Evidence for multiple AMPA receptor complexes in hippocampal CA1/CA2 neurons

Abstract

The AMPA receptor, which is involved in most fast glutamatergic transmission in the mammalian brain and is expressed in most neurons, is made up of four subunits, GluR1-4. In situ hybridzation, immunocytochemistry studies, and single-cell PCR analyses show that the number and type of AMPA receptor subunits expressed vary among neuronal populations and that two to four subunits usually are expressed in each neuron. Neurons that express two or more subunits theoretically could produce multiple pentameric receptor complexes that differ in their subunit compositions, and these complexes could be targeted to different synaptic populations. To determine whether a single neuronal population produces multiple AMPA receptor complexes, we used a preparation of CA1/CA2 hippocampal pyramidal neurons and immunoprecipitation with subunit-specific antibodies to characterize the receptor complexes. The CA1/CA2 pyramidal neurons express high levels of GluR1-3 and receive multiple excitatory inputs, offering the possibility that distinct receptor complexes may be assembled and expressed selectively at different synaptic populations. Our results suggest the presence of two major populations of AMPA receptor complexes: those made up of GluR1 and GluR2 and those made up of GluR2 and GluR3. Very few complexes contained both GluR1 and GluR3, whereas approximately 8% of the total AMPA receptor complexes was homomeric GluR1. The integrity of the receptor complex was verified by measuring [3H]AMPA binding activity in the immunoprecipitated fractions. These results show that AMPA receptor complexes with different subunit compositions are present in CA1/CA2 pyramidal neurons and suggest an additional mechanism to regulate receptor expression in neurons.

Synaptic AMPA receptor composition in development, plasticity and disease

“…Moreover, single cell deletion studies reported that ~80% of synaptic AMPARs in CA1 hippocampal neurons comprise GluA1/GluA2 hetromers 8 . However, other studies of subunit abundance in rat hippocampus and cortex suggest AMPARs comprise mainly heteromers containing GluA1 and GluA2 or GluA2 and GluA3 [8][9][10] with approximately equivalent amounts of each heteromer complex 11 . GluA4, on the other hand is tightly developmentally regulated and is sparsely expressed at glutamatergic synapses in principal neurons in adult brain 12 .…”

“…Although relatively uncommon, Ca 2+ -permeable AMPARS (CP-AMPARs) are also present in mature neurons 9 and, as discussed below, their expression can be dynamically regulated under basal, activated and stressed conditions. While CP-AMPARs can arise from either the lack of GluA2 or the presence of an unedited GluA2 in the receptor complex, the fact that less than 1% of all GluA2 RNA encodes unedited GluA2(Q) in adult brain 41 argues that most CP-AMPARs lack GluA2.…”

Regulation of AMPA receptors and synaptic plasticity

“…AMPARs present in the adult hippocampus contain GluR1 and GluR2, or GluR3 and GluR2 subunits (Wenthold et al, 1996). Several lines of evidence point to a central role of GluR1 in hippocampal LTP.…”

“…Thus, phosphorylation of GluR1 on Ser831 and Ser845 increases the apparent single-channel conductance (Derkach et al, 1999) and the apparent open-channel probability (Banke et al, 2000), respectively. However, under normal conditions GluR1 phosphorylation on Ser831 may not affect its electrophysiological properties, since a recent study showed no phosphorylation-induced increase in single AMPA channel properties when GluR1 is oligomerized with GluR2 (Oh and Derkach, 2005), which is the case in most native AMPARs (Wenthold et al, 1996).…”

Presynaptic PICK1 facilitates trafficking of AMPA-receptors between active zone and synaptic vesicle pool

“…AMPARs are assembled from subunits GluA1-4 into functional homo-or hetero-tetrameric cationic channels that are permeable to sodium and calcium (Hollmann and Heinemann, 1994;Bettler and Mulle, 1995;Traynelis et al, 2010). In the hippocampus, the majority of the AMPARs consist of the heteromers GluA1-GluA2 and GluA2-GluA3 (Wenthold et al, 1996). At the excitatory Schaffer collateral/commissural synapses onto CA1 hippocampal pyramidal cells, about 80 % of postsynaptic AMPARs and >95 % of extrasynaptic AMPARs are GluA1-GluA2 heteromers, and most of the remaining receptors are GluA2-GluA3 heteromers (Lu et al, 2009).…”