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 glutamate-gated, 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 neurotransmission
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 .