If you give a rat cocaine…does he become an addict? Most would say, “Yes, of course he does.” Researchers at the Bordeaux Institute for Neurosciences, however, would say, “There’s a chance he could.”
Drug addiction is extremely costly and harmful, making research on prevention and treatment critical. Since much of this research is done through animal models like rats, Dr. Deroche-Gamonet urges that “Fundamentally, we have to wonder: do rats develop addiction as humans do?”*
The Diagnostic and Statistical Manual of Mental Disorders (DSM) is used to diagnose humans with various psychological ailments, including substance use disorders, or, drug addictions.1 Yes, it would be difficult to study some symptoms of addiction in rats, such as “failure to fulfill major role obligations at work, school, or home.”1[DSM-5, p.577] But how, you ask, can we observe any of the symptoms of a complex human disorder in rats? Through the marvels of behavioral neuroscience.
The research team’s study2, published in Science, began by allowing rats to voluntarily self-administer cocaine. After three months of this, rats were assessed for three addiction-like symptoms, according to the DSM.
(1) Having difficulty “cutting down or controlling use” of the substance.1[p.577] The rats’ nose-poking efforts were measured when this action would no longer deliver cocaine. It was observed that some rats increased drug-seeking behavior even when they knew it was unavailable, suggesting they met this diagnostic criterion.
(2) Possessing “a strong desire or urge” to obtain and use the substance.1[p.577] By progressively increasing the number of nose-pokes required to obtain a dose of cocaine, the motivation to use the drug was measured. Some rats were willing to poke over 700 times for one dose, suggesting that excessive motivation was clearly present.
(3) “Recurrent use…in situations in which it is physically hazardous.”1[p.577]
When each dose of cocaine was paired with a painful shock to the foot, some rats still continued to self-administer.
Next was a test for relapse following withdrawal—an unfortunate reality for approximately 90% of human addicts. Relapse most often occurs after exposure to a drug-related cue (e.g., rolled up dollar bills), or the drug itself. After both long and short periods of withdrawal, exposure to either cocaine-associated cues or cocaine caused some rats to relapse—to reinstate their drug-seeking behavior.
A closer look at the data revealed the most striking similarity between our furry friends and us. Seventeen percent of the rats met all three DSM criteria studied, and were subsequently “diagnosed” with addiction. The percentage of humans diagnosed with cocaine addiction? Fifteen percent.2 It is clear that rats can be used as a highly reliable model of human addiction, mirroring its complexity. And both rats and humans inform us of the same surprising finding: not all who choose to take cocaine become addicts. Addiction is rooted in our genetics, conserved evolutionarily across species. From rats to humans, drug-taking does not equal addiction and its harmful consequences. What will happen when we, as a society, restructure our thinking to align with that of the scientific community?
- Deroche-Gamonet, V., Belin, D., & Piazza, P. V. (2004). Evidence for addiction-like behavior in the rat. Science, 305(5686), 1014-1017.
- American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders: DSM-5. Washington, D.C: American Psychiatric Association.