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International Journal of Molecular... Jan 2023Olfactory capacity declines with aging, but increasing evidence shows that smell dysfunction is one of the early signs of prodromal neurodegenerative diseases such as... (Review)
Review
Olfactory capacity declines with aging, but increasing evidence shows that smell dysfunction is one of the early signs of prodromal neurodegenerative diseases such as Alzheimer's and Parkinson's disease. The study of olfactory ability and its role in neurodegenerative diseases arouses much interest in the scientific community. In neurology, olfactory impairment is a potential early marker for the onset of neurodegenerative diseases, but the underlying mechanism is poorly understood. The loss of smell is considered a clinical sign of early-stage disease and a marker of the disease's progression and cognitive impairment. Highlighting the importance of biological bases of smell and molecular pathways could be fundamental to improve neuroprotective and therapeutic strategies. We focused on the review articles and meta-analyses on olfactory and cognitive impairment. We depicted the neurobiology of olfaction and the most common olfactory tests in neurodegenerative diseases. In addition, we underlined the close relationship between the olfactory and cognitive deficit due to nasal neuroepithelium, which is a direct extension of the CNS in communication with the external environment. Neurons, Nose, and Neurodegenerative diseases highlights the role of olfactory dysfunction as a clinical marker for early stages of neurodegenerative diseases when it is associated with molecular, clinical, and neuropathological correlations.
Topics: Humans; Neurodegenerative Diseases; Smell; Olfaction Disorders; Cognitive Dysfunction; Neurons; Alzheimer Disease
PubMed: 36768440
DOI: 10.3390/ijms24032117 -
Neuropsychology Review Mar 2024Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating... (Review)
Review
Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.
Topics: Humans; Brain; Cognition; Olfaction Disorders; Olfactory Training; Smell
PubMed: 36725781
DOI: 10.1007/s11065-022-09573-0 -
Physiological Reviews Jan 2023Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and... (Review)
Review
Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and obesity. Thus there is growing interest in the study of the biological mediators of fat taste and associated olfaction as potential targets for pharmacologic and nutritional interventions in the context of obesity and health. The number of studies examining mechanisms underlying fat taste and smell has grown rapidly in the last 5 years. Therefore, the purpose of this systematic review is to summarize emerging evidence examining the biological mechanisms of fat taste and smell. A literature search was conducted of studies published in English between 2014 and 2021 in adult humans and animal models. Database searches were conducted using PubMed, EMBASE, Scopus, and Web of Science for key terms including fat/lipid, taste, and olfaction. Initially, 4,062 articles were identified through database searches, and a total of 84 relevant articles met inclusion and exclusion criteria and are included in this review. Existing literature suggests that there are several proteins integral to fat chemosensation, including cluster of differentiation 36 (CD36) and G protein-coupled receptor 120 (GPR120). This systematic review will discuss these proteins and the signal transduction pathways involved in fat detection. We also review neural circuits, key brain regions, ingestive cues, postingestive signals, and genetic polymorphism that play a role in fat perception and consumption. Finally, we discuss the role of fat taste and smell in the context of eating behavior and obesity.
Topics: Animals; Humans; Feeding Behavior; Obesity; Smell; Taste; Taste Buds
PubMed: 36409650
DOI: 10.1152/physrev.00061.2021 -
Proceedings. Biological Sciences Dec 2022Among the many wonders of nature, the sense of smell of the fly might seem, at first glance, of esoteric interest. Nevertheless, for over a century, the 'nose' of this... (Review)
Review
Among the many wonders of nature, the sense of smell of the fly might seem, at first glance, of esoteric interest. Nevertheless, for over a century, the 'nose' of this insect has been an extraordinary system to explore questions in animal behaviour, ecology and evolution, neuroscience, physiology and molecular genetics. The insights gained are relevant for our understanding of the sensory biology of vertebrates, including humans, and other insect species, encompassing those detrimental to human health. Here, I present an overview of our current knowledge of olfaction, from molecules to behaviours, with an emphasis on the historical motivations of studies and illustration of how technical innovations have enabled advances. I also highlight some of the pressing and long-term questions.
Topics: Animals; Humans; Drosophila; Drosophila melanogaster; Smell; Behavior, Animal; Ecology; Insecta
PubMed: 36515118
DOI: 10.1098/rspb.2022.2054 -
Trends in Neurosciences Jan 2023The mechanisms of olfactory dysfunction in COVID-19 are still unclear. In this review, we examine potential mechanisms that may explain why the sense of smell is lost or... (Review)
Review
The mechanisms of olfactory dysfunction in COVID-19 are still unclear. In this review, we examine potential mechanisms that may explain why the sense of smell is lost or altered. Among the current hypotheses, the most plausible is that death of infected support cells in the olfactory epithelium causes, besides altered composition of the mucus, retraction of the cilia on olfactory receptor neurons, possibly because of the lack of support cell-derived glucose in the mucus, which powers olfactory signal transduction within the cilia. This mechanism is consistent with the rapid loss of smell with COVID-19, and its rapid recovery after the regeneration of support cells. Host immune responses that cause downregulation of genes involved in olfactory signal transduction occur too late to trigger anosmia, but may contribute to the duration of the olfactory dysfunction.
Topics: Humans; COVID-19; Smell; SARS-CoV-2; Olfaction Disorders; Olfactory Mucosa
PubMed: 36470705
DOI: 10.1016/j.tins.2022.11.003 -
Nutrients Jul 2023Taste and olfaction are sensory modalities that act synergistically to orchestrate the behaviors essential for survival, such as interactions with the environment,...
