Olfaction is important in the life of most insects, they use odors to find food, oviposition sites, mates, and
avoid predators. Insects are excellent model systems for studying how olfaction works, because their
olfactory system is numerically simpler –but functionally equivalent- than that of vertebrates.

But it doesn’t matter if you’re a mouse, a lizard, or a cockroach, all olfactory systems have to deal with
the same kind of problems! Odorant molecules bear different functional groups (alcohols, ketones,
aldehydes, ketones) and have varying carbon chain lengths, and that’s why they smell different to as.
We also need to know how much of an odorant is in the air (its concentration, or in other words, how
strong it smells) and recognize mixtures of odorant mixtures (smells like roses, a banana, an apple, a mate?).
Odors also vary over time, sometimes in a very short time scale (milliseconds or less), and the olfactory
system also has to be able to deal with that.

In insects olfaction starts in the antennae. Upon hitting the antennae, odor molecules interact with olfactory receptor
cells generating a message which travels down their axons reaching distinct olfactory neuropil –called glomeruli-
in the first relay station in the olfactory pathway, the antennal lobe. It is believed that each glomerulus process
information about a particular odorant or a chemically related group of odorant molecules.

Glomeruli are the landmarks of the primary olfactory centers: their positions and numbers are conserved
across individuals and are characteristic of each animal species. For instance, in the mice there’re about
1800 glomeruli, and in the sphinx moth there’re 63.

In the moth (as in other insects) some glomeruli are sexually dimorphic. Male moths (but not females) have
a set of glomeruli exclusively devoted to process information about the conspecific female sex pheromone.
Similarly, female moths have a set of glomeruli probably involved in finding and recognizing suitable oviposition sites.

In the glomeruli, olfactory receptor cells synapse with neurons that mediate interactions between glomeruli –
so called local neurons- and with projection neurons.

Projection neurons, which are the output elements of the antennal lobes, project to higher brain centers
(centers involved in learning and memory, and in integration of information of different sensory modalities).

In the lab I study how odors are represented in the first relay station in the olfactory pathway, the antennal lobe.
How I do that?

I stimulate the antenna with host-plant odorants, and I simultaneously record the electrical activity of
neurons in the brain. I use fluorescent dyes to stain the neuron I’ve been recording from and later visualize
its glomerular affiliation using a laser-scanning confocal microscope.

For instance, using these kind of techniques, I found that projection neurons with dendritic arborizations
restricted to one of the sexually dimorphic glomeruli n the female, a lateral large female glomerulus (latLFG),
are preferentially responsive to one enantiomer (molecules which have identical physical and chemical
properties and are just non-superimposable mirror images, like our right and left hands) of a common
host-plant volatile, linalool. They responded much better to the (+) than to the (-) enantiomer of linalool.
It was exciting to find that projection neurons arborizing in another nearby glomeruli responded better
to the (-) enantiomer of linalool, and that projection neurons in other nearby glomeruli might respond
equally well to both enantiomers of linalool! (Do you want to learn more about this?)

But what is so important that neurons in the brain care about these enatiomers? That question –linking neurons
and behavior- was really appealing to me. One thing I’m doing together with another posdoc in the lab, Jeff
Rifley, and Prof. Wittko Francke, is to look at natural sources of (+) and (-)linalool. We collect volatiles from
plants and then analyze their chemical composition using gas chromatography (to separate compounds) coupled
to mass spectrometry (to identify the compounds).

In other projects, I’m studying how information about odorants which are behaviorally relevant for both
sexes (food, for instance) are processed in the antennal lobe, and how glomeruli interact to process
information about behaviorally relevant odor blends. Also, when we have time, Heather Stein and I have
fun with gynandromorphic moths –insects with a transplanted antennal imagined disk from the opposite sex.
These gynandromorphs give us an excellent opportunity for studying the role of olfactory receptor cells in
conferring odor specificity to their postsynaptic targets.