According to Murphy, the memory tests revealed that, relatively early in their short lives, the worms began to lose their ability to learn and retain information, with deficits starting to appear in the second day of adulthood. By the fourth day of adulthood, the worms had lost the ability to form long-term memories entirely.
After using the learning and memory tests to assess cognitive function in normal worms, the biologists did the same tests on two strains of C. elegans mutants with abnormally long lifespans.
One of the mutants tested has a defect in a gene known as daf-2, which controls the formation of the worm's insulin receptor, the researchers explained. This defect reduces the worm's ability to respond to the insulin hormone, and the gene is known to regulate survival, resistance to stress and the maintenance of motility in the worms. A similar gene in humans is known to regulate aging.
The other mutant has a genetic defect that makes it difficult for the worms to ingest food, forcing the animals to eat less. To date, caloric restriction has been observed to extend lifespan in every organism tested, including worms, mice and monkeys, Murphy said. While the reasons for this are still under investigation, scientists generally believe that the benefits of caloric restriction go well beyond preventing diseases associated with obesity, such as heart disease and diabetes, Murphy added. It appears that limiting food intake actually slows the aging process.
When the Princeton biologists conducted the learning and memory tests on the two strains of C. elegans mutants, they were surprised at the different effects on learning and memory arising from caloric restriction and reduction in the activities of the insulin-signaling pathways.
Young worms whose calories were restricted had normal short-term memo
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