Tryptophan intake is related to a lower prevalence of depressive symptoms during pregnancy in Japan: baseline data from the Kyushu Okinawa Maternal and Child Health Study

OBJECTIVE

Tryptophan is an essential amino acid wholly derived from diet. While the majority of tryptophan is degraded through the kynurenine pathway into neuroactive metabolites like quinolinic acid and kynurenic acid, a small proportion of ingested tryptophan is metabolized into the neurotransmitter serotonin. The current cross-sectional study in Japan examined the association between tryptophan intake and depressive symptoms during pregnancy.

METHODS

Study subjects were 1744 pregnant women. Dietary intake during the preceding month was assessed using a self-administered diet history questionnaire. Depressive symptoms were defined as a score ≥ 16 on the Center for Epidemiologic Studies Depression Scale. Adjustment was made for age, gestation, region of residence, number of children, family structure, history of depression, family history of depression, smoking, secondhand smoke exposure at home and at work, employment, household income, education, body mass index, and intake of saturated fatty acids, eicosapentaenoic acid plus docosahexaenoic acid, calcium, vitamin D, and isoflavones.

RESULTS

The prevalence of depressive symptoms during pregnancy was 19.2%. After adjustment for confounding factors, higher tryptophan intake was independently inversely associated with the prevalence of depressive symptoms during pregnancy: the adjusted prevalence ratios (95% confidence intervals) for depressive symptoms during pregnancy in the first, second, third, and fourth quartiles of tryptophan intake were 1 (reference), 0.99 (0.76-1.28), 0.94 (0.71-1.25), and 0.64 (0.44-0.93), respectively (p for trend = 0.04).

CONCLUSIONS

Higher estimated tryptophan intake was cross-sectionally independently associated with a lower prevalence of depressive symptoms during pregnancy in Japanese women.

Quinolinate dehydrogenase and 6-hydroxyquinolinate decarboxylase involved in the conversion of quinolinic acid to 6-hydroxypicolinic acid by Alcaligenes sp. strain UK21

In the conversion of quinolinic acid to 6-hydroxypicolinic acid by whole cells of Alcaligenes sp. strain UK21, the enzyme reactions involved in the hydroxylation and decarboxylation of quinolinic acid were examined. Quinolinate dehydrogenase, which catalyzes the first step, the hydroxylation of quinolinic acid, was solubilized from a membrane fraction, partially purified, and characterized. The enzyme catalyzed the incorporation of oxygen atoms of H(2)O into the hydroxyl group. The dehydrogenase hydroxylated quinolinic acid and pyrazine-2,3-dicarboxylic acid to form 6-hydroxyquinolinic acid and 5-hydroxypyrazine-2,3-dicarboxylic acid, respectively. Phenazine methosulfate was the preferred electron acceptor for quinolinate dehydrogenase. 6-Hydroxyquinolinate decarboxylase, catalyzing the nonoxidative decarboxylation of 6-hydroxyquinolinic acid, was purified to homogeneity and characterized. The purified enzyme had a molecular mass of approximately 221 kDa and consisted of six identical subunits. The decarboxylase specifically catalyzed the decarboxylation of 6-hydroxyquinolinic acid to 6-hydroxypicolinic acid, without any co-factors. The N-terminal amino acid sequence was homologous with those of bacterial 4,5-dihydroxyphthalate decarboxylases.

Molecular mode of inhibition of glycogenolysis in rat liver by the dihydropyridine derivative, BAY R3401: inhibition and inactivation of glycogen phosphorylase by an activated metabolite

