Short-term manganese pretreatment partially protects against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that induces parkinsonism in human and non-human primates. Its mechanism of action is not fully elucidated.Recently, the participation of trace metals, such as manganese, on its neurotoxic action has been postulatted. In this work, we studied the effect of manganese administration on the neurochemical consequences of MPTP neurotoxic action. Male Swiss albino mice were treated with manganese chloride (MnCl₂ ·4H₂O; 0.5 mg/ml or 1.0 mg/ml of drinking water) for 7 days, followed by three MPTP administrations (30 mg/Kg, intraperitoneally). Seven days after the last MPTP administration, mice were sacrificed and dopamine and homovanillic acid contents in corpus striatum were analyzed. Striatal concentration of dopamine was found increased by 60% in mice pretreated with 0.5 mg/ml and 52% in the group treated of 1.0 mg/ml as compared versus animals treated with MPTP only. Hornovanillic acid content in both groups treated with manganese was the same as those in control animals. The results indicate that manganese may interact with MPTP, producing an enhancement of striatal dopamine turnover, as the protective effect of manganese was more pronounced in the metabolite than in the neurotransmitter.     

Acupuncture enhances the synaptic dopamine availability to improve motor function in a mouse model of Parkinson's disease

Parkinson's disease (PD) is caused by the selective loss of dopaminergic neurons in the substantia nigra (SN) and the depletion of striatal dopamine (DA). Acupuncture, as an alternative therapy for PD, has beneficial effects in both PD patients and PD animal models, although the underlying mechanisms therein remain uncertain. The present study investigated whether acupuncture treatment affected dopamine neurotransmission in a PD mouse model using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found that acupuncture treatment at acupoint GB34 improved motor function with accompanying dopaminergic neuron protection against MPTP but did not restore striatal dopamine depletion. Instead, acupuncture treatment increased dopamine release that in turn, may lead to the enhancement of dopamine availability in the synaptic cleft. Moreover, acupuncture treatment mitigated MPTP-induced abnormal postsynaptic changes, suggesting that acupuncture treatment may increase postsynaptic dopamine neurotransmission and facilitate the normalization of basal ganglia activity. These results suggest that the acupuncture-induced enhancement of synaptic dopamine availability may play a critical role in motor function improvement against MPTP.     

Enhanced susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity in high-fat diet-induced obesity

Currently, obesity is considered a systemic inflammation; however, the effects of obesity on the vulnerability of dopaminergic neurons to oxidative stress are not fully defined. We evaluated the effects of high-fat diet-induced obesity (HF DIO) on neurotoxicity in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Eight weeks after a HF or matched normal diet, a severe decrease in the levels of striatal dopamine and of nigral microtubule-associated protein 2, manganese superoxide dismutase, and tyrosine hydroxylase was observed in obese mice treated with subtoxic doses of MPTP (20 mg/kg) compared with the matched lean group. In addition, the levels of nitrate/nitrite and thiobarbituric acid-malondialdehyde adducts in the substantia nigra of obese mice were reciprocally elevated or suppressed by MPTP. Interestingly, striatal nNOS phosphorylation and dopamine turnover were elevated in obese mice after MPTP treatment, but were not observed in lean mice. The nitrotyrosine immunoreactivity for evaluation of nigral nitrogenous stress in obese mice with MPTP was higher than that in matched lean mice. At higher doses of MPTP (60 mg/kg), the mortality was higher in obese mice than in lean mice. These results suggest that DIO may increase the vulnerability of dopaminergic neurons to MPTP via increased levels of reactive oxygen and nitrogen species, and the role of nNOS phosphorylation in the MPTP toxicities and dopamine homeostasis should be further evaluated.     

