Mark Guttman

Brain serotonin transporter binding in non-depressed patients with Parkinson's disease

Early post‐mortem data suggest that damage to brain serotonin neurones might play a role in some features (e.g., depression) of Parkinsons disease (PD). However, it is not known whether such damage is a typical characteristic of living patients with PD or whether the changes are regionally widespread. To address this question we measured, by positron emission tomography imaging, levels of the brain serotonin transporter (SERT), a marker for serotonin neurones, as inferred from binding of [11C]‐3‐amino‐4‐(2‐dimethylaminomethyl‐phenylsulfanyl)‐benzonitrile (DASB), a second generation SERT radioligand, in subcortical and cerebral cortical brain areas of clinically advanced non‐depressed (confirmed by structured psychiatric interview) patients with PD. SERT binding levels in PD were lower than those in controls in all examined brain areas, with the changes statistically significant in orbitofrontal cortex (−22%), caudate (−30%), putamen (−26%), and midbrain (−29%). However, only a slight non‐significant reduction (−7%) was observed in dorsolateral pre‐frontal cortex, an area implicated in major depression. Our imaging data suggests that a modest, regionally widespread loss of brain serotonergic innervation might be a common feature of advanced PD. Further investigation will be required to establish whether SERT binding is more or less decreased in those patients with PD who also have major depressive disorder.

Decreased cerebral cortical serotonin transporter binding in ecstasy users: a positron emission tomography/[11C]DASB and structural brain imaging study

Animal data indicate that the recreational drug ecstasy (3,4-methylenedioxymethamphetamine) can damage brain serotonin neurons. However, human neuroimaging measurements of serotonin transporter binding, a serotonin neuron marker, remain contradictory, especially regarding brain areas affected; and the possibility that structural brain differences might account for serotonin transporter binding changes has not been explored. We measured brain serotonin transporter binding using [(11)C] N,N-dimethyl-2-(2-amino-4-cyanophenylthio) benzylamine in 50 control subjects and in 49 chronic (mean 4 years) ecstasy users (typically one to two tablets bi-monthly) withdrawn from the drug (mean 45 days). A magnetic resonance image for positron emission tomography image co-registration and structural analyses was acquired. Hair toxicology confirmed group allocation but also indicated use of other psychoactive drugs in most users. Serotonin transporter binding in ecstasy users was significantly decreased throughout all cerebral cortices (range -19 to -46%) and hippocampus (-21%) and related to the extent of drug use (years, maximum dose), but was normal in basal ganglia and midbrain. Substantial overlap was observed between control and user values except for insular cortex, in which 51% of ecstasy user values fell below the lower limit of the control range. Voxel-based analyses confirmed a caudorostral gradient of cortical serotonin transporter binding loss with occipital cortex most severely affected. Magnetic resonance image measurement revealed no overall regional volume differences between groups; however, a slight left-hemispheric biased cortical thinning was detected in methamphetamine-using ecstasy users. The serotonin transporter binding loss was not related to structural changes or partial volume effect, use of other stimulant drugs, blood testosterone or oestradiol levels, major serotonin transporter gene promoter polymorphisms, gender, psychiatric status, or self-reported hyperthermia or tolerance. The ecstasy group, although grossly behaviourally normal, reported subnormal mood and demonstrated generally modest deficits on some tests of attention, executive function and memory, with the latter associated with serotonin transporter decrease. Our findings suggest that the typical/low dose (one to two tablets/session) chronic ecstasy-polydrug user might display a highly selective mild to marked loss of serotonin transporter in cerebral cortex/hippocampus in the range of that observed in Parkinsons disease, which is not gender-specific or completely accounted for by structural brain changes, recent use of other drugs (as assessed by hair analyses) or other potential confounds that we could address. The striking sparing of serotonin transporter-rich striatum (although possibly affected in heavier users) suggests that serotonergic neurons innervating cerebral cortex are more susceptible, for unknown reasons, to ecstasy than those innervating subcortical regions and that behavioural problems in some ecstasy users during abstinence might be related to serotonin transporter changes limited to cortical regions.