The racemic prodrug BAY R3401 suppresses hepatic glycogenolysis. BAY W1807, the active metabolite of BAY R3401, inhibits muscle glycogen phosphorylase a and b. We investigated whether BAY R3401 reduces hepatic glycogenolysis by allosteric inhibition or by phosphatase-catalyzed inactivation of phosphorylase. In gel-filtered liver extracts, racemic BAY U6751 (containing active BAY W1807) was tested for inhibition of phosphorylase in the glycogenolytic (in which only phosphorylase a is active) and glycogen-synthetic (for the evaluation of a:b ratios) directions. Phosphorylase inactivation by endogenous phosphatase was also studied. In liver extracts, BAY U6751 (0.9-36 micromol/l) inhibited glycogen synthesis by phosphorylase b (notwithstanding the inclusion of AMP), but not by phosphorylase a. Inhibition of phosphorylase-a-catalyzed glycogenolysis was partially relieved by AMP (500 micromol/l). BAY U6751 facilitated phosphorylase-a dephosphorylation. Isolated hepatocytes and perfused livers were tested for BAY R3401-induced changes in phosphorylase-a:b ratios and glycogenolytic output. Though ineffective in extracts, BAY R3401 (0.25 micromol/l-0.5 mmol/l) promoted phosphorylase-a dephosphorylation in hepatocytes. In perfused livers exposed to dibutyryl cAMP (100 micromol/l) for maximal activation of phosphorylase, BAY R3401 (125 micromol/l) inactivated phosphorylase by 63% but glucose output dropped by 83%. Inhibition of glycogenolysis suppressed glucose-6-phosphate (G6P) levels. Activation of glycogen synthase after phosphorylase inactivation depended on the maintenance of G6P levels by supplementing glucose (50 mmol/l). We conclude that the metabolites of BAY R3401 suppress hepatic glycogenolysis by allosteric inhibition and by the dephosphorylation of phosphorylase a.

The structure of glycogen phosphorylase b with an alkyldihydropyridine-dicarboxylic acid compound, a novel and potent inhibitor

BACKGROUND

In muscle and liver, glycogen concentrations are regulated by the reciprocal activities of glycogen phosphorylase (GP) and glycogen synthase. An alkyl-dihydropyridine-dicarboxylic acid has been found to be a potent inhibitor of GP, and as such has potential to contribute to the regulation of glycogen metabolism in the non-insulin-dependent diabetes diseased state. The inhibitor has no structural similarity to the natural regulators of GP. We have carried out structural studies in order to elucidate the mechanism of inhibition.

RESULTS

Kinetic studies with rabbit muscle glycogen phosphorylase b (GPb) show that the compound (-)(S)-3-isopropyl 4-(2-chlorophenyl)-1,4-dihydro-1-ethyl-2-methyl-pyridine-3,5, 6-tricarboxylate (Bay W1807) has a Ki = 1.6 nM and is a competitive inhibitor with respect to AMP. The structure of the cocrystallised GPb-W1807 complex has been determined at 100K to 2.3 A resolution and refined to an R factor of 0.198 (Rfree = 0.287). W1807 binds at the GPb allosteric effector site, the site which binds AMP, glucose-6-phosphate and a number of other phosphorylated ligands, and induces conformational changes that are characteristic of those observed with the naturally occurring allosteric inhibitor, glucose-6-phosphate. The dihydropyridine-5,6-dicarboxylate groups mimic the phosphate group of ligands that bind to the allosteric site and contact three arginine residues.

CONCLUSIONS

The high affinity of W1807 for GP appears to arise from the numerous nonpolar interactions made between the ligand and the protein. Its potency as an inhibitor results from the induced conformational changes that lock the enzyme in a conformation known as the T' state. Allosteric enzymes, such as GP, offer a new strategy for structure-based drug design in which the allosteric site can be exploited. The results reported here may have important implications in the design of new therapeutic compounds.

Macrophage Activation Factors in the Brains of AIDS Patients

HIV, soluble HLA class I (sHLA-I), quinolinic acid (QUIN), and the monokines IL-1β, IL-6, and TNF-α were measured by ELISA and PCR in brain tissue of 60 AIDS autopsies without evidence of CNS opportunistic infections. Individual cases showed good interrogational correlations for the factors measured. There was a positive correlation between concentrations of IL-1β and IL-6. Brain viral burden correlated with intraparenchymal levels of sHLA-I, IL-1β, and IL-6. Comparison of neuritic damage and levels of immune mediators implicates macrophage activation factors in the etiology of neurologic damage in AIDS.

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.

