Abstract
Capsaicin is a naturally occurring vanilloid that causes a hot, pungent sensation in the human oral cavity. This trigeminal stimulus activates TRPV1 receptors and stimulates an influx of cations into sensory cells. TRPV1 receptors function as homotetramers that also respond to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Kinase-mediated phosphorylation of TRPV1 leads to increased sensitivity to both chemical and thermal stimuli. In contrast, desensitization occurs via a calcium-dependent mechanism that results in receptor dephosphorylation. Human psychophysical studies have shown that capsaicin is detected at nanomole amounts and causes desensitization in the oral cavity. Psychophysical studies further indicate that desensitization can be temporarily reversed in the oral cavity if stimulation with capsaicin is resumed at short interstimulus intervals. Pretreatment of lingual epithelium with capsaicin modulates the perception of several primary taste qualities. Also, sweet taste stimuli may decrease the intensity of capsaicin perception in the oral cavity. In addition, capsaicin perception and hedonic responses may be modified by diet. Psychophysical studies with capsaicin are consistent with recent findings that have identified TRPV1 channel modulation by phosphorylation and interactions with membrane inositol phospholipids. Future studies will further clarify the importance of capsaicin and its receptor in human health and nutrition.
Highlights
The chemosensory properties of capsaicin have been widely examined in the human oral cavity
This reapplication of stimulus may result in maximal intensities that were previously observed during sensitization with agonist [105, 154]. These findings suggest that capsaicin desensitization could be reversed by further application of this irritant and that desensitization and stimulus induced recovery (SIR) were likely facilitated by opposing cellular processes
Capsaicin is a naturally occurring compound that causes a pungent sensation in the human oral cavity when this vanilloid binds to TRPV1 receptors
Summary
The chemosensory properties of capsaicin have been widely examined in the human oral cavity. TRPV1 is widely expressed in central nervous system (CNS) tissue and highly expressed in sensory neurons of the dorsal root ganglion [19] This receptor localizes to neurons that line the oral and nasal cavities [10], where it is found in a subpopulation of sensory afferent nociceptive nerve fibers [20]. TRPV1 receptors localize to both plasma membranes and internal membranes (such as ER membranes) where this channel mobilizes internal calcium (Ca2+) stores [18] This nonselective cation channel has a tenfold higher preference for Ca2+ where it functions as a biosensor of noxious heat and chemical agonists [19]. This depletion can interfere with a variety of sensory functions, including the response of animals to noxious heat stimuli [42]
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