Regional localization of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) uptake: mismatch between its uptake and neurotoxic sites.

Three to 24 h following intraventricular injections of radioactive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the rat, accumulations of radiolabel were widely detected, in varying degree, over neuronal perikarya in motor-related structures below the midbrain. Pretreatment with the monoamine oxidase B inhibitor pargyline largely eliminated the perikaryal radiolabeling in the substantia nigra, dorsal raphe and cerebellum, leaving that in the other regions intact. These results indicate that there exists a certain mismatch between MPTP uptake and neurotoxic sites, and that invulnerable cells can accumulate MPTP without being converted to its major active metabolite 1-methyl-4-phenylpyridine (MPP+).     

Differential effects of acute and chronic nicotine treatment on MPTP-(1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induced degeneration of nigrostriatal dopamine neurons in the black mouse

Summary Evidence exists for a negative correlation between Parkinson's disease and smoking. The present and previous studies indicate that nicotine treatment can markedly alter the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity in the black mouse based on biochemical determinations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in neostriatum and substantia nigra 2 weeks after MPTP injection. Acute intermittent treatment with (–)nicotine starting 10 min before the MPTP injection partly protected against MPTP-induced neurotoxicity in the neostriatum and substantia nigra. Also, a partial protection was observed in the substantia nigra when (–)nicotine was given together with MPTP in an acute intermittent treatment schedule. Conversely, chronic infusion of (–)nicotine via minipumps produced a dose-related enhancement of MPTP-induced DA neurotoxicity in the neostriatum. It is suggested that the protective activity of nicotine in the MPTP model is related to a blockade of MPP + uptake into the DA cells via increased DA release. Conversely, the nicotine enhancement of MPTP-induced DA toxicity is suggested to be caused by a failure of the nicotinic cholinoceptors to desensitize to the chronic (–)nicotine exposure, leading to increased chronic influx of Na⁺ and Ca²⁺ ions via the ion channels of the nicotinic cholinoceptors located on the DA neurons with associated increased Ca ion toxicity and increased energy demands.Abbreviations DA dopamine - DOPAC 3,4-dihydroxyphenylacetic acid - HPLC high performance liquid chromatography - HVA homovanillic acid - MPP⁺a 1-methyl-4-phenyl-pyridinium ion - MPTP 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine     

Partial protection from the dopaminergic neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by four different antioxidants in the mouse

C57 black mice given a single injection of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 40 mg/kg, developed marked reduction of striatal dopamine content and loss of dopaminergic neurons in the zona compacta of the substantia nigra. However, pretreatment with any one of four different antioxidants, alpha-tocopherol, beta-carotene, ascorbic acid or N-acetylcysteine, significantly decreased MPTP-induced striatal dopamine loss, and alpha-tocopherol prevented neuronal loss in the substantia nigra. Four chemical analogues of MPTP (cinnamaldehyde, N,N-dimethylcinnamylamine, arecoline and 2-methyl-1,2,3,4-tetrahydro-6,7-isoquinolinediol) were all found to lack dopaminergic nigrostriatal neurotoxicity in the mouse.     

MPTP toxicity in the mouse brain and vitamin E

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) caused transient alterations in vitamin E levels in every brain region examined. However, vitamin E returned to normal levels within a few hours in all brain regions but the substantia nigra, where at 2 days vitamin E levels first rose above normal levels. Vitamin E deficient mice were much more susceptible to MPTP toxicity than controls, in terms of lethality and DOPAC depletion in the substantia nigra. However, in the same vitamin E deficient mice, the striatum was partially protected from neurotransmitter and metabolite depletion by MPTP. The mechanism of toxicity of MPTP may differ in the striatum and the midbrain.     

