generated at different life stages in mice can impact aspects of their
olfactory sense and behavior, revealed a new research from North Carolina State University. The work could have implications for our
understanding of neurodevelopmental processes or traumatic brain
injuries in humans.
Troy Ghashghaei, associate professor of neurobiology at NC State,
studies the ways neurons develop and integrate into the "circuitry" of
the brain. Mice are an excellent model for study, because even in
adulthood they continue to produce neurons in two regions, one of which
deals with the smell, or olfactory, centers of the brain.
‘Stopping activity of adult-born neurons in mice affected their ability to recognize and develop memories for novel food odors - odors that they had never been exposed to before.’
Working with a population of young adult mice, Ghashghaei and his
team looked at olfactory neurons that were generated when the mice were
either newborn or young adults. The team wanted to know if there was a
difference between the function of neurons that developed at different
"One way to study the function of different populations of neurons
is to shut them off during different behavioral paradigms," says
Ghashghaei. To shut off neurons, they introduced a gene into olfactory
stem cells in the mice. The gene encoded a protein that would respond to
a particular drug by turning off those olfactory neurons after they had
matured. Thus the researchers could shut off neurons that were
generated at different developmental time points.
In young adult mice, stopping activity of adult-born neurons
affected their ability to recognize and develop memories for novel food
odors - odors that they had never been exposed to before. In contrast,
if the odor was aversive, or indicated danger - like the scent of a fox,
for example - shutting off the adult-generated neurons had no effect;
the mice responded normally by freezing in place. The adult-generated
neurons, therefore, did not appear to have a role in mediating the
innate response the mice had to aversive odors.
Puzzled by this finding, Ghashghaei and the team wondered if neurons
generated immediately after mice are born were connected with responses
to aversive odors. So they shut off 'early-born' neurons in the mice
and found that the usual response to aversive odors was interrupted: the
mice seemed unaffected by presence of a fox odor.
"Developmentally, there is a progression of neuronal addition to the
olfactory system in mice," Ghashghaei says. "What this study
demonstrates is that there are developmentally defined circuits -
generated at specific points in time - that regulate different values of
new sensory stimuli, and how sensory responses are processed and
"The next questions to explore are how specific sets of neurons,
generated at specific points in time, work together in complex
behaviors, and how they may or may not be working in neurodevelopmental
diseases or in conditions such as autism. Additionally, we want to look
at how the neurons we have discovered are wired to other brain regions
and whether or not these networks are responsible for regulating hedonic
aspects of sensory perception."