AMPA receptor subunit GluR2 gates injurious signals in ischemic stroke

Ischemic stroke, or a brain attack, is the third leading cause of death in developed countries. A critical feature of the disease is a highly selective pattern of neuronal loss; certain identifiable subsets of neurons--particularly CA1 pyramidal neurons in the hippocampus are severely damaged, whereas others remain intact. A key step in this selective neuronal injury is Ca2+/Zn2+ entry into vulnerable neurons through alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels, a principle subtype of glutamate receptors. AMPA receptor channels are assembled from glutamate receptor (GluR)1, -2, -3, and -4 subunits. Circumstance data have indicated that the GluR2 subunits dictate Ca2+/Zn2+ permeability of AMPA receptor channels and gate injurious Ca2+/Zn2+ signals in vulnerable neurons. Therefore, targeting to the AMPA receptor subunit GluR2 can be considered a practical strategy for stroke therapy.     

Rat gustatory neurons in the geniculate ganglion express glutamate receptor subunits

Taste receptor cells are innervated by primary gustatory neurons that relay sensory information to the central nervous system. The transmitter(s) at synapses between taste receptor cells and primary afferent fibers is (are) not yet known. By analogy with other sensory organs, glutamate might a transmitter in taste buds. We examined the presence of AMPA and NMDA receptor subunits in rat gustatory primary neurons in the ganglion that innervates the anterior tongue (geniculate ganglion). AMPA and NMDA type subunits were immunohistochemically detected with antibodies against GluR1, GluR2, GluR2/3, GluR4 and NR1 subunits. Gustatory neurons were specifically identified by retrograde tracing with fluorogold from injections made into the anterior portion of the tongue. Most gustatory neurons in the geniculate ganglion were strongly immunoreactive for GluR2/3 (68%), GluR4 (78%) or NR1 (71%). GluR1 was seen in few cells (16%). We further examined if glutamate receptors were present in the peripheral terminals of primary gustatory neurons in taste buds. Many axonal varicosities in fungiform and vallate taste buds were immunoreactive for GluR2/3 but not for NR1. We conclude that gustatory neurons express glutamate receptors and that glutamate receptors of the AMPA type are likely targeted to synapses within taste buds.     

Absolute quantification of AMPA receptor subunit mRNAs in single hippocampal neurons

alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor subunit (GluR1-4) mRNAs expressed by single neurons in rat hippocampal cultures were quantified by single-cell RT-PCR using an internal standard RNA after whole-cell patch-clamp recording. The internal standard RNA, derived from GluR2 with a single nucleotide substitution, was reverse-transcribed and PCR-amplified with the same efficiency as GluR1-4 mRNAs. The mean mRNA numbers harvested in vitro from pyramidal-like neurons on day 9 were 1150 +/- 324 molecules of GluR1, 1080 +/- 273 molecules of GluR2, 100 +/- 20 molecules of GluR3, and 50 +/- 10 molecules of GluR4 (mean +/- SEM, n = 12). In a non-pyramidal neuronal population that expresses AMPA receptors characterized by high Ca(2+) permeability, the numbers of GluR1, GluR3 and GluR4 mRNA molecules harvested per cell were 354 +/- 64, 25 +/- 17 and 168 +/- 36, respectively (n = 8). The GluR2 mRNA was not detected in this cell type. The calculated ratio of AMPAR mRNA molecules per total mRNA molecules was 1/240 in pyramidal-like neurons (1/500 for GluR2), being in the range obtained with total RNA from rat forebrain and cerebellum (1/170 and 1/380, respectively). Finally, our results indicated that the proportion of GluR1-4 mRNA located in neurites reached approximately 60% in pyramidal-like neurons. However, we found no evidence of preferential subcellular distribution of a given subunit.     

