Melatonin protects 6-OHDA-induced neuronal death of nigrostriatal dopaminergic system

Effect of the Flavonoid Rutin on the Modulation of the Myenteric Plexuses in an Experimental Model of Parkinson's Disease

Recent discoveries have shown that enteric glial cells play an important role in different neurodegenerative disorders, such as Parkinson's disease (PD), which is characterized by motor dysfunctions caused by the progressive loss of dopaminergic neurons in the substance nigra pars compacta and non-motor symptoms including gastrointestinal dysfunction. In this study, we investigated the modulatory effects of the flavonoid rutin on the behavior and myenteric plexuses in a PD animal model and the response of enteric glia. Adult male Wistar rats were submitted to stereotaxic injection with 6-hydroxydopamine or saline, and they were untreated or treated with rutin (10 mg/kg) for 14 days. The ileum was collected to analyze tissue reactivity and immunohistochemistry for neurons (HuC/HuD) and enteric glial cells (S100β) in the myenteric plexuses. Behavioral tests demonstrated that treatment with rutin improved the motor capacity of parkinsonian animals and improved intestinal transit without interfering with the cell population; rutin treatment modulated the reactivity of the ileal musculature through muscarinic activation, reducing relaxation through the signaling pathway of nitric oxide donors, and increased the longitudinal contractility of the colon musculature in parkinsonian animals. Rutin revealed modulatory activities on the myenteric plexus, bringing relevant answers regarding the effect of the flavonoid in this system and the potential application of PD adjuvant treatment.

Targeting neuroendocrine abnormalities in Parkinson's disease with exercise

Parkinson's Disease (PD) is a prevalent and complex age-related neurodegenerative condition for which there are no disease-modifying treatments currently available. The pathophysiological process underlying PD remains incompletely understood but increasing evidence points to multiple system dysfunction. Interestingly, the past decade has produced evidence that exercise not only reduces signs and symptoms of PD but is also potentially neuroprotective. Characterizing the mechanistic pathways that are triggered by exercise and lead to positive outcomes will improve understanding of how to counter disease progression and symptomatology. In this review, we highlight how exercise regulates the neuroendocrine system, whose primary role is to respond to stress, maintain homeostasis and improve resilience to aging. We focus on a group of hormones - cortisol, melatonin, insulin, klotho, and vitamin D - that have been shown to associate with various non-motor symptoms of PD, such as mood, cognition, and sleep/circadian rhythm disorder. These hormones may represent important biomarkers to track in clinical trials evaluating effects of exercise in PD with the aim of providing evidence that patients can exert some behavioral-induced control over their disease.

The effects of regular swimming exercise and melatonin on the neurons localized in the striatum of hemiparkinsonian rats

Parkinson's disease is a progressive neurodegenerative movement disorder. We aimed to investigate the effects of regular swimming exercise and melatonin applied in the 6-Hydroxydopamine-induced Parkinson's disease rats by analysing dendritic spine of striatal neurons. Twenty-four male Wistar albino rats were used. 6-Hydroxydopamine unilaterally injected four (control, exercise, melatonin and exercise + melatonin) groups were included in the study. Tyrosine hydroxylase expression was detected by immunohistochemistry. Neurons and structures were identified from three-dimensional images by Neurolucida software. There was not any apparent difference for tyrosine hydroxylase positive neurons in the substantia nigra pars compacta and fibres in the striatum between the lesion sides of hemiparkinsonian groups. The treatment groups blocked the apomorphine-induced increase in rotations compared to the control group. In stepping test, the treatment groups prevented the loss of stepping in the contralateral side of hemiparkinsonian groups. The melatonin mostly had a positive effect on motor activity tests. In morphological analyses, the 6-Hydroxydopamine-induced lesion led to the reduction of the total dendritic length and number of branches. In the treatment groups, the reduction of the dendritic parameters was not observed. 6-Hydroxydopamine lesion led to a decrease in the total spine density, spine densities of thin and mushroom types. The exercise and melatonin treatments prevented the loss of spine density. The exercise treatment prevented the loss of spine density of mushroom type spines. The melatonin treatment blocked the loss of spine density of stubby type. In conclusion, these results provide evidence for effective additional protective therapeutic strategies for Parkinson's disease. In conclusion, results from the current study provide evidence for swimming exercise and melatonin as a promising candidate for effective additional protective strategies for PD.

Role of Melatonin in the Management of Sleep and Circadian Disorders in the Context of Psychiatric Illness

PURPOSE OF REVIEW

We present a review of research on the role of melatonin in the management of sleep and circadian disorders, stressing current overall view of the knowledge across psychiatric disorders.

RECENT FINDINGS

Dysregulation of sleep and circadian rhythms has been established in several psychiatric and neurocognitive disorders for long. Recent research confirms this finding consistently across disorders. The secretion of melatonin in schizophrenia and neurocognitive disorders is reduced due to a smaller volume and enlarged calcification of the pineal gland. On the other hand, melatonin dysregulation in bipolar disorder may be more dynamic and caused by light-sensitive melatonin suppression and delayed melatonin secretion. In both cases, exogenous melatonin seems indicated to correct the dysfunction. However, a very limited number of well-designed trials with melatonin to correct sleep and circadian rhythms exist in psychiatric disorders, and the evidence for efficacy is robust only in autism, attention deficit hyperactivity disorder (ADHD), and neurocognitive disorders. This topic has mainly not been of interest for recent work and well-designed trials with objective circadian parameters are few. Overall, recent studies in psychiatric disorders reported that melatonin can be effective in improving sleep parameters such as sleep onset latency, sleep efficiency, and sleep quality. Recent meta-analysis suggests that optimal dosage and dosing time might be important to maximize the efficacy of melatonin. The knowledge base is sufficient to propose well-designed, larger trials with circadian parameters as inclusion and outcome criteria. Based on the partly fragmentary information, we propose testing efficacy in disorders with neurocognitive etiopathology with later and higher dosing, and affective and anxiety disorders with lower and earlier dosing of melatonin. Melatonin is promising for the correction of sleep and circadian abnormalities in psychiatric disorders. However, research results on its effect are still few and need to be accumulated. For effective use of melatonin, it is necessary to consider the appropriate dosage and administration time, depending on the individual abnormality of sleep and circadian rhythms.

