Researchers at the University of Tsukuba have found neurons in the brain that link narcolepsy, cataplexy, and rapid eye movement (REM) sleep behavior disorder and could provide a target for treatments.
These cells were located in the ventral medial medulla and received input from the sublaterodorsal tegmental nucleus, or SLD. "The anatomy of the neurons we found matched what we know," explains Takeshi Sakurai, senior author of a paper published in the Journal of Neuroscience last month. "They were connected to neurons that control voluntary movements, but not those that control muscles in the eyes or internal organs. Importantly, they were inhibitory, meaning that they can prevent muscle movement when active." When the researchers blocked the input to these neurons, the mice began moving during their sleep, just like someone with REM sleep behavior disorder.
Sakurai and his team suspected that the neurons they found were related to narcolepsy and cataplexy as well. They tested their hypothesis using a mouse model of narcolepsy in which cataplexic attacks could be triggered by chocolate. "We found that silencing the SLD-to-ventral medial medulla reduced the number of cataplexic bouts," says Sakurai.
Overall, the experiments showed these special circuits control muscle atonia in both REM sleep and cataplexy. "The glycinergic neurons we have identified in the ventral medial medulla could be a good target for drug therapies for people with narcolepsy, cataplexy, or REM sleep behavior disorder", adds Sakurai. "Future studies will have to examine how emotions, which are known to trigger cataplexy, can affect these neurons."