Histochemistry of MPTP oxidation in the rat brain: sites of synthesis of the parkinsonism-inducing toxin MPP+

Systemic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is toxic to the nigrostriatal dopaminergic neurons and produces a syndrome similar to Parkinson's disease. Conversion of MPTP to 1-methyl-4-phenylpyridine (MPP+) by monoamine oxidase-B (MAO-B) appears necessary for this neurotoxicity. When MPTP was used as the substrate for the histochemical localization of monoamine oxidase activity on sections of the rat brain, only a few specific sites were found in which MPTP oxidation to MPP+ occurs. These include the noradrenergic and serotoninergic neurons of the brainstem and the histamine neurons of the caudal hypothalamus. Dopamine neurons themselves do not display the capacity to oxidize MPTP. It is proposed that the conversion of MPTP to MPP+ occurs via MAO-B within serotonin and histamine neurons which may innervate the substantia nigra where the toxin MPP+ could be released and then taken up into the dopamine neurons.     

Age-related severity of dopaminergic neurodegeneration to MPTP neurotoxicity causes motor dysfunction in C57BL/6 mice

This study investigated the influence of advancing age on dopaminergic neuronal degeneration induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication from the perspective concerning the relationship between dopaminergic function and behavioral features. Young (10 weeks) and older (14-15 months) C57BL/6 mice were treated with one to four injections of MPTP (20 mg/kg at 2h intervals). Although young mice showed no mortality in either MPTP treatment, older mice exhibited mortality from only two injections of MPTP during the experimental period. An extensive dopaminergic cell loss was found in both the striatum and substantia nigra of older mice given one and two injections of MPTP with marked decrease in striatal dopamine (DA) levels, but not young mice. We also found a behavioral change in the tail suspension test associated with the extent of decrease in striatal DA levels in MPTP-treated older mice, but not in young mice. These results clearly present age-related vulnerability to MPTP neurotoxicity in C57BL/6 mice and strongly support our previous report showing that there is a critical threshold level of the decrement in striatal DA contents causing motor dysfunction in this mouse model of Parkinson's disease.     

Striatal dopaminergic toxicity following intranigral injection in rats of 2-methyl-norharman, a beta-carbolinium analog of N-methyl-4-phenylpyridinium ion (MPP+)

Methylated beta-carboline compounds are mammalian indole metabolites that we have proposed to be endogenous neurotoxins due to their structural similarity to MPP+, the active oxidized product of the dopaminergic toxin, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Several laboratories have demonstrated that MPP+ administration into the substantia nigra or median forebrain bundle of rats results in extensive depletion of striatal dopamine and its metabolites. We now report that three weeks after intranigral injection of the beta-carboline, 2-methyl-norharman, striatal dopamine, DOPAC, and homovanillic acid (HVA) concentrations ipsilateral to the injection are reduced 41-64% compared to vehicle-injected controls; in individual animals dopamine depletions of 96% were achieved. In addition, at the 2-methyl-norharman injection site in the substantia nigra, large lesions and gliosis were apparent under light microscopic examination. This is the first direct demonstration that a 2-methyl-beta-carbolinium ion is neurotoxic. It lends further validity to the hypothesis that MPP+-like beta-carbolines may be endogenous causative agents in Parkinson's disease.     

The neurotoxin MPTP does not reproduce in the rhesus monkey the interregional pattern of striatal dopamine loss typical of human idiopathic Parkinson's disease

Using high-pressure liquid chromatography with electrochemical detection, we measured dopamine (DA) and homovanillic acid (HVA) in caudate nucleus, putamen and substantia nigra in 4 untreated rhesus monkeys and 4 monkeys with permanent parkinsonism produced by repeated injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; total dose: 2.1-6.45 mg/kg, i.m.). MPTP consistently produced a severe striatal and nigral loss of DA and HVA and an increase in the ratio 'HVA/DA'. In this respect, MPTP mimicked the changes found in human Parkinson's disease (PD). However, MPTP lowered the DA in caudate (-99.6%) to the same degree as in putamen (-99.5%). This is in contrast to idiopathic PD where the caudate is significantly less affected by DA loss (-84%) than the putamen (-98%). Thus, in our rhesus monkeys MPTP failed to reproduce the interregional caudate-putamen gradient characteristic of idiopathic PD. The DA pattern produced by MPTP was similar to the DA loss in caudate (-98%) and putamen (-99%) observed in patients with postencephalitic parkinsonism.     

