Until Now, the Exact Mechanism Remained Unclear Because Many Molecular Components of These Odors Break Down Quickly

Researchers have for the first time decoded how domestic cats communicate through urine scent marks, solving a mystery that has puzzled scientists for over a century. Cats' sense of smell is roughly 14 to 40 times more sensitive than that of humans, allowing them to detect scent marks in the urine of other animals and gather information. Until now, the exact mechanism remained unclear because many molecular components of these odors break down quickly.

The international team led by Masao Miyazaki of Japan's Iwate University reports in the journal "Current Biology" that the animals' "chemical calling card" is based on 13 branched-chain fatty acids (BFAs). The precise combination of these compounds differs between individuals but remains fairly stable within each cat, enabling cats to match urine odors to familiar companions. In the study, cats sniffed familiar scent marks only briefly, even when they had not been exposed to the odor for months.

The team concluded that these scents are stored in the animals' memory over extended periods. In contrast, cats sniffed urine from unfamiliar cats significantly longer, frequently displaying the so-called flehmen response, a behavior common to many mammals in which they smell with their mouths open. "After confirming that cats can distinguish between individual urine odors, we used the flehmen response as a clue to identify the urine molecules that contribute to individual scent recognition, explained study leader Miyazaki.

This approach led the researchers to identify the 13 BFA compounds, which appear to be quite stable: the BFA profiles in urine lasted at least 24 hours at 25 degrees Celsius ambient temperature. Based on the cats' sniffing behavior, the team confirmed that the animals responded specifically to the particular BFA compositions when other urine components were identical. According to the study, cats store BFAs in the kidney, specifically in lipid droplets in the renal cortex.

Biologists had long known about these fat droplets in cat kidneys, but their function had remained a mystery. "Lipid droplets in the cat kidney have been known for over a century, but it has remained a secret why cats have so many of them, Miyazaki said. Our results suggest that one of their functions could be to support a stable chemical signature in the urine. This mechanism stabilizes the individual chemical signature of domestic cats, though it remains unclear how the BFAs stored in the droplets reach the urine.