The researchers added a bacterial product — rapamycin — to the diet of healthy mice throughout their life span. Rapamycin, first isolated from soil on Easter Island, enhanced learning and memory in young mice and improved these faculties in old mice, studies showed.
Mice with less anxiety are more curious to explore the catwalk. "We observed that the mice fed with a diet containing rapamycin spent significantly more time out in the open arms of the catwalk than the animals fed with a regular diet," Halloran said.
The second test measured depression-like behavior in the rodents. Mice do not like to be held by their tails, which is the way they are moved from cage to cage. Inevitably they struggle to find a way out. "How much and how often they struggle is a measure of the motivation they have to get out of an uncomfortable situation," Dr. Galvan said.
Some mice barely struggle to get free, but if an antidepressant is administered they struggle a lot more. "We found rapamycin acts like an antidepressant — it increases the time the mice are trying to get out of the situation," Dr. Galvan said. Anxiety and depression-like behavior decreased in all ages of mice fed with the rapamycin-enhanced diet.
The researchers measured levels of three "happy, feel-good" neurotransmitters: serotonin, dopamine and norepinephrine. All were significantly augmented in the midbrains of mice treated with rapamycin. "This is super-interesting, something we are going to pursue in the lab," Dr. Galvan said.
Rapamycin rescued learning and memory in mice affected by Alzheimer’s-like deficits, the team previously reported. In the new studies, the enhancements are demonstrated even in healthy mice. The elevation of the three neurotransmitters, which are chemical messengers in the brain, may explain how rapamycin accomplished this, Dr. Galvan said.
Rapamycin is an antifungal agent administered to transplant patients to prevent organ rejection. The drug is named for Rapa Nui, the Polynesian title for Easter Island. This island, 2,000 miles from any population centers, is the famed site of nearly 900 monolithic statues (pictured above). If rapamycin proves to be a suitable therapy for human cognition, this mysterious atoll could be called the Easter Island of learning and memory.
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