Researchers at the University of Tsukuba in Japan discovered a group of neurons in the mouse brain stem that suppress unwanted movement during REM sleep.
Tsukuba, Japan – We laugh when we see Homer Simpson sleeping while driving, while at church, and even while the nuclear reactor is running. In reality, though, sleep behavior disorder induced by compulsive sleep, cataplexy, and rapid eye movement (REM) are all serious sleep-related diseases. Researchers at the University of Tsukuba led by Professor Takeshi Sakurai have found nerve cells in the brain that connect to all three disorders and could provide a target for treatment.
REM sleep is associated with when we dream. Our eyes move back and forth, but our bodies remain still. This near paralysis of muscles during dreaming is called REM-atonia, and it is lacking in people with REM sleep. Instead of remaining still during REM sleep, the muscles around them move, often going so far as to stand up and jump, yell, or punch. Sakurai and his team set out to find neurons in the brain that normally prevent this type of behavior during REM sleep.
Working with mice, the team identified a specific group of neurons as potential candidates. These cells were located in an area of the brain called the medial ventral medulla and received input from another area called the tantalic nucleus below the superficial layer, or SLD. “The anatomy of the neurons that we found matches what we know,” explains Sakurai. They were related to neurons that control voluntary movements, but not those that control muscles in the eye or internal organs. Most importantly, it was inhibitory, which means it can inhibit muscle movement when it is active. ”When the researchers blocked input to these neurons, the mice began to move while they slept, just like someone with REM sleep.
Narcolepsy, as explained by Homer Simpson, is characterized by falling asleep suddenly at any time during the day, even in the middle of a sentence (he was diagnosed with narcolepsy). Cataplexy is an associated disease in which people suddenly lose muscle tone and collapse. Even though they are awake, their muscles behave as if they were in REM sleep. Sakurai and his team suspected that the special neurons they found were linked to the two disorders. They tested their hypothesis with a mouse model of narcolepsy in which chocolate can trigger seizures. “We found that silencing the medial to ventral medial SLD reduces the number of cataplexy attacks,” says Sakurai.
In general, experiments have shown that these special circuits control muscle tension in both REM sleep and cataplexy. “The glycine neurons that we have identified in the medial and abdominal medulla may be a good target for drug treatments for people with narcolepsy, cataplexy, or REM sleep,” says Sakurai. “Future studies will have to examine how emotions, which are known to induce cataplexy, affect these neurons.”
The article, “A separate neuronal group for glycinergic in the mid-ventral medulla that induces muscle tension during REM sleep and freezing in mice,” was published in The Journal of Neuroscience In DOI: http: doi.org/10.1523/JNEUROSCI.0688-20.2020.