Johns Hopkins researchers say they’re getting closer to developing a blood test that would identify changes in the brain associated with psychiatric and neurological disorders — an advancement that could enable doctors to detect the early signs of mental health emergencies.

In a study published last month in the peer-reviewed scientific journal Molecular Psychiatry, researchers focused on the potential of particles called extracellular vesicles to provide a window into what’s happening inside a person’s brain.

Extracellular vesicles are fatty sacs of genetic material that are released by every tissue in the body, including the brain.

Sarven Sabunciyan, an assistant professor of pediatrics at the Johns Hopkins School of Medicine and the paper’s senior author, compared them to rafts that travel between cells. They sometimes carry messenger RNA — a type of molecule also called mRNA that contains the instructions for how cells should make proteins.

“It’s basically a way of cells communicating,” he said.

The study, led by the Johns Hopkins Children’s Center, was inspired by a previous study by Johns Hopkins researchers, Johns Hopkins Medicine said in a news release Thursday. That study found that communication between cells is altered in pregnant women who go on to develop postpartum depression after they give birth.

In the new study, scientists first proved that mRNA from specific tissues are found in extracellular vesicles circulating in the blood. Then, using lab-grown human brain tissue derived from stem cells, scientists found that mRNA in extracellular vesicles released from brain tissues reflected mRNA changes happening inside those tissues.

According to the researchers, that means it is possible to gather biological information from hard-to-access tissues — like the placenta or the brain — by examining mRNA inside of extracellular vesicles circulating in the blood.

The study’s results suggest that mRNA in extracellular vesicles are likely an ideal biological marker for identifying brain disorders that involve mood, schizophrenia, epilepsy and substance abuse.

“This is very exciting, because right now, there isn’t a blood marker for disorders affecting the brain,” said Lena Smirnova, a co-author of the paper, said in the Hopkins news release about the study. Smirnova is an assistant professor in the Department of Environmental Health and Engineering at the Johns Hopkins Bloomberg School of Public Health.

Also in the latest study, researchers discovered 13 brain-specific mRNAs in the blood that were found to be associated with postpartum depression.

Using the lab-grown brain tissue, the researchers discovered that while cellular and extracellular mRNA levels are not identical, they do correlate, which means it is possible to figure out what’s happening inside the brain by looking at extracellular vesicles in the blood.

The team’s eventual goal, Sabunciyan said, is to create a simple blood test that could detect changes in levels of mRNA in extracellular vesicles linked to changes in the brain associated with mental disorders.

“One of the biggest obstacles — not just in psychiatric disorders, but in brain disorders — is, we don’t really know what’s happening in the brain,” Sarbunciyan said. “We can’t just do a blood test or take an X-ray.”

Moving forward, Sarbunciyan and his colleagues plan to conduct further research, including with people who have psychiatric conditions like bipolar disorder to identify how markers in their blood change as they fluctuate between periods of mania, depression and stability.

Besides forming the foundation of a new way to test for mental health conditions, scientists hope their research will lead to the “next generation” of prenatal tests, where doctors will be able to simply draw blood from the mother to screen her baby for a health issue, rather than conduct an invasive procedure like amniocentesis.

Other authors on the paper included Sergio Modafferi and Charlotte Schlett from Johns Hopkins; Lauren Osborne from Weill Cornell Medicine; and Jennifer Payne from the University of Virginia.