A single injection of rapamycin reversed autism-like brain changes and behavioral problems in adult mice within two hours, a UCLA Health study found. The discovery suggests that even in adulthood, neural circuits altered by early inflammation may retain surprising flexibility.
Researchers exposed pregnant mice to mild inflammation early in pregnancy. Their offspring developed persistent inflammatory markers throughout the brain and body, along with mild brain overgrowth, disrupted neuronal communication patterns, and behaviors resembling autism spectrum traits.
When these adult mice received one dose of rapamycin, an immune-suppressing drug, nearly every measured abnormality improved rapidly. Neurons that had been firing excessively normalized. Seizure vulnerability dropped. Brain networks began communicating more typically. Repetitive behaviors, sound sensitivity, and sensory overreaction all declined within roughly two hours.
Speed Reveals New Clues About Treatment
The speed of improvement proved crucial to the research. Physical rebuilding of brain synapses typically takes far longer than two hours. This timing led researchers to conclude that rapamycin was correcting how brain circuits functioned rather than repairing structural damage formed during fetal development.
"The level of functional normalization achieved over this short time suggests new mechanisms by which possible treatments may act," said Dr. Harley Kornblum, director of the UCLA Intellectual and Developmental Disabilities Research Center. "It suggests the adult brain may be more adaptable than we assumed, even when the underlying structural changes from early development are still there."
Analysis of gene activity before and after treatment showed that rapamycin reversed abnormal patterns in genes linked to autism, epilepsy, and ion channel function. The strongest effects appeared in excitatory neurons, cells that stimulate activity across brain networks. This suggested the drug rapidly rebalanced how actively these neurons fired, restoring healthier communication patterns.
The research, published in Nature Communications, builds on earlier findings showing that inflammation during pregnancy can produce lasting consequences in offspring. Children born to mothers who experienced infection or immune activation during the second trimester show elevated rates of autism-related traits, including social difficulties, repetitive behavior, sensory processing differences, and enlarged brain size that persist into adulthood.
Rapamycin works in part by suppressing the mTOR pathway, a cellular signaling system controlling growth and proliferation. Overactive mTOR function has been implicated in certain autism-related conditions, making the pathway a long-standing research target.
But whether adult brains permanently reshaped by early inflammation could still be altered remained unknown. Rapamycin's rapid effects answered that question: functional circuits in the adult brain retain modifiability even when structural abnormalities persist.
This distinction reshapes how researchers think about treating autism symptoms. "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 Dr. Janel Le Belle, the paper's first author and an associate professor in UCLA's Department of Neurosurgery.
However, rapamycin itself will not become a practical treatment. Its benefits lasted only hours. When researchers tested repeated dosing, the mice developed tolerance within weeks, causing the drug's effectiveness to fade. Rapamycin's potential for toxicity with prolonged use, combined with the fact that these findings come from animal studies, makes it unsuitable for widespread human application.
Dr. Neil Harris, a co-senior author and UCLA neurosurgery professor, stressed that the real value lies in what the drug revealed about possible targets. "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.
The findings suggest researchers should focus on approaches that restore functional balance in brain circuits rather than attempting to physically rewire structural abnormalities formed in utero. Sensory over-responsivity, a symptom that appears frequently in autism and often resists treatment, may particularly benefit from such circuit-focused approaches.
Author Jessica Williams: "This study matters not because rapamycin is going to treat autism, but because it proves the adult brain isn't locked in stone from early development,a finding that could redirect the entire field toward smarter, function-focused therapies."
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