Melatonin as a Chronobiotic and Cytoprotective Agent in Parkinson's Disease

This article discusses the role that melatonin may have in the prevention and treatment of Parkinson’s disease (PD). In parkinsonian patients circulating melatonin levels are consistently disrupted and the potential therapeutic value of melatonin on sleep disorders in PD was examined in a limited number of clinical studies using 2–5 mg/day melatonin at bedtime. The low levels of melatonin MT1 and MT2 receptor density in substantia nigra and amygdala found in PD patients supported the hypothesis that the altered sleep/wake cycle seen in PD could be due to a disrupted melatonergic system. Motor symptomatology is seen in PD patients when about 75% of the dopaminergic cells in the substantia nigra pars compacta region degenerate. Nevertheless, symptoms like rapid eye movement (REM) sleep behavior disorder (RBD), hyposmia or depression may precede the onset of motor symptoms in PD for years and are index of worse prognosis. Indeed, RBD patients may evolve to an α-synucleinopathy within 10 years of RBD onset. Daily bedtime administration of 3–12 mg of melatonin has been demonstrated effective in RDB treatment and may halt neurodegeneration to PD. In studies on animal models of PD melatonin was effective to curtail symptomatology in doses that allometrically projected to humans were in the 40–100 mg/day range, rarely employed clinically. Therefore, double-blind, placebo-controlled clinical studies are urgently needed in this respect.

Electroacupuncture alleviates Parkinson disease and regulates the expression of brain-gut peptides

The non-motor symptoms (NMS) of Parkinson's disease (PD) are found in more than 90% of patients with PD. Here, we explored the effects of electroacupuncture (EA) stimulation at Zhong wan (CV-12), Qihai (RN-7), Zusanli (ST-36) and Taichong (LR-3) on NMS and brain-gut peptides of PD. We found that EA intervention alleviated the motor deficit induced by 6-OHDA in rats indicated by the decreased abnormal involuntary movements (AIMs) scores and the net number of rotations and increased cylinder test grade. It also improved the spatial memory and attenuated anxiety-like and depression of PD model rats. EA treatment significantly inhibited neuronal apoptosis in PD model animals, as demonstrated by the increased number of TH positive cells and reduced number of apoptotic cells in the substantia nigra. The expression of cleaved caspase-3 and cleaved PARP in PD model rats was markedly suppressed by EA stimulation. Moreover, EA remarkably inhibited the inflammatory response in PD model rats, as revealed by the decreased levels of TNF-α, IL-1β, and COX-2 mRNA expression. It also attenuated the oxidative stress in rats, as indicated by the increased levels of SOD and GSH and the decreased level of MDA. EA treatment contributed to alleviating PD by regulating brain-gut peptides in rats, such as NPY, CCK, SST, GAS, and PYY. In conclusion, EA stimulation at CV-12, RN-7, ST-36, and LR-3 effectively alleviates the NMS of PD partly through regulating the levels of brain-gut peptides.

The use of melatonin in adult psychiatric disorders: Expert recommendations by the French institute of medical research on sleep (SFRMS)

Melatonin is a hormone secreted by the pineal gland at night. This hormone has many physiological functions, the main one being to synchronise individuals' biological rhythms. Exogenous melatonin has the same chronobiotic action, even at small doses (0.125mg). In addition, a sleep-inducing (soporific) action appears to occur in a dose-effect relationship, i.e. as the dose increases. In psychiatric disorders, these two effects could have interesting applications in clinical practice. The French institute of medical research on sleep (SFRMS) appointed a group of experts to conduct a consensus conference to study the indications of melatonin and the conditions of its prescription. An account of the conclusions on adult psychiatric disorders (presented orally at the Congress on Sleep in Marseille, 23 November 2017) is given here. Exogenous melatonin proves to be useful among patients with a stabilized psychiatric disorder or in remission, to prevent relapse in case of associated complaints of insomnia, poor quality sleep or delayed sleep phase syndrome. During acute phases, melatonin could be used as an adjuvant treatment when there are insomnia symptoms, in mood disorders (bipolar disorder, major depressive disorder, seasonal affective disorder), in attention deficit hyperactivity disorder (ADHD), in peri-surgical anxiety and in schizophrenia. In somatoform disorders, melatonin is a possible treatment for painful symptoms in fibromyalgia, irritable bowel syndrome, functional dyspeptic syndrome and temporomandibular joint dysfunction.

Melatonin Ameliorates Neuropharmacological and Neurobiochemical Alterations Induced by Subchronic Exposure to Arsenic in Wistar Rats

An experimental study was conducted in Wistar rats to characterize the arsenic ("As")-induced alterations in neurobiochemistry in brain and its impact on neuropharmacological activities with or without the melatonin (MLT) as an antioxidant given exogenously. Male Wistar rats were randomly divided in to four groups of six each. Group I served as untreated control, while group II received As [sodium (meta) arsenite; NaAsO₂] at 10 mg/kg bw (p.o.) for a period of 56 days. Experimental rats in group III received treatment similar to group II but in addition received MLT at 10 mg/kg bw (p.o.) from day 32 onwards. Rats in group IV received MLT alone from day 32 onwards similar to group III. Sub-chronic exposure to As (group II) significantly reduced both voluntary locomotor and forced motor activities and melatonin supplementation (group III) showed a significant improvement in motor activities, when subjected to test on day 42 or 56. Rats exposed to As showed a significant increase in anxiety level and a marginal nonsignificant reduction in pain latency. Sub-chronic administration of As induced (group II) significant increase in the levels of thiobarbituric acid reactive substance (TBARS) called malondialdehyde (MDA) in the brain tissue (5.55 ± 0.57 nmol g^-1), and their levels were significantly reduced by MLT supplementation (group III 3.96 ± 0.15 nmol g^-1). The increase in 3-nitrotyrosine (3-NT) levels in As-exposed rats indicated nitrosative stress due to the formation of peroxynitrite (ONOO^-). However, exogenously given MLT significantly reduced the 3-NT formation as well as prostaglandin (PGE₂) levels in the brain. Similarly, MLT administration have suppressed the release of pro-inflammatory cytokines (viz., IL-1β, IL-6, and TNF-α) and amyloid-β_1-40 (Aβ) deposition in the brain tissues of experimental rats. To conclude, exogenous administration of melatonin can overcome the sub-chronic As-induced oxidative and nitrosative stress in the CNS, suppressed pro-inflammatory cytokines, and restored certain disturbed neuropharmacological activities in Wistar rats.

