Researchers discuss the role of chemical senses in disease and social interactions in humans, animals

Across 5 days in August (3rd-7th), scientists from around the world gathered virtually to present and discuss new information on the role of the chemical senses in disease, nutrition, and social interactions in humans and animals.

The chemical senses, olfaction (smell), gustation (taste), and chemesthesis (touch, temperature, irritation), play essential roles in our daily lives - they serve as important warning systems, alerting us to the presence of potentially harmful situations or substances, including gas leaks, smoke, and spoiled food.

Flavors and fragrances are also important in determining what foods we eat and the commercial products we use. The pleasures derived from eating are mainly based on the chemical senses.

Thousands of Americans experience loss or dysfunction of the chemical senses each year resulting from head trauma, sinus disease, cancer, and neurological disorders, such as stroke, multiple sclerosis, and Alzheimer's disease, among others.

Indeed, loss of smell and/or taste is a notable and troubling symptom of the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has infected millions globally in just the first half of 2020. By providing a better understanding of the function of chemosensory systems, scientific and biomedical research is leading to improvements in the diagnosis and treatment of many disorders.

Among those presenting their research advancements were members of the Association for Chemoreception Sciences , which held its 41st annual meeting in conjunction with the 2020 International Symposium on Olfaction and Taste.

During AChemS/ISOT, scientists from around the world presented their latest research findings on myriad topics around chemosensation, ranging from molecular mechanisms through cognitive processes and associated behaviors.

Selected new discoveries presented at the meeting include:

Understanding the sense of smell via synthetic odors

To study the sense of smell, we generated "synthetic odors" in mice by direct control of brain activity. We measured how mice responded to careful manipulation of artificial odors, discovering that odors are represented by precisely-timed sequences of brain activity akin to timed notes in a melody.

Odors change when we know their names

Odors are invisible, and not always easy to identify. Even so, most people agree on which things smell similar and which are different. Reading the name of an odor while sniffing conjures up a mental image of the odor source and transforms the smell itself.

The enhanced evolutionary mechanism of olfaction

How did mammals end up with many odorant receptors allowing us to smell thousands of odors? A few highly functional ancestral odorant receptors evolved into numerous less functional receptors that rely on external proteins to function.

Decreased sense of smell leads to future depression in older US adults

We show for the first time that poor sense of smell predicts the development of depression in older U.S. adults (and not vice versa). These results support mental health screening programs for people with decreased sense of smell.

Smelling with single cells: testing the sensitivity limits of olfaction

Using two-photon holographic optogenetics, we showed that mice can reliably detect single spikes across small sets of targeted olfactory bulb neurons. We found that detection performance depends strongly on neuronal synchrony but not on latency relative to inhalation.

Factors impacting refreshment

Refreshment is one key reason that consumers enjoy beer, however, there is very limited understanding of impact factors on beer refreshment. This study was aimed to investigate the impact of flavor (citrus, cucumber, lime) and alcohol (0%, 2.5%, 5.0%, 7.5% abv.) on liking and intensity of 12 formulated beers evaluated by 322 participants. The results indicated that refreshing perception was significantly dependent on the likings and intensities of alcohol level and both overall and tested beer flavor.

No differences for liking or taste sensitivity after ultraprocessed and non-processed foods

A randomized, crossover study, twenty participants received ultraprocessed or unprocessed diet for two weeks then two weeks on the other diet. There were no differences in sweet or salt taste measures between the diets. A positive relationship between salt taste preference with blood pressure, body weight, and BMI was observed following the processed diet. The different diets may not initially contribute to changes in taste preference or sensitivity. However, two weeks of a processed diet may be sufficient to detect a relationship between salt taste preference and health parameters.

Beta-caryophyllene (BCP) improves wound healing in mice

BCP enhanced cell proliferation/migration, suppressed inflammation, and enhanced re-epithelialization. RNA sequencing showed genes related to embryonic growth, cell proliferation/migration, and hair follicle bulge stem cells are up-regulated in response to BCP treatment.

A psychological stressor conveyed by appetite-linked neurons

Using single cell RNA-sequencing, retrograde viral tracing, and chemogenetics, we discovered that POMC neurons linked to appetite suppression also play a key role in stress hormone responses to physical restraint, a psychological stressor.

Filiform papillae are "in the thick" of viscosity

Longer filiform papillae or a higher density on the tongue confer sensitivity to viscous solutions. Interestingly, the hard palate is equally responsive, suggesting people may compensate for lack of sensitivity in one tissue by using the other.

Autism gene affects processing of unfamiliar odors

Autism can produce odor hypersensitivity. A mouse with a gene mutation associated with autism showed deficits in odor identification only with unfamiliar background odors, but not familiar ones. Hypersensitivity occurred only for new odors.

Reliable readout of mixture components from small populations of anterior piriform cortical neurons Numerous compounds are inhaled in a single sniff. Piriform cortex is central in analyzing mixtures, yet the nature of mixture representations is largely unknown. We show that a simple model accounts for most mixture responses and that individual compounds can be identified from neural activity.

Bitter taste receptors (TAS2Rs) mediate food allergy (FA)

Food allergen peptides can stimulate TAS2Rs which may mediate allergy reactions. We observed FA patients have higher bitter taste sensitivity and a lower expression of TAS2Rs than non-FA group, which might cause the failure of allergen tolerance.

Ethanol perception varies with thermal taste status

Thermal tasters report phantom taste sensations simply by having the tip of their tongue warmed or cooled while thermal non-tasters do not and tend to rate intensity of sensations elicited by wine and beer higher than thermal non-tasters.

Here, consumers rated taste and mouthfeel sensations from ethanol at levels found in beer, wine, and spirits. Results suggest that thermal tasters experience a wider set of sensations from alcoholic beverages, which may impact their preferences and, ultimately, their alcoholic beverage purchase choices.

The life and death of a taste cell

The cells in mammalian taste buds turn over continuously--new cells enter the bud, and old cells die and leave the bud. We examined cell death with detailed images of a mouse taste bud. We found that healthy taste cells might be eating up dying taste cells!

Cranberry polyphenols and individual differences in salivary proteins

Drinking astringent beverages rich in polyphenols can alter salivary protein levels. We tested saliva of subjects after they drank cranberry-derived beverages and found that certain people in the population may have higher levels of key salivary proteins and that this variation is related to bitter taste genetics and gender.