This is your baby's brain on alcohol.

A dose of alcohol equivalent to two or three cocktails turns on a stress-related gene in the brains of newborn rats, according to a new study. The finding may pave the way for a biochemical explanation of fetal alcohol syndrome, the mental and physical damage suffered by some babies exposed to alcohol in the womb.

Tara Fletcher and her colleagues at the State University of New York at Albany fed newborn rat pups -- whose stage of brain development equals that of third-trimester human fetuses -- an alcohol-spiked milk formula for two days. The researchers found that the gene encoding glial fibrillary acidic protein (GFAP) was twice as active in the brain cortexes of these alcohol-fed pups as in the cortexes of control pups that were either nursed by their dams or fed a sugar-milk solution.

GFAP forms the springy inner filaments that give shape to glia, the support cells that enfold and nourish nerve cells in the brain and spinal cord. Glia often overproduce GFAP when subjected to chemical or mechanical injury, perhaps as a means of shoring themselves up following such an insult. One type of glia, known as astrocytes, helps organize brain development.

The cortex -- the brain region responsible for cognition in humans -- is particularly vulnerable to stress during mammalian development. Fletcher says the enhanced production of GFAP in the presence of alcohol serves as a marker that potentially damaging biochemical changes are taking place within the brains of alcohol-exposed fetuses.

The New York team has also found a particular DNA sequence within the GFAP gene that alcohol may use as an "on" switch to activate the gene. Fletcher says she and her colleagues are now looking for other genes that have this DNA sequence, in order to identify those that might play a more direct role in the brain damage associated with fetal alcohol syndrome.