AMPA and NMDA glutamate receptors are found in both peptidergic and non-peptidergic primary afferent neurons in the rat

Two distinct classes of nociceptive primary afferents, peptidergic and non-peptidergic, respond similarly to acute noxious stimulation; however the peptidergic afferents are more likely to play a role in inflammatory pain, while the non-peptidergic afferents may be more characteristically involved in neuropathic pain. Using multiple immunofluorescence, we determined the proportions of neurons in the rat L4 dorsal root ganglion (DRG) that co-express AMPA or NMDA glutamate receptors and markers for the peptidergic and non-peptidergic classes of primary afferents, substance P and P2X(3), respectively. The fraction of DRG neurons immunostained for the NR1 subunit of the NMDA receptor (40%) was significantly higher than that of DRG neurons immunostained for the GluR2/3 (27%) or the GluR4 (34%) subunits of the AMPA receptor. Of all DRG neurons double-immunostained for glutamate receptor subunits and either marker for peptidergic and non-peptidergic afferents, a significantly larger proportion expressed GluR4 than GluR2/3 or NR1 and in a significantly larger proportion of P2X(3)- than SP-positive DRG neurons. These observations support the idea that nociceptors, involved primarily in the mediation of neuropathic pain, may be presynaptically modulated by GluR4-containing AMPA receptors.     

Activation of D1 dopamine receptors increases surface expression of AMPA receptors and facilitates their synaptic incorporation in cultured hippocampal neurons

Considerable evidence indicates that neuroadaptations leading to addiction involve the same cellular processes that enable learning and memory, such as long-term potentiation (LTP), and that psychostimulants influence LTP through dopamine (DA)-dependent mechanisms. In hippocampal CA1 pyramidal neurons, LTP involves insertion of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors into excitatory synapses. We used dissociated cultures to test the hypothesis that D1 family DA receptors influence synaptic plasticity in hippocampal neurons by modulating AMPA receptor trafficking. Brief exposure (5 min) to a D1 agonist increased surface expression of glutamate receptor (GluR)1-containing AMPA receptors by increasing their rate of externalization at extrasynaptic sites. This required the secretory pathway but not protein synthesis, and was mediated mainly by protein kinase A (PKA) with a smaller contribution from Ca2+-calmodulin-dependent protein kinase II (CaMKII). Prior D1 receptor stimulation facilitated synaptic insertion of GluR1 in response to subsequent stimulation of synaptic NMDA receptors with glycine. Our results support a model for synaptic GluR1 incorporation in which PKA is required for initial insertion into the extrasynaptic membrane whereas CaMKII mediates translocation into the synapse. By increasing the size of the extrasynaptic GluR1 pool, D1 receptors may promote LTP. Psychostimulants may usurp this mechanism, leading to inappropriate plasticity that contributes to addiction-related behaviors.     

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

Fast excitatory synaptic responses in basolateral amygdala (BLA) neurons are mainly mediated by ionotropic glutamate receptors of the alpha-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 subunit-specific 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 receptor- mediated 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.     

Immunocytochemical localization of the AMPA receptor subunits in the mesencephalic trigeminal nucleus of the rat

The mesencephalic trigeminal nucleus is composed of large (35-50 microns) pseudo-unipolar neurons. Closely associated with them are small (< 20 microns) multipolar neurons. An unique peculiarity of the pseudo-unipolar perikarya is that they receive synaptic input from various sources, which sets them apart from the dorsal root and cranial nerves sensory ganglia neurons. Whereas glutamate is the best neurotransmitter candidate in pseudo-unipolar neurons, glutamatergic input into them has not yet been reported. AMPA glutamate receptors are implicated in fast excitatory glutamatergic synaptic transmission. They have been localized ultrastructurally at postsynaptic sites. This study demonstrates that the pseudo-unipolar neurons of the mesencephalic trigeminal nucleus express AMPA glutamate receptor subunits, which indicates that these neurons receive glutamatergic input. Serial sections from the rostral pons and midbrain of Sprague-Dawley rats were immunostained with antibodies against C-terminus of AMPA receptor subunits: GluR1, GluR2/3, and GluR4. The immunoreaction was visualized with avidin-biotin-peroxidase/DAB for light and electron microscopy. With GluR1 antibody only the smallest multipolar neurons were recognized as immunopositive within the mesencephalic trigeminal nucleus. GluR2/3 stained the pseudo-unipolar neurons intensely within the entire rostro-caudal extent of the nucleus. In addition the former antibody stained small multipolar neurons within the mesencephalic trigeminal nucleus, though with somewhat larger dimensions than those immunoreactive for GluR1. Whereas the overall staining with GluR4 antibody was scant, those pseudo-unipolar neurons that were stained, were strongly stained. Furthermore, a considerable number of microglial cells within and surrounding the mesencephalic trigeminal nucleus displayed very intense immunoreactivity for GluR4. These results are discussed in the light of the glutamate receptor subunit composition.     

