Showing papers on "Olfaction published in 2018"

Access to the odor world: olfactory receptors and their role for signal transduction in insects.

Abstract: The sense of smell enables insects to recognize and discriminate a broad range of volatile chemicals in their environment originating from prey, host plants and conspecifics. These olfactory cues are received by olfactory sensory neurons (OSNs) that relay information about food sources, oviposition sites and mates to the brain and thus elicit distinct odor-evoked behaviors. Research over the last decades has greatly advanced our knowledge concerning the molecular basis underlying the reception of odorous compounds and the mechanisms of signal transduction in OSNs. The emerging picture clearly indicates that OSNs of insects recognize odorants and pheromones by means of ligand-binding membrane proteins encoded by large and diverse families of receptor genes. In contrast, the mechanisms of the chemo-electrical transduction process are not fully understood; the present status suggests a contribution of ionotropic as well as metabotropic mechanisms. In this review, we will summarize current knowledge on the peripheral mechanisms of odor sensing in insects focusing on olfactory receptors and their specific role in the recognition and transduction of odorant and pheromone signals by OSNs.

Olfactory Dysfunction in Neurodegenerative Diseases.

Abstract: The sense of smell is today one of the focuses of interest in aging and neurodegenerative disease research. In several neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease, the olfactory dysfunction is one of the initial symptoms appearing years before motor symptoms and cognitive decline, being considered a clinical marker of these diseases’ early stages and a marker of disease progression and cognitive decline. Overall and under the umbrella of precision medicine, attention to olfactory function may help to improve chances of success for neuroprotective and disease-modifying therapeutic strategies. The use of olfaction, as clinical marker for neurodegenerative diseases is helpful in the characterization of prodromal stages of these diseases, early diagnostic strategies, differential diagnosis, and potentially prediction of treatment success. Understanding the mechanisms underlying olfactory dysfunction is central to determine its association with neurodegenerative disorders. Several anatomical systems and environmental factors may underlie or contribute to olfactory loss associated with neurological diseases, although the direct biological link to each disorder remains unclear and, thus, requires further investigation. In this review, we describe the neurobiology of olfaction, and the most common olfactory function measurements in neurodegenerative diseases. We also highlight the evidence for the presence of olfactory dysfunction in several neurodegenerative diseases, its value as a clinical marker for early stages of the diseases when combined with other clinical, biological, and neuroimage markers, and its role as a useful symptom for the differential diagnosis and follow-up of disease. The neuropathological correlations and the changes in neurotransmitter systems related with olfactory dysfunction in the neurodegenerative diseases are also described.

Combinatorial Codes and Labeled Lines: How Insects Use Olfactory Cues to Find and Judge Food, Mates, and Oviposition Sites in Complex Environments.

Abstract: Insects, including those which provide vital ecosystems services as well as those which are devastating pests or disease vectors, locate their resources mainly based on olfaction. Understanding insect olfaction not only from a neurobiological but also from an ecological perspective is therefore crucial to balance insect control and conservation. However, among all sensory stimuli olfaction is particularly hard to grasp. Our chemical environment is made up of thousands of different compounds, which might again be detected by our nose in multiple ways. Due to this complexity, researchers have only recently begun to explore the chemosensory ecology of model organisms such as Drosophila, linking the tools of chemical ecology to those of neurogenetics. This cross-disciplinary approach has enabled several studies that range from single odors and their ecological relevance, via olfactory receptor genes and neuronal processing, up to the insects' behavior. We learned that the insect olfactory system employs strategies of combinatorial coding to process general odors as well as labeled lines for specific compounds that call for an immediate response. These studies opened new doors to the olfactory world in which insects feed, oviposit, and mate.

Algorithms for Olfactory Search across Species.

Abstract: Localizing the sources of stimuli is essential. Most organisms cannot eat, mate, or escape without knowing where the relevant stimuli originate. For many, if not most, animals, olfaction plays an essential role in search. While microorganismal chemotaxis is relatively well understood, in larger animals the algorithms and mechanisms of olfactory search remain mysterious. In this symposium, we will present recent advances in our understanding of olfactory search in flies and rodents. Despite their different sizes and behaviors, both species must solve similar problems, including meeting the challenges of turbulent airflow, sampling the environment to optimize olfactory information, and incorporating odor information into broader navigational systems.

