According to a new study at UNC-Chapel Hill, mice that were forced to abstain after a month of moderate drinking developed depression a few weeks into teetotalism.

The UNC-CH team gave the mice a choice of two drinking bottles: one with water and one with a 10 percent solution of ethanol. During the 28-day period, the mice went for the alcoholic beverage over the water 80 percent of the time. In mouse terms, that's moderate drinking.

"Moderate drinking has a lot of definitions, but in this case what it meant is that the mice did not appear dependent," said Clyde Hodge, professor of psychiatry and pharmacology in the UNC School of Medicine and senior author of the study. "There were no withdrawal symptoms."

After 28 days, the researchers replaced the ethanol solution with a second bottle of regular water.

Then they tested the mice for depression using something called the Porsolt Swim Test, which has been a laboratory standard since it was introduced in the late 1970s. It gauges the will to live.

"The mice are put in a beaker full of water, and then we let them swim there for a while," Hodge said. Mice are good swimmers, so they usually swim around looking for a way out, but eventually they give up and float around, seemingly resigned to being stuck in the beaker. The time it takes for the mice to give up is a measure of their despair, a symptom of depression.

The researchers expected to see a change in the mice's moods immediately after they took the alcohol away, but to their surprise, nothing significant happened.

But not for long.

"We began to see a trend toward depression emerging in the first few days," Hodge said, "although it wasn't until two weeks after that we really saw it. And that's really interesting. What that implied was that it's not the drinking that is the cause, it's something going on in the brain."

Sure enough, when the team looked at the mice's brains, they found that up to 50 percent fewer brain cells were being generated in the area that controls learning, memory and mood. This made their brains less able to change and adapt.

Lee-Ann Kaskutas, a senior scientist at the Alcohol Research Group in California, is skeptical.

"Depression is not just a biological thing," she said. "There are contextual elements that make it very complex in humans. I'm just concerned about how the results translate to the human condition."

If the result does translate, however, it could have a big effect on the way doctors treat alcoholism.

"Alcoholics trying to quit report that negative mood is one of the top reasons for going back to drinking," Hodge said. Antidepressants, which encourage the growth of brain cells, could be a solution for people trying to get back on the wagon.

"It's important that we understand that there are changes in the brain that occur after drinking," said Hodge, "and identifying those changes are critical. That's the bottom line."

The findings appear online in the journal Neuropsychopharmacology.