The TrkB-Positive Dopaminergic Neurons are Less Sensitive to MPTP Insult in the Substantia Nigra of Adult C57/BL Mice

Tyrosine kinase receptors TrkB and TrkC mediate neuroprotective effects of the brain-derived neurotrophic factor (BDNF) and neurotrophins in the dopaminergic nigro-striatal system, but it is obscure about their responses or expression changes in the injured substantia nigra under Parkinson’s disease. In present study, immunofluorescence, Fluoro-Jade staining and laser scanning confocal microscopy were applied to investigate distribution and changes of TrkB and TrkC in the dopamine neurons of the substantia nigra by comparison of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. It revealed that TrkB and TrkC-immunoreactivities were substantially localized in cytoplasm and cell membrane of the substantia nigra neurons of control adults. While neurons double-labeled with tyrosine hydroxylase (TH)/TrkB, or TH/TrkC were distributed in a large numbers in the substantia nigra of controls, they apparently went down at 36.2–65.7% of normal level, respectively following MPTP insult. In MPTP model, cell apoptosis or degeneration of nigral neurons were confirmed by caspase-3 and Fluoro-Jade staining. More interestingly, TH/TrkB-positive neurons survived more in cell numbers in comparison with that of TH/TrkC-positive ones in the MPTP model. This study has indicated that TrkB-containing dopamine neurons are less sensitive in the substantia nigra of MPTP mouse model, suggesting that specific organization of Trks may be involved in neuronal vulnerability to MPTP insult, and BDNF-TrkB signaling may play more important role in protecting dopamine neurons and exhibit therapeutic potential for Parkinson’s disease.     

Differential effects of L-deprenyl on MPP+- and MPTP-induced dopamine overflow in microdialysates of striatum and nucleus accumbens

The present studies investigated the effects of L-deprenyl, 1-methyl-4-phenylpyridinium ion (MPP+) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the efflux of dopamine and its metabolites in microdialysates of striatum and nucleus accumbens in rats. L-Deprenyl or L-amphetamine perfusion into striatum had no effects on basal dopamine efflux, though L-deprenyl reduced the basal efflux of dihydroxyphenylacetic acid and homovanillic acid. MPP+ or MPTP perfusion into striatum significantly increased the dopamine efflux, and the action of MPTP was more potent than that of MPP+. Pretreatment with L-deprenyl antagonized the actions of MPP+ and MPTP. The striatal dopamine efflux of rats was gradually restored by itself after the overflow caused by 2-h perfusion of the dopaminergic neurotoxins, while L-deprenyl could not accelerate the recovery. Perfusion with L-deprenyl or L-amphetamine, but not pargyline, into nucleus accumbens increased the dopamine efflux in a dose-dependent fashion, which could be antagonized by haloperidol pretreatment. MPP+ or MPTP perfusion into nucleus accumbens also increased the dopamine efflux, and the action of MPTP was also more potent than that of MPP+. Pretreatment with L-deprenyl could not antagonize the actions of MPP+ and MPTP. These findings suggest that L-deprenyl, MPP+ and MPTP induce differential effects on nigrostriatal and mesolimbic dopaminergic pathways in vivo. L-Deprenyl has neuroprotective rather than neurorestorative action against MPP+- and MPTP-induced dopamine overflow from striatum. Further, L-deprenyl-induced dopamine overflow from nucleus accumbens may explain the amphetamine-like reinforcing property of L-deprenyl.     

Partial protection from the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by Pro-Leu-Gly-NH2(PLG; MIF-1)

The administration of MPTP to man and monkey has been shown to cause a neurotoxic effect on the nigrostriatal dopamine system. MPTP was injected in C57-BL black mice, 36 mg per kg for 7 days, which resulted in permanent reduction of dopamine and serotonin levels in the striatum. In the mice pretreated with PLG, although the striatal dopamine level was also reduced, mean dopamine and serotonin levels were significantly higher than in mice given MPTP alone. It is concluded that PLG could protect at least partially the neurotoxic effect of MPTP.     

Binding and uptake of MPTP by preparations of human and animal brain

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to cause parkinsonism in man and animals, producing acute behavioral effects within minutes of administration. This syndrome has been attributed to specific effects on dopaminergic systems. MPTP blocked the binding of haloperidol to membranes from rat and human brain (IC₅₀ = 2.5 μM), but it did not block the binding of flupenthixol to these membranes. These results indicate that MPTP is a ligand for D-2 dopamine receptors but not for D-1 dopamine receptors. Synaptosomes from rat, mouse or guinea-pig corpus striatum or from monkey caudate nucleus exhibited little ability to take up MPTP from the incubation medium. The synaptosomes took up at least 20–50 times more dopamine than MPTP. These results indicate that MPTP could cause acute effects by binding to dopamine receptors and that the specific toxicity MPTP exerts for dopaminergic neuron is not primarily based on the specific uptake of MPTP into these neurons.     