Deficits in behavioral initiation and execution processes in monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to two monkeys led to hypokinesia, tremor, rigidity, adipsia and aphagia. Quantitative assessment of hypokinesia revealed increased reaction time, delayed onset of muscle activity and prolonged movement time in a forelimb reaching task after selective degeneration of the nigrostriatal dopamine (DA) system sparing mesocortical dopamine neurons. The losses of pars compacta cells of substantia nigra, of striatal [3H]mazindol binding and of striatal DA content (more than 90%) quantitatively paralleled the severity of behavioral deficits. Additional monoamine systems were affected with stronger MPTP effects.     

Participation of brain monoamine oxidase B form in the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine: relationship between the enzyme inhibition and the neurotoxicity

A neurotoxin for nigrostriatal dopaminergic neurons, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its oxidized metabolite, 1-methyl-4-phenylpyridine (MPP+), both dose-dependently inhibited rat striatal and forebrain monoamine oxidase (MAO) activity with monoamine oxidase A (MAO-A) selectively reversible (competitive, Ki = 4.5 and 2.0 microM) inhibition. A comparison of the Ki values indicated the affinity of MPP+ for MAO-A to be greater than that of MPTP. MPTP inhibited monoamine oxidase B (MAO-B) with both a reversible (competitive, Ki = 116 microM) and an irreversible time-dependent component, but inhibition by MPP+ was reversible and competitive (Ki = 180 microM). These results, together with previous findings on metabolism of MPTP to MPP+ by brain MAO-B, suggest that MPP+ is a simple inhibitor of MAO-A and MAO-B, but MPTP might be a 'suicide substrate' inhibitor for MAO-B.     

Central hypothermic effects of some analogues of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium ion (MPP+)

Effects of some MPTP or MPP+ analogues on mouse body temperature were studied. Of the analogues tested, 4-phenylpyridine (PPY) and 4-phenyl-1,2,3,6-tetrahydropyridine (PTP) given in single i.p. doses to mice caused marked hypothermia. Intracerebroventricular (i.c.v.) injection of PPY or PTP caused similar hypothermia. Pretreatment with clorgyline or (-)-deprenyl greatly prevented hypothermia induced by i.c.v. PPY, but hypothermia by i.c.v. PTP was prevented only by (-)-deprenyl. These results indicate that, in order to cause central hypothermia, PTP does not seem to require metabolism to PPY and both analogues per se may cause hypothermia.     

Tumor necrosis factor-alpha receptor ablation in a chronic MPTP mouse model of Parkinson's disease

Recently, we demonstrated that mice deficient of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) were partly protected against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Here we extended the study and investigated TNF-alpha receptor 1 (-/-) (TNFR1) and TNF-alpha receptor 2 (-/-) (TNFR2) mice using a chronic MPTP dosing regimen (15 mg/kg MPTP on 8 consecutive days). One week after the last MPTP treatment, HPLC determination of striatal dopamine (DA) and immunostaining for the dopamine transporter (DAT) in the substantia nigra pars compacta (SNpc) was performed. MPTP treatment reduced striatal DA levels significantly; nigral DAT immunoreactivity was reduced to a lower extent. However, there was no difference in DA levels and the number of DAT positive neurons between TNFR1 (-/-), TNFR2 (-/-) and wild type mice after MPTP treatment. In contrast to TNF-alpha deficiency neither TNFR1 nor TNFR2 gene ablation showed protection against MPTP neurotoxicity, which argues for a protective mechanism of TNF-alpha not mediated by TNFR1 and TNFR2 signaling.     

