The effect of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on uridine uptake in the mouse brain

Male white mice were injected with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) 40 mg/kg. After 2 h, 24 h, 2, 4 and 8 days 0.25 mCi [5-3H]uridine was injected i.v. and 1 h later the animals were sacrificed. In microautoradiograms the number of grains over the nerve cell nuclei was counted in the substantia nigra, the cerebral cortex, the hippocampus and the neostriatum. In the substantia nigra there was a significant increase in grain number after 2, 4 and 8 days. In a group of animals injected 3 days with MPTP and sacrificed 2 days after the last injection the same increase was found. In the other brain regions only an insignificant increase in grain counts was found. In a special group of animals the total radioactivity and distribution of label on metabolites in blood, brain and liver was determined. No significant changes were found.     

Evaluation of a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black mouse model for parkinsonism

We evaluated neurochemically, behaviorally, and neuropathologically the availability of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated C57 black (BL) mice as a model for Parkinson's disease. The dopamine and 3,4-dihydroxyphenyl acetic acid content in the striatum, measured by high-performance liquid chromatography with an alectrochemical detector, decreased by 70% at 10 and 20 days after the withdrawal of MPTP (30 mg/kg, i.p. twice daily for 5 days). During these days, the mice showed a decrease in locomotor activity and exhibited akinesia in both pole and traction tests. Light microscopically, 44% of the MPTP-treated mice showed neuronal degeneration in the substantia nigra 1 month after the withdrawal (damaged group), and 56% showed no change (undamaged group). Morphometric analysis revealed that the number of neurons in the substantia nigra decreased by 33% on the average in both groups. Electron microscopically, an electron-dense degeneration of most neurons was seen in the substantia nigra of the damaged group, and even in the undamaged group, loss of rough endoplasmic reticulum and mitochondrial deformity were seen in 50–70% of the neurons. Electron-dense bodies were seen in the striatum of both groups. These results show the validity of the MPTP-treated C57 BL mice as a suitable model fro parkinsonism, including Parkinson's disease.     

Behavioural effects in the rat after acute unilateral intranigral infusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced a dose-dependent contralateral circling in the rat when infused unilaterally into the central region of the pars reticulata of the substantia nigra. This action of MPTP seems to be nigral dopamine-mediated since rotation was potentiated by intranigral amphetamine (50 μg unilaterally) and blocked by haloperidol (5 μg bilaterally) as well as by picrotoxin (5μg bilaterally) and by unilateral lesions of the internal capsule. MPTP was not effective in inducing rotation in rats with unilateral 6-hydroxydopamine lesions of the median forebrain bundle in contrast to intranigral apomorphine which produced robust turning. The data suggest that MPTP may not act as a dopamine receptor agonist but induce rotation by other mechanisms, for example, by enhancing the accumulation of dopamine release from dendrites in the pars reticulata.     

Mild parkinsonism in persons exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) produces moderate to severe parkinsonism in humans, but has not been reported to cause a syndrome similar to early Parkinson's disease. We now report 22 cases of mild parkinsonism resulting from exposure to MPTP.     

Enhanced N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in mice deficient in CuZn-superoxide dismutase or glutathione peroxidase

Administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mammals causes damage to the nigrostriatal dopaminergic pathway similar to that observed in Parkinson disease (PD). Reactive oxygen species (ROS) are thought to be involved in the pathogenesis of MPTP-mediated dopaminergic neurodegeneration. To further clarify the role of superoxide anion radical (*O2-) and to study the possible involvement of hydroperoxides in MPTP-mediated neurodegeneration, MPTP neurotoxicity was induced in mice deficient in either CuZn superoxide dismutase (SOD), a scavenger enzyme for *O2-, or cellular glutathione peroxidase (GSHPx-1), a scavenger enzyme for hydroperoxides. Littermate control and homozygous deficient mice were injected intraperitoneally with a total cumulative dose of 0, 75, or 150 mg/kg of MPTP delivered over 5 d. All mice were killed 5 d after the last injection and the brains were processed for immunohistological analysis for tyrosine hydroxylase (TH) in the striatum and the substantia nigra pars compacta (SNc), as well as for direct measurements of dopamine concentrations in the striatum. The intensity of TH immunoreactivity in the striatum was evaluated by measuring the relative optical density (OD) with NIH IMAGE, and expressed as Log (OD of striatum)/Log (OD of white matter). Degeneration of TH-containing neurons was assessed by counting TH-positive neurons in the SNc. We found that this MPTP exposure protocol produced dose-dependent depletion of TH immunoreactivity and dopamine in the striatum in littermate control mice and both strains of knockout mice; however. reduction in TH immunoreactivity and dopamine content were significantly greater in CuZn-SOD or GSHPx-1 deficient mice compared with littermate controls. MPTP exposure did not significantly alter the number of TH-positive neurons in the SNc in littermate control or knockout mice. These data suggest that some of the deleterious effects of MPTP on striatal dopaminergic nerve terminals are mediated by both *O2- and hydroperoxides, and that they occur prior to dopaminergic neurodegeneration in the SNc. The similarity between the MPTP model and PD raises the possibility that both types of ROS may play a significant role in the early pathogenesis of dopaminergic neurodegeneration in PD.     

