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Biomedical subjects

M F Beal

Publications and source records attributed to M F Beal.

At least 19 recordsLinked to original sources
PubMed1992

The effect of peripheral loading with kynurenine and probenecid on extracellular striatal kynurenic acid concentrations.

Kynurenic acid (KYA) is the only known endogenous excitatory amino acid antagonist in mammalian brain. In the present study we examined the effects of precursor loading with kynurenine (KYN) and blockade of organic acid transport with probenecid, either alone or in combination, on extracellular striatal KYA concentrations in unanesthetized rats. Baseline KYA concentrations were 1.61 +/- 0.29 pmol/ml. Following administration of KYN 150 mg/kg with increasing doses of probenecid a maximal increase in KYA to 946 +/- 210 pmol/ml was seen with probenecid 200 mg/kg. Probenecid 200 mg/kg alone increased KYA levels to 16.0 +/- 5.2 pmol/ml. The combination of probenecid 200 mg/kg with KYN 450 mg/kg produced a maximal increase of KYA to 2085 +/- 391 pmol/ml, a 1300-fold increase indicating marked potentiation. These results show that pharmacologic manipulation can markedly increase extracellular fluid concentrations of KYA into a range which may be useful in attempts to block NMDA receptor-mediated neurotoxicity.

Animals↗
PubMed1992

Behavioral and pharmacological effects of centrally administered aminooxyacetic acid in rats.

In the present experiment unilateral intrastriatal injections of aminooxyacetic acid (1, 2.5, 5 mumol) to freely moving animals and pentobarbital-anesthetized rats produced contralateral jerks and dose-dependent mortality, but no barrel rotation. At 10-12 days there were no significant differences in exploratory activity, passive avoidance behavior, and elevated plus-maze test in aminooxyacetic acid-treated animals as compared with controls. However freely moving animals microinjected with aminooxyacetic acid (but not the pentobarbital-pretreated group) had impaired learning activity in an active avoidance conditioning test, and showed reduced striatal concentrations of substance P and GABA. Intrastriatal injections of aminooxyacetic acid therefore result in both acute and chronic behavioral changes which are attenuated by pentobarbital anesthesia.

Aminooxyacetic Acid↗
PubMed1992

Developmental changes in brain kynurenic acid concentrations.

The cerebral distribution and regulation of excitatory amino acid levels may play a crucial role in neuronal development. In the present study we examined concentrations of the endogenous excitatory amino acid antagonist kynurenic acid and related substances during development in fetal and neonatal rat brain and fetal non-human primate cerebral cortex. Kynurenic acid concentrations in rat fetal whole brain were significantly increased 4-5 fold prenatally, then declined rapidly at 1 day after birth, and reached adult concentrations at 7 days after birth. L-Kynurenine concentrations were also markedly increased prior to birth and then declined to adult concentrations at 1 day after birth. L-Tryptophan was increased 3 fold before birth, and decreased to adult concentrations 1 day after birth. In contrast concentrations of dopamine, norepinephrine, 3,4-dihydroxyphenylacetic acid and homovanillic acid increased 1 day prior to birth and continued to increase following birth. Fetal baboon cerebral cortex showed significant increases in kynurenic acid concentrations both pre-term and near-term as compared with adult concentrations. These results show that marked changes in kynurenic acid concentrations occur prior to and following birth. It is possible that high levels of kynurenic acid prior to birth inhibit neurite branching and development of excitatory synapses, which then develop rapidly in parallel with the decrease in kynurenic acid levels.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1992

Does impairment of energy metabolism result in excitotoxic neuronal death in neurodegenerative illnesses?

