Dissecting the neuronal circuitry of the sleep homeostat

Thesis

Sleep is essential to every animal’s life and sleep deprivation can be detrimental to the animal’s health and wellbeing. The timing and length of sleep are tightly regulated by the circadian rhythm and the homeostatic process. In the fruit fly Drosophila melanogaster, the homeostatic control of sleep was mapped to neurons projecting to the dorsal fan-shaped body (dFBN). These neurons change their firing rate with increasing sleep pressure and subsequently induce sleep in the animal. While the molecular mechanisms involved in sensing sleep pressure in dFBNs are being delineated, their synaptic connections have not been analysed functionally. Here, I analysed the published connectomes to identify relevant connected cell types and found strong synaptic connections to and from interneurons in the fan-shaped body. I performed a behavioural screen to delineate the role of sleep regulation in these connected neurons and found several cell types that might be relevant in the sleep control circuitry. dFBNs connect strongest to hDeltaF neurons, which form columnar neurons in the fan-shaped body, and I showed that these neurons have wake-promoting effects upon activation. I further studied two cell types that connect dFBNs to another sleep regulatory centre, the ellipsoid body, and manipulating these neurons also revealed wake-promoting effects. Further analysis of the synaptic connection of dFBNs and hDeltaF neurons via patch-clamp electrophysiology uncovered a synapse of dual polarity, suggesting that one neurotransmitter, glutamate, can be both inhibitory and excitatory between the same synaptic partners. Overall, dFBNs are interconnected with many different cell types and their synaptic connection might be more diverse than expected, suggesting a modulatory role on downstream circuits.

Authors: Ballenberger, L

• DOI: 10.5287/ora-b7y5pjz8k
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: neuronal circuitry; connectome; Drosophila melanogaster; sleep; patch clamp electrophysiology
• Subjects: Neurosciences