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Effects of Essential Oils on Human Cognition
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
It has been shown in experimental animals that due to their lipophilic properties, fragrances do not only penetrate the skin (Hotchkiss 1998), but also the blood–brain barrier (Buchbauer et al. 1993). Also, odorants have been found to bind to several types of brain receptors (Aoshima and Hamamoto 1999; Elisabetsky et al. 1999; Okugawa et al. 2000), and it has been suggested that these odorant–receptor interactions are responsible for psychoactive effects of fragrances in experimental animals. With regard to these findings, it is important to note that Heuberger and co-workers have observed differential effects of fragrances as a function of chirality (Heuberger et al. 2001). It seems likely that such differences in effectiveness are related to enantiomeric selectivity of receptor proteins. However, the question remains whether effects of fragrances on human arousal and cognition rely on a similar psychopharmacological mechanism.
Dopamine Receptors, Signaling Pathways, and Drugs
Published in Nira Ben-Jonathan, Dopamine, 2020
The Rhodopsin subfamily is the largest and most diverse among the GPCRs. It comprises about 720 receptors that respond to light, odorants, catecholamines, small peptides, and glycoprotein hormones. There are approximately 240 non-odorant receptors and the remainder are odorant receptors, accounting for the highly diverse responsiveness of these receptors to olfactory cues. Several consensus motifs are unique to this class of GPCRs, including an E/DRY sequence in TM3 and an NPXXY motif in TM7, which together contribute to a common activation mechanism. There are also distinct structural characteristics that are involved in receptor stabilization and ligand-induced conformational changes. For instance, studies using electron microscopy and confirmed by X-ray crystallography have shown that the TM helices are bent at points positioned near proline residues or Gly-Gly sequences. These regions appear to act as hinges for the relative movement of transmembrane domains within the helical bundle.
Phytochemistry, Pharmacology, and Safety Issues of Essential Oils: Applications in Aromatherapy
Published in Megh R. Goyal, Hafiz Ansar Rasul Suleria, Ademola Olabode Ayeleso, T. Jesse Joel, Sujogya Kumar Panda, The Therapeutic Properties of Medicinal Plants, 2019
Anindya Sundar Ray, Suman Kalyan Mandal, Chowdhury Habibur Rahaman
Stimulation of the mammalian olfactory system depends on the accuracy of recognizing and discriminating different chemically distinct odorant molecules that are present in EOs. Detection of these odorants probably results from the association of odorous ligands with specific receptors present on the neurons of the olfactory system. It is estimated that humans can identify more than 10,000 distinct odorous ligands [20]. However, it does not imply that humans possess an equally large number of receptors for all structurally distinct odors. Each individual receptor can only sense structurally related (stereochemically) odor molecules. The genes, which code for about 1000 different types of odorant receptors, form the largest gene family so far described in mammals: larger than the immunoglobulin and T-cell receptor gene families combined. The amino acid sequences of odorant receptors (Olfactory receptors) are very diverse, but all odorant receptors are coupled to heterotrimeric G-proteins.
Olfactory dysfunction in chronic rhinosinusitis: insights into the underlying mechanisms and treatments
Published in Expert Review of Clinical Immunology, 2023
Jing Song, Ming Wang, Chengshuo Wang, Luo Zhang
In CRS patients with OD, OSNs show an abnormal morphology with no discernible dendrites and/or axons [39]. Similar changes in axons and dendrites of OSNs can also be observed in animal model of CRS. For example, the axons of OSNs have been shown to undergo degeneration in a mouse model of lipopolysaccharide-induced nasal inflammation and the degree of axon degeneration correlates with individual olfactory status [53,54]. In a rat model of nasosinusitis induced by staphylococcus, OSNs have been shown to lose part of the dendrites or ciliary structures, affecting the detection of olfaction [55]. Additionally, extensive ciliary damage and downregulation of expression of odorant receptors has been shown to occur in the OE of anosmia/hyposmia patients infected with SARS-CoV-2 [56,57]. It has been suggested that the loss of sensory cilia causes chemosensory anosmia [58]. Collectively, these findings suggest that morphologic changes and decreased olfactory G protein-coupled receptors interfere with the ability of OSNs to perform their normal function and this leads to the development of OD in CRS patients.
Inter-organ regulation by the brain in Drosophila development and physiology
Published in Journal of Neurogenetics, 2023
Sunggyu Yoon, Mingyu Shin, Jiwon Shim
Drosophila sense odors and tastes to recognize their habitat and discriminate whether their surroundings are beneficial or harmful. Chemical compounds of putative food are perceived by external organs. The information from peripheral neurons is processed in the central brain. Drosophila larvae exhibit 21 odorant receptor neurons (ORNs) that are localized in the central dome sensillum of the dorsal organ (DO). Collected in the dorsal organ ganglion (DOG), ORNs project onto the larval antennal lobe, which connects with the mushroom body calyx or lateral horn to modulate behavior and memory in Drosophila larvae (Ramaekers et al., 2005). In the presence of the olfactory co-receptor Or83b, also known as Orco, up to 60 odorant receptors (ORs) distinguish volatile compounds via different modes of heterodimeric receptors. For example, olfactory receptor neurons expressing Or42b are stimulated by yeast or vinegar (Semmelhack & Wang, 2009) thus mediating attractive behaviors, whereas Or85a-, Or33b-, and Or45a-expressing ORNs elicit aversive actions (Bellmann et al., 2010; Root et al., 2011). After metamorphosis, the olfactory receptor neurons of adult flies exhibit increased complexity compared to larval stages and express ∼1200 and 120 ORNS in the antenna and maxillary palp, respectively (Hallem & Carlson, 2006).
Neurological manifestations and pathogenic mechanisms of COVID-19
Published in Neurological Research, 2022
Matteo Galea, Michaela Agius, Neville Vassallo
Gustation is also closely linked with olfaction, as during mastication there is the release of odorants which then bind to the odorant receptors. Indeed, the perception of flavor is actually an amalgamation of olfactory and gustatory sensation [95]. This could potentially imply that the gustatory dysfunction being observed amongst those infected may actually be attributed to the onset of anosmia. In fact, the exact mechanism through which SARS-CoV-2 may cause disruption in taste perception has not been fully elucidated. However, studies have observed a high ACE2 receptor expression on tongue epithelial cells [96]. Moreover, potential activation of toll-like receptors through cytokine release, particularly IL-6 and interferon gamma, may lead to taste bud inflammation and death. This in turn may cause alterations in taste perception.