Gain modulation and odor concentration invariance in early olfactory networks

Abstract

A conserved principle of the olfactory system, in most, if not all animals, is that each olfactory receptor interacts with different odorant molecules and each odorant molecule interacts with different olfactory receptors. This broad receptive field of the receptors constitutes the basis of a combinatorial code that allows animals to discriminate many more odorants than the actual number of receptor types that they express. A drawback is that high odorant concentrations recruit lower affinity receptors, which can give rise to the perception of qualitatively different odors. Here we addressed the contribution that early signal-processing in the honey bee antennal lobe does to keep odor representation stable across concentrations. We describe the contribution that GABA-A and GABA-B receptors-dependent-inhibition plays in terms of the amplitude and temporal profiles of the signals that convey odor information from the antennal lobes to the mushroom bodies. GABA reduces the amplitude of odor elicited signals and the number of glomeruli that are recruited in a concentration-dependent way. Blocking GABA-A and GABA-B receptors decreases the correlation among glomerular activity 1 patterns elicited by different concentrations of the same odor. Based on the results we built a realistic computational model of the antennal lobe that could be further used to evaluate the signal processing properties of the AL network under conditions that cannot be achieved in physiology experiments. Interestingly, even though based on rather simplistic topology and interactions among cells solely mediated by GABA-A and GABA-B interactions, the AL model reproduced the key features of the AL stable response in relation to different concentrations.

Multielectrode recordings of cockroach antennal lobe neurons in response to temporal dynamics of odor concentrations

“…Several studies conducted with different techniques have shown that gain control achieved by the AL network may be thought of as an amplifier of neural communication, supporting a certain degree of concentration invariant odor representation (Olsen and Wilson 2008;Olsen et al 2010;Zhang et al 2013;Marachlian et al 2019;Gjorgjieva et al 2019;Martelli and Storace 2021). In Drosophila, gain control is mediated by lateral interactions across many olfactory glomeruli and helps to equalize the population response of projection neurons (PNs).…”