Dopamine Agonist 3-PPP Fails to Protect Against MPTP-Induced Toxicity

We investigated the neuroprotective effect of the dopamine agonist, 3-PPP [3-(3-hydroxyphenyl)-N-propylpiperidine] against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. MPTP (30 mg/kg, i.p., twice, 16 h apart) causes significant dopamine depletion in nucleus caudatus putamen (NCP) by 1 week. 3-PPP had no effect on the monoamine oxidase-B activity (MAO-B) activity in NCP. 3-PPP did not affect dopamine uptake, whereas mazindol significantly blocked the uptake of dopamine dose dependently. MPTP-induced behavioral changes in mice were not reduced by pretreatment with 3-PPP. This dopamine agonist did not prevent dopamine depletion caused by MPTP. MPP+ (20 microM) significantly inhibited the cell proliferation of SH-SY5Y dopaminergic neuronal cells. 3-PPP had no effect on the SH-SY5Y neuronal cell growth in culture and did not block the MPP(+)-induced cytotoxicity. This study shows that the dopamine agonist 3-PPP failed to protect against MPTP-induced dopaminergic neurotoxicity.     

Evaluation of the capability of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and pyridine derivatives to evoke parkinsonism

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produce an irreversible parkinsonian-like syndrome in humans, monkeys and mice C57BL/6. Experimental parkinsonism produced by MPTP on mice C57BL/6 were studied with the aim of working up the method for testing MPTP-like substances. It has been shown that intraperitoneal administration the maximal tolerated doses of MPTP cause significant decrease (by 40-60%) of dopamine content on the mice brain. Number of injections did not influence the results. The similar administration of 4-phenyl-pyridyl and 4,4'-dipyridyl derivates, including known herbicides paraquat and cyperquat, produce neither decrease of dopamine content in the brain, nor the development of parkinsonian-like behavioral syndrome.     

Ventricular injection of nerve growth factor increases dopamine content in the striata of MPTP-treated mice

Experimental depletion of dopaminergic striatal neurons was induced in mice with the neurotoxin MPTP. To investigate a possible effect of nerve growth factor on the damaged neurons, we injected 4 g into the right cerebral ventricle of mice three days after the last administration of MPTP. We found a significant increase of dopamine and homovanillic acid in the striatum of MPTP treated mice after NGF administration when compared with dopamine and HVA levels in MPTP-treated control mice (p<0.001). The increase of dopamine and homovanillic acid seems to be related to a partial restorative effect of NGF on the damaged dopaminergic cells, since ventricular administration of NGF to normal mice did not increase dopamine or homovanillic acid contents above the levels measured in untreated controls. It appears that administration of nerve growth factor prcduces a beneficial effect on damaged dopaminergic neurons; this effect could be due to stimulation of neuron sprouting from neurons that survived the toxic effect of MPTP. The increase of dopamine levels was seen 8 days after injection of nerve growth factor and was maintained at least until day 25, showing a lasting persistence of the restorative effect.     

The effect of MPTP on the neuronal uptake of monoamines]

The results of kinetic analysis of synaptosomal uptake of dopamine, noradrenaline, adrenaline and serotonin showed the presence of their own carrier systems with high or low affinity for each monoamine. The low affinity system of the uptake of monoamines by nerve endings differs from extraneuronal one by higher affinity. MPTP noncompetitively inhibits the system of highly effective uptake of the studied monoamines by nerve endings, competitively inhibiting synaptosomal uptake with low affinity of noradrenaline, adrenaline and noncompetitively serotonin and dopamine. The constant values of inhibition showed that MPTP most strongly blocks the system of synaptosomal uptake of low affinity serotonin and approximately 2-times weaker affects its system of high affinity. Carrier systems of high affinity of dopamine, adrenaline and noradrenaline block MPTP 150-500 times weaker than that of serotonin, and as for low affinity--in 2000-4000 times. It may be supposed that synaptosomal uptake of low affinity serotonin is most perceptible to the effect of MPTP and is of a particular importance in the development of Parkinson's disease symptoms.     

