Abstract
Nausea is the most characteristic negative experience that typically accompanies toxin-induced illness. Because most plant-derived toxins taste bitter, there is a rational link between bitter tasting compounds in the mouth and nausea that often results from their ingestion. It is surprising then that there are no experimental data demonstrating this connection. There are, however, data consistent with this notion. For example, people who are the most sensitive to bitter stimuli are more prone to motion sickness [1], and bitter taste sensitivity and pregnancy associated nausea are positively related, a response postulated to protect the fetus from poisoning [2]. Moreover, we know that bitter taste slows gastric emptying, a correlate of nausea [3]. Bitter taste is strongly sensed by the glossopharyngeal and vagus nerves [4], which innervate the posterior oral cavity and the gastrointestinal tract, respectively. The two projection fields of these sensory nerves are immediately adjacent within the nucleus of the solitary tract as well as in other brain relays [5], thus establishing a neuro-anatomical substrate for taste inputs to influence gastrointestinal states. Here, we report the first direct demonstration that bitter taste stimulation, but not sweet, salty, or umami taste, induces nausea, showing that the body not only detects potential toxins but anticipates their ingestion by inducing a prophylactic aversive state.