Lateral axonal modulation is required for stimulus-specific olfactory conditioning in Drosophila

Julia E. Manoim, Andrew M. Davidson, Shirley Weiss, Toshihide Hige*, Moshe Parnas*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Effective and stimulus-specific learning is essential for animals’ survival. Two major mechanisms are known to aid stimulus specificity of associative learning. One is accurate stimulus-specific representations in neurons. The second is a limited effective temporal window for the reinforcing signals to induce neuromodulation after sensory stimuli. However, these mechanisms are often imperfect in preventing unspecific associations; different sensory stimuli can be represented by overlapping populations of neurons, and more importantly, the reinforcing signals alone can induce neuromodulation even without coincident sensory-evoked neuronal activity. Here, we report a crucial neuromodulatory mechanism that counteracts both limitations and is thereby essential for stimulus specificity of learning. In Drosophila, olfactory signals are sparsely represented by cholinergic Kenyon cells (KCs), which receive dopaminergic reinforcing input. We find that KCs have numerous axo-axonic connections mediated by the muscarinic type-B receptor (mAChR-B). By using functional imaging and optogenetic approaches, we show that these axo-axonic connections suppress both odor-evoked calcium responses and dopamine-evoked cAMP signals in neighboring KCs. Strikingly, behavior experiments demonstrate that mAChR-B knockdown in KCs impairs olfactory learning by inducing undesired changes to the valence of an odor that was not associated with the reinforcer. Thus, this local neuromodulation acts in concert with sparse sensory representations and global dopaminergic modulation to achieve effective and accurate memory formation.

Original languageEnglish
Pages (from-to)4438-4450.e5
JournalCurrent Biology
Volume32
Issue number20
DOIs
StatePublished - 24 Oct 2022

Funding

FundersFunder number
National Science Foundation2034783, R01DC018874
National Institutes of HealthP40OD018537, 2P40OD010949
National Institute of Mental HealthF32MH125582
Bloom's Syndrome Foundation2019026, 2020636
New York University
University of Sheffield
Weizmann Institute of Science
United States-Israel Binational Science Foundation
Israel Science Foundation343/18

    Keywords

    • Drosophila
    • Kenyon cells
    • associative learning and memory
    • axo-axonal lateral neuromodulation
    • axonal modulation
    • muscarinic receptors
    • mushroom body
    • non-specific conditioning

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