Melatonin: Clinical Perspectives in Neurodegeneration

Prevention of neurodegenerative diseases is presently a major goal for our Society and melatonin, an unusual phylogenetically conserved molecule present in all aerobic organisms, merits consideration in this respect. Melatonin combines both chronobiotic and cytoprotective properties. As a chronobiotic, melatonin can modify phase and amplitude of biological rhythms. As a cytoprotective molecule, melatonin reverses the low degree inflammatory damage seen in neurodegenerative disorders and aging. Low levels of melatonin in blood characterizes advancing age. In experimental models of Alzheimer's disease (AD) and Parkinson's disease (PD) the neurodegeneration observed is prevented by melatonin. Melatonin also increased removal of toxic proteins by the brain glymphatic system. A limited number of clinical trials endorse melatonin's potentiality in AD and PD, particularly at an early stage of disease. Calculations derived from animal studies indicate cytoprotective melatonin doses in the 40-100 mg/day range. Hence, controlled studies employing melatonin doses in this range are urgently needed. The off-label use of melatonin is discussed.

Melatonin as a mitochondrial protector in neurodegenerative diseases

Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.

Melatoninergic System in Parkinson's Disease: From Neuroprotection to the Management of Motor and Nonmotor Symptoms

Melatonin is synthesized by several tissues besides the pineal gland, and beyond its regulatory effects in light-dark cycle, melatonin is a hormone with neuroprotective, anti-inflammatory, and antioxidant properties. Melatonin acts as a free-radical scavenger, reducing reactive species and improving mitochondrial homeostasis. Melatonin also regulates the expression of neurotrophins that are involved in the survival of dopaminergic neurons and reduces α-synuclein aggregation, thus protecting the dopaminergic system against damage. The unbalance of pineal melatonin synthesis can predispose the organism to inflammatory and neurodegenerative diseases such as Parkinson's disease (PD). The aim of this review is to summarize the knowledge about the potential role of the melatoninergic system in the pathogenesis and treatment of PD. The literature reviewed here indicates that PD is associated with impaired brain expression of melatonin and its receptors MT₁ and MT₂. Exogenous melatonin treatment presented an outstanding neuroprotective effect in animal models of PD induced by different toxins, such as 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat, and maneb. Despite the neuroprotective effects and the improvement of motor impairments, melatonin also presents the potential to improve nonmotor symptoms commonly experienced by PD patients such as sleep and anxiety disorders, depression, and memory dysfunction.

Effect of chronic L-dopa or melatonin treatments after dopamine deafferentation in rats: dyskinesia, motor performance, and cytological analysis

The present study examines the ability of melatonin to protect striatal dopaminergic loss induced by 6-OHDA in a rat model of Parkinson's disease, comparing the results with L-DOPA-treated rats. The drugs were administered orally daily for a month, their therapeutic or dyskinetic effects were assessed by means of abnormal involuntary movements (AIMs) and stepping ability. At the cellular level, the response was evaluated using tyrosine hydroxylase immunoreactivity and striatal ultrastructural changes to compare between L-DOPA-induced AIMs and Melatonin-treated rats. Our findings demonstrated that chronic oral administration of Melatonin improved the alterations caused by the neurotoxin 6-OHDA. Melatonin-treated animals perform better in the motor tasks and had no dyskinetic alterations compared to L-DOPA-treated group. At the cellular level, we found that Melatonin-treated rats showed more TH-positive neurons and their striatal ultrastructure was well preserved. Thus, Melatonin is a useful treatment to delay the cellular and behavioral alterations observed in Parkinson's disease.

Melatonin as a neuroprotective agent in the rodent models of Parkinson's disease: is it all set to irrefutable clinical translation?

Parkinson's disease (PD), a neurodegenerative disorder, is characterized by the selective degeneration of the nigrostriatal dopaminergic neurons, continuing or permanent deficiency of dopamine, accretion of an abnormal form of alpha synuclein in the adjacent neurons, and dysregulation of ubiquitin proteasomal system, mitochondrial metabolism, permeability and integrity, and cellular apoptosis resulting in rigidity, bradykinesia, resting tremor, and postural instability. Melatonin, an indoleamine produced almost in all the organisms, has anti-inflammatory, anti-apoptotic, and anti-oxidant nature. Experimental studies employing 1-methyl 4-phenyl 1, 2, 3, 6-tetrahydropyridine (MPTP), 6-hydroxydopamine (6-OHDA), methamphetamine, rotenone, and maneb and paraquat models have shown an enormous potential of melatonin in amelioration of the symptomatic features of PD. Although a few reviews published previously have described the multifaceted efficacy of melatonin against MPTP and 6-OHDA rodent models, due to development and validation of the newer models as well as the extensive studies on the usage of melatonin in entrenched PD models, it is worthwhile to bring up to date note on the usage of melatonin as a neuroprotective agent in PD. This article presents an update on the usage and applications of melatonin in PD models along with incongruous observations. The impending implications in the clinics, success, limitations, and future prospective have also been discussed in this article.

The promise of neuroprotective agents in Parkinson's disease

Parkinson’s disease (PD) is characterized by loss of dopamine neurons in the substantia nigra of the brain. Since there are limited treatment options for PD, neuroprotective agents are currently being tested as a means to slow disease progression. Agents targeting oxidative stress, mitochondrial dysfunction, and inflammation are prime candidates for neuroprotection. This review identifies Rasagiline, Minocycline, and creatine, as the most promising neuroprotective agents for PD, and they are all currently in phase III trials. Other agents possessing protective characteristics in delaying PD include stimulants, vitamins, supplements, and other drugs. Additionally, combination therapies also show benefits in slowing PD progression. The identification of neuroprotective agents for PD provides us with therapeutic opportunities for modifying the course of disease progression and, perhaps, reducing the risk of onset when preclinical biomarkers become available.

