The Studying of The Sleep-wake Behaviour in Drosophila.

Sleep has always been an intriguing question as we spend most of our lifetime sleeping, So it interests many scientists to find out what exactly is the function of sleep. Sleep is defined as a naturally occurring state of mind and body characterized by altered consciousness, relatively inhibited. The state when our senses are disconnected. Sleep is exquisitely regulated there are complex mechanisms in our brain that increase the duration or the depth of sleep after sleep deprivation to permit the recovery of some of what was lost which is called homeostatic regulation. Sleep Mechanism:- There are also neural mechanisms that tend to consolidate sleep at a certain phase of the 24-hour cycle that is circadian regulation. To understand sleep, two distinct aspects of it must be addressed. These are the timing of sleep and the length/quality of sleep.

Both are maintained to be approximately the same from day to day. The timing of sleep is well established as a function of the circadian system in the brain. The circadian system is important for driving many aspects of behavior and physiology with a ~24-h period through a set of molecular oscillators. How our body knows how much sleep we need is less understood. Based on the rebound, or compensatory sleep, that follows sleep deprivation, sleep is thought to be an essential process whose amount is controlled by a homeostatic system Now the question is why natural selection favored sleep as it puts the individual in rather a dangerous situation because it reduces the ability to promptly respond to stimuli that signal threat and it also reduces the time spent foraging, reproducing, or monitoring the environment. So there must be a strong function related to sleep which makes it so important. Many groups are working on unfolding different layers of sleep functions one of them is related to synaptic plasticity.

Genes involved in sleep are ABCC9, DEC2, PAX8, VRK2. Importance of Sleep It has been seen that sleep is related to synaptic modulation and memory. Researchers first began mapping the general circuitry that controls wakefulness and sleeps over 50 years ago, and in the last 10–20 years, much has been learned about the specific systems that regulate sleep states(REM and non REM sleep). Other new work has examined the ways in which behavioral drives, including homeostatic, circadian, and allostatic influences, may affect these switching mechanisms.

Sleep has been identified as a state that optimizes the consolidation of newly acquired information in memory, depending on the specific conditions of learning and the timing of sleep. Consolidation during sleep promotes both quantitative and qualitative changes of memory representations. Sleep involves various neuronal connections .mutations in any of the circadian-related genes can affect the amount of sleep and in turn, the other problems which may arise due to sleep deprivation. Background:- The invertebrate whose sleep has been most intensively studied is the fruit fly Drosophila melanogaster. The fact that the fruit fly displays all of the core behavioral properties of sleep has engendered great enthusiasm and implies that sleep may have been present in the common ancestor of arthropods and vertebrates. The fruit fly central nervous system has over 200,000 neurons and does not have anatomic structures that clearly correspond to their vertebrate counterparts. But the fly genome has about 14,000 genes, many of which are highly conserved between flies and humans at the level of sequence and even function. Flies use many of the same or similar neurotransmitters, receptors and ion channels as mammals, although some transmitters (for example, octopamine) are used more commonly in flies than in mammals and other transmitters (for example, hypocretin/orexin) present in mammals have not been observed in flies.

Method for monitoring fly sleep:- Fly sleep is not typically monitored using video-based approaches but rather using the ‘Drosophila activity monitoring system’. Here, a single fly is placed into a small glass tube with agar food at one end. The tube is placed into a monitor containing 32 infrared emitter/detector pairs, one for each tube. Infrared beam breaks are counted as activity. Using this assay, the fly exhibits long periods of immobility, sometimes lasting for hours. A close examination of these immobile flies reveals a typical posture and place preference (near food when solitary). This behavioral quiescence is accompanied by increases in arousal threshold saturating at five minutes of immobility during the dark period, leading to the five-minute criterion for sleep that is commonly used.

Sleep depriving flies leads to a compensatory homeostatic rebound. Sleep is usually regulated by a circadian clock, which (at least) times sleep and wake to occur at particular times of day in most organisms. The fly also demonstrates robust circadian regulation of its sleep state and has been one of the best models for understanding the molecular basis of circadian clocks