Neuronal glial interaction in different neurological diseases studied by ex vivo 13C NMR spectroscopy

Nuclear magnetic resonance spectroscopy (NMRS) has been used extensively for several decades to elucidate metabolic pathways in biological systems and has led to new insights into cerebral metabolism. Many of these insights have been gained by NMRS using in vitro models, such as tissue extracts, cell cultures or brain slices. Extracts of cells or tissue provide an excellent basis for metabolic studies and facilitate the interpretation of in vivo spectra. (13)C NMRS is at present mostly used for in vitro or animal studies. Conclusions from the epilepsy models presented in this review are that turnover of metabolites is time-dependent in kainate-injected rats with limbic seizures. Early and only temporarily enhanced astrocytic activity is followed by altered metabolism in neurons with an increased turnover of important amino acids such as GABA and glutamate. However, pentylenetetrazole (PTZ) kindling affects astrocytes in younger and glutamatergic neurons in older animals. In the presence of PTZ, phenobarbital decreases labeling of most metabolites in all cell types, except GABAergic neurons, from both labeled precursors in the younger animals. However, in older animals only GABAergic neurons are affected by phenobarbital, as indicated by an increase in GABA labeling. In kaolin-induced hydrocephalus it was shown that astrocyte metabolism is disturbed in the early phase, particularly in the cerebrum. These alterations continue into the chronic period. Only then do the first signs of neuronal metabolic impairment appear, which might explain why dementia is a prominent clinical feature in patients with chronic hydrocephalus.