Taste and olfaction are sensory modalities that act synergistically to orchestrate the behaviors essential for survival, such as interactions with the environment, nutrient-rich food identification, and the avoidance of noxious substances [...].
Topics: Smell; Taste; Taste Perception; Nutritional Status; Nutrients
PubMed: 37571348
DOI: 10.3390/nu15153412 -
Frontiers in Neural Circuits 2022Despite major anatomical differences with other mammalian sensory systems, olfaction shares with those systems a modulation by sleep/wake states. Sleep modulates odor... (Review)
Review
Despite major anatomical differences with other mammalian sensory systems, olfaction shares with those systems a modulation by sleep/wake states. Sleep modulates odor sensitivity and serves as an important regulator of both perceptual and associative odor memory. In addition, however, olfaction also has an important modulatory impact on sleep. Odors can affect the latency to sleep onset, as well as the quality and duration of sleep. Olfactory modulation of sleep may be mediated by direct synaptic interaction between the olfactory system and sleep control nuclei, and/or indirectly through odor modulation of arousal and respiration. This reciprocal interaction between sleep and olfaction presents novel opportunities for sleep related modulation of memory and perception, as well as development of non-pharmacological olfactory treatments of simple sleep disorders.
Topics: Animals; Smell; Olfactory Pathways; Odorants; Sleep; Arousal; Olfactory Perception; Mammals
PubMed: 36619661
DOI: 10.3389/fncir.2022.1076354 -
Chemical Senses Jan 2021As vectors of disease, mosquitoes are a global threat to human health. The Anopheles mosquito is the deadliest mosquito species as the insect vector of the... (Review)
Review
As vectors of disease, mosquitoes are a global threat to human health. The Anopheles mosquito is the deadliest mosquito species as the insect vector of the malaria-causing parasite, which kills hundreds of thousands every year. These mosquitoes are reliant on their sense of smell (olfaction) to guide most of their behaviors, and a better understanding of Anopheles olfaction identifies opportunities for reducing the spread of malaria. This review takes a detailed look at Anopheles olfaction. We explore a range of topics from chemosensory receptors, olfactory neurons, and sensory appendages to behaviors guided by olfaction (including host-seeking, foraging, oviposition, and mating), to vector management strategies that target mosquito olfaction. We identify many research areas that remain to be addressed.
Topics: Animals; Anopheles; Behavior, Animal; Olfactory Receptor Neurons; Receptors, Odorant; Smell
PubMed: 33885760
DOI: 10.1093/chemse/bjab021 -
Proceedings of the American Thoracic... Mar 2011Olfaction represents an ancient, evolutionarily critical physiologic system. In humans, chemosensation mediates safety, nutrition, sensation of pleasure, and general... (Review)
Review
Olfaction represents an ancient, evolutionarily critical physiologic system. In humans, chemosensation mediates safety, nutrition, sensation of pleasure, and general well-being. Factors that affect human olfaction included structural aspects of the nasal cavity that can modulate airflow and therefore odorant access to the olfactory cleft, and inflammatory disease, which can affect both airflow as well as olfactory nerve function. After signals are generated, olfactory information is processed and coded in the olfactory bulb and disseminated to several areas in the brain. The discovery of olfactory receptors by Axel and Buck sparked greater understanding of the molecular basis of olfaction. However, the precise mechanisms used by this system are still under great scrutiny due to the complexity of understanding how an enormous number of chemically diverse odorant molecules are coded into signals understood by the brain. Additionally, it has been challenging to dissect olfactory sensation due to the multiple areas of areas of the brain that receive and modulate this information. Consequently, our knowledge of olfactory dysfunction in humans remains primitive. Aging represents the major cause of loss of smell, although a number of clinical and environmental factors are thought to affect chemosensory function. Treatment options focus on reducing sinonasal inflammation when present, ruling out other treatable causes, and counseling patients on safety measures.
Topics: Chemoreceptor Cells; Female; Humans; Male; Nasal Cavity; Olfaction Disorders; Olfactory Mucosa; Olfactory Receptor Neurons; Signal Transduction; Smell
PubMed: 21364221
DOI: 10.1513/pats.201005-035RN -
Neuron Apr 2023The coincidence between conditioned stimulus (CS) and unconditioned stimulus (US) is essential for associative learning; however, the mechanism regulating the duration...
The coincidence between conditioned stimulus (CS) and unconditioned stimulus (US) is essential for associative learning; however, the mechanism regulating the duration of this temporal window remains unclear. Here, we found that serotonin (5-HT) bi-directionally regulates the coincidence time window of olfactory learning in Drosophila and affects synaptic plasticity of Kenyon cells (KCs) in the mushroom body (MB). Utilizing GPCR-activation-based (GRAB) neurotransmitter sensors, we found that KC-released acetylcholine (ACh) activates a serotonergic dorsal paired medial (DPM) neuron, which in turn provides inhibitory feedback to KCs. Physiological stimuli induce spatially heterogeneous 5-HT signals, which proportionally gate the intrinsic coincidence time windows of different MB compartments. Artificially reducing or increasing the DPM neuron-released 5-HT shortens or prolongs the coincidence window, respectively. In a sequential trace conditioning paradigm, this serotonergic neuromodulation helps to bridge the CS-US temporal gap. Altogether, we report a model circuitry for perceiving the temporal coincidence and determining the causal relationship between environmental events.
Topics: Animals; Smell; Serotonin; Drosophila; Conditioning, Classical; Neurons; Mushroom Bodies
PubMed: 36706757
DOI: 10.1016/j.neuron.2022.12.034