Two decades ago, Clifford B. Saper, MD/Ph.D., Chairman of the Department of Neurology at Beth Israel Deaconess Medical Center (BIDMC), and colleagues discovered a set of nerve cells they thought might be the switch that turns the brain off, allowing it to sleep. In a new study published in Nature Communications today, Saper and colleagues demonstrate in mice that these cells — located in a region of the hypothalamus called the ventrolateral preoptic nucleus (VLPO) — are in fact essential to normal sleep.

“Our paper is the first test of what happens when you activate the VLPO neurons,” said Saper, who is also James Jackson Putnam Professor of Neurology and Neuroscience at Harvard Medical School. “The findings support our original observation that the VLPO cells are essential to normal sleep.”

Working with genetically engineered mice, Saper’s team artificially activated the VLPO neurons using several different tools. In one set of experiments, the scientists activated the neuron cells using a laser light beam to make them fire, a process called optogentics. In another test, the team used a chemical to selectively activate the VLPO neurons. In both cases, activating these cells profoundly drove sleep.

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