Elementary sensory-motor transformations underlying olfactory navigation in walking fruit-flies.

Abstract: Odor attraction in walking Drosophila melanogaster is commonly used to relate neural function to behavior, but the algorithms underlying attraction are unclear. Here, we develop a high-throughput assay to measure olfactory behavior in response to well-controlled sensory stimuli. We show that odor evokes two behaviors: an upwind run during odor (ON response), and a local search at odor offset (OFF response). Wind orientation requires antennal mechanoreceptors, but search is driven solely by odor. Using dynamic odor stimuli, we measure the dependence of these two behaviors on odor intensity and history. Based on these data, we develop a navigation model that recapitulates the behavior of flies in our apparatus, and generates realistic trajectories when run in a turbulent boundary layer plume. The ability to parse olfactory navigation into quantifiable elementary sensori-motor transformations provides a foundation for dissecting neural circuits that govern olfactory behavior.

Olfactory training with older people.

Abstract: Background/objectives Loss of olfactory function is largely found with aging. Such a reduction in olfactory function affects quality of life and enhances likelihood of depressive symptoms. Furthermore, it has been shown that reduction in olfactory function is associated with cognitive impairment and several diseases such as major depression. Because several studies suggest that discontinuous exposure to odors may improve general olfactory function, the primary aim of this study was to investigate whether such “olfactory training” has positive effects on subjective well-being and cognitive function. Design We performed a controlled, unblinded, longitudinal study Setting The study took place at an outpatients' clinic of a Department of Otorhinolaryngology at a Medical University. Participants A total of 91 participants (age 50 to 84 years) completed testing. They were randomly assigned to an olfactory training (OT) group (N = 60) and a control group (N = 31). The study included two appointments at the Smell and Taste Clinic. Measurements Olfactory and cognitive function as well as subjective well-being was tested using standardized tests. Intervention During the 5-month interval between sessions, the OT group completed daily olfactory exposure. During the same time, the control group completed daily Sudoku problems. Results Analyses show a significant improvement of olfactory function for participants in the OT group and improved verbal function and subjective well-being. In addition, results indicated a decrease of depressive symptoms. Conclusion Based on the present results, OT may constitute an inexpensive, simple way to improve quality of life in older people. Copyright © 2017 John Wiley & Sons, Ltd.

Antagonism in olfactory receptor neurons and its implications for the perception of odor mixtures

Abstract: When ordering in a coffee shop, you probably recognize and enjoy the aroma of freshly roasted coffee beans. But as well as coffee, you can also smell the croissants behind the counter and maybe even the perfume or cologne of the person next to you. Each of these scents consists of a collection of chemicals, or odorants. To distinguish between the aroma of coffee and that of croissants, your brain must group the odorants appropriately and then keep the groups separate from each other. This is not a trivial task. Odorants bind to proteins called odorant receptors found on the surface of cells in the nose called olfactory receptor neurons. But each odorant does not have its own dedicated receptor. Instead, a single odorant will bind to multiple types of odorant receptors, and thus, each olfactory receptor neuron may respond to multiple odorants. So how does the brain encode mixtures of odorants in a way that allows us to distinguish one aroma from another? Reddy, Zak et al. have developed a computational model to explain how this process works. The model assumes that an odorant triggers a response in an olfactory receptor neuron via two steps. First, the odorant binds to an odorant receptor. Second, the bound odorant activates the receptor. But the odorant that binds most strongly to a receptor will not necessarily be the odorant that is best at activating that receptor. This allows a phenomenon called competitive antagonism to occur. This is when one odorant in a mixture binds more strongly to a receptor than the other odorants, but only weakly activates that receptor. In so doing, the strongly bound odorant prevents the other odorants from binding to and activating the receptor. This helps tame the dominating influence of background odors, which might otherwise saturate the responses of individual olfactory receptor neurons. Reddy, Zak et al. show that processes such as competitive antagonism enable olfactory receptor neurons to encode all of the odors within a mixture. The model can explain various phenomena observed in experiments and it adds to our understanding of how the brain generates our sense of smell. The model may also be relevant to other biological systems that must filter weak signals from a dominant background. These include the immune system, which must distinguish a small set of foreign proteins from the much larger number of proteins that make up our bodies.

