Anxiety and Alcohol Use Linked to Genes in Fruit Flies

Fruit flies can get anxious and drunk too, at least judging by behavioral similarities with people. Even the effects of anti-anxiety drugs seem similar.

Since they multiply so quickly, their brains are so small, and their genes can be manipulated so readily, they make an attractive model to study the biology of alcohol use and anxiety disorders in people. That is especially important since alcohol use disorder is said to affect as many as 6% and anxiety disorders 14-20% of US adults in a 12-month period. And differences in people’s likelihood of developing either disorder leads to interest in inherited traits that might lead to these disorders.

Neuroscientist Gregory Engel and his associates at Middlebury College, writing in Behavior and Brain Functions (2019), reviewed the genetics of alcohol use in the fruit fly, starting with the observation that fruit flies, like humans, have a natural variation in alcohol sensitivity and how it can be studied with the “inebriometer:”

“Flies exposed to increasing concentrations of alcohol in a large vertical tube would gradually fall due to the loss of postural control and sedation,” they wrote. “Flies will also become sedated following exposure to long periods of low concentration alcohol vapor. The inebriometer assay has been refined to quantify subtle behavioral changes due to alcohol exposure, and to increase the efficiency of screening large numbers of genotypes at once.”

By measuring these behaviors along with manipulating genes, researchers have focused on individual genes or networks of genes responsible for differences in alcohol sensitivity. A natural step after that is to see if similar genes contribute to alcohol sensitivity in humans.

Fruit flies can show anxious behavior too, some more than others. Neuroscientist Farhan Mohamed and colleagues wrote in the journal Current Biology that more anxious flies spent more time near the walls of an enclosed glass chamber, while others hovered near the center.

They found that the anti-anxiety drug diazepam was able to reduce the wall-clinging behavior, while stressful experiences like social isolation increased it. They were able to change the wall-clinging behavior associated with anxiety “by manipulating the d5-HT1A, d5-HT1B, and dSerT genes. These are similar to genes that influence serotonin release and uptake in mammals, and whose deletion or over-expression in mice changes anxious behavior.”

One conclusion is that your sensitivity to anxiety or alcohol might be partly linked to genes and neural transmitters that are widespread in the animal kingdom. And think twice before leaving out over-ripe fruit, since the fruit flies show a strong preference for the fermenting juice.