Role of intracellular Ca2+ stores shaping normal activity in brain

The role of intracellular Ca2+ stores in the control of brain activity was investigated in microdialysis experiments by monitoring changes in the extr acellular concentration of amino acids (AA) in the hippocampus of the rat a fter intracerebroventricular (icv) administration of the intracellular Ca2 release blocker, dantrolene in vivo, as well as in D-aspartate release and transmembrane Ca2+ flux measurements in dam trolene-treated. (50 mu M) hip pocampal homogenates containing resealed plasmalemma fragments and nerve en dings in vitro. Microdialysis data demonstrate that icy injection of 0.6 mM dantrolene significantly decreases (similar to 20%) the background (Glu) i n the hippocampus. Both the (Glu; similar to 300%) and the inhibitory effec t of dantrolene thereupon (similar to 50%) was significantly increased when 0.5 mM of the Glu uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylic a cid, was dialysed into the hippocampus. NMDA and (S)-AMPA induced [H-3]-D-a spartate release in hippocampal homogenates. Preincubation of these homogen ates with 50 mu M dantrolene was found to reduce the response to NMDA, but not to (S)-AMPA, in a NMDA-dependent manner. Increased rates of transmembra ne influx and efflux of Ca2+ in hippocampal homogenates with halftimes of 4 ms and 200 ms, respectively, can be observed by the addition of 100 mu M N MDA as recorded using a stopped-how UV/fluorescence spectrometer in combina tion with the Ca2+ indicator dye, bisfura-2, Both the Ca2+ influx and efflu x rates of the NMDA response were reduced (25-fold and >5-fold, respectivel y) in homogenates preloaded with 50 mu M dantrolene, These results suggest a role for NMDA-inducible intracellular Ca2+ stores in the control of norma l brain activity in vivo. (C) 1999 Wiley-Liss, Inc.