Evidence found of evolution influencing number of neurons that sense certain odors

An international team of researchers has found evidence of changes that influence the number of neurons that detect certain odours in mammals. In their article published in the journal Science Advances, the group describes their genetic study of the smell mucosa in several mammals and what they found.

Smell is, of course, one of the five basic senses - it allows us to detect odours in the air around us. Being able to feel something helps us and other animals to determine what to eat and, in some cases, what not to eat to avoid getting sick. In this new effort, the researcher began his work with a hypothesis - suggesting that it was likely that mammals tend to have more sensory neurons of the type they need to find the particular types of foods they eat. To find out if this is the case, they collected mucosal samples from several mammalian species: mice, macaques, humans, dogs, rats and marmosets. In humans, this mucosa is not found in the nose, but in the forehead, above the nose.

In mammals, the sense of smell develops as a result of the activation of olfactory receptors by chemicals in the air. These receptors are in turn expressed by sensory neurons, which are located in the mucosa. The nerves then send signals to the brain that describe what particular smells are felt. To learn more about olfactory receptors in mammals, the team performed a mRNA analysis of each of the samples obtained to determine which genes were activated when a mammal was feeling something.

The researchers report that they found that the expression of odorous genes was "largely preserved" in all the species they studied. But they also found that the number of sensory neurons activated by different chemicals varied among species. They suggest that this discovery is evidence that evolution plays a role in determining the abundance of odorous receptors in mammals - there are more food-related types that a given species consumes.