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Glutamate receptor mapping technique
glutamate-evoked current
FIGURE 8.22 Mapping glutamate receptor location during synaptogenesis. A. To map the location of glu-
tamate receptors, an iontophoretic pipette (red) ejects glutamate focally, and the evoked response is recorded
at the soma. B. Glutamate-evoked currents become restricted to the site of synaptic contacts (green) after
the dendrites become innervated. White dots show the positions of glutamate application; the rela-
tive distance of the yellow dot indicates the evoked current magnitude for each position. Representative
glutamate-evoked currents are shown (cyan). When neurons are cultured in the presence of TTX to block all
action potentials, the synaptic localization of glutamate receptors occurs nonetheless. (Adapted from Cottrell
et al., 2000)
ET/SXV, that serves as an important phosphorylation
site (Niethammer et al., 1996; Cohen et al., 1996).
One of the first MAGUKs to be isolated was postsy-
naptic density protein-95 (PSD-95; aka, SAP-90). PSD-95
is located in the postsynaptic densities of hippocampal
neurons, and some evidence suggests that it participates
in clustering both NMDA receptors and potassium
channels (Kim et al., 1995; Kornau; et al., 1995; Kim and
Sheng, 1996; Niethammer et al., 1996). However, hip-
pocampal synapses look normal and cluster NMDA
receptors in PSD-95 knocked mice (Migaud et al., 1998);
studies suggest that its role may be to decrease internal-
ization of NMDA receptors (Roche et al., 2001). In con-
trast, deletion of a second MAGUK, called PSD-93, leads
to decreased expression of NMDA receptor subunits at
the membrane surface and smaller NMDA receptor-
mediated synaptic potentials (Tao et al., 2003). This
result implies that PSD-93 is necessary for the insertion
of new NMDA receptors; to the extent that PSD-93 itself
is localized to the postsynaptic site, it will promote
receptor clustering. A third member of the family, SAP-
97, is driven into the spine heads when CaMKII is acti-
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