Australasian Science: Australia's authority on science since 1938

Nurture Immunises Against Addiction

By Stephen Luntz

Nurturing of infants could be a powerful factor in their propensity to addiction.

The brain’s immune system has an unexpectedly important role in the response of rats to opiate addiction, a paper in the Journal of Neuroscience reveals. Moreover, this response is determined by the level of maternal care. The findings may transform responses to all forms of addiction in humans.

“Morphine activates the glial cells of the brain to produce inflammatory molecules which signal a reward centre of the brain, contributing to addiction,” says Dr Mark Hutchinson of Adelaide University’s School of Medical Sciences. But if the inflammatory response can be controlled, the rats do not appear to experience opiate addiction.

Nurturing of infants controls the tendency to inflammation, indicating that this could be a powerful factor in addiction control, although Hutchinson warns that the implications are not as straightforward as they might appear.

Nurturing was induced by separating the baby rats from their mothers for 15 minutes each day. While counterintuitive, it has been demonstrated in previous studies that this prompts the mother rat to pay more attention to the baby after its return, inducing an ultimately better nurtured cub.

Cubs raised in this way produced more interleukin-10 (IL-10), an immune system molecule in the brain. “IL-10 works against that inflammation and reward. It completely knocks out this drug-seeking behaviour,” Hutchinson says. “The more IL-10 produced in the brain, the less likely morphine causes an increase in craving or relapse weeks after initially being exposed to the drug.”

The importance of nurturing is profound, with maternal care after daily separation producing a fourfold increase in IL-10 relative to controls.

It is unlikely that separating human babies from their parents would produce a directly similar response, and Hutchinson notes that 60% of the factors controlling drug addiction are thought to be genetic. He notes, however, that “if parental care is 20–30% you’re still looking at a large proportion of addiction accounted for”.

The idea that failures in early childhood care contribute to addiction is hardly new, and improving parental care is a difficult public health challenge. However, Hutchinson says that the most exciting aspect of the research is the demonstration that the brain’s immune response is involved rather than the neuronal wiring alone, as previously thought. “We’re pursuing a drug that generally decreases the activity of these immune cells in the brain,” Hutchinson says.

Some early evidence suggests this may reduce withdrawal cravings. Other research suggests that a large portion of the genetic susceptibility to drug addiction – up to 25% of the total variation – may lie in differences in the immune response in the brain.