Hisamasa Imai

Clinical heterogeneity of α-synuclein gene duplication in Parkinson's disease

Recently, genomic multiplications of α‐synuclein gene (SNCA) have been reported to cause hereditary early‐onset parkinsonism. The objective of this study was to assess the frequency of SNCA multiplications among autosomal dominant hereditary Parkinsons disease (ADPD).

Excitotoxic lesions of the pedunculopontine tegmental nucleus produce contralateral hemiparkinsonism in the monkey.

Dopaminergic nigrostriatal neurons, degeneration of which causes Parkinsons disease, are known to receive excitatory input almost exclusively from the pedunculopontine tegmental nucleus (PPN). We report here that excitotoxic lesions of the PPN produce abnormal motor signs relevant to hemiparkinsonism in the macaque monkey. Under the guidance of extracellular unit recordings, the electrophysiologically identified PPN was injected unilaterally with kainic acid. These PPN-lesioned monkeys exhibited mild to moderate levels of flexed posture and hypokinesia in the upper and lower limbs contralateral to the lesion. In most of the monkeys, such pathophysiological events were gradually improved and became stationary in 1-2 weeks. The hemiparkinsonian symptoms observed after PPN destruction might be ascribed to a decrease in nigrostriatal neuron activity due to excitatory input ablation.

Iron accumulation in the substantia nigra of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian monkeys

The mechanism of abnormal iron accumulation in the substantia nigra (SN) pars compacta of patients with Parkinsons disease (PD) is unknown. To explore this question, we made a hemiparkinsonism model in monkeys by injecting 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the caudate or putamen on one side, and compared iron content in the SN and other basal ganglia structures by histochemistry. The injected side, especially the SN pars compacta, showed a marked increase in iron staining. Our study indicates that an injury to the nigrostriatal system by MPTP injection can induce iron accumulation in the SN.

Expanding the clinical phenotype of SNCA duplication carriers.

SNCA duplication is a recognized cause of familial Parkinsons disease (PD). We aimed to explore the genetic and clinical variability in the disease manifestation. Molecular characterization was performed using real‐time PCR, SNP arrays, and haplotype analysis. We further studied those patients who were found to harbor SNCA duplication with olfactory function tests, polysomnography, and PET. We identified four new families and one sporadic patient with SNCA duplication. Eleven symptomatic patients from these four families presented with parkinsonism, of which three subsequently developed dementia. The lifetime estimate of overall penetrance was 43.8%. FDG–PET study of symptomatic patients showed hypometabolism in the occipital lobe, whereas asymptomatic carriers of SNCA duplication demonstrated normal glucose metabolism. Symptomatic patients showed abnormal olfactory function and polysomnography and asymptomatic carriers showed normal results. The clinical features of SNCA duplication include parkinsonism with or without dementia. Asymptomatic carriers displayed normal test results with the eldest individual aged 79 years; thus, even a carrier of SNCA duplication may escape the development of PD. This difference in age‐associated penetrance may be due to the genetic background or environmental exposures. Further studies of SNCA duplication carriers will help identify disease‐modifiers and may open novel avenues for future treatment.

Hemiparkinsonism in monkeys after unilateral caudate nucleus infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): behavior and histology

Systematically administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is biotransformed into 1-methyl-4-phenylpyridinium ion (MPP+), which enters dopaminergic neurons via the dopamine uptake system to destroy nigral cells. Either MPP+ is retrogradely transported to the cell body after being taken up at the nerve terminals, or the dopamine uptake sites on the cell body and its dendritic processes are responsible for the toxin directly entering the neuron. Using a 200 microliter osmotic minipump, we administered 4 mg of MPTP HCl directly into the unilateral caudate nucleus, i.e., the dopamine nerve terminal area, of monkeys for 14 days. Persistent hemiparkinsonism began to appear in a week. Each monkey exhibited a flexed posture and hypokinesia of the contralateral limbs and circling toward the MPTP-treated side. These disturbances developed within 3 months and maintained a plateau for 3 months until the day of sacrifice. After treatment with apomorphine, there appeared a striking circling away from the MPTP-treated side. Selective cell loss in the MPTP-treated side of the substantia nigra pars compacta was found along the entire rostrocaudal extent relative to the untreated side. In conclusion, MPP+ uptake only at the dopamine nerve terminals and retrograde axonal transport to the cell body seemed sufficient to destroy nigral dopamine cells in the monkey.

Protection against dopaminergic nigrostriatal cell death by excitatory input ablation

The importance of enhanced glutamatergic neurotransmission in the basal ganglia and related structures has recently been highlighted in the development of Parkinsons disease. The pedunculopontine tegmental nucleus (PPN) is the major origin of excitatory, glutamatergic input to dopaminergic nigrostriatal neurons of which degeneration is well known to cause Parkinsons disease. Based on the concept that an excitatory mechanism mediated by glutamatergic neurotransmission underlies the pathogenesis of neurodegenerative disorders, we made an attempt to test the hypothesis that removal of the glutamatergic input to the nigrostriatal neurons by PPN lesions might prevent 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced parkinsonism in the macaque monkey. The PPN was lesioned unilaterally with microinjection of kainic acid, and, then, MPTP was administered systemically. In these monkeys, the degree of parkinsonian motor signs was behaviourally evaluated, and the histological changes in the dopaminergic nigrostriatal system were analysed by means of tyrosine hydroxylase immunohistochemistry. The present results revealed that nigrostriatal cell loss and parkinsonian motor deficits were largely attenuated in the MPTP‐treated monkey group whose PPN had been lesioned, compared with the control, MPTP‐treated monkey group with the PPN intact. This clearly indicates that the onset of MPTP neurotoxicity is suppressed or delayed by experimental ablation of the glutamatergic input to the nigrostriatal neurons. Such a protective action of excitatory input ablation against nigrostriatal cell death defines evidence that nigral excitation driven by the PPN may be implicated in the pathophysiology of Parkinsons disease.

