Abstract
Glutamate is the major excitatory neurotransmitter in the mammalian brain, with receptors on every neuron in the central nervous system; it has major roles in fast synaptic transmission and in the establishment of certain forms of memory. More than 20 years ago Olney and his colleagues described the 'Excitotoxic Hypothesis' which postulates that, in addition to its normal function in the healthy brain, glutamate can kill neurons by prolonged, receptor-mediated depolarization resulting in irreversible disturbances in ion homeostasis. Therefore, glutamate is a two-edged sword; in certain undefined, adverse conditions it undergoes a transition from neurotransmitter to neurotoxin. Its toxicity has been implicated in the death of neurons in ischemia, epilepsy, and the neurodegenerative disorders such as Alzheimer's, Huntington's, and Parkinson's disease. Recent advances in the molecular cloning of the genes for the glutamate family of receptors has revealed a plethora of receptor subtypes and an unexpected level of complexity in the mechanisms of receptor expression and function.
