(R,S)-3,4-dichlorobenzoylalanine (FCE 28833A) causes a large and persistent increase in brain kynurenic acid levels in rats

Kynurenic acid is an endogenous excitatory amino-acid receptor antagonist with neuroprotective and anticonvulsant properties. We demonstrate here that systemic administration of the new and potent kynurenine 3-hydroxylase inhibitor (R,S)-3,4-dichlorobenzoylalanine (FCE 28833A) causes a dose-dependent elevation in endogenous kynurenine and kynurenic acid levels in rat brain tissue. In hippocampal microdialysates, peak increases of 10- and 80-fold above basal kynurenic acid concentrations, respectively, were obtained after a single oral or intraperitoneal administration of 400 mg/kg FCE 28833A. After intraperitoneal treatment with FCE 28833A, extracellular brain kynurenic acid levels remained significantly elevated for at least 22 h, rendering this compound a far more effective enhancer of kynurenic acid levels than the previously described kynurenine 3-hydroxylase blocker m-nitrobenzoylalanine. FCE 28833A and similar molecules may have therapeutic value in diseases which are linked to a hyperfunction of excitatory amino-acid receptors.

Seizure activity causes elevation of endogenous extracellular kynurenic acid in the rat brain

This study was designed to examine the effects of several classic convulsants on the extracellular concentration of the anticonvulsant and neuroprotective brain metabolite kynurenic acid (KYNA) in the rat brain. Drug effects were investigated in vivo, mostly by unilateral microdialysis in the dorsal hippocampus. Systemic administration of pentylenetetrazole (60 mg/kg, SC), pilocarpine (325 mg/kg, SC), bicuculline (6 mg/kg, SC), or kainic acid (10 mg/kg, SC) caused characteristic clonic and/or tonic convulsions. In all seizure paradigms, KYNA levels in the dialysate began to rise within 1 h and gradually reached a plateau approximately 4 h after administration of the convulsants. Peak increases were 1.5-3-fold over basal levels. The duration of the elevation in KYNA levels was significantly prolonged following kainic acid application. In the kainic acid model, extracellular KYNA was also measured and found to be increased in the ventral hippocampus, piriform cortex, and striatum. Moreover, temporary intrahippocampal infusion of the KYN synthesis inhibitor aminooxyacetic acid (1 mM) in the kainic acid- and pentylenetetrazole models attenuated the increase in extracellular KYNA levels, demonstrating that de novo production of KYNA in the brain accounts for the seizure-induced KYNA overflow. A separate group of animals received a unilateral intrahippocampal injection of the endogenous convulsant excitotoxin quinolinic acid (120 nmol) and showed long-lasting (> 24 h) bilateral increases in extracellular KYNA levels. Taken together, these data indicate that an increase in extracellular KYNA may constitute a common occurrence in response to seizures and that KYNA elevations may signify the brain's attempt to counteract seizure activity.

Electrical kindling is associated with a lasting increase in the extracellular levels of kynurenic acid in the rat hippocampus

Endogenous kynurenic acid (KYNA), an excitatory amino acid receptor antagonist with antineurotoxic and anticonvulsant activity, was assessed by microdialysis in the hippocampus of kindled rats. One week after the completion of amygdala or hippocampal kindling (stage 5), the dialysate concentration of KYNA in the hippocampus of both hemispheres was 1.7 +/- 0.1-fold higher than in shams (P < 0.01). Veratridine (50 microM), applied through the probe, reduced extracellular KYNA by 28% within 1 h in controls (P < 0.05), but was ineffective in stage 5 kindled rats. At the preconvulsive stage 2, dialysate KYNA concentration and the effect of veratridine were similar to controls. The activity of KYNA's biosynthetic enzyme, kynurenine aminotransferase, did not change in the hippocampus 1 week after stage 5 seizures. These data indicate an enhanced liberation of KYNA in teh hippocampus of fully kindled animals due to an impairment of normal regulatory mechanisms. This may be of relevance for the control of hippocampal excitability during epileptogenesis.

