Search PubMed⌕ Search

Biomedical subjects

P Jenner

Publications and source records attributed to P Jenner.

At least 235 records · Page 13Linked to original sources
PubMed1991

Oxidative stress as a cause of Parkinson's disease.

The cause of dopamine cell death in Parkinson's disease remains unknown. Present interest centres on the possible involvement of a toxin mediated mechanism such as that produced, by MPTP. In post-mortem studies there is evidence in the substantia nigra for an on-going toxic process involving increased lipid peroxidation, altered iron metabolism and impairment of mitochondrial function at the level of complex I. Although the precise relationship between these biochemical changes is not known, present evidence points to oxidative stress as an important factor contributing to neuronal loss. Altered mitochondrial function and increased iron levels may not initiate Parkinson's disease but rather act to accelerate cell death. Future strategies for the treatment of Parkinson's disease should be aimed at preventing oxidative stress and stopping or slowing the progression of the underlying pathology.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1991

Peripheral pharmacokinetic handling and metabolism of L-dopa in the rat: the effect of route of administration and carbidopa pretreatment.

The effect of carbidopa (L-alpha-methyldopa hydrazine; 25 mg kg-1 i.p.) pretreatment on the pharmacokinetics and peripheral metabolism of orally and intra-aortically administered L-3,4-dihydroxyphenylalanine (L-dopa; 50 mg kg-1) has been examined in rats. Following intra-aortic (i.a.) administration, plasma levels of the drug declined biexponentially. Pretreatment with carbidopa resulted in higher plasma concentrations after i.a. administration of L-dopa, but had no effect on the half-life (t1/2) for its distribution or elimination. Oral L-dopa gave peak plasma concentrations at 1.5 h and then a log-linear decline between 1.5 and 6 h. Pretreatment with carbidopa also produced higher plasma concentrations of L-dopa given orally, and the t1/2 for its elimination tended to be increased compared with values achieved after the drug alone. Pretreatment with carbidopa decreased volume of distribution and total plasma clearance and increased area under the curve (0-infinity) after L-dopa i.a. and increased AUC0-infinity after L-dopa p.o. The fraction of the oral dose absorbed through the gut was not affected. Carbidopa pretreatment enhanced the accumulation of 3-O-methyldopa and decreased dopamine levels in plasma after both i.a. and oral administration of L-dopa. Higher plasma concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA) were detected in the plasma after i.a. rather than oral administration of L-dopa and pretreatment with carbidopa greatly reduced these plasma concentrations. However, following oral L-dopa, only HVA levels were reduced by carbidopa pretreatment.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗
PubMed1990

Toxication of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and analogs by monoamine oxidase. A structure-reactivity relationship study.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) elicits motor deficits similar to those observed in Parkinson's disease. Before exerting its neurotoxic action, MPTP must be activated by brain monoamine oxidase (MAO) to the neurotoxic metabolite MPP+ (1-methyl-4-phenylpyridinium). MPTP derivatives differ in their reactivity as MAO substrates and in their neurotoxicity. A structure-reactivity relationship study based on literature data was undertaken in order to determine the key features in the structure of MPTP and analogs that are responsible for the reactivity towards MAO. Thirty-three MPTP derivatives (including MPTP itself) were included in the study. To explain the reactivity towards MAO of the 33 MPTP analogs, different statistical methods (principal component analysis, multiple linear regression analysis) as well as the CoMFA (Comparative Molecular Field Analysis) approach, a new tool in structure-activity correlations, were used. Linear regression analysis failed to yield any predictive model, but suggested some trends. In contrast, the CoMFA approach was successful in correlating structural features and MAO reactivity. Coefficient contour maps showed where differences in the steric field (van der Waals' interactions) are most highly associated with differences in MAO reactivity. Several positive (in the ortho- and meta-position of the phenyl group) and negative (in the para-position of the phenyl group; beyond the N-methyl group) interaction regions were identified. Some structural features of the MAO active site could be postulated. First, the N-methyl group has the ideal size and elicits ideal interactions within the MAO active pocket, while smaller or larger groups are less favorable; second, para-substituent on the phenyl ring produce steric hindrances and are unfavorable to reactivity; third, ortho- and meta-substituents may have stabilizing interactions within the active pocket and are favorable to the reactivity. Moreover the model derived by CoMFA allowed us to make successful predictions of reactivity towards MAO for several additional tetrahydropyridines.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1990

1-Methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-methyl-MPTP) is less neurotoxic than MPTP in the common marmoset.

