Scientists from Tokyo Metropolitan University have uncovered key parts of the biochemical pathways that link stress to sexual dysfunction. Studying Drosophila fruit flies, they showed that the neurotransmitter dopamine was responsible for determining when male flies exhibited persistent courtship suppression after being confined to a small space, but not whether mating was initially suppressed. Their findings in a key model organism illuminate neurobiological factors that cause sexual dysfunction in other organisms, including humans.
The biochemistry of stress is a critical but poorly understood aspect of neurobiology. Exposure to internal or external stimuli is known to trigger changes in the brain that continue to affect organisms well beyond the duration of the event. An example is how stress affects sexual behavior. People suffering from PTSD are known to often experience sexual dysfunction. But despite strong evidence, the molecular mechanisms by which stress causes reduced sex drive are not yet understood.
A team led by Professor Takaomi Sakai of Tokyo Metropolitan University used the fly Drosophila to study the relationship between stress and behavioral changes. Fruit flies are vital “model organisms,” whose biochemical pathways are similar enough to a wide range of animals, including mammals, to reveal key aspects of their function while being much easier to study. The team examined how “small space” stress, the impact of placing male flies in a confined space, led to the suppression of courtship behavior. Confinement stress is known to affect many organisms, but this was the first time it was applied to the study of fruit flies.
The team found that the length of time the male flies were stressed affected how long the suppressive courtship behavior lasted. Flies confined for ten minutes showed no suppression, while those confined for 30 or 60 minutes revealed clearly suppressed courtship. The more stressed the flies were, the longer the effect lasted. In fact, those subjected to 7 or 24 hours of stress showed suppression of courtship for at least five days. Interestingly, this was not simply due to reduced mobility or appetite.
To identify the biochemical origin of this phenomenon, they investigated dopamine, a neurotransmitter known to be involved in stress responses. Studying fruit flies with dopamine production either genetically or pharmacologically suppressed, they found that neither showed any difference in whether courtship suppression occurred or not. However, it did significantly affect whether the stress-induced response lasted. Thus, dopamine is specifically involved in persistence of stress-induced behavior change. They traced this effect to the mushroom body, a part of the brain associated with sensory processing, where specific dopamine receptors have been found to mediate the maintenance of stress-induced behavior.
The team’s findings illuminate the specific role that dopamine plays in mediating the effect of stress on sexual dysfunction. This is critical to elucidate how stress affects behavior and well-being in other organisms, including humans.
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