Differential expression of the astrocytic enzymes 3-hydroxyanthranilic acid oxygenase, kynurenine aminotransferase and glutamine synthetase in seizure-prone and non-epileptic mice.

Previous investigations in seizure-prone mice have suggested that an abnormally elevated production of the astrocyte-derived neuroexcitant, quinolinic acid (QUIN), plays a role in seizure susceptibility. In order to evaluate further the role of QUIN metabolism in genetic murine seizure models, the activities of its biosynthetic enzyme 3-hydroxyanthranilic acid oxygenase (3HAO), and of two other astrocytic enzymes, kynurenine aminotransferase (KAT) and glutamine synthetase (GS), were measured in the brains of seizure-prone EL and DBA/2 mice and two non-epileptic strains (BALB/c and Swiss-Webster). 3HAO activity was found to be markedly higher in both EL and DBA/2 mice than in the non-epileptic strains in all brain regions examined.

Molecular cloning and functional expression of human 3-hydroxyanthranilic-acid dioxygenase.

Increased cerebral levels of the endogenous excitotoxin quinolinic acid (QUIN) have been speculatively linked to neuronal damage following neurological and inflammatory disorders. 3-Hydroxyanthranilic-acid dioxygenase (3-HAO; 3-hydroxyanthranilate 3,4-dioxygenase, EC 1.13.

Excitatory amino acid-induced excitation of dopamine-containing neurons in the rat substantia nigra: modulation by kynurenic acid.

Kynurenic acid (KYNA), an endogenous antagonist of ionotropic excitatory amino acid (EAA) receptors, was tested for its ability to modulate N-methyl-D-aspartate (NMDA)- and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced excitation of dopamine (DA)-containing neurons in the zona compacta of the rat substantia nigra (SNc). Experiments were conducted using extracellular recording techniques in conjunction with an in vitro brain slice preparation. Bath application of NMDA (1-20 microM) or AMPA (0.

Purification and characterization of kynurenine aminotransferase I from human brain.

Two kynurenine aminotransferases (KATs), arbitrarily termed KAT I and KAT II, are capable of producing the neuroinhibitory brain metabolite kynurenic acid from L-kynurenine in human brain tissue. Here we describe the purification of KAT I to homogeneity and the subsequent characterization of the enzyme using physicochemical, biochemical, and immunological methods. KAT I was purified from human brain approximately 2,000-fold with a yield of 2%.

4-Chloro-3-hydroxyanthranilate inhibits quinolinate production in the rat hippocampus in vivo.

Quinolinic acid (QUIN) is a potential pathogen in a variety of excitotoxic and neuroviral brain diseases. In the present study, the ability of the QUIN synthesis inhibitor 4-chloro-3-hydroxyanthranilic acid to attenuate the production of QUIN was assessed in the hippocampus of awake rats. To this end, QUIN's immediate bioprecursor 3-hydroxyanthranilic acid (30 microM) was applied through a microdialysis probe, and QUIN production was monitored hourly in the perfusate.

Increased brain quinolinic acid production in mice infected with a hamster neurotropic measles virus.

In order to examine the status of quinolinic acid (QUIN) metabolism in a model of delayed excitotoxic neurodegeneration, the de novo production of QUIN from 3-hydroxyanthranilic acid was assessed in brain homogenates and brain slices of mice injected with hamster neurotropic measles virus. In the hippocampus, which presents exclusive nerve cell loss in this model, the activity of 3-hydroxyanthranilic acid oxygenase, an astrocytic enzyme responsible for the biosynthesis of QUIN, was increased 3.3-fold by 7 days after virus inoculation.

gamma-Acetylenic GABA produces axon-sparing neurodegeneration after focal injection into the rat hippocampus.

In exploring the recently discovered phenomenon of indirect excitotoxicity, we noted that intrahippocampal injections of the nonspecific aminotransferase inhibitor gamma-acetylenic GABA (GAG; 60-240 nmol) caused excitotoxic lesions in rats. When assessed 3 days following the injection, GAG was shown to be approximately equally toxic to CA3/hilar neurons and CA1 pyramids, while CA2 neurons and granule cells were clearly less vulnerable. Choline acetyltransferase activity, a marker of extrinsic afferents, remained unchanged in the GAG-lesioned hippocampus, indicating the axon-sparing nature of the insult.

