Once a human dies so does their body, we might assume. All major systems shut down, muscles gradually atrophy and all organs, including the brain, are rendered obsolete.
Not quite so, researchers at the University of Illinois have discovered. Turns out some cells in the human brain don’t take kindly to being told their services are no longer needed and instead grow in size and ramp up their activity for hours after death.
Scientists studying samples of brain tissue collected during routine brain surgery, watched as these cells, aptly named ‘zombie genes’, sprouted tentacles and went on to clean things up in the brain for several hours post-mortem.
Only glial cells, inflammatory cells that support the neurons, were observed carrying out the post-mortem maintenance, the researchers wrote in their study.
“That glial cells enlarge after death isn’t too surprising given that they are inflammatory and their job is to clean things up after brain injuries like oxygen deprivation or stroke,” Dr. Jeffrey Loeb, a neurologist at the University of Illinois and corresponding author on the paper, said in a news release.
Most previous work on neurological gene expression and brain disorders has been done on brain tissues that have been dead for 12 hours or more.
However, Loeb and his team, noticing differences between the global pattern of activity in fresh human brain tissue versus older tissue, decided to run a simulated death experiment to observe the level of activity in the brain immediately after it was declared dead to about a day post-mortem.
They used samples of recently collected brain tissues, which had been kept at room temperature to “replicate the postmortem interval.”
About 80 per cent of the genes analyzed in the brain remained relatively stable for 24 hours, researchers reported, which include genes that provide the basic cellular functions of the brain. Another group of genes connected to human brain activity such as memory, thinking and seizure activity, quickly degraded after death.
However, as the neuronal genes slowed, the ‘zombie genes’ ramped up their activity, researchers found. This pattern in post-mortem changes continued for several hours, peaking at about 12 hours.
The discovery, Loeb said, could change the way research studies use postmortem brain tissues to research cures for mental illnesses such as Alzheimer’s, and schizophrenia and developmental disorders such as autism.
“Most studies assume that everything in the brain stops when the heart stops beating, but this is not so,” Loeb said. “Our findings will be needed to interpret research on human brain tissues. We just haven’t quantified these changes until now.”
“The good news from our findings is that we now know which genes and cell types are stable, which degrade, and which increase over time so that results from postmortem brain studies can be better understood,” he said.