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Similar to human stress also causes depression in fruit flies
It has been known for a long time that people have a connection between mental health problems and high levels of stress. However, the processes by which stress levels lead to depression and other mental disorders remain largely unclear. Scientists at the Johannes Gutenberg University Mainz (JGU) have now investigated the effects of stress on fruit flies and found that these also fall under high stress in a depression-like condition, which, however, can be alleviated by lithium medication as well as by sugar.
The research team around the neurobiologist Professor dr. Roland Strauss was able to show on the basis of the fruit flies (Drosophila melanogaster) that they degenerate into a depressive state, which is controlled by serotonin and can be treated by lithium medication, said the JGU. Surprisingly, even when feeding sugar, an improvement was shown that was comparable to the lithium treatment of flies, the scientists report. The results of the current study were published in the journal "Nature Communications".
Even fruit flies show signs of depression under stress. (Image: Rainer Fuhrmann / fotolia.com) Fruit flies under uncontrollable stress
Fruit fly are widely used as a model organism for medical investigations, in particular to investigate genetic, developmental and neurobiological issues, the researchers explain. For the current study, the fruit flies were exposed for several days to uncontrollable stress caused by repeated vibrations of 300 hertz. At the same time, the scientists observed the behavior of the animals. For example, over the course of three stress days, "the willingness of animals to climb a gap of a certain width continuously decreased from 50 to 30 percent," reports the JGU.
Signs of depression in stressed fruit flies
In addition to the declining climbing tests, the stressed flies were also less motivated in their running activity and the courtship behavior than the non-stressed control group, the researchers explain. The escape behavior, however, worked normally, which made it clear that the flies were not physically impaired. Study author Ariane-Saskia Ries emphasizes that fruit flies under stress show signs of depression. Here are all "behaviors that are self-generated and require motivation, so not like escape behavior from the outside are stimulated, massively reduced."
Antidepressants and sugar relieve the symptoms of fruit flies
"As in humans, the depression-like state of Drosophila is associated with a serotonin deficiency and can be remedied by antidepressants," the researchers report. Surprisingly, however, the feeding of sugar has also improved and is almost as effective as the treatment of flies with lithium. With regular sugar administration after stress attacks even a preventive effect can be determined.
Lithium medication with reliable effect
Lithium has been used successfully for over 50 years against bipolar disorders and depression. The administration of lithium chloride in depressed or manic-depressive patients can often alleviate the symptoms successfully, but the exact mode of action remains unknown until today, according to the JGU. The fruit flies showed relief of the depressive state after three days of stress when 50 thousandths of lithium chloride were administered, and the flies also developed manic climbing behavior, the researchers report. Already the gift of only 5 thousandth mol was sufficient to relieve the stressed flies and restore normal climbing motivation.
Serotonin system with decisive influence
"The neurotransmitter serotonin plays an important role in the transmission of signals in the brain and thus in the motivation system," explain the scientists. Serotonin deficiency is thought to be the cause of depression in mammals. In the fruit flies, feeding with the serotonin precursor L-5-hydroxytryptophan led to a recovery from the depression-like state, which again suggests a connection with the neurotransmitter. By accident, the scientists discovered in this experiment also that a five percent sugar solution has the same effect, because they had the L-5-Hydroxytryptophan first marked with sugary, blue food coloring. With regular sugar administration after stress attacks even a preventive effect was to be achieved, the researchers report.
Different impact in different brain areas
The serotonin deficiency was found in the depressive states only in a certain area of the brain of fruit flies - in the alpha lobes of the mushroom body, according to the JGU. The mushroom body is the most important learning station of the brain and comparable to the vertebrate hippocampus. Activation of alpha lobules, for example by sugar, promoted the climbing behavior of Drosophila, while activation of gamma lobus inhibited climbing. In a complete destruction of the gamma-lobe, no more depression could be triggered, report the Mainz neurobiologists.
New strategies against stress and depressive illnesses
"We can specifically trigger both manic behavior and normal relaxation of depressive states," suggesting that "biochemical signaling pathways that have been preserved from an evolutionary perspective have played a role in both human and stressed flies," notes Professor Strauss the results together. The serotonin system keeps the animals in balance. "A bit of stress is healthy and promotes activity, too much stress causes depression and listlessness," says Strauss. Scientists hope that, based on the new findings, strategies can be developed in the future to strengthen resilience to stress and depressive disorders. (Fp)