Immunocytochemical localization of neurons containing the AMPA GluR2/3 subunit in the hamster visual cortex

AMPA glutamate receptors play a crucial role in brain functions such as synaptic plasticity and development. We have studied the chemo-architecture of the AMPA glutamate receptor subtype GluR2/3 in the hamster visual cortex by immunocytochemistry and compared it with the distribution of the calcium-binding proteins, calbindin D28K and calretinin. Anti-GluR2/3-immunoreactive (IR) neurons were predominantly located in layers II/III, V, and VI, and the majority of the labeled neurons were round or oval. However, many pyramidal cells in layer V were also labeled. Two-color immunofluorescence revealed that none of the GluR2/3-IR neurons contained calbindin D28 K or calretinin. Thus specific layers of neurons express the GluR2/3 subunit and these do not correlate with expression of calbindin D28K and calretinin.     

AMPA receptor-dependent clustering of synaptic NMDA receptors is mediated by Stargazin and NR2A/B in spinal neurons and hippocampal interneurons

Under standard conditions, cultured ventral spinal neurons cluster AMPA- but not NMDA-type glutamate receptors at excitatory synapses on their dendritic shafts in spite of abundant expression of the ubiquitous NMDA receptor subunit NR1. We demonstrate here that the NMDA receptor subunits NR2A and NR2B are not routinely expressed in cultured spinal neurons and that transfection with NR2A or NR2B reconstitutes the synaptic targeting of NMDA receptors and confers on exogenous application of the immediate early gene product Narp the ability to cluster both AMPA and NMDA receptors. The use of dominant-negative mutants of GluR2 further showed that the synaptic targeting of NMDA receptors is dependent on the presence of synaptic AMPA receptors and that synaptic AMPA and NMDA receptors are linked by Stargazin and a MAGUK protein. This system of AMPA receptor-dependent synaptic NMDA receptor localization was preserved in hippocampal interneurons but reversed in hippocampal pyramidal neurons.     

Distribution of AMPA glutamate receptor GluR1 subunit-immunoreactive neurons and their co-localization with calcium-binding proteins and GABA in the mouse visual cortex

The neuronal localization of alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptor (GluR) subunits is vital as they play key roles in the regulation of calcium permeability. We have examined the distribution of the calcium permeable AMPA glutamate receptor subunit GluR1 in the mouse visual cortex immunocytochemically. We compared this distribution to that of the calcium-binding proteins calbindin D28K, calretinin, and parvalbumin, and of GABA. The highest density of GluR1-immunoreactive (IR) neurons was found in layers II/III. Enucleation appeared to have no effect on the distribution of GluR1-IR neurons. The labeled neurons varied in morphology; the majority were round or oval and no pyramidal cells were labeled by the antibody. Two-color immunofluorescence revealed that 26.27%, 10.65%, and 40.31% of the GluR1-IR cells also contained, respectively, calbindin D28K, calretinin, and parvalbumin. 20.74% of the GluR1-IR neurons also expressed GABA. These results indicate that many neurons that express calcium-permeable GluR1 also express calcium binding proteins. They also demonstrate that one fifth of the GluR1-IR neurons in the mouse visual cortex are GABAergic interneurons.     