Four adult marmosets were treated with increasing doses of 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'-methyl-MPTP) in the range 0.23-4.3 mg/kg i.p. to give a cumulative dose of 11.0-11.6 mg/kg over a 6-10 day period. After 4 days of treatment, and as the dosage was gradually increased, the animals exhibited mild motor deficits. These abnormalities slowly declined over the following 1-6 week period. In contrast, similar treatment of common marmosets with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (1-4 mg/kg i.p.) for 3-5 days in a cumulative dose of 6.9-9.2 mg/kg produced gross impairment of motor function which persisted throughout the 5 weeks period of observation. Administration of 2'-methyl-MPTP for 6-10 days caused some decrease in dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), but not homovanillic acid (HVA) content in the caudate nucleus in animals 5-6 weeks after the start of treatment. There was a small decrease in [3H]dopamine uptake into putamen synaptosomes. This contrasted with the marked decreases in all these parameters observed after MPTP treatment of common marmosets. Histological examination of the substantia nigra from the four animals treated with 2'-methyl-MPTP did not show degeneration or loss of dopamine-containing cell bodies in the zona compacta. In contrast, MPTP caused severe destruction of these pigmented nigral neurones. In the common marmoset 2'-methyl-MPTP does not appear to show the same neurotoxic action as MPTP itself. This contrasts with findings in the mouse where 2'-methyl-MPTP is more toxic to dopamine-containing cells of substantia nigra than MPTP.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1990

Lack of change in striatal DARPP-32 levels following nigrostriatal dopaminergic lesions in animals and in parkinsonian syndromes in man.

The present study was performed to determine the effect of a nearly complete nigrostriatal dopaminergic denervation on DARPP-32 levels in the striatum from animals and parkinsonian patients. DARPP-32 levels were estimated by in vitro phosphorylation in the presence of cAMP, or after inactivation of endogenous kinases and phosphatases, in the presence of the catalytic subunit of cAMP-dependent protein kinase. Intranigral 6-hydroxydopamine (6-OHDA) infusion in rats, or peripheral administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to common marmosets, did not change striatal DARPP-32 levels. Postmortem studies, carried out on brains obtained shortly after death, from patients with Parkinson disease, or from patients with progressive supranuclear palsy, showed that the levels of striatal DARPP-32 were not different from controls. These results indicate that dopaminergic striatal denervation did not modify the amount of DARPP-32 in the striatum, suggesting that the expression of DARPP-32, a protein which mediates some of the effects of dopamine in striatal neurons, is independent from the dopaminergic innervation.

Aged↗
PubMed1990

Mitochondrial DNA analysis in Parkinson's disease.

The reduced form of nicotinamide adenine dinucleotide coenzyme Q reductase (complex I) activity has recently been shown to be deficient in the substantia nigra of patients dying with Parkinson's disease. This biochemical defect is identical to that produced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which also produces parkinsonism in humans. Complex I comprises 25 polypeptides, seven of which are encoded by mitochondrial DNA. Restriction fragment analysis of substantia nigra DNA from six patients with Parkinson's disease did not show any major deletion. In two cases, there were different novel polymorphisms that were not observed in control brain (n = 6) or blood (n = 34) samples.

DNA Damage↗
PubMed1990

Differential ability of selective and non-selective dopamine agonists to induce climbing in the rat indicates the involvement of both D-1 and D-2 receptors in this behaviour.

