Spoilt appetite

2019-03-07 04:19:01

By Philip Cohen SWEET things taste less sweet after a meal, say researchers who have found that a full belly numbs the tongues of rats. “We’ve been eating for millions of years without understanding why we do it or why we stop,” says Andras Hajnal, a behavioural scientist at the Pennsylvania State University in Hershey. Previously, Hajnal’s group had found that a small amount of corn oil injected into the duodenum, the first part of the intestine, makes rats stop eating and rest as if thoroughly sated. To understand the neural underpinnings of this response, Hajnal and his colleagues Kaoru Takenouchi and Ralph Norgren implanted electrodes into the pontine parabrachial nuclei of rats, a brain region involved in the detection and processing of taste. When the researchers infused corn oil into the rodents’ intestine, the firing rate of neurons that responded mostly or only to sucrose dropped by 55 and 77 per cent respectively. To the rat, this probably means sugary tastes are less intense or less pleasant. In contrast, those neurons that responded only to salt continued to fire at the same rate (The Journal of Neuroscience, vol 19, p 7182). The researchers speculate that the responses to oil and sugar are linked because they are markers for the calorific value of food. Hajnal suspects the same mechanism operates in humans and could one day help food scientists to design more delectable desserts. More immediately, he thinks his findings will interest researchers who study the neurological basis of cravings such as drug addiction or sexual desire. “Like hunger, these are strongly motivated states,