Taste sensing and sugar detection mechanisms in Drosophila larval primary taste center

Abstract

Despite the small number of gustatory sense neurons, Drosophila larvae are able to sense a wide range of chemicals. Although evidence for taste multimodality has been provided in single neurons, an overview of gustatory responses at the periphery is missing and hereby we explore whole-organ calcium imaging of the external taste center. We find that neurons can be activated by different combinations of taste modalities including of opposite hedonic valence and identify distinct temporal dynamics of response. Although sweet sensing has not been fully characterized so far in the external larval gustatory organ, we recorded responses elicited by sugar. Previous findings established that larval sugar sensing relies on the Gr43a pharyngeal receptor, but the question remains if external neurons contribute to this taste. Here we postulate that external and internal gustation use distinct and complementary mechanisms in sugar sensing and we identify external sucrose sensing neurons.

The larva and adult of Helicoverpa armigera use differential gustatory receptors to sense sucrose

“…This is most likely due to the fact that fruit fly larvae prefer to feed on rotting fruits at the optimum stage of fermentation, which contain fructose as the main sugar. Anyway, the sucrose sensing neurons were recently identified in the larval primary taste center ( Maier et al, 2021 ). In honeybees, AmGr1 acts as a GR for certain sugars other than fructose, and AmGr2 acts as a coreceptor with AmGr1 ( Jung et al, 2015 ).…”

The larva and adult ofHelicoverpa armigerause differential gustatory receptors to sense sugars

“…Sugar perception in Drosophila larvae has been assigned to the fructose receptor Gr43a , which, however, is expressed in pharyngeal sensory organs, foregut, and in the brain, but absent from external taste neurons (Mishra et al, 2013). Anyway, the sucrose sensing neurons were recently identified in the larval primary taste center (Maier et al, 2021). In honeybees, AmGr1 acts as a GR for certain sugars other than fructose, and AmGr2 acts as a coreceptor with AmGr1 (Jung et al, 2015).…”

Gustation in insects: taste qualities and types of evidence used to show taste function of specific body parts

“…Some GRNs responded to all 12 tastants. Similarly, when D. melanogaster larvae were tested with tastants from each of the five canonical taste modalities (sweet, bitter, sour, salt, amino acids), more than 30% of GRNs responded to more than one taste modality, i.e., were multimodal for taste ( Maier et al 2021 ). At least in D. melanogaster larvae, a single GRN may even be activated by tastants of presumed opposite effects, e.g., a sugar, which was presumed attractive, and bitter or high salt, which were presumed aversive ( van Giesen et al 2016 , Maier et al 2021 ).…”

“…1 of Bernays et al 2000 , Seada et al 2016 ). A more reliable way to document activity of an individual neuron is by calcium imaging, i.e., detecting the influx of Ca 2+ ions that accompanies the electrical activity of a neuron ( Apostolopoulou et al 2016 , Raad et al 2016 , Maier et al 2021 ).…”