GluR3 flip and flop: differences in channel opening kinetics

Ample evidence from earlier studies of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, GluR3 included, suggests that alternative splicing not only enriches AMPA receptor diversity but also, more importantly, creates receptor variants that are functionally different. However, it is not known whether alternative splicing affects the receptor channel opening that occurs in the microsecond time domain. Using a laser-pulse photolysis technique combined with whole-cell recording, we characterized the channel opening rate process for two alternatively spliced variants of GluR3, i.e., GluR3flip and GluR3flop. We show that the alternative splicing that generates flip and flop variants of GluR3 receptors regulates the channel opening process by controlling the rate of channel closing but not the rate of channel opening or the glutamate binding affinity. Specifically, the flop variant closes its channel almost 4-fold faster than the flip variant. We therefore propose that the function of the flip-flop sequence module in the channel opening process of AMPA receptors is to stabilize the open channel conformation, presumably by its pivotal structural location. Furthermore, a comparison of the flip isoform among all AMPA receptor subunits, based on the magnitude of the channel opening rate constant, suggests that GluR3 is kinetically more similar to GluR2 and GluR4 than to GluR1.     

Brain-derived neurotrophic factor regulates surface expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid receptors by enhancing the N-ethylmaleimide-sensitive factor/GluR2 interaction in developing neocortical neurons

In hippocampal neurons, the exocytotic process of alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA)-type glutamate receptors is known to depend on activation of N-methyl-d-aspartate channels and its resultant Ca(2+) influx from extracellular spaces. Here we found that brain-derived neurotrophic factor (BDNF) induced a rapid surface translocation of AMPA receptors in an activity-independent manner in developing neocortical neurons. The receptor translocation became evident within hours as monitored by [(3)H]AMPA binding and was resistant against ionotropic glutamate receptor antagonists as evidenced with surface biotinylation assay. This process required intracellular Ca(2+) and was inhibited by the blockers of conventional exocytosis, brefeldin A, botulinum toxin B, and N-ethylmaleimide. To explore the translocation mechanism of individual AMPA receptor subunits, we utilized the human embryonic kidney (HEK) 293 cells carrying the BDNF receptor TrkB. After the single transfection of GluR2 cDNA or GluR1 cDNA into HEK/TrkB cells, BDNF triggered the translocation of GluR2 but not that of GluR1. Subsequent mutation analysis of GluR2 carboxyl-terminal region indicated that the translocation of GluR2 subunit in HEK293 cells involved its N-ethylmaleimide-sensitive factor-binding domain but not its PDZ-interacting site. Following co-transfection of GluR1 and GluR2 cDNAs, solid phase cell sorting revealed that GluR1 subunits were also able to translocate to the cell surface in response to BDNF. An immunoprecipitation assay confirmed that BDNF stimulation can enhance the interaction of GluR2 with N-ethylmaleimide-sensitive factor. These results reveal a novel role of BDNF in regulating the surface expression of AMPA receptors through a GluR2-NSF interaction.     

Differential effects of chronic hyperammonemia on modulation of the glutamate-nitric oxide-cGMP pathway by metabotropic glutamate receptor 5 and low and high affinity AMPA receptors in cerebellum in vivo

