In the hours after we die, certain cells in the human brain are still active.
In a new study, researchers found that some cells even increase their activity and grow to gargantuan proportions.
They analyzed gene expression in fresh brain tissue — which was collected during routine brain surgery — at multiple times after removal to simulate the post-mortem interval and death.
They found that gene expression in some cells actually increased after death.
These ‘zombie genes’ — those that increased expression after the post-mortem interval — were specific to one type of cell: inflammatory cells called glial cells.
The researchers observed that glial cells grow and sprout long arm-like appendages for many hours after death.
The research was conducted by a team from the University of Illinois Chicago.
According to the team, glial cells enlarge after death isn’t too surprising because they are inflammatory and their job is to clean things up after brain injuries like oxygen deprivation or stroke.
What’s significant is the implications of this discovery — most research studies that use postmortem human brain tissues to find treatments and potential cures for disorders such as autism, schizophrenia and Alzheimer’s disease, do not account for the post-mortem gene expression or cell activity.
In the study, the team looked at the expression of all human genes, at time points from 0 to 24 hours, from a large block of recently collected brain tissues, which were allowed to sit at room temperature to replicate the postmortem interval.
They found that about 80% of the genes analyzed remained relatively stable for 24 hours — their expression didn’t change much.
These included genes often referred to as housekeeping genes that provide basic cellular functions and are commonly used in research studies to show the quality of the tissue.
Another group of genes, known to be present in neurons and shown to be intricately involved in human brain activity such as memory, thinking and seizure activity, rapidly degraded in the hours after death.
These genes are important to study disorders like schizophrenia and Alzheimer’s disease.
The third group of genes — the ‘zombie genes’ — increased their activity at the same time the neuronal genes were ramping down. The pattern of post-mortem changes peaked at about 12 hours.
The findings suggest that researchers need to take into account these genetic and cellular changes, and reduce the post-mortem interval as much as possible to reduce the magnitude of these changes.
The study is published in Scientific Reports. One author of the study is Dr. Jeffrey Loeb.
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