Near-future CO2 levels impair the olfactory system of a marine fish

Abstract: Survival of marine fishes that are exposed to elevated near-future CO2 levels is threatened by their altered responses to sensory cues Here we demonstrate a physiological and molecular mechanism in the olfactory system that helps to explain altered behaviour under elevated CO2 We combine electrophysiology measurements and transcriptomics with behavioural experiments to investigate how elevated CO2 affects the olfactory system of European sea bass (Dicentrarchus labrax) When exposed to elevated CO2 (approximately 1,000 µatm), fish must be up to 42% closer to an odour source for detection, compared with current CO2 levels (around 400 µatm), decreasing their chances of detecting food or predators Compromised olfaction correlated with the suppression of the transcription of genes involved in synaptic strength, cell excitability and wiring of the olfactory system in response to sustained exposure to elevated CO2 levels Our findings complement the previously proposed impairment of γ-aminobutyric acid receptors, and indicate that both the olfactory system and central brain function are compromised by elevated CO2 levels Marine fishes exposed to elevated CO2 levels can have altered responses to sensory cues Research now reveals a physiological and molecular mechanism in the olfactory system that helps to explain this altered behaviour under elevated CO2

Olfactory receptor OR2AT4 regulates human hair growth

Abstract: Olfactory receptors are expressed by different cell types throughout the body and regulate physiological cell functions beyond olfaction In particular, the olfactory receptor OR2AT4 has been shown to stimulate keratinocyte proliferation in the skin Here, we show that the epithelium of human hair follicles, particularly the outer root sheath, expresses OR2AT4, and that specific stimulation of OR2AT4 by a synthetic sandalwood odorant (Sandalore®) prolongs human hair growth ex vivo by decreasing apoptosis and increasing production of the anagen-prolonging growth factor IGF-1 In contrast, co-administration of the specific OR2AT4 antagonist Phenirat® and silencing of OR2AT4 inhibit hair growth Together, our study identifies that human hair follicles can engage in olfactory receptor-dependent chemosensation and require OR2AT4-mediated signaling to sustain their growth, suggesting that olfactory receptors may serve as a target in hair loss therapy

Olfactory epithelium: Cells, clinical disorders, and insights from an adult stem cell niche.

Abstract: Disorders causing a loss of the sense of smell remain a therapeutic challenge. Basic research has, however, greatly expanded our knowledge of the organization and function of the olfactory system. This review describes advances in our understanding of the cellular components of the peripheral olfactory system, specifically the olfactory epithelium in the nose. The article discusses recent findings regarding the mechanisms involved in regeneration and cellular renewal from basal stem cells in the adult olfactory epithelium, considering the strategies involved in embryonic olfactory development and insights from research on other stem cell niches. In the context of clinical conditions causing anosmia, the current view of adult olfactory neurogenesis, tissue homeostasis, and failures in these processes is considered, along with current and future treatment strategies. Level of evidence NA.

The nasal microbiome mirrors and potentially shapes olfactory function

Abstract: Olfactory function is a key sense for human well-being and health, with olfactory dysfunction having been linked to serious diseases. As the microbiome is involved in normal olfactory epithelium development, we explored the relationship between olfactory function (odor threshold, discrimination, identification) and nasal microbiome in 67 healthy volunteers. Twenty-eight subjects were found to have normal olfactory function, 29 had a particularly good sense of smell ("good normosmics") and 10 were hyposmic. Microbial community composition differed significantly between the three olfactory groups. In particular, butyric acid-producing microorganisms were found to be associated with impaired olfactory function. We describe the first insights of the potential interplay between the olfactory epithelium microbial community and olfactory function, and suggest that the microbiome composition is able to mirror and potentially shape olfactory function by producing strong odor compounds.

