Dopaminergic modulation of appetitive long-term memory in Apis mellifera

KLAPPEBACH MARTIN; LOCATELLI FERNANDO

Buenos AIres

Congreso; ISN Special Conference 2012; 2012

The understanding of how reinforcements are encoded in the central nervous system during learning and memory formation is a current issue in neurobiology. In contrast to our knowledge from vertebrates, dopamine (DA) was found to mediate aversive reinforcements and facilitate aversive memory in several invertebrate species. However, the assumption that DA is exclusively involved in aversive memory was recently challenged by a study in crabs that revealed that dopamine impairs appetitive memory (Klappenbach et al 2012). In this work we extend this study to an insect, the honey bee Apis mellifera, and test if DA affects appetitive learning and memory in the olfactory modality. We found that systemic injection of DA before the training session impairs appetitive long-term memory without affecting acquisition or short-term memory. On a second experiment we tested if it is only the administration of exogenous DA that affects appetitive memory or if also the endogenous level DA plays a role in modulation of appetitive memory formation. We injected the DA-antagonist flupentixol immediately before a weak training protocol and found that blocking DA receptors during training mimics the effect of a strong appetitive training protocol and facilitates the induction of long-term appetitive memory. These results reveal a novel action of DA in appetitive memory in honey bees and together with results in the crab suggests a conserved dual role of DA across species. The results indicate that DA signal mediates the reinforcement for aversive memory, but also interferes with appetitive memory. The result supports the hypothesis that DA and octopamine (OA) have dual and complementary roles during learning and memory. They mediate the reinforcement signal throughout aversive or appetitive training respectively, but also interfere with the formation of memories of the opposite sign. Calcium imaging studies are being performed now to evaluate if DA modulates the processing and encoding of conditioned and unconditioned stimuli in the honey bee brain.