M.P. Piccardi

Association between dopamine receptor genes and migraine without aura in a Sardinian sample

Background: Migraine seems to be caused by a combination of environmental and genetic factors. Clinical and pharmacologic evidence supports the hypothesis that dopaminergic transmission is involved in the pathogenesis of migraine. Objective: The current report concerns a genetic study to test the involvement of genes for dopamine (DA) receptors D2 (DRD2), D3 (DRD3), and D4 (DRD4) in migraine without aura, particularly in a subgroup with enhanced DA sensitivity. Methods: For the first time, a family-based association method-the Transmission Disequilibrium Test (TDT)-was used to examine an isolated population, such as Sardinians. We studied 50 nuclear families of patients affected by migraine without aura. The subgroup of dopaminergic migraineurs was selected based on the presence of both nausea and yawning immediately before or during the pain phase of migraine. Results: No association was detected using the TDT between DRD3, DRD4, and migraine without aura either in the overall sample or in the subgroup. No difference was observed in DRD2 allelic distribution in the overall sample, although the allelic distribution at the DRD2 locus differed significantly in the subgroup of dopaminergic migraineurs (p = 0.004). Allele 1 of the TG dinucleotide intronic noncoding polymorphism of the DRD2 locus was the individual allele that appeared to be in disequilibrium with migraine without aura (p = 0.02). Conclusions: Our data suggest that a genetic approach could be useful in providing molecular support to the hypothesis that hypersensitivity of the dopaminergic system may represent the pathophysiologic basis of migraine, at least in a subgroup of patients.

Selective MPP+ uptake into synaptic dopamine vesicles: possible involvement in MPTP neurotoxicity.

1 In the present study we provide evidence for a saturable, Mg2+/ATP‐ and temperature‐dependent, tetrabenazine‐, dopamine‐, and amphetamine‐sensitive uptake of 1‐methyl‐4‐phenylpyridinium ion (MPP+) in synaptic vesicles from mouse striatum. 2 Similarity in the properties of the vesicular uptake suggests that in the striatum dopamine and MPP+ share the vesicular carrier. 3 The presence of MPP+ vesicular uptake in dopamine‐rich regions such as striatum, olfactory, tubercles and hypothalamus, as well as its absence in cerebellum, cortex and pons‐medulla, suggest that monoamine vesicular carriers differ between highly and poorly dopamine‐innervated regions. 4 The restriction of active MPP+ uptake to the dopaminergic regions, which reflects the previously shown distribution of [3H]‐MPP+ binding sites in mouse brain membranes, indicates MPP+ as a marker of the vesicular carrier for dopamine in dopaminergic neurones. 5 A role in MPP+ neurotoxicity is suggested for this region‐specific, vesicular storage of the toxin.

Chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to monkeys: Behavioural, morphological and biochemical correlates

The behavioural, biochemical and morphological effects of a chronic administration of low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were studied in the common marmoset. Monkeys received the toxin (1 mg/kg i.p.) twice a week for four months. Group A monkeys were studied one week after the last injection of MPTP; group B monkeys were studied eight months after the last toxic injection. The monkey behaviour was observed throughout the experiment; the biochemical and morphological correlates were studied post mortem in the neostriatum and in the substantia nigra, respectively. Data collected from MPTP-treated marmosets were compared to those obtained from sham-injected control monkeys. The results can be summarized as follows. (1) In all MPTP-treated marmosets a progressive Parkinsonism occurred. In group B monkeys, a gradual behavioural recovery was observed after MPTP was discontinued. (2) Biochemical analysis of group A marmosets showed a depletion of dopamine, of 3,4-hydroxyphenylacetic acid and of homovanillic acid, and no variations in dopamine turnover in the neostriatum of MPTP-treated marmosets. In group B, biochemical analysis showed no differences between controls and MPTP-treated animals. (3) Morphological analysis showed that the density of midbrain dopaminergic neurons located in the substantia nigra was unchanged in group A monkeys, but was reduced by 6.8% in MPTP-treated monkeys of group B. The measurement of cross-sectional area showed that midbrain dopaminergic neurons were swollen in MPTP-treated monkeys of group A, with a 11.0% increase of cell size as compared to controls. In group A the nuclei were also swollen, being 304.8% larger in MPTP-treated monkeys, with a nucleus-to-cytoplasm ratio of 65.9% (as compared to 34.0% of controls). In group B monkeys cell size was increased by 18.4% in MPTP-treated marmosets, but the nuclei were of comparable size. The present data show that a chronic administration of low doses of MPTP brings about biochemical and morphological abnormalities. The first occur acutely in terminals and are reverted early after discontinuance of exposure to the toxin; the latter occur in dopaminergic perikarya, last longer than biochemical abnormalities and, at variance with them, increase in severity after MPTP is discontinued. Morphological abnormalities include early events, such as a transient swelling of nuclei or a long-lasting swelling of neurons, and late events, such as a decrease in the number of tyrosine hydroxylase-positive perikarya.(ABSTRACT TRUNCATED AT 400 WORDS)

1 ‐Methyl‐4‐Phenyl‐ 1,2,3,6‐Tetrahydropyridine: Correspondence of Its Binding Sites to Monoamine Oxidase in Rat Brain, and Inhibition of Dopamine Oxidative Deamination In Vivo and In Vitro

Abstract: A saturable, specific, high‐affinity binding site for [3H] 1 ‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine was found in rat brain homogenates. The CNS regional distribution, the subcellular fractionation, and the displacement by pargyline, clorgyline, and deprenyl suggest that this binding site may correspond to monoamine oxidase. I ‐Methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine inhibited the oxidative deamination of dopamine, both in vivo and in vitro. Striatal levels of 3,4‐dihydroxyphenylacetic acid were significantly reduced shortly after intravenous administration, and returned to normal values after a few hours. The in vitro formation of 3,4‐dihydroxyphenylacetic acid from dopamine was inhibited by concentrations of 1‐methyl‐4‐phenyl‐ 1,2,3,6‐tetrahydropyridine comparable to those of pargyline.