The etiology of nerve cell death in neuronal degenerative disease is unknown, but it has been hypothesized that excitotoxic mechanisms may play a role. Such mechanisms may play a role in diseases such as Huntington's disease, Parkinson's disease, amyotropic lateral sclerosis, and Alzheimer's disease. In these illnesses, the slowly evolving neuronal death is unlikely to be due to a sudden release of glutamate, such as occurs in ischemia. One possibility, however, is that a defect in mitochondrial energy metabolism could secondarily lead to slow excitotoxic neuronal death, by making neurons more vulnerable to endogenous glutamate. With reduced oxidative metabolism and partial cell membrane depolarization, voltage-dependent N-methyl-D-aspartate (NMDA) receptor ion channels would be more easily activated. In addition, several other processes involved in buffering intracellular calcium may be impaired. Recent studies in experimental animals showed that mitochondrial toxins can result in a pattern of neuronal degeneration closely resembling that seen in Huntington's disease, which can be blocked with NMDA antagonists. NMDA antagonists also block neuronal degeneration induced by 1-methyl-4-phenylpyridium, which has been implicated in experimental models of Parkinson's disease. The delayed onset of neurodegenerative illnesses could be related to the progressive impairment of mitochondrial oxidative phosphorylation, which accompanies normal aging. If defective mitochondrial energy metabolism plays a role in cell death in neurodegenerative disorders, potential therapeutic strategies would be to use excitatory amino acid antagonists or agents to bypass bioenergetic defects.

Aging↗
PubMed1992

The cortical lesion of Huntington's disease: further neurochemical characterization, and reproduction of some of the histological and neurochemical features by N-methyl-D-aspartate lesions of rat cortex.

Huntington's disease is a progressive neurodegenerative disease in which the basal ganglia are preferentially affected. Recent evidence, however, suggests involvement of the cerebral cortex as well, with sparing of neurochemically defined subsets of gamma-aminobutyric acid (GABA)-ergic interneurons. In the present study, we examined changes in concentrations of the amino acid neurotransmitters GABA, glutamate, and aspartate in nine cortical regions from 23 patients with advanced Huntington's disease and 12 control brains. GABA concentrations were significantly increased in eight of the nine regions, consistent with a sparing of GABAergic local circuit neurons in the context of progressive cortical atrophy. Small but significant increases in glutamate were found in six of the nine regions, while aspartate levels were generally unaffected. Striate cortex (Brodmann's area 17) showed the most profound increases in GABA and glutamate. We also investigated the effects of powdering the excitotoxins N-methyl-D-aspartate (NMDA) or kainic acid onto the dura of rats. The resulting lesions were examined at 1 week and 6 months. The NMDA-induced lesions showed striking sparing of parvalbumin-positive neurons (a subset of GABAergic interneurons), and this sparing was reflected in neurochemical measurements of GABA; kainic acid lesions failed to display this selectivity. Somatostatin, cholecystokinin, and vasoactive intestinal polypeptide concentrations were spared by the NMDA-induced lesions, and substance P levels were significantly increased. These results provide evidence that NMDA excitotoxic lesions of cerebral cortex can produce a selective pattern of neuronal damage similar to that which occurs in Huntington's disease.

Age Factors↗
PubMed1992

Kynurenic acid concentrations are reduced in Huntington's disease cerebral cortex.

Huntington's disease (HD) is characterized by gradually evolving selective neuronal death. Several lines of evidence suggest that an excitotoxic mechanism may play a role. Tryptophan metabolism leads to production of quinolinic acid, an N-methyl-D-aspartate (NMDA) receptor agonist, and to kynurenic acid, an antagonist at these same receptors. We recently found increased kynurenine to kynurenic acid ratios in HD postmortem putamen and decreased kynurenic acid concentrations in cerebrospinal fluid, consistent with decreased formation of kynurenic acid in HD brain. In the present study we used HPLC with 16 sensor coulometric electrochemical detection to measure kynurenic acid and 18 other electrochemically active compounds in 6 cortical regions, caudate and cerebellum from controls, HD, Alzheimer's disease (AD), and Parkinson's disease (PD) patients. Significant reductions in kynurenic acid concentrations were found in 5 of 6 cortical regions examined. Smaller reductions of kynurenic acid in the caudate, cerebellum and frontal pole were not significant. No significant reductions were found in the AD and PD patients. Both uric acid and glutathionine were significantly reduced in several regions of HD cerebral cortex, which could signify abnormal energy metabolism in HD. Since kynurenic acid is an antagonist of excitatory amino acid receptors, a deficiency could contribute to the pathogenesis of neuronal degeneration in HD.

Aged↗
PubMed1992

Kynurenine and probenecid inhibit pentylenetetrazol- and NMDLA-induced seizures and increase kynurenic acid concentrations in the brain.