Riluzole (2-amino-6-trifluoromethoxy benzothiazole) attenuates MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) neurotoxicity in mice

The protective effects of 2-amino-6-trifluoromethoxy benzothiazole (riluzole), a Na(+) channel blocker with antiglutamatergic activity were investigated in the model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced depletion of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels in mice. The mice were injected intraperitoneally (i.p.) with four administrations of MPTP (10 mg/kg) at 1 h intervals and then the brains were analyzed at 3 and 7 days after the treatments. Dopamine, DOPAC and HVA levels were significantly decreased in the striatum 3 days after MPTP treatments. Riluzole dose-dependently antagonized the MPTP-induced decrease in dopamine, DOPAC and HVA levels in the striatum. MPTP treatment also caused a severe decrease in the amount of nigral tyrosine hydroxylase protein (TH) and microtuble-associated protein 2 (MAP 2) and produced a marked increase in the striatal glial fibrillary acidic protein (GFAP). Our immunohistochemical study with TH and MAP 2 staining showed that riluzole can protect against MPTP-induced neuronal damage in the substantia nigra. Furthermore, riluzole markedly increased the striatal GFAP-positive astrocytes 3 days after MPTP treatments. These results suggest that riluzole is effective against MPTP-induced neurodegeneration of the nigrostriatal dopaminergic neuronal pathway. Our findings also may provide a rationale for the identification of astrocytes as a prominent target for the development of new therapies of Parkinson's disease.     

Selective retention of MPP+ within the monoaminergic systems of the primate brain following MPTP administration: an in vivo autoradiographic study

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) selectively destroys dopaminergic neurons of the substantia nigra pars compacta in humans and other primates, producing a parkinsonian condition. MPTP is metabolized to the toxin 1-methyl-4-phenylpyridine (MPP+) which is taken up by dopamine terminals. The subsequent events culminating in cell death in the substantia nigra pars compacta are not understood. To examine these events we first produced a chronic hemiparkinsonian condition in monkeys by administering a toxic dose of MPTP via the right carotid artery. One year later, these monkeys were given a trace dose of [14C]MPTP intravenously and allowed to survive 1, 3, or 10 days. In two acute conditions, monkeys were either given the radiolabeled trace dose intravenously immediately following the toxic intracarotid dose, or were given a single toxic intracarotid radiolabeled dose, and allowed to survive 1, 3, or 10 days. We show by histology and autoradiography that the chronic hemiparkinsonian condition is characterized by selective unilateral loss of nigrostriatal dopamine neurons and absence of MPP+ retention in the caudate-putamen. In the acute conditions, MPP+ is accumulated and selectively retained in high concentrations in the caudate-putamen bilaterally and throughout the nigrostriatal pathway only on the side receiving the toxic dose. In the substantia nigra pars compacta. MPP+ is accumulated in very low concentrations in the dopamine cell bodies and is not selectively retained there. At 10 days survival, the caudate-putamen on the side receiving the toxic dose loses its ability to retain MPP+. The apparent degeneration of the dopamine axon terminals in the caudate-putamen and the development of Parkinson-like behavioral signs seen at 10 days survival were observed to precede the loss of cell bodies in the substantia nigra, which appeared normal by the criteria of Nissl staining and neuromelanin content at all time points in the acute conditions. Other areas of dense MPP+ retention in all cases include noradrenergic and serotonergic cell groups and noradrenergic pathways. MPP+ in the locus coeruleus and other caudal catecholaminergic cell groups is apparently retrogradely transported there after uptake in terminal regions, and although it is retained in high concentrations, no cell loss occurs. These findings suggest that experimentally induced Parkinsonism results from molecular events initiated in the neostriatum and selectively elaborated in the nigrostriatal pathway, ultimately resulting in the death of substantia nigra pars compacta dopamine neurons. They do not support a significant role for neuromelanin binding in the toxicity of MPP+.     

Mouse model of Parkinsonism: a comparison between subacute MPTP and chronic MPTP/probenecid treatment

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is widely used to induce an animal model of Parkinsonism. The conventional mouse model, which usually involves acute or subacute injections of MPTP, results in a significant but reversible loss of dopaminergic functions. We have developed an alternative mouse model, in which co-administration of MPTP with probenecid results in the chronic loss of striatal dopamine for at least 6 months after cessation of treatment. In the present study, we compare the neurochemical, morphological and behavioral changes that occur in this alternative, chronic model with those in the conventional, subacute model. In the chronic model, we demonstrate an almost 80% loss of striatal dopamine and dopamine uptake 6 months after withdrawal from treatment. The neurochemical signs match unbiased stereological measures that demonstrate gradual loss of substantia nigra neurons. Rotarod performance further substantiates these findings by showing a progressive decline in motor performance.Based on the comparisons made in this study in mice, the chronic MPTP/probenecid model shows considerable improvements over the conventional, subacute MPTP model. The sustained alterations in the nigrostriatal pathway resemble the cardinal signs of human Parkinson's disease and suggest that this chronic mouse model is potentially useful to study the pathophysiology and mechanisms of Parkinsonism. It should also prove useful for the development of neuroprotection strategies.     

