TOKYO -- A University of Tokyo team has found a protein in the brains of mice that softens memories of horrific experiences, a discovery the researchers say could lead to treatments for post-traumatic stress disorder (PTSD). Their findings were published in the scientific journal Cell Reports.
Living things use so-called "molecular motor" proteins of various types to transport substances vital to life processes, from the cell level up to whole organs. The team led by specially appointed professor Nobutaka Hirokawa and specially appointed researcher Momo Morikawa found that one such protein -- KIF21B -- was heavily concentrated in the hippocampus, a part of the brain that plays a major role in learning and memory formation.
To test the protein's hitherto unknown function and its potential connection to learning and memory, the University of Tokyo researchers then placed mice -- half normal animals and half engineered to have no KIF21B -- in a chamber designed to deliver uncomfortable electrical stimulation. The team found that, if not subjected to the stimulation for several days in a row, the normal mice ceased showing signs of fear such as freezing in place when put in the chamber, and returned to normal behavior. However, the mice deprived of the KIF21B protein continued to display signs of terror, suggesting the memory of the shocks remained fresh.
Furthermore, the team ascertained that the fearful memories softened as KIF21B carried proteins to the hippocampus. The mice without the "molecular motor" also returned to normal behavior after receiving injections of a chemical substance that connects with this particular protein.
Human beings have those substances in their systems, and professor Hirokawa commented, "It's possible that KIF21B activity has declined in people with very strong memories of horrific episodes. I hope that (this discovery) leads to treatments for PTSD, especially as Japan is a country beset by many natural disasters."
(Japanese original by Yasuyoshi Tanaka, Medical Welfare News Department)