Previous studies show that chronic hyperammonemia impairs learning ability of rats by impairing the glutamate-nitric oxide (NO)-cyclic guanosine mono-phosphate (cGMP) pathway in cerebellum. Three types of glutamate receptors cooperate in modulating the NO-cGMP pathway: metabotropic glutamate receptor 5 (mGluR5), (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptors. The aim of this work was to assess whether hyperammonemia alters the modulation of this pathway by mGluR5 and AMPA receptors in cerebellum in vivo. The results support that in control rats: (1) low AMPA concentrations (0.1mM) activate nearly completely Ca(2+)-permeable (glutamate receptor subunit 2 (GluR2)-lacking) AMPA receptors and the NO-cGMP pathway; (2) higher AMPA concentrations (0.3 mM) also activate Ca(2+)-impermeable (GluR2-containing) AMPA receptors, leading to activation of NMDA receptors and of NO-cGMP pathway. Moreover, the data support that chronic hyperammonemia: (1) reduces glutamate release and activation of the glutamate-NO-cGMP pathway by activation of mGluR5; (2) strongly reduces the direct activation by AMPA receptors of the NO-cGMP pathway, likely due to reduced entry of Ca(2+) through GluR2-lacking, high affinity AMPA receptors; (3) strongly increases the indirect activation of the NO-cGMP pathway by high affinity AMPA receptors, likely due to increased entry of Na(+) through GluR2-lacking AMPA receptors and NMDA receptors activation; (4) reduces the indirect activation of the NO-cGMP pathway by low affinity AMPA receptors, likely due to reduced activation of NMDA receptors.     

Protein kinase C gamma associates directly with the GluR4 alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor subunit. Effect on receptor phosphorylation

Ionotropic glutamate receptors mediate the majority of excitatory synaptic transmission in the brain and are thought to be involved in learning and memory formation. The activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-type glutamate receptors can be regulated by direct phosphorylation of their subunits, which affects the electrophysiological properties of the receptor, and the receptor association with numerous proteins that modulate membrane traffic and synaptic targeting of the receptor. In the present study we investigated the association of protein kinase C (PKC) gamma isoform with the GluR4 AMPA receptor subunit. PKC gamma was co-immunoprecipitated with GluR4 AMPA receptor subunit in rat cerebellum and in cultured chick retina cell extracts, and immunocytochemistry experiments showed co-localization of GluR4 and PKC gamma in cultured chick retinal neurons. Pull-down assays showed that native PKC gamma binds the GluR4 C-terminal membrane-proximal region, and recombinant PKC gamma was retained by GST-GluR4 C-terminal fusion protein, suggesting that the kinase binds directly to GluR4. Furthermore, GST-GluR4 C-terminal protein was phosphorylated on GluR4 Ser-482 by bound kinases, retained by the fusion protein, including PKC gamma. The GluR4 C-terminal segment that interacts with PKC gamma, which lacks the PKC phosphorylation sites, inhibited histone H1 phosphorylation by PKC, to the same extent as the PKC pseudosubstrate peptide 19-31, indicating that PKC gamma bound to GluR4 preferentially phosphorylates GluR4 to the detriment of other substrates. Additionally, PKC gamma expression in GluR4 transfected human embryonic kidney 293T cells increased the amount of plasma membrane-associated GluR4. Our results suggest that PKC gamma binds directly to GluR4, thereby modulating the function of GluR4-containing AMPA receptors.     

Subunit-specific surface mobility of differentially labeled AMPA receptor subunits

Lateral mobility of AMPA-type glutamate receptors as well as their trafficking between plasma membrane and intracellular compartments are major mechanisms for the regulation of synaptic plasticity. Here we applied a recently established labeling technique in combination with lentiviral expression in hippocampal neurons to label individual ACP-tagged AMPA receptor subunits specifically at the surface of neurons. We show that this technique allows the differential labeling of two receptor subunits on the same cell. Moreover, these subunits are integrated into heteromeric receptors together with endogenous subunits, and these labeled receptors are targeted to active synapses. Sequential labeling experiments indicate that there is basal surface insertion of GluR1, GluR2 and GluR3, and that this insertion is strongly increased following potassium depolarization. Moreover, we found that ACP-labeled GluR3 shows the highest surface mobility among GluR1, GluR2, and GluR3. In double-infected neurons the diffusion coefficient of labeled GluR2 at the surface of living neurons is significantly higher in GluR2/GluR3-infected neurons compared to GluR1/GluR2-infected neurons suggesting a higher mobility of GluR2/3 receptors compared to GluR1/2 receptors. These results indicate that surface mobility is regulated by different subunit compositions of AMPA receptors.     

