Yanagisawa's Knock-out Mice

To study the role that orexin played in mice, Yanagisawa and his team bred a strain of what are called knock-out mice. These animals did not possess a functional orexin receptor gene (the gene was ‘knocked out’) and thus orexin did not have its normal effects in them. After raising many generations of these knock-out mice, Yanagisawa began to videotape their behavior to observe the results of orexin deficiency, expecting to see appetite changes. What the team at University of Texas Southwestern Medical Center in Dallas did see was quite different. At first the results were discouraging because the mice showed no behavior changes. But the researchers soon realized that they were overlooking a very important factor – mice are nocturnal creatures, and observing them during the daytime was like watching humans at night, whilst they sleep. So Yanagisawa began to videotape them in complete darkness during the night with an infrared camera. What he observed was truly startling.

Richard Chamelli, one of the research fellows in the laboratory, noticed that suddenly, while the knock-out mice were running around and grooming themselves or burrowing, they would drop down and turn over on one side. Then, just as suddenly they would be up and scampering around again. Comparing this sudden behavioral phenomenon to the flipping of a switch, Yanagisawa studied it further (using electroencephalograms and electromyograms to record the brain activity of the mice during these periods, initially thinking they were seizures), and eventually hypothesized that the missing orexin was somehow linked to the regulation of the mice’s sleep and wake cycles, and produced a condition very similar to human narcolepsy.

The reason Mignot described the work of Yanagisawa’s team and his team as an ‘amazing convergence’ was that it turned out that the neuropeptides orexin and hypocretin were one and the same thing. Yanagisawa named the protein he found in the brain orexin after the Greek word “orexis” which meant appetite, since he originally thought that was what it was implicated in. He found that it was produced only in the hypothalamus (see figure on Hypocretin Model page) of the brain, mainly in the lateral hypothalamus, which is exactly where hypocretin is produced. In fact, hypocretin was named for the place it is produced (hypo, for hypothalamus) and the hormone it resembles (cretin, for secretin).

Watch a video (avi format, best viewed with Windows Media Player) of the narcoleptic symptoms in knock-out mice, as observed by Dr. Masashi Yanagisawa's research team and filmed with an infrared video camera during the dark part of their day/night cycles. The yellow arrow in the clip signifies the mouse before one of its cataplectic attacks; the red arrow appears during the brief attack; and the green arrow appears after the mouse has recovered from the attack. (This video is courtesy the Center of Narcolepsy at the Stanford School of Medicine, and was originally obtained from Dr. Yanagisawa's lab in Texas.)