For the study, researchers examined five narcoleptic brains and seven control brains from human cadavers. Prior to death, all the narcoleptics had been diagnosed by a sleep disorder center as having narcolepsy with cataplexy. These brains were also compared with the brains of three narcoleptic mouse models and to the brains of narcoleptic dogs.
The researchers found that the humans with narcolepsy had an average of 64 percent more histamine neurons. Interestingly, the team did not see an increased number of these cells in any of the animal models of narcolepsy.
"Humans and animals with narcolepsy share the same symptoms, but we did not see the histamine cell changes we saw in humans in the animal models we examined," said Siegel, who directs the Center for Sleep Research at the UCLA Semel Institute for Neuroscience and Human Behavior and is the senior author of the research. "We know that narcolepsy in the animal models is caused by engineered genetic changes that block hypocretin function. However, in humans, we did not know why the hypocretin cells die.
"Our current findings indicate that the increase of histamine cells that we see in human narcolepsy may cause the loss of hypocretin cells," he said.
The study results may also further our understanding of brain plasticity, Siegel noted. While scientists have known of the existence of neurogenesis the process by which the brain is populated with new neurons it was thought to function mainly to replace existing cells that had died.
"This paper shows for the first time that neuronal numbers can increase greatly and not just serve as replacement cells," he said. "In the current example, this appears to be pathological with the destruction of hypocretin, but in other circumstances, it may underlie recovery and learning and open new routes to treatment of a number of neurological disorders."
|Contact: Mark Wheeler|
University of California - Los Angeles