Using sophisticated techniques to switch specific populations of brain cells on and off, researchers have discovered a neuronal circuit that can potently initiate and maintain deep sleep. While more work needs to be done to find out how this bundle of nerves interacts with other known sleep and wake-promoting regions, the researchers believe that the new findings may eventually help scientists develop treatments for various sleep disorders such as insomnia. The work has been published in Nature Neuroscience.
Sleep is essential to rest our bodies and restore energy levels. While we’re out like a light, sometimes drooling and snoring, our brains use this time to consolidate learning and memory by strengthening and weakening connections between brain cells.
Broadly, there are two basic sleep states—rapid eye movement (REM) and non-rapid eye movement (NREM)—which we cycle between during sleep. NREM is split into four stages, the last two of which are known as slow-wave sleep (SWS) or deep sleep. Scientists have suspected for some time that a SWS-promoting circuit exists in the mammalian brainstem, but whether nerves in this region are capable of initiating and maintaining SWS was unknown.
To find out more, neuroscientists from Harvard and the University at Buffalo reversibly switched on a bundle of cells in a lower brainstem (medulla) region called the parafacial zone (PZ). To do this, they used a virus to insert “designer” genes into PZ neurons in mice. These genes produced a type of receptor that the researchers could selectively activate, which in turn caused the cells to fire. They found that switching on these neurons potently initiated SWS in mice, regardless of the time of day.
After these neurons were activated, they released a neurotransmitter called GABA onto neighboring neurons. These cells then released a different neurotransmitter called glutamate onto neurons within a region called the magnocellular basal forebrain, an area that is known to be important for sleep-wake regulation.
Since the brainstem is known to house many of the control centers for vital body functions such as breathing and blood pressure, this research “highlights the evolutionary importance of sleep in the brain,” says study co-author Caroline Bass.
While further research needs to be done to characterize how this region interacts and communicates with other networks involved in sleep and wakefulness, it is hoped that one day the findings could help researchers develop safer anesthetics and novel treatment avenues for sleep disorders.
“We are at a truly transformative point in neuroscience where the use of designer genes gives us unprecedented ability to control the brain,” Bass said in a news release. “We can now answer fundamental questions of brain function, which have traditionally been beyond our reach, including the ‘why’ of sleep, one of the more enduring mysteries in neuroscience.”
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