Ionotropic glutamate receptors are ligand-gated ion channels involved in fast excitatory transmission in the CNS. There are several types of glutamate ionotropic receptors including AMPA, kainate, and NMDA-receptor subunits. Most ionotropic glutamate receptors are located postsynaptically, although some are located presynaptically and on glia cells as well (Fig. 2). Similar to the mGlu receptors, they are found throughout the brain including cortical regions, hippocampus, amygdala, basal ganglia, midbrain, hind-brain, and brainstem nuclei.44–49 A recent functional addition to the iono-tropic glutamate receptors are the delta1 and delta2 subunits symbolized by Glud1 and Glud2. In the past these subunits were considered orphans and not functional but more recent findings indicate that they are indeed functional, by modulating LTD and prepulse inhibition of the acoustic startle response (sensorimotor gating), and their localization is not restricted to the cerebellum but includes cortical and limbic regions as well.50–54
