PART of the brain circuitry necessary for forming the vital bond between mother and infant has been identified. The same pathways might play a role in behavioural disorders such as autism.
Previous work suggested that the morphine-like opiates produced by the body play a role in behaviours such as mother-child bonding. So Francesca D’Amato’s team at the National College of the Research Institute of Neuroscience, Psychobiology and Psychopharmacology in Rome created mice that cannot respond to opiates because they lack the gene for the mu-opioid receptor.
The altered mice failed to make anywhere near the usual number of ultrasonic squeaks when separated from their mothers. And unlike ordinary mice, they showed little preference for nesting materials suffused with the smell of their mother (Science, vol 304, p 1983).
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“The work is the most robust demonstration yet that brain opioids are very important in regulating social emotions,” says Jaak Panksepp of Bowling Green State University in Ohio, a pioneer in the field.
D’Amato speculates that the opioid system might be involved in autism. “These little mice don’t display attachment to their mothers. Nor can they discriminate between their own and other mothers,” she says. “This is the basis for all social behaviour in adulthood, so disruption in early attachment can affect all adult socialisation as well.”
The next step, says Jan Buitelaar of the St Radboud University Medical Centre in Nijmegen, the Netherlands, would be to screen people with autism to see if they have unusual variants of the mu-opioid receptor gene. Different mutations might explain the variation in symptoms. “For example, there are autistic children who have no problems with maternal attachment,” D’Amato says.
But other neurochemical pathways may be far more important. A decade ago, Buitelaar found that some children with autism improved very slightly when given adrenocorticotropic hormone, which stimulates the opioid receptor, while naltrexone, which blocks the receptor, had no effect. “We concluded that the opioids are fine-tuning the system, but they are not the major biochemical system underlying social behaviour,” he says.
Whatever the underlying mechanisms turn out to be, treating autism may not be easy. By the time the disorder has been diagnosed, it might be too late for drug therapy to make any difference, D’Amato says.