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,
caution-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 neuro-transmission by
glutamate, whereas the NMDA receptors are functionally characterized by a
slow kinetic and a high permeability for Ca2+ ions. The NMDA receptors consist
of five subunits: epsilion 1, 2, 3, 4 and one zeta subunit. The zeta subunit
is expressed throughout the brainstem, whereas the four epsilon subunits
display limited distribution.