It's well-known that our senses of smell and taste get weaker as we get older, and new research now suggests that the way animals process odours (or fail to) could be used to predict how long they will ultimately live.
Researchers at the Salk Institute for Biological Studies in the US measured the way worms hone in on a pleasant, food-based smell and could subsequently predict whether the animals would be long-lived or not.
"We're not saying that your ability to smell is going to make you live longer," Sreekanth Chalasani of the Salk Institute's Molecular Neurobiology Laboratory, said in a statement. "But this odour behaviour is likely indicative of some kind of underlying physiology."
The researchers investigated how the brain activity of nematode worms (Caenorhabditis elegans) responded to benzaldehyde, a chemical with an almond-like scent. They found that the cells that respond to environmental stimuli are divided into two categories: primary neurons respond to the benzaldehyde, while secondary neurons respond to signals sent by the primary neurons.
In young worms, this neural circuit works just fine, but as worms get older, the secondary neurons become less active in responding to the signals from the primary neurons. Having observed this, the researchers were able to show a correlation between poor smelling performance (tracked by the worms' movement towards the benzaldehyde), the activity of secondary neurons, and the worm's lifespan.
Ultimately, older worms that showed better smelling ability lived about 16 percent longer than those that struggled to find the benzaldehyde source.
"Even though all these animals are siblings and have similar genomes, if you look at neuron activity, behavioural performance, or lifespan, there are significant differences," said Chalasani. "Perhaps that's because some animals have better signalling between primary and secondary cells."
The findings, published in eLife, could help us better understand how to fight the effects of ageing, according to the researchers. If we can find a way to manipulate the nervous system and control how these primary and secondary neurons interact with one another, we might be able to rejuvenate brain functions that are lost as we age – not only in worms, but also in other animals.
"There are a lot of questions that remain about what exactly is changing as an animal ages," said one of the team, Sarah Leinwand. "We want to keep looking at what is changing to cause some animals to have better functioning nervous systems and to live longer."