Research reportExperimental subarachnoid hemorrhage induces changes in the levels of hippocampal NMDA receptor subunit mRNA
Introduction
Subarachnoid hemorrhage (SAH) represents 5–10% of all stroke incidents, and is a major cause of permanent disability and death in adult humans [38]. In rodents, SAH leads to nerve cell death in the brain, including the hippocampal formation [18], [22], [29], [39], which is especially vulnerable to ischemia [17], [30]. In fact, SAH results in a decrease in cerebral blood flow (CBF) in the acute phase [2], [29], [39].
After SAH, there is a massive release of glutamate [3], [28], [31] which may cause an excessive Ca2+ influx through NMDA receptors resulting in cell death. However, it is not known whether SAH produces alterations in the NMDA receptors. Nor is it known whether the expression of individual NMDA receptor subunits is affected by SAH. There are seven different types of NMDA receptor subunits, NR1, NR2A–D, and NR3A–B [1], [25]. Both glutamate and glycine are required to activate NMDA receptors; the glycine site resides on the NR1 subunit and the glutamate site on the NR2 subunits [19]. Hence, both NR1 and NR2 subunits are required to achieve functional NMDA receptors. The NR3 subunits confer a reduced Ca2+ influx when coexpressed with NR1 and NR2 subunits in vitro [5], [6], [20], [21], [25], [35], but their regulation or functional role in vivo is little known [8]. Hence, the relative expression of these subunits may affect the functional properties of the NMDA receptors and thereby enhance or diminish SAH-induced cell death.
In the present work, we have investigated whether experimental SAH causes changes in the expression of NMDA receptor subunits and how such changes correlate to subsequent cell death in the hippocampal formation.
Section snippets
Induction of SAH
All animal treatments were approved by the Northern Committee for Animal Experimentation, Stockholm, Sweden. Thirty-three male Sprague–Dawley rats (B & K Universal AB, Sollentuna, Sweden), weighing 300–400 g, were endotracheally intubated and artificially ventilated with 70% N2O and 30% O2. Surgery was performed under 1% halothane (Fluothane®, Zeneca, Gothenburg, Sweden) and body temperature was maintained at 37.5 ± 0.5 °C. The tail artery was cannulated to obtain blood samples and to monitor
Changes in CBF after SAH
The reduction in CBF induced by the vascular rupture varied greatly and it was generally more pronounced on the ipsilateral side (Fig. 1). CBF30 was 4.5 (1, 17) min (median, 1st, and 3rd quartiles) on the ipsilateral side and 2 (0, 11) min on the contralateral side (P < 0.05 by Wilcoxon's paired test, N = 33).
Analysis of neuronal cell death in the hippocampal formation
At 2–7 days after SAH in the moderate hypoperfusion group, a massive neuronal damage appeared in the ipsilateral CA1 and CA3, but not in the dentate gyrus or on the contralateral side.
Discussion
Following experimental SAH, a CBF-dependent early decrease in the gene expression of specific NMDA receptor subunits was observed in the hippocampal formation. Since the subunit composition of NMDA receptors are known to affect its function [23], [25], this finding suggests that NMDA receptor function is altered by SAH, which may have implications for subsequent neuronal death.
We found ipsilateral, but not contralateral, CBF30 to correlate to mortality and delayed cell death, in line with
Acknowledgments
We thank Britt Meijer for excellent technical assistance. This work was supported by the Swedish Research Council (M-12593), the Magn. Bergvall's Foundation, Swedish Society for Medical Research, the Stroke Foundation, and Funds of the Karolinska Institutet.
References (42)
- et al.
Nucleotide sequence, genomic organization and chromosomal localization of genes for the human NMDA receptor subunits NR3A (GRIN3A) and NR3B (GRIN3B)
Genomics
(2001) - et al.
Reproducible loss of CA1 neurons following carotid artery occlusion combined with halothane-induced hypotension
Brain Res.
(2005) - et al.
Synaptic plasticity in ischemia: role of NMDA receptors
Prog. Brain Res.
(1998) - et al.
Intraischemic but not postischemic hypothermia prevents non-selective hippocampal downregulation of AMPA and NMDA receptor gene expression after global ischemia
Brain Res. Mol. Brain Res.
(2001) - et al.
Glutamate-induced overexpression of NMDA receptor messenger RNAs and protein triggered by activation of AMPA/kainate receptors in rat hippocampus following forebrain ischemia
Brain Res.
(1994) - et al.
Transient ischemia causes a reduction of Mg2+ blockade of NMDA receptors
Neurosci. Lett.
(1994) - et al.
Appearance of NMDA receptors triggered by anoxia independent of voltage in vivo and in vitro
Exp. Neurol.
(1991) Delayed neuronal death in the gerbil hippocampus following ischemia
Brain Res.
(1982)- et al.
Molecular determinants of agonist discrimination by NMDA receptor subunits: analysis of the glutamate-binding site on the NR2B subunit
Neuron
(1997) - et al.
Cloning and characterization of a novel NMDA receptor subunit NR3B, a dominant subunit that reduces calcium permeability
Mol. Brain Res.
(2002)
Alteration in NMDA receptor subunit mRNA expression in vulnerable and resistant regions of in vitro ischemic rat hippocampal slices
Neurosci. Lett.
NMDA receptor (NMDAR1) expression in the rat hippocampus after forebrain ischemia
Neurosci. Lett.
The alterations of N-methyl-d-aspartate receptor expressions and oxidative DNA damage in the CA1 area at the early time after ischemia–reperfusion insult
Neurosci. Lett.
Cortical blood flow and cerebral perfusion pressure in a new noncraniotomy model of subarachnoid hemorrhage in the rat
Stroke
Acute vasoconstriction after subarachnoid hemorrhage
Neurosurgery
Excitatory glycine receptors containing the NR3 family of NMDA receptor subunits
Nature
Cloning and characterization of χ−1: a developmentally regulated member of a novel class of the ionotropic glutamate receptor family
J. Neurosci.
Increased NMDA receptor current and spine density in mice lacking the NMDA receptor subunit NR3A
Nature
NMDA and glycine receptor mRNA expression following transient global ischemia in the gerbil brain
J. Cereb. Blood Flow Metab.
Decreased expression and functionality of NMDA receptor complexes persist in the CA1, but not in the dentate gyrus after transient cerebral ischemia
J. Cereb. Blood Flow Metab.
Attenuation of focal cerebral infarct in mice lacking NMDA receptor subunit NR2C
NeuroReport
Cited by (0)
- 1
These authors contributed equally to this work.