Neurotoxins: free radical mechanisms and melatonin protection

Toxins that pass through the blood-brain barrier put neurons and glia in peril. The damage inflicted is usually a consequence of the ability of these toxic agents to induce free radical generation within cells but especially at the level of the mitochondria. The elevated production of oxygen and nitrogen-based radicals and related non-radical products leads to the oxidation of essential macromolecules including lipids, proteins and DNA. The resultant damage is referred to as oxidative and nitrosative stress and, when the molecular destruction is sufficiently severe, it causes apoptosis or necrosis of neurons and glia. Loss of brain cells compromises the functions of the central nervous system expressed as motor, sensory and cognitive deficits and psychological alterations. In this survey we summarize the publications related to the following neurotoxins and the protective actions of melatonin: aminolevulinic acid, cyanide, domoic acid, kainic acid, metals, methamphetamine, polychlorinated biphenyls, rotenone, toluene and 6-hydroxydopamine. Given the potent direct free radical scavenging activities of melatonin and its metabolites, their ability to indirectly stimulate antioxidative enzymes and their efficacy in reducing electron leakage from mitochondria, it would be expected that these molecules would protect the brain from oxidative and nitrosative molecular mutilation. The studies summarized in this review indicate that this is indeed the case, an action that is obviously assisted by the fact that melatonin readily crosses the blood brain barrier.

Haloperidol causes cytoskeletal collapse in N1E-115 cells through tau hyperphosphorylation induced by oxidative stress: Implications for neurodevelopment

Haloperidol a typical antipsychotic commonly used in the treatment of schizophrenia causes neuronal damage and extrapiramidal symptoms after several years of treatment. These symptoms have been associated with increased levels of oxidative stress. Reactive oxygen species produce cytoskeletal collapse and an excessive phosphorylation of tau, a microtubule-associated protein that plays a key role in microtubule stabilization, and in growth cone and neurite formation, which are cytoskeletal phenotypes that participate in neurodevelopment. Thus, we hypothesized that haloperidol produces neurocytoskeletal disorganization by increasing free radicals and tau hyperphosphorylation, and consequently, the loss of neurodevelopmental cytoskeletal phenotypes, neurites and growth cones. The purpose of this work was the characterization of neuronal cytoskeletal changes caused by haloperidol in neuroblastoma N1E-115 cells. We also studied the mechanisms by which haloperidol causes cytoskeletal changes. The results showed that haloperidol at 100microM caused a complete cytoskeleton collapse in the majority of the cells. Melatonin, a free radical scavenger, blocks tau hyperphosphorylation, and microtubule disorganization caused by haloperidol in a dose-response mode. Additionally, the indole blocks lipoperoxide formation in haloperidol treated cells. The results indicate that free radicals and tau hyperphosphorylation produced by haloperidol caused a cytoskeletal collapse and the lost of growth cones and neurites. These effects were blocked by melatonin. Data suggest that extrapiramidal symptoms in schizophrenic patients can be produced by cytoskeletal disorganization during adult brain neurodevelopment after prolonged haloperidol treatment that can be prevented by melatonin.

Melatonin protects SK-N-SH neuroblastoma cells from amphetamine-induced neurotoxicity

Several hypotheses regarding the mechanism underlying amphetamine-induced neurotoxicity have been proposed. One of them is based on the observation of free radical formation and oxidative stress produced by auto-oxidation of dopamine (DA). The formation of DA-related reactive oxygen species (ROS) such as superoxide and hydroxyl radicals appears to play an important role in amphetamine-induced neurotoxicity. Melatonin, the main secretory product of pineal gland, is well known for its protective effects that are currently attributed mainly to its radical scavenging and antioxidant properties. The present study was conducted to investigate the protective effects of melatonin on d-amphetamine (AMPH)-induced neurotoxicity in cultured human dopaminergic neuroblastoma SK-N-SH cells. Our data indicate that AMPH significantly reduces cell viability, induces oxidative stress (enhances ROS production and malondialdehyde levels), up-regulates alpha-synuclein expression and decreases intracellular ATP levels. However, pretreatment of SK-N-SH cells with melatonin prevents AMPH-induced loss of cell viability and induction of oxidative stress, while reducing alpha-synuclein expression and increasing ATP production. These results suggest that the antioxidant properties of melatonin may provide a protective mechanism against AMPH-induced neuronal degeneration.

M30, a novel multifunctional neuroprotective drug with potent iron chelating and brain selective monoamine oxidase-ab inhibitory activity for Parkinson's disease

Iron and monoamine oxidase activity are increased in brain of Parkinson's disease (PD). They are associated with autoxidation and oxidative deamination of dopamine by MAO resulting in the generation of reactive oxygen species and the onset of oxidative stress to induce neurodegeneration. Iron chelators (desferal, Vk-28 and clioquinol) but not copper chelators have been shown to be neuroprotective in the 6-hydroxydoapmine and MPTP models of Parkinson's disease (PD), as are monoamine oxidase B inhibitors such as selegiline and rasagiline. These findings prompted the development of multifunctional anti PD drugs possessing iron chelating phamacophore of VK-28 and the propargylamine MAO inhibitory activity of rasagiline. M30 is a potent iron chelator, radical scavenger and brain selective irreversible MAO-A and B inhibitor, with little inhibition of peripheral MAO. It has neuroprotective activity in in vitro and in vivo models of PD and unlike selective MAO-B inhibitors it increases brain dopamine, serotonin and noradrenaline. These findings indicate beside its anti PD action, it may also possess antidepressant activity, similar to selective MAO-A and nonselective MAO inhibitors. These properties make it an ideal anti PD drug for which it is being developed.