Inhibition of Monoamine Oxidase Contributes to the Protective Effect of 7-Nitroindazole Against MPTP Neurotoxicity

Abstract: The ability of 7-nitroindazole (7-NI) to protect against MPTP-induced neurotoxicity has been attributed to its inhibition of neuronal nitric oxide synthase. In the present study, 7-NI was found to counteract almost completely striatal dopamine depletion caused by a single subcutaneus injection of 20 mg/kg MPTP in mice. This effect, however, was accompanied by a significant reduction in the striatal levels of MPP⁺, the toxic metabolite generated via monoamine oxidase B-catalyzed MPTP oxidation. In the presence of 7-NI, a dose of 40 mg/kg MPTP produced MPP⁺ concentrations similar to those measured after treatment with 20 mg/kg MPTP alone. A comparison of neurotoxicity in these two experimental conditions (i.e., mice treated with 20 mg/kg alone versus 40 mg/kg MPTP plus 7-NI) revealed only a slight (20%), but statistically significant, protection of dopamine depletion with 7-NI. These data indicate that the mechanism by which 7-NI counteracts MPTP neurotoxicity in mice is not due solely to inhibition of neuronal nitric oxide synthase, but involves a reduction in MPP⁺ formation.     

Aging of the dopaminergic system and motor behavior in mice intoxicated with the parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

J. Neurochem. (2012) 122, 1032-1046. ABSTRACT: 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication of mice is a standard model of Parkinson's disease (PD). However, it does not reproduce functionally PD. Given the occurrence of PD during aging, symptoms might only be detected in MPTP-intoxicated mice after aging. To address this, mice injected with MPTP at 2.5?months were followed up to a maximum age of 21?months. There was no loss of dopamine cells with aging in control mice; moreover, the initial post-MPTP intoxication decrease in dopamine cell was no longer significant at 21?months. With aging, striatal dopamine level remained constant, but concentrations of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were markedly reduced in both groups. There was also a late impairment of fine motor skills. After MPTP intoxication, hyperactivity was immediately detected and it became greater than in control mice from 14?months of age; fine motor skills were also more impaired; both these symptoms were correlated with striatal dopamine, DOPAC and HVA concentrations. In bothgroups, neither motor symptoms nor dopamine changes worsened with age. These findings do not support the notion that PD develops with age in mice after MPTP intoxication and that the motor deficits seen are because of an aging process.     

N-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Increases Acetylcholine and Decreases Dopamine in Mouse Striatum: Both Responses Are Blocked by Anticholinergic Drugs

The neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces neuropathology and clinical symptoms that resemble Parkinsonism in primates and humans. In mice it induces a long-lasting depletion of neostriatal 3,4-dihydroxyphenylethylamine (dopamine) content. Using the mouse, we found that MPTP induces a fall of dopamine and a rise of acetylcholine in the neostriatum. Both responses to MPTP can be blocked by prior treatment with atropine or trihexyphenidyl.     

Central and peripheral catecholamine depletion by 1-methyl-4-phenyl-tetrahydropyridine (MPTP) in rodents

1-Methyl-4-phenyl-tetrahydropyridine (MPTP) given in single doses to rats depleted norepinephrine concentration in heart and mesenteric artery but had little effect on catecholamine concentration in brain. MPTP did not share with amphetamine the ability to cause persistent depletion of striatal dopamine in iprindole-treated rats. Administration of MPTP via osmotic minipumps implanted s.c. for 24 hrs after a loading dose of MPTP in rats resulted in depletion of striatal dopamine and its metabolites one week later. MPTP in vitro was a reasonably potent, competitive and reversible inhibitor of MAO-A (monoamine oxidase type A). MPTP appeared to inhibit MAO-A in rat brain in vivo as determined by its antagonism of the inactivation of MAO-A by pargyline and by its antagonism of the increase in dopamine metabolites resulting from the administration of Ro 4-1284, a dopamine releaser. The inhibition of MAO-B by MPTP in vitro was noncompetitive, time-dependent, and not fully reversed by dialysis, consistent with the findings of others that MPTP is acted upon by MAO-B. In mice, four successive daily doses of MPTP is acted upon by MAO-B. In mice, four successive daily doses of MPTP given s.c. resulted in marked depletion of dopamine and its metabolites one week later, and the depletion of dopamine was completely prevented by pretreatment with deprenyl, which inhibited MAO-B but not MAO-A. These and other studies in rodents may help in elucidating the mechanisms involved in the destructive effects of MPTP on striatal dopamine neurons that lead to symptoms of Parkinson's disease in humans and in monkeys.     

