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Journal of Neurochemistry Jun 2009Sensing the chemical environment is critical for all organisms. Diverse animals from insects to mammals utilize highly organized olfactory system to detect, encode, and... (Review)
Review
Sensing the chemical environment is critical for all organisms. Diverse animals from insects to mammals utilize highly organized olfactory system to detect, encode, and process chemostimuli that may carry important information critical for health, survival, social interactions and reproduction. Therefore, for animals to properly interpret and react to their environment it is imperative that the olfactory system recognizes chemical stimuli with appropriate selectivity and sensitivity. Because olfactory receptor proteins play such an essential role in the specific recognition of diverse stimuli, understanding how they interact with and transduce their cognate ligands is a high priority. In the nearly two decades since the discovery that the mammalian odorant receptor gene family constitutes the largest group of G protein-coupled receptor (GPCR) genes, much attention has been focused on the roles of GPCRs in vertebrate and invertebrate olfaction. However, is has become clear that the 'family' of olfactory receptors is highly diverse, with roles for enzymes and ligand-gated ion channels as well as GPCRs in the primary detection of olfactory stimuli.
Topics: Animals; Humans; Odorants; Olfactory Perception; Receptors, G-Protein-Coupled; Smell
PubMed: 19383089
DOI: 10.1111/j.1471-4159.2009.06085.x -
Brazilian Journal of Otorhinolaryngology 2022SARS-CoV-2 is the pathogen of COVID-19. The virus is composed of the spike, membrane and envelope. On physiological smell, odoriferous substances bind to proteins... (Review)
Review
INTRODUCTION
SARS-CoV-2 is the pathogen of COVID-19. The virus is composed of the spike, membrane and envelope. On physiological smell, odoriferous substances bind to proteins secreted by sustentacular cells in order to be processed by olfactory receptor neurons. Olfactory disorder is one of the main manifestations of COVID-19, however, research is still required to clarify the mechanism involved in SARS-CoV-2 induced anosmia.
OBJECTIVE
This article aims to analyze current scientific evidence intended to elucidate the pathophysiological relationship between COVID-19 and the cause of olfactory disorders.
METHODS
Pubmed, Embase, Scopus and ScienceDirect were used to compose this article. The research was conducted on November 24th, 2020. Original articles with experimental studies in human, animal and in vitro, short communications, viewpoint, published in the English language and between 2019 and 2020 were included, all related to the pathophysiological relationship between olfactory disorders and COVID-19 infection.
RESULTS
Both human cell receptors ACE2 and TMPRSS2 are essential for the SARS-CoV-2 entrance. These receptors are mostly present in the olfactory epithelium cells, therefore, the main hypothesis is that anosmia is caused due to damage to non-neuronal cells which, thereafter, affects the normal olfactory metabolism. Furthermore, magnetic resonance imaging studies exhibit a relationship between a reduction on the neuronal epithelium and the olfactory bulb atrophy. Damage to non-neuronal cells explains the average recovery lasting a few weeks. This injury can be exacerbated by an aggressive immune response, which leads to damage to neuronal cells and stem cells inducing a persistent anosmia. Conductive anosmia is not sufficient to explain most cases of COVID-19 induced anosmia.
CONCLUSION
Olfactory disorders such as anosmia and hyposmia can be caused by COVID-19, the main mechanism is associated with olfactory epithelium damage, targeting predominantly non-neuronal cells. However, neuronal cells can also be affected, worsening the condition of olfactory loss.
Topics: Angiotensin-Converting Enzyme 2; Animals; Anosmia; COVID-19; Humans; Olfaction Disorders; SARS-CoV-2; Smell
PubMed: 33965353
DOI: 10.1016/j.bjorl.2021.04.001 -
Trends in Neurosciences Oct 2016Behavioral evidence from phylogenetically diverse animals and from humans suggests that, by extracting temporal information inherent in the olfactory signal, olfaction... (Review)
Review
Behavioral evidence from phylogenetically diverse animals and from humans suggests that, by extracting temporal information inherent in the olfactory signal, olfaction is more involved in interpreting space and time than heretofore imagined. If this is the case, the olfactory system must have neural mechanisms capable of encoding time at intervals relevant to the turbulent odor world in which many animals live. Here, we review evidence that animals can use populations of rhythmically active or 'bursting' olfactory receptor neurons (bORNs) to extract and encode temporal information inherent in natural olfactory signals. We postulate that bORNs represent an unsuspected neural mechanism through which time can be accurately measured, and that 'smelling time' completes the requirements for true olfactory scene analysis.
