Data for: Chronic exposure to odors at naturally occurring concentrations triggers limited plasticity in early stages of Drosophila olfactory processing

In insects and mammals, olfactory experience in early life alters
olfactory behavior and function in later life. In the vinegar
fly Drosophila, flies chronically exposed to a high concentration
of a monomolecular odor exhibit reduced behavioral aversion to the
familiar odor when it is re-encountered. This change in olfactory behavior
has been attributed to selective decreases in the sensitivity of
second-order olfactory projection neurons (PNs) in the antennal lobe that
respond to the overrepresented odor. However, since odorant compounds do
not occur at similarly high concentrations in natural sources, the role of
odor experience-dependent plasticity in natural environments is unclear.
Here, we investigated olfactory plasticity in the antennal lobe of flies
chronically exposed to odors at concentrations that are typically
encountered in natural odor sources. These stimuli were chosen to each
strongly and selectively excite a single class of primary olfactory
receptor neuron (ORN), thus facilitating a rigorous assessment of the
selectivity of olfactory plasticity for PNs directly excited by
overrepresented stimuli. Unexpectedly, we found that chronic exposure to
three such odors did not result in decreased PN sensitivity but rather
mildly increased responses to weak stimuli in most PN types. Odor-evoked
PN activity in response to stronger stimuli was mostly unaffected by odor
experience. When present, plasticity was observed broadly in multiple PN
types and thus was not selective for PNs receiving direct input from the
chronically active ORNs. We further investigated the DL5 olfactory coding
channel and found that chronic odor-mediated excitation of its input ORNs
did not affect PN intrinsic properties, local inhibitory innervation, ORN
responses, or ORN-PN synaptic strength; however, broad-acting lateral
excitation evoked by some odors was increased. These results show that PN
odor coding is only mildly affected by strong persistent activation of a
single olfactory input, highlighting the stability of early stages of
insect olfactory processing to significant perturbations in the sensory
environment.