While love doesn’t always conquer all, it can be a potent antidote to addiction, according to a growing body of research. The latest study on the matter examined male prairie vole behavior, finding that those that had bonded to a female partner were less interested in taking amphetamine than bachelor voles.
“These results indicate that the pair-bonding experience decreased the rewarding properties of amphetamine,” says Kimberly Young, an author of the study and a postdoctoral student at Florida State University.
Unlike rats or mice, prairie voles form lifelong bonds with their mates, more closely approximating human social behavior, which is why scientists like to study them. For the current research, which was published in the Journal of Neuroscience, researchers looked closely at how pair-bonding and amphetamine affected voles’ brains.
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The first experiment involved 30 male voles, 17 of which had been allowed to mate and form pair bonds; the rest were virgins. The voles were allowed to explore a set of two cages, connected by a tube, to see which cage they preferred. Then, the animals were given either amphetamine or a saline injection in the place that they did not like. The idea was to determine whether the voles would begin to prefer the cage in which they’d received the pleasurable drug. Only the virgin voles given amphetamine did.
In a second experiment, researchers studied brain activity in single and pair-bonded voles. They found that singletons derived more pleasure from amphetamine than the mated animals. In the bachelor voles, amphetamine increased the availability of dopamine D1 receptors in the nucleus accumbens, a pleasure-related region of the brain. In bonded voles, however, the availability of these receptors decreased.
“Amphetamine exposure had opposite neurobiological effects in sexually naïve and pair-bonded voles,” Young notes.
But longtime vole researcher Larry Young of Emory University, who was not affiliated with the current research, expressed caution. “While this study is very interesting, it will be important to determine whether pair-bonded voles would be less likely to work for drugs of abuse if given unlimited access,” he said in a statement. Like “place preference,” determining how hard an animal will work to get drugs is another way to measure how pleasurable — or, as regulators put it, “liable to abuse” — a substance is.
Still, previous research in humans has suggested that social bonds help reduce the likelihood of drug use. Teens with closer relationships with their parents are less likely to become addicted to drugs, for instance. For people in recovery from addictions, social support is often essential to avoiding relapse. Indeed, the positive effects of social support may account for the fact that those who voluntarily affiliate with self-help groups like 12-step programs after addiction treatment tend to have better outcomes.
Some of the classic animal experiments that have been used as evidence that drugs like cocaine and heroin are inexorably addictive are complicated by the fact that the test animals were socially isolated before being exposed to the drugs. Critics of these studies argue that that’s like giving crack to prisoners in solitary confinement to demonstrate that it’s overwhelmingly addictive.
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The new findings are reminiscent of the famous “Rat Park” experiments from the late 1970s and early ’80s conducted by Canadian psychologist Bruce Alexander, who was curious about how social conditions would affect addiction in rats. He compared behavior in rats that were either kept in cramped, bare and isolated cages or allowed to roam freely with other rats in a 95-sq.-ft. space filled with items desirable to rodents (like food, balls and running wheels) that he called “Rat Park.”
The findings were eye-opening. Given the choice between plain water and morphine-laced water, “Rat Park” residents chose the former, even when the morphine-containing water was made intensely sweet. The caged rats, however, preferred the drug-laced drink.
Even after rats were forced to drink the morphine solution long enough to become physically dependent, they again chose plain water in Rat Park, despite suffering withdrawal. The caged, solitary rats, however, remained much more enamored of the dope.
Since the Rat Park studies, most other research has shown that warm social bonds tend to counter the risk of addiction. Studies of nursing rats find that they choose to take cocaine less than virgin females do, and show less of a pleasure-related dopamine response to the drug. Other research finds that rats reared in isolation take more cocaine or amphetamine than those reared in normal social circumstances—and they also quit seeking the drugs more rapidly than isolated rats.
These effects also work in the opposite direction: in a study previously published by Young and her colleagues, virgin male prairie voles failed to bond with females after sex if they had previously received daily amphetamine injections for three days. Young notes that such findings may have implications for the therapeutic use of amphetamines in humans — for instance, to treat children with attention deficit hyperactivity disorder (ADHD), which is estimated to affect 6% to 16% of the population.
“Given our findings concerning the deleterious effects of amphetamine exposure on pair bonding in prairie voles, investigation into the effects of amphetamine treatment on social behaviors and social bonding in humans may be worthwhile,” she says.
Obviously, there’s a big difference between voles and humans. And the drugs used to treat ADHD have already been studied extensively over their decades of use. Indeed, there’s some evidence that early ADHD treatment with amphetamines may reduce the risk of later addiction, which is ordinarily higher in people with ADHD.
The evidence is clear, however, that lack of affection increases people’s risk of addiction, and researchers must remain mindful of the effects of child neglect and social isolation when they study risks and recovery.