Brain α-synuclein accumulation in multiple system atrophy, Parkinson's disease and progressive supranuclear palsy: a comparative investigation

Alpha-synuclein is a major component of Lewy bodies and glial cytoplasmic inclusions, pathological hallmarks of idiopathic Parkinsons disease and multiple system atrophy, and it is assumed to be aetiologically involved in these conditions. However, the quantitative status of brain alpha-synuclein in different Parkinsonian disorders is still unresolved and it is uncertain whether alpha-synuclein accumulation is restricted to regions of pathology. We compared membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein, both the full-length 17 kDa and high molecular weight species, by western blotting in autopsied brain of patients with Parkinsons disease (brainstem-predominant Lewy body disease: n = 9), multiple system atrophy (n = 11), progressive supranuclear palsy (n = 16), and of normal controls (n = 13). Brain of a patient with familial Parkinsonism-dementia due to alpha-synuclein locus triplication (as positive control) showed increased membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein levels with abundant high molecular weight immunoreactivity. In multiple system atrophy, a massive increase in 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein was observed in highly pathologically affected regions, including putamen (+1760%, range +625-2900%), substantia nigra [+1000% (+356-1850%)], and white matter of internal capsule [+2210% (+430-6830%)] together with numerous high molecular weight species. Levels of 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein were only modestly increased in less affected areas (cerebellar cortex, +95%; caudate, +30%; with both also showing numerous high molecular weight species) and were generally normal in cerebral cortices. In both Parkinsons disease and progressive supranuclear palsy, membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein levels were normal in putamen and frontal cortex whereas a trend was observed for variably increased 17 kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein concentrations [+184% (-60% to +618%)] with additional high molecular weight species in Parkinsons disease substantia nigra. No obvious correlation was observed between nigral membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation and Lewy body density in Parkinsons disease. Two progressive supranuclear palsy cases had membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation in substantia nigra similar to multiple system atrophy. Several Parkinsons disease patients had very modest high molecular weight membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulation in putamen. Levels of 17-kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein were generally positively correlated with those of high molecular weight membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein and there was a trend for a positive correlation between striatal dopamine loss and 17-kDa membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein concentrations in multiple system atrophy. Brain membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein accumulations in Parkinsons disease and multiple system atrophy are regionally specific, suggesting that these sporadic alpha-synucleinopathies, unlike familial Parkinsonism-dementia, are not associated with a simple global over-expression of the protein. Despite a similar extent of dopamine depletion, the magnitude of brain membrane-associated, sodium dodecyl sulfate-soluble alpha-synuclein changes is disease specific, with multiple system atrophy clearly having the most severe accumulation. Literature discrepancies on alpha-synuclein status in Parkinsons disease might be explained by inclusion of cases not having classic brainstem-predominant Lewy body disease and by variable alpha-synuclein accumulation within this diagnostic classification.

Elevated Serotonin Transporter Binding in Depressed Patients with Parkinson's Disease : A Preliminary PET Study with [11C]DASB

This study investigated whether abnormalities in serotonin transporter binding occur in Parkinsons disease (PD) patients with concurrent depression. We estimated serotonin transporter levels in seven clinically depressed early‐stage PD patients and in seven healthy matched‐control subjects during a single positron emission tomography (PET) scan with the serotonin transporter radioligand, [11C]DASB. Depressed PD patients displayed a wide‐spread increase (8–68%) in [11C]DASB specific binding outside of the striatum, which was significant in dorsolateral (37%) and prefrontal (68%) cortices. Elevated [11C]DASB binding was positively correlated with depressive symptoms but not with disease severity or duration. Compatible with recent PET/[11C]DASB findings in major depression, the present preliminary data suggest that increased [11C]DASB binding, possibly reflecting greater serotonin transporter density (up‐regulation), might be a pathological feature of depression in Parkinsons disease—and possibly a characteristic of depressive illness in general.

Striatal dopaminergic and serotonergic markers in human heroin users.

To establish whether chronic opiate exposure might impair brain dopaminergic or serotonergic function in humans, we assessed biochemical indices of monoaminergic neurotransmitter activity and integrity in post mortem striatum of nine chronic heroin users and 14 control subjects. Striatal levels of the vesicular monoamine transporter were normal, suggesting that the density of dopamine nerve terminals is not reduced in heroin users. In nucleus accumbens, levels of tyrosine hydroxylase protein (-25%) and those of the dopamine metabolite homovanillic acid (-33%) were reduced significantly together with a trend for decreased dopamine (-32%) concentration. These changes could reflect either a compensatory downregulation of dopamine biosynthesis in response to prolonged dopaminergic stimulation caused by heroin, or reduced axoplasmic transport of tyrosine hydroxylase. Striatal levels of serotonin were either normal or elevated whereas concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were decreased by 27–38%. Our data suggest that chronic heroin exposure might produce a modest reduction in dopaminergic and serotonergic activity that could affect motivational state and impulse control, respectively.