When the Nose Doesn't Know: Canine Olfactory Function Associated With Health, Management, and Potential Links to Microbiota

Abstract: The impact of health, management, and microbiota on olfactory function in canines has not been examined in review. The most important characteristic of the detection canine is its sense of smell. Olfactory receptors are primarily located on the ethmoturbinates of the nasal cavity. The vomeronasal organ is an additional site of odor detection that detects chemical signals that stimulate behavioral and/or physiological changes. Recent advances in the genetics of olfaction suggest that genetic changes, along with the unique anatomy and airflow of the canine nose, are responsible for the macrosmia of the species. Inflammation, alterations in blood flow and hydration, and systemic diseases alter olfaction and may impact working efficiency of detection canines. The scientific literature contains abundant information on the potential impact of pharmaceuticals on olfaction in humans, but only steroids, antibiotics, and anesthetic agents have been studied in the canine. Physical stressors including exercise, lack of conditioning, and high ambient temperature impact olfaction directly or indirectly in the canine. Dietary fat content, amount of food per meal, and timing of meals have been demonstrated to impact olfaction in mice and dogs. Gastrointestinal (GI) microbiota likely impacts olfaction via bidirectional communication between the GI tract and brain, and the microbiota is impacted by exercise, diet, and stress. The objective of this literature review is to discuss the specific effects of health, management, and microbiota shifts on olfactory performance in working canines.

Olfaction written in bone: cribriform plate size parallels olfactory receptor gene repertoires in Mammalia

Abstract: The evolution of mammalian olfaction is manifested in a remarkable diversity of gene repertoires, neuroanatomy and skull morphology across living species. Olfactory receptor genes (ORGs), which initiate the conversion of odorant molecules into odour perceptions and help an animal resolve the olfactory world, range in number from a mere handful to several thousand genes across species. Within the snout, each of these ORGs is exclusively expressed by a discrete population of olfactory sensory neurons (OSNs), suggesting that newly evolved ORGs may be coupled with new OSN populations in the nasal epithelium. Because OSN axon bundles leave high-fidelity perforations (foramina) in the bone as they traverse the cribriform plate (CP) to reach the brain, we predicted that taxa with larger ORG repertoires would have proportionately expanded footprints in the CP foramina. Previous work found a correlation between ORG number and absolute CP size that disappeared after accounting for body size. Using updated, digital measurement data from high-resolution CT scans and re-examining the relationship between CP and body size, we report a striking linear correlation between relative CP area and number of functional ORGs across species from all mammalian superorders. This correlation suggests strong developmental links in the olfactory pathway between genes, neurons and skull morphology. Furthermore, because ORG number is linked to olfactory discriminatory function, this correlation supports relative CP size as a viable metric for inferring olfactory capacity across modern and extinct species. By quantifying CP area from a fossil sabertooth cat (Smilodon fatalis), we predicted a likely ORG repertoire for this extinct felid.

Depression, Olfaction, and Quality of Life: A Mutual Relationship.

Abstract: Olfactory dysfunction has been well studied in depression. Common brain areas are involved in depression and in the olfactory process, suggesting that olfactory impairments may constitute potential markers of this disorder. Olfactory markers of depression can be either state (present only in symptomatic phases) or trait (persistent after symptomatic remission) markers. This study presents the etiology of depression, the anatomical links between olfaction and depression, and a literature review of different olfactory markers of depression. Several studies have also shown that olfactory impairment affects the quality of life and that olfactory disorders can affect daily life and may be lead to depression. Thus, this study discusses the links between olfactory processing, depression, and quality of life. Finally, olfaction is an innovative research field that may constitute a new therapeutic tool for the treatment of depression.

Single olfactory receptors set odor detection thresholds

Abstract: In many species, survival depends on olfaction, yet the mechanisms that underlie olfactory sensitivity are not well understood. Here we examine how a conserved subset of olfactory receptors, the trace amine-associated receptors (TAARs), determine odor detection thresholds of mice to amines. We find that deleting all TAARs, or even single TAARs, results in significant odor detection deficits. This finding is not limited to TAARs, as the deletion of a canonical odorant receptor reduced behavioral sensitivity to its preferred ligand. Remarkably, behavioral threshold is set solely by the most sensitive receptor, with no contribution from other highly sensitive receptors. In addition, increasing the number of sensory neurons (and glomeruli) expressing a threshold-determining TAAR does not improve detection, indicating that sensitivity is not limited by the typical complement of sensory neurons. Our findings demonstrate that olfactory thresholds are set by the single highest affinity receptor and suggest that TAARs are evolutionarily conserved because they determine the sensitivity to a class of biologically relevant chemicals.