Differential effects of excitotoxic basolateral and corticomedial lesions of the amygdala on the behavioural and endocrine responses to either sexual or aggression-promoting stimuli in the male rat

The effects of discrete excitotoxic lesions of the basolateral (BL) and corticomedial (CM) amygdaloid areas on both male rat sexual behaviour and inter-male agonistic behaviour were investigated. The effects of the same lesions on the hormonal responses (luteinising hormone (LH) following sexual behaviour, corticosterone following aggressive interactions) which accompany these behavioural responses were measured. Basolateral lesions had no effect on male sexual behaviour but significantly reduced the level of aggressive inter-male behaviour. However, the increase in plasma corticosterone concentration which occurs after such an interaction was not affected by basolateral lesions. In contrast, corticomedial lesions did not affect inter-male offence but severely affected copulatory behaviour, including a significant decrease in the males' investigation of the receptive female. However, the increase in plasma LH concentrations induced by the presence of a receptive female was not affected by the CM lesion. These results demonstrate a dissociation between the two amygdaloid regions with respect to the contributions made to the two social behaviours under study. This anatomical division may reflect differential amygdaloid sensory control of these behaviours. A further dissociation between amygdaloid contribution to behavioural and hormonal responses was also revealed. Neither hormonal response showed a parallel decline with the relevant behavioural response, suggesting that neither the basolateral nor corticomedial amygdaloid complex is responsible for coordinating behavioural and endocrine responses to a specific stimulus.

[The action of 3-indolepyruvate in quinolinate-induced convulsions in mice]

The experiments on 286 mice of two lines (SHR and C57BL/6) showed that 3-indoipyruvate, a natural keto analogue of tryptophan and a precursor of serotonin and kynurenic acid) possesses the selective dose-dependent (100-500 mg/kg, intraperitoneally) protective effect against quinolinate-induced convulsions. At prolonged administration (50-100 mg/kg for 10 days twice a day) its efficiency drastically increased. It is supposed that the mechanism of the anticonvulsant action of 3-indolpyruvate involves an enhancement of synthesis of kynurenic acid, a blocker of N-methyl-D-aspartate receptors, and at chronic administration--also an increase of sensitivity and density of these receptors.

Effects of l-daurisoline on quinolinic acid-induced Ca2+ influx in hippocampus neurons in freely moving rats

In freely moving rats, hippocampus neuronal extracellular calcium concentration (Ca2+)e and seizures were investigated. Application of quinolinic acid 156 nmol (exciting N-methyl-D-aspartate receptor, NMDA) to dorsal hippocampus elicited a decrease in (Ca2+)e by 48 +/- 5% in the infusion area and produced a characteristic abnormal EEG. l-Daurisoline dramatically prevented the reduction in (Ca2+)e, but not seizures (EEG). The results suggest that NMDA-operated calcium channels, but not NMDA-receptors, are involved in the effects of l-daurisoline on Ca2+ influx observed.

A comparison of excitotoxic lesions of the basal forebrain by kainate, quinolinate, ibotenate, N-methyl-D-aspartate or quisqualate, and the effects on toxicity of 2-amino-5-phosphonovaleric acid and kynurenic acid in the rat

1. It has been suggested that an NMDA1 receptor subtype might be activated by N-methyl-D-aspartate (NMDA) and ibotenate and an NMDA2 subtype by NMDA or quinolinate, and that the NMDA2 site might be more susceptible to blockade by kynurenic acid. 2. Experiments were carried out to examine the ability of 2-amino-5-phosphonovaleric acid (AP5) and kynurenic acid to antagonize the neurotoxic properties of kainate, ibotenate, NMDA, quinolinate and quisqualate injected into the rat basal forebrain. 3. Following histological analysis of the injection sites, lesion volume was assessed parametrically. Each of the toxins except quisqualate was found to make lesions of parvocellular neurones within the basal forebrain with a relative order of potency: kainate much greater than quinolinate greater than ibotenate = NMDA. 4. Equimolar doses of AP5 abolished the toxicity produced by quinolinate and NMDA; toxicity to kainate and ibotenate was attenuated to approximately 40% of the toxin-alone condition. 5. The antagonistic properties of kynurenate were dose-dependent: equimolar kynurenate had no effect on quinolinate but attenuated the actions of ibotenate, kainate and NMDA; 2 x equimolar kynurenate had no effect on quinolinate or ibotenate but attenuated the toxicity of kainate and NMDA; and 3 x equimolar kynurenate had no effect on the toxicity of kainate or ibotenate, attenuated the actions of NMDA and abolished the toxic action of quinolinate. 6. The results are discussed in terms of the actions of the various toxins at different receptors, differentially sensitive to AP5 and kynurenate.

