Brain Cell Changes Linked to Opiate Addiction, Narcolepsy

UCLA researchers have made two discoveries that provide new information on chemical messengers in the brain regulating addiction and sleep. One of the new findings involves the brain of people living with a heroin addiction and the other involves the brain of drowsy mice.

In 2000, scientists at the University of California Los Angeles found that narcolepsy (a sleep disorder whose symptoms include excessive sleepiness, sleep attacks, hallucinations and loss of muscle control) is caused by loss of approximately 90 percent of the brain cells that contain the neurotransmitter hypocretin. This chemical messenger is normally present in 80,000 brain cells.

Narcolepsy and Heroin Addiction

Narcolepsy is not a common disorder, affecting about one in 2,000-3,000 people. It can go undiagnosed for a number of years, with the patient usually starting to experience symptoms in childhood or adolescence.

The results of a new study have revealed that heroin addicts have 54 percent more hypocretin-secreting neurons that non-addicts, on average. Tests performed on mice have confirmed that opiate use is responsible for this increase. The jump in hypocretin cells lasted for up to four weeks after morphine treatment stopped, which is well after the morphine would have left the mice’s bodies.

The researchers thought morphine, which is the active ingredient in heroin, may restore the hypocretin-producing neurons which are missing in narcolepsy patients. To put this idea to the test, they gave narcoleptic mice morphine. The researchers found that morphine increased the number of hypocretin-producing cells, and the symptoms of narcolepsy disappeared.

Brain Neurotransmitter May Contribute to Opioid Cravings

The mice continued to produce hypocretin after they were taken off morphine. To the researchers, this observation led to a theory that humans may continue producing hypocretin after going through heroin detox (detoxification). The researchers thought the increase in hypocretin levels may be linked to opiate cravings and that bringing them close to “normal” levels might potentially reverse narcolepsy symptoms in humans.

More work will be needed with mice before this treatment approach can be recommended for human patients. Researchers would like to discover whether reducing the number of “excess” hypocretin cells could have a role in relieving withdrawal symptoms for long-term opiate users and preventing relapse once they are clean.