Scientists at the Brown University discovered in a new study on unsuspecting lab mice that the tiny rodents may have a specialized neural system responsible for processing their initial reaction to smells that are instinctually important.
In other words, the neural network may also play a role in the initial detection and recognition of smells in this category, including those released by predators. Evolutionarily, this may represent an early-warning mechanism, setting the mouse in motion before its brain even begins to process the events.
An interesting prospect brought up by the new investigation is whether or not the response mice exhibit to such smells is hardwired or not. Details of the research effort appear in this week's online issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS).
According to BU researchers, it could be that other mammals have similar neural pathways as well. This capability essentially triggers an instinctive behavior whenever a certain smell is detected.
The corresponding author of the PNAS paper, BU Robert and Nancy Carney assistant professor of neuroscience Gilad Barnea, says that a subset of nerve cells in the mouse nose displays a number of key biological differences from more common olfactory neurons.
The special cells express members of the gene family of trace amine-associated receptors (TAAR), as opposed to the other cells, which express members of the olfactory receptor gene family, the team says.
“Our observations suggest that the TAAR-expressing sensory neurons constitute a distinct olfactory subsystem that extracts specific environmental cues that then elicit innate responses,” Barnea explains.
“The logic of gene choice in TAAR neurons is different. Their patterns of projection [to the bulb] are different, and the mechanisms that control their projections are different. Altogether these observations suggest that it’s a different subsystem,” the investigator goes on to say.
Interestingly, he adds, humans still have a few intact TAAR genes, raising the interesting prospect that we had two distinct olfactory pathways in the brain. However, it is unlikely that more than vestigial remnants of such pathways remain to be found today.
Now that investigators established the existence of the new olfactory neurons in mice, they plan to take their work one step forward, and study how these nerve cells influence the brain.
The research effort is supported by grant money from the US National Institutes of Health (NIH).