Zingerone [4-(4-hydroxy-3-methoxyphenyl)-2-butanone] prevents 6-hydroxydopamine-induced dopamine depression in mouse striatum and increases superoxide scavenging activity in serum

As superoxide (*O(2)-) and hydroxyl radical (*OH) have been implicated in pathogenesis of Parkinson's disease, free radical scavenging, antioxidant, and neuroprotective agents have attracted attention as ways to prevent progression. We examined effects of zingerone, an alkaloid extracted from ginger root, on 6-hydroxydopamine (6-OHDA)-induced dopamine (DA) reduction in mouse striatum. Zingerone administration 1 h before and for 6 more days following one intracerebroventricular 6-OHDA injection prevented reductions of striatal DA and its metabolites, and increased serum *O(2)- scavenging activity. Zingerone did not change activities of catalase or glutathione peroxidase in striatum or serum, or *O(2)- scavenging activity in striatum. Treatment with diethyldithiocarbamate, SOD inhibitor, abolished the protective effect of zingerone against 6-OHDA-induced DA reduction. In vitro, zingerone scavenged *O(2)- and *OH and suppressed lipid peroxidation only weakly. Thus, direct antioxidant effects may be a minor component of its putative neuroprotective effect; instead, zingerone acted mainly by increasing systemic superoxide dismutase activity. Effects of zingerone treatment in this model suggest possible value in treatment of Parkinson's disease.

Effect of acupuncture on 6-hydroxydopamine-induced nigrostratal dopaminergic neuronal cell death in rats

In this study, we investigated the effect of acupuncture at the Zusanli acupoint (ST36) on the nigrostriatal dopaminergic neuronal cell death in the rats with Parkinson's disease. Two weeks after unilateral injection of 6-hydroxydopamine (6-OHDA) into the striatum, an apomorphine-induced rotational behavior test showed significant rotational asymmetry in the rats with Parkinson's disease. Immunostaining for tyrosine hydroxylase demonstrated a dopaminergic neuronal loss in the substantia nigra and dopaminergic fiber loss in the striatum. Acupuncture at the ST36 for 14 days significantly inhibited rotational asymmetry in the rats with Parkinson's disease, and also protected against 6-OHDA-induced nigrostriatal dopaminergic neuronal loss. These effects of acupuncture were not observed for the non-acupoint (hip) acupuncture. The present study shows that acupuncture at the ST36 acupoint can be used as a useful strategy for the treatment of Parkinson's disease.

Recovery of experimental Parkinson's disease with the melatonin analogues ML-23 and S-20928 in a chronic, bilateral 6-OHDA model: a new mechanism involving antagonism of the melatonin receptor

Over the past 10 years, there has been a resurgence of interest in examining the role of melatonin in health and disease. While the brunt of research in this area has portrayed melatonin in a favorable light, there is a growing body of evidence suggesting that melatonin may possess adverse effects contributing to the development of various neuropsychiatric disease states. In preclinical models of Parkinson's disease (PD), melatonin has been shown to enhance the severity of this condition while its antagonism, using constant light or pinealectomy, facilitates recovery. To test this hypothesis further, the present study employed the melatonin analogues ML-23 and S-20928 in a post-6-OHDA injection regime to determine whether they may have a favorable effect on the symptoms of this more chronic model of PD. When ML-23 was injected I.P. in a dose of 3 mg/kg twice daily for 3.5 days after 6-OHDA, significant improvement in motor function and regulatory deficits was observed. Similarly, the injection of S-20928 in a 1 mg/kg dose (I.P.), in the same regimen, facilitated modest improvement in motor function and regulatory deficits while the larger dose enhanced the severity of behavioural deficits and produced severe side effects causing deterioration in condition during the course of drug administration. ML-23 administration totally abolished the 6-OHDA-induced mortality, which accompanies dopamine (DA) degeneration, while S-20928 had no effect on this parameter. These results suggest that some melatonin analogues can aid in recovery from DA depleting lesions after DA degeneration has commenced and the recovery is not attributable to the antioxidative properties of this hormone. While the exact mechanism by which ML-23 and S-20928 are exerting their therapeutic effect is unclear, it is possible that antagonism of melatonin receptors may play some role and this should be considered when assessing the potential of melatonin analogues for treatment of human neuropsychiatric disorders.

Potential neuroprotective effect oft-butylhydroquinone against neurotoxicity?Induced by 1-methyl-4-(2?-methylphenyl)-1,2,3,6-tetrahydropyridine (2?-methyl-MPTP) in mice

Dopaminergic damage inducing Parkinson's disease (PD) is ubiquitous neurodegenerative disorder, characterized by the progressive loss of dopaminergic neurons in the nigrostriatal pathways. The etiology and pathogenic factors implicated in dopaminergic damage are still unexplored to develop causal therapeutic strategies aimed to halt its progressive loss. The neurotoxicity induced by 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'CH3-MPTP), which is more potent neurotoxic than MPTP in mice, is one of the most valuable models for analyzing pathological feature of dopaminergic damage. Herein, we investigated the neuroprotective effect of the potent antioxidant tertiary butylhydroquinone (TBHQ) against 2'CH3-MPTP-induced neurotoxicity in mice as well as the possible mechanism underlying such neurotoxicity. Male albino mice were injected with two doses of 2'CH3-MPTP (20 mg/kg, i.p.) for two consecutive days. Animals were killed after 2 weeks from the last dose of 2'CH3-MPTP. Control animals received 10 mL/kg body weight i.p. of distilled water. In both groups, brain stems containing the nigrostriatal pathways were dissected and reduced glutathione (GSH), malonyldialdehyde (MDA) contents, and superoxide dismutase (SOD) activity were estimated. Also, brain stem histopathological and histochemical changes were examined. The results of this study revealed that i.p. injection of 2'CH3-MPTP caused decrease in the brain stem content of GSH. On the other hand, the content of MDA and SOD activity was increased as compared with control groups. Also, 2'CH3-MPTP showed severe histopathological changes including swelling of cytoplasm, interstitial edema, and complete loss of the neurons with reactive microglial proliferation and gliosis. Furthermore, histochemical examination of brain stem qualitatively showed depletion of dopaminergic neurons of nigrostriatum. Oral administration of TBHQ (100 mg/kg) prior to 2'CH3-MPTP for 7 days caused normalization of GSH content and SOD activity and ameliorated the MDA content but still above the control value. Pretreatment with TBHQ slightly mitigated the histopathological and histochemical changes observed in 2'CH3-MPTP-treated mice. Based on these observations, it can be concluded that the antioxidant TBHQ has the ability to reverse the oxidative stress caused by 2'CH3-MPTP in mice while failed to challenge the histopathological and histochemical changes induced by that toxicant.

