Neurons responsible for rapid eye movements/REM during sleep
December 20, 2019
Science Daily/University of Bern
Why do we move our eyes fast in the paradoxical sleep -- in that sleep phase, in which most dreams take place? The secret is not yet fully aired, but we are on his track: A team has identified the nerve cells behind this curious phenomenon.
REM -- Rapid Eye Movement -- is not only the name of a successful American rock band, but also and not least a characteristic eye movement in paradoxical sleep, so in the stage with high dream activity. This sleep phase has a peculiarity: Although the muscle tone of the sleeping person completely relaxed, the eyes suddenly move back and forth. The name "paradoxical sleep" is well deserved. Characteristic of these are signs of deep sleep (muscle atony) in connection with a brain activity, which is very similar to those in the waking state, and eye movements. This sleep phase was discovered in the 1950s by French and American researchers and consequently called rapid eye movement sleep (REM sleep), i.e. sleep with rapid eye movements. Why can this strange phenomenon be useful? For 70 years, scientists have been dreaming of getting to the bottom of the mystery. Thanks to the productive cooperation between the universities of Bern and Fribourg, this dream could now come true.
Butterfly wings arranged neurons
For several years, the team led by Franck Girard and Marco Celio at the University of Freiburg has studied neurons under the microscope, which occur in the brain stem and form a structure that is reminiscent of butterfly wings, which is why she was baptized Nucleus papilio. "These neurons are associated with multiple nerve centers, especially those responsible for eye movement, and those involved in sleep control," explains Franck Girard. "Therefore, we asked ourselves the following question: may the nucleus papilio neurons play a role in the control of eye movements during sleep?"
Stronger together
To test this hypothesis, the Freiburg researchers turned to the research group headed by Dr. C. Gutiérrez Herrera and Prof. A. Adamantidis at the Department of Neurology at the Inselspital, University Hospital Bern, and Department for BioMedical Research of the University of Bern, who are investigating sleep in mice. "To our surprise, we found that these neurons are particularly active in the phase of paradoxical sleep," reports Dr. Carolina Gutierrez. The researchers from Bern gathered the loop around the nucleus papilio neurons even more closely and were able to demonstrate with the help of optogenetic methods (combined optical and genetic techniques) that their artificial activation causes rapid eye movement, especially during this sleep phase. Conversely, the inhibition or elimination of these same neurons blocks the movement of the eyes.
After the "how" the "why"!
Now that it is clear that the nucleus papilio neurons play an important role in eye movement during REM sleep, it is important to find out what function this phenomenon has. Is it due to the visual experience of dreams? Does it matter in preserving memories? "Now that we are able to specifically activate the nucleus papilio 'on demand' in mice by optogenetic methods, we may be able to find answers to these questions," says Antoine Adamantidis. The next step, however, will be to confirm the activation of nucleus papilio neurons during REM sleep in humans. The researchers have not yet found the key to their dreams, but they've come a long way.
A better understanding of the neural circuits involved in paradoxical sleep is therefore a prerequisite for understanding for instance how these neurons are prone to degenerative changes in diseases such as Parkinson's.
https://www.sciencedaily.com/releases/2019/12/191220150557.htm
'Goldilocks' neurons promote REM sleep
June 19, 2019
Science Daily/University of Bern
It has been a mystery why REM sleep, or dream sleep, increases when the room temperature is 'just right'. Neuroscientists show that melanin-concentrating hormone neurons within the hypothalamus increase REM sleep when the need for body temperature defense is minimized, such as when sleeping in a warm and comfortable room temperature. These data have important implications for the function of REM sleep.
Every night while sleeping, we cycle between two very different states of sleep. Upon falling asleep, we enter non-rapid eye movement (non-REM) sleep where our breathing is slow and regular and movement of our limbs or eyes are minimal. Approximately 90 minutes later, how-ever, we enter rapid eye movement (REM) sleep. This is a paradoxical state where our breathing becomes fast and irregular, our limbs twitch, and our eyes move rapidly. In REM sleep, our brain is highly active, but we also become paralyzed and we lose the ability to thermoregulate or maintain our constant body temperature. "This loss of thermoregulation in REM sleep is one of the most peculiar aspects of sleep, particularly since we have finely-tuned mechanisms that control our body temperature while awake or in non-REM sleep," says Markus Schmidt of the Department for BioMedical Research (DBMR) of the University of Bern, and the Department of Neurology, Inselspital, Bern University Hospital. On the one hand, the findings confirm a hypothesis proposed earlier by Schmidt, senior author of the study, and on the other hand represent a breakthrough for sleep medicine. The paper was published in Current Biology and highlighted by the editors with a comment.
A control mechanism saving energy
The need to maintain a constant body temperature is our most expensive biological function. Panting, piloerection, sweating, or shivering are all energy consuming body reactions. In his hypothesis, Markus Schmidt suggested that REM sleep is a behavioral strategy that shifts energy resources away from costly thermoregulatory defense toward, instead, the brain to enhance many brain functions. According to this energy allocation hypothesis of sleep, mammals have evolved mechanisms to increase REM sleep when the need for defending our body temperature is minimized or, rather, to sacrifice REM sleep when we are cold. "My hypothesis predicts that we should have neural mechanisms to dynamically modulate REM sleep expression as a function of our room temperature," says Schmidt. Neuroscientists at the DBMR at the University of Bern and the Department of Neurology at Inselspital, Bern University Hospital, now confirmed his hypothesis and found neurons in the hypothalamus that specifically increase REM sleep when the room temperature is "just right."
REM sleep promoting neurons
The researchers discovered that a small population of neurons within the hypothalamus, called melanin-concentrating hormone (MCH) neurons, play a critical role in how we modulate REM sleep expression as a function of ambient (or room) temperature. The researchers showed that mice will dynamically increase REM sleep when the room temperature is warmed to the high end of their comfort zone, similar to what has been shown for human sleep. However, genetically engineered mice lacking the receptor for MCH are no longer able to increase REM sleep during warming, as if they are blind to the warming temperature. The authors used optogenetics technics to specifically turn on or off MCH neurons using a laser light time locked to the temperature warming periods. Their work confirms the necessity of the MCH system to increase REM sleep when the need for body temperature control is minimized.
Breakthrough for sleep medicine
This is the first time that an area of the brain has been found to control REM sleep as a function of room temperature. "Our discovery of these neurons has major implications for the control of REM sleep," says Schmidt. "It shows that the amount and timing of REM sleep are finely tuned with our immediate environment when we do not need to thermoregulate. It also con-firms how dream sleep and the loss of thermoregulation are tightly integrated."
REM sleep is known to play an important role in many brain functions such as memory consolidation. REM sleep comprises approximately one quarter of our total sleep time. "These new data suggest that the function of REM sleep is to activate important brain functions specifically at times when we do not need to expend energy on thermoregulation, thus optimizing use of energy resources," says Schmidt.
https://www.sciencedaily.com/releases/2019/06/190619111248.htm