Post-natal depression can be debilitating
American scientists say they are closer to understanding why some mothers suffer post-natal depression.
They found mice lacking a chemical receptor in their brains developed similar symptoms.
The study suggests the receptor helps stop brain cells firing too often in response to changes in hormone levels during pregnancy and birth.
A British specialist said the research, published in Neuron, could lead to better treatments for the disorder.
Between 5% and 25% of all new mothers are thought to suffer some form of post-natal depression, and can find it hard to cope with the demands of the baby, or even to form a bond with it.
The precise reasons why some women develop it and some do not are uncertain, but the team at the University of California in Los Angeles say they may have some more answers.
They focused their work on a chemical messaging system in the brain already known to play a key part in the regulation of mood and anxiety.
A chemical called GABA can decrease the activity of certain nerve cells after coming into contact with receptors on that cell's surface.
The Californian team noticed that a particular type of this receptor appeared to be highly active during pregnancy and the period after birth in mice.
Their theory is that this variety of receptor might help, in normal circumstances, to keep control over the brain's response to huge hormonal changes during and immediately after pregnancy.
Failure to do this effectively may be the root of some post-natal mood problems, they said.
To test this, they bred mice to have fewer of these receptors.
These genetically-altered mice behaved like mothers with post-natal depression, being more lethargic, and shunning their newborn pups.
When they were then given a drug known to boost the function of these receptors, the symptoms eased and pup deaths fell.
Dr Jamie Maguire, one of the researchers involved, said: "Targeting this subunit (receptor type) might be a promising strategy in developing new treatments for post-natal depression."
Dr Delia Belelli, from the University of Dundee, has studied the role of GABA in mood disorders for more than two decades.
She said it was possible that the drug used to boost receptor function might have a role in treatment of women.
She said: "It is fascinating to see something like this coming out after we have speculated about it for all this time.
"What they are suggesting is not surprising, and could in theory be applied not only to post-natal depression but to other mood disorders, such as those during the menstrual cycle in women."