Excitotoxins are a class of substances that cause neurons to fire spasmodically. This eventually burns out, or damages, the neurons through overactivity.

Common excitotoxins include monosodium glutatmate (MSG) and aspartame.  

Excitotoxicity has been found to be involved in migraines, hypoglycemia, spinal cord injury, stroke, traumatic brain injury and neurodegenerative diseases of the central nervous system (CNS) such as Multiple sclerosis, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS), Parkinson's disease, Alcoholism and Huntington's disease.

References

Manev H, Favaron M, Guidotti A, and Costa E. Delayed increase of Ca2+ influx elicited by glutamate: role in neuronal death. Molecular Pharmacoloy. 1989 Jul;36(1):106-112. PMID 2568579. Retrieved on January 31, 2007. Kim AH, Kerchner GA, and Choi DW. Blocking Excitotoxicity. Chapter 1 in CNS Neuroproteciton. Marcoux FW and Choi DW, editors. Springer, New York. 2002. Pages 3-36