Ischemia and Ischemic Tolerance Induction Differentially Regulate Protein Expression of GluR1, GluR2, and AMPA Receptor Binding Protein in the Gerbil Hippocampus

Abstract

Background and Purpose-Postischemic delayed neuronal death (DND) of hippocampal CA1 neurons has been suggested to occur as a result of formation of calcium-permeable ␣-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors lacking the GluR2 subunit (GluR2 hypothesis). DND can be prevented by a short tolerance-inducing ischemic period. The present study was designed to assess whether postischemic protein levels of GluR2 predict neuronal death. Additionally, the role of AMPA receptor binding protein (ABP) was investigated with respect to neuronal death or survival. Methods-Postischemic protein expression of GluR1, GluR2, and ABP was analyzed in 3 experimental paradigms of transient global ischemia with the use of subunit-specific antisera and semiquantitative densitometric evaluation. Gerbils were subjected (1) to a 5-minute ischemic period resulting in DND of CA1 neurons; (2) to a 2.5-minute period of ischemia mediating tolerance induction; and (3) to 5 minutes of ischemia in the ischemia-tolerant state (2.5ϩ5 minutes of ischemia 4 days apart). Results-The major finding was that GluR2 protein levels were significantly downregulated in neuronal subpopulations destined to survive, ie, in CA1 principal neurons after ischemic tolerance induction and in the ischemia-tolerant state, as well as in CA3 neurons after a 5-minute period of ischemia. ABP expression remained unaffected. Conclusions-Our results modify the GluR2 hypothesis in that postischemic GluR2 reduction also occurs in hippocampal CA1 and CA3 principal neurons without subsequent neuronal death. ABP is obviously not involved in mechanisms of DND or ischemic tolerance induction. (Stroke. 2002;33:1093-1100.)

Comparison of Single- and Repeated-Ischemia-Induced Changes in Expression of Flip and Flop Splice Variants of AMPA Receptor Subtypes GluR1 and GluR2 in the Rats Hippocampus CA1 Subregion

“…It has been reported that short anoxia / hypoglycemia increases GluR1 and GluR2 / 3 subunits 1 h, but not 15 min, after the episode (43). Moreover, occlusion of the common carotid artery alone for 5 min decreases GluR2, but not the GluR1, in the CA1 (41). In this study, reduction of GluR1 was observed on day 1 after the SI, whereas reduction of GluR2 variants was observed 1 -3 days after the RI.…”

“…Although both GluR1 and GluR2 are expressed in the CA1 subregion (40), it could be suggested that reduction of GluR2 is important in the hippocampal neuronal death and the subsequent behavioral disorders. It has been reported that the CA1 neurons destined to die after ischemia exhibit reduced levels of GluR2 protein expression immediately before cell death (41). The reduced GluR2 level could be restored by fimbria-fornix deafferentiation, which interrupts the afferent input to the CA1 and protects the CA1 neurons at 7 days post- ischemia (42).…”

[ 3 H]Muscimol Binding to γ-Aminobutyric Acid A Receptors Is Upregulated in CA1 Neurons of the Gerbil Hippocampus in the Ischemia-Tolerant State

“…A second group was subjected to a short ischemic period of 2.5 minutes, which we normally use for ischemia tolerance induction. 10,11 Control gerbils (nϭ8) were subjected to a sham operation consisting of anesthesia and all surgical procedures, except clamping of the carotid arteries. At the determined end point of the experiment, ie, 30 minutes, 8 hours, 24 hours, 48 hours, and 96 hours after reperfusion (nϭ4 to 5 per time point), animals were decapitated, and brains were rapidly removed, frozen in isopentane at Ϫ30°C for 10 minutes, and stored at Ϫ80°C until analysis.…”

“…11 Briefly, immunoreactivity was visualized with the use of the avidinbiotin complex method (Vectastain, Vector Laboratories). Sections were developed in 0.02% diaminobenzidine with 0.02% hydrogen peroxide.…”

“…The former possibility seems to be relatively unlikely: immunohistochemically, protein expression of AMPA receptor subunits GluR1 and GluR2 in CA1 is not increased. 11 Alsbo and colleagues 46 demonstrated that GluR3 expression is unaltered after a preconditioning ischemic period in the rat CA1 subfield. The remaining GluR4 subunit, however, is only expressed at low levels in CA1 47 and is unlikely to contribute to the marked increase in [ 3 H]AMPA ligand binding, as observed in the present study.…”