The worm that learned: Diet found to affect learning in older nematodes

Newswise — A team from Nagoya University in Japan has made an intriguing discovery regarding the impact of diet on the cognitive abilities of nematodes, minute worms measuring less than a millimeter in length. The researchers found that when these worms consume the bacteria Lactobacillus reuteri, they do not experience the usual decline in associative learning ability associated with aging. These findings may have implications for mitigating age-related cognitive decline in various animals, including humans. The study documenting their results was published in the scientific journal eLife.

Associate Professor Kentaro Noma from Nagoya University's Graduate School of Science remarked on the significance of the research, stating, "This study provides a valuable approach to investigating the effects of diet on brain function in aging individuals. By employing nematodes and bacteria as food sources and utilizing the nematodes' capacity to measure both individual lifespan and age-related changes in brain function, we identified dietary conditions that sustain brain function without extending lifespan. While we typically attribute the decline in brain function to aging, it is possible that the mechanisms governing the aging of brain function and individual lifespan are distinct."

The research community is keen on understanding how diet can contribute to maintaining optimal brain activity. However, the intricate effects of diet make it a challenging subject to study. As a result, scientists often investigate simpler organisms to gain insights into the fundamental mechanisms involved in these processes.

One such organism is the nematode Caenorhabditis elegans, which is favored by researchers due to its uncomplicated anatomy, short lifespan of merely two weeks, and genetic manipulability. The research team specifically employed this nematode species, as it possesses a simple nervous system and exhibits memory and learning behaviors, allowing for the examination of brain function.

Noma had a particular fascination with thermotaxis, which refers to the movement of an organism towards a preferred temperature. He explained that nematodes appear to learn by associating the presence or absence of food with the temperature at which they are raised. If a certain temperature is accompanied by food during their development and they are later placed on a temperature gradient without food, they will move towards the temperature they were reared at. However, if they are raised at the same temperature without food, they will not exhibit thermotaxis towards that temperature. Noma saw thermotaxis as an indicator of associative learning ability.

To investigate the influence of diet on learning, the research team examined 35 different strains of lactic acid bacteria owned by Megmilk Snow Brand Co. Their goal was to identify potential diets that could preserve the nematodes' associative learning ability as they aged. Among the strains tested, they discovered Lactobaillus reuteri, a probiotic that has been studied for its potential health benefits, particularly in managing gastrointestinal disorders. This bacterium was found to be associated with maintaining the nematodes' ability to learn, without affecting their lifespan.

To understand how L. reuteri affects nematodes, the group identified a crucial protein called the DAF-16 transcription factor, which regulates the functioning of the nematodes' neurons when they are fed L. reuteri. This discovery was significant because the DAF-16 gene is involved in regulating the processes of aging and longevity.

Noma remarked, "Since our intestines host numerous bacteria, including E. coli and lactobacilli, the balance of these bacteria may also impact our brain function. Moreover, genes similar to those identified in this study are also present in humans. This suggests that the mechanism explaining the effect of diet on changes in brain function with age may exist in humans as well. With further research, it is possible that maintaining optimal brain function in old age through dietary interventions will become a reality."