Alpha-Chain cross-linking in fibrin(ogen) Marburg

The fibrinogen structural variant, Marburg (A alpha 1-460B beta gamma)2, is comprised of normal B beta and gamma chains but contains severely truncated A alpha chains that are missing approximately one half of their factor XIIIa cross-linking domain. Immunochemical studies of fibrin(ogen) Marburg were conducted to characterize the degree to which deletion of a defined A alpha-chain segment, A alpha 461-610, can affect the process of fibrin stabilization, ie, the factor XIIIa-mediated covalent interaction that occurs between alpha chains of neighboring fibrin molecules and between alpha chains and alpha 2 antiplasmin (alpha 2PI). The ability of Marburg (and control) alpha chains to serve as a substrate for factor XIIIa and undergo cross-linking was examined in an in vitro plasma clotting system. The capacity for alpha-chain cross-linking was evaluated both as the covalent incorporation of the small synthetic peptide, NQEQVSPLTLLK (which represents the first 12 amino acids of alpha 2PI and includes the factor XIIIa-sensitive glutamine residue responsible for the cross-linking of alpha 2PI to fibrin), and as the appearance of native (ie, natural), high-molecular-weight, cross-linked alpha-chain species. Antibodies specific for the (A)alpha and gamma/gamma-gamma chains of fibrin(ogen) and for the peptide and its parent protein, alpha 2PI (68 kD), were used as immunoblotting probes to visualize the various cross-linked products formed during in vitro clotting. Recalcification of Marburg plasma in the presence of increasing concentrations of peptide resulted in the formation of peptide-decorated Marburg alpha-chain monomers. Their size at the highest peptide concentration examined indicated the incorporation of a maximum of 3 to 4 mol of peptide per mole of alpha-chain. In the absence of alpha 2PI 1-12 peptide, the alpha chains of Marburg fibrin cross-linked to form oligomers and polymers, as well as heterodimers that included alpha 2PI. Both the peptide-decorated monomers and the native cross-linked alpha-chain species of Marburg fibrin were smaller than their control plasma counterparts, consistent with the truncated structure of the parent Marburg A alpha chain. Collectively, the findings indicate that, although deletion of the A alpha chain region no. 461-610 in fibrinogen Marburg prevents formation of an extensive alpha polymer network (presumably due to the absence of critical COOH-terminal lysine residues), it does not interfere with initial events in the fibrin stabilization process, namely, factor XIII binding and the ability of alpha chains to undergo limited cross-linking to one another and to alpha 2PI.

L-alpha-aminoadipic acid as a regulator of kynurenic acid production in the hippocampus: a microdialysis study in freely moving rats

L-alpha-Aminoadipic acid is a lysine metabolite with neuroexcitatory properties, and has previously been shown to inhibit the production of the broad spectrum excitatory amino acid receptor antagonist kynurenic acid in brain tissue slices. The effects of L-alpha-aminoadipic acid on the levels of extracellular kynurenic acid were now studied by microdialysis in the dorsal hippocampus of freely moving rats. Application of L-alpha-aminoadipic acid through the microdialysis probe dose dependently decreased both the concentration of endogenous kynurenic acid and of kynurenic acid which was produced de novo from its bioprecursor L-kynurenine (500 microM applied through the probe). 500 microM L-alpha-aminoadipic acid lowered the kynurenic acid concentration in the dialysate by 47% and 28% with and without precursor loading, respectively, whereas D-alpha-aminoadipic acid was without effect. Co-administration of 500 microM L-alpha-aminoadipic acid with 50 microM veratridine, which by itself produces a substantial decrease in the levels of extracellular kynurenic acid, did not result in a further reduction in kynurenic acid concentrations. Extensive neuronal degeneration caused by an intrahippocampal injection of quinolinic acid (120 nmol) did not interfere with the effect of L-alpha-aminoadipic acid. Taken together, these data suggest that the effect of L-alpha-aminoadipic acid on extracellular kynurenic acid levels is likely due to its direct action on astrocytes, which are known to harbor kynurenic acid's biosynthetic enzyme, kynurenine aminotransferase. L-alpha-Aminoadipic acid may modulate kynurenic acid function in the brain and thus play a role in the pathogenesis of neurodegenerative and seizure disorders.

