD prediction was low at 46.2%, although specificity was high at 81.9%. Semantic memory impairment at baseline was not significantly related to AD conversion, although, when naming objects, significant differences were found between AD patients and all other groups and between naMCI and aMCI patients compared to controls and SCD patients.

CONCLUSIONS

Objective olfactory assessments are promising instruments for predicting the conversion to AD among MCI patients. However, due to their low sensitivity and high specificity, a combination with other neuropsychological tests might lead to an improved predictive accuracy. Further longitudinal studies with more participants are required to investigate the usefulness of semantic memory tests in this case.

Predatory lizards perceive plant-derived volatile odorants

Many lizards are olfactory foragers and prey upon herbivorous arthropods, yet their responses to common herbivore-associated plant volatiles remain unknown. As such, their role in mediating plant indirect defenses also remains largely obscured. In this paper, we use a cotton-swab odor presentation assay to ask whether lizards respond to two arthropod-associated plant-derived volatile compounds: 2-(E)-hexenal and hexanoic acid. We studied the response of two lizard species, Sceloporus virgatusand Aspidoscelis exsanguis, because they differ substantially in their foraging behavior. We found that the actively foraging A. exsanguisresponded strongly to hexanoic acid, whereas the ambush foraging S. virgatus responded to 2-(E)-hexenal-an herbivore-associated plant volatile involved in indirect defense against herbivores. These findings indicate that S. virgatus may contribute to plant indirect defense and that a species' response to specific odorants is linked with foraging mode. Future studies can elucidate how lizards use various compounds to locate prey and how these responses impact plant-herbivore interactions.

The effect of odor exposure time on olfactory cognitive processing: An ERP study

The present study aimed to investigate the effects of stimulus time duration on central nervous odor processing. Twenty-one young healthy males participate in our study. There are three odor mixtures in this study and every odor mixture has two different duration time (300 ms; 500 ms). The odor was presented via a computer - controlled olfactometer and EEG was recorded from 64 scalp locations. At behavioral level, the longer the odor stimulus was presented, the greater the concentration was perceived by participants. Electrophysiological data showed that longer duration time lengthened the latency of Negative waves of about 200 ms appeared in stimulation (N2) and Positive waves of about 300 ms appeared in stimulation (P3) components, besides, have a larger N2 amplitude than the shorter duration time condition in the mid-frontal and left frontal-temporal areas. These results revealed that duration time of odor mixture do have an influence on the central nervous odor processing.

Aedes aegypti Mosquitoes Detect Acidic Volatiles Found in Human Odor Using the IR8a Pathway

Mosquitoes use olfaction as a primary means of detecting their hosts. Previously, the functional ablation of a family of Aedes aegypti olfactory receptors, the odorant receptors (ORs), was not sufficient to reduce host seeking in the presence of carbon dioxide (CO₂). This suggests the olfactory receptors that remain, such as the ionotropic receptors (IRs), could play a significant role in host detection. To test this, we disrupted the Ir8a co-receptor in Ae. aegypti using CRISPR/Cas9. We found that Ir8a mutant female mosquitoes are not attracted to lactic acid, a behaviorally active component of human sweat, and they lack odor-evoked responses to acidic volatiles. The loss of Ir8a reduces mosquito attraction to humans and their odor. We show that the CO₂-detection pathway is necessary but not sufficient for IR8a to detect human odor. Our study reveals that the IR8a pathway is crucial for an anthropophilic vector mosquito to effectively seek hosts. VIDEO ABSTRACT.