In vivo incorporation of N-acetyl-D-[U-14C]mannosamine into brain gangliosides of rats with quinolinic acid-induced lesions of the forebrain nucleus basalis magnocellularis

Quinolinic acid, an excitotoxic agent, was applied unilaterally to the nucleus basalis magnocellularis of the rat forebrain, which resulted in neuronal destructions and consequently, loss of cholinergic projections to the cortex. The effects on ganglioside metabolism in brain cortical matter were studied. Total ganglioside contents in lesioned brains (n = 8) were found to be significantly decreased (range, 20-60%) but changes in brain ganglioside patterns on thin layer chromatograms were not apparent. On the other hand, in vivo incorporation of N-acetyl-D-[U-14C]mannosamine into brain gangliosides ranged from 19 to 36% (mean, 26%) of radiolabel in controls, and 5 to 21% (mean, 13%), a significant reduction in lesioned brains. Labeling of brain glycoproteins or of nonganglioside lipids was not affected. Since central cholinergic hypofunctions are also important neurochemical characteristics of Alzheimer's disease, abnormal ganglioside metabolism found in the lesioned rats may be of significance in the human disorder, where reduced brain ganglioside contents have also been reported.

Neural grafts and pharmacological intervention in a model of Huntington's disease

Using the excitotoxic animal model of Huntington's disease, two experimental treatments were evaluated. The first experiment explored the effect of MK801 (a systemically active anticonvulsant, and noncompetitive NMDA antagonist) pretreatment on quinolinic acid (QA)-induced striatal degeneration and behavioral deficits. MK801 prevented QA-induced neuropathological changes in the striatum and the anatomical protection was correlated with the absence of deficits in the cataleptic response to haloperidol. The second experiment tested the ability of three types of fetal grafts to reverse behavioral deficits induced by kainic acid (KA) lesion. Fetal (E15-16) striatal, cortical and tectal grafts were delivered into the KA-lesioned striatum one week or one month after lesion. Animals in this experiment were evaluated on a motor coordination task, haloperidol-induced catalepsy and amphetamine-induced locomotor activity. Striatal grafts attenuated the deficits induced by KA in all of the tasks observed, and no effect of time of grafting was detected. Tectal grafts had a partial beneficial effect, attenuating the decrease in the cataleptic response to haloperidol observed after KA lesions. No effect of time of grafting was detected for these grafts. In contrast, a clear effect of time of grafting was detected for the cortical grafts. Early cortical grafts reversed the exaggerated response to amphetamine observed after KA lesions whereas late cortical grafts resulted in sham-like scores on the catalepsy test. Histochemical analysis showed that most of the grafts survived, had acetylcholinesterase (AChE) positive fibers and cell bodies, and were metabolically active as indicated by cytochrome oxidase (CO) positive staining. It is suggested that striatal grafts may have restored to some extent the striatal GABAergic control over output structures, and that trophic factors play a role in behavioral recovery as is evident from the beneficial effects of the tectal grafts. Although the mechanisms underlying the differential effects observed after early or late cortical grafts are unknown, the interaction between the cellular components and trophic factors present in the cortical grafts and the condition of the lesioned host at the time of grafting may yield a host-graft complex with a unique profile.

Effect of catecholaminergic drugs on quinolinate- and kynurenine-induced seizures in mice

Administration of reserpine, trifluperidol, chlorpromazine, haloperidol, spiroperidol, and thioproperazine to adult mice shortened the latency and increased the number of animals with clonic seizures induced by 1-kynurenine sulfate or its metabolite quinolinic acid. Haloperidol dose-dependently intensified kynurenine-induced seizures and did not alter pentylenetetrazole seizures. Dopamine abolished the effect of haloperidol while serotonin was ineffective. Pretreatment with 6-hydroxydopamine potentiated kynurenine-induced seizures, but not quinolinic acid-induced seizures. The seizure thresholds of kynurenine and quinolinic acid were not affected by pretreatments with yohimbine, clonidine, piperoxan, phentolamine and tricyclic antidepressants. Apomorphine and amphetamine (i.p.), noradrenaline and adrenaline (i.c.v.) possess anticonvulsant action against kynurenine and not against quinolinic acid. The data obtained suggest a similarity of kynurenine and known convulsants in the involvement of the catecholaminergic processes in their convulsant action. Quinolinic acid markedly differs from kynurenine in its mechanism of action as indicated by their interactions with numerous endogenous substances.

