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Thursday, 27 July, 2000, 18:28 GMT 19:28 UK
'Lasting effects' of newborn pain
premature baby
Premature babies are likely to endure uncomfortable tests and checks
Pain experienced as a newborn baby may determine an individual's sensitivity throughout life, claim researchers.

But other experts suggest the findings, reported in the journal Science, should be treated with caution.

The team from the National Institute of Dental and Craniofacial Research in Bethesda tested newborn rat pups to see if early exposure to pain shaped their future response to it.

Their theory was that the development of key brain pathways related to pain can be influenced by what happens in the first days of life.

They believe that babies born prematurely - with the relevant neural pathways far less mature - could be even more vulnerable to this effect.

The rat pups were given injections of an irritant into a hind paw - one group at one day old, the other two weeks later, the rat equivalent of adolesence.

Swelling and redness continued for up to week after each injection.

The researchers found that, in the newborns, some nerve fibres leading from the affected foot were thicker than those from the unaffected foot. There was no difference in the older rats.

The adult rats were tested for pain sensitivity
And, when the rats' pain response was tested in adulthood, those given the injection shortly after birth reacted more strongly than rats not given any injections.

Dr Marianne Ruda, who led the research, said: "Although we have yet to directly link animal research findings to what happens in the human infants, one is tempted to speculate that similar changes as those identified in the animals may occur in newborn humans.

"A premature infant can be thought of as still in the foetal time of their life when the basic elements of brain development are occurring."

However, Dr Katharine Andrews and Dr Mariah Fitzgerald, both from the Children's Nationwide Health Research Centre at the anatomy department of University College London, both counselled caution in the interpretation of the results.

The irritant used by the researchers was an extremely powerful one, they said, and given in large doses, which made it hard to compare with the experience of even a premature baby which is likely to encounter many uncomfortable medical treatments and tests.

Dr Andrews said: "If you are using a sledgehammer like this, it's really not surprising that these changes happen.

"But is that comparable with what doctors would be doing to pre-term babies?"

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