Kynurenine is a direct precursor of kynurenic acid, the only known endogenous antagonist of excitatory amino acid receptors in the brain. Kynurenine administered intraperitoneally (150, 450, 900 mg/kg) 2 h before pentylenetetrazol injection dose-dependently increased the time to seizures, the time to death and the survivorship of mice. Kynurenine dose-dependently increased the time to seizures and the time to death in mice with NMDLA-induced seizures. Kynurenine, 900 mg/kg, was equally efficacious to diazepam, 2 mg/kg. Probenecid dose-dependently increased the time to seizures, the time to death and the survivorship of mice with pentylenetetrazol-induced seizures. Probenecid had no significant effects on NMDLA-induced seizures, although the time to death was prolonged in the NMDLA 500 mg/kg group. Probenecid potentiated the effects of kynurenine in these tests. Both probenecid and kynurenine significantly increased kynurenine and kynurenic acid concentrations in mouse cerebral cortex and striatum. These findings suggest that kynurenine (metabolized to kynurenic acid) has anticonvulsant effects, and probenecid potentiates these effects in mice.

Analysis of Variance↗
PubMed1992

Role of excitotoxicity in human neurological disease.

An increasing body of evidence has implicated excitoxicity as a mechanism of neuronal death in both acute and chronic neurological diseases. A major recent advance has been the successful cloning and expression of the non-NMDA, NMDA, and metabotropic glutamate receptors. The cellular mechanisms responsible for cell death following activation of these receptors are still being clarified. A recent advance in conceptualizing excitotoxicity is the notion that a slow excitotoxic process may occur as a consequence of either a receptor abnormality or an impairment of energy metabolism. It is possible that such a mechanism may occur in neurodegenerative illnesses. Recent therapeutic studies have focused on glycine site antagonists and on the efficacy of non-NMDA antagonists in ischemia.

Amino Acids↗
PubMed1992

Neuroprotective effects of L-kynurenine on hypoxia-ischemia and NMDA lesions in neonatal rats.

Kynurenic acid is the only known endogenous excitatory amino acid receptor antagonist in the central nervous system. In the present study, we examined whether increasing brain concentrations of kynurenic acid by loading with its precursor L-kynurenine, or blocking its excretion with probenecid, could exert neuroprotective effects. Neuroprotective effects were examined in a neonatal model of hypoxia-ischemia, and following intrastriatal injection of N-methyl-D-aspartate (NMDA). Seven-day-old rats underwent unilateral ligation of the carotid artery, followed by exposure to 8% oxygen for 1.5 h. L-kynurenine administered 1 h before the hypoxia-ischemia showed a dose-dependent significant neuroprotective effect, with complete protection at a dose of 300 mg kg-1. The induction of c-fos immunoreactivity in cerebral cortex was also blocked by this dose of L-kynurenine. Probenecid alone had moderate neuroprotective effects, while a combination of a low dose of probenecid with doses of 50-200 mg kg-1 of L-kynurenine showed significant dose-dependent neuroprotection. Kynurenine dose-dependently protected against NMDA neurotoxicity in 7-day-old rats. Neurochemical analysis confirmed that L-kynurenine with or without probenecid markedly increased concentrations of kynurenic acid in cerebral cortex of 7-day-old rats. These results show for the first time that pharmacologic manipulation of endogenous concentrations of kynurenic acid can exert neuroprotective effects.

Animals↗
PubMed1992

Mitochondrial DNA deletions in human brain: regional variability and increase with advanced age.

We have examined the role of somatic mitochondrial DNA (mtDNA) mutations in human ageing by quantitating the accumulation of the common 4977 nucleotide pair (np) deletion (mtDNA4977) in the cortex, putamen and cerebellum. A significant increase in the mtDNA4977 deletion was seen in elderly individuals. In the cortex, the deleted to total mtDNA ratio ranged from 0.00023 to 0.012 in 67-77 year old brains and up to 0.034 in subjects over 80. In the putamen, the deletion level ranged from 0.0016 to 0.010 in 67 to 77 years old up to 0.12 in individuals over the age of 80. The cerebellum remained relatively devoid of mtDNA deletions. Similar changes were observed with a different 7436 np deletion. These changes suggest that somatic mtDNA deletions might contribute to the neurological impairment often associated with ageing.

Adult↗
PubMed1992

1-Methyl-4-phenylpyridinium produces excitotoxic lesions in rat striatum as a result of impairment of oxidative metabolism.