Budesonide irrigation with olfactory training improves outcomes compared with olfactory training alone in patients with olfactory loss.

Abstract: Background Olfactory training (OT) helps many patients with olfactory loss, but unfortunately it is ineffective for a significant number of patients. Budesonide irrigations are widely used to help patients with paranasal sinus inflammation, but have never been tested as a treatment for olfactory loss. We sought to examine the effect of adding budesonide irrigation to olfactory training on patients with olfactory loss without any visible sign of sinonasal inflammation. Methods In this randomized, controlled trial, 138 patients with olfactory loss and without any visible sign of sinonasal inflammation were randomized to either OT with saline irrigations or OT with budesonide irrigations. The University of Pennsylvania Smell Identification Test (UPSIT) was administered at the beginning of the study and at 6 months. Results A total of 133 patients completed the study. Forty-seven patients (35.3%) had a clinically significant change in UPSIT score. Among those in the budesonide irrigation + olfactory therapy group, 43.9% improved, compared with 26.9% in the saline irrigation + olfactory therapy group (p = 0.039); this corresponds to an odds ratio of 3.93 (95% confidence interval, 1.20-12.88) in a fully adjusted model (p = 0.024). Younger age and shorter duration of olfactory loss were also significant predictors of improvement. Conclusion Adding budesonide irrigation to olfactory training significantly improved olfactory ability compared with olfactory training plus saline irrigation.

Olfactory and middle meatal cytokine levels correlate with olfactory function in chronic rhinosinusitis.

Abstract: OBJECTIVES/HYPOTHESIS The etiology of chronic rhinosinusitis (CRS)-associated olfactory loss is unclear, but may result from inflammatory changes in the olfactory epithelium that result in signaling dysfunction or loss of olfactory neurons. Several proinflammatory cytokines have been associated with CRS, but their expression within the olfactory cleft microenvironment and association with olfactory function is unknown. STUDY DESIGN Prospective case-control study. METHODS Mucus was collected from the olfactory cleft and middle meatus of 31 CRS without nasal polyps subjects, 36 CRS with nasal polyps (CRSwNP) subjects, and 12 healthy controls. Olfactory function was assessed using the validated Smell Identification Test (SIT). Site-specific levels of 14 cytokines/chemokines (interleukin [IL]-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12, IL-13, IL-17A, tumor necrosis factor-α, Eotaxin, RANTES [regulated on activation, normal T cell expressed and secreted]) were assessed using a multiplex flow cytometric bead assay and correlated with SIT scores. RESULTS Mucus cytokine levels in the olfactory cleft were strongly or moderately correlated with levels in the middle meatus for all but one measured inflammatory mediators. SIT scores were inversely correlated with levels of IL-2 (P = .006), IL-5 (P < .0001), IL-6 (P = .0009), IL-10 (P < .0001), and IL-13 (P < .0001), with significance largely driven by CRSwNP patients. CONCLUSIONS The inflammatory microenvironment within the olfactory cleft mirrors that within the middle meatus. Elevated levels of IL-2, IL-5, IL-6, IL-10, and IL-13 in olfactory cleft mucus are associated with reduced olfactory identification scores in CRS patients. Altered levels of select olfactory mucus cytokines could potentially have deleterious effects on olfactory neuron function and turnover. LEVEL OF EVIDENCE NA. Laryngoscope, 128:E304-E310, 2018.

The Two Main Olfactory Receptor Families in Drosophila , ORs and IRs: A Comparative Approach.

