The third session here at the Janelia Farm Conference “Learning and Memory: A Synthesis of Flies and Honeybees” covered the action of dopamine. Hiromu Tanimoto started with his experiments trying to identify the dopaminergic neurons involved in aversive clssical olfactory conditioning. They found three different subpopulations of neurons that differed in the strength of the memory induced by driving activity in these neurons as a replacement for an aversive US. He showed nice anatomical images showing the different mushroom-body regions where these subpopulations project to, presumably releasing dopamine in response to the aversive US during conditioning. Current work in his lab entails finding the neural pathway by which the electric shock is transmitted to the dopaminergic neurons.

Next up was Krystyna Keleman, talking about dopamine in courtship conditioning. Courtship conditioning happens when naive males encounter a mated females. Mated females do not want to mate a second time, meaning that all courtship efforts by the male are rejected by the female. This rejection serves as negative feedback ('positive punishment' in operant terms) and the animals learn the odor of the mated female (which is different from that of a virgin female) and selectively suppress courtship to mated females in the future. This memory is dependent, of course, on being able to smell the difference between mated and virgin females, so if the odor receptors for the smell that makes the two females different - cVA - are genetically ablated, there is no specific courtship suppression. Interestingly, cVA is not required during training, suggesting that trained males are sensitized to detect cVA. This entails that this form of conditioning is not associative in nature: the males simply become more sensitive to cVA, allowing them to distinguish mated from virgin females. Activating dopaminergic neurons mimics training with an unreceptive female. this allows them to use the same strategy as in Tanimoto's lab to identify the subpopulations involved in courtship conditioning. Indeed, they find that this form of learning requires different dopaminergic neurons than classical olfactory conditioning. Specifically, input into the mushroom-body gamma neurons is required for this type of learning.

Final speaker of this session was Thomas Préat, who educated us on three dopaminergic neurons regulating memory consolidation after training. He first showed that the activity during dopaminergic neurons suppress anaestesia resistant memory (ARM) after training. The three dopaminergic neurons labeled by the NP47 driver line are the neurons responsible for this suppression. Imaging these neurons in naive flies showed strong spontaneous activity, synchronized between left and right hemisphere, in neurons MP1 and MV1 but not neuron V1. This activity is rhythmic in each fly, but there does not appear to be a specific frequency where all flies show oscillations at. A series of very nice experiments showed that the formation of long term memory inhibits ARM via these three neurons. Spaced training (which leads to long term memory and inhibits ARM) leads to synhronized oscillations in these two dopaminergic neurons at a specific frequency in all animals. It thus seems as if these neurons with their oscillations act as gates for regulating the amount of ARM and long term memory being formed.