Scientists have long used laboratory rats and mice as models for studying human disorders and disease, evaluating the safety and efficacy of new medications and dietary supplements, and testing the effects of carcinogens (i.e., cancer-causing agents). In the 1960s, studies of rodents placed in an operant conditioning chamber (i.e., Skinner box) were popularly used to study addiction. During these experiments, scientists would observe rats in Skinner boxes repeatedly pressing a lever as they consumed large amounts of dangerous and powerful drugs, including cocaine, morphine and heroin. The uncontrollable self-administration of these illicit drugs by the laboratory rats led scientists to conclude that such drugs were overwhelmingly addictive.
Between 1960 and 1980, Canadian psychologist Bruce K. Alexander hypothesized that the cramped, socially isolated and near-abusive living conditions of the rodents played a major role in their self-administration of drugs. The famous “Rat Park” study, conducted in 1978 by Alexander and his colleagues at Simon Fraser University, examined the effect of such living conditions on the rats’ use of addictive drugs.
In comparing the drug intake of rats who were left in the standard solitary confinement laboratory cages with rats of both sexes who were housed together, in what they called a “Rat Park,” or a spacious box filled with wood chips, running wheels, tin cans and platforms for climbing, hiding and doing all of the things that rats normally liked to do, they found that the rats living in the “Rat Park” actually consumed much less of the drug solution than the rats living in the solitary confinement cages. Importantly, this study suggested that the rats’ environments played a major role in the self-administration of drugs.
Depression-like behaviors reduced following a trip to rat ‘Disneyland’
Similar to training rodents to self-administer heroin or cocaine to study drug addiction, scientists have also bred rats to be genetically depressed to study human depression. When it comes to the genetic vulnerability, a one-month trip to rat “Disneyland” provides relief from depressive-like behaviors in genetically depressed rats, according to a new study conducted by Eva Redei, Ph.D., David Lawrence Stein professor of psychiatry, and her colleagues from the Feinberg School of Medicine at Northwestern University.
Redei and her colleagues examined how adverse (negative) or enriched (positive) environments and genetic vulnerability influenced the display of depression-like behavior in rats. Rats from an established model of adolescent and adult major depression were genetically bred for despair across multiple generations, and a genetically similar, but behaviorally distinct, strain of rats served as the controls. Ten adult male rats from each strain were chronically stressed from being placed in flexible plastic bags that only had an opening for their mouth and nose, leaving them unable to turn around or move in the apparatus for two hours per day for two weeks.
The chronic, mild stress induced by the apparatus increased anhedonia-like behavior in the genetically depressed rats. Following the month-long environmental enrichment, the depression-like behavior of the rats decreased. In other words, rats bred to have a genetic vulnerability for depression became happy again and were less stressed when they received “rodent psychotherapy” by living in a positive and enriched environment, which allowed them to hide, play and have contact with other rats.
The important role of the environment
This research shows that genetic vulnerability for depression can be changed by the environment, which is important for understanding the role that both the environmental factors and genetic vulnerability play in humans’ susceptibility for major depressive disorder (MDD), one of the most debilitating and common mental disorders in the United States and worldwide. The findings of this study indicated that the environmental enrichment, or rat “Disneyland,” acted as psychotherapy to attenuate the depression-like behavior in the rats. Thus, by changing the environment, humans who have a genetic vulnerability for depression may also find relief from their symptoms.
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About the author
Amanda Habermann is a writer for the Sovereign Health Group. A graduate of California Lutheran University, she received her M.S. in clinical psychology with an emphasis in psychiatric rehabilitation. She brings to the team her background in research, testing and assessment, diagnosis and recovery techniques. For more information and other inquiries about this article, contact the author at firstname.lastname@example.org.