Metabolism is Normal in Astrocytes in Chronically Epileptic Rats: A ¹³C NMR Study of Neuronal—Glial Interactions in a Model of Temporal Lobe Epilepsy

Abstract

The aim of the present work was to study potential disturbances in metabolism and interactions between neurons and glia in the lithium-pilocarpine model of temporal lobe epilepsy. Rats chronically epileptic for 1 month received [1-13 C]glucose, a substrate for neurons and astrocytes, and [1,2-13 C]acetate, a substrate for astrocytes only. Analyses of extracts from cerebral cortex, cerebellum, and hippocampal formation (hippocampus, amygdala, entorhinal, and piriform cortices) were performed using 13 C and 1 H nuclear magnetic resonance spectroscopy and HPLC. In the hippocampal formation of epileptic rats, levels of glutamate, aspartate, N-acetyl aspartate, adenosine triphosphate plus adenosine diphosphate and glutathione were decreased. In all regions studied, labeling from [1,2-13 C]acetate was similar in control and epileptic rats, indicating normal astrocytic metabolism. However, labeling of glutamate, GABA, aspartate, and alanine from [1-13 C]glucose was decreased in all areas possibly reflecting neuronal loss. The labeling of glutamine from [1-13 C]glucose was decreased in cerebral cortex and cerebellum and unchanged in hippocampal formation. In conclusion, no changes were detected in glial-neuronal interactions in the hippocampal formation while in cortex and cerebellum the flow of glutamate to astrocytes was decreased, indicating a disturbed glutamate-glutamine cycle. This is, to our knowledge, the first study showing that metabolic disturbances are confined to neurons inside the epileptic circuit.

Brain Mitochondrial Metabolic Dysfunction and Glutamate Level Reduction in the Pilocarpine Model of Temporal Lobe Epilepsy in Mice

“…To assess the effects of SE induced by pilocarpine on brain energy metabolism and amino-acid neurotransmitter homeostasis in mice, concentrations of metabolites and incorporation of 13 C label into metabolites were analyzed in extracts of cortex and HF using 1 H and 13 C NMR spectroscopy, HPLC, and GC-MS. Table 1 shows the total amounts and percentage 13 C enrichment with [1,2-13 C]glucose, [2,[3][4][5][6][7][8][9][10][11][12][13] C]lactate, and [2,3-13 C]alanine, which were quantified using 1 H-NMR spectroscopy, except for the amount of alanine, which was measured using HPLC. Pilocarpine-SE mice received less [1,2-13 C]glucose, as their body weight was significantly lower compared with controls, 33.92 ± 1.42 g vs. 38.60±1.25 g (P ¼ 0.024, n ¼ 10 pilocarpine-SE, n ¼ 11 control mice), respectively.…”

“…Natural abundance of glucose cannot be reliably calculated as the level of brain glucose before administration of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]glucose to the animals is unknown. Calculating natural abundance based on measured total glucose amount (1.1% Â 1.1% Â (amount of 12 C glucose þ 13 C glucose)) will overestimate natural abundance, whereas calculating natural abundance based on 12 C glucose concentration (1.1% Â 1.1% Â amount of 12 C glucose) will underestimate 13 C natural abundance.…”

“…5,6 Changes in brain metabolism in rat models of TLE resemble those reported in human TLE such as interictal glucose hypometabolism demonstrated in lithium-pilocarpine rats, 7 as well as alterations in NAA and glutamate reported in post-status epilepticus (SE) models induced by kainic acid and lithiumpilocarpine. [8][9][10] There are, however, few comprehensive studies on brain metabolism in mouse models of TLE, although this should be of interest owing to advantages of using mice in epilepsy research such as a wider range of opportunities for genetic manipulation and potentially shorter experiment duration with reduced expenses.…”

“…14, 15 We utilized 1 H nuclear magnetic resonance (NMR) spectroscopy and highpressure liquid chromatography (HPLC) to obtain detailed maps of the metabolite content in cerebral cortex and hippocampal formation (HF) in pilocarpine-SE mice. To be able to determine glucose metabolism, we injected animals with [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]glucose 15 minutes before microwave fixation of the head, and evaluated brain extracts using 13 C NMR spectroscopy and gas chromatography-mass spectrometry (GC-MS).…”

“…5,6 Changes in brain metabolism in rat models of TLE resemble those reported in human TLE such as interictal glucose hypometabolism demonstrated in lithium-pilocarpine rats, 7 as well as alterations in NAA and glutamate reported in post-status epilepticus (SE) models induced by kainic acid and lithiumpilocarpine. [8][9][10] There are, however, few comprehensive studies on brain metabolism in mouse models of TLE, although this should be of interest owing to advantages of using mice in epilepsy research such as a wider range of opportunities for genetic manipulation and potentially shorter experiment duration with reduced expenses.In the present study, we aimed to investigate glucose, aminoacid, and energy metabolism in a well-established mouse model of TLE, specifically 3.5-4 weeks after SE was induced by pilocarpine. Injection of the muscarinic agonist pilocarpine leads to SE with the subsequent appearance of spontaneous recurrent seizures, which have been characterized in many laboratories by electroencephalography [11][12][13] and behaviorally in most mouse strains.…”