Although many things have gone wrong in the autistic brain, scientists have recently been focusing on one of the most glaring: a surplus of connections, or synapses.

Neuroscientists reported on Thursday that, at least in lab mice, a drug that restores the healthy "synaptic pruning" that normally occurs during brain development also reverses autistic-like behaviors such as avoiding social interaction.

"We were able to treat mice after the disease had appeared," neurobiologist David Sulzer of Columbia University Medical Center, who led the study published in the journal Neuron, said in a telephone interview. That suggests the disease could one day be treated in teenagers and adults, "though there is a lot of work to be done," he said.

Sulzer's team used rapamycin, an immunosuppressant drug that prevents organ rejection and is sold by Pfizer as Rapamune. They chose rapamycin because it works by inhibiting a protein called mTOR whose overactivity, they found, inhibits synapse pruning.

Even if the findings are confirmed — and Sulzer notes that treatments that work in lab animals often fail in people — it is unlikely that rapamycin would be used in people with autism, as its wide-scale immune-suppressing effects would likely cause serious side effects.

"But there could be better drugs," Sulzer said, such as a molecule that dials up production of synapse-pruning proteins.