The principal determinants of taste threshold are genetic, and taste thresholds do not vary considerably from day to day. Taste is an important protective sense, evolved to drive food intake and aid in the avoidance of poison. In addition, we show that the general anxiety level is directly related to taste perception, suggesting that altered taste and appetite seen in affective disorders may reflect an actual change in the gustatory system. We present a model to explain these findings. We show that 5-HT and NA participate in setting taste thresholds, that human taste in normal healthy subjects is plastic, and that modulation of these neurotransmitters has distinct effects on different taste modalities. In addition, the anxiety level was positively correlated with bitter and salt taste thresholds. In contrast, enhancing NA significantly reduced bitter taste threshold by 39% and sour threshold by 22%.
Measurement of taste function in healthy humans before and after a 5-HT reuptake inhibitor, NA reuptake inhibitor, or placebo showed that enhancing 5-HT significantly reduced the sucrose taste threshold by 27% and the quinine taste threshold by 53%. In this study, we show for the first time that human taste thresholds are plastic and are lowered by modulation of systemic monoamines.
Circumstances in which serotonin (5-HT) and noradrenaline (NA) are altered, such as in anxiety or depression, are associated with taste disturbances, indicating the importance of these transmitters in the determination of taste thresholds in health and disease.