Glutamate

Glutamate (the salts of the amino acid glutamic acid) acts as a neurotransmitter in the brain. It carries nerve signals across a synapse by activating receptors on the postsynaptic nerve. It is an excitatory neurotransmitter, which means that it increases the likelihood that a nerve cell will fire an action potential. Out of all the transmitters in the brain, glutamate is the most important for normal brain function. Aside from being the most abundant excitatory neurotransmitter, it also plays important roles in learning and memory.

What Does Glutamate Do?

Glutamate’s main function is to transmit information that regulates brain development and determines cellular survival. Glutamate is present throughout the brain in high concentrations, but too much glutamate, as well as too little glutamate, can be dangerous. There must be exactly the right concentration in the correct location of the brain and for the proper length of time for processes to be carried out without cell damage.

Because glutamate is also an amino acid that makes proteins and performs metabolic functions, it was not immediately recognized as a neurotransmitter. Glutamate can enable long-term potentiation, which is the strengthening of signals between two neurons that occurs with frequent use. This process is associated with neuroplasticity, and because of glutamate’s role in this function, it heavily influences cognition, learning, and long-term memory, and to a lesser extent, spatial memory.

Glutamate in the Diet

Foods high in protein—meats, dairy, eggs, cheese, and high-protein vegetables—all contain high levels of glutamic acid. Glutamate is also commonly used as a flavor enhancer in the form of monosodium glutamate (MSG). MSG activates flavor receptors for umami, a savory, salty flavor that is one of the five basic human tastes. MSG is commonly added to prepackaged foods such as potato chips, as well as some Asian foods. MSG is also naturally present in relatively large proportions in breast milk.

The flavor of MSG can make food more appealing, though there have been claims that it is addictive. Its use as a flavoring agent is controversial, as some people have reported headaches and other neurological problems immediately after consuming MSG. However, the U.S. Food and Drug Administration considers MSG safe, and studies generally indicate that, while some people may be sensitive to MSG, it is not connected to long-term neurological problems.

Glutamate Toxicity

Glutamate can damage nerve cells in the brain in two ways. If there is too much glutamate present, the nerve cell receiving its signals can become overexcited. The other scenario occurs when the receptor cell is oversensitive, requiring fewer molecules to excite it, and can therefore become overexcited by the normal amount of glutamate. These overexcited cells can become permanently damaged and die.

Sensitivity of receptor cells to glutamate is a characteristic of Huntington’s, as even low levels of glutamate can be toxic to some people with the condition. Thus, slowing glutamate activity in these individuals may be somewhat therapeutic. Amyotrophic lateral sclerosis (ALS), on the other hand, is characterized by elevated levels of glutamate. Although there is no cure for ALS, riluzole, a drug that controls glutamate levels, has been proven to slow its progress.

References:

1. Audesirk, T., Audesirk, G., & Byers, B. E. (2008). Biology: Life on Earth With Physiology. Upper Saddle River, NJ: Pearson Prentice Hall.
2. Danbolt, N. (2001, January 1). Glutamate as a Neurotransmitter. Retrieved from http://www.neurotransporter.org/glutamate.html
3. Glutamate. (2014, January 1). Retrieved from http://www.alsa.org/research/about-als-research/glutamate.html.
4. Tan, E. (2001, September 22). About Glutamate Toxicity. Retrieved from http://web.stanford.edu/group/hopes/cgi-bin/wordpress/2011/06/about-glutamate-toxicity.
5. The Facts on Monosodium Glutamate. (n.d.). European Food Information Council. Retrieved from http://www.eufic.org/article/en/artid/monosodium-glutamate/

Last Updated: 05-24-2017