AMPA receptor subunits expressed by single Purkinje cells.

Several subunits of the glutamate receptor of the AMPA subtype have been cloned recently. These subunits, named GluR1, GluR2, GluR3, and GluR4, exist as two splicing variants (flip and flop). We have determined the subset of AMPA receptor subunits expressed by single cerebellar Purkinje cells in culture. This was achieved by combining whole-cell patch-clamp recordings and a molecular analysis, based on the polymerase chain reaction, of the messenger RNAs harvested into the patch pipette at the end of each recording. We found that each single cell expresses the messenger RNAs encoding the following five subunits: the flip and flop versions of GluR1 and GluR2 as well as GluR3flip, GluR2 being the most abundant. In addition, GluR3flop and GluR4flip were scarcely expressed in half of these neurons, and GluR4flop was never detected.     

Differential regulation of dendrite complexity by AMPA receptor subunits GluR1 and GluR2 in motor neurons

Activity-dependent developmental mechanisms in many regions of the central nervous system are thought to be responsible for shaping dendritic architecture and connectivity, although the molecular mechanisms underlying these events remain obscure. Since AMPA glutamate receptors are developmentally regulated in spinal motor neurons, we have investigated the role of activation of AMPA receptors in dendritic outgrowth of spinal motor neurons by overexpression of two subunits, GluR1 and GluR2, and find that dendrite outgrowth is differentially controlled by expression of these subunits. Overexpression of GluR1 was associated with greater numbers of filopodia, and an increase in the length and complexity of dendritic arbor. In contrast, GluR2 expression did not alter dendritic complexity, but was associated with a moderate increase in length of arbor, and decreased numbers of filopodia. Neither GluR1 nor GluR2 had any effect on the motility of filopodia. In addition, GluR1 but not GluR2 expression increased the density of dendritic puncta incorporating a GFP-labeled PSD95, suggesting that GluR1 may mediate its effect in part by augmenting the number of excitatory synapses within motor neuron dendrites. Together these results suggest that in spinal motor neurons, AMPA receptors composed of GluR1 subunits may facilitate neurotrophic mechanisms in these neurons, permitting sustained dendrite outgrowth and synaptogenesis, whereas expression of AMPA receptors containing GluR2 acts to preserve existing dendritic arbor. Thus, the observed downregulation of GluR1 in motor neurons during postnatal development may limit the formation of new dendrite segments and synapses, promoting stabilized synaptic connectivity.     

Expression of 15 glutamate receptor subunits and various splice variants in tissue slices and single neurons of brainstem nuclei and potential functional implications

Abstract: Brainstem nuclei serve a diverse array of functions in many of which ionotropic glutamate receptors are known to be involved. However, little detailed information is available on the expression of different glutamate receptor subunits in specific nuclei. We used RT‐PCR in mice to analyze the glutamate receptor subunit composition of the pre‐Bötzinger complex, the hypoglossal nucleus, the nucleus of the solitary tract, and the inferior olive. Analyzing 15 receptor subunits and five variants, we found all four α‐amino‐3‐hydroxy‐5‐methyl‐4‐propionic acid (AMPA) and six NMDA receptor (NR) subunits as well as three of five kainate (KA) receptors (GluR5, GluR6, and KA1) to be expressed in all nuclei. However, some distinct differences were observed: The inferior olive preferentially expresses flop variants of AMPA receptors, GluR7 is more abundant in the pre‐Bötzinger complex than in the other nuclei, and NR2C is most prominent in the nucleus of the solitary tract. In single hypoglossal motoneurons and interneurons of the pre‐Bötzinger complex investigation of GluR2 editing revealed strong expression of the GluR2‐R editing variant, suggesting low Ca²⁺ permeability of AMPA receptors. Thus, Ca²⁺ ‐permeable AMPA receptors are unlikely to be the cause for the reported selective vulnerability of hypoglossal motoneurons during excitotoxic events.