Abstract: Most insect species rely on the detection of olfactory cues for critical behaviors for the survival of the species, e.g., finding food, suitable mates and appropriate egg-laying sites. Although insects show a diverse array of molecular receptors dedicated to the detection of sensory cues, two main types of molecular receptors have been described as responsible for olfactory reception in Drosophila, the odorant receptors (ORs) and the ionotropic receptors (IRs). Although both receptor families share the role of being the first chemosensors in the insect olfactory system, they show distinct evolutionary origins and several distinct structural and functional characteristics. While ORs are seven-transmembrane-domain receptor proteins, IRs are related to the ionotropic glutamate receptor (iGluR) family. Both types of receptors are expressed on the olfactory sensory neurons (OSNs) of the main olfactory organ, the antenna, but they are housed in different types of sensilla, IRs in coeloconic sensilla and ORs in basiconic and trichoid sensilla. More importantly, from the functional point of view, they display different odorant specificity profiles. Research advances in the last decade have improved our understanding of the molecular basis, evolution and functional roles of these two families, but there are still controversies and unsolved key questions that remain to be answered. Here, we present an updated review on the advances of the genetic basis, evolution, structure, functional response and regulation of both types of chemosensory receptors. We use a comparative approach to highlight the similarities and differences among them. Moreover, we will discuss major open questions in the field of olfactory reception in insects. A comprehensive analysis of the structural and functional convergence and divergence of both types of receptors will help in elucidating the molecular basis of the function and regulation of chemoreception in insects.

Olfactory dysfunction in Alzheimer's disease Systematic review and meta-analysis.

Abstract: Alzheimer’s disease (AD), a neurodegenerative condition, is one of the most prevalent kinds of dementia, whose frequency doubles for every 5 years of age in elderly. Objective: To determine the correlation between AD and olfactory alterations, identifying the most affected domains and exploring the utility of olfactory tests for complementing early diagnosis. Methods: Databases were searched using the terms “olfactory OR smell OR olfaction AND alzheimer” for articles related to the proposed theme. The selected studies were categorized and evaluated separately depending on the method of analysis of the olfactory tests: identification of odors, discrimination and recognition, and a meta-analysis was carried out. Results: Fifty-one articles were selected for analysis. The effect size for most studies was large, as were the summary values for each category of individualized olfactory analysis. Conclusion: Among the olfactory domains, except memory, identification appears to be the most altered in AD. The possibility of including tests that specifically evaluate the identification of odors as an item in early diagnostic evaluation should be explored. PROSPERO registration: CRD42018089076.

Multimodal integration and stimulus categorization in putative mushroom body output neurons of the honeybee.

Abstract: Flowers attract pollinating insects like honeybees by sophisticated compositions of olfactory and visual cues. Using honeybees as a model to study olfactory–visual integration at the neuronal level, we focused on mushroom body (MB) output neurons (MBON). From a neuronal circuit perspective, MBONs represent a prominent level of sensory-modality convergence in the insect brain. We established an experimental design allowing electrophysiological characterization of olfactory, visual, as well as olfactory–visual induced activation of individual MBONs. Despite the obvious convergence of olfactory and visual pathways in the MB, we found numerous unimodal MBONs. However, a substantial proportion of MBONs (32%) responded to both modalities and thus integrated olfactory–visual information across MB input layers. In these neurons, representation of the olfactory–visual compound was significantly increased compared with that of single components, suggesting an additive, but nonlinear integration. Population analyses of olfactory–visual MBONs revealed three categories: (i) olfactory, (ii) visual and (iii) olfactory–visual compound stimuli. Interestingly, no significant differentiation was apparent regarding different stimulus qualities within these categories. We conclude that encoding of stimulus quality within a modality is largely completed at the level of MB input, and information at the MB output is integrated across modalities to efficiently categorize sensory information for downstream behavioural decision processing.

Sensorimotor pathway controlling stopping behavior during chemotaxis in the Drosophila melanogaster larva.

Abstract: Sensory navigation results from coordinated transitions between distinct behavioral programs. During chemotaxis in the Drosophila melanogaster larva, the detection of positive odor gradients extends runs while negative gradients promote stops and turns. This algorithm represents a foundation for the control of sensory navigation across phyla. In the present work, we identified an olfactory descending neuron, PDM-DN, which plays a pivotal role in the organization of stops and turns in response to the detection of graded changes in odor concentrations. Artificial activation of this descending neuron induces deterministic stops followed by the initiation of turning maneuvers through head casts. Using electron microscopy, we reconstructed the main pathway that connects the PDM-DN neuron to the peripheral olfactory system and to the pre-motor circuit responsible for the actuation of forward peristalsis. Our results set the stage for a detailed mechanistic analysis of the sensorimotor conversion of graded olfactory inputs into action selection to perform goal-oriented navigation.

