Seizures are a common neurological problem. A number of investigators have tried to better understand the pathological neurochemistry associated with epileptic brain tissue using in vitro and in vivo nuclear magnetic resonance spectroscopy (NMRS) in animal models of seizures and in patients with epilepsy. One of the problems in vivo NMRS cannot assess concerns the cellular and sub-cellular heterogeneity of the brain. Spectroscopic imaging can not distinguish between neurons, astrocytes, and oligodendrocytes located within the sensitive volumes directly. Separating cerebral tissues into synaptic nerve terminals (synaptosomes), neuronal cell bodies (neurosomes), and astrocytes (gliosomes) is one approach which should yield insight into neurochemical heterogeneity at a cellular level. NMRS studies of synaptosomes can offer insights into the changes observed in vivo studies. NMRS studies of such preparations have the same features that make such measurements unique in vivo - chemical specificity and repeatability unlimited by disturbance of tissue - but in addition, they can be done with complete control of the extracellular space and at the sensitivity and resolution of the most powerful spectrometers available. The overall goal o this project is to investigate cerebral metabolism at rest and after stimulation in synaptosomes freshly prepared from rat cerebrum and human cortex. The study will focus on determining the changes in carbohydrate, organic acid, and amino acid metabolism in these two parts of the neuron using 1H and 13C NMRS. Specifically, methods will be developed to measure rates of 13C incorporation into and steady fractional enrichments of lactate, alanine, aspartate, glutamate, glutamine, GABA, succinate, and acetate. Measurements of the pattern of 13C-labelling of these metabolites will provide information concerning the flow of label through the glycolytic, anaplerotic, tricarboxylic acid cycle, """"""""GABA shunt"""""""", and pentose cycle pathways.
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