The development of assays for the detection of fibrin(ogen)olysis based on COOH-terminal A alpha chain epitopes

The COOH-terminal two-thirds of the fibrinogen A alpha chain is a substrate for both factor XIIIa and plasmin and is, therefore, a source of structural markers for the clinical detection of fibrin(ogen)olysis. Monoclonal antibodies (MoAbs) that bind to epitopes within this region (F-102, A alpha 563-578; F-103, A alpha 259-276) have been applied towards the development of two sensitive and specific enzyme-linked immunosorbent assays (ELISAs). The first assay, a capture (F-102)-tag (F-103) ELISA, measures plasma fibrinogen molecules whose A alpha chains are intact. The second assay, a solution phase competitive ELISA based on MoAb F-102, quantifies circulating COOH-terminal A alpha chain degradation products (A alpha FDPs), among the earliest peptides released from fibrinogen during plasmin-mediated fragment X formation. This assay features a novel preliminary plasma absorption step on concanavalin A to recover A alpha FDPs (if present in the sample) in a milieu free of immunologically cross-reactive fibrinogen. Both ELISAs use highly purified fibrinogen as the assay standard for quantitation. In control plasmas, circulating A alpha FDPs accounted for less than 2% of their respective intact fibrinogen A alpha chain concentration, suggesting a physiologic low level of proteolysis occurring at the extreme COOH-terminal portion of the molecule. Plasma A alpha FDPs were elevated (2.3% to 7.8% of their respective intact fibrinogen A alpha chain concentration) in a group of plasma from patients with documented, high serum FDPs (21 to 41 micrograms/mL). Application of the two ELISAs to characterize the course of A alpha chain proteolysis during thrombolytic therapy (TIMI phase 1) indicated that A alpha FDPs were a very early marker of the lytic state (detectable 15 minutes after treatment had been initiated), and that streptokinase and recombinant tissue plasminogen activator appeared to produce significantly different A alpha chain degradation profiles.

Induction of microsomal and peroxisomal enzymes by dehydroepiandrosterone and its reduced metabolite in rats

Dehydroepiandrosterone (DHEA) given to rodents in pharmacological doses induces several hepatic enzymes including cytochromes P4504A, NADPH:P450 oxidoreductase, palmitoyl coenzyme A oxidase, and other enzymes associated with the peroxisomal beta-oxidation pathway, leading to peroxisome proliferation and development of hepatocellular carcinoma in rodents. Comparison of the inductive potency of DHEA and other intermediates of the steroid biosynthetic path demonstrated that only DHEA, 5-ene-androstene-3 beta,17 beta-diol (ADIOL), and to a lesser extent, 17 alpha-hydroxypregnenolone, a precursor of DHEA, induce cytochromes P4504A protein and other enzymes associated with the peroxisome proliferative response in vivo. ADIOL exerted its inductive response at a somewhat lower dosage than DHEA, whereas ADIOL and DHEA both induced the microsomal enzymes (P4504A and its oxidoreductase) at somewhat lower dosages than those required to induce peroxisomal enzymes. Northern analysis demonstrated increases in the mRNAs encoding the cytochromes P4504A (> 20-fold) and NADPH:P450 oxidoreductase (> 10-fold) in the livers of DHEA- and ADIOL-treated rats. Run-on transcription analysis demonstrated that DHEA induces CYP4A gene expression 11-fold at the level of transcription initiation. Comparison of the responsiveness of individual rat CYP4A genes (4A1, 4A2, and 4A3) to DHEA and ADIOL in immature versus mature male rats revealed 2-3-fold higher levels of induced CYP4A1 and 4A3 mRNAs in immature rat livers. In contrast, hepatic CYP4A2 mRNA was induced to 6-10-fold higher levels in mature rats. No basal or significant inducible expression of mRNA for CYP4A1 and 4A3 was noted in rat kidney. Significant basal levels of kidney CYP4A2 mRNA were observed only in mature animals, where they were inducible by ADIOL and DHEA to a 3-5-fold greater extent than in the kidneys of immature rats. These studies demonstrate developmental differences in the responsiveness of CYP4A mRNA levels to DHEA and ADIOL in rat kidney and liver. Moreover, the striking inducibility of CYP4A protein and mRNAs, together with the increased rates of synthesis of nascent CYP4A mRNA transcripts in hepatic nuclei from DHEA-treated rats, establish that DHEA increases the expression of these microsomal enzymes at the transcriptional level.

