Manipulation of synaptic pruning via the ecdysone signaling pathway and its effects on complex learning

Official URL: https://risc01.sabanciuniv.edu/record=b3074168_(Table of contents)

Critical periods are important milestones in the maturation of an organism. It is characterized by hormonal fluctuations and an outburst of dendritic branching and axonal growth, followed by an experience dependent pruning of weaker synapses. In honey bees there is a critical period during the transition from an in-hive bee to a forager. Drosophila studies show that signaling via EcR and Usp heterodimer is necessary for synaptic pruning to take place. Both HR39 and HR38 inhibit or suppress this pathway. Expression of HR38 gradually increases as the bee ages and gains experience; concurrently, synaptic bouton numbers increase with age and experience. Increased synaptic bouton numbers are associated with a decrease in reversal learning assay performance. In addition, HR38 expression peaks after obtaining a sucrose reward during foraging. Because of this, HR38 is theorized to play a role in synapse stabilization as well. I aimed to induce synaptic pruning in experienced old foragers by performing a HR39/HR38 double knockdown via siRNAs. I observed decreased synaptic bouton numbers in the MB of the honeybee brain. These treated bees’ acquisition of extinction during reversal learning was not affected, but the consolidation 4 of the extinction memory was blocked. I suspect that either the HR39/HR38 double knockdown directly disrupts molecular mechanisms of extinction learning or the reduction of the synaptic boutons leads to allocation of resources such that excitatory memory formed after pruning was better reinforced compared to extinction memory formed later.