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Lesku, John (2011): Avian Sleep Homeostasis: Electrophysiological, Molecular and Evolutionary Approaches. Dissertation, LMU München: Fakultät für Biologie



The function of slow wave sleep (SWS) and rapid eye movement (REM) sleep in mammals is an unanswered question in neuroscience. Aside from mammals, only birds engage in these states. Because birds independently evolved SWS and REM sleep, the study of sleeping birds may help identify shared traits related to the function of these states. Throughout this dissertation, we apply such a bird’s perspective to the sleeping brain. We begin with a review on knowledge gained through the study of sleep in animals (Chapter 1). Next, we present results from the first electrophysiological study of sleep in the most basal group of living birds by studying ostriches (Chapter 2). Although ostriches engage in unequivocal SWS, their REM sleep electrophysiology is unique and resembles features of REM sleep present only in basal mammals. Thus, the evolution REM sleep may have followed a recurring sequence of steps in mammals and birds. The remaining chapters deal with the regulation of sleep (or sleep homeostasis). Sleep homeostasis refers to an increase in the intensity of sleep (typically quantified as slow wave activity, SWA) following an extended period of wakefulness. Although such a response has long been known to occur in mammals, it has been unclear whether birds are capable of similar changes in SWA following sleep loss. We provide the first experimental evidence for a mammalian-like increase in SWA following enforced wakefulness in birds (Chapter 3). In mammals, SWA increases locally in brain regions used more during prior wakefulness. To see if SWS is regulated locally in birds, we stimulated one part of the pigeon brain during enforced wakefulness and observed a local increase in SWA during subsequent sleep (Chapter 4). Brain regions not stimulated asymmetrically during wakefulness showed a symmetric increase in SWA. These patterns of a/symmetry may reflect changes in the strength of synapses, as they do in mammals, because they are mirrored by changes in the slope of slow waves during SWS – a purported marker of synaptic strength. Lastly, we investigate whether local increases in SWA in birds are mediated by similar molecular mechanisms to those of mammals (Chapter 5). Surprisingly, mRNA levels of such proteins did not respond to unilateral visual stimulation during enforced wakefulness in the manner predicted based on work derived from mammals, but further study is needed to resolve the meaning of this difference. Overall, this dissertation presents several novel findings on the evolution and regulation of avian sleep.