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Behavioral adaptation to environmental changes is crucial for animals’ survival. The prediction of the outcome of one owns action, like finding reward or avoiding punishment, requires recollection of past experiences and comparison with current situation, and adjustment of behavioral responses. The process of memory acquisition is called learning, and the Drosophila larva came up to be an excellent model organism for studying the neural mechanisms of memory formation. In Drosophila, associative memories are formed, stored and expressed in the mushroom bodies. In the last years, great progress has been made in uncovering the anatomical architecture of these brain structures, however there is still a lack of knowledge about the functional connectivity.
Dopamine plays essential roles in learning processes, as dopaminergic neurons mediate information about the presence of rewarding and punishing stimuli to the mushroom bodies. In the following work, the function of a newly identified anatomical connection from the mushroom bodies to rewarding dopaminergic neurons was dissected. A recurrent feedback signaling within the neuronal network was analyzed by simultaneous genetic manipulation of the mushroom body Kenyon cells and dopaminergic neurons from the primary protocerebral anterior (pPAM) cluster, and learning assays were performed in order to unravel the impact of the Kenyon cells-to-pPAM neurons feedback loop on larval memory formation.
In a substitution learning assay, simultaneous odor exposure paired with optogenetic activation of Kenyon cells in fruit fly larvae in absence of a rewarding stimulus resulted in formation of an appetitive memory, whereas no learning behavior was observed when pPAM neurons were ablated in addition to the KC activation. I argue that the activation of Kenyon cells may induce an internal signal that mimics reward exposure by feedback activation of the rewarding dopaminergic neurons. My data further suggests that the Kenyon cells-to-pPAM communication relies on peptidergic signaling via short neuropeptide F and underlies memory stabilization.
Honeybees (Apis mellifera) forage on a great variety of plant species, navigate over large distances to crucial resources, and return to communicate the locations of food sources and potential new nest sites to nest mates using a symbolic dance language. In order to achieve this, honeybees have evolved a rich repertoire of adaptive behaviours, some of which were earlier believed to be restricted to vertebrates. In this thesis, I explore the mechanisms involved in honeybee learning, memory, numerical competence and navigation. The findings acquired in this thesis show that honeybees are not the simple reflex automats they were once believed to be. The level of sophistication I found in the bees’ memory, their learning ability, their time sense, their numerical competence and their navigational abilities are surprisingly similar to the results obtained in comparable experiments with vertebrates. Thus, we should reconsider the notion that a bigger brain automatically indicates higher intelligence.