Electroconvulsive shock does not modify striatal contents of dopamine in MPTP-treated mice

It has been suggested that the therapeutic response to electroconvulsive therapy in depressed patients could be mediated by functional changes in the dopaminergic pathways; a favorable response to electroconvulsive therapy was also observed recently in patients with Parkinson's disease. To study a possible interference of electroconvulsive shock in the course of MPTP-induced parkinsonism in rodents, we measured the striatal content of dopamine in MPTP-treated mice that received electroconvulsive shock at various intervals in the course of MPTP neurotoxicity. Our results showed no immediate or delayed differences in striatal dopamine content of animals that received MPTP and electroconvulsive shock when compared with animals that received only MPTP, thus suggesting that the strong biological effects of MPTP and electroconvulsive shock on the brain may follow different biochemical mechanisms.     

Investigate the chronic neurotoxic effects of diquat

Chronic exposure to agricultural chemicals (pesticides/herbicides) has been shown to induce neurotoxic effects or results in accumulation of various toxic metabolic by-products. These substances have the relevant ability to cause or increase the risk for neurodegeneration. Diquat is an herbicide that has been extensively used in the United States of America and other parts of the world. Diquat is constantly released into the environment during its use as a contact herbicide. Diquat structurally resembles 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) and paraquat. Rotenone, paraquat, maneb and MPTP reproduce features of movement disorders in experimental animal models. Based on the structural similarity to other neurotoxins, chronic exposure of diquat can induce behavioral and neurochemical alterations associated with dopaminergic neurotoxicity. However, in the present study, diquat unlike other neurotoxins (rotenone, 6-hydroxydopamine, MPTP, paraquat and maneb) did not induce dopamine depletion in the mouse striatum. Although, notable exacerbation in motor impairment (swimming score, akinesia and open field) were evident that may be due to the decreased dopamine turnover and mild nigrostriatal neurodegeneration. These data indicate that, despite the apparent structural similarity to other dopaminergic neurotoxins, diquat did not exert severe deleterious effects on dopamine neurons in a manner that is unique to rotenone and MPTP.     

Sodium diethyldithiocarbamate protects against the MPTP-induced inhibition of immune responses in mice

The effects of 1-methyl-4-phenyl - 1,2,3,6-tetrahydropyridine (MPTP) on immune parameters, and the restorative influence of sodium diethyldithiocarbamate (DTC) or deprenyl were evaluated in mice. The concentrations of dopamine (DA), 3-methoxytyramine (3-MT), 3-4-dihydroxyphenyl acetic acid (DOPAC), and homovanillic acid (HVA), were concomitantly measured in the striatum. MPTP depressed T-cell responses. DTC restored these responses as well as the concentration of striatal DA. Deprenyl had no effect on the concentrations of DA and its metabolites, yet it modified the immune responses alike MPTP. The findings suggest a dopamine pathway could be involved in the brain-controlled immunostimulation afforded by DTC.     

The protective effect of 1-tert.butyl-4,4-diphenylpiperidine against the nigrostriatal neurodegeneration caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces a Parkinson syndrome in humans and in monkeys. In the rat, treatment with MPTP for a month resulted in permanently reduced dopamine and serotonin levels in the caudate nucleus. However, if the rats were pretreated with budipine, no MPTP-induced reduction in the dopamine and serotonin levels in the caudate nucleus was observed although one month recovery and observation time had elapsed between the last budipine injection and decapitation. It is surmised that budipine antagonises the neurotoxic effect of MPTP.     

Studies on the mechanism of action of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Explants of embryonic rat substantia nigra in organotypic culture are sensitive to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at concentrations approximating the doses given in vivo to monkeys. Fluorescence microscopy and 3H-dopamine uptake measurements reveal that the toxicity is selective for dopamine neurons, whereas other neurons and cells in the culture appear normal by phase contrast microscopy. Reduced MPTP (piperidine analog) is inactive in the tissue culture model, while fully oxidized MPTP (pyridinium analog) destroys dopamine neurons. Pargyline and deprenyl, two monoamine oxidase inhibitors, inhibit the neurotoxic action of MPTP. Pargyline and deprenyl also protect monkeys in vivo. The results implicate monoamine oxidase in the mechanism of action of MPTP. Two possible mechanisms for protection by monoamine oxidase are discussed.