A state-dependent memory for sodium chloride in Drosophila melanogaster and comparative neural transcriptomic analyses of Drosophila and Apis mellifera

Thesis

Associative learning and memory, combined with internal state signals, optimise the behaviours of foraging animals. The Mushroom Bodies (MBs) of insects coordinate associative learning and are comprised of intrinsic neurones called Kenyon Cells (KCs). KCs represent sensory information in a parallel stream. Valence information, like rewarding nutrient signals, is provided to the MB by dopaminergic neurones (DANs). DANs direct learning-relevant plasticity of connections between KCs and downstream MB output neurones. This thesis investigates a state-dependent NaCl-memory in Drosophila melanogaster and explores midbrain transcriptomic changes in response to NaCl-feeding. In addition, transcriptomic profiles of Apis mellifera KCs and DANs were characterised and compared to those of Drosophila to understand conserved transcriptomic cell profiles between the two species.

Using an olfactory associative learning paradigm, with a naively appetitive (low) or naively aversive (high) concentration of NaCl as the unconditioned stimulus, we tested the existence of a state-dependent NaCl memory in Drosophila. Nutrient-deprived Drosophila form an immediate, but short-lived, low NaCl memory. A long-lasting memory was found for high NaCl; the valence of this memory depended on nutrient status. Nutrient-deprived Drosophila approached the conditioned odour, NaCl-fed Drosophila showed no detectable preference for either the conditioned nor alternative odour and satiated Drosophila avoided the conditioned odour. This aversive behaviour was more pronounced in females. To understand the transcriptional changes that occur in the brain in response to NaCl feeding, we analysed single-cell RNA sequencing (scRNA-seq) data of nutrient-deprived or NaCl-fed Drosophila midbrains. However, the quality of this data was impacted by a high level of adapter sequence contamination in sequenced reads, but preliminary analysis identified potential nutrient-deficit signals.

ScRNA-seq analysis of twelve pollen-foraging Apis dorsal protocerebra identified nine KC clusters. Transcriptomic comparison of Drosophila and Apis KC clusters found little similarity; however, marker genes for Drosophila reward and punishment-encoding DANs annotated two discrete Apis DAN clusters.

Authors: Morgan, I

• DOI: 10.5287/ora-2a40kdq9y
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Neurosciences; Computational biology