Permanent human parkinsonism due to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): seven cases

Seven patients developed chronic and severe parkinsonism after repeatedly injecting 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intravenously. Levodopa and bromocriptine controlled the symptoms; however, within months, five of the seven patients experienced dyskinesias or on-off fluctuations. Therefore, neither prolonged levodopa treatment nor progressive disease was necessary for on-off phenomena. Because the neurotoxic effects of MPTP seem limited to the substantia nigra, damage to this system alone may produce all the motor features of Parkinson's disease. MPTP differs from other neurotoxins in that it consistently produces a pure parkinsonian state.     

Alpha-tocopherol and beta-carotene do not protect marmosets against the dopaminergic neurotoxicity of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Idiopathic Parkinson's disease (PD) may possibly be caused by one or more unidentified neurotoxins present in the environment, or formed endogenously, which progressively damage dopaminergic nigrostriatal neurons. N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is an experimental neurotoxin which produces biochemical and neuropathological changes in humans, lower primates and mice that closely resemble those found in PD. Because the mechanisms of neuronal damage in both idiopathic PD and in the MPTP model of PD may involve free radical formation in the substantia nigra, antioxidants might protect dopaminergic neurons. Previously, we found that both alpha-tocopherol and beta-carotene partially protected mice against MPTP. However, in the experiments described in this paper, neither alpha-tocopherol nor beta-carotene, each administered in massive doses, had any demonstrable protective effect for dopaminergic nigrostriatal neurons in marmosets injected with low doses of MPTP. Without more knowledge about the identity of the neurotoxin(s) causing idiopathic PD, and their mechanism of action, it is not possible at this time to predict whether these 2 antioxidants might be clinically useful in preventing or ameliorating PD.     

Suppression of mating behaviour in the male rat by intracerebroventricular infusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Acute microinfusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the third cerebral ventricle (III V) of sexually experienced male rats produced a dose-related suppression of masculine sexual behaviour. This inhibition of male sexual performance could be reversed by simultaneous infusions of small doses of pargyline. Three analogues of MPTP, namely, 4-phenyl-1,2,3,6-tetrahydropyrididine, 4-cyano-4-phenylpiperidine and 4-hydroxy-4-phenylpiperidine had no significant effects on any of the parameters of male sexual behaviour. These findings suggest that MPTP may have potent effects on the mechanisms regulating male sexual behaviour in the rat by acting on sites around the third ventricle (arcuate and periventricular hypothalamic nuclei) where there are high MPTP receptor densities and thus provide further evidence for MPTP in neuroendocrine regulation. These responses depend upon the unique structural properties of the MPTP molecule.     

Neurotoxic effects of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the cat. Tyrosine hydroxylase immunohistochemistry

N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces substantia nigra pars compacta (SNc) cell death in several species including the mouse, dog and monkey. MPTP is presently shown to cause apparent nigral cell death in the SNc of the cat as noted by a long-lasting decrease in tyrosine-hydroxylase (TH)-like cell staining. A transient loss of TH-like staining is also observed in the ventral tegmental area, locus coeruleus and retrorubral area. These latter areas appear normal 1.5-5.0 months after MPTP administration. The caudate nucleus (CD) showed a greater TH depletion than the nucleus accumbens (ACC) and only recovered slightly over time. After 7 days of MPTP, an apparent axonopathy, characterized by lightly staining fibers with large TH-positive varicosities, is seen in the CD and to a lesser extent, in the ACC. These findings demonstrate that MPTP is toxic to the cat's nigrostriatal dopaminergic system and suggests that the cat is a good intermediate species in which to study the responses of dopaminergic neurons to MPTP.     