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 (0.5-10 microM) produced a concentration-dependent increase in the firing rate of SNc DA neurons but had no effect on firing pattern. The highest concentration of both agonists produced a rapid and reversible cessation of activity that was attributed to acute induction of depolarization block. Addition of glycine (GLY) (up to 100 microM) to the bathing solution had no effect on either basal firing rate or the increase in activity produced by NMDA. KYNA (10 microM-1 mM) antagonized the excitatory effects of both NMDA (15 microM) and AMPA (3 microM) in a concentration-dependent fashion (IC50:102 microM and 64 microM, respectively) without affecting basal firing rate. Perfusion of tissue slices with a modified Ringer's solution containing low Mg2+ (0.12 mM) increased NMDA-induced excitation but did not affect the antagonist properties of KYNA. D-serine (100 microM) reversed the ability of KYNA to block the excitatory effects of NMDA, suggesting that KYNA attenuates NMDA-induced excitation of SNc DA neurons via blockade of the GLY allosteric site on the NMDA receptor. The ability of KYNA to modulate the excitatory effects of both NMDA and non-NMDA agonists implies that endogenous KYNA may play a physiological role in regulating DA cell excitability.

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. After 3 h, 4-chloro-3-hydroxyanthranilic acid (3 microM-3 mM) was included in the perfusion medium, and dialysis was continued for another 3 h. The drug caused dose-dependent inhibition of QUIN neosynthesis, with an apparent IC50 value of 32 microM. Discontinuation of drug administration, with continued perfusion of 3-hydroxyanthranilic acid, revealed that the drug effect was reversible. Intravenous application of 4-chloro-3-hydroxyanthranilic acid (14 mg/kg) resulted in a significant decrease in extracellular QUIN, reaching a nadir of 67% of saline-treated controls after 3 h. The data indicate that both intracerebral and systemic administration of 4-chloro-3-hydroxyanthranilic acid effectively interferes with QUIN production in the rat brain. The results suggest that QUIN synthesis inhibitors such as 4-chloro-3-hydroxyanthranilic acid may become of value in brain diseases that are caused by hyperphysiological quantities of QUIN.

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. In contrast, a lesion caused by 240 nmol of GAG resulted in a significant reduction in 3H-MK-801 binding, which was used as a marker for NMDA receptor-bearing hippocampal neurons. GAG-induced lesions were blocked by the NMDA receptor antagonists MK-801 and AP7 but were not influenced by the nature of the anesthetic used during surgery. Iontophoretic application of GAG did not excite CA1/CA3 cells in the rat hippocampus. In vitro, GAG proved to be a relatively potent inhibitor (IC50: 43 microM) of kynurenine aminotransferase, the biosynthetic enzyme of the endogenous neuroprotectant kynurenic acid. GAG also inhibited the neosynthesis of kynurenic acid in hippocampal slices (IC50: 790 microM). Thus, GAG shares several characteristics of the recently described indirect excitotoxin aminooxyacetic acid (AOAA; Exp. Neurol. 113: 378, 1991). GAG and AOAA appear to belong to a new family of excitotoxic agents which produce lesions indirectly by metabolic derangement and/or inhibition of kynurenate production.

