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Depression-like symptoms seen in flies

April 22, 2013
Courtesy of Cell Press
and World Science staff

When faced with im­pos­si­ble cir­cum­stances be­yond their con­trol, an­i­mals, in­clud­ing peo­ple, of­ten hun­ker down as they de­vel­op sleep or eat­ing dis­or­ders, ul­cers, and oth­er phys­i­cal man­i­festa­t­ions of de­pres­sion. 

Now, re­search­ers say the same kind of thing hap­pens to flies, as they un­dergo a con­di­tion called “learn­ed help­less­ness” that al­so af­flicts oth­er an­i­mals. 

A study on the sub­ject, re­ported in the April 18 is­sue of the re­search jour­nal Cur­rent Bi­ol­o­gy, is a step to­ward un­der­stand­ing the bi­ol­o­gy of de­pres­sion and pre­s­ents a new way to test an­ti­de­pres­sant drugs, the re­search­ers say. They add that find­ing such symp­toms in an in­sect shows the roots of de­pres­sion are deep in­deed.

“De­pres­sions are so dev­as­tat­ing be­cause they go back to such a bas­ic prop­er­ty of be­hav­ior,” said Mar­tin Hei­sen­berg of the Ru­dolf Vir­chow Cen­ter in Würzburg, Ger­ma­ny. Hei­sen­berg said that the idea for the study came out of a long dis­cus­sion with a col­league about how to tell wheth­er flies can feel fear. Fran­co Ber­to­luc­ci, a co­au­thor of the stu­dy, had found that flies can quick­ly learn to sup­press in­nate be­hav­iors, a phe­nom­e­non that’s part of learn­ed help­less­ness.

The re­search­ers found that flies suf­fer­ing un­com­fort­a­ble lev­els of heat will walk to es­cape it. But if the bugs real­ize the heat is be­yond their con­trol and un­avoid­a­ble, they’ll stop re­spond­ing, walk­ing more slowly and tak­ing long­er and more fre­quent rests, as if they were “de­pressed.”

In­tri­guing­ly, fe­male flies slow down more un­der those stress­ful cir­cum­stances than males do, Hei­sen­berg said. It’s not clear just what that means, he added, but he ar­gued: “if we real­ize that the fly trapped in a strange, dark box, un­able to get rid of the dan­ger­ous heat pulses, has to find a com­pro­mise be­tween sav­ing en­er­gy and not mis­sing any chance of es­cape, we can un­der­stand that such a com­pro­mise may come out dif­fer­ently for males and fe­males, as their re­sources and goals in life are dif­fer­ent.”

Hei­sen­berg’s team now in­tends to ex­plore oth­er ques­tions, such as: How long does the flies’ de­pres­sion-like state last? How does it af­fect oth­er be­hav­iors, like court­ship and ag­gres­sion? What’s hap­pen­ing in their brain? And more.

Hei­sen­berg said that the find­ings are a re­minder of a les­son that chil­dren’s books are of­ten best at show­ing: “An­i­mals have lots in com­mon with us hu­mans. They breathe the same air, share many of the same re­sources, ac­tively ex­plore space, and have dis­tinct so­cial roles. Their brains serve the same pur­pose, too: they help them to do the right thing.”


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When faced with impossible circumstances beyond their control, animals, including people, often hunker down as they develop sleep or eating disorders, ulcers, and other physical manifestations of depression. Now, researchers say the same kind of thing happens to flies, as they undergo a condition called “learned helplessness” that also afflicts other animals. A study on the subject, reported in the April 18 issue of the journal Current Biology, is a step toward understanding the biology of depression and presents a new way to test antidepressant drugs, the researchers say. They add that finding such symptoms in an insect shows the roots of depression are deep indeed. “Depressions are so devastating because they go back to such a basic property of behavior,” said Martin Heisenberg of the Rudolf Virchow Center in Würzburg, Germany. Heisenberg said that the idea for the study came out of a long discussion with a colleague about how to ask whether flies can feel fear. Franco Bertolucci, a coauthor on the study, had found that flies can rapidly learn to suppress innate behaviors, a phenomenon that’s part of learned helplessness. The researchers found that flies suffering uncomfortable levels of heat will walk to escape it. But if the bugs realize the heat is beyond their control and unavoidable, they’ll stop responding, walking more slowly and taking longer and more frequent rests, as if they were “depressed.” Intriguingly, female flies slow down more under those stressful circumstances than males do, Heisenberg said. It’s not clear just what that means, he added, but he argued: “if we realize that the fly trapped in a strange, dark box, unable to get rid of the dangerous heat pulses, has to find a compromise between saving energy and not missing any chance of escape, we can understand that such a compromise may come out differently for males and females, as their resources and goals in life are different.” Heisenberg’s team now intends to explore other questions, such as: How long does the flies’ depression-like state last? How does it affect other behaviors, like courtship and aggression? What’s happening in their brain? And more. Heisenberg said that the findings are a reminder of a lesson that children’s books are often best at showing: “Animals have lots in common with us humans. They breathe the same air, share many of the same resources, actively explore space, and have distinct social roles. Their brains serve the same purpose, too: they help them to do the right thing.”