HOW MANY? –

Jan. 12, 2022 – In 2000, UCLA sleep researchers discovered that human narcolepsy – a condition where people are overwhelmed with daytime drowsiness and sudden attacks of sleep – was caused by a loss of roughly 90% of the 80,000 brain cells containing hypocretin (also called orexin), a chemical messenger important in the regulation of sleep and wakefulness. Typically, people with narcolepsy are treated with drugs that for most people would be highly addictive, but interestingly these patients show little, if any, signs of drug addiction or withdrawal themselves.

The lack of hypocretin-producing neurons and addiction seen in narcolepsy took on a different twist when nearly two decades later the researchers made the surprising discovery that the brains of people addicted to heroin (a commonly abused opioid) have, on average, 54% more hypocretin-producing neurons than people who don’t have a substance abuse disorder – and confirmed the same finding in mice. However, when they stopped the opioid treatment in the mice, they found that the increase in hypocretin remained, lasting as long as four weeks.

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