Neuronal and glial mGluR5 modulation prevents stretch-induced enhancement of NMDA receptor current.
Neuronal stretching in culture has been used to model diffuse axonal injury caused by head trauma, and activation of N-methyl-D-aspartate receptors (NMDARs) has been implicated in the pathophysiology of such injury. Here we report the effects of modulating injury severity and the metabotropic glutamate receptor subtype 5 (mGluR5) on NMDAR activity after stretch injury. Following mild stretch, cortical neurons plated upon a confluent layer of astrocytes (NG) exhibited both increased maximal current (I(NMDA)) and reduction in the voltage-dependent Mg2+ block. In contrast, neurons grown without an astrocyte monolayer (PN) only exhibited increased I(NMDA). In NG, surprisingly, pretreatment with either the mGluR5 agonist CHPG or the mGluR5 antagonist MPEP decreased the enhancement of I(NMDA). In contrast, in PN, MPEP similarly limited I(NMDA) changes, but CHPG was without effect. In both culture conditions, MPEP, but not CHPG, limited the stretch-reduced Mg2+ block. Severe stretch had no effect on I(NMDA) or the Mg2+ block in either culture condition, despite a correlation between injury severity and the release of lactose dehydrogenase measured postinjury. Neither CHPG nor MPEP had any direct effects upon the NMDA receptor. We conclude that mGluR5 regulates NMDAR activity during mild stretch injury, but not severe injury, by modulating both the Mg2+ block and I(NMDA).
Lea
Paul M
PM
Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20007-2197, USA.
Custer
Stephanie J
SJ
Vicini
Stefano
S
Faden
Alan I
AI
D000818:Animals; D016923:Cell Death / Q000502:physiology; D002478:Cells, Cultured; D004594:Electrophysiology; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D015636:Magnesium Chloride / Q000494:pharmacology; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*
C578937:Grm5 protein, rat; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D015636:Magnesium Chloride; D007770:L-Lactate Dehydrogenase