Effect of dizocilpine maleate on cerebral anoxia and ischemic damage in rodents

The Protective effects of dizocilpine maleate (DM) against anoxia in mice and ischemic damage in rats of 4-vessel occlusion (4-VO) were studied. DM 0.5 or 1.0 mg.kg-1 ip significantly prolonged the survival time of mice in closed containers. DM 0.5 and 1.0 mg.kg-1 ip 30 min prior to 4-VO obviously accelerated the electroencephalographic recovery, reduced the neuronal loss in the hippocampus, and increased the survival rate after 72-h reperfusion. These effects followed a dose-dependent manner. Our results indicate that selective non-competitive N-methyl-D-aspartate receptor blocker DM protects against anoxic and ischemic cerebral damage.

Effect of dizocilpine maleate on monoamines and their metabolites in rat brain

Systemic (ip) injection of dizocilpine maleate (DM, 0.1 and 0.5 mg.kg-1) increased the levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid but did not bring about any noticeable change in the dopamine (DA) level in the striatum and limbic area. DM also increased the levels of norepinephrine in the limbic area and 5-hydroxyindoleacetic acid in the hippocampus. Amphetamine increased DA level and reduced DOPAC level in the striatum and limbic area. The behavioral manifestations revealed that DM predominantly evoked circling behavior and ataxia. The results indicate that the mechanism of the behavioral effect of DM may be different from that of amphetamine.

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. These steady state levels were more than doubled in gliotic quinolinate-lesioned tissue. The non-specific inhibitor of kynurenine aminotransferase, aminooxyacetic acid (300 microM), and the depolarizing agent veratridine (50 microM), introduced through the dialysis membrane, caused a 69 and 57% decrease, respectively, in extracellular kynurenic acid. The effect of veratridine was rapidly reversible and was blocked by 5 microM tetrodotoxin or in the quinolinate-lesioned hippocampus. In contrast, the effect of aminooxyacetic acid was longer lasting upon drug discontinuation, and was not reversed by tetrodotoxin or in lesioned tissue. These data demonstrate that hippocampal kynurenic acid can be regulated by direct interference with its biosynthetic enzyme and by a distinct process involving neuron-glia interactions.

Systemic kainic acid administration in rats: effects on kynurenic acid production in vitro and in vivo

The endogenous broad spectrum excitatory amino acid receptor antagonist kynurenic acid (KYNA) has anti-convulsant properties and has been hypothetically linked to the pathogenesis of seizure disorders. Using brain slices and in vivo microdialysis in unanesthetized rats, KYNA synthesis from its bioprecursor kynurenine was therefore examined in the kainate model of temporal lobe epilepsy. Tissue slices obtained during status epilepticus from animals injected with kainate (10 mg/kg, sc) did not show changes in KYNA production. One month after kainate injection, KYNA synthesis was substantially increased in slices of piriform cortex (380% of control) and hippocampus (227% of control) but not in striatal slices. Since KYNA production takes place preferentially in glia, these increases are likely to be due to the selective neuronal loss and reactive astrogliosis known to exist in chronically kainate-lesioned brains. Microdialysis, performed in the piriform cortex only, confirmed the in vitro results. Thus, no change in extracellular KYNA concentration was detected within 4 h after systemic kainate administration but a significant increase was observed 1 month later. Moreover, the veratridine-induced decrease in KYNA production detectable in normal tissue was not observed in the neuron-depleted piriform cortex. The data are discussed with regard to a possible role of glia-derived KYNA in temporal lobe epilepsy.

Effect of intrahippocampal quinolinic acid infusion on the amygdala kindling in rat

The effect of intrahippocampal infusion of quinolinic acid (Quin), an endogenous excitatory amino acid, was studied on the amygdala kindling. Quin 120 nmol injected intrahippocampally 2 wk prior to the beginning of amygdala kindling significantly not only produced dorsal hippocampal pyramidal and granule cell loss but also decreased the number of stimuli to trigger the stage 5 seizures of amygdala kindling. In kindled rats, intrahippocampal 20 nmol Quin infusion fully inhibited the stage 5 of amygdala-kindled seizures. The inhibitory effect of Quin was antagonized by dl-2-amino-7-phosphonoheptanoic acid, a selective antagonist of N-methyl-D-aspartate (NMDA) type receptors. The results suggest that NMDA-type receptors in the hippocampus may play a role in the control of the seizure threshold in the amygdala.