Approximately 50% of female Wistar rats examined exhibited a continuous climbing response to a screening dose of apomorphine. In animals identified as climbing, the mixed D-1/D-2 agonists apomorphine, pergolide and L-dopa, and the indirectly acting agonists nomifensine and (+)-amphetamine, induced a dose-related climbing response. The selective D-1 agonist SKF 38393 caused only minimal climbing, and the selective D-2 agonists bromocriptine, lisuride and LY 141865 induced a weak climbing response. All agonists examined, except SKF 38393, caused a dose-related stereotypy response. The selective D-1 antagonist SCH 23390, and the selective D-2 antagonist sulpiride, both produced maximum inhibition of apomorphine-induced climbing. SCH 23390 also inhibited stereotyped behaviour, but sulpiride was less effective. In animals identified as "non-climbers" using the screening dose of apomorphine, only L-dopa induced a marked climbing response. Nomifensine and bromocriptine produced weak or discontinuous climbing in this group, while the other agonists examined had little or no effect. In contrast all drugs examined, except SKF 38393, induced stereotyped behaviour of the same intensity observed in the "climbers". It is concluded that stimulation of both D-1 and D-2 receptors is necessary to induce a continuous climbing behaviour in rats. D-2, but not D-1 stimulation, alone can induce a weak or discontinuous climbing response, but concomitant stimulation of D-1 receptors potentiates this effect. Failure of some rats to climb does not appear to be related to relative degrees of D-1 and D-2 stimulation.

Amphetamine↗
PubMed1990

Increased [Met]enkephalin and decreased substance P in spinal cord following thermal injury to one limb.

Thermal injury to one hind limb of rats was induced by immersion into water at 62 degrees C. Both a mild (15 s) or severe (30 s) lesion caused inflammation of the limb when observed 24 h later; but at this time the animals used the injured limb when they walked. Animals with a severe lesion of the injured limb subsequently withdrew it from use when walking. Limb withdrawal did not occur following a mild lesion. At 24 h following the lesion, lumbar spinal cord levels of [Met]enkephalin, as measured by radioimmunoassay, were elevated (70%) bilaterally in both hemisegments, ipsi- and contralateral to the lesion. At seven days following either mild or severe hind limb lesion [Met]enkephalin levels were elevated only in the ipsilateral lumbar hemisegment. At that time no changes in thoracic [Met]enkephalin levels were observed. Substance P levels were decreased (20-25%) bilaterally in the lumbar cord 24 h following a severe limb lesion, but no change was observed at seven days in any cord segment following a mild or severe lesion. Changes in spinal cord [Met]enkephalin content occur in response to thermal injury to one hind limb. However, the changes do not appear to be related to the withdrawal of the damaged limb from use following a severe lesion. Peptide changes in the spinal cord may reflect pain or injury to the damaged limb following a thermal lesion. In contrast, limb withdrawal may be a physiological rest mechanism related to altered basal ganglia peptide function.

Animals↗
PubMed1990

Variability in the fibrinogen and von Willebrand factor content of cryoprecipitate. Implications for reducing donor exposure.

Advances in the preparation of commercial Factor VIII concentrates have decreased the clinical use of cryoprecipitate to replace Factor VIII coagulant activity. Cryoprecipitate is now frequently transfused as a source of fibrinogen or von Willebrand factor (vWF). The minimum acceptable content of Factor VIII is prescribed, but no attempt is made to optimize, standardize, or assess the content of fibrinogen or vWF in cryo. If reasonably accurate information on the composition of cryoprecipitate were available, the physician could calculate an appropriate dose of cryo, thus avoiding unnecessary donor exposures and waste of product. This study was designed to measure the functionally active vWF and fibrinogen in cryoprecipitate prepared by three techniques in an attempt to optimize the yield of these hemostatically important components, and to obtain accurate information on the composition of the product. Cryoprecipitate was made from 82 units of fresh frozen plasma (FFP) as follows: (1) most of the supernatant plasma was expressed from "dry" cryo; (2) about 15 mL of plasma was left in each "regular" unit; and (3) "overnight" units were made from FFP thawed overnight in a refrigerator rather than in a 4 degrees C water bath as for the dry and regular units. Dry, regular, and overnight units had volumes of 8.8 +/- 1.5, 16.6 +/- 3.9, and 15.1 +/- 2.4 mL/bag, respectively. Dry cryoprecipitate units had significantly less fibrinogen and vWF than regular or overnight units. The vWF multimer pattern for all three types of cryoprecipitate was indistinguishable from that of normal pooled plasma. Thus, the amount of plasma expressed during preparation has a significant impact on the vWF and fibrinogen content of the resulting product. The amounts of these clinically important proteins should be assayed as a step toward rational determination of optimal cryoprecipitate doses in specific clinical settings.

