The role of cAMP-dependent protein kinase A in the formation of long-term memory in Bactrocera dorsalis

The cAMP-dependent protein kinase A(PKA)signaling pathway has long been considered critical for long-term memory(LTM)formation.Previous studies have mostly focused on the role of PKA signaling in LTM induction by multiple spaced conditioning with less attention to LTM induction by a single conditioning.Here,we conducted behavioral-pharmacology,enzyme immunoassay and RNA interference experiments to study the role of the PKA signaling pathway in LTM formation in the agricultural pest Bactrocera dorsalis,which has a strong memory capacity allowing it to form a two-day memory even from a single conditioning trial.We found that either blocking or activating PKA prior to conditioning pretreatment affected multiple spaced LTM,and conversely,they did not affect LTM formed by single conditioning.This was further confirmed by enzyme-linked immunosorbent assay(ELISA)and silencing of the protein kinase regulatory subunit 2 and catalytic subunit 1.Taken together,these results suggest that activating PKA during memory acquisition helps to induce the LTM formed by multiple spaced conditioning but not by a single conditioning.Our findings challenge the conserved role of PKA signaling in LTM,which provides a basis for the greater diversity of molecular mechanisms underlying LTM formation across species,as well as possible functional and evolutionary implications.

Formation characteristics of long-term memory in Bactrocera dorsalis

Studies on insects have contributed significantly to a better understanding of learning and memory,which is a necessary cognitive capability for all animals.Although the formation of memory has been studied in some model insects,more evidence is required to clarify the characteristics of memory formation,especially long-term memory(LTM),which is important for reliably storing information.Here,we explored this question by examining Bactrocera dorsalis,an agricultural pest with excellent learning abilities.Using the classical conditioning paradigm of the olfactory proboscis extension reflex(PER),we found that paired conditioning with multiple trials(>3)spaced with an intertrial interval(≥10 min)resulted in stable memory that lasted for at least 3 d.Furthermore,even a single conditioning trial was sufficient for the formation of a 2-d memory.With the injection of protein inhibitors,protein-synthesis-dependent memory was confirmed to start 4 h after training,and its dependence on translation and transcription differed.Moreover,the results revealed that the dependence of memory on protein translation exhibited a time-window effect(4-6 h).Our findings provide an integrated view of LTM in insects,suggesting common mechanisms in LTM formation that play a key role in the biological basis of memory.

Octopaminergic neurons function in appetitive but not aversive olfactory learning and memory in Bactrocera dorsalis

The biogenic amine octopamine(OA,invertebrate counterpart of nora-drenaline)plays critical roles in the regulation of olfactory behavior.Historically,OA has been thought to mediate appetitive but not aversive learning in honeybees,fruit flies(Drosophila),and crickets.However,this viewpoint has recently been challenged because OA activity through aβ-adrenergic-like receptor drives both appetitive and aversive learn-ing.Here,we explored the roles of OA neurons in olfactory learning and memory retrieval in Bactrocera dorsalis.We trained flies to associate an orange odor with a sucrose reward or to associate methyl eugenol,a male lure,with N,N-diethyl-3-methyl benzoyl amide(DEET)punishment.We then treated flies with OA receptor antagonists before appetitive or aversive conditioning and a memory retention test.Injection of OA receptor antagonist mianserin or epinastine into the abdomen of flies led to impaired of appetitive learning and memory retention with a sucrose reward,while aversive learning and memory reten-tion with DEET punishment remained intact.Our results suggest that the OA signaling participates in appetitive but not aversive learning and memory retrieval in B.dorsalis through OA receptors.