Topics: Animals; Humans; Odorants; Olfactory Pathways; Olfactory Receptor Neurons; Periodicity; Smell; Time Factors
PubMed: 27594700
DOI: 10.1016/j.tins.2016.08.002 -
Scientific Reports Feb 2021Most current knowledge about dogs' understanding of, and reacting to, their environment is limited to the visual or auditory modality, but it remains unclear how...
Most current knowledge about dogs' understanding of, and reacting to, their environment is limited to the visual or auditory modality, but it remains unclear how olfaction and cognition are linked together. Here we investigate how domestic dogs search for their owners using their excellent olfactory sense. We raise the question whether dogs have a representation of someone when they smell their track. The question is what they expect when they follow a trail or whether they perceive an odour as a relevant or non-relevant stimulus. We adopted a classical violation-of-expectation paradigm-and as targets we used two persons that were both important to the dog, usually the owners. In the critical condition subjects could track the odour trail of one target, but at the end of the trail they find another target. Dogs showed an increased activity when the person did not correspond with the trail compared to a control condition. Moreover, we found huge individual differences in searching behaviour supporting the assumption that dogs are only able to smell when they really sniff, and that the temperature has an influence on dogs performance. Results are discussed in the light of how cognitive abilities, motivation and odour perception influence each other.
Topics: Animals; Appetitive Behavior; Dogs; Female; Male; Motivation; Smell
PubMed: 33558638
DOI: 10.1038/s41598-021-82952-4 -
International Journal of Environmental... Oct 2018A major step in our understanding of brain function is to determine how neural circuits are altered in their function by signaling molecules or neuromodulators.... (Review)
Review
A major step in our understanding of brain function is to determine how neural circuits are altered in their function by signaling molecules or neuromodulators. Neuromodulation is the neurochemical process that modifies the computations performed by a neuron or network based on changing the functional needs or behavioral state of the subject. These modulations have the effect of altering the responsivity to synaptic inputs. Early sensory processing areas, such as the main olfactory bulb, provide an accessible window for investigating how neuromodulation regulates the functional states of neural networks and influences how we process sensory information. Olfaction is an attractive model system in this regard because of its relative simplicity and because it links primary olfactory sensory neurons to higher olfactory and associational networks. Likewise, centrifugal fibers from higher order brain centers target neurons in the main olfactory bulb to regulate synaptic processing. The neuromodulatory systems that provide regulatory inputs and play important roles in olfactory sensory processing and behaviors include the endocannabinoid system, the dopaminergic system, the cholinergic system, the noradrenergic system and the serotonergic system. Here, we present a brief survey of neuromodulation of olfactory signals in the main olfactory bulb with an emphasis on the endocannabinoid system.
Topics: Brain; Humans; Neurotransmitter Agents; Olfactory Bulb; Smell; Synaptic Transmission
PubMed: 30297631
DOI: 10.3390/ijerph15102194 -
Current Opinion in Insect Science Oct 2023Extracting spatial information from temporal stimulus patterns is essential for sensory perception (e.g. visual motion direction detection or concurrent sound... (Review)
Review
Extracting spatial information from temporal stimulus patterns is essential for sensory perception (e.g. visual motion direction detection or concurrent sound segregation), but this process remains understudied in olfaction. Animals rely on olfaction to locate resources and dangers. In open environments, where odors are dispersed by turbulent wind, detection of wind direction seems crucial for odor source localization. However, recent studies showed that insects can extract spatial information from the odor stimulus itself, independently from sensing wind direction. This remarkable ability is achieved by detecting the fine-scale temporal pattern of odor encounters, which contains information about the location and size of an odor source, and the distance between different odor sources.
Topics: Animals; Odorants; Insecta; Smell; Wind
PubMed: 37419251
DOI: 10.1016/j.cois.2023.101082 -
Trends in Cognitive Sciences Jun 2021
Topics: Humans; Language; Olfactory Perception; Smell
PubMed: 33757701
DOI: 10.1016/j.tics.2021.02.004 -
Brain and Behavior Apr 2023In patients with mild cognitive impairment, pathological changes begin in the amygdala (AMG) and hippocampus (HI), especially in the parahippocampal gyrus and entorhinal...
INTRODUCTION
In patients with mild cognitive impairment, pathological changes begin in the amygdala (AMG) and hippocampus (HI), especially in the parahippocampal gyrus and entorhinal cortex (ENT). These areas play an important role in olfactory detection and recognition. It is important to understand how subtle signs of olfactory disability relate to the functions of the above-mentioned regions, as well as the orbitofrontal cortex (OFC). In this study, we evaluated brain activation using functional magnetic resonance imaging (fMRI), performed during the presentation of olfactory stimuli (classified as "normal odors" not inducing memory retrieval), and investigated the relationships of the blood oxygen level-dependent (BOLD) signal with olfactory detection and recognition abilities in healthy elderly subjects.
