Swiss
The way in which the outside world is perceived is unique to every species, and often shapes some of their most predominant characteristics and behaviours. Ivan Rodriguez and his team from the University of Geneva have been studying the neuronal circuits that allow mammals to extract information from the world, in this case chemicals, and translate it into adequate behavioral responses.
understanding innate behaviours
“Our lab uses genetics as a tool,” says Rodriguez, “and our aim is to achieve a molecular understanding of the neural processes that are involved in innate behaviours. The
olfactory system is what you might call the entry door to what triggers these behaviours in most mammals, and that is why we are looking at this system at a genetic and molecular level.” Recent work,
that started
with the discovery of odorant receptors by Linda Buck and Richard
Axel in 1991 (who would later win the Nobel Prize for their work), has revealed that verebrates use various olfactory perceive
chemoreceptors their
to surroundings. system.
“The use of these receptors is at the base of the best chemical detector on earth, the olfactory Its
level of sophistication,
versatility and sensitivity is not even approached by man-made tools; electronic noses can be trained to identify
a
molecules Rodriguez.
few at Circuit function
Olfactory receptor genes include not only those coding for
44 best”
specific adds
Rodriguez. “In this way, we hope to understand how specific molecules can end up triggering specific innate behaviours.” These behaviors are only a handful mammals:
in aggression, that only exist fear at and very sexual
activity being the main three, as well as some
precise
moments in life, such as suckling. “Trying to understand how these circuits are established and how they function is a
“This rapid birth of receptor genes in a given species is quite unusual in biology and is one of the hallmarks of chemical sensing”
odorant receptors but also those for vomeronasal receptors which are responsible for the detection of pheromones, chemicals that are secreted by individuals that trigger predetermined and stereotyped responses in other members of the same species. “It is now apparent that the diversity of chemoreceptor families is linked to their function, and so we study them by trying to associate these receptors with specific circuits in the brain,” says
Neurogenetics: a key to
complex task,” says Rodriguez. “There are millions of neurons that make these circuits, and these neurons express thousands of different receptors. We mammals have to make sense out of the outside world by wiring these neurons, in a way that will be readable by our brains. It is a big challenge to guide and connect over a thousand different sensory populations that all project to a tiny structure in the brain called the olfactory bulb.” The olfactory system is one of the only
neuronal systems that is renewed during adulthood; neurons are constantly born to replenish it, so the task of wiring is not just an embryonic one but one that continues throughout the lifespan of mammals. “The whole thing is rewired completely about every two months, so another challenge for us is to understand how these circuits are rewired and maintained. It is a great model of neuronal regeneration”
Diverse chemosensory systems Olfactory receptor genes represent the largest gene families of mammalian genomes. How did this remarkable variety of sensors arise? Various mechanisms to achieve receptor diversity outside the olfactory system have been selected during evolution. For example in immune cells where receptors that can recognise the inside world and outside pathogens are needed, the diversity is provided by the
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