Disappearance of circadian rhythms in Parkinson''s disease model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in dogs

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to dogs produces clinical, pathological and neurological features in dog resembling human Parkinson's disease. Using this animal model, we studied the changes in diurnal rhythms of urine volume, creatinine in urine, and vasopressin, aldosterone and renin activity in plasma. Before MPTP treatment, urine volume showed a peak between 17.00 and 1.00 and plasma vasopressin concentration also showed a clear circadian rhythm with a peak at 13.00 and a minimum level at 5.00. Two weeks after MPTP treatment (2.5 mg/kg i.v.), the rhythm of urine volume disappeared and that of vasopressin became less clear. Plasma renin activity increased 2 and 4 weeks after MPTP treatment. The increase was, however, not enough to change the concentration of plasma aldosterone. We examined the effect of L-3,4-dihydroxyphenylalanine (levodopa), on the circadian pattern of urine volume and vasopressin attenuated by MPTP. Levodopa (4 mg/kg/day) was administered orally every day from the first week after MPTP treatment. The circadian rhythms of urine volume and vasopressin reappeared within one week after the start of levodopa administration.     

Promethazine protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

Promethazine (PMZ) is an FDA-approved antihistaminergic drug that was identified as a potentially neuroprotective compound in the NINDS screening program. PMZ accumulates in brain mitochondria in vivo and inhibits Ca2+-induced mitochondrial permeability transition pore (PTP) in rat liver mitochondria in vitro. We hypothesized that PMZ may have a protective effect in a mitochondrial toxin model of Parkinson's disease (PD). Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) sustained a significant loss of dopaminergic neurons within the SNpc that was strongly attenuated by PMZ treatment. However, neither striatal MPP+ concentrations nor MPTP-induced inhibition of mitochondrial complex I were affected by PMZ treatment. In isolated mouse brain mitochondria, PMZ partially prevented and reversed MPP+-induced depolarization of membrane potential and inhibited the Ca2+-induced PTP in brain mitochondria. The sum of data indicates that PMZ is a strong neuroprotective agent capable of protecting dopaminergic neurons against MPTP toxicity in vivo.     

Transplacental effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on brain dopaminergic neurons in the mouse

Summary Immunohistochemical studies of monoamme neurons werè performed to evaluate toxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on young adult mice and compare them with chose of their offspring. Mice, 9–11 weeks old (C57BL/6J), injected subcutaneously with a large dose of MPTP (17 mg/kg per day) during pregnancy on Day 9 and 12 of gestation (G9 and G12) miscarried and were examined at 13 weeks of age. Conversely, mice treated during pregnancy with sequential low dose of MPTP (2.8 mg/kg per day at G9–G17 for 8 days) successfully delivered their babies and were examined at the age of 15 weeks. Baby mice were examined at 1 and 6 weeks of age. The tyrosine hydroxylase-, aromatic l-amino acid decarboxylase-and dopamine (DA)-immunoreactive density of caudoputamen was reduced in 13-week-old mice treated with high dose of MPTP but not in the 15-week-old mothers exposed to a low dose of MPTP as compared to their respective controls. The DA-immunoreactive density of the caudoputamen was the only staining that was reduced in both 1- and 6-week-old baby mice. In conclusion, these results demonstrate that MPTP injected to pregnant mice causes a DA depletion in the striatum of their offspring indicating a transplacental effect of MPTP. The findings also indicate that fetal brain is more susceptible to MPTP toxicity than the brain of young pregnant mice.Supported by Grant-in-Aid for Scientific Research on Priority Areas, Ministry of Education, Science and Culture, Japan (62623002, 62480226), and by a Fujita-Gakuen Health University Grant, Japan     

Intrahypothalamic infusions of a synthetic heroin substitute, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, potentiate mating behaviour in the female rat

Acute microinfusions of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) bilaterally into the arcuate-ventromedial area of the hypothalamus (ARC-VMH) produced a dose-dependent facilitation of lordosis behaviour in oestrogen- and oestrogen—progesterone-treated ovariectomized female rats. This facilitation could be blocked by pretreatment of the ARC-VMH site with pargyline but not by a potent antagonist analogue of gonadotropin releasing hormone (GnRH). MPTP was not effective in potentiating lordosis when microinfused into other brain sites which are intimately involved in the neural circuitry for this oestrogen-dependent behavioural response. This action of MPTP in the ARC-VMH may be dependent upon the high MPTP receptor densities which are known to occur in the arcuate and periventricular hypothalamic nuclei. Chronic infusions of MPTP (once daily for 21 days) into the ARC-VMH did not result in any significant cell loss and did not interfere with the ability of a later acute MPTP infusion to potentiate lordosis nor with the ability of oestrogen and progesterone to promote the full display of lordosis behaviour. These results provide the first demonstration of neurally placed MPTP in the regulation of a specific hormone-dependent neuroendocrine response.     

