Functional NMDA Receptor Subtype 2B Is Expressed in Astrocytes after IschemiaIn Vivoand AnoxiaIn Vitro

Abstract

NMDA-type glutamate receptors play a critical role in neuronal synaptogenesis, plasticity, and excitotoxic death. Recent studies indicate that functional NMDA receptors are also expressed in certain glial populations in the normal brain. Using immunohistochemical methods, we detected the presence of the NMDA receptor 2B (NR2B) subunit of the NMDA receptor in neurons but not astrocytes in the CA1 and subicular regions of the rat hippocampus. However, after ischemia-induced neuronal death in these regions, double immunohistochemical labeling revealed that NR2B subunits colocalized with the astrocyte marker glial fibrillary acid protein and with NR1 subunits that are required for functional NMDA receptors. NR2B expression was first observed 3 d after ischemia and reached a peak at 28 d. At 56 d, only a few NR2B-expressing astrocytes were still present. In vitro, when postnatal hippocampal cultures were subjected to 5 min of anoxia, it resulted in NR2B expression on astrocytes in the glial feed layer. Imaging of intracellular calcium with postanoxic cultures and astrocytes isolated acutely from the ischemic hippocampus revealed a rise in intracellular [Ca2+] after stimulation with the specific agonist NMDA. The response could be blocked reversibly with the competitive antagonist 2-amino-5-phosphonovalerate and attenuated by the NR2B-selective antagonist ifenprodil. Control astrocytes were not responsive to NMDA but responded to glutamate. An understanding of the role of astrocytes that express functional NMDA receptors in response to ischemia may guide development of novel stroke therapies.

Novel regional and developmental NMDA receptor expression patterns uncovered in NR2C subunit-β-galactosidase knock-in mice

“…The fact that we were not able to immunologically detect the NR1 subunit in these cells suggests that, at rest, astrocytes lack the capacity to express functional NMDAR channels or that NR1 levels are below detection. An intriguing possibility is that NR1 expression is upregulated in hippocampal astrocytes by ischemia or anoxia, as previously reported (Krebs et al, 2003). Consistent with the idea that functional NR2C-containing NMDARs may be expressed in response to ischemia, cerebral vascular occlusion selectively increases NR2C mRNA expression in vulnerable areas (Small et al, 1997) and mutation of the NR2C gene reduces ischemic injury in mice (Kadotani et al, 1996).…”

Long-lasting dephosphorylation of connexin 43 in acute seizures is regulated by NMDA receptors in the rat cerebral cortex

“…NMDA receptors are known to be expressed in neurons (45), while astrocytes react to glutamate by metabotropic receptors and express NMDA subunits only under pathological conditions such as ischemia or anoxia (46). In contrast, recent studies have clearly demonstrated the presence of functional NMDA subunits in cortical astrocytes in the normal brain (47,48).…”

Characterisation of glucose transporters in the intact coronary artery endothelium in rats: GLUT-2 upregulated by long-term hyperglycaemia

“…Cross-sections of these tissues were cut on a cryostat, thaw-mounted on Superfrost slides (VWR, Edmonton, Alta, Canada), fixed, and labelled as described above. Primary cultures of rat neurons were obtained from K. Baimbridge (Department of Physiology, University of British Columbia, Vancouver, BC, Canada) [19,20]. The neurons were fixed, and then labelled as described above.…”