Opioid addiction in the United States is at crisis levels, with drug overdoses now the leading cause of death for people under the age of 50. Treating those addictions, however, is tough; scientists still haven’t fully studied the physiology of addiction. But, as Heather Brady reports for National Geographic, hydrocodone-addicted zebrafish could help in the search.
A new study, published in the journal Behavioural Brain Research, investigates the surprisingly similar of addiction pathways of humans and zebrafish. The fish have already become a common tool to study human mental disorders due to their small size and genetic similarity (they share 70 percent of their genes with humans). But humans and zebrafish also have the same opioid receptors, according to a press release. And if the addiction in fish proves to follow the same pattern in humans, the tiny creatures could help in the search for addiction treatments.
To study these effects, researchers at the University of Utah placed zebrafish in a specially modified tank with a white platform and a yellow platform at the bottom, reports Alessandra Potenza at The Verge. Whenever the fish swam over the white platform there was no response. But if they swam over the yellow platform, a bit of food was released. Soon after, the food was replaced by hydrocodone, an opioid, that was squirted in the water. The fish were placed in the tank for 50 minutes a day over the course of five days.
On day one, the fish swam over the platforms equally. On the fifth day, however, the fish swam exclusively over the yellow pad, and were even willing to swim into shallow water to get their fix, something non-addicted fish were not willing to do. As Emily Underwood at Science reports, some fish visited the platform 2,000 times during their 50 minute swim. And when researchers made it harder to get a hit, some fish visited the platform up to 20 times to get a single dose. After 48 hours, the little swimmers also exhibited signs of withdrawal.
Brady reports that the researchers were able to confirm at the end of the study that the same molecular pathway that causes addiction in other animals, including humans, was also activated in the fish. This means that the fish, which are small and inexpensive, could be used in addiction studies to test the ability of different drugs to reduce or stop addiction. “The hope is that those drugs, when we find them, would also be useful in reducing the impulse to seek opioids in humans,” study co-author and chemical biologist Randall Peterson tells Potenza.
Currently, one of the most popular methods of treating opioid addicts is dosing patients with an alternative opioid like methadone to reduce symptoms of withdrawal and cravings for other drugs. Using these medically supervised drugs also keeps addicted patients from sharing needles and injecting heroin of unknown strength and origin. But critics argue that it is just replacing one opioid with another, as methodone itself is also addictive. The hope of this study and others is to find new treatments that break the addiction. “There is still a compelling need for therapies that work in different ways, not just by replacing one opioid with another,” Peterson tells Brady.
There is some progress being made in finding these treatments. Last year, the FDA approved Probuphine, an implant that releases the drug buprenorphine into the bloodstream, which binds up opioid receptors. Naloxone, another opiate antagonist, also blocks the body from responding to opioids and has also gained wider use in recent years. But perhaps with help from our finned friends, even more cures will be on the horizon.