A Scalable, Multiplexed Assay for Decoding GPCR-Ligand Interactions with RNA Sequencing

G protein-coupled receptors (GPCRs) are central to how mammalian cells sense and respond to chemicals. Mammalian olfactory receptors (ORs), the largest family of GPCRs, mediate the sense of smell through activation by small molecules, though for most bonafide ligands, they have not been identified. Here, we introduce a platform to screen large chemical panels against multiplexed GPCR libraries using next-generation sequencing of barcoded genetic reporters in stably engineered human cell lines. We mapped 39 mammalian ORs against 181 odorants and identified 79 interactions that have not been reported to our knowledge, including ligands for 15 previously orphaned receptors. This multiplexed receptor assay allows the cost-effective mapping of large chemical libraries to receptor repertoires at scale.

Phantom odor perception and vascular conditions among adults in the United States: National Health and Nutrition Examination Survey 2011-2014

OBJECTIVES/HYPOTHESIS

Phantom odor perception has been correlated with burden of vascular risk among older adults. We evaluated associations between vascular conditions and phantom odor perception among adults in the United States.

STUDY DESIGN

Cross-sectional analysis.

METHODS

Cross-sectional data were collected as part of the 2011 to 2014 National Health and Nutrition Examination Survey, yielding a nationally representative sample of 7,417 adults aged 40 years and older. Phantom odor perception was defined as report of an unpleasant, bad, or burning odor when nothing is there. Participants reported on vascular conditions including history of stroke. Total cholesterol and glycated hemoglobinwere measured. High blood pressure was ascertained during an examination.

RESULTS

Stroke was associated with a 76% greater likelihood of phantom odor perception. Congestive heart failure and angina were associated with three times and 2.8 times the odds of phantom odor perception among adults 40 to 59 years and 60 years and older, respectively. Adults with diagnosed, but controlled, high cholesterol reported phantom odors more frequently than those without high cholesterol. Adults with diagnosed, but controlled, high blood pressure reported phantom odors more frequently than those without high blood pressure. We observed a threefold greater odds of phantom odor perception among adults aged 60 years and older with diabetes, but only among those who use both insulin and oral medications.

CONCLUSIONS

Stroke, angina, congestive heart failure, well-managed high blood pressure, and well-managed high cholesterol are associated with phantom odor perception. Vascular or metabolic conditions or their treatments may contribute to reporting of phantom odor perception.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:332-337, 2020.

The Impact of Acoustic fMRI-Noise on Olfactory Sensitivity and Perception

Sensory perception is neither static nor simple. The senses influence each other during multisensory stimulation and can be both suppressive and super-additive. As most knowledge of human olfactory perception is derived from functional neuroimaging studies, in particular fMRI, our current understanding of olfactory perception has systematically been investigated in an environment with concurrent loud sounds. To date, the confounding effects of acoustic fMRI-noise during scanning on olfactory perception have not yet been investigated. In this study we investigate how acoustic noise derived from the rapid switching of MR gradient coils, affects olfactory perception. For this, 50 subjects were tested in both a silent setting and an fMRI-noise setting, in a randomised order. We found that fMRI-related acoustic noise had a significant negative effect on the olfactory detection threshold score. No significant effects were identified on olfactory discrimination, identification, identification certainty, hedonic rating, or intensity rating.

A Novel Olfactometer for Efficient and Flexible Odorant Delivery

Understanding how sensory space maps to neural activity in the olfactory system requires efficiently and flexibly delivering numerous odorants within single experimental preparations. Such delivery is difficult with current olfactometer designs, which typically include limited numbers of stimulus channels and are subject to intertrial and interchannel contamination of odorants. Here, we present a novel olfactometer design that is easily constructed, modular, and capable of delivering an unlimited number of odorants in air with temporal precision and no detectable intertrial or interchannel contamination. The olfactometer further allows for the flexible generation of odorant mixtures and flexible timing of odorant sequences. Odorant delivery from the olfactometer is turbulent but reliable from trial to trial, supporting operant conditioning of mice in an odorant discrimination task and permitting odorants and concentrations to be mapped to neural activity with a level of precision equivalent to that obtained with a flow dilution olfactometer. This novel design thus provides several unique advantages for interrogating olfactory perception and for mapping sensory space to neural activity in the olfactory system.

