RENOU, M. | Search bioRxiv

bioRxiv2025

A method to estimate absolute odorant concentration of olfactory stimuli

The accurate quantification and delivery of odorant concentrations remain a significant challenge. Traditional methods estimate stimulus intensity based on the amount of odorant in the source, but this does not reflect the actual concentration sent due to variable evaporation rates and delivery devices. This leads to inconsistencies in stimulus delivery, complicating cross-laboratory comparisons, threshold evaluations, and the replication of natural olfactory conditions in the lab. To address this, we present a model based on mass transfer theory to predict the concentration of odorants delivered by a simple and versatile odor delivery system commonly used in insect electrophysiological experiments. This model, built with adaptable compartments, accounts for airflow, source size, and the physicochemical properties of odorants. It helps to better design and use odor delivery systems, especially for stimuli required to mimic natural odor environments. Calibration uses known partition coefficients. The model also considers the dynamic shape of odor stimuli, which affects neuronal responses and must be carefully interpreted, especially when using tools like photoionisation detectors (PID). This approach was applied to study the impact of a plant volatile known to activate pheromone-sensitive neurons, (Z)-3-hexenyl acetate, on pheromone detection in Agrotis ipsilon moths. While interference occurs in laboratory conditions at 160 ppb, such concentrations are unlikely in natural settings, suggesting these effects are less relevant ecologically.

synthetic biology↗

bioRxiv2020

Effects of an odor background on moth pheromone communication: constituent identity matters more than blend complexity

Olfaction allows insects to communicate with pheromones even in complex olfactory landscapes. It is generally admitted that, due to the binding selectivity of the receptors, general odorants should weakly interfere with pheromone detection. However, laboratory studies show that volatile plant compounds (VPCs) modulate responses to the pheromone in male moths. We used extracellular electrophysiology and calcium imaging to measure the responses to the pheromone of receptor and central neurons in males Agrotis ipsilon while exposed to simple or composite backgrounds of VPCs. Maps of activities were built using calcium-imaging to visualize which areas in antennal lobes (ALs) were affected by VPCs. To mimic a natural olfactory landscape short pheromone puffs were delivered over VPC backgrounds. We chose a panel of VPCs with different chemical structures and physicochemical properties representative of the odorant variety encountered by a moth. We evaluated the intrinsic activity of each VPC and compared the impact of VPC backgrounds at antenna and antennal lobe levels. Then, we prepared binary, ternary and quaternary combinations to determine whether blend activity could be deduced from that of its components. Our data confirm that a VPC background interfere with the moth pheromone system in a dose-dependent manner. Interference with the neuronal coding of pheromone signal starts at the periphery. VPCs showed differences in their capacity to elicit Phe-ORN firing response that cannot be explained by differences in stimulus intensities because we adjusted the source concentrations to vapor pressures. Thus, these differences must be attributed to the selectivity of ORs or any other olfactory proteins. The neuronal network in the ALs, which reformats the ORN-input, did not improve pheromone salience. We postulate that the AL network might have evolved to increase sensitivity and encode for fast changes over a wide range of concentrations, possibly at some cost for selectivity. Comparing three- or four-component blends to binary blends or single compound indicated that a blend showed the activity of its most active compound. Thus, although the diversity of a background might increase the probability of including a VPC interacting with the pheromone system, chemical diversity does not seem to be a prominent factor per se. Global warming is significantly affecting plant metabolism so that the emissions of VPCs and resulting odorscapes are modified. Increase in atmospheric mixing rates of VPCs will change olfactory landscapes which, as confirmed in our study, might impact pheromone communication.

neuroscience↗