METHODS
Twenty-four healthy elderly subjects underwent fMRI during olfaction, and raw mean BOLD signals were extracted from regions of interest, including bilateral regions (AMG, HI, parahippocampus, and ENT) and orbitofrontal subregions (frontal inferior OFC, frontal medial OFC, frontal middle OFC, and frontal superior OFC). Multiple regression and path analyses were conducted to understand the roles of these areas in olfactory detection and recognition.
RESULTS
Activation of the left AMG had the greatest impact on olfactory detection and recognition, while the ENT, parahippocampus, and HI acted as a support system for AMG activation. Less activation of the right frontal medial OFC was associated with good olfactory recognition. These findings improve our understanding of the roles of limbic and prefrontal regions in olfactory awareness and identification in elderly individuals.
CONCLUSION
Functional decline of the ENT and parahippocampus crucially impacts olfactory recognition. However, AMG function may compensate for deficits through connections with frontal regions.
Topics: Humans; Aged; Odorants; Amygdala; Brain; Smell; Recognition, Psychology; Magnetic Resonance Imaging
PubMed: 36897168
DOI: 10.1002/brb3.2956 -
Neuroscience and Biobehavioral Reviews Feb 2024Domestic dogs (Canis familiaris) have excellent olfactory processing capabilities that are utilized widely in human society e.g., working with customs, police, and army;... (Review)
Review
Domestic dogs (Canis familiaris) have excellent olfactory processing capabilities that are utilized widely in human society e.g., working with customs, police, and army; their scent detection is also used in guarding, hunting, mold-sniffing, searching for missing people or animals, and facilitating the life of the disabled. Sniffing and searching for odors is a natural, species-typical behavior and essential for the dog's welfare. While taking advantage of this canine ability widely, we understand its foundations and implications quite poorly. We can improve animal welfare by better understanding their olfactory world. In this review, we outline the olfactory processing of dogs in the nervous system, summarize the current knowledge of scent detection and differentiation; the effect of odors on the dogs' cognitive and emotional processes and the dog-human bond; and consider the methodological advancements that could be developed further to aid in our understanding of the canine world of odors.
Topics: Dogs; Humans; Animals; Smell; Emotions; Odorants; Nervous System; Cognition
PubMed: 38160722
DOI: 10.1016/j.neubiorev.2023.105527 -
BMC Biology Jan 2023Camponotus floridanus ant colonies are comprised of a single reproductive queen and thousands of sterile female offspring that consist of two morphologically distinct...
BACKGROUND
Camponotus floridanus ant colonies are comprised of a single reproductive queen and thousands of sterile female offspring that consist of two morphologically distinct castes: smaller minors and larger majors. Minors perform most of the tasks within the colony, including brood care and food collection, whereas majors have fewer clear roles and have been hypothesized to act as a specialized solider caste associated with colony defense. The allocation of workers to these different tasks depends, in part, on the detection and processing of local information including pheromones and other chemical blends such as cuticular hydrocarbons. However, the role peripheral olfactory sensitivity plays in establishing and maintaining morphologically distinct worker castes and their associated behaviors remains largely unexplored.
RESULTS
We examined the electrophysiological responses to general odorants, cuticular extracts, and a trail pheromone in adult minor and major C. floridanus workers, revealing that the repertoire of social behaviors is positively correlated with olfactory sensitivity. Minors in particular display primarily excitatory responses to olfactory stimuli, whereas major workers primarily manifest suppressed, sub-solvent responses. The notable exception to this paradigm is that both minors and majors display robust, dose-dependent excitatory responses to conspecific, non-nestmate cuticular extracts. Moreover, while both minors and majors actively aggress non-nestmate foes, the larger and physiologically distinct majors display significantly enhanced capabilities to rapidly subdue and kill their adversaries.
CONCLUSIONS
Our studies reveal the behavioral repertoire of minors and majors aligns with profound shifts in peripheral olfactory sensitivity and odor coding. The data reported here support the hypothesis that minors are multipotential workers with broad excitatory sensitivity, and majors are dedicated soldiers with a highly specialized olfactory system for distinguishing non-nestmate foes. Overall, we conclude that C. floridanus majors do indeed represent a physiologically and behaviorally specialized soldier caste in which caste-specific olfactory sensitivity plays an important role in task allocation and the regulation of social behavior in ant colonies.
Topics: Animals; Female; Ants; Smell; Social Behavior; Pheromones; Odorants
PubMed: 36617574
DOI: 10.1186/s12915-022-01505-x