Determination of extracellular kynurenic acid in the striatum of unanesthetized rats: effect of aminooxyacetic acid

Kynurenic acid (KYNA) production from its bioprecursor L-kynurenine (KYN) was assessed in vivo by intrastriatal microdialysis in freely moving rats. In the absence of KYN, the extracellular concentration of KYNA was below the limit of assay sensitivity (i.e. less than 8 pmol/30 microliters). In the presence of KYN (50-2000 microM), KYNA concentration in the dialysate increased continuously to reach steady-state levels after 2h of perfusion. Introduction of the unspecific transaminase inhibitor aminooxyacetic acid (AOAA) through the dialysis probe caused a progressive decrease of extracellular KYNA, which reached dose-dependent minimal levels within 2 h. One mM AOAA caused an almost complete depletion of KYNA in the dialysate. These data demonstrate that extracellular KYNA can be assessed by microdialysis and that AOAA can be used as a tool to examine the neurobiology of KYNA in awake, freely moving animals.

Modulation of neuronal activity of locus coeruleus in rats induced by excitatory amino acids

The excitatory actions on the unit activities of locus coeruleus induced by excitatory amino acids were studied. Quinolinic acid 10 nmol and N-methyl-D-aspartate (NMDA) 4 nmol icv markedly increased unit discharge of locus coeruleus neurons. The excitatory action was fully antagonized by icv 4 nmol D,L-2-amino-7-phosphonoheptanoic acid, a specific NMDA receptor antagonist. Excitatory effect induced by quinolinic acid is possibly mediated by excitatory amino acid receptors in locus coeruleus.

Studies on the potential neurotoxic and convulsant effects of increased blood levels of quinolinic acid in rats with altered blood-brain barrier permeability

Intravenous injection of 450 mg/kg quinolinic acid (Quin), an endogenous kynurenine metabolite with excitotoxic properties, induced only minor electroencephalographic (EEG) modifications and no neurotoxicity in rats with a mature blood-brain barrier (BBB). BBB permeability was altered in rats by focal unilateral irradiation of the cortex (7 mm in diameter and 5 mm in depth) with protons (60 Gy, 9 Gy/min). Three days after irradiation, Evans blue dye staining showed BBB breakdown in the dorsal hippocampus of the irradiated hemisphere. No neurotoxic or convulsant effects were observed as a consequence of the radiation itself. When BBB-lesioned rats were challenged with 225 mg/kg Quin iv, epileptiform activity was observed on EEG analysis. Tonic-clonic seizures were induced by 225-450 mg/kg Quin. Light microscopic analysis showed a dose-related excitotoxic type of lesion restricted to the hippocampus ipsilateral to the irradiated side. Neuro-degeneration was prevented by local injection of 120 nmol D(-)2-amino-7-phosphonoheptanoic acid, a selective N-methyl-D-aspartate receptor antagonist. No lesions or EEG or behavioral modifications occurred after 450 mg/kg nicotinic acid, an inactive analog of Quin. The potential neurotoxic and convulsant effects of increased blood levels of Quin under conditions of altered BBB permeability are discussed.