The acute convulsant effect of MPTP is dependent on intracerebral MPP+.

The administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to C57 black mice causes an acute seizure syndrome the severity of which is dose dependent; there is also a good correlation between the seizure inducing potential of MPTP and the neostriatal dopamine (DA) depletion caused by MPTP. The simultaneous administration of MPTP and MAO B inhibitors attenuates both epileptiform phenomena and neostriatal DA depletion. On the contrary diethyldithiocarbamate (DDC) exacerbates both responses. All these pharmacological manipulations are known to affect the accumulation of 1-methyl-4-phenylpyridinium ion (MPP+) the main metabolite of MPTP. Thus the present data support the hypothesis of a strict dependence of the epileptiform phenomena on the presence of MPP+. Furthermore the tight correlation existing between the severity of epileptic events and DA depletion suggests that the acute excitotoxic syndrome may contribute to the long-term toxicity of MPTP. *On leave from the Department of Neurology, University of Pisa, Pisa, Italy.     

The neurotoxic actions of 6-hydroxydopamine infused into the rat substantia nigra

6-Hydroxydopamine (6-OHDA) 10 and 40 μg/24 h infused bilaterally for 4 days into the rat substantia nigra (SN) caused a ‘freezing’ akinetic response which was apparent within 24 h and which persisted throughout the period of infusion. The infusion of 10 or 40 μg/24 h 6-OHDA into the SN failed to cause any change in motor coordination, or induce limb and body rigidity. The infusion of 40 μg/24 h 6-OHDA led to significant reductions in the striatal levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid and noradrenaline; no changes were observed following the 4-day infusion of 10 μg 6-OHDA. The consequences of infusing 6-OHDA into the SN are discussed in relation to those induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridine (MPP⁺) where the spectrum of behavioural and biochemical change caused by 6-OHDA is shown not to mimic the actions of either MPTP or MPP⁺.     

Neuroprotective effects of (±)-catechin against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurotoxicity in mice

The neuroprotective effects of (±)-catechin against toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were investigated in mice. MPTP caused the death of dopaminergic neurons in the substantia nigra and decreased the level of striatal dopamine. Additionally, MPTP increased the level of phospho-c-Jun, a known substrate of c-Jun N-terminal kinase (JNK) and caused a rapid activation of GSK-3β, evidenced by the decrease in the level of phospho-Ser9 of GSK-3β. However, pretreatment with (±)-catechin was found to protect dopaminergic neurons in the substantia nigra against MPTP toxicity, and restore the depletion of striatal dopamine in mice. (±)-Catechin attenuated the phosphorylation of c-Jun and recovered the phosphorylation of GSK-3β (Ser9). These results suggested that the suppression of JNK and GSK-3β signaling cascades might contribute to the neuroprotective effect of (±)-catechin against toxicity of MPTP.     

Does ORP150/HSP12A protect dopaminergic neurons against MPTP/MPP(+)-induced neurotoxicity?

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and its metabolite 1-methyl-4-phenylpyridinium (MPP(+)) are drugs that are widely used in experimental Parkinson disease (PD) models. What is the significance of ORP150/HSP12A, a molecular chaperone in the endoplasmic reticulum (ER), in the nigrostriatal system? Dopaminergic neuroblastoma SH-SY5Y cells and dopaminergic neurons of the substantia nigra pars compacta (SNpc) were examined. Our observations led to the hypothesis that ORP150 protects against MPTP/MPP(+)-induced neurotoxicity, and indicate the importance of the ER environment in maintaining the nigrostriatal pathways.