Jeff Donlea

Sleep is a vital, evolutionarily conserved phenomenon, whose function is unclear. Although mounting evidence supports a role for sleep in the consolidation of memories, until now, a molecular connection between sleep, plasticity, and memory formation has been difficult to demonstrate. We establish Drosophila as a model to investigate this relation and demonstrate that the intensity and/or complexity of prior social experience stably modifies sleep need and architecture. Furthermore, this experience-dependent plasticity in sleep need is subserved by the dopaminergic and adenosine 3',5'-monophosphate signaling pathways and a particular subset of 17 long-term memory genes.

Although it is widely accepted that sleep must serve an essential biological function, little is known about molecules that underlie sleep regulation. Given that insomnia is a common sleep disorder that disrupts the ability to initiate and maintain restorative sleep, a better understanding of its molecular underpinning may provide crucial insights into sleep regulatory processes. Thus, we created a line of flies using laboratory selection that share traits with human insomnia. After 60 generations, insomnia-like (ins-l) flies sleep 60 min a day, exhibit difficulty initiating sleep, difficulty maintaining sleep, and show evidence of daytime cognitive impairment. ins-l flies are also hyperactive and hyperresponsive to environmental perturbations. In addition, they have difficulty maintaining their balance, have elevated levels of dopamine, are short-lived, and show increased levels of triglycerides, cholesterol, and free fatty acids. Although their core molecular clock remains intact, ins-l flies lose their ability to sleep when placed into constant darkness. Whole-genome profiling identified genes that are modified in ins-l flies. Among those differentially expressed transcripts, genes involved in metabolism, neuronal activity, and sensory perception constituted over-represented categories. We demonstrate that two of these genes are upregulated in human subjects after acute sleep deprivation. Together, these data indicate that the ins-l flies are a useful tool that can be used to identify molecules important for sleep regulation and may provide insights into both the causes and long-term consequences of insomnia.

STUDY OBJECTIVES: Multiple lines of evidence indicate that sleep is important for the developing brain, although little is known about which cellular and molecular pathways are affected. Thus, the aim of this study was to determine whether the early adult life of Drosophila, which is associated with high amounts of sleep and critical periods of brain plasticity, could be used as a model to identify developmental processes that require sleep. SUBJECTS: Wild type Canton-S Drosophila melanogaster. DESIGN; INTERVENTION: Flies were sleep deprived on their first full day of adult life and allowed to recover undisturbed for at least 3 days. The animals were then tested for short-term memory and response-inhibition using aversive phototaxis suppression (APS). Components of dopamine signaling were further evaluated using mRNA profiling, immunohistochemistry, and pharmacological treatments. MEASUREMENTS AND RESULTS: Flies exposed to acute sleep deprivation on their first day of life showed impairments in short-term memory and response inhibition that persisted for at least 6 days. These impairments in adult performance were reversed by dopamine agonists, suggesting that the deficits were a consequence of reduced dopamine signaling. However, sleep deprivation did not impact dopaminergic neurons as measured by their number or by the levels of dopamine, pale (tyrosine hydroxylase), dopadecarboxylase, and the Dopamine transporter. However, dopamine pathways were impacted as measured by increased transcript levels of the dopamine receptors D2R and dDA1. Importantly, blocking signaling through the dDA1 receptor in animals that were sleep deprived during their critical developmental window prevented subsequent adult learning impairments. CONCLUSIONS: These data indicate that sleep plays an important and phylogenetically conserved role in the developing brain.

To test the hypothesis that sleep can reverse cognitive impairment during Alzheimer's disease, we enhanced sleep in flies either co-expressing human amyloid precursor protein and Beta-secretase (APP:BACE), or in flies expressing human tau. The ubiquitous expression of APP:BACE or human tau disrupted sleep. The sleep deficits could be reversed and sleep could be enhanced when flies were administered the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Expressing APP:BACE disrupted both Short-term memory (STM) and Long-term memory (LTM) as assessed using Aversive Phototaxic Suppression (APS) and courtship conditioning. Flies expressing APP:BACE also showed reduced levels of the synaptic protein discs large (DLG). Enhancing sleep in memory-impaired APP:BACE flies fully restored both STM and LTM and restored DLG levels. Sleep also restored STM to flies expressing human tau. Using live-brain imaging of individual clock neurons expressing both tau and the cAMP sensor Epac1-camps, we found that tau disrupted cAMP signaling. Importantly, enhancing sleep in flies expressing human tau restored proper cAMP signaling. Thus, we demonstrate that sleep can be used as a therapeutic to reverse deficits that accrue during the expression of toxic peptides associated with Alzheimer's disease.