At first glance, fruit flies and people appear to have very little in common. It is possible to learn more about human nature, particularly with regard to depressive disorders, by studying these flies. On the basis of this, researchers at Johannes Gutenberg University Mainz (JGU) are working to better understand states that resemble depression and, consequently, develop methods for treating them. The journal Current Biology recently published the findings.
Natural ingredients used in traditional Asian medicine may be advantageous.
In response, Professor Roland Strauss of the JGU Institute of Developmental Biology and Neurobiology stated, “We have been examining the effects of natural substances used in traditional Asian medicine, such as in Ayurveda, in our Drosophila fly model (IDN). Some of these may have antidepressant properties or preventatively build resilience to long-term stress, preventing the onset of a depressive state altogether. Among other things, the researchers want to show how effective these ingredients are, figure out how best to use them, and separate the pure active ingredients from the original plant material. These might eventually be sold as medicines. However, there is still much work to be done because this is only basic research.
Because we can examine the entire signaling chain in the Drosophila model, we can determine precisely where these substances are active, Strauss noted. Additionally, each step of the signaling pathway can be demonstrated. The researchers apply a mild form of recurrent stress, such as irregular phases of substrate vibration, to the flies. The flies that receive this treatment eventually develop a depression-like state (DLS), meaning that they move more slowly, don’t stop to look at unexpected sugar, and are less inclined to climb large gaps than their more relaxed counterparts. How do the flies behave differently after ingesting the various natural substances? How each natural substance was prepared, like whether it was taken out with water or alcohol, has a big effect on the results.
Evening incentives can lessen depression.
The research team has also found that rewarding the flies for 30 minutes in the evening of a stressful day can prevent the development of a DLS. This can be done by giving them food with a higher sugar content than usual or by activating the reward signaling pathway. What transpires, though, if the flies receive a sugar reward? The tarsi, or lower part of the legs, and the proboscis of the flies are known to contain sugar receptors, and the location of the signaling pathway’s end, where serotonin is released onto the mushroom body, was also established. The body of the mushroom, which is similar to the hippocampus in people, is where the fly’s associative learning centers are.
Investigations by the researchers revealed that the pathway was much more complicated than predicted. Until the serotonin deficiency in the mushroom body, which is present in flies in a DLS, is made up for by reward, three different neurotransmitter systems must be engaged. The dopaminergic system, which also conveys reward in humans, is one of these three systems. But despite these findings, people shouldn’t make the assumption that eating foods with a lot of sugar in them is a good idea. In contrast to how humans can achieve the same effect through other, healthier means, flies view sweetness as a reward.
Preventing depression while increasing resilience
The scientists also decided to search the fly genome for resilient elements. Drosophila flies are genetically unique, just like humans; no two flies are alike in this regard. Because of this, the team wants to know if and how the genomes of flies that can handle stress better and those that produce a DLS in response to repeated mild stress differ. In the future, it may be possible to find out a person’s genetic risk for depression and then treat them with the natural remedies that are also being researched for this project.
