Date Published: 19 July 2005
Recent research suggests a mechanism to fill gaps in existing theory of taste
It has long been established that the human tongue can distinguish between five main tastes. Different areas of the tongue have different sensitivites such that maps of the tongue can be drawn indicating the areas that best respond to the different types of taste, e.g. sweet, salty, sour, and bitter.
The sensation of taste has been generally understood to occur via the "taste buds", which are tiny bumps on our tongues that consist of clusters of 50-100 cells. Nerve fibres connect each bud to the brain to send signals about taste, but only a few of the cells in each bud touch these fibres. Scientists therefore assumed that those cells that do not have a direct connection to a nerve fibre must have some other way of sending a signal to it, but the mechanism by which this occurs was not known.
Research has identified two chemical messengers:
- The chemical that corresponds to bitter taste is called CCK and was discovered a few years ago.
- A chemical corresponding to a sweet taste has recently been found in the tongue's taste buds. This has been called "Neuropeptide Y", or NPY.
The two chemicals CCK and NPY are believed to act in contrast (a "push-pull mechanism") to each other to form the bitter-sweet tastes we experience when consuming some foods.
Dr Scott Herness and his team at Ohio State University have recently suggested that the chemical messenger CCK may tell neighbouring cells that are attached to the nerve fibres that a bitter taste is on the tongue, while the presence of NPY may tell them that the taste is sweet.
In their recent study, they compared the electrical signals given off from taste bud cells when NPY was applied with those signals given off with exposure to CCK. It was found that NPY activated a completely different signal than CCK, suggesting that these two chemicals trigger different responses in the same individual cells. NPY had the exact opposite action of CCK - which would ensure that the brain gets a clear message of what kind of taste is on the tongue.
Professor Tim Jacob, an expert in smell and taste at Cardiff University, said the work was very interesting and that these chemicals might be released by the same cell into the outside spaces surrounding taste receptor cells rather than into the narrow gap that cells normally use to communicate, which is called the synaptic cleft.
He concluded that
"Classical synaptic transmission may have to be revisited".
Source: UK News Media.
See for example http://news.bbc.co.uk/1/hi/health/4692475.stm.