The diacylglycerol kinase eta gene and bipolar disorder : a replication study in a Sardinian sample

The diacylglycerol kinase eta gene and bipolar disorder: a replication study in a Sardinian sample

Migraine and tumour necrosis factor gene polymorphism. An association study in a Sardinian sample

To assess the possibility of an association between TNF gene polymorphisms and migraine without aura, a case-control study was performed in a Sardinian sample.Migraine without aura is a complex genetic disease in which susceptibility and environmental factors contribute towards its development. Several studies suggest that tumour necrosis factors (TNF) (TNF-α and lymphotoxin-alpha or TNF-ß) may be involved in the pathophysiology of migraine. The TNF-α and TNF-ß genes are located on chromosome 6p21.3 in the human leukocyte antigene (HLA) class III region. We evaluated 299 patients affected by migraine without aura (I.H.S. criteria 2004) and 278 migraine-free controls. The polymorphisms G308A of the TNF- α gene, and G252A of TNF-β gene were determined by NcoI restriction fragment length polymorphism analysis.We found a statistically significant difference in allele (p = 0.018; OR = 1.46 95 % CI: 1.066 to 2.023) and genotype (trend χ2 = 5.46, df = 1, p = 0.019) frequencies of TNF-β gene, between cases and controls. Allele and genotype frequencies of TNF-α polymorphism did not differ significantly between the two groups.These data suggest that subjects with the TNFB2 allele have a low risk of developing migraine without aura and/or that the polymorphism of the TNF-β gene is in linkage disequilibrium with other migraine responsible genes in the HLA region.

Evaluation of the toxicity of the dopaminergic neurotoxins MPTP and MPP+ in PC12 pheochromocytoma cells: binding and biological studies

This study was designed to investigate the toxicity of both MPTP and MPP+ using some simple cell systems, such as PC12 and C6 cultures, as models. Exposure of PC12 cells to 0.5 mM MPTP for 72 h resulted in a 50% cell loss with respect to the control cells, and clorgyline, a MAO-A inhibitor, antagonized this toxic effect. Higher concentrations of MPTP demonstrated only a weak cytostatic effect on C6 cells. Moreover, MPP+ showed a toxic effect which was 100 times more evident than MPTP toxicity in the PC12. We found a single, saturable class of [3H]MPP+ binding sites with a relatively high affinity both in PC12 and C6 cell lines. Moreover, the most susceptible cell line towards the toxic effects of both MPTP and MPP+, i.e. PC12, has the higher number of MPP+ binding sites. Our results suggest that MPTP can be toxic not only via MAO-B, but also via MAO-A activity and we propose PC12 as a model to study the intracellular mechanisms of MPTP and MPP+ toxicity.

MPTP fails to induce lipid peroxidation in vivo

It has been speculated that the conversion of MPTP to MPP+ destroys dopaminergic neurons by promoting the generation of hydroxyl radicals and causes lipid peroxidation. The results obtained in the present work indicate that the primary products of lipid peroxidation are not detectable in MPTP treated animals and thus other mechanisms besides lipid peroxidation should be considered to explain the cytotoxicity of this neurotoxin.

Characterization of a putatively vesicular binding site for [3H]MPP+ in mouse striatal membranes

[3H] N-Methyl-4-phenylpyridinium ion (MPP+) binds with a fully reversible, high affinity process to a population of sites mainly localized in the mouse striatum (Bmax = 168 +/- 15 fmol/mg protein, KD = 1.4 +/- 0.4 nM). The majority of specifically-bound radioactivity was localized in the synaptosomal fraction. Unilateral, striatal denervation with 6-hydroxydopamine (6-OHDA) markedly (by 65-70%) decreased the number of [3H]MPP+ sites. Besides dopamine, the vesicular markers tyramine, tetrabenazine and reserpine inhibited [3H]MPP+, while mazindol was a poor displacer. Adenosine triphosphate (ATP) and Mg(2+)-ions did not affect [3H]MPP+ binding. It is concluded that these sites may represent a marker of striatal storage vesicles for dopamine.

[3H]1‐Methyl‐4‐Phenyl‐2,3‐Dihydropyridinium Ion Binding Sites in Mouse Brain: Pharmacological and Biological Characterization

Abstract: Because 1‐methyl‐4‐phenyl‐2,3‐dihydropyridinium ion (MPP+) appears to damage the dopaminergic neuron and cause neuronal death, we characterized [3H]MPP+ binding sites in mouse brain membranes. Among several compounds tested, debrisoquin [3,4‐dihydro‐2(1 H)‐isoquinolinecarboxamidine] and some analogues were able to antagonize [3H]MPP+ binding. Debrisoquin is able to block adrenergic transmission and inhibit the activity of monoamine oxidase A (MAO‐A). We found a certain correlation between the ability of these agents to displace [3H]MPP+ from its binding sites and their capacity to inhibit MAO‐A activity. These data and the finding of a higher number of [3H]MPP+ binding sites in human placenta compared to mouse brain suggest that these sites may correspond to MAO‐A enzymes. Recently it has been demonstrated in human brain that neurons in regions rich in catecholamines are positive for MAO‐A. Accordingly, we suggest MAO‐A as a possible accumulation site of MPP+ within the dopaminergic neuron. We also indicate the chemical structural requirement associated with the best binding of debrisoquin analogues with [3H]MPP+ sites. It would be reasonable to test the effects of debrisoquinlike drugs able to pass the blood‐brain barrier on 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine toxicity.