Blood Preservation↗
PubMed1990

Mitochondrial complex I deficiency in Parkinson's disease.

The structure and function of mitochondrial respiratory-chain enzyme proteins were studied postmortem in the substantia nigra of nine patients with Parkinson's disease and nine matched controls. Total protein and mitochondrial mass were similar in the two groups. NADH-ubiquinone reductase (Complex I) and NADH cytochrome c reductase activities were significantly reduced, whereas succinate cytochrome c reductase activity was normal. These results indicated a specific defect of Complex I activity in the substantia nigra of patients with Parkinson's disease. This biochemical defect is the same as that produced in animal models of parkinsonism by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and adds further support to the proposition that Parkinson's disease may be due to an environmental toxin with action(s) similar to those of MPTP.

Electron Transport Complex II↗
PubMed1990

Anatomic and disease specificity of NADH CoQ1 reductase (complex I) deficiency in Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is thought to produce parkinsonism in humans and other primates through its inhibition of complex I. The recent discovery of mitochondrial complex I deficiency in the substantia nigra of patients with Parkinson's disease has provided a remarkable link between the idiopathic disease and the action of the neurotoxin MPTP. This article shows that complex I deficiency in Parkinson's disease is anatomically specific for the substantia nigra, and is not present in another neurodegenerative disorder involving the substantia nigra. Evidence is also provided to show that there is no correlation between L-3,4-dihydroxyphenylalanine therapy and complex I deficiency. These results suggest that complex I deficiency may be the underlying cause of dopaminergic cell death in Parkinson's disease.

Citrate (si)-Synthase↗
PubMed1990

Decreased ferritin levels in brain in Parkinson's disease.

Ferritin levels were measured in postmortem brain tissue from patients dying with Parkinson's disease [treated with L-3,4-dihydroxyphenylalanine (L-DOPA)] and from control patients. Ferritin levels were decreased in the substantia nigra, caudate-putamen, globus pallidus, cerebral cortex, and cerebellum when compared with age-matched control tissues. However, in CSF from L-DOPA-treated patients and in serum from L-DOPA-treated and untreated parkinsonian patients, ferritin levels were normal. Previous studies have suggested an increased total iron content in substantia nigra of parkinsonian brain. The failure of substantia nigra ferritin formation to be stimulated by increased iron levels suggests some defect in iron handling in this critical brain region in Parkinson's disease. The reason for decreased ferritin levels throughout the parkinsonian brain is not clear but does not seem to reflect a general system deficit in ferritin.

Brain Chemistry↗
PubMed1989

Treatment of narcolepsy with L-tyrosine: double-blind placebo-controlled trial.

A randomised, double-blind, placebo-controlled study of L-tyrosine was done in ten subjects with narcolepsy and cataplexy. Of twenty-eight visual analogue scales rating mood and arousal, the subjects' ratings in the tyrosine treatment (9 g daily) and placebo periods differed significantly for only three (less tired, less drowsy, more alert). Ratings of daytime drowsiness, cataplexy, sleep paralysis, night-time sleep, overall clinical response, and measurements of multiple sleep latency and tests of speed and attention did not differ significantly between tyrosine and placebo periods. Dietary supplementation with tyrosine 9 g daily for 4 weeks seems to have a mild stimulant action on the central nervous system but this effect is not clinically significant in the treatment of the narcoleptic syndrome.

Adult↗