Study reveals how a cat's nose can identify food scents

Washington [US], July 1 : Scientists have figured out how cats can locate food, allies and enemies.

This research was published in PLoS Computational Biology.

A complicated network of tightly coiling bony airway structures is to blame, according to the first thorough investigation of the domestic cat's nasal airway.

In order to mimic how air containing typical cat food scents would pass through the coiled structures during an inhalation, the researchers built a 3D computer model of the cat's nose. They found that the air divides into two flow streams, one of which purifies and humidifies the air, and another of which swiftly and effectively transports the odorant to the part of the body responsible for smell, the olfactory region.

According to the experts, the cat nose serves as a highly effective and dual-purpose gas.A complicated network of tightly coiling bony airway structures is to blame, according to the first thorough investigation of the domestic cat's nasal airway.

In order to mimic how air containing typical cat food scents would pass through the coiled structures during an inhalation, the researchers built a 3D computer model of the cat's nose. They found that the air divides into two flow streams, one of which purifies and humidifies the air, and another of which swiftly and effectively transports the odorant to the part of the body responsible for smell, the olfactory region.

According to the experts, the cat nose serves as a highly effective and dual-purpose gas.In fact, the cat nose is so effective at this that its structure may inspire improvements to today's gas chromatographs.

While the long alligator nose has been found to mimic gas chromatography, scientists believe that the compact cat head drove an evolutionary change that resulted in the labyrinthine airway structure that not only fits but also helps cats adapt to diverse environments.

"It's a good design if you think about it," said Kai Zhao, associate professor of otolaryngology at Ohio State's College of Medicine and senior author of the study.

"For mammals, olfaction is very important in finding prey, identifying danger, finding food sources and tracking the environment. In fact, a dog can take a sniff and know what has passed through - was it a friend or not?" he said. "That's a fantastic olfactory system - and I think potentially there have been different ways to evolve to enhance that.

"By observing these flow patterns and analyzing details of these flows, we think they could be two different flow zones that serve two different purposes."

Zhao's lab has previously created models of the rat and human nose to study airflow patterns, but the high-resolution cat model and simulation experiments are his most complicated to date, based on micro-CT scans of a cat's head and microscopic-level identification of tissue types throughout the nasal cavity.

"We spent a lot of time developing the model and more sophisticated analysis to understand the functional benefit that this structure serves," he said. "The cat nose probably has a similar complexity level as the dog's, and it's more complex than a rodent's - and it begs the question - why was the nose evolved to be so complex?"

Computer simulations of breathing revealed the answer: During a simulated inhalation, researchers observed two distinct regions of airflow - respiratory air that gets filtered and spreads slowly above the roof of the mouth on its way to the lungs, and a separate stream containing odorant that moves rapidly through a central passage directly to the olfactory region toward the back of the nasal cavity. The analysis considered both the flow location and the speed of its movement through turbinates, the bony structures inside the nose.

"We measured how much flow goes through specific ducts - one duct that delivers most odorant chemicals into the olfactory region, versus the rest, and analyzed the two patterns," Zhao said. "For respirator breathing, turbinates branch to divert flow into separate channels, sort of like a radiator grid in a car, which would be better for cleansing and humidifying.

"But you want odour detection to be very fast, so there is one branch that delivers odour at high speed, potentially allowing for quick detection rather than waiting for the air to filter through the respiratory zone - you could lose most of the odour if air has been cleansed and the process is slowed down."

The simulation also showed that the air shuttled to the olfactory region is then recirculated in parallel channels when it gets there. "That was actually a surprise," Zhao said. "It's like you take a sniff, the air is shooting back there and then is being processed for a much longer."

This study is the first to quantify the difference in gas chromatography between mammals and other species - Zhao and colleagues estimate the cat's nose is more than 100 times more efficient at odour detection than an amphibian-like straight nose in a similarly sized skull - and to come up with a parallel gas chromatography theory: parallel olfactory coils feeding from the high-speed stream to increase the effective length of the flow path while slowing down the local airflow speed, potentially for better odour processing.

"We know so much about vision and hearing, but not so much about the nose. This work could lead to more understanding of the evolutionary pathways behind different nose structures, and the functional purpose they serve," Zhao said.