Knocking out a key mouse gene involved in the brain's response to painkilling drugs interferes with the bonding between infants and their mothers, Italian scientists report. Newborn mice lacking the gene, which makes a protein that interacts with opioids such as morphine, show reduced distress when separated from their mothers. The study could shed light on social attachment disorders like autism, say the researchers, who are based at the CNR Institute of Neuroscience, Psychology and Psychopharmacology in Rome.
Autism is a lifelong developmental disability that typically appears during the first three years of life. The disorder affects social and language skills, and the way in which a child relates to people, objects and events. Autism often affects more than one child in a family, suggesting that it has a genetic basis, although it is thought that the combined effects of at least 5-10 different genes are involved. Some scientists think that the underlying cause of autism could be a fault in the brain's 'reward system', which making it incapable of forming strong social bonds. 'Brain opiates play a fundamental role in the reward circuitry - that is to say they help an individual to understand what is good for them, in evolutionary terms', said study leader Francesca D'Amato.
The researchers decided to test the theory by breeding genetically altered mice that lack an opioid receptor gene, which makes a protein crucial to this reward system. When the scientists separated the newborn mice from their mothers, the pups made far fewer distress calls, compared to normal mice. And when given the option of returning to their mother's nest, only a third of the altered mice did so, compared to all of the normal mice. The study appeared in the journal Science.
Commenting on the work, US neuroscientist Jaak Pankskepp said it provides robust evidence that a mouse pup 'needs opiate activity in order to find its mother rewarding'. However, he stresses that opioids are by no means the whole story, pointing to the role of the hormone oxytocin in mother-infant bonding. He also told Science that 'the biggest societal bottom line of this research is not autism', but the fact that 'young people can feel the warmth of human love pharmacologically, if they are not getting enough of it from their social networks'.
Sources and References
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Study details possible cause of autism
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Gene 'lets infants bond with mum'
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The mice that don't miss mom
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Brain pathway, mother-infant bond linked
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