New Scientist - USA (2020-03-28)

16 | New Scientist | 28 March 2020

CAN you taste the difference

between sugar and a zero-calorie

sweetener? It seems specialised

cells in your gut probably can

within milliseconds.

Research in the 1950s revealed

that food doesn’t need to pass

through the mouth to stimulate

the brain – mice respond in this

way when foods are put directly

into their stomachs, too.

Two years ago, Diego

Bohorquez at Duke University in

North Carolina and his colleagues

identified a new type of cell that

gives the gut its own ability to

sense nutrients. These neuropod

cells were spotted in the intestines

of mice, and rapidly sent signals

via the vagus nerve, which links

the gut to the brain, related to

the presence of sugary snacks.

To find out whether these cells

can tell the difference between

sugar and zero-calorie sweeteners,

the researchers put a range of

sugars and sweeteners into the

guts of mice. At the same time,

the team used a device to measure

vagus nerve activity. All of the

sugars triggered the neuropod

cells to send a signal to the vagus

nerve – except for fructose.

The fact that fructose, a natural

sugar found in fruit, doesn’t seem

to trigger a rapid signal to the

brain may explain why fruit

doesn’t give our brains the same

reward as chocolate, says Elisa Hill

at RMIT University in Australia.

“It would be great to know if these

systems can be trained to favour

fruit over chocolate,” she says.

In another set of experiments,

Bohorquez and his team studied

organoids, small lumps of living

tissue grown from cells taken from

the intestines of mice or humans.

The team found that only sugars

that contained calories triggered

release of a compound called

glutamate as a signal to the vagus

nerve. Zero-calorie sweeteners

delivered an entirely separate

signal to the vagus nerve, via a

compound called ATP (bioRxiv,

doi.org/dp43).

The findings suggest the gut

senses the sweet taste and calorie

content of substances separately,

and sends both signals to the brain

within milliseconds. This sense

might have evolved to enable

animals to find energy-rich foods,

says Jonathan Swann at Imperial

College London. “Determining

what’s energy-dense and what’s

energy-scarce would be very

important in seeking out foods.”

It is likely that similar cells are

doing the same thing in people’s

guts, says Hill. If so, tinkering

with the way the cells work may

influence the way our brains

respond to sweet foods. In the

future, the cells could be targeted

in treatments to modify eating

behaviours and for some people

with obesity, she says.

Neuropod cells may also be

a way for gut bacteria to rapidly

communicate with the brain, says

Swann. Disruptions to the gut

microbiome have been linked to

a range of neurological disorders,

including Parkinson’s disease and

mood disorders. ❚

“ It would be great to know

if sweet-sensing gut cells

can be trained to favour

fruit over chocolate”

Diet

Jessica Hamzelou

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News

Even without tasting them,

our bodies may tell sugars

from sweeteners

Animal behaviour

Penguins call out

under water but

we don’t know why

WE KNOW that whales, dolphins,

seals and even sea turtles vocalise

under water – and now we have

discovered that penguins do it

too. It is the first time seabirds

have been found to produce such

sound beneath the waves.

“The use of acoustic signals

at sea could potentially enhance

seabirds’ foraging success, but

this remains largely unexplored,”

says Andréa Thiebault at Nelson

Mandela University in South Africa.

She and her team fixed cameras

and audio recorders to a variety of

penguins – six king, 10 gentoo and

two macaroni – at Marion Island,

South Africa. The kit was designed

for pressures up to 300 metres

down, where the animals hunt.

They recorded a total of

203 vocalisations during nearly

5 hours of underwater footage.

The sounds were very short

chirps – 0.06 seconds on average –

and differed from the penguins’

land vocalisations, which are

around 3 seconds long, much

louder and include a variety

of sounds (PeerJ, doi.org/dp49).

Prior to the study, the team had

been studying how Cape gannets

and African penguins interact with

their own species on the surface

of the sea during foraging trips.

“With African penguins, we found

their calling increased in frequency

when they went out feeding on

their own. This told us that they

call to aggregate or attract other

penguins... as their foraging success

is greater when they forage in

groups,” says Pierre Pistorius

at Nelson Mandela University.

While they are still figuring out

what the penguins are saying under

water, most of the vocalisations

took place just before capturing

prey. Pistorius says the calls could

mean anything from “Hooray,

food” to “Help me catch it”. The

sounds might even be used to

disorientate prey. ❚

Nicky Willemse

Beneath the

ocean surface,

penguins make

short chirps as

they chase prey

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Sugar or sweetener? Your gut

can tell the difference

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