Brain proteasomal function in sporadic Parkinson's disease and related disorders

Because genetic defects relating to the ubiquitin–proteasome system were reported in familial parkinsonism, we evaluated proteasomal function in autopsied brains with sporadic Parkinsons disease. We found that proteasome peptidase activities in a fraction specific to the proteasome were preserved in five brain areas (including the striatum) of Parkinsons disease where neuronal loss is not observed. Striatal protein levels of two proteasome subunits were normal in Parkinsons disease but reduced mildly in disease controls (multiple system atrophy). Our brain data suggest that a systemic, global disturbance in the catalytic activity and degradation ability of the proteasome itself is unlikely to explain the cause of Parkinsons disease.

Regional distribution of methamphetamine in autopsied brain of chronic human methamphetamine users

We measured levels of methamphetamine and those of its metabolite amphetamine in 15 autopsied brain regions of 14 human methamphetamine users. Only slight regional differences were observed in drug concentrations among the brain areas. Although, some redistribution of the drugs probably occurred postmortem, these data suggest that methamphetamine might not be preferentially retained in dopamine-rich brain areas but is heterogenously distributed in brain of chronic human users of the drug. The possible pharmacological actions of methamphetamine in both dopamine-rich and poor brain areas of chronic drug users need to be considered.

Nigral glutathione deficiency is not specific for idiopathic Parkinson's disease.

The consistent findings of decreased levels of the major antioxidant glutathione in substantia nigra of patients with idiopathic Parkinsons disease (PD) has provided most of the basis for the oxidative stress hypothesis of the etiology of PD. To establish whether a nigral glutathione deficiency is unique to PD, as is generally assumed, or is present in other Parkinsonian conditions associated with nigral damage, we compared levels of reduced glutathione (GSH) in postmortem brain of patients with PD to those with progressive supranuclear palsy (PSP) and multiple system atrophy (MSA). As compared with the controls, nigral GSH levels were decreased in the PD and PSP patient groups (P < 0.05 for PD [−30%], PSP [−21%]), whereas a similar decrease in the MSA patient group did not reach statistical significance (P = 0.078, MSA [−20%]). GSH levels were normal in all examined normal and degenerating extra‐nigral brain areas in PSP and MSA. A trend for decreased levels of uric acid (antioxidant and product of purine catabolism) also was observed in nigra of all patient groups (−19 to −30%). These data suggest that glutathione depletion, possibly consequent to overutilisation in oxidative stress reactions, could play a causal role in nigral degeneration in all nigrostriatal dopamine deficiency disorders, and that antioxidant therapeutic approaches should not be restricted to PD.

Dopa-responsive dystonia due to a large deletion in the GTP cyclohydrolase I gene.

Although it is assumed that most patients with autosomal dominant dopa‐responsive dystonia (DRD) have a GTP cyclohydrolase I dysfunction, conventional genomic DNA sequencing of the gene (GCH1) coding for this enzyme fails to reveal any mutations in about 40% of DRD patients, which makes molecular genetic diagnosis difficult. We found a large heterozygous GCH1 deletion, which cannot be detected by the usual genomic DNA sequence analysis, in a three‐generation DRD family and conclude that a large genomic deletion in GCH1 may account for some “mutation‐negative” patients with dominantly inherited DRD. Ann Neurol 2000;47:517–520.

Regional Distribution of Cocaine in Postmortem Brain of Chronic Human Cocaine Users

We measured concentrations of cocaine and its major metabolites (benzoylecgonine, ecgonine methylester, norcocaine, and cocaethylene) in 15 autopsied brain regions of 14 human chronic cocaine users. Only slight differences were observed in concentrations of cocaine and its metabolites amongst the examined brain areas. Although it is likely that some postmortem redistribution of the drug must have occurred, our data are consistent with the possibility that behaviorally relevant doses of cocaine are widely distributed throughout the brain of humans who use the drug on a chronic basis. Consideration should therefore be given to the possible pharmacological and toxicological actions of cocaine in both striatal and extra-striatal brain areas in human users of the drug.