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.

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)

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.

Covalent protein binding of a metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to mouse and monkey brain in vitro and in vivo.

We have recently reported that a reactive metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is formed in rat brain in vitro by type B monoamine oxidase (MAO). In the present study, we further characterize the irreversible binding in vitro using tissues from mice and monkeys, two species more sensitive than rats to MPTP neurotoxicity. We also report the occurrence of irreversible binding of radioactivity after administration of tritiated MPTP in the same species in vivo. Tissue homogenates were incubated at 37 degrees with 1-[methyl-3H]MPTP in in vitro experiments. Animals were injected with labeled MPTP and sacrificed at different times in in vivo experiments. The perchloric acid precipitates of tissue homogenates from either procedure were washed exhaustively with organic solvents and counted for radioactivity. The amount of recovered radioactivity in in vitro experiments was similar using brain homogenates from mice and monkeys, whereas a considerably lower amount was found in mouse liver. MAO-B inhibitors decreased the covalent binding. However, the combined MAO-B/MAO-A inhibitor pargyline had no effect if added after 2 hr of incubation. Sulfhydryl-containing compounds decreased the covalent binding in a concentration-related manner. GSH reduced the rate of the reaction throughout the incubation. The covalent binding slowly increased in time in vivo in mouse brain, not in liver. There was a two-fold variation of covalently bound radioactivity in different brain areas of 3H2-MPTP-treated monkey. This reactive metabolite may play a role in MPTP neurotoxicity.

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.

Family-based association study between bipolar disorder and DRD2, DRD4, DAT, and SERT in Sardinia.

Association analysis of candidate genes may represent a strategy for clarifying the genetic components involved in bipolar disorder. Polymorphism at dopamine receptor genes DRD2, DRD4, and dopamine and serotonin transporter genes (DAT, SERT) has been used in previous association studies. Some authors have reported positive association between certain alleles and bipolar disorder, using the case-control design. In this family-based association study of DRD2, DRD4, DAT, and SERT, the distribution of parental nontransmitted alleles was compared with that of alleles transmitted to 53 Sardinian probands suffering from bipolar disorder. The transmission disequilibrium test (TDT) was used to detect any disproportionate transmission of alleles by heterozygous parents to affected children. No differences were found between the allele distribution of polymorphisms at DRD2, DRD4, DAT, and SERT in probands and parental nontransmitted chromosomes. TDT did not reveal any difference between transmitted and nontransmitted alleles. Our results do not support the hypothesis of a role for DRD2, DRD4, DAT, or SERT in bipolar disorder. Previously reported positive associations between DRD2 or SERT and bipolar disorder were conceivably due to stratification dependent on the case-control design, even though our sample might have failed to detect small associations due to limited power.

No evidence of association between dopamine D3 receptor gene and bipolar affective disorder.

A recent study reported a possible association between allele 1 of the dopamine D3 receptor gene and bipolar affective disorder using the haplotype relative risk approach. In attempt to replicate these findings, we used similar family-based methods, such as the Haplotype-Based Haplotype Relative Risk method and the Transmission Disequilibrium Test, in a sample of 44 bipolar probands from Sardinia with both parents available. Using the Bal I restriction enzyme site polymorphism of Lannfelt et al. (1992), no differences were found between transmitted and non-transmitted alleles and no evidence of linkage disequilibrium was observed.

Effects of tiapride on homovanillic acid levels in human cerebrospinal fluid drawn at pneumoencephalography.

The effect of tiapride on HVA and 5-HIAA levels in the CSF drawn at pneumoencephalography (PEG) was studied. Five consecutive 5 ml fractions of CSF were drawn from control and tiapride-treated subjects. In both groups, a linear increase in HVA concentrations was found between the first and subsequent fractions. On the contrary, no significant difference in 5-HIAA concentrations was found in sequential CSF samples. Tiapride increased the mean HVA concentrations and caused a steeper caudocranial gradient of this metabolite but failed to modify 5-HIAA concentrations. The results suggest that tiapride blocks dopamine (DA) receptors and increases DA synthesis.

Maternal inheritance of manic depression in hemizygotes for the G6PD-Mediterranean mutation. Indirect evidence for Xq28 transmission in Sardinia.

