Insomnia is a sleep disorder generally characterized by an inability to fall and stay asleep for extended periods of time. With one in three adults experiencing some form of the disorder during the course of their life, the condition is not only life altering but prevalent as well. Wake and sleep states are coordinated through interactions in the hypothalamus and brainstem (Konadhode et al. 2013). The hypothalamus is located near the base of the brain and plays roles in metabolic processes and hormone secretion and release. The brainstem is located below the hypothalamus and is responsible for regulating things like respiratory and cardiac functions.
Neurons are specialized communicating cells that use chemicals called neurotransmitters to send information to other cells. One neurotransmitter linked to sleep is called melanin concentrating hormone or MCH. Neurons that use MCH are found in the hypothalamus. To understand the role of MCH in the sleep of mice, Konadhode et al. (2013) needed to find a way to activate them while leaving other neurons alone. A virus was used to target a gene specifically to the MCH neurons. The gene constructs channels in the neuron that can be activated by the presence of light. The channel activation, triggered by optic fibers implanted in the hypothalamus, causes the release of MCH. This allowed the researchers to activate the MCH neurons very easily (Konadhode et al. (2013).
The investigators altered the level of MCH neuronal stimulation by varying the frequencies of the optic light pulses (low, medium and high frequencies). By changing the light output, Konadhode et al. (2013) hoped to figure out which frequencies could best activate the implanted channels and thus the MCH neurons. The researchers paid specific interest to the time spent in REM (rapid eye movement) and non-REM sleep. With respect to activity in the brain, REM sleep states and wakeful states share several similarities. Non-REM sleep states present different activity patterns and most researchers agree that the function of non-REM sleep probably has something to do with restoration (Purves et al. 2001).
It was discovered that the medium stimulation ended up being most effective in terms of increasing time spent in the sleep state. When focusing on the first 6 hours of stimulation, the researchers discovered that the medium treatment increased non-REM sleep by 60% and REM sleep by 95% as compared to a 48 hour period involving no stimulation. The high treatment increased non-REM sleep by 44.0% and REM sleep by 73%. The low-level stimulation gave similar results to that of the control. Along with studying the effects of stimulation on sleep time, the researchers also measured the amount of time the mice spent awake after falling asleep. During night time testing the medium-level treatment decreased the average length of wake-times by half. Konedhode et al. (2013) also wanted to investigate the effects of MCH during the day cycle. They discovered that medium-level stimulation had no effect on non-REM sleep, REM sleep or wakeful states compared to no treatment.
In conclusion, the study serves as an innovative and interesting way to investigate some of the potential causal mechanisms behind sleep disorders. By showing that specific neurons related to sleep initiation regulation can be targeted and activated in such a way as to increase sleep time and decrease waking time, the study could prove to be helpful in designing more effective clinical treatments for patients suffering from insomnia and other related sleeping disorders.
“I love sleep. My life has the tendency to fall apart when I’m awake, you know?”
– Ernest Hemingway
Sources
Konadhode, R.R., Pelluru, D., Blanco-Centurion, C., Zayachkivsky, A., Liu, M., Uhde, T., Glen, W.B., van den Pol, A.N., Mulholland, P.J., Shiromani, P.J. 2013. Optogenetic Stimulation of MCH Neurons Increases Sleep. The Journal of Neuroscience 33 (25): 10257-10263.
Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. The Possible Functions of REM Sleep and Dreaming. Available from: http://www.ncbi.nlm.nih.gov/books/NBK11121/.