Transcriptional Basis of Copper-Induced Olfactory Impairment in the Sea Lamprey, a Primitive Invasive Fish

Olfaction mediates behaviors necessary for survival and reproduction in fishes. Anthropogenic inputs of contaminants into aquatic environments, specifically copper, are known to disrupt a broad range of olfactory-mediated behaviors and can cause long-lasting damage even at low concentrations that have profound impacts on the biology of aquatic organisms. The sea lamprey (Petromyzon marinus) is a primitive fish species invasive to the North American Great Lakes that relies on olfaction to navigate during natal homing and in mate choice during reproduction. To investigate effects of copper on sea lamprey olfaction and the potential for maintenance of olfactory function during copper exposure, we exposed juvenile sea lamprey to environmentally ecologically relevant copper concentrations (0, 5, 10 and 30 µg/L) for 24 hr and characterized gene transcription response in olfactory tissue (i.e., peripheral olfactory organ and olfactory bulb) and forebrain using whole transcriptome sequencing. Copper exposure induced a pattern of positive dose-dependent transcriptional response. Expression changes primarily reflected up-regulation of genes involved in apoptosis and wound healing. Unlike higher vertebrates, genes specifically related to the olfactory senses of the sea lamprey, e.g., olfactory receptors, exhibited little transcriptional response to copper exposure, suggesting the mechanism of copper-induced olfactory impairment is through necrosis of the olfactory bulb and not copper-selective inhibition of olfactory receptors. Fully two-thirds of the differentially expressed genes at higher doses of copper have no known function and thus represent important candidates for further study of the responses to copper-induced olfactory injury. Our results shed light on the evolution of vertebrate olfactory repair mechanisms and have important implications for the conservation and management of both invasive and native populations of lamprey.

Brain cholesterol metabolism and Parkinson's disease

BACKGROUND

Circulating cholesterol levels have been linked to PD, but not directly to brain physiology.

OBJECTIVE

To assess whether brain cholesterol metabolism is related to PD.

METHODS

Sixty PD patients and 64 controls were recruited from an academic movement disorder clinic (2009-2012). Thirty-five PD patients and 33 controls returned approximately 36 months later. Fasting plasma (S)24-OH-cholesterol (brain-derived cholesterol metabolite) and 27-OH-cholesterol (peripheral cholesterol metabolite) were quantified. Odds ratios for PD were derived from logistic regression models, adjusting for potential confounders. Relationships between the oxysterols and clinical measurements were explored using Spearman correlation coefficients.

RESULTS

Mean age of PD subjects was 63.8 ± 8.3 years and disease duration was 5.0 ± 5.4 years. Plasma (S)24-OH-cholesterol levels were inversely associated with the odds of having PD, with an odds ratio of 0.92 (95% confidence interval: 0.87-0.97) for each 1-ng/mL increase (P = 0.004). Compared to the lowest tertile, the odds ratio was 0.34 (0.12-0.98) for the second tertile (P = 0.045) and 0.08 (0.02-0.31) for the highest tertile (P < 0.001). Higher (S)24-OH-cholesterol levels also were correlated with better sense of smell (r = 0.35; P = 0.01). No significant associations were found between clinical measures and 27-OH-cholesterol, a peripheral cholesterol metabolite. Furthermore, (S)24-OH-cholesterol levels were stable over time, whereas 27-OH-cholesterol decreased with time in both cases and controls.

CONCLUSIONS

Results indicate that plasma (S)24-OH-cholesterol (possibly reflecting brain cholesterol metabolism) is inversely linked to PD, is relatively stable over time, and may serve as a new biomarker for PD. Further investigation is necessary to determine the mechanistic and clinical implications. © 2019 International Parkinson and Movement Disorder Society.