The quinolinic acid model of Huntington's disease: locomotor abnormalities

In contrast to other excitotoxins, such as kainic acid, quinolinic acid (QA) may spare a specific population of striatal neurons that is also spared in Huntington's disease (HD). Although several histological and biochemical experiments support the use of QA as a model for HD, to date no behavioral experiments have been performed to examine the suitability of this model. The present study explored the behavioral effects of bilateral intrastriatal microinjections of four doses (75, 150, 225, 300 nmol) of QA in the male rat. Using a multidimensional analysis of spontaneous locomotion (Digiscan activity) and a record of metabolic indicators, such as weight loss, a dose-dependent effect was found. The 75-nmol dose had no significant effect on locomotion or feeding behavior. In contrast, the 150- and 225-nmol doses induced hyperactivity and weight loss, whereas the 300-nmol dose was lethal. The results obtained suggest that striatal injections of 150-225 nmol of QA induce behavioral deficits qualitatively similar though quantitatively less than those which are seen after similar injection of 3 nmol of kainic acid and which have been reported to be comparable to the symptomatology of HD. Together with QA's possible greater histological selectivity, the present results support the use of QA-induced striatal lesions as a behavioral model of Huntington's disease.

Amino acid neurotransmitter abnormalities in Huntington's disease and the quinolinic acid animal model of Huntington's disease

Concentrations of gamma-aminobutyric acid (GABA), glutamate, aspartate, and taurine were measured in postmortem tissue from the brains of patients with Huntington's disease (HD) and in the quinolinic acid (QA) lesioned rat striatum. The aim of the study was to assess further the ability of the QA model of HD to reproduce the neurochemical features of the disease. Nine cortical and 9 subcortical regions were examined from 17 pathologically graded cases of HD and 10 controls. Significant reductions in both GABA and glutamate were found in HD striatum. The reductions were greater in the more severely affected grades of HD, and there was a gradient of amino acid loss across the striatal nuclei (caudate greater than putamen greater than nucleus accumbens) which was consistent with the known pattern of pathological involvement. Taurine and aspartate concentrations showed no significant change. GABA reductions were found in both segments of the globus pallidus (external greater than internal) and both parts of the substantia nigra (reticulata greater than compacta). In advanced cases of HD, there were significant reductions in glutamate in Brodmann cortical areas 3-1-2, 6, 9, and 17, but GABA, aspartate, and taurine were unaltered in the cortex. The QA lesions reproduced the striatal deficits of both GABA and glutamate but, in contrast to HD, there was a decrease in taurine, possibly due to species differences. Chronic QA lesions resulted in a secondary dying back of corticostriatal glutamatergic terminals, but did not produce a change in cortical glutamate concentration. This suggests that reductions in cortical glutamate in HD may reflect a primary loss of glutamatergic neurons. Our findings extend previous observations on amino acid neurotransmitters in HD and, with the exception of taurine, confirm the general applicability of the QA model.

The compensatory role of the parvocellular division of the red nucleus in operantly conditioned rats

To assess the role of the parvocellular division of the red nucleus in motor control, rats were operantly conditioned to walk on a rotating bar and their red nuclei were lesioned with the fiber sparing agent, quinolinic acid. Since both parvocellular and magnocellular divisions of the red nucleus overlap in the rat, they both became involved in this lesion. To differentiate between them, two paradigms were used. (1) Prior to the lesion, the magnocellular division was dysfunctioned by transecting its spinal output, namely, the rubrospinal tract, in the dorso-lateral funiculus (DLF) of the spinal cord. After compensation for this transection had occurred in a few days, the red nucleus was lesioned with quinolinic acid. Rats again compensated rapidly, suggesting that the remaining red nuclear outflow systems, such as the rubro-olivary tract, play no detectable role in the control of on-going movements. (2) In the second paradigm, the red nucleus was lesioned without a preceding DLF transection. This lesion involved both the rubro-bulbar and rubro-spinal projections. Rats did not compensate, or did so very slowly. For compensation to occur, therefore, rubro-bulbar projections need to be intact. This suggests that such projections, that include the rubro-olivary tract, play a role in the compensation for DLF transections.

