Taste stimuli

Simultaneous stimulation of the tongue with the appHcation of different taste stimuli produces an interaction, modification, or blending of the stimuli in some instances but not in others. Warm and cold sensations are reported to act similarly on the tongue in two groups bitter, warm, and sweet and sour, cold, and salty (24). The theory of the specificity of the taste buds may be subject to modification (25). 

Jigeusia. Lack or impairment of sensitivity to taste stimuli. 

Parageusia. Gustatory disturbance resulting ia erroneous identification of taste stimuli. 

Studies on the biochemistry of the taste system should take into account results obtained at other levels, such as electrophysiological recordings and, particularly, behavioral responses to taste stimuli. The term sweetness should strictly be used only in studies conducted on humans, because the description of taste modality is a verbal response. It is usually concluded that positive behavioral responses in animals, that is, preferences, or electrophysiological response to a stimulus compound that is known to be sweet to man, are due to the sweet taste. This may not necessarily be true in some cases, because behavioral or electrophysiological response may result from other taste modalities. It is, therefore, critical that comparative aspects be carefully interpreted. 

The chemical complexity of taste stimuli suggests that taste receptor cells utilize multiple molecular mechanisms... 

Fish have receptor cells specific for certain compounds. Examples are the reception of the fish toxins tetrodotoxin (TTX) and saxitoxin (STX) by rainbow trout, Salmo gairdneri, and Arctic chart, Salvelinus alpinus. Both toxins are extremely potent taste stimuli. Not only are the receptors extremely sensitive... 

One-day old rat pups show strong negative responses to strong taste stimuli such as strong acids or quinine solutions. They gape and flail with their forelimbs. At 12 days of age, they scrape their chin and tread with their paws (Johanson and Shapiro, 1986). 

Attempts to label dangerous substances with either characteristic or outright unpleasant odors have not been successful with children, the primary victims of accidental poisonings by toxic household products. Children tolerate odors that adults find unpleasant, such as that of butyric acid. The range between the most pleasant and unpleasant odors is much narrower for children around 4years of age than for adults, and also much narrower than for taste stimuli. This means that olfactory cues are not suited to produce aversive responses in children (Engen, 1974b, Cain, 1978). 

Johanson, I. B. and Shapiro, E. G. (1986). Intake and behavioral responsiveness to taste stimuli in infant rats from 1 to 15 days of age. Developmental Psychobiology 19, 593-606. 

Subjective Intensity Scale for Umami. Thresholds do not always express the relative potency of different taste stimuli, because the intensity of taste does not increase with concentration in the same manner for each substance. 

Novelty being a prerequisite for the stimulation of DA release in the NAc shell but not for behavioral hedonic reactions, release of DA in this area is likely to be a consequence rather than the cause of the appetitive properties of taste stimuli, consistent with the idea that taste-hedonia does not depend on DA (Berridge and Robinson, 1998). These observations, however, leave open the issue of a role of DA in state-hedonia (euphoria, eutimia) as distinct from stimulus-bound (e.g. taste) hedonia. 

Taste transduaion is initiated when taste stimuli interact with exposed cells in the apical microvilli of the tongue. The receptor-ligand interaction leads to membrane depolarization and to activation of afferent gustatory neurons. The perception of the common human taste qualities— sweet, bitter, salty, and sour—has been assigned to groups of taste neurons. But a characteristic property of taste transduction is that the taste cells can also be stimulated directly without the intervention of receptors. 

In contrast to visual perception, where the sole stimulus is a photon, and even in contrast to olfaction with its structurally much more diversified stimuli, taste perception is exceptional, because the taste stimuli differ even more than odorants in size and chemical complexity, ranging from H+ ions to carbohydrates, amino adds, and proteins. Consequently, taste transduction mi t involve different mechanisms for different stimuli. In the ihesus monkey, taste reception has been located anatomically to defined loci at either the anterior or the posterior part of the tongue. 

G protein-coupled receptors are a large class of transmembrane receptors. They have seven transmembrane helices. Therefore, they are called heptahelical or serpentine receptors. They bind watersoluble hormones, such as adrenaline but also peptides and accept sensory signals, light, odorants and some taste stimuli. On binding the ligand they transmit the signal to heterotrimeric, a,p,y-G proteins. 

Danilova V, Hellekant G (2003) Comparison of the responses of the chorda tympani and glossopharyngeal nerves to taste stimuli in C57BL/6J mice. BMC Neurosci 4 5 Dellisanti CD, Yao Y, Stroud JC, Wang ZZ, Chen L (2007) Crystal structure of the extracellular domain of nAChR alpha 1 bound to alpha-bungarotoxin at 1.94 A resolution. Nat Neurosci 10 953-962... 

Saitoh O, Hirano A, Nishimura Y (2007) Intestinal STC-1 cells respond to five basic taste stimuli. Neuroreport 18 1991-1995... 

James CE, Laing DG, Oram N. A comparison of the ability of 8-9-year-old children and adults to detect taste stimuli. Physiol Behav 1997 62 193-197. 

James CE, Laing DG, Oram N, et al. Perception of sweetness in simple and complex taste stimuli by adults and children. Chem Senses 1999 24 281-287. 

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