Type 2/Th2-driven inflammation impairs olfactory sensory neurogenesis in mouse chronic rhinosinusitis model

BACKGROUND

Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) is a chronic inflammatory disease often accompanied by impairment of sense of smell. This symptom has been somewhat overlooked, and its relationship to inflammatory cytokines, tissue compression, neuronal loss, and neurogenesis is still unclear.

METHODS

In order to elucidate potential mechanisms leading to CRS in humans, we have established a type 2/T helper type 2 cell (Th2)-mediated allergic CRS mouse model, based on house dust mite (HDM) and Staphylococcus aureus enterotoxin B (SEB) sensitization. The inflammatory status of the olfactory epithelium (OE) was assessed using histology, biochemistry, and transcriptomics. The sense of smell was evaluated by studying olfactory behavior and recording electro-olfactograms (EOGs).

RESULTS

After 22 weeks, a typical type 2/Th2-mediated inflammatory profile was obtained, as demonstrated by increased interleukin (IL)-4, IL-5, and IL-13 in the OE. The number of mast cells and eosinophils was increased, and infiltration of these cells into the olfactory mucosa was also observed. In parallel, transcriptomic and histology analyses indicated a decreased number of immature olfactory neurons, possibly due to decreased renewal. However, the number of mature sensory neurons was not affected and neither the EOG nor olfactory behavior was impaired.

CONCLUSION

Our mouse model of CRS displayed an allergic response to HDM + SEB administration, including the type 2/Th2 inflammatory profile characteristic of human eosinophilic CRSwNP. Although the sense of smell did not appear to be altered in these conditions, the data reveal the influence of chronic inflammation on olfactory neurogenesis, suggesting that factors unique to humans may be involved in CRSwNP-associated anosmia.

An Extreme Value Theory Model of Cross-Modal Sensory Information Integration in Modulation of Vertebrate Visual System Functions

We propose a computational model of vision that describes the integration of cross-modal sensory information between the olfactory and visual systems in zebrafish based on the principles of the statistical extreme value theory. The integration of olfacto-retinal information is mediated by the centrifugal pathway that originates from the olfactory bulb and terminates in the neural retina. Motivation for using extreme value theory stems from physiological evidence suggesting that extremes and not the mean of the cell responses direct cellular activity in the vertebrate brain. We argue that the visual system, as measured by retinal ganglion cell responses in spikes/sec, follows an extreme value process for sensory integration and the increase in visual sensitivity from the olfactory input can be better modeled using extreme value distributions. As zebrafish maintains high evolutionary proximity to mammals, our model can be extended to other vertebrates as well.

Bed Bug (Hemiptera: Cimicidae) Attraction to Human Odors: Validation of a Two-Choice Olfactometer

Bed bugs (Cimex lectularius L.) (Hemiptera: Cimicidae) are obligate hematophagous ectoparasites, and, therefore, must locate suitable hosts to ensure survival and reproduction. Their largely nocturnal activity suggests that chemosensory and thermosensory cues would play critical roles in host location. Yet, the importance of olfaction in host attraction of bed bugs remains unclear. We developed and validated a Y-tube, two-choice olfactometer and tested its suitability for investigating attraction to human odors (from skin swabs). Olfactometer orientation significantly affected the percentage of bed bugs that were activated by human odors, with significantly more bed bugs responding when the olfactometer was oriented vertically (bug introduced at bottom of the olfactometer) compared with all other orientations. Starved (7-10 d) adult males, mated females, and nymphs responded (47-77% moved up the olfactometer and made a choice) when human odors were present in the olfactometer, while starved, unmated females did not respond. Skin swabs from all five human participants elicited high response rates (65-82%), and bed bugs from four different populations responded to skin swabs (40-82% response rate). However, in all assays including those resulting in relatively low response rates, bed bugs exhibited >90% preference for human odors over blank controls. These results provide strong evidence that bed bugs can respond and orient towards human odors, independently of all other host cues. Furthermore, the validated olfactometer should enable rapid and efficient evaluations of bed bug behavioral responses to semiochemicals.