3-Nitropropionic acid neurotoxicity in organotypic striatal and corticostriatal slice cultures is dependent on glucose and glutamate.

Mitochondrial inhibition by 3-nitropropionic acid (3-NPA) causes striatal degeneration reminiscent of Huntington's disease. We studied 3-NPA neurotoxicity and possible indirect excitotoxicity in organotypic striatal and corticostriatal slice cultures. Neurotoxicity was quantified by assay of lactate dehydrogenase in the medium and glutamic acid decarboxylase in tissue homogenates. 3-NPA toxicity (25-100 microM in 5 mM glucose, 24-48 h) appeared to be highly dependent on culture medium glucose levels. 3-NPA treatment caused also a dose-dependent lactate increase, reaching a maximum of threefold increase above control at 100 microM. Both a high dose of glutamate (5 mM) and glutamate uptake blockade by dl-threo-beta-hydroxyaspartate potentiated 3-NPA neurotoxicity in corticostriatal slice cultures. Furthermore, striatum from corticostriatal cocultures was more sensitive to 3-NPA than striatum without cortex and tetrodotoxin, MK-801, and d-2-amino-5-phosphonopentanoic acid prevented or attenuated 3-NPA neurotoxicity, suggesting that membrane depolarization and/or neuronal activity of the glutamatergic corticostriatal pathway contributes to striatal pathology. The results indicate that in vivo characteristics of 3-NPA toxicity can be reproduced in organotypic corticostriatal slice cultures.

Rat brain slices produce and liberate kynurenic acid upon exposure to L-kynurenine.

The incorporation of L-kynurenine (L-KYN) into kynurenic acid (KYNA) was examined in rat brain slices. KYNA was measured in the slices and in the incubation medium after purification by ion-exchange and HPLC chromatography. In pilot experiments, the formation of KYNA was confirmed by gas chromatography. KYNA was produced stereoselectively from L-KYN, and approximately 90% of the newly synthesized KYNA was recovered from the incubation medium. Intracellular KYNA was not actively retained by the tissue and was lost from the cells upon repeated washes. Thus, regulation of the levels of extracellular KYNA appears to occur at the level of L-KYN uptake and/or kynurenine transaminase, the biosynthetic enzyme of KYNA. KYNA production from L-KYN was linear up to 4 h and reached a plateau at a L-KYN concentration of 250 microM. The process was effectively inhibited by the transaminase inhibitor aminooxyacetic acid (IC50, approximately 25 microM), and showed pronounced regional distribution (hippocampus greater than cortical areas greater than thalamus much greater than cerebellum). The conversion of L-KYN to KYNA was dependent on oxygenation and on the presence of glucose in the incubation medium. Neither deletion of Ca2+ or Mg2+ nor addition of 20 mM Mg2+ had any effect. However, KYNA production was significantly attenuated in the absence of Cl- or in the presence of 50 mM K+ in the incubation medium. In Na+-free medium, the production of KYNA from L-KYN was increased by 30%.(ABSTRACT TRUNCATED AT 250 WORDS)

Imaging of the degeneration of neurons and their processes in rat or cat brain by 45CaCl2 autoradiography or 55CoCl2 positron emission tomography.

The possibility of using radiolabeled divalent cations to visualize nerve cell degeneration in the brain was investigated after intoxication with neurotoxins. At different survival times after the intracerebral injection of kainic acid or 6-hydroxydopamine, autoradiographs were made from brain sections of rats that had received 45CaCl2 intravenously 24 h before death. Brain sections, adjacent to those used for autoradiography, of the 6-hydroxydopamine-treated rats were used for histofluorescence of catecholamines to check the neurochemical effect of the treatment. These experiments show that radioactive Ca accumulates in brain tissue during a particular phase of degeneration. Not only could degenerating cell bodies be traced by 45Ca autoradiography, but also degenerating nerve terminals in the striato-nigral and nigro-striatal projection systems. In positron emission tomography (PET) studies, 55CoCl2 was used as a marker for Ca2+. Unilateral lesions of the cat forebrain, produced by kainic acid, could be imaged in vivo by PET with 55CoCl2. PET with this radiolabel may provide diagnostic potentials for human neurodegenerative disorders.

A correlative study on hippocampal cation shifts and amino acids and clinico-pathological data in Alzheimer's disease.

Amino acid transmitters and cations were assessed in the frontal cortex and hippocampus of 12 Alzheimer's disease (AD), 4 multi-infarct dementia (MID) patients, and 12 age-matched controls. In the hippocampus, but not in the frontal cortex of AD patients we observed an increase of sodium (Na) and a decrease of potassium (K) and magnesium (Mg) content as compared to controls. Calcium (Ca) was not changed. These cation shifts were highly correlated with glutamate, which was significantly decreased in AD hippocampus. Hippocampal Na and K levels correlated also highly with gamma-aminobutyrate, cholineacetyltransferase and noradrenaline levels in the hippocampus and dementia scores. These results show that Na and K changes are sensitive markers for neurodegenerative processes in AD and suggest a loss of glutamatergic neurons in AD hippocampus.

Cerebral cation shifts and amino acids in Huntington's disease.

The cations, calcium, magnesium, sodium, and potassium, putative amino acid transmitters, and total protein contents were assessed in the frontal cortex, putamen, and substantia nigra of Huntington's disease (HD) patients and age-matched nonneurologic control subjects. In the HD frontal cortex and HD substantia nigra, only small increases in sodium levels and decreases in potassium levels were observed, but in the HD putamen there were major cation shifts, suggesting a twofold increase of the extracellular space. In all three brain areas that were investigated, potassium was positively correlated with gamma-aminobutyric acid and in the putamen sodium was negatively correlated with the amino acid. These correlations suggest loss of gamma-aminobutyric acidergic neurons or nerve terminals in these areas. The elevation of sodium in the HD basal ganglia may be visualized in vivo by nuclear magnetic resonance of sodium.