Weaker Ligands Can Dominate an Odor Blend due to Syntopic Interactions

Abstract

Most odors in natural environments are mixtures of several compounds. Perceptually, these can blend into a new “perfume,” or some components may dominate as elements of the mixture. In order to understand such mixture interactions, it is necessary to study the events at the olfactory periphery, down to the level of single-odorant receptor cells. Does a strong ligand present at a low concentration outweigh the effect of weak ligands present at high concentrations? We used the fruit fly receptor dOr22a and a banana-like odor mixture as a model system. We show that an intermediate ligand at an intermediate concentration alone elicits the neuron’s blend response, despite the presence of both weaker ligands at higher concentration, and of better ligands at lower concentration in the mixture. Because all of these components, when given alone, elicited significant responses, this reveals specific mixture processing already at the periphery. By measuring complete dose–response curves we show that these mixture effects can be fully explained by a model of syntopic interaction at a single-receptor binding site. Our data have important implications for how odor mixtures are processed in general, and what preprocessing occurs before the information reaches the brain.

Data-driven honeybee antennal lobe model suggests how stimulus-onset asynchrony can aid odour segregation

“…The detailed connectivity of the model is given below. In order to obtain realistic receptor responses to mixtures, we implemented a rate description of binding, unbinding, activation and inactivation of receptors which implements a syntopic mixture model that has been found to be accurate for many observations in bee olfaction (Münch et al, 2013). We then generate Poisson spike trains from the receptor activation data to take account of the known unreliability of ORNs.…”

“…First of all, the PN response pattern is determined by the ORN responses to the mixture. These are described with our syntopic mixture model which is known to reproduce non-trivial mixture interactions on the receptor level (Rospars et al, 2008;Münch et al, 2013). Then, this ORN activation pattern is modified by the PN response characteristics and eventually the inhibition from the currently active LN 28 .…”

“…While recent work (Münch et al, 2013) has demonstrated that syntopic mixture models (Rospars et al, 2008) are highly successful in predicting the interaction of odourants at receptors, it is well-known that additional interactions between odourants can occur on the receptor or neuron level (Nikonov and Leal, 2002;Hillier and Vickers, 2011;Su et al, 2012). Inaccuracies in the model predictions for the synchronous and asynchronous mixture responses based on mixture interactions not captured by our syntopic mixture model could easily lead to a change in the dominance of any of the components in the mixture and hence the slightly different results.…”

Compound valence is conserved in binary odor mixtures in Drosophila melanogaster

“…In principle, peripheral mechanisms such as ligand-induced OSN inhibition at the receptor level (de Bruyne et al, 1999;de Bruyne et al, 2001;Hallem and Carlson, 2006;Hallem et al, 2004;Su et al, 2011), ephaptic interactions within the sensillum (Su et al, 2012) or syntopic interactions (Münch et al, 2013) may already contribute to shaping the input signal in a valence-specific way. This would require a system layout in which positive receptors are consistently inhibited (or weakly activated) by compounds of negative valence, or that positive and negative OSNs are co-localized within the same sensilla to allow for valence-specific bilateral inhibition.…”

“…Components of odor mixtures have been shown to influence each other's reception on the level of OSNs (Deisig et al, 2012;Hillier and Vickers, 2011;Münch et al, 2013;Pregitzer et al, 2012;Schuckel et al, 2009;Su et al, 2011;Su et al, 2012). Furthermore, olfactory information is significantly modulated by a dense network of local neurons in the first olfactory center of the insect brain, the antennal lobe (AL) (reviewed in Galizia and Rössler, 2010;Masse et al, 2009;Wilson, 2013;Wilson and Mainen, 2006).…”