Interaction between circadian neurons and sleep homeostat to regulate sleep/wake cycles in Drosophila melanogaster

Abstract

Sleep is a period of quiescence that is widespread in the animal kingdom and while its quantity and quality may differ between different animals, certain characteristic features remain conserved across taxa. These include electrophysiological signatures such as reduced overall brain activity and muscle tone. Additionally, mammals and birds have characteristic waves of activity of specific frequencies which define different stages of sleep such as Rapid Eye Movement (REM) and non-REM sleep. However, in animals lacking complex nervous systems where such features may not be present and/or detection of such features maybe technically difficult, several behavioural features are used to characterize sleep. These include species-specific posture during sleep, preference for certain sites to sleep, reduced responsiveness to sensory cues and increased arousal thresholds. Most importantly, sleep is regulated by a sleep homeostat, which regulates how much and how well an animal sleeps, and by circadian clocks, which are internal time-keeping mechanisms that regulate the timing of sleep and wake behaviours. How the two processes overlap and interact in their regulation of sleep is a question that remains unanswered and I sought to address this question in my studies on sleep/wake cycles in fruit flies Drosophila melanogaster that form a part of this thesis. A small part of my thesis also addresses the question of significance of sleep by examining the relationship between sleep and reproductive output in female fruit flies.