Evidence for low GluR2 AMPA receptor subunit expression at synapses in the rat basolateral amygdala

Abstract

Fast excitatory synaptic responses in basolateral amygdala (BLA) neurons are mainly mediated by ionotropic glutamate receptors of the a-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) subtype. AMPA receptors containing an edited GluR2 subunit are calcium impermeable, whereas those that lack this subunit are calcium permeable and also inwardly rectifying. Here, we sought to determine the extent to which synapses in the rat BLA have AMPA receptors with GluR2 subunits. We assessed GluR2 protein expression in the BLA by immunocytochemistry with a GluR2 subunitspecific antiserum at the light and electron microscopic level; for comparison, a parallel examination was carried out in the hippocampus. We also recorded from amygdala brain slices to examine the voltage-dependent properties of AMPA receptormediated evoked synaptic currents in BLA principal neurons. At the light microscopic level, GluR2 immunoreactivity was localized to the perikarya and proximal dendrites of BLA neurons; dense labeling was also present over the pyramidal cell layer of hippocampal subfields CA1 and CA3. In electron micrographs from the BLA, most of the synapses were asymmetrical with pronounced postsynaptic densities (PSD). They contained clear, spherical vesicles apposed to the PSD and were predominantly onto spines (86%), indicating that they are mainly with BLA principal neurons. Only 11% of morphological synapses in the BLA were onto postsynaptic elements that showed GluR2 immunoreactivity, in contrast to hippocampal subfields CA1 and CA3 in which 76% and 71% of postsynaptic elements were labeled (p < 0.001). Synaptic staining in the BLA and hippocampus, when it occurred, was exclusively postsynaptic, and particularly heavy over the PSD. In whole-cell voltage clamp recordings, 72% of BLA principal neurons exhibited AMPA receptor-mediated synaptic currents evoked by external capsule stimulation that were inwardly rectifying. Although BLA principal neurons express perikaryal and proximal dendritic GluR2 immunoreactivity, few synapses onto these neurons express GluR2, and a preponderance of principal neurons have inwardly rectifying AMPA-mediated synaptic currents, suggesting that targeting of GluR2 to synapses is restricted. Many BLA synaptic AMPA receptors are likely to be calcium permeable and could play roles in synaptic plasticity, epileptogenesis and excitoxicity.

The Early Stage Formation of PI3K-AMPAR GluR2 Subunit Complex Facilitates the Long Term Neuroprotection Induced by Propofol Post-Conditioning in Rats

“…Of these, the GluR2 subunit plays a crucial role in controlling the calcium permeability of AMPA receptors. GluR2 mRNA ordinarily undergoes post-transcriptional editing so that the expressed protein contains a positively-charged arginine in place of the gene-encoded glutamate at a critical position in the M2 membrane loop that forms the lining of the AMPA receptor's pore [44]. Therefore, GluR2-lacking AMPAR-mediated excitotoxicity is thought to play a critical role in CNS ischemic insults [10], [45].…”

AMPA receptors as a molecular target in epilepsy therapy

“…Scale bar represents 500 nm for the right panel and 390 nm for the left panel. Reproduced from , with permission of J ohn W iley and S ons.…”

Stimulation of NMDA and AMPA glutamate receptors elicits distinct concentration dynamics of nitric oxide in rat hippocampal slices

“…This inconsistency might be resolved considering that a fraction of hippocampal AMPAR (25%) could not be labeled after immunocytochemical localization of GluR2-containing AMPAR (Gryder et al, 2005). Furthermore, the small size of our sensors affords a spatial discrimination between regions, but not so much between layers of the same region.…”