Striatal lesions and transplants demonstrate that cholecystokinin receptors are localized on intrinsic striatal neurones: a quantitative autoradiographic study

Considerable evidence supports the existence of modulatory interactions between cholecystokinin and dopamine in the striatum. In order to explore further the nature of such interactions, the anatomical localization of CCK receptors in rat striatum was investigated autoradiographically following selective lesions. Infusion of 6-hydroxydopamine into the medial forebrain bundle had no effect on striatal CCK receptor content. In contrast, destruction of striatal cell bodies with ibotenic acid or quinolinic acid markedly reduced the number of striatal [125I]CCK-8 binding sites. CCK receptor levels were restored to normal following transplantation of neonatal striatal tissue into rats previously treated with ibotenic acid. These results suggest that CCK receptors are located primarily on intrinsic striatal neurones and not on nigrostriatal afferent fibres.

Oxidative reactivity of the tryptophan metabolites 3-hydroxyanthranilate, cinnabarinate, quinolinate and picolinate

The oxidative reactivities of four tryptophan metabolites in the kynurenine pathway were examined as a potential mechanism for their reported neurotoxicities and carcinogenicities. Neither quinolinic acid, a neurotoxin, nor its monocarboxylic analogue, picolinic acid, auto-oxidized over a wide pH range. However, 3-hydroxyanthranilic acid (3-HAT), a carcinogen, readily auto-oxidized and the reaction rate increased exponentially with increasing pH. 3-HAT auto-oxidation likely involves two steps: auto-oxidation of 3-HAT to the semiquinoneimine (anthranilyl radical) which oxidizes to the quinoneimine, followed by condensation and oxidation reactions to yield a second carcinogen, cinnabarinic acid. 3-HAT auto-oxidation to cinnabarinate required molecular oxygen and generated superoxide radicals and H2O2. Superoxide dismutase (SOD) accelerated 3-HAT auto-oxidation 4-fold, probably by preventing back reactions between superoxide and either the anthranilyl radical or the quinoneimine formed during the initial step of auto-oxidation. Catalase did not accelerate 3-HAT auto-oxidation, but it did prevent destruction of cinnabarinate by H2O2. Interconversion between oxyhemoglobin and methemoglobin occurred during 3-HAT auto-oxidation, although neither form of hemoglobin altered rates of 3-HAT auto-oxidation. Mn2+, Mn3+ and Fe3+-EDTA did not directly catalyze cinnabarinate formation in the absence of O2, but they did accelerate cinnabarinate formation under aerobic conditions.

Anticonvulsant activity of two novel piperazine derivatives with potent kainate antagonist activity

Two dicarboxylic piperazine derivatives, 1-(p-chlorobenzoyl)-piperazine-2,3-dicarboxylic acid (pCB-PzDA) and 1-(p-bromobenzoyl)-piperazine-2,3-dicarboxylic acid (pBB-PzDA), that block excitation at glutamate receptors have been evaluated as anticonvulsants in rodent models of epilepsy by i.c.v. or i.p. injection. In DBA/2 mice, pBB-PzDA (0.01 mumol i.c.v.) or pCB-PzDA (0.03 mumol i.c.v.) protects against the clonic and tonic seizures induced by loud sound. Protection is also seen following i.p. injection of pBB-PzDA (0.33-1.0 mmol/kg) or pCB-PzDA (0.66-1.0 mmol/kg). In Swiss S mice suppression of seizure activity induced by i.c.v. injection of excitatory amino acid agonists shows that both compounds are preferentially active against alpha-kainate, with the following rank orders (for pBB-PzDA); alpha-kainate greater than quisqualate greater than N-methyl-D-aspartate greater than quinolinate greater than L-glutamate; and (for pCB-PzDA): alpha-kainate greater than quinolinate greater than N-methyl-D-aspartate greater than quisqualate greater than L-glutamate. These compounds are the most potent preferential alpha-kainate antagonists so far tested. The relationship between antagonism at the various receptor subtypes and anticonvulsant action is not adequately defined.