Production of a Parkinson-like syndrome in the cat with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): behavior, histology, and biochemistry

N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a potent dopaminergic neurotoxin, was administered to cats systemically for 5 to 7 days. This treatment produced a behavioral syndrome characterized by akinesia, ataxia, bradykinesia, and feeding difficulties, lasting for several weeks. During this period of severe behavioral impairment, caudate and nucleus accumbens dopamine and norepinephrine concentrations were quite depleted. Behavioral recovery ensued over the next several weeks as did some recovery of striatal catecholamines. MPTP destroyed the majority of substantia nigra pars compacta neurons while affecting a much lesser number of locus ceruleus and ventral tegmental neurons. These results demonstrated for the first time that MPTP can cause long-lasting deficits in nigrostriatal functioning in the cat and may provide a means for studying the apparently selective neurotoxic effects of MPTP as well as for understanding the pathophysiology of Parkinson's disease.     

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on presynaptic dopamine uptake sites in the mouse striatum

The effects of the specific dopaminergic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), were studied on the kinetics of [3H]mazindol binding to striatal membranes of C57 black mice. This radioligand was used to label dopamine uptake sites and when administered in vivo, MPTP caused an irreversible, non-competitive inhibition of mazindol binding, consistent with damage to dopaminergic terminals. This effect was abolished by pretreatment with pargyline, a MAOB inhibitor, suggesting that oxidation of MPTP to the pyridinium moiety, MPP+, is a necessary step for toxicity when mazindol binding is used as an end point. In keeping with these findings, pretreatment of mice with mazindol protected against the dopamine-depleting effects of MPTP in vivo. This data suggests that MPTP exerts its toxic effects via MPP+ which is concentrated intraneuronally via the dopamine uptake system. During this process the neurotoxin irreversibly inactivates the dopamine uptake sites.     

Regional and temporal effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on dopamine uptake sites in mouse brain

When the regional effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on brain dopamine uptake sites in C57 Black mice were studied using [3H]mazindol autoradiography, marked regional differences in effect were seen: the mesolimbic system was less affected than the nigrostriatal tract and within each system the effect was more severe in the terminal fields of the striatum than in the cells of origin. Within the striatum itself there was inhomogeneity of effect, with relative sparing of the dorsomedial aspect compared to the remainder. Complete recovery of [3H]mazindol binding to striatal membranes occurred over 12 months, while dopamine levels recovered more slowly. This supports the concept that MPTP has a highly selective effect within dopaminergic systems and that the initial effect is more pronounced on distal terminals compared to cell bodies. The possibility that recovery of mazindol binding with time may be associated with terminal regrowth needs to be investigated further.     

Neuropathological study on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine of the crab-eating monkey

Summary Experimental parkinsonism was induced by systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to the crab-eating monkey (Macaca fascicularis). In the acute stage, the substantia nigra showed necrotic nerve cells, extracellular release of pigment granules and histiocytic infiltration. The nerve cells underwent vacuolation of the cytoplasm with chromatin clumping of the nucleus and disintegration of the nucleolus. The striking feature was the presence of variously-shaped inclusion bodies within abnormal mitochondria which sometimes disclosed a distortion of the cristae. Golgi apparatus and endoplasmic reticulum were also dilated. In the locus ceruleus swollen nerve cells were observed with vacuolated cytoplasm and pyknotic nucleus where expanded mitochondria also contained the inclusions. Some of the inclusion bodies are probably insoluble precipitations due to inhibition of mitochondrial oxidation by a certain metabolite of MPTP. In the protracted stage the substantia nigra revealed a considerable loss of the nerve cells associated with melanophagia and astrocytic proliferation. A few surviving nerve cells showed an increased number of Golgi apparatus and rough endoplasmic reticula, and the presence of autophagosomes, dense bodies and intra-mitochondrial inclusions. These changes are interpreted as being a part of the reparative process from the cellular damage.Supported in part by a grant from CNS Degeneration Disease Research Committee, the Ministry of Health and Welfare of Japan