So this is my second post to do with insects…not a theme, they just happen to be amazing little creatures, both in their natural abilities (see my Honeybee post) and as research tools (see current post). The study I’m referring to below was published in Science on June 24, 2011. Fascinating stuff!
Aaahhh, sleep. We know we need it and can’t function properly without it. If you’ve been unfortunate enough to experience insomnia, you can attest to the importance of sleep. However, the purposes of sleep that we are all likely familiar with (such as restoration and memory processing), have not actually been proven. Currently, the only way for scientists to really study the function of sleep is to withhold it and observe the consequences. It is not yet possible to put subjects to sleep on demand and study the benefits of sleep…that is, UNLESS your subject is a fruitfly…in which case you are in luck.
Researchers out of Washington University have found a way to actually induce spontaneous sleep in Drosophila (aka. fruitflies). With some molecular magic, researchers were able to express a specific channel that is temperature sensitive (TrpA1) in neurons that project to the part of the brain involved in sleep regulation. By then moving the flies to an environment with a temperature of 31°C, the flies basically fell asleep. Since the goal is to study the effects of natural sleep, researchers had to be sure that this induced sleep was indeed molecularly and behaviourally similar to “real” sleep. Locomotion following induced sleep was not affected, flies were woken with mechanical pertubation (I assume this to mean shaking of the tube the flies had been placed in), and feeding the flies caffeine prior to exposure to the 31°C environment weakened sleep induction. As well, genes that are normally down-regulated with real sleep were also shown to be down-regulated with the move to the 31°C environment. These functional and molecular findings are all characteristic of spontaneous sleep, suggesting the researchers were successful in inducing a real-type sleep.
Now convinced that they could induce sleep, the researchers set out to determine whether sleep had a function in long-term memory. First a little background. There is something called the synaptic homeostasis model which hypothesizes that synaptic connections (think of this as communication between neurons) are increased while we are awake, and decreased during sleep. This downtime during sleep is believed to be necessary, otherwise brain circuits would become overloaded and we would be unable to learn new things and memory would start to be affected (just think of how your ability to learn or remember things is affected after even 1 night without sleep). When flies are placed in large social groups (~90 flies) the synaptic connections are increased (causing overload of brain circuits), so without sleep, long-term memory in these flies is affected. (BTW, long-term memory in flies is measured by something called courtship conditioning in which male flies learn who are the appropriate receptive females to mate with via certain cues, such as pheromones.). However, when flies expressing the TrpA1 gene were placed in a large social group (thereby overloading the brain circuits), and then moved to 31°C where sleep was induced, long-term memory was restored. To take this a step further, induced sleep was even able to result in long-term memory formation of a behavioral protocol that normally only induces short-term memory. Wild!!
So, here we are with the first steps in really uncovering the true functions of sleep. How can this research be extended to humans? Well, we are far from being able to induce natural sleep in people, but we can at least uncover mechanisms occurring in other species and glean from these findings the functions of sleep as well how sleep interacts and affects other biological processes.
(Reference: Donlea JM et al. Science 2011;332:1571.)