Peptide Identified as Potential Appetite Suppressant in Fl

05 Oct 2016 --- Scientists from the University of Würzburg have identified a peptide that could assume a key role in the complex interactions of hunger, sleep and digestion in the fruit fly Drosophila. The receptors that these peptides act on have closely related counterparts in humans and could potentially trigger interest from a human nutrition standpoint.

The study looked at a type of peptide found in fruit flies, called allatostatin, and revealed new information about how the peptide impacts hunger.

Although the cells of humans do not produce allatostatin, the receptor on which the peptide acts has a comparable counterpart, called the galanin receptor. This controls sleep, eating behavior and the peristalsis of the digestive system, making the results of the study very interesting from a human nutrition point of view.

Researchers investigated what influences the allatostatin peptide has on the flies' behavior, and studied fruit flies that were genetically modified to have only six allatostatin-producing neurons in their brains.

These cells were fitted with a temperature-controlled molecular "switch". An ambient temperature above 29 degrees Celsius caused the allatostatin signal to be "switched on" whereas it was "switched off" at lower temperatures.

When the cells released allatostatin, the fruit flies consumed much less food than insects from the control group. At the same time, they moved much less compared with the non-modified animals.

The cause of the reduced movement was uncertain. "When looking at the insects, it's not evident whether they don't have the energy to walk because they don't eat or whether they are unable to move for other reasons. Also it is unclear whether they are hungry or whether they just don't need so much because they exhibit so little activity," Professor Wegener outlined.

When the scientists lowered the ambient temperature back to values below 29 degrees, thereby switching peptide release off, the insects did not consume more food than the control group, so they were clearly not hungry.

Their locomotor system also worked normally, and they exhibited no differences compared to the control group in terms of the speed with which they climbed up a tube.

However, there was one distinct difference in the locomotor behavior. Fruit flies that are temporarily exposed to slight shaking on a kind of "vibrating plate" usually respond with a significant increase in locomotor activity.

Insects with a high allatostatin level did not deviate from this behavior, however only in the morning. At noon and in the evening, their activity patterns were unaffected by the shaking, and the flies remained stationary.

This finding lead the scientists to discover that the reason why the flies previously moved less was because they were asleep. In fact, the fruit flies with activated allatostatin A cells sleep during 1,400 minutes of the day's 1,440 minutes.

The scientists noticed that the six allatostatin-producing neurons in the brain of Drosophila are located in the direct vicinity of clock neuron terminals. They found was that allatostatin neuron arborisations overlap exactly with clock neuron arborisations, and carry receptors for the neuropeptide PDFwhich is released by the clock neurons.

The researchers commented that the results might show that the recently discovered mechanism is not a main path but an ancillary path of sleep control that connects sleeping with feeding habits.

Further studies are planned, with focus to study the fruit fly larvae, which eat constantly and never sleep.