Seizure activity and lesions after intrahippocampal quinolinic acid injection

Electroencephalographic, behavioral, and neuropathologic changes were monitored after infusions of the endogenous excitatory amino acid, quinolinic acid (QUIN), into the dorsal hippocampus of unanesthetized, freely moving rats. A dose of 120 nmol QUIN was required to reliably precipitate seizures although EEG changes were observed with doses as small as 3 nmol. Seizure episodes were characterized by repetitive periods of high-voltage spiking typically lasting 20 s but occasional longer multicomponent episodes (60 s) were also observed. The latency of specific QUIN-induced seizures was similar for all doses tested (19 to 32 min); however, the total number of seizures and total time in seizures increased in a dose-dependent fashion from 30 to 300 nmol QUIN. Seizure episodes were often associated with a frozen appearance of the animal and intermittent "wet dog shakes". Ataxia was apparent in animals receiving 120 and 300 nmol QUIN. Using light microscopic analyses, pyramidal cell degeneration was observed in the QUIN-injected hippocampus (CA3 and CA1 cells more susceptible than CA2 cells); dentate granule cells showed signs of degeneration only at the largest QUIN dose. No neuropathologic changes were found outside the injected hippocampus. Seizures and neuropathologic changes induced by 120 nmol QUIN were completely blocked by pre- or cotreatment with 12 nmol (-)2-amino-7-phosphonoheptanoic acid. Experiments with [3H]QUIN indicated that only 3% of the injected radioactivity was present in the dorsal hippocampus at the average time of seizure onset (25 min), and consisted entirely of unmetabolized QUIN. The potent convulsant properties of QUIN, an endogenous metabolite, may prove to be of relevance for the etiology of human temporal lobe epilepsy.

[Increase in the activity of an epileptogenic focus in frog hippocampus as a result of kynurenines and its reduction by serotonin]

In frogs with epileptogenic focus induced by injection of penicillin (1000 U in 0.4 microliter) into the primordial hippocampus it was shown that pretreatment with two kynurenines (quinolinic acid -- 0.1 microgram, and d,l-kynurenine -- 1 microgram) into the focus region and their injection into the functioning epileptogenic focus led to a sharp increase of the interparoxysmal epileptiform discharges and electrographic correlates of the fit on the EEG. Anthranilic acid (5 microgram) did not influence the activity of epileptogenic foci, and serotonin (1 microgram) and 5-methoxytryptamine (1 microgram) decreased it significantly. It is suggested that the effect of kynurenines on neurones in the epileptogenic foci may play a certain role in the pathogenesis of epilepsy.

Effect of leucine at different levels of pyridoxine on hepatic quinolinate phosphoribosyl transferase (EC 2.4.2.19) and leucine aminotransferase (EC 2.6.1.6) in rats

1. Effects of incorporating 30 g leucine/kg into diets on quinolinate phosphoribosyl transferase (QPRT; EC 2.4.2.19) activity and leucine aminotransferase (EC 2.6.1.6) activity were studied in groups of rats receiving 5, 30 and 60 micrograms of pyridoxine/10 g diet. 2. The results indicated that 30 g leucine/kg diet significantly reduced the QPRT activity when the diets provided 5 micrograms pyridoxine/10 g and that the effect was only marginal when the diet included 30 micrograms pyridoxine/10 g. The inhibitory effect was completely absent when the diet provided higher amounts of pyridoxine (60 microgram/10 g). 3. These results suggest that additional amounts of pyridoxine are necessary to counteract the effects of excess of leucine in the diet. 4. Leucine aminotransferase activity was increased in rats given diets containing higher amounts of pyridoxine; supplementary leucine also increased the enzyme activity.

