Researchers have already succeeded in understanding how the receptors in our mouths pick up on sweet tastes; they are now claiming to have identified the role of the membrane proteins responsible for signaling bitterness in taste cells of the tongue.
The findings appear in the upcoming issue of Nature.
A group of special receptors known as T2Rs have been previously implicated in bitter-taste sensitivity, but until now their role remained relatively unclear, said the researchers led by Charles Zuker.
To investigate their action, Zuker and his colleagues bred genetically altered mice that lacked T2R receptors.
They found that these animals showed a dramatic loss in sensitivity to bitter compounds and therefore no longer avoided these substances, suggesting that T2R receptors are necessary and sufficient to detect bitterness.
Moreover, the scientists discovered that mice designed to have a certain type of T2R receptor on their sweet-taste cells actually enjoyed bitter liquids. This implied that bitter substances tasted sweet to them and highlighted the idea that specific taste cells are tuned to particular tastes, whatever receptors are present.
Taste is a key driver in the $4.3 trillion global food industry and a greater understanding of the physiology of consumers, could lead to strong market advantages.
Earlier this month, researchers in the US discover that activity in the nucleus accumbens (Nac) neurons is associated with the response to the tastes.
The brain "centre" called the NAc is a key component of the brain's "reward" pathways. Scientists at the University of North Carolina found that not only does the NAc decide whether stimuli - in this case sweet sucrose or bitter quinine - are rewarding or aversive, but the centre's neurons also encode learning associated with the stimuli.
The NAc is located in the brain's limbic system, which generates feelings and emotions.
Publishing their findings in Neuron, (volume 45, number 4, February 17, 2005, pages 587-597), the researchers found neurons in the NAc fired in response to both the sucrose and the quinine, showed that the brain centre played a role in judging both rewarding and aversive stimuli.
They also found that different sets of NAc neurons responded to the sucrose than to the quinine, revealing different circuitry for processing rewarding and aversive stimuli.
"The findings presented here continue to support the idea that the NAc comprises part of the brain's reward circuit," wrote the researchers. "Neural responses are organized on a microcircuit level--that is, rewarding and aversive responses are segregated."