Fruit fly brain cells hold the answer to smell

A research team at Cold Spring Harbour Laboratory (CSHL) has identified an important component in fruit fly brain circuits - the point at which incoming sensory information begins to be transformed into a signal that instructs a fly's response.

Responding appropriately to the smell of food or the scent of danger can mean life or death to a fruit fly and brain circuits are in place to make sure the fly gets it right.

The cells, called mushroom body output neurons (MBONs), appear to distil nuanced information about an odour into clear instructions - approach or flee.

By genetically labelling and following the activity of the same MBONs in multiple flies, the scientists found that each cell had a characteristic response pattern in each individual.

The pattern, in other words, differed between flies. This suggests that MBONs may underlie individual odour preferences that develop as flies learn to associate smells with positive or negative experiences.

A fly's behavioural response to an odour depends on the message that these output neurons relay to neurons farther along the circuit.

"As a fly lives its life and encounters a bunch of different odours, that olfactory experience may induce some plasticity in the circuit," said lead researcher professor Glenn Turner.

Researchers measured how MBONs responded to 10 different smells - an assortment of potentially enticing food smells, like yeast and vinegar, aversive smells such as citronella and more neutral aromas.

Responses varied greatly between cells, with each cell most strongly attuned to certain aromas.

When the team analysed the cells' responses, some patterns emerged. In general, food smells elicited response patterns that were distinct from those elicited by repellent odours, suggesting that although mushroom body output cells probably don't identify specific odours, they may communicate each odour's most essential quality -- whether it is good or bad. This can be the basis for action - to pursue the odour or fly away from it.