Stimulation of [3H]norepinephrine release from hippocampal slices by excitatory amino acids

[3H]norepinephrine efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids (EAA) in the following potency order: N-methyl-D-aspartic acid (NMDA) greater than kainic acid greater than L-glutamic acid greater than or equal to D,L-homocysteic acid greater than L-aspartic acid greater than quinolinic acid greater than quisqualic acid. The effect of EAA was blocked by physiological concentration of Mg2+, with the exception of kainic acid. D,L-2-amino-7-phosphonoheptanoic acid (APH) dose-dependently inhibited NMDA effect (IC50 = 69 mumol/L), whereas at 1 mmol/L it was ineffective versus kainic acid. The release of [3H]norepinephrine induced by quinolinic acid was blocked by APH 0.1 mmol/L. gamma-D-glutamylglycine dose-dependently inhibited kainic acid effect with an IC50 = 1.15 mmol/L. Tetrodotoxin 2 mumol/L reduced NMDA and kainic acid effects by 40 and 20%, respectively. The data indicate a possible involvement of central noradrenergic system in the modulation of excitotoxic action of EAA and offer a reliable system for testing new compounds acting at EAA-receptors by measuring norepinephrine release in vitro.

Induction of microsomal NADPH-cytochrome P-450 reductase and cytochrome P-450IVA1 (P-450LA omega) by dehydroepiandrosterone in rats: a possible peroxisomal proliferator

Dehydroepiandrosterone (DHEA) is a naturally occurring C19-steroid that is found in the peripheral circulation of mammals, including humans. The feeding of DHEA to rodents has been shown to inhibit chemical carcinogenesis in colon, liver, and lung. Therefore, the effect of DHEA on hepatic enzyme activities that are associated with carcinogen metabolism was assessed. Microsomal NADPH-cytochrome P-450 reductase activity and the content of cytochrome b5 were induced 1.8- and 1.4-fold, respectively, upon feeding male Sprague-Dawley rats a synthetic diet containing 0.45% DHEA (w/w). No significant changes in total content of microsomal cytochrome P-450 or the activities of microsomal NADH-cytochrome b5 reductase and cytosolic or microsomal NAD(P)H-quinone oxidoreductase were noted at day 7 of feeding. Cytosolic glutathione S-transferase activity was decreased to 68% of control activity. Administration of DHEA p.o. or by i.p. injection for 5 days led to the same extent of induction of NADPH-cytochrome P-450 reductase activity. Maximal induction of this flavoprotein reductase was noted between days 3 and 4 of feeding or at a dose of 80-120 mg/kg i.p. A small but statistically significant increase in total microsomal cytochrome P-450 was observed after DHEA administration i.p. Rats fed DHEA had a slower growth rate compared with rats fed control diet, whereas rats treated with DHEA i.p. had growth rates identical to those of controls. The liver weights of rats given DHEA by p.o. or i.p. routes were increased significantly compared to those of control rats. Pair feeding of rats with DHA-containing or control diets served to demonstrate that the levels of induction of hepatic microsomal NADPH-cytochrome P-450 reductase and at least one form of cytochrome P450 (P-450IVA1) were the same as those seen in livers of rats fed DHEA ad libitum. This finding suggested that the induction of the flavoprotein and at least one form of the cytochrome was not due to caloric restriction. The increase in NADPH-cytochrome P-450 reductase content of liver microsomes prepared from rats either fed or treated i.p. with DHEA was also observed by Western blotting techniques. DHEA did not appear to induce any of the major forms of rat liver microsomal cytochrome P-450 that are normally increased by either phenobarbital, beta-naphthoflavone, or dexamethasone pretreatment of rats in vivo. However, the measurement of androstenedione and testosterone metabolism in vitro showed pronounced decreases in the 16 alpha-hydroxylase activities of liver microsomes following DHEA feeding.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicological studies on the organophosphorous insecticide methyl-ISP

Methyl-ISP, a newly developed organophosphorous insecticide, is used in China to treat and protect plants from pest infestation. Our studies demonstrated that methyl-ISP is metabolized rapidly in rat and mouse. Its toxicity was low, no obvious accumulative toxicity, chronic toxicity, teratogenicity, mutagenicity, reproductive toxicity or delayed neurotoxicity could be observed. It is therefore concluded that methyl-ISP is relatively safe to animals and human subjects. methyl-ISP is now employed to replace the other commonly used insecticide hexachlorobenzene (666) in agriculture. A preliminary study was performed to elucidate the mechanism of intoxication at subcellular levels.