Circadian effects of dopaminergic treatment in restless legs syndrome

BACKGROUND AND PURPOSE

Although an essential diagnostic feature of restless legs syndrome (RLS) is the presence of circadian symptom variations, with an increase in the evening or at night, the mechanisms underlying this time-bound variation remain unknown. Since dopaminergic mechanisms seem to play a central role in the pathophysiology of RLS, it is likely that circadian variations in the dopaminergic system or factors affecting it cause the nightly increase. The reverse is also possible; dopaminergic medication might affect melatonin function, a key element of the circadian system. The present study investigated the effects of dopaminergic medication on melatonin secretion in RLS.

PATIENTS AND METHODS

Eight previously untreated patients diagnosed with idiopathic RLS underwent a three-week, open-labeled treatment with 400 mg L-DOPA (+100 mg CarbiDOPA). Dim Light Melatonin Onset (DLMO), a marker of circadian phase, was determined before and after treatment.

RESULTS

Compared to baseline, earlier DLMO was found in L-DOPA treated patients (21:00+/-1:20 vs. 18:50+/-0:55; P < 0.05). Anticipation of DLMO was more marked in the subgroup of patients showing augmentation. A positive correlation was observed between change of DLMO, sleep latency and time of onset of symptoms following treatment with L-DOPA.

CONCLUSIONS

Our results suggest that L-DOPA may exert chronobiotic effects in RLS.

Acupuncture prevents 6-hydroxydopamine-induced neuronal death in the nigrostriatal dopaminergic system in the rat Parkinson's disease model

Parkinson's disease (PD) is a chronic neurodegenerative disorder, and it has been suggested that treatments promoting survival and functional recovery of affected dopaminergic neurons could have a significant and long-term therapeutic value. In the present study, we investigated the neuroprotective effects of acupuncture on the nigrostriatal system in rat unilaterally lesioned with 6-hydroxydopamine (6-OHDA, 4 microg/microl, intrastriatal injection) using tyrosine hydroxylase (TH) and receptor for brain-derived neurotrophic factor, trkB, immunohistochemistries. Two weeks after the lesions were made, rats presented with asymmetry in rotational behavior (118.3 +/- 17.5 turns/h) following injection with apomorphine, a dopamine receptor agonist (0.5 mg/kg, sc). In contrast, acupunctural treatment at acupoints GB34 and LI3 was shown to significantly reduce this motor deficit (14.6 +/- 13.4 turns/h). Analysis via TH immunohistochemistry revealed a substantial loss of cell bodies in the substantia nigra (SN) (45.7% loss) and their terminals in the dorsolateral striatum ipsilateral to the 6-OHDA-induced lesion. However, acupunctural treatment resulted in the enhanced survival of dopaminergic neurons in the SN (21.4% loss) and their terminals in the dorsolateral striatum. Acupuncture also increased the expression of trkB significantly (35.6% increase) in the ipsilateral SN. In conclusion, we observed that only acupuncturing without the use of any drug has the neuroprotective effects against neuronal death in the rat PD model and these protective properties of acupuncture could be mediated by trkB.

Possible mechanism of action in melatonin attenuation of haloperidol-induced orofacial dyskinesia

Tardive dyskinesia (TD) is a late complication of prolonged neuroleptic treatment characterized by involuntary movements of the oral region. In spite of high incidence and much research, the pathophysiology of this devastating movement disorder remains elusive. Chronic treatment with neuroleptics leads to the development of abnormal oral movements in rats, referred to as vacuous chewing movements (VCMs). VCMs in rats are widely accepted as an animal model of TD. Rats chronically treated with haloperidol (1.5 mg/kg ip) significantly developed VCMs and tongue protrusions. Melatonin dose-dependently (1, 2, and 5 mg/kg) reversed the haloperidol-induced VCM and tongue protrusions frequencies. Biochemical analysis reveals that chronic haloperidol treatment significantly induced lipid peroxidation and decreased the forebrain glutathione (GSH) levels in the rats. Chronic haloperidol-treated rats also showed decreased levels of antioxidant defense enzymes, superoxide dismutase (SOD), and catalase. Coadministration of melatonin (1, 2, and 5 mg/kg) along with haloperidol significantly reduced the lipid peroxidation and restored the decreased GSH levels by chronic haloperidol treatment, and significantly reversed the haloperidol-induced decrease in forebrain SOD and catalase levels in rats. However, a lower dose of melatonin (1 mg/kg) failed to reverse chronic haloperidol-induced decreases in forebrain GSH, SOD, and catalase levels. In conclusion, melatonin could be screened as a potential drug candidate for the prevention or treatment of neuroleptic-induced orofacial dyskinesia.

Ultrastructural and MRI study of the substantia nigra evolving exofocal post-ischemic neuronal death in the rat

To clarify the morphological characteristics of exofocal post-ischemic neuronal death (EPND) in the substantia nigra (SN), we investigated the course of light- and electron-microscopic changes of the SN of rats subjected to occlusion of the left middle cerebral artery (MCA) for 1, 2, 4, 7 and 12 days. To assess cellular edema, sequential magnetic resonance (MR) mapping of the apparent diffusion coefficient (ADC) and the T2 value test was performed. Histological and electron-microscopic examination on day 1 showed dotted chromatin clumps in the nuclei of some neurons and mild swelling of the perivascular endfeet of astrocytes in the ipsilateral SN. On day 2, a few cells of the ipsilateral SN pars reticulata (SNr) revealed key morphological signs of apoptosis--apoptotic body-like condensation and segregation of the chromatin and DNA fragmentation-like nuclear remnants. On day 4, 38% of neurons became swollen (pale neurons) with cytoplasmic microvacuoles, which appeared to originate from rough endoplasmic reticulum (rER), mitochondria and Golgi apparatus. Twenty percent of neurons showed massive proliferation of the cisternae of the rER, some of which were fragmented or had lost their normal parallel arrangement. In addition, MR mapping revealed a transient ADC decrease with a T2 increase (signifying a phase of cellular edema), which coordinated with the phase of ultrastructural cellular swelling. Further, the total number of neurons started to decrease gradually, the perivascular endfeet of astrocytes were markedly swollen, and the neuropil became loose on day 4. On day 7, reactive astrocytes and dark neurons occurred most frequently. These results suggest that the EPND in the SN after occlusion of the MCA in adult rats is due to both apoptosis and necrosis, although necrosis seems to be the dominant mechanism of the EPND. However, the morphologic resemblances of EPND to delayed neuronal death suggest these processes have a common pathomechanism.