An intrinsic association between olfactory identification and spatial memory in humans

Abstract: It was recently proposed that olfaction evolved to aid navigation. Consistent with this hypothesis, olfactory identification and spatial memory are linked to overlapping brain areas which include the orbitofrontal cortex and hippocampus. However, the relationship between these two processes has never been specifically investigated. Here, we show that olfactory identification covaries with spatial memory in humans. We also found that the cortical thickness of the left medial orbitofrontal cortex, and the volume of the right hippocampus, predict both olfactory identification and spatial memory. Finally, we demonstrate deficits in both olfactory identification and spatial memory in patients with lesions of the medial orbitofrontal cortex. Our findings reveal an intrinsic relationship between olfaction and spatial memory that is supported by a shared reliance on the hippocampus and medial orbitofrontal cortex. This relationship may find its roots in the parallel evolution of the olfactory and hippocampal systems.

Insect Pheromone Receptors - Key Elements in Sensing Intraspecific Chemical Signals.

Abstract: Pheromones are chemicals that serve intraspecific communication. In animals, the ability to detect and discriminate pheromones in a complex chemical environment substantially contributes to the survival of the species. Insects widely use pheromones to attract mating partners, to alarm conspecifics or to mark paths to rich food sources. The various functional roles of pheromones for insects are reflected by the chemical diversity of pheromonal compounds. The precise detection of the relevant intraspecific signals is accomplished by specialized chemosensory neurons housed in hair-like sensilla located on the surface of body appendages. Current data indicate that the extraordinary sensitivity and selectivity of the pheromone-responsive neurons (PRNs) is largely based on specific pheromone receptors (PRs) residing in their ciliary membrane. Besides these key elements, proper ligand-induced responses of PR-expressing neurons appear to generally require a putative co-receptor, the so-called "sensory neuron membrane protein 1" (SNMP1). Regarding the PR-mediated chemo-electrical signal transduction processes in insect PRNs, ionotropic as well as metabotropic mechanisms may be involved. In this review, we summarize and discuss current knowledge on the peripheral detection of pheromones in the olfactory system of insects with a focus on PRs and their specific role in the recognition and transduction of volatile intraspecific chemical signals.

Olfactory Loss and Regain: Lessons for Neuroplasticity:

Abstract: For the visual and auditory senses, an array of studies has reported on neuronal reorganization processes after sensory loss. In contrast to this, neuroplasticity has been investigated only scarcely after loss of the olfactory sense. The present review focuses on the current extent of literature on structural and functional neuroplasticity effects after loss, with a focus on magnetic resonance imaging-based studies. We also include findings on the regain of the olfactory sense, for example after successful olfactory training. Existing studies indicate that widespread structural changes beyond the level of the olfactory bulb occur in the brain after loss of the olfactory sense. Moreover, on a functional level, loss of olfactory input not only entails changes in olfaction-related brain regions but also in the trigeminal system. Existing evidence should be strengthened by future longitudinal studies, a more thorough investigation of the neuronal consequences of congenital anosmia, and the application of state-of-the-art neuroimaging methods, such as connectivity analyses and joint analyses of brain structure and function.

Adult-born neurons boost odor-reward association.

Abstract: Olfaction is an important sensory modality driving fundamental behaviors. During odor-dependent learning, a positive value is commonly assigned to an odorant, and multiple forms of plasticity are involved when such odor-reward associations are formed. In rodents, one of the mechanisms underlying plasticity in the olfactory bulb consists in recruiting new neurons daily throughout life. However, it is still unknown whether adult-born neurons might participate in encoding odor value. Here, we demonstrate that exposure to reward-associated odors specifically increases activity of adult-born neurons but not preexisting neurons. Remarkably, adult-born neuron activation during rewarded odor presentation heightens discrimination learning and enhances the ability to update the odor value during reversal association. Moreover, in some cases, activation of this interneuron population can trigger olfactory learning without sensory stimulation. Taken together, our results show a specific involvement of adult-born neurons in facilitating odor-reward association during adaptive learning.