The effects of 1-methyl-4-phenylpyridinium (MPP+) were studied in rat striatum. Using freeze-clamp, microwave, and water-suppressed proton chemical shift magnetic resonance imaging techniques, MPP+ resulted in marked increases in lactate and a depletion of ATP for up to 48 h after the injections. MPP+ produced dose-dependent depletions of dopamine, serotonin, gamma-aminobutyric acid, and substance P that were partially blocked at 1 week by prior decortication or completely blocked by MK-801 at 24 h. The lesions showed relative sparing of somatostatin-neuropeptide Y neurons, consistent with N-methyl-D-aspartate (NMDA) excitotoxicity. MPP+ produces impairment of oxidative phosphorylation in vivo, which may result in membrane depolarization with persistent activation of NMDA receptors and excitotoxic neuronal degeneration. An impairment of energy metabolism may therefore underlie slow excitotoxic neuronal death in neurodegenerative diseases.

1-Methyl-4-phenylpyridinium↗
PubMed1992

Kynurenine pathway abnormalities in Parkinson's disease.

We measured metabolites of tyrosine and tryptophan (TRP) in the frontal cortex, putamen (PT), and pars compacta of the substantia nigra (SN) of control and Parkinson's disease (PD) brain tissues. Dopamine concentrations were significantly decreased in the PT and SN of PD tissue, regardless of L-dopa therapy. However, 3-O-methyldopa (3OMD) concentration showed a significant increase in each region of the PD group treated with L-dopa (PD[+]) as compared with both the control group and the PD group without L-dopa therapy (PD[-]). Therefore, 3OMD concentration appears to be a reliable marker of L-dopa therapy. Serotonin concentration was lower in each region of the PD groups than in the control group. Although the magnitude of decrease was greater in the PD(+) group, there was no statistical significance between the two PD groups. The same patterns of decrease were present in kynurenine (KYN) and kynurenic acid (KYA) concentrations, but the molar ratios of TRP to KYN and KYN to KYA were unchanged among three groups. In contrast, 3-hydroxykynurenine (3OHKY) concentration was increased in the PT PD(-) group and in three regions of the PD(+) group. Since the KYN pathway leads to formation of nicotinamide-adenine dinucleotide (NADH), the present results may be a further indication of a defect in NADH:ubiquinone oxidoreductase (complex I) in mitochondria in PD.

Aged↗
PubMed1992

Mechanisms of excitotoxicity in neurologic diseases.

Excitotoxicity refers to neuronal cell death caused by activation of excitatory amino acid receptors. A substantial body of evidence has implicated excitotoxicity as a mechanism of cell death in both acute and chronic neurologic diseases. A major recent advance has been the successful cloning and expression of the N-methyl-D-aspartate (NMDA), non-NMDA, and metabotropic glutamate receptors. The cellular mechanisms responsible for cell death after activation of these receptors are still being clarified. In acute neurologic diseases such as stroke and head trauma, excitotoxicity may be related to excessive glutamate release. In chronic neurodegenerative diseases, however, a slow excitotoxic process is more likely to occur as a consequence of either a receptor abnormality or an impairment of energy metabolism. Recent therapeutic studies have demonstrated the efficacy of non-NMDA receptor antagonists in experimental studies of global ischemia.

Animals↗
PubMed1991

Effects of aging on quinolinic acid lesions in rat striatum.

Several neurologic illnesses in which excitotoxic mechanisms may play a role increase in prevalence with age. In the present study we examined the susceptibility of rats to quinolinic acid striatal lesions at 1, 4 and 20 months of age, and susceptibility to N-methyl-D-aspartate (NMDA) at 1 and 4 months of age. The extent of the lesions was quantitated with measurements of substance P-like immunoreactivity (SPLI) and gamma-aminobutyric acid (GABA). The lesions in the 4- and 20-month-old age groups showed significantly smaller depletions of SPLI and GABA than those in 1-month-old animals. Neuropeptide Y-like immunoreactivity (NPYLI) and somatostatin-like immunoreactivity (SLI) were unchanged in the lesioned striata. NMDA lesions were also attenuated in 4-month- and 12-month-old animals as compared with 1-month-old animals. Uric acid concentrations showed marked dose-dependent increases in the lesioned striatum, and to a lesser extent in the overlying cerebral cortex, in all 3 age groups. There were no changes of SLI, NPYLI or SPLI with aging in the cerebral cortex or hippocampus. Kynurenine and kynurenic acid concentrations showed significant increases with aging in frontal cortex. The present results show a reduced susceptibility of animals to striatal quinolinic acid and NMDA lesions with normal aging. The delayed onset of several neurodegenerative illnesses is therefore unlikely to be due to an increasing susceptibility to excitotoxin lesions with aging.

