Dopamine neuromodulation in learning and memory has been extensively studied in the insect mushroom bodies, but it is unclear to what extent learning occurs in primary sensory brain areas. In olfaction, there is growing evidence from Diptera (flies) that dopamine signaling in the antennal lobes is necessary for certain types of learning and may contribute to increasing signal to noise for odors that are most salient to an animal. How does dopamine modulation alter the encoding of olfactory stimuli into long term memory? To approach this question, we combined 2-photon calcium imaging to map odor encoding to specific glomeruli, immunohistochemistry to localize dopaminergic neurons, and classical conditioning to assess which odors are learned by different fly and mosquito species. While flies can learn to associate certain odors with an aversive stimulus like mechanical shock, other odors are not learned. Our working hypothesis is that “learnable” odors are encoded in glomeruli that receive significantly higher levels of dopaminergic innervation. Even at an early stage of olfactory processing, dopamine modulation plays a role in learning, but the specific mechanism is yet to be uncovered. In this talk I will discuss our current understanding of dopamine’s role in the antennal lobe, development of dopaminergic neurons in the antennal lobe, and the evolution of this particular dopaminergic circuit in Diptera. Considering the extensive dopaminergic innervation observed in vertebrate olfactory bulb glomeruli, early-stage neuromodulation in olfactory learning may be relevant across the Animal Kingdom.
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