2003 Director's Summary Synopsis

UNDERSTANDING EXCITOTOXICITY: A MECHANISM FOR SECONDARY INJURY
John R. Bethea, Ph.D.

After spinal cord trauma, it is known that some nerve cell damage is caused by excitotoxicity – an excessive release of neurotransmitters within the nervous system. One of these neurotransmitters, glutamate, helps normally functioning cells to communicate with one another. After SCI, however, glutamate is overexpressed, creating what is believed to be a toxic environment for cells and contributes to secondary damage.

For the proper functioning of the nervous system, another chemical component – the excitatory amino acid transporter (EAAT) – helps keep an appropriate balance of glutamate and other neurotransmitters. There are five EAATs known to researchers. Three of the five EAATs are associated with neurons and help regulate neurotransmitters within nerve cells. The other two EAATs are associated with glial cells, another cell of the nervous system that supports nerve cells.

In this study, Dr. Bethea discovered that EAAT4, which is normally found in neurons, is also found in glial cells called astrocytes. One role astrocytes have is to break down and remove chemicals that might be harmful to neurons. This new discovery may mean that EAAT4 has a role in preventing excitotoxicity caused by glutamate overexpression in several types of cells in the nervous system. This study helps to more clearly understand the chemical processes that occur following SCI. With this new information, researchers hope to gain further insight into designing treatments to prevent secondary injury caused by excitotoxicity.

Synopsis Publications

 Hu W-H, Walters WM, Xia X-M, Karmally SA, Bethea JR (2003) Neuronal glutamate transporter EAAT4 is expressed in astrocytes. Glia 44:13-25.