After a devastating spinal cord injury, mice’s nerve cells balloon up in size. Some of these neurons stay swollen longer than expected and begin to die, a study published September 25 in Science Translational Medicine shows. A drug that brought this swelling down improved the mice’s recovery, though it’s not yet known if the approach would work in people.

Until now, the details of neuron swelling in the spinal cord weren’t clear, says Bo Chen, a neuroscientist at the University of Texas Medical Branch at Galveston. “We didn’t know how long [the cells stay swollen], or if they’re going to die,” he says. “We were guessing.”

Chen and his colleagues devised a way to watch these cells in the aftermath of a spinal cord injury. The approach relied on genetic engineering, transparent spinal cord tissue and machine learning to help analyze cell shapes. It ultimately yielded views of more than 30,000 neurons spread across a 3-millimeter span of spinal cord of each mouse.

Cells called inhibitory neurons, which dampen other cells’ activity, swelled quickly after an injury, peaking at day two and returning to their normal size by day 14, the team found. But excitatory neurons showed a very different pattern. These cells, which ramp up other cells’ activity, ballooned up and stayed swollen longer, some for up to 35 days. More of these kinds of cells died, too.

A drug called bumetanide, which is used to treat edema in people, reduced this cellular swelling and resulting cell death in mice. Mice given the drug after an injury were better able to move their legs than mice not given the drug, the researchers report.

The results point to neuron swelling as an important part of spinal cord injuries. Still, more research needs to be done to understand how this process works in people, and whether bumetanide might help, Chen says.