Effect of diet restriction on some key enzymes tryptophan-NAD pathway in rats

Dietary intake of rats was restricted by feeding varying amounts of a 20% protein diet. After 6 weeks of feeding, some key enzymes of the tryptophan and nicotinic acid-NAD pathway, liver nicotinamide nucleotide concentration, and urinary metabolites of tryptophan and nicotinic acid were studied. With an increase in diet restriction, liver tryptophan oxygenase (EC 1.13.1.12) activity increased. Quinolinate phosphoribosyltransferase (EC 2.4.2.a) activity, on the other hand, was found to decrease with moderate diet restriction up to 50% restriction, but increased again with more severe diet restriction in rats fed 25% of ad libitum intake. Liver nicotinate phosphoribosyltransferase (EC 2.4.2.11) activity was also observed to decrease with moderate diet restriction and did not further change when the restriction was severe while picolinate carboxylase (EC 4.1.1.45) activity increased significantly only in severe diet restriction. In rats fed 25% of ad libitum intake, urinary quinolinic acid excretion was low whereas N'-methylnicotinamide excretion was elevated. Alterations in the enzyme activities accompanied by changes in the levels of urinary metabolites, observed in the present study, suggest that the potential efficiency of conversion of tryptophan to nicotinamide nucleotides is not constant and is influenced by dietary intake.

Effect of inhibition of gluconeogenesis on ammonia production in the perfused rat kidney

1. Gluconeogenesis from lactate or from glutamine is inhibited by 90-100% by sodium quinolinate (1 mmol/l) or 3-mercaptopicolinate (150 nmol/l) in the perfused rat kidney. L-Tryptophan is not metabolized and is without effect. 2. Lactate uptake and glucose production are inhibited to the same degree by 3-mercaptopicolinate in the kidneys of well-fed or starved rats. 3. Inhibition of gluconeogenesis from glutamine (1 mmol/l) by 3-mercaptopicolinate is accompanied by 50% inhibition of ammonia production, and 34% inhibition of glutamine uptake, in the kidneys of acidotic rats. Ammonia production from glutamine was not inhibited in kidneys from non-acidotic rats. 4. It is concluded that the increased rate of gluconeogenesis from glutamine which occurs in acidotic rats is an essential and primary event regulating all of the increase in ammonia formation.

The effects of inhibition of gluconeogenesis on ketogenesis in starved and diabetic rats

Experiments were performed in which the effects of inhibiting gluconeogenesis on ketone-body formation were examined in vivo in starved and severely streptozotocin-diabetic rats. The infusion of 3-mercaptopicolinate, an inhibitor of gluconeogenesis (DiTullio et al., 1974), caused decreases in blood [glucose] and increases in blood [lactate] and [pyruvate] in both normal and ketoacidotic rats. Patterns of liver gluconeogenic intermediates after 3-mercaptopicolinate infusion suggested inhibition at the level of phosphoenolpyruvate carboxykinase. This was confirmed by measurement of hepatic oxaloacetate concentrations which were increased 5-fold after 3-mercaptopicolinate administration. The infusion of 3-mercaptopicolinate caused a decrease in total ketone-body concentrations of 30% in starved rats and 73% in the diabetic animals. Blood glycerol and hepatic triglyceride concentrations remained unchanged. The decreases in ketone-body concentrations were associated with increases in the calculated hepatic cytosolic and mitochondrial [NADH]/[NAD+] ratios. The decrease in ketogenesis seen after inhibition of gluconeogenesis may have resulted from an inhibition of hepatic fatty acid oxidation by the more reduced mitochondrial redox state. It was concluded that gluconeogenesis may stimulate ketogenesis by as much as 30% in severe diabetic ketoacidosis.

Isolation of a metabolite capable of differentially supporting the growth of nicotinamide adenine dinucleotide auxotrophs of Escherichia coli

A compound, isolated from the culture fluid of a nadC auxotroph of Escherichia coli grown in a minimal medium, supports the growth of both a nadA and a nadB mutant. This metabolite exhibits an ultraviolet light absorption spectrum and a mass spectrum, different from quinolinic acid. This compound may be the precursor of quinolinic acid, an intermediate in the biosynthesis of nicotinamide adenosine dinucleotide.