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A group of neuroscientists of Johns Hopkins discovered that the psychoactive drug MDMA, or ecstasy, causes a neuronal response called "critical period", when the brain is sensitive to learning the reward value of social behaviors.
The results, reported Wednesday in Nature, may explain why MDMA may be useful in treating people with post-traumatic stress disorder.
Scientists first studied the critical periods in the 1930s. About 24 hours after hatching of a fledgling, the researchers observed that if the mother of goose was not found, the neonate would bind to an object, including non-living objects. However, if the mother of goose disappears after the critical period, about 48 hours later, the newborn will not bind to an object.
Since the study of snow lee, studies have shown that critical periods smooth the development of language, touch and vision. For the MDMA study, scientists at the Johns Hopkins School of Medicine wanted to determine if there was a critical time to learn the benefits of social behavior and, if so, whether the drug could reopen the critical period.
If MDMA reopened the critical learning period of social reward, then it could explain why the drug has been successful in treating people with PTSD, perhaps by strengthening the psychotherapist-patient relationship.
Neuroscientist Gül Dölen and his team studied groups of mice in pens with different bedding. They put several mice together in the same enclosure with one litter type for 24 hours and, within 24 hours, placed the same mice alone in another enclosure with a different type of litter. The mice began to associate certain types of bedding with isolation or with the company. Then, they let the mice wander between the speakers with both types of litter and followed the time spent by the mice in each enclosure. More time spent by mice in the bedding associated with their companions indicated more fruitful social learning.
"That's why people gather around the water fountain," says Dölen, assistant professor of neuroscience at the Johns Hopkins University School of Medicine. People are conditioned to know that the water cooler is a great place to chat with mates.
In their experiments, Dölen and his colleagues discovered that the critical period of social reward learning in mice is around puberty and declines once they have become mature adults. To determine if they could reopen the critical period, scientists administered MDMA to mature mice, waited 48 hours for the drug to be removed from their system and observed how the mice had explored their pens and behaved with mice. other mice. After MDMA treatment, most animals responded to social interactions in the same way as juveniles, forming a positive association between social interactions and litter. This effect lasted at least two weeks after MDMA treatment and was not observed in mice injected with saline.
"This suggests that we have reopened a critical period in mice, giving them the ability to learn social reward behaviors at a time when they are less likely to adopt these behaviors," Dölen said.
MDMA only reopened the critical period if the drug was administered to mice while they were with other mice, but not when it was administered to mice alone.
Dölen and his postdoctoral fellow and first author of the present study, Romain Nardou, also observed that MDMA only reopened the critical period if the drug was administered to mice while they were with other mice. . are alone. This suggests that the reopening of the critical period with the help of MDMA may depend on the fact that the animals are in a social context, say the scientists.
The mice retained their ability to learn the benefits of social behavior up to two weeks after receiving MDMA. Meanwhile, Dölen and his colleagues also discovered that the brain of mice had corresponding responses to oxytocin, called "love hormone", which is produced in the hypothalamus and acts in the brain as a signal between neurons that code information on social rewards. They found these answers by looking more closely at synapses, the spaces between brain cells called neurons. Their experiments have shown that in mature mice given MDMA, oxytocin triggers signaling in synapses that codes for learning and memory, which is not usually the case at home. mature mice.
According to Dölen, opening the critical window of reward social behavior could also have consequences on the treatment of psychiatric problems. A strong link between a psychotherapist and a patient is recognized as important for successful treatment. If MDMA reopened the critical learning period of social reward in humans in the same way as in mice, then it could explain why the drug has been successful in treating people with PTSD, possibly to be reinforcing the psychotherapist-patient relationship.
The USDA (Food and Drug Administration) has designated MDMA as a "revolutionary therapy" for PTSD, which means the agency will accelerate the development and revision of clinical trials to test it. The researchers warned, however, that MDMA may not work for all psychiatric problems related to social behaviors.
"When we develop new therapies or determine when to give these therapies," says Dölen, "it is essential to know the biological mechanism they are acting on."
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