Memantine exacerbates myoclonic jerks in a rat model of posthypoxic myoclonus

Region-specific role for GluN2B-containing NMDA receptors in injury to Purkinje cells and CA1 neurons following global cerebral ischemia

Motor deficits are present in cardiac arrest survivors and injury to cerebellar Purkinje cells (PCs) likely contribute to impairments in motor coordination and post-hypoxic myoclonus. N-Methyl-D-aspartic acid (NMDA) receptor-mediated excitotoxicity is a well-established mechanism of cell death in several brain regions, but the role of NMDA receptors in PC injury remains understudied. Emerging data in cortical and hippocampal neurons indicate that the GluN2A-containing NMDA receptors signal to improve cell survival and GluN2B-containing receptors contribute to neuronal injury. This study compared neuronal injury in the hippocampal CA1 region to that in PCs and investigated the role of NMDA receptors in PC injury in our mouse model of cardiac arrest and cardiopulmonary resuscitation (CA/CPR). Analysis of cell density demonstrated a 24% loss of PCs within 24 h after 8 min CA/CPR and injury stabilized to 33% by 7 days. The subunit promiscuous NMDA receptor antagonist MK-801 protected both CA1 neurons and PCs from ischemic injury following CA/CPR, demonstrating a role for NMDA receptor activation in injury to both brain regions. In contrast, the GluN2B antagonist, Co 101244, had no effect on PC loss while protecting against injury in the CA1 region. These data indicate that ischemic injury to cerebellar PCs progresses via different cell death mechanisms compared to hippocampal CA1 neurons.

Amiloride but not memantine reduces neurodegeneration, seizures and myoclonic jerks in rats with cardiac arrest-induced global cerebral hypoxia and reperfusion

It has been reported that both activation of N-methyl-D-aspartate receptors and acid-sensing ion channels during cerebral ischemic insult contributed to brain injury. But which of these two molecular targets plays a more pivotal role in hypoxia-induced brain injury during ischemia is not known. In this study, the neuroprotective effects of an acid-sensing cation channel blocker and an N-methyl-D-aspartate receptor blocker were evaluated in a rat model of cardiac arrest-induced cerebral hypoxia. We found that intracisternal injection of amiloride, an acid-sensing ion channel blocker, dose-dependently reduced cerebral hypoxia-induced neurodegeneration, seizures, and audiogenic myoclonic jerks. In contrast, intracisternal injection of memantine, a selective uncompetitive N-methyl-D-aspartate receptor blocker, had no significant effect on cerebral hypoxia-induced neurodegeneration, seizure and audiogenic myoclonic jerks. Intracisternal injection of zoniporide, a specific sodium-hydrogen exchanger inhibitor, before cardiac arrest-induced cerebral hypoxia, also did not reduce cerebral hypoxia-induced neurodegeneration, seizures and myoclonic jerks. These results suggest that acid-sensing ion channels play a more pivotal role than N-methyl-D-aspartate receptors in mediating cerebral hypoxia-induced brain injury during ischemic insult.