Glutamate receptors mediate most excitatory neurotransmission in the brain
and play an important role in neural plasticity, neural development and neurodegeneration.
Ionotropic glutamate receptors are categorized into NMDA
receptors and kainate/AMPA receptors, both of which contain glutamategated,
cation-specific ion channels. Kainate/AMPA receptors are co-localized
with NMDA receptors in many synapses and consist of seven structurally
related subunits designated GluR-1 to -7. The kainate/AMPA receptors are
primarily responsible for the fast excitatory neurotransmission by glutamate,
whereas the NMDA receptors exhibit slow kinetsis of Ca2+ ions and a high
permeability for Ca2+ ions. The NMDA receptors consist of five subunits:
ε 1, 2, 3, 4 and one ζ subunit. The ζ subunit is expressed throughout the
brainstem whereas the four ε subunits display limited distribution.