Aging↗
PubMed1991

An in vivo model for the neurodegenerative effects of beta amyloid and protection by substance P.

Deposition of the beta-amyloid protein in senile plaques is a pathologic hallmark of Alzheimer disease (AD). Focal deposition of beta amyloid in the adult rat cerebral cortex caused profound neurodegenerative changes, including neuronal loss and degenerating neurons and neurites. Chronic induction of the Alz-50 antigen appeared in neurons around focal cortical deposits of beta amyloid. Immunoblot analysis showed that beta amyloid induced Alz-50-immunoreactive proteins in rat cerebral cortex that were very similar to the proteins induced in human cerebral cortex from patients with AD. The neuropeptide substance P prevented beta-amyloid-induced neuronal loss and expression of Alz-50 proteins when coadministered into the cerebral cortex. Systemic administration of substance P also provided protection against the effects of intracerebral beta amyloid. Thus, beta amyloid is a potent neurotoxin in the adult brain in vivo, and its effects can be blocked by substance P.

Amyloid beta-Peptides↗
PubMed1991

2-Chloroadenosine attenuates NMDA, kainate, and quisqualate toxicity.

Excitatory amino acid (EAA)-induced cell death in the striatum is dependent upon intact glutamatergic afferents arising from the cerebral cortex. Through a mechanism possibly related to inhibition of glutamate release, adenosine receptor agonists attenuate EAA induced toxicity in the rat striatum. In the present study, we examined whether 2-chloroadenosine (2CLA), a stable adenosine analog, protects against toxicity induced by kainate (KA), quisqualate (QUIS), N-methyl-D-aspartate (NMDA), and ibotenate (IBO). In vivo intrastriatal injections of 2CLA (50 nmol) with each EAA tested provided a partial but significant protective effect versus injection of the EAA alone, as measured by striatal concentrations of gamma-aminobutyric acid (GABA) and substance P-like immunoreactivity (SP-LI). These results show that 2CLA attenuates both NMDA- and non-NMDA-mediated neuronal cell death.

2-Chloroadenosine↗
PubMed1991

Comparative behavioral and pharmacological studies with centrally administered kynurenine and kynurenic acid in rats.

In the present study the effects of kynurenine and its metabolite kynurenic acid were compared in different behavioral and pharmacological tests. Kynurenic acid administered i.c.v. resulted in ataxia and stereotypy in a dose-dependent manner (0.025-1.6 mumol). Administration of 0.8 mumol of kynurenic acid resulted in sleeping and an approximate 25% mortality of the animals. At a dose of 1.6 mumol all of the animals died within 2-5 min from cardiorespiratory failure. One hour after lower doses of kynurenic acid the behavior of the rats appeared normal (neither stereotypy nor ataxia were observed in their familiar environemnt), but their exploratory activity (0.025-0.2 mumol) was significantly lower in a novel environment (open-field box) compared to the control group. Twenty four hours after the injection of kynurenic acid the exploratory activity of the animals did not differ from the control group. Kynurenine administered i.c.v. in equimolar doses did not result in stereotypy, ataxia, sleeping or mortality of the animals although, immediately after high doses short-lasting (1-2 min) immobility was observed. The rearing activity of the high dose kynurenine-treated animals was lower 1 h after injection, but this effect disappeared 24 h after the treatment. Post-trial injection of kynurenic acid (0.2 mumol) slightly, but not significantly, inhibited the learning ability of the rats in an active avoidance paradigm. Kynurenine administered in an equimolar dose had no effect on the speed of learning, but significantly attenuated the intertrial activity of the rats. Kynurenic acid (0.2 mumol, 0.4 mumol) did not significantly inhibit the passive avoidance latency of the animals after post-trial treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