Preferential neuronal loss in layer III of the entorhinal cortex in patients with temporal lobe epilepsy.

We report a characteristic pattern of neuropathological change in the entorhinal cortex (EC) from four patients with temporal lobe epilepsy. Specimens of the EC were obtained during the surgical treatment of intractable partial seizures and were studied by light microscopy in Nissl-stained sections. A distinct loss of neurons was observed in the anterior portion of the medial EC in the absence of apparent damage to temporal neocortical gyri.

Regional differences in the ontogenetic pattern of kynurenine aminotransferase in the rat brain.

The ontogenetic pattern of kynurenine aminotransferase (KAT), the biosynthetic enzyme of the neuroprotective excitatory amino acid receptor antagonist, kynurenic acid, was examined in the rat in six brain regions and in the liver. KAT activity increased in all brain areas (but not in the liver) between 3 days and 3 months post-natum, and substantial differences were observed in the rates of the increase. For example, KAT activity in the parietal cortex increased 34-fold during the observation period, whereas enzyme activity in the cerebellum and substantia nigra increased only 3-5 fold over the same interval.

Kynurenine pathway enzymes in a rat model of chronic epilepsy: immunohistochemical study of activated glial cells.

The kynurenine pathway metabolites quinolinic acid and kynurenic acid have been hypothetically linked to the occurrence of seizure phenomena. The present immunohistochemical study reports the activation of astrocytes containing three enzymes responsible for the metabolism of quinolinic acid and kynurenic acid in a rat model of chronic epilepsy. Rats received 90 min of patterned electrical stimulation through a bipolar electrode stereotaxically positioned in one hippocampus.

Characterization of human brain kynurenine aminotransferases using [3H]kynurenine as a substrate.

The brain metabolite kynurenic acid is an established broad-spectrum antagonist at ionotropic excitatory amino acid receptors. In the human brain, two distinct enzymes are capable of synthesizing kynurenic acid from its bioprecursor L-kynurenine. Using [3H]kynurenine as the substrate, the two kynurenine aminotransferases (kynurenine aminotransferase I and kynurenine aminotransferase II) are now characterized using partially purified enzyme preparations.

Measles virus-induced hippocampal neurodegeneration in the mouse: a novel, subacute model for testing neuroprotective agents.

The hamster neurotropic (HNT) strain of measles virus causes non-inflammatory encephalopathy in Balb/c mice, associated with neurodegeneration in hippocampal CA1 and CA3 regions. This loss of pyramidal cells can be prevented by twice daily systemic treatment with 1 mg/kg dizocilpine (5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine maleate; MK-801) for 7 days. By varying the MK-801 treatment protocol, we now found that drug administration during the last 4 days prior to sacrifice (i.

Intravenous administration of L-kynurenine to rhesus monkeys: effect on quinolinate and kynurenate levels in serum and cerebrospinal fluid.

L-Kynurenine was administered intravenously at doses of 25, 75 and 200 mg/kg to 4 rhesus monkeys to examine the acute metabolism of kynurenine to its neuroactive products quinolinate (QUIN) and kynurenate (KYNA). Eleven serum and 6 cerebrospinal fluid (CSF) samples, the latter obtained through indwelling cisternal catheters, were collected periodically for 4 hr after the kynurenine infusion. In both serum and CSF, basal concentration of QUIN exceeded KYNA concentrations several-fold (2715 +/- 356 vs 122 +/- 16 nM in serum and 84 +/- 34 vs 6 +/- 1 nM in CSF).

On the production and disposition of quinolinic acid in rat brain and liver slices.

