The good, the bad, and the hungry: how the central brain codes odor valence to facilitate food approach in Drosophila

Abstract

All animals must eat in order to survive but first they must successfully locate and appraise food resources in a manner consonant with their needs. To accomplish this, external sensory information, in particular olfactory food cues, need to be detected and appropriately categorized. Recent advances in Drosophila point to the existence of parallel processing circuits within the central brain that encode odor valence, supporting approach and avoidance behaviors. Strikingly, many elements within these neural systems are subject to modification as a function of the fly’s satiety state. In this review we describe those advances and their potential impact on the decision to feed.

Continuous lateral oscillations as a core mechanism for taxis in Drosophila larvae

“…Current theory supports the view that memory expression is due to efficacy changes in synapses converging to mushroom body output neurons (MBONs) that encode valence; stimulating these neurons can elicit attraction or aversion (Aso et al, 2014;  Sachse and Beshel, 2016). However, our model suggests that the mushroom body pathway is yet another pathway that converges to modify the effective gain in the motor system, and thus MBON valence would also be sensitive to activation timing.…”

Olfactory and neuromodulatory signals reverse visual object avoidance to approach in Drosophila

“…Although we have not tested an exhaustive panel of odorants, our work to date suggests that visual valence reversal is mediated by appetitive but not aversive odors, a result that provides key insight into the putative organization of olfactory inputs to OA neuromodulation. In the Drosophila olfactory system, diverse lines of evidence suggest that attractive and aversive odorants are encoded by anatomically segregated pathways that reside within subdomains of hierarchical olfactory neuropils (Grabe and Sachse, 2018;Masse et al, 2009;Sachse and Beshel, 2016;Schultzhaus et al, 2017) . Our finding that the observed odor-induced visual valence reversal takes place only in the presence of attractive odorants (ACV and EtOH, Figure 1F & 2B) and not aversive odorants (BA, Figure 2C) specifically implicates the attractive olfactory pathway (Masse et al, 2009;Sachse and Beshel, 2016;Strutz et al, 2014) .…”

“…Another third-order olfactory neuropil, the lateral horn (LH), mediates olfactory behaviors in a rapid, experience-independent manner (Fişek and Wilson, 2014;Grabe and Sachse, 2018;Sachse and Beshel, 2016;Schultzhaus et al, 2017) . This neuropil houses neurons that encode odor features such as hedonic valence and odor intensity (Grabe and Sachse, 2018;Sachse and Beshel, 2016;Schultzhaus et al, 2017) .…”

“…Another third-order olfactory neuropil, the lateral horn (LH), mediates olfactory behaviors in a rapid, experience-independent manner (Fişek and Wilson, 2014;Grabe and Sachse, 2018;Sachse and Beshel, 2016;Schultzhaus et al, 2017) . This neuropil houses neurons that encode odor features such as hedonic valence and odor intensity (Grabe and Sachse, 2018;Sachse and Beshel, 2016;Schultzhaus et al, 2017) . LH projection neurons innervate the superior medial protocerebrum (SMP), superior lateral protocerebrum (SLP), and the ventral nerve cord (VNC) (Dolan et al, 2018;Fişek and Wilson, 2014;Jefferis et al, 2007;Sachse et al, 2007;Tanaka et al, 2012Tanaka et al, , 2004 .…”

Genetic analysis of mosquito detection of humans

“…The sensillar lymph surrounding the ORNs is densely packed with odorant-binding proteins (OBPs) that are hypothesized to be involved in odorant uptake and odor delivery to the ORs, but their role remains unclear [37]. The neural processing of olfactory information has been extensively studied in Drosophila [38, 39]. The axons of the ORNs project to the antennal lobe where they synapse with projection neurons (PN).…”