Both X-linkage and a parent-of-origin effect have been hypothesized in manic-depressive disorder. We have previously shown an allelic association between X-linked G6PD deficiency and manic depression in Mediterranean populations. To test both X-linkage and a parent-of-origin effect in manic depression further, we have studied 274 Sardinian manic-depressive probands and their parents. Excess of maternal transmission (P = 0.005) of major affective disorder was found in male probands carrying the G6PD-Mediterranean mutation. Our results provide indirect molecular support for an association between manic depression and the Xq28 chromosome region in Sardinia. Further studies on Xq28 using tests of allelic association and transmission disequilibrium with multiple DNA markers are required, to clarify the nature of the association we have found. Our study cannot implicate or exclude a direct role for G6PD deficiency in the aetiology of manic depression.

Involvement of monoamine oxidase enzymes in the action of 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine, a selective neurotoxin, in the squirrel monkey: binding and biochemical studies.

1-Methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) is a new neurotoxin that causes degeneration of the dopaminergic nigrostriatal neurons and induces a Parkinson-like state in several species, including humans and monkeys. The present study was designed to better characterize the properties of [3H]MPTP binding sites and to evaluate the interaction of MPTP with the oxidation of dopamine by monoamine oxidase (MAO) in an animal species (Saimiri Sciureus) shown to be lesioned by MPTP. Our data confirm the presence of high affinity and saturable binding sites for [3H]MPTP in the squirrel monkey. Specific binding with analogous characteristics also occurs in peripheral tissues. Various substances failed to inhibit the [3H]MPTP binding, whereas only MAO inhibitors (MAOI) were able to antagonize this binding to brain and peripheral tissues. In particular, deprenyl, a selective inhibitor of MAO type B enzyme, was relatively more potent as a displacer of [3H]MPTP from its binding sites both in brain and in peripheral tissues. Our results further suggest a correspondence between [3H]MPTP sites and MAO, particularly MAO-B, in monkey brain. Moreover, our data show that the oxidative deamination of dopamine is inhibited by MPTP in vitro. In conclusion, these data are consistent with the hypothesis of the involvement of MAO in the neurotoxic effects of MPTP, even though further experiments are necessary to better clarify the molecular mechanism of MPTP neurotoxicity.

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.

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.

Primate-rodent 3H-MPTP binding differences, and biotransformation of MPTP to a reactive intermediate in vitro.

Specific binding of 3H-MPTP to brain homogenates is displaced predominantly by MAO-A inhibitor clorgyline in rat, and by MAO-B inhibitor deprenyl in monkey. A covalently bound metabolite is formed by MAO-B in vitro from MPTP, through a reaction almost completely inhibited by physiological concentrations of glutathione and significantly reduced by other sulfhydryl containing compounds. The difference in binding site pharmacological properties may account for the relative resistance of rat to the neurotoxic effect produced by MPTP in primates. The glutathione-prevented metabolic conversion to a reactive intermediate may be important for the mechanism of MPTP neurotoxicity and relevant to idiopathic Parkinson's disease.

Heterogeneity of monoaminergic vesicular carriers: pharmacological evidence using MPP+ as a marker.

MPP-production and uptake by dopaminergic terminals are critical steps in MPTP-induced Parkinson-like disorder. We reported evidence for a specific uptake of MPP by synaptic vesicles from mouse striatum. Its regional distribution suggests it as a marker of the dopamine vesicular carrier. We decided to further characterize such an MPP uptake. Tetrabenazine inhibits the dopamine uptake both in the striatum and in the cerebellum with similar Km values suggesting an identify of the vesicular carrier in these areas. On the contrary, 3H-MPP vesicular uptake had in the striatum a t1/2 of 60 sec, but was not detectable at any time in the cerebellum. Moreover, MPP inhibited the uptake of 3H-DA (Ki: 1.6 +/- 0.03 microM) and 3H-NE (Ki 2.6 +/- 0.01 microM) in the striatum but not in the cerebellum, even at molar concentration. These pharmacological data indicate that in nondopaminergic areas the monoamine carrier may be similar but not identical from that located in dopaminergic areas.

Apomorphine as a preferential stimulant of self-inhibitory dopamine receptors in man.

In man, non emetic doses of apomorphine elicit a series of behavioural, neurological and psychological changes which are difficult to ascribe to the stimulation of postsynaptic dopamine receptors. Since similar effects are elicited by neuroleptic drugs, the functional changes induced by apomorphine in man might be interpreted as being the result of a decreased dopaminergic activity. The sedation and sleep, the improvement of choreic movements and the antipsychotic effect induced by non emetic doses of apomorphine are prevented by specific dopamine receptor blockers. These responses therefore are mediated through a stimulation of dopamine receptors leading to a decreased dopaminergic transmission. This new type of receptors might be identified with the so called "self-inhibitory" dopamine receptors.