Rapamycin briefly reverses autism-like symptoms in adult mice

A UCLA Health study on rapamycin autism mice found that one dose of the drug rapidly improved brain signaling and several autism-like behaviors in adult animals. The findings matter because they suggest some affected brain circuits may remain adjustable in adulthood, even after early developmental changes.

The study, published in Nature Communications, examined mice whose mothers were exposed to mild inflammation early in pregnancy. UCLA Health Sciences said the offspring later showed persistent brain overactivity, sensory sensitivity, repetitive behavior, higher seizure vulnerability and abnormal communication among brain networks.

The researchers reported that rapamycin improved nearly every measure they studied within about two hours. They said the speed of the response was too fast to reflect repair of underlying brain structure, pointing instead to rapid changes in how circuits function.

Can rapamycin treat autism-like symptoms in mice?

In this mouse model, UCLA researchers found that a single rapamycin dose temporarily reduced several autism-like symptoms and brain changes. They also stressed that rapamycin is not a practical treatment for people because the effects did not last, repeated dosing became less effective, the drug can be toxic, and the work was done in animals.

Rapamycin is an immune-suppressing drug that affects the mTOR pathway, a signaling system involved in cell growth and proliferation. UCLA Health Sciences said excessive mTOR activity has been linked to some autism-related conditions, and earlier mouse studies had found improvements after rapamycin treatment.

Dr. Harley Kornblum, senior author of the study and director of the UCLA Intellectual and Developmental Disabilities Research Center in the Semel Institute for Neuroscience and Human Behavior, said the rapid functional improvement points to possible treatment mechanisms. He said the results suggest the adult brain may be more adaptable than assumed, even when structural changes from early development remain.

How did pregnancy inflammation affect the mice?

To model inflammation during pregnancy, the UCLA team exposed pregnant mice to a mild inflammatory stimulus early in gestation. According to UCLA Health Sciences, the dose was low enough that the mothers did not become significantly ill.

Their offspring later developed inflammation in the brain and body, mild brain overgrowth, excessive mTOR signaling and disorganized functional brain networks. The animals also showed behaviors associated with autism, according to the researchers.

After adult offspring received a single rapamycin dose, neurons that had been unusually active shifted toward more typical firing. UCLA Health Sciences said seizure susceptibility declined, brain regions communicated in more typical patterns, and repetitive behaviors and sensory over-responsiveness were reduced.

Dr. Janel Le Belle, the paper’s first author and an associate professor in the UCLA Department of Neurosurgery, said the findings change how autism-associated symptoms might be addressed. She said some features may be treated by targeting brain function without correcting structural differences.

Why does the effect fade?

Dr. Neil Harris, co-senior author and a professor in the UCLA Department of Neurosurgery, said the benefits were temporary. The team also found that daily treatment became less effective after several weeks as the mice developed tolerance.

Gene activity analysis showed that rapamycin reversed abnormal expression patterns tied to autism, epilepsy and ion channel function, with the strongest effects in excitatory neurons. UCLA Health Sciences said that points to a rapid rebalancing of neuronal excitability rather than physical rebuilding of brain circuits.

Harris said the work points toward targets such as sensory circuit neuromodulation or balancing neuronal inhibition and excitation, rather than rapamycin itself as a therapy. The researchers said future work could use these mechanisms to search for safer and more targeted approaches.

This story draws on original reporting from ScienceDaily.