Group I Metabotropic Receptor Antagonism Blocks Depletion of Calcium Stores and Reduces Potentiated Capacitative Calcium Entry in Strain-Injured Neurons and Astrocytes

Antagonism of the group I metabotropic receptor subtype 1 (mGluR₁) with (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) has been shown to reduce deficits after in vivo or in vitro traumatic brain injury. We have previously demonstrated that AIDA prevents elevation of astrocyte IP₃ subsequent to injury-induced activation of mGluRs and phospholipase C. Since IP₃ can cause release of intracellular Ca²⁺ stores we tested the hypothesis that pre- or post-injury treatment with AIDA can affect (1) the depletion of Ca²⁺ stores which occurs soon after strain injury of cultured neurons and astrocytes and (2) the delayed potentiation of capacitative calcium entry in strain-injured neurons. Astrocyte or neuronal plus glial cultures were grown on Silastic membranes that were subjected to a 50-msec pulse of compressed gas, which caused membrane displacement and biaxial strain (stretch) injury of the adhering cells. Cells were treated 10 min before or immediately after injury with 100 μ M AIDA and the intracellular free Ca²⁺ ([Ca²⁺]_i) response to thapsigargin, which inhibits the ability of the stores to sequester Ca²⁺, was measured at 15 min or 3 h after injury. AIDA pre- or post-injury treatment prevented the depletion of intracellular calcium stores at 15 min post-injury in astrocytes and neurons and reduced the potentiated neuronal capacitative calcium influx 3 h after injury. Since Ca²⁺ and Ca²⁺ stores influence many factors, including neuronal excitability, plasticity, protein synthesis, and neuronal-glial interactions, prevention of Ca²⁺ store depletion and subsequent exaggerated capacitative calcium entry may be an important subcellular mechanism by which antagonism of mGluR₁ receptors exert an injury-reducing effect. More globally, the results further emphasize the importance of altered signaling and calcium regulatory mechanisms in the immediate and delayed sequelae of traumatic brain injury.