Dr. Danielle Reed "Introduction to Taste and Smell"“There are several sensory systems in mammals, the major categories being vision, hearing, pain and touch, taste and smell, as well as other minor categories. These sensory systems have several features in common: (1) specific adequate stimuli (the stimuli that are sufficient to evoke the sensory process), (2) modality or how the stimuli information is conveyed, (3) parameters that affect the intensity of the experience, (4) adaptation, (5) receptive fields (where in or on the body the stimuli can be perceived), and (6) how the system extracts and reacts to the sensory information. For taste and smell, the adequate stimuli are chemical. The ability to detect chemicals plays many roles in mammals, for example, to help an animal find wholesome food and desirable mates, to strengthen mother-infant and other social relationships, and to warn others way from territory. The exact modality of taste and smell has been a matter of debate, with several opposing theories. There are a variety of ways to measure the relationship between chemical stimulus concentration and perception, such as detection and recognition thresholds, perceived intensity, just-noticeable differences, with other types of related measures, such as hedonic ratings. Taste and smell display adaptation, although the chemical stimuli remain in the environment, the experience of intensity can decrease over time. The receptive fields for taste and smell are limited to the tongue and mouth for taste, and the olfactory epithelium in the nose for smell. There is a ‘general chemical sense’ on some parts of the body, for instance, acid on the skin is perceived, but this mechanism differs from perception that results from stimulation of the tongue. Taste and smell begins when specialized receptors within specialized cell types are stimulated, a nerve impulse is generated and relayed to the brain, where it is processed and interpreted. Some taste and smells generate the same response in almost everyone tested, e.g., bitter is bad, but more flexibility exists in the interpretation of other chemical stimuli, e.g., certain smells are good to some people but not others, or are only good in a specials context. Although taste and smell share many of the same properties with other sensory systems, the range of chemical stimuli that can be perceived and their diverse effects (e.g., food, sex, social dominance) make the study of these systems especially rewarding.”
Dr. Xia Li "Evolution of Sweet Taste in Carnivores"
Sweet taste is transduced primarily by one receptor, a dimer of two related proteins, T1R2 and T1R3 (genes symbols Tas1r2 and Tas1r3). Mutations in either protein could have a spectrum of consequences, from little or no alterations, to complete loss of activity of the receptor. Previous behavioral studies demonstrated that animals in Felidae, including domestic cats and wild cats, are indifferent to sweet stimuli, and likely cannot perceive their taste. We argued that this indifference could be explained by the observation that in cats the sweet receptor gene, Tas1r2, is a pseudogene showing many stop codons,
deletions and substitutions. To explore when the alteration of Tas1r2 occurred, we examined the sequences of Tas1r2 in 33 species of Order Carnivora by PCR, and performed taste-tests on five selected species to evaluate their preference of sweet stimuli. Neither stop codons nor deletions were detected in exons 3, 4 and 6 of Tas1r2 of these species, this being consistent with our behavioral tests and with their strict carnivorous or omnivorous behavior. These observations suggest that Tas1r2 is functional in selected carnivore species and that the pseudogenization of Tas1r2 in cats occurred in the lineage of Felidae after it split from other families of Feliformia around 30-35 MYA.
Dr. Stuart McCaughey "Please and Reward in Feeding"
“Human beings and other species eat for a variety of reasons, including the simple fact that it feels good. The pleasure derived from feeding is useful, in that it motivates animals to obtain the calories and nutrients that they need to survive. I will discuss some of the brain areas and neurochemicals that are involved in controlling the intake of palatable foods, such as sugars. A distinction will be made between the pleasure derived from food (“liking”) and the motivation to obtain it (“wanting”), since there is evidence that these two processes involve different mechanisms. In addition, I will describe how addictive drugs, including
cocaine, stimulate some of the same neural pathways that are activated by sugars. Finally, there will be a consideration of how the palatability of minerals, such as sodium and calcium, can be enhanced by physiological need in rats.”
Dr. Beth Gordesky-Gold "Taste Behavior in the Fly"
“The fruit fly, Drosophila melanogaster, is a versatile experimental organism. It is small in size, easy to care for and reproduces quickly; the fruit fly is only 10 days from egg to adult (25°C), so it can be backcrossed and its genes can be isolated in a short amount of time. The fruit fly has a well-organized visual and chemosensory nervous system and a complex behavioral repertoire. The molecular and behavioral aspects of taste in a fruit fly are very similar to humans; and, as many of you know, the fly even likes to eat many of the same foods. We have tested the fruit fly for preferences for a variety of tastants in order to
learn how far the similarities extend. For instance, artificial sweeteners taste sweet to humans. We want to know if the fly will also consider them appetitive and ingest them even though they are non-nutritive. Like mammals, the fruit fly utilizes G protein-coupled receptors with seven transmembrane domains to mediate taste responses. Ligands for only two of the sixty prospective receptors have been discovered. Gr5a binds the sugar trehalose and Gr66a is a caffeine receptor.”