A single dose reversed autism-like symptoms in adult mice within hours

Previous research has shown that even mild inflammation in the middle of pregnancy can affect developing offspring. Reported consequences include autism-like behaviors, unusual brain growth, seizures, and greater sensitivity to ordinary sounds, touch, and other sensory experiences. These effects can continue into adulthood.

In the new study, published in Nature Communications, UCLA scientists found that one dose of rapamycin improved brain communication and behavior in the affected mice in about two hours. That response was far too fast for the drug to have repaired the underlying physical changes in the brain caused by maternal inflammation.

A Rapid but Temporary Brain Response

The researchers stressed that rapamycin should not be considered a practical treatment for these symptoms in people. Its benefits were temporary, repeated use can be toxic, and the study was conducted in mice. Instead, the rapid response helped reveal biological processes that could guide the development of safer and more targeted therapies.

"The level of functional normalization achieved over this short time suggests new mechanisms by which possible treatments may act," said the study's senior author Dr. Harley Kornblum, director of the UCLA Intellectual and Developmental Disabilities Research Center in the Semel Institute for Neuroscience and Human Behavior. "It suggests the adult brain may be more adaptable than we assumed, even when the underlying structural changes from early development are still there. This points us toward the brain's functional circuitry, not just its physical structure, as a target for future treatment approaches."

Earlier studies have found that children born to mothers who experience inflammation during pregnancy may have a greater likelihood of developing traits associated with autism. These can include repetitive behavior, challenges with social interaction, enlarged brain growth, and altered sensory processing that persists later in life.

Rapamycin has also produced improvements in earlier mouse studies of autism. The drug works in part by reducing activity in the mTOR pathway, a biological signaling system that regulates cell growth and proliferation. Excessive mTOR activity has been linked to some autism-related conditions.

However, scientists did not know whether the brain effects caused by maternal inflammation could still be altered in adulthood. It was also uncertain whether rapamycin worked by gradually repairing brain structure or by producing faster changes in how brain circuits functioned.

Modeling Inflammation During Pregnancy

To investigate, the researchers exposed pregnant mice to a mild inflammatory stimulus early in pregnancy. The dose was low enough that the mothers did not become significantly ill.

Their offspring later developed persistent inflammation in both the brain and the rest of the body. They also showed mild brain overgrowth, excessive signaling through the mTOR pathway, poorly organized communication across functional brain networks, and behaviors associated with autism.

The researchers then gave the adult offspring a single dose of rapamycin. Improvements appeared across nearly every measurement they examined.

Neurons that had been unusually active began firing more normally. The animals became less vulnerable to seizures. Brain regions that had not been communicating properly shifted toward more typical patterns. Repetitive behaviors, sensory sensitivity, and excessive responses to sensory input also declined.

All of these changes emerged within about two hours. Because physical remodeling of brain synapses generally takes longer, the scientists concluded that rapamycin was changing brain function rather than rebuilding the brain's underlying structure.

"These results reframe how autism-associated symptoms might be treated. If the adult brain remains capable of functional normalization, then some features of autism may be successfully addressed without needing to correct underlying structural differences," said the paper's first author Dr. Janel Le Belle, an associate professor in the UCLA Department of Neurosurgery.

Rapamycin Rebalanced Neuron Activity

To determine how the drug acted so quickly, the team analyzed gene activity in brain cells before and after treatment.

Rapamycin reversed abnormal patterns of gene expression involving autism, epilepsy, and ion channel function. The strongest effects appeared in excitatory neurons, which stimulate activity in brain networks.

This suggests that the drug rapidly restored a healthier balance in neuronal excitability rather than repairing structural differences formed during early development.

The results point to several possible targets for future treatments, including mTOR pathway activity, the organization of brain networks, and the balance of excitation among neurons. Such approaches could potentially address specific autism symptoms, including sensory over-responsivity, which is common and often difficult to treat.

Why Rapamycin Is Not the Treatment

Dr. Neil Harris, co-senior author and a professor in the UCLA Department of Neurosurgery, warned that the benefits did not last. The researchers also found that daily treatment became less effective after several weeks as the mice developed tolerance.

Those limitations, combined with rapamycin's potential toxicity and the fact that the findings come from animal experiments, make the drug unsuitable for widespread use in humans.

"This points toward new therapeutic targets like sensory circuit neuromodulation or balancing neuronal inhibition and excitation, rather than toward rapamycin itself as a treatment," Harris said.

Key Takeaways

• In mice, inflammation during pregnancy caused long-lasting autism-like changes in brain activity and behavior, indicating that early immune disruption can influence brain development well into adulthood.
• One dose of rapamycin quickly improved brain overactivity, seizure susceptibility, sensory sensitivity, repetitive behavior, and abnormal communication between brain networks.
• The rapid response suggests that some autism-related functional changes may remain modifiable in adulthood, even when physical differences in brain structure are still present.
• Rapamycin's effects were temporary, and repeated treatment became less effective. Its toxicity and the animal-based nature of the research mean it is unlikely to become a broadly used treatment, but the findings may help scientists identify safer therapeutic targets.