A1-2, Micrographs of isolated taste buds immunostained for serotonin (5-HT).
Two immunopositive taste cells (red) are visible in this plane of focus. A3, Micrograph of a
Fura2-loaded (green) biosensor cell abutted against an isolated taste bud in a living preparation.
(adapted from Journal of Neuroscience (2005) 25(4): 843-847; Journal of Neuroscience
(2015) 35(37): 12714-12724).
In addition to transmitting gustatory responses to prototypic taste stimuli, taste transmitters may contribute to regulating the function of adjacent taste cells. It is now being recognized there is a significant degree of information processing in the taste buds during gustatory stimulation. We are learning that cell-to-cell communication between neighboring taste cells is a key event before signals are sent to the brain via primary sensory fibers. My lab studies functions of peripheral gustatory sensory organs -- taste buds, using sophisticated anatomical and physiological methods. We apply an innovated technique, including real-time functional calcium imaging with cellular biosensor cells, to detect the secretion of transmitters, and to examine signal processing in taste buds. We used transgenic mice expressing GFP in taste cells. This will allow us to identify specific types of taste cells, and to selectively test transmitter release from taste bud cells. For instance, we, using GAD67-GFP transgenic mice, identified GABA, which inhibits ATP secretion from adjacent Receptor (Type II) cells, secreted from Presynaptic (Type III) cells.
(click for larger pdf image) GABA immunostaining of an isolated taste bud from a GAD67-GFP mouse. Many GABA immunopositive taste cells express GFP (thick arrows), but some do not (thin arrows). This latter category may be Type I cells (adapted from PLoS ONE 6(10): e25471).
Science News and Information:
Mouse Taste Cells Discriminate Sweet and Sour Tastes by Releasing Neurotransmitters Sensory signals from the oral cavity are carried to the brain in chemosensory fibers that contribute to chemesthesis, the general chemical sensitivity of the skin and mucus membranes in the oronasal cavities and being perceived as pungency, irritation or heat. Taste perception alterations follow condition changes in the mouth, such as temperature. For instance, the pungency of foods and beverages is likely highly influenced by the temperature at which they are consumed, their acidity, and, for beverages, their carbonation. Furthermore, electrophysiology revealed that taste perception is enhanced as the temperature of food and beverage products increases. The mechanism why/how this occurs is not fully known. Intriguingly, despite the profusion of work identifying mechanisms of chemosensation, little information has been generated regarding irritant–taste interactions. By the use of the cellular biosensor strategy, we reported that calcitonin gene-related peptide (CGRP), which may be released from peripheral axon terminals, modulated taste-evoked ATP secretion from taste buds, which is a key transmitter for communication from taste buds to gustatory nerves. Indeed, unambiguously, our findings suggest that the complex interplay between taste cells and chemosensory neurons may play an important role during the processing of the complex stimuli involving both spicy and tasty components.
(click for larger pdf image) Double immunohistochemistry on an isolated taste bud. RCP-immunoreactive (red) taste cells (arrowheads) and SNAP25-immunoreactive (green) Presynaptic (Type III) cells (large arrow) were revealed. Some taste cells exhibit double labeling, suggesting that these Presynaptic (Type III) cells express RCP (small arrows), representing CGRP receptors. (adapted from Journal of Neuroscience (2015) 35(37): 12714-12724).
The characterization of local transmitters and their effects in the taste bud is essential not only for basic understanding of sensory afferent excitation but also for potential clinical applications. These include development of taste modifiers for potential use in management of obesity, compliance in taking medications (particularly in pediatrics), and pharmaceutical development in the context of diminished taste sensation or ageusia (lack of taste) related to age or disease chemotherapy. Indeed, taste perceptions are altered by medications that inadvertently also act on taste bud transmitters. For example, selective serotonin reuptake inhibitors such as, e.g., Prozac - a selective serotonin reuptake inhibitor (SSRI) antidepressant, have known taste side effects. Additionally, our latest findings indicate that Imiquimod, an immune modulator approved for the treatment of basal cell carcinoma, cause abnormal transmitter secretion in taste buds, which may be the basis for taste disturbances that has long been observed in people taking these drugs but has never understood. Nevertheless, my lab plays a pioneering role in exploring the mechanisms of taste reception, and in providing the important information for sensory processing in human health and diseases.
(click for larger pdf image) Schematic drawing represents the postulated scenario of CGRP, a putative efferent transmitter, in taste buds. A, Red box represents approximate position of the taste buds in B. B, Numerous CGRP-immunoreactive nerve fibers forming a dense network (large arrows) are seen in the connective tissue core of the papilla, and fine fibers (small arrows) run within, or in close association with, taste buds (areas of dashed lines). C, Chemesthetic stimulation activates sensory afferent fibers that propagate signals centrally (double-headed arrows) and have the ability to release the stored transmitter, CGRP (orange curved arrow). The activation of the CGRP receptors triggers Presynaptic (Type III) cells to secrete 5-HT, which inhibits ATP release from Receptor (Type II) cells (black symbol). (adapted from Journal of Neuroscience (2015) 35(37): 12714-12724).
Science News and Information:
Chemesthesis Affects Taste
Recent Publications (since 2005)