The de novo production and subsequent disposition of the endogenous excitotoxin quinolinic acid (QUIN) was investigated in vitro in tissue slices from rat brain and liver. Incubation of tissue with QUIN's immediate bioprecursor 3-hydroxyanthranilic acid (3-HANA) in oxygenated Krebs-Ringer buffer yielded measurable amounts of QUIN both in the tissue and in the incubation medium. Saturation was reached between 16 and 64 microM 3-HANA (166 pmol of QUIN formed per milligram of protein after a 60-min incubation with 64 microM 3-HANA).

Aminooxyacetic acid causes selective neuronal loss in layer III of the rat medial entorhinal cortex.

Aminooxyacetic acid (AOAA) was used to produce a selective lesion in the rat entorhinal cortex (EC). As assessed 7 days following the injection of AOAA (75 micrograms/0.75 microliter) into the EC, neuronal loss in layer III of the medial EC, particularly in its ventral portion, was consistently observed in Nissl-stained horizontal sections.

Immunocytochemical localization of kynurenine aminotransferase in the rat striatum: a light and electron microscopic study.

Kynurenine aminotransferase is the biosynthetic enzyme for kynurenic acid, an antagonist of excitatory amino acid receptors. Because of the possible role of kynurenic acid in basal ganglia diseases, the distribution of kynurenine aminotransferase immunoreactivity was examined in the adult rat striatum at the light and electron microscopic levels. Kynurenine aminotransferase immunoreactivity was detected in glial cells and in neurons.

Age-related changes in kynurenic acid production in rat brain.

Two separate in vitro assays were used to examine the biosynthesis of the broad spectrum excitatory amino acid receptor antagonist kynurenic acid (KYNA) during the life span of the adult rat. Assessment of KYNA's anabolic enzyme kynurenine aminotransferase revealed steady increases between 3 and 24 months of age in all five brain regions examined. No changes were observed in the liver.

Localization of kynurenine aminotransferase immunoreactivity in the rat hippocampus.

The localization and distribution of kynurenine aminotransferase (KAT), the biosynthetic enzyme of the excitatory amino acid receptor antagonist, kynurenic acid, was studied in the rat hippocampal formation with immunohistochemical methods. The enzyme was found mainly in glial cells that could be distinguished as 3 types on the basis of their shapes and locations. Typically, these cells shared the morphological features of astrocytes and exhibited glial fibrillary acidic protein immunoreactivity as demonstrated by a double-labeling technique.

Regulation of kynurenic acid synthesis studied by microdialysis in the dorsal hippocampus of unanesthetized rats.

The production of the broad spectrum excitatory amino acid receptor antagonist kynurenic acid was assessed by hippocampal microdialysis in freely moving rats. Extracellular kynurenic acid, determined spectrophotometrically, was measured following the perfusion of its bioprecursor L-kynurenine (500 microM) through the dialysis probe. In this paradigm, the concentration of kynurenic acid reached plateau levels within 2 h.

Kynurenic Acid in the Quinolinate-lesioned Rat Hippocampus: Studies In Vitro and In Vivo.

The present study was designed to examine the cellular localization and biosynthetic machinery of the broad-spectrum excitatory amino acid receptor antagonist kynurenic acid in the lesioned rat hippocampus. Seven days after an intrahippocampal injection of 120 nmol quinolinic acid, which causes massive neurodegeneration in the dorsal hippocampus, kynurenic acid tissue levels and the activity of kynurenic acid's anabolic enzyme, kynurenine aminotransferase, were increased by 92% and 67%, respectively, as compared to controls. The steady-state levels of extracellular kynurenic acid, examined by microdialysis in unanaesthetized rats, were also increased in the lesioned tissue (from 93.

Phosphatidylglycerol determination in the amniotic fluid from a PAD placed over the vulva: a method for diagnosis of fetal lung maturity in cases of premature ruptured membranes.

Four hundred and forty seven pregnant women with ruptured membranes, were prospectively studied in order to assess the diagnostic capacity of Phosphatidylglycerol (PhG) determination in amniotic fluid recovered from vulval pads in the diagnosis of Hyaline Membrane Disease (HMD). The identification of PhG was performed using one dimensional silica gel thin layer chromatography. The sensitivity of PhG determination in the diagnosis of HMD in newborns of the total population was found to be 88.