Sleep homeostasis in Drosophila melanogaster.
OBJECTIVE
The fruit fly Drosophila melanogaster is emerging as a promising model system for the genetic dissection of sleep. As in mammals, sleep in the fruit fly is a reversible state of reduced responsiveness to the external world and has been defined using an array of behavioral, pharmacologic, molecular, and electrophysiologic criteria. A central feature of mammalian sleep is its homeostatic regulation by the amount of previous wakefulness. Dissecting the mechanisms of homeostatic regulation is likely to provide key insights into the functions of sleep. Thus, it is important to establish to what extent sleep homeostasis is similar between mammals and flies. This study was designed to determine whether in flies, as in mammals, (1) sleep rebound is dependent on prior time awake; (2) sleep deprivation affects the intensity, in addition to the duration, of sleep rebound; (3) sleep loss impairs vigilance and performance; (4) the sleep homeostatic response is conserved among different wild-type lines, and between female and male flies of the same line.


METHODS
Motor activity of individual flies was recorded at 1-minute intervals using the infrared Drosophila Activity Monitoring System during 2 baseline days; during 6, 12, and 24 hours of sleep deprivation; and during 2 days of recovery. Sleep was defined as any period of uninterrupted behavioral immobility lasting > 5 minutes. Sleep continuity was measured by calculating the number of brief awakenings, the number and duration of sleep episodes, and a sleep continuity score. Vigilance before and after sleep deprivation was assessed by measuring the escape response triggered by 2 different aversive stimuli.


METHODS
Fly sleep research laboratory at UW-Madison.


METHODS
Adult flies of the Canton-S (CS) strain and 116 other wild-type lines (> or = 16 female and > or = 16 male flies per line).


RESULTS
In wild-type CS flies, as in mammals, the amount of sleep recovered after sleep deprivation was dependent on prior time awake. Relative to baseline sleep, recovery sleep in CS flies was less fragmented, with longer sleep episodes, and was associated with a higher arousal threshold. Sleep deprivation in CS flies also reduced performance. Sleep duration and continuity increased after 24 hour of sleep deprivation in all the other wild-type lines tested.


CONCLUSIONS
The sleep homeostatic response in fruit flies is a stable phenotype and shares most of, if not all, the major features of mammalian sleep homeostasis, thus supporting the use of Drosophila as a model system for the genetic dissection of sleep mechanisms and functions.
Huber
Reto
R
Department of Psychiatry, University of Wisconsin, Madison 53719, USA.
Hill
Sean L
SL
Holladay
Carie
C
Biesiadecki
Melissa
M
Tononi
Giulio
G
Cirelli
Chiara
C
D000818:Animals; D001143:Arousal / Q000502:physiology; D001522:Behavior, Animal; D004331:Drosophila melanogaster; D004924:Escape Reaction / Q000502:physiology; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006358:Hot Temperature; D007103:Immobilization / Q000502:physiology; D008124:Locomotion / Q000502:physiology; D008297:Male; D010641:Phenotype; D012892:Sleep Deprivation / Q000503:physiopathology*; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology