Role of ionotropic receptors in olfaction learning and memory in Drosophila melanogaster

Abstract

In the field of behavioral neuroscience, Drosophila melanogaster is an excellent model newlineorganism to study olfactory responses and learning. Phenylacetaldehyde (PAH), an newlinearomatic compound, is present in a diverse range of fruits including overripe bananas and newlineprickly pear cactus, the two major host fruits for D. melanogaster. These fruits are sources newlineof food and oviposition sites for the fly. Further, PAH acts as a potent ligand for the newlineIonotropic receptor 84a (IR84a) in the adult fruit fly and is detected by the IR84a/IR8a newlineheterotetrameric complex. Its role in the male courtship behavior through IR84a, newlinefunctioning as an environmental aphrodisiac, is of additional importance. Thus, PAH, with newlineits ability to activate an IR olfactory pathway for mediating responses towards food and newlinemate, is a crucial olfactory cue for D. melanogaster in the wild. In D. melanogaster, two newlinedistinct kinds of olfactory receptors i.e., odorant receptors (ORs) and ionotropic receptors newline(IRs) perceive the odorant stimuli. They display unique structural, molecular, and newlinefunctional characteristics in addition to having different evolutionary origins. While ORs newlineare receptor proteins with seven transmembrane domains, IRs belong to the family of newlineionotropic glutamate receptors (iGluR). Traditionally, olfactory cues detected by the ORs newlinesuch as ethyl acetate, 1-butanol, isoamyl acetate, 1-octanol, 4-methylcyclohexanol etc. newlineclassified as aliphatic esters and alcohols have been employed in olfactory classical newlineconditioning using fruit flies. This underlines the participation of OR-activated olfactory newlinepathways in learning and formation of memory. The first part of our study is focused on to newlineelucidate that likewise ethyl acetate (EA) (an OR-responsive odorant sensed by OR42a and newlineOR42b in association with Orco), PAH (an IR-responsive odorant detected by the newlineIR84a/IR8a heteromeric complex) too can form learning and memory when associated with newlinean appetitive gustatory reinforcer. The association of PAH with sucrose (PAH/SUC) led to newlinelearning and formation of the