Trisialoganglioside GT1b induces in vivo degeneration of nigral dopaminergic neurons: role of microglia

We recently showed that trisialoganglioside (GT1b) induces cell death of dopaminergic neurons in rat mesencephalic cultures (Chung et al., Neuroreport 12:611-614, 2001). The present study examines the in vivo neurotoxic effects of GT1b on dopaminergic neurons in the substantia nigra (SN) of Sprague-Dawley rats. Seven days after GT1b injection into the SN, immunocytochemical staining of SN tissue revealed death of nigral neurons, including dopaminergic neurons. Additional immunostaining using OX-42 and OX-6 antibodies showed that GT1b-activated microglia were present in the SN where degeneration of nigral neurons was found. Western blot analysis and double-labeled immunohistochemistry showed that inducible nitric oxide synthase (iNOS) was expressed in the SN, where its levels were maximal at 8 h post-GT1b injection, and that iNOS was localized exclusively within microglia. GT1b-induced loss of dopaminergic neurons in the SN was partially inhibited by N(G)-nitro-L-arginine methyl ester hydrochloride, an NOS inhibitor. Our results indicate that in vivo neurotoxicity of GT1b against nigral dopaminergic neurons is at least in part mediated by nitric oxide released from activated microglia. Because GT1b exists abundantly in central nervous system neuronal membranes, our data support the hypothesis that immune-mediated events triggered by endogenous compounds such as GT1b could contribute to the initiation and/or the progression of dopaminergic neuronal cell death that occurs in Parkinson's disease.

Antioxidant compounds protect dopamine neurons from death due to oxidative stress in vitro

Using tissue culture models of oxidative stress caused by serum deprivation or MPTP/MPP+ toxicity, the present study establishes that the antioxidants epigallocatechin gallate, lazaroids U74389G and U83836E, reservatrol, MnTBAP, MCI 186, trolox, and melatonin protect 68-100% of dopamine (DA) neurons from cell death. In contrast, the nitric oxide inhibitor LY83583, the caspase inhibitors Z-VAD-FMK, Ac-DQMD-CHO and Z-DEVD-FMK, and the CDK-5 inhibitor, roscovotine were not neuroprotective, although death was often delayed by 1 day in vitro. We conclude that antioxidants are more effective at preventing cell death in vitro than are inhibitors at later stages in the death cascade.

Melatonin attenuates MPTP-induced dopaminergic neuronal injury associated with scavenging hydroxyl radical

To clarify the relationship between melatonin's hydroxyl radical (*OH) scavenging ability and its protective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuronal injury, in the present study, the salicylate trapping method combined with high-performance liquid chromatography (HPLC)-electrochemical detection were used to measure the contents of dihydroxybenzoic acid (DHBA) and dopamine (DA) in brain tissues of C57BL/6 mice. Immunocytohistochemistry was used to detect tyrosine hydroxylase (TH)-like positive staining neurons. Results show that MPTP treatment induced an increase in the content of DHBA and decrease in the level of DA as well as the number of TH positive stained neurons in the mouse brain. However, melatonin dose-dependently inhibited the increase of DHBA levels in ventral midbrain tissues, the decrease of DA content and the loss of dopaminergic neurons. Moreover, the relationship between the changes of DHBA and DA levels in the brain of mice following MPTP and melatonin treatment showed a statistically significant negative correlation. Present results suggest that melatonin can ameliorate MPTP-induced dopaminergic neuronal lesions probably, at least partially, because of its inhibition of *OH generation.

Melatonin-dopamine interactions: from basic neurochemistry to a clinical setting

To review the interaction between melatonin and the dopaminergic system in the hypothalamus and striatum and its potential clinical use in dopamine-related disorders in the central nervous system. Medline-based search on melatonin-dopamine interactions in mammals. Melatonin. the hormone produced by the pineal gland at night. influences circadian and seasonal rhythms, most notably the sleep-wake cycle and seasonal reproduction. The neurochemical basis of these activities is not understood yet. Inhibition of dopamine release by melatonin has been demonstrated in specific areas of the mammalian central nervous system (hypothalamus, hippocampus, medulla-pons, and retina). Antidopaminergic activities of melatonin have been demonstrated in the striatum. Dopaminergic transmission has a pivotal role in circadian entrainment of the fetus, in coordination of body movement and reproduction. Recent findings indicate that melatonin may modulate dopaminergic pathways involved in movement disorders in humans. In Parkinson patients melatonin may, on the one hand, exacerbate symptoms (because of its putative interference with dopamine release) and, on the other, protect against neurodegeneration (by virtue of its antioxidant properties and its effects on mitochondrial activity). Melatonin appears to be effective in the treatment of tardive dyskinesia. a severe movement disorder associated with long-term blockade of the postsynaptic dopamine D2 receptor by antipsychotic drugs in schizophrenic patients. The interaction of melatonin with the dopaminergic system may play a significant role in the nonphotic and photic entrainment of the biological clock as well as in the fine-tuning of motor coordination in the striatum. These interactions and the antioxidant nature of melatonin may be beneficial in the treatment of dopamine-related disorders.

