An amino ACID-based substance that causes overstimulation of neurotransmitter receptors in the brain, resulting in neuron death. Most excitotoxins enter the body as food additives. There are about 70 identified excitotoxins, one of the most common of which is glutamate (found in foods as the flavor enhancer monosodium glutamate [MSG]). Injuries to the brain, such as from trauma or stroke, also cause the release of excitatory neurotransmitters (neurotransmitters that stimulate, as opposed to suppress, neuron activity) that then function as excitotoxins: That is, when they are present in the brain at abnormally high levels, their actions are toxic and they result in cell death. Researchers believe that excitotoxins cause cell death by causing the cell to release excess calcium; intensification of the cell’s metabolism results. This in turn causes the cell to deplete its protein resources, at which point the cell can no longer survive.
Some scientists believe that excitotoxins provide the environmental impetus that sets in motion the events that cause neurodegenerative conditions such as Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), multiple sclerosis, and Parkinson’s disease to develop. Glutamate, although as yet not directly implicated as having a role in Parkinson’s disease, is present in areas of the brain affected by Parkinson’s, including the striatum and subthalamic nucleus (STN). Much research remains to be done in this area before scientists will fully understand the role of excitotoxins. Some researchers recommend that as much as possible, people with Parkinson’s avoid processed foods, which commonly contain excitotoxins as flavor enhancers.