Ionotropic receptors mediate olfactory learning and memory in Drosophila

Phenylacetaldehyde(PAH),an aromatic compound,is present in a diverse range of fruits including overripe bananas and prickly pear cactus,the two major host fruits for Drosophila melanogaster.PAH acts as a potent ligand for the ionotropic receptor 84a(IR84a)in the adult fruit fly and it is detected by the IR84a/IR8a heterotetrameric complex.Its role in the male courtship behavior through IR84a as an environmental aphrodisiac is of additional importance.In D.melanogaster,two distinct kinds of olfactory receptors,that is,odorant receptors(ORs)and ionotropic receptors(IRs),perceive the odorant stimuli.They display unique structural,molecular,and functional characteristics in addition to having different evolutionary origins.Traditionally,olfactory cues detected by the ORs such as ethyl acetate,1-butanol,isoamyl acetate,1-octanol,4-methylcyclohexanol,etc.classified as aliphatic esters and alcohols have been employed in olfactory classical conditioning using fruit flies.This underlines the participation of OR-activated olfactory pathways in learning and memory formation.Our study elucidates that likewise ethyl acetate(EA)(an OR-responsive odorant),PAH(an IR-responsive aromatic compound)too can form learning and memory when associated with an appetitive gustatory reinforcer.The association of PAH with sucrose(PAH/SUC)led to learning and formation of the long-term memory(LTM).Additionally,the Orco^(1),Ir84a^(MI00501),and Ir8a^(1)mutant flies were used to confirm the exclusive participation of the IR84a/IR8a complex in PAH/SUC olfactory associative conditioning.These results highlight the involvement of IRs via an IR-activated pathway in facilitating robust olfactory behavior.

The differential requirement of mushroom body α/β subdivisions in long-term memory retrieval in Drosophila

The mushroom body(MB),a bilateral brain structure pos-sessing about 2000-2500 neurons per hemisphere,plays a central role in olfactory learning and memory in Dros-ophila melanogaster.Extensive studies have demonstrat-ed that three major types of MB neurons(α/β,α’/β’andγ)exhibit distinct functions in memory processing,including the critical role of approximately 1000 MBα/βneurons in retrieving long-term memory.Inspired by recent fi ndings that MBα/βneurons can be further divided into three subdivisions(surface,posterior and core)and wherein theα/βcore neurons play an permissive role in long-term memory consolidation,we examined the functional differ-ences of all the three morphological subdivisions of MBα/βby temporally precise manipulation of their synaptic outputs during long-term memory retrieval.We found the normal neurotransmission from a combination of MBα/βsurface and posterior neurons is necessary for retrieving both aversive and appetitive long-term memory,whereas output from MBα/βposterior or core subdivision alone is dispensable.These results imply a specifi c requirement of about 500 MBα/βneurons in supporting long-term memory retrieval and a further functional partitioning for memory processing within the MBα/βregion.