F-19 NMR CALCIUM CHANGES, EDEMA AND HISTOLOGY IN NEONATAL RAT-BRAIN SLICES DURING GLUTAMATE TOXICITY

Respiring neonatal cerebrocortical slices (350 mu m thick), loaded wit h the free calcium indicator 5F-BAPTA, were perfused in a 20-mm-diamet er glass NMR tube with oxygenated artificial CSF, exposed to extracell ular glutamate and studied at 4.7 Tesla with F-19 NMR spectroscopy. (3 1)p/H-1 NMR spectra, obtained concurrently, were used to assess slice integrity from determinations of intracellular pH, ATP, PCr, lactate a nd N-acetylaspartate. 60-min periods were induced of recoverable and n onrecoverable glutamate toxicity-defined from changes in NMR metabolit es. In other NMR studies, where 5F-BAPTA was not used, metabolic toxic ity was modulated by three glutamate receptor antagonists: dizocilpine , NBQX and kynurenic acid. Outcome measurements were made of edema, de termined invasively in isolated slices from % swelling and water conte nt and from histological changes in Nissl stains of slice sections. Ed ema was (1) detectable in all slices within minutes after onset of glu tamate exposure, though never in untreated control slices, and (2) mod ulated differently by dizocilpine, NBQX and kynurenate. Correlations w ere observed between edema and NMR decreases in PCr and ATP. Nissl sta ins of sections from slices treated with the most protective agent, di zocilpine, showed preservation of neuronal processes. As was expected in 7-day-old rats with immature NMDA receptors, F-19 NMR spectroscopy revealed only small increases in free intracellular calcium ([Ca2+](i) ). These occurred late during glutamate exposure and reversed early du ring glutamate washout. The studies demonstrate that it is possible to study correlations between repeated noninvasive NMR spectra in ensemb les of brain slices and invasive measures of early cellular responses.