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Chemosensation
Published in Emily Crews Splane, Neil E. Rowland, Anaya Mitra, Psychology of Eating, 2019
Emily Crews Splane, Neil E. Rowland, Anaya Mitra
The chemical analysis of odorant molecules is performed by detectors called olfactory receptors that are clustered on the dendrites of olfactory receptor neurons that are embedded in the olfactory epithelium, a specialized structure lining the roof of the nasal cavity, about 3 cm x 3 cm in humans (Figure 5.1). Although small in size, this sensory surface expresses some 400 distinct olfactory receptors all of which belong to a superfamily called G-protein coupled receptors (GPCRs). GPCRs are protein chains of at least 300 amino acids that thread through the cell membrane seven times forming three domains or loops outside the cell that define a specific size and shape of pocket or “nest” for binding their ligands. Different GPCRs have different amino acid sequences in these loops that yield different shaped pockets. Some of these receptors seem to have a high threshold for activation and respond to a relatively narrow range of odorant shapes while others seem to have low threshold for activation but respond to a broad range of odorant shapes (Yu et al., 2015).
Fundamentals in nasal drug delivery
Published in Anthony J. Hickey, Heidi M. Mansour, Inhalation Aerosols, 2019
Zachary Warnken, Yu Jin Kim, Heidi M. Mansour, Robert O. Williams, Hugh D.C. Smyth
In addition to enzymes, the olfactory epithelium also contains binding proteins, which bind hydrophobic odorants and mediate internalization of the substances into lysosomes within the supporting cells of the epithelium, the sustentacular cells (29,49). This also leads to rapid clearance of hydrophobic odorants and may play a role in the clearance of hydrophobic drugs from the tissue. The enzymes in the olfactory epithelium are largely located in the sustentacular cells, the olfactory receptor neurons having very little xenobiotic-metabolizing capacity. Enzyme differences between species may play an important role in studying drug delivery in animal models. cytochrome P450 family 2 subfamily G (CYP2G), for example, has two copies in humans; however, neither function in the majority of individuals. However, Cynomolgus moneys have a functional copy expressed that is active toward coumarin, a common fluorescent molecule used for testing intranasal drug delivery systems. While the enzyme locations in specific cell types are similar across various species, the distribution and concentrations of enzymes can vary greatly (29,44).
Identifying Pharmaceutical-Grade Essential Oils and Using Them Safely and Effectively in Integrative Medicine
Published in Aruna Bakhru, Nutrition and Integrative Medicine, 2018
Essential oils are unique remedies because they simultaneously influence psychological, biological, and cognitive health. The sense of smell—10,000 times more powerful than the sense of taste—is the only of the major senses that is directly connected to the brain (through the olfactory bulb). Airborne odor molecules enter the nostrils and dissolve in the nasal mucosa. Under the nasal mucosa, olfactory receptor neurons detect the odor molecules and transmit information to the olfactory bulb at the back of the nasal cavity. Sensory receptors of the olfactory bulb are part of the brain and send messages to the most primitive brain centers (limbic system structures) and the neo-cortex, which influence memory, emotions, and conscious thought. Therefore, the administration of essential oils produces a complete psychophysiological response that causes automatic adaptations by the central nervous system.
World Trade Center dust induces nasal and neurological tissue injury while propagating reduced olfaction capabilities and increased anxiety behaviors
Published in Inhalation Toxicology, 2022
Michelle Hernandez, Joshua Vaughan, Terry Gordon, Morton Lippmann, Sam Gandy, Lung-Chi Chen
Molecular studies tend to contain biological data which inform on the occurrence of significant biological changes. However, these studies are often deficient, in that many of the observed molecular changes may or may not be directly related to functional changes at a whole- tissue or organism level. Given the complex dynamic of molecular pathophysiology, it is important to question – if exposure-related molecular changes are observed, do phenotypic evaluations exist that could inform on disease pathogenesis or overt disease progression? Within the nasal passages, olfactory information is processed in olfactory epithelial cells lining the upper regions of the nasal cavity. The remaining nasal cavity is lined with neuron-lacking respiratory epithelia which serve as a protective surface. Within the olfactory epithelia, olfactory sensing neurons/receptor neurons are responsible for transmitting olfactory information back to the CNS. Of utmost importance are olfactory sensing neurons- the only CNS tissue with direct links to the external world, which contain unique stem cells that give rise to new olfactory neurons throughout adult life, with capacity to replace olfactory receptor neurons after damage to the olfactory nerve. Olfactory receptor neuron turnover is critical and key considering it is the only CNS tissue to also regenerate (Suzuki et al. 2000; Slotnick et al. 2010).
Extracellular vesicles isolated from human olfactory ensheathing cells enhance the viability of neural progenitor cells
Published in Neurological Research, 2020
Olfactory ensheathing cells (OECs) are a unique type of glia present in the lamina propria of the olfactory mucosa, the outer layer of the olfactory bulb, and both inner and outer layers of the nerve fiber [1,2]. OECs ensheathe non-myelinated primary olfactory axons and enhance neural regeneration by migrating and promoting olfactory sensory axon extension from the nasal epithelium towards the olfactory bulb [3,4]. These cells sustain continuous axon extension and successful topographic targeting of olfactory receptor neurons. Numerous studies have demonstrated that OECs support neural regeneration by stimulating axonal myelination [5], secreting important survival factors for regenerated axons such as neurotrophic factors [6–8] and extracellular matrix (ECM) molecules [9–11], and regulating cell debris phagocytosis [12] and neuroinflammation [13]. Thus, these cells play critical roles in neurogenesis and neural regeneration, which are specific features of the mammalian olfactory system. Because of their distinctive properties and autologous origin, transplantation of OECs has emerged as an alternative potential therapy for repairing central nervous system (CNS) damage, particularly for spinal cord injury [14].
Cellular and circuit mechanisms of olfactory associative learning in Drosophila
Published in Journal of Neurogenetics, 2020
Tamara Boto, Aaron Stahl, Seth M. Tomchik
The mushroom body (MB) is a critical anatomical structure involved in olfactory memory formation, as well as some types of visual and courtship memory (McBride et al., 1999; Vogt et al., 2014). The MB is situated in the olfactory pathway, as the tertiary structure, hierarchically similar to the mammalian amygdala or piriform cortex (Su, Menuz, & Carlson, 2009). Olfactory stimuli are initially detected by olfactory receptor neurons (ORNs) in the periphery, which transmits information to projection neurons (PNs), and subsequently the MB and another structure, the lateral horn (Davis, 2005; Fiala, 2007). The intrinsic MB neurons, also called Kenyon Cells (KCs), relay information to mushroom body output neurons (MBONs) (Aso et al., 2014a; Tanaka, Tanimoto, & Ito, 2008) via cholinergic synapses (Barnstedt et al., 2016). The MB is innervated by modulatory neurons, such as dopaminergic neurons (DANs), which are critical for learning and memory (Tanaka et al., 2008). This description includes the basic circuit elements (ORN→PN→KC→MBON; w/modulatory DANs) (Figure 1(A,B)), and will be further elaborated below. Note that while the general flow of information is most easily conceptualized as unidirectional, some of these connections exhibit both pre- and post-synaptic zones indicative of bidirectional communication (Christiansen et al., 2011; Pauls, Selcho, Gendre, Stocker, & Thum, 2010; Rolls et al., 2007) (Figure 1(C)). This bidirectional communication adds a layer of complexity with behavioral and computational implications that are largely unknown currently.