Analyses of the MAPT, PGRN, and C9orf72 mutations in Japanese patients with FTLD, PSP, and CBS

BACKGROUND Mutations in the microtubule associated protein tau (MAPT) and progranulin (PGRN) have been identified in several neurodegenerative disorders, such as frontotemporal lobar degeneration (FTLD), progressive supranuclear palsy (PSP), and corticobasal syndrome (CBS). Recently, C9orf72 repeat expansion was reported to cause FTLD and amyotrophic lateral sclerosis (ALS). To date, no comprehensive analyses of mutations in these three genes have been performed in Asian populations. The aim of this study was to investigate the genetic and clinical features of Japanese patients with MAPT, PGRN, or C9orf72 mutations. METHODS MAPT and PGRN were analyzed by direct sequencing and gene dosage assays, and C9orf72 repeat expansion was analyzed by repeat-primed PCR in 75 (48 familial, 27 sporadic) Japanese patients with FTLD, PSP, or CBS. RESULTS We found four MAPT mutations in six families, one novel PGRN deletion/insertion, and no repeat expansion in C9orf72. Intriguingly, we identified a de novo MAPT p.S285R mutation. All six patients with early-onset PSP and the abnormal eye movements that are not typical of sporadic PSP had MAPT mutations. The gene dosages of MAPT and PGRN were normal. DISCUSSION MAPT p.S285R is the first reported de novo mutation in a sporadic adult-onset patient. MAPT mutation analysis is recommended in both familial and sporadic patients, especially in early-onset PSP patients with these abnormal eye movements. Although PGRN and C9orf72 mutations were rare in this study, the PGRN mutation was found in this Asian FTLD. These genes should be studied further to improve the clinicogenetic diagnoses of FTLD, PSP, and CBS.

An immuno-histochemical study of ferritin in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian monkeys

Iron is increased in the substantia nigra of patients with Parkinsons disease, but the mechanism of its accumulation is unknown. We report the distribution of ferritin in the basal ganglia of hemiparkinsonian monkeys made by MPTP. We stereotactically injected MPTP unilaterally into the caudate nucleus of four monkeys, and the substantia nigra and the basal ganglia regions were stained for L-ferritin by an immunohistochemical method. The ferritin immuno-staining was most intense in the pallidum and the pars reticulata of the substantia nigra on both injected and non-injected sides. No significant difference was noted in the immunostaining for ferritin in the pars compacta of the substantia nigra between the injected and the non-injected side. Iron was increased in the pars compacta of the substantia nigra of this hemiparkinsonian monkeys in our previous study. Normal ferritin immunostaining on the injected side would indicate that iron accumulation is not related to altered metabolism of L-ferritin in this model.

Clinicophysiological features of akinesia.

Among the motor tetrad of Parkinsons disease, akinesia is not easy to define and controversies still exist on the nature of akinesia. In 1972 Barbeau first described pure akinesia without rigidity or tremor responsive to L-dopa therapy, that is, akinesia due to striatal dopamine deficiency. Since 1974, Imai and Narabayashi have described a different type of pure akinesia, unresponsive to L-dopa treatment. This new condition exhibits only the freezing symptom, which is a breakdown of repetitive voluntary movements emerging through festination or suddenly, e.g., freezing of gait, micrographia and inaudible speech. Kinésie paradoxale is always accompanied by this type of akinesia. The author suggested that the main pathological structure of the condition was different from the nigrostriatal dopaminergic system and that the condition was different from Parkinsons disease. Subsequently we expanded our experience to more than 30 patients. All patients were sporadic and slowly progressive, and some had been followed for more than 10 years, still without rigidity or tremor. Slowly progressive supranuclear opthalmoplegia appeared later in several patients, in which progressive supranuclear palsy (PSP) was strongly suggested. Autopsy cases associated with this condition have been reported and pathologically revealed PSP. The nosological position and responsible lesion sites of this condition are discussed.

Dimethoxyphenylethylamine and tetrahydropapaverine are toxic to the nigrostriatal system

We report the toxic effects of 3,4-dimethoxyphenylethylamine (DMPEA), and tetrahydropapaverine (THP) on the rat nigrostriatal system; THP is a tetrahydroisoquinoline compound which may be derived from DMPEA by conjugation of DMPEA and its oxidative metabolite, dimethoxyphenylacetaldehyde; both are potent inhibitors of mitochondrial complex I. These compounds were introduced to the unilateral caudate-putamen of male Sprague-Dawley rats over 7 days using a 200-microl mini-osmotic pump. Striatal dopamine on the injected side showed a significant decrease to 86% of the non-injected side after 16.55 micromol/7 days infusion of DMPEA, and to 73% of the non-injected side after 7.90 micromol/7 days of THP infusion; as the non-injected side dopamine also reduced in the THP-injected rats, dopamine on the injected side was 55% of the saline control. Tyrosine hydroxylase (TH)-positive nigral neurons were decreased to 76% of the non-injected side after 16.55 micromol/7 days infusion of DMPEA and to 77% after 7.90 micromol/7 days of THP infusion. Dimethoxyphenyl-tetrahydroisoquinoline compounds appear to be potent nigral neurotoxins.