Melatonin protects against 6-OHDA-induced neurotoxicity in rats: a role for mitochondrial complex I activity

Unilateral injection into the right substantia nigra of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA) produces extensive loss of dopaminergic cells ('hemi-parkinsonian rat'). The pineal hormone melatonin, which is a potent antioxidant against different reactive oxygen species and has been reported to be neuroprotective in vivo and in vitro, was evaluated for potential anti-Parkinson effects in this model. Imbalance in dopaminergic innervation between the striata produced by intranigral administration of 6-OHDA results in a postural asymmetry causing rotation away from the nonlesioned side. Melatonin given systemically prevented apomorphine-induced circling behavior in 6-OHDA-lesioned rats. Reduced activity of mitochondrial oxidative phosphorylation enzymes has been suggested in some neurodegenerative diseases; in particular, selective decrease in complex I activity is observed in the substantia nigra of Parkinson's disease patients. Analysis of mitochondrial oxidative phosphorylation enzyme activities in nigral tissue from 6-OHDA-lesioned rats by a novel BN-PAGE histochemical procedure revealed a clear loss of complex I activity, which was protected against in melatonin-treated animals. A good correlation between behavioral parameters and enzymatic (complex I) analysis was observed independent of melatonin administration. A deficit in mitochondrial complex I could conceivably contribute to cell death in parkinsonism via free radical mechanisms, both directly via reactive oxygen species production and by decreased ATP synthesis and energy failure. Melatonin may have potential utility in the treatment of neurodegenerative disorders where oxidative stress is a participant.

Melatonin is protective in necrotic but not in caspase-dependent, free radical-independent apoptotic neuronal cell death in primary neuronal cultures

To assess the neuroprotective potential of melatonin in apoptotic neuronal cell death, we investigated the efficacy of melatonin in serum-free primary neuronal cultures of rat cortex by using three different models of caspase-dependent apoptotic, excitotoxin-independent neurodegeneration and compared it to that in necrotic neuronal damage. Neuronal apoptosis was induced by either staurosporine or the neurotoxin ethylcholine aziridinium (AF64A) with a delayed occurrence of apoptotic cell death (within 72 h). The apoptotic component of oxygen-glucose deprivation (OGD) unmasked by glutamate antagonists served as a third model. As a model for necrotic cell death, OGD was applied. Neuronal injury was quantified by LDH release and loss of metabolic activity. Although melatonin (0.5 mM) partly protected cortical neurons from OGD-induced necrosis, as measured by a significant reduction in LDH release, it was not effective in all three models of apoptotic cell death. In contrast, exaggeration of neuronal damage by melatonin was observed in native cultures as well as after induction of apoptosis. The present data suggest that the neuroprotectiveness of melatonin strongly depends on the model of neuronal cell death applied. As demonstrated in three different models of neuronal apoptosis, the progression of the apoptotic type of neuronal cell death cannot be withhold or is even exaggerated by melatonin, in contrast to its beneficial effect in the necrotic type of cell death.

The therapeutics of melatonin: a paediatric perspective

The production of melatonin by the pineal gland and its functions are considered, and then its possible uses in the treatment of children. Institutionalized children, and those with severe learning disorders, often have irregular sleep-wake patterns, and there is evidence that melatonin can result in improvement to the benefit of both the child and the carers. The affected children can become less irritable, calmer, happier, and content. Also they may socialize better and become more attentive, with an improvement in their cognitive abilities. Another group of children who are likely to suffer from disturbed sleep are those who are visually handicapped. Melatonin given in the evening can improve their sleep patterns, and often their performance. No important side-effects have been reported. It is generally accepted that if a child is liable to epileptic seizures sleep deprivation may well exacerbate them. There is some evidence from clinical trials that in that event melatonin can be helpful. There are many other problems in which it is claimed that treatment with melatonin is justifiable. These are mentioned, but further confirmatory studies are needed in most of them. There is no doubt that melatonin can effect the circadian system, and shift the sleep-wake cycle; and that there are situations in which this can be desirable.

Melatonin fails to protect against long-term MPTP-induced dopamine depletion in mouse striatum

Several laboratories recently have reported that melatonin may possess neuroprotective properties. The present paper presents the results of our studies on the long term in vivo neuroprotective effects of melatonin in a well-defined neurotoxicity model using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the C57BL/6 mouse. MPTP is bioactivated by brain monoamine oxidase B (MAO-B) to its neurotoxic pyridinium metabolite 1-methyl-4-phenylpyridinium (MPP(+)) which destroys dopaminergic nerve terminals leading to the depletion of neostriatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC). Our initial study compared striatal DA and DOPAC levels in MPTP-only-treated animals and animals treated with melatonin 30 min prior to and 3 times hourly post-MPTP. DA/DOPAC levels measured 7 days after MPTP were similar in both groups. A second study was designed to address the possibility that melatonin cleared from the brain prior to MPP(+). Animals, that had been administered the same regimen of melatonin as in the first study plus a fourth post-MPTP melatonin dose, were maintained on melatonin in drinking water until 5 days post-MPTP. Striatal DA/DOPAC levels of these melatonin-plus-MPTP treated animals also were the same as the MPTP-only-treated animals. In vitro studies confirmed that melatonin is not an inhibitor of MAO-B. These data demonstrate that melatonin does not have any significant protective effects against the long-term striatal DA and DOPAC depletion induced by MPTP in the C57BL/6 mouse.

Melatonin as a pharmacological agent against neuronal loss in experimental models of Huntington's disease, Alzheimer's disease and parkinsonism

This review summarizes the experimental findings related to the neuroprotective role of melatonin. In particular, it focuses on research directed at models of Huntington's disease, Alzheimer's disease and Parkinsonism. Melatonin has been shown to be highly effective in reducing oxidative damage in the central nervous system; this efficacy derives from its ability to directly scavenge a number of free radicals and to function as an indirect antioxidant. In particular, melatonin detoxifies the highly toxic hydroxyl radical as well as the peroxyl radical, peroxynitrite anion, nitric oxide, and singlet oxygen, all of which can damage macromolecules in brain cells. Additionally, melatonin stimulates a variety of antioxidative enzymes including superoxide dismutase, glutathione peroxidase and glutathione reductase. One additional advantage melatonin has in reducing oxidative damage in the central nervous system is the ease with which to crosses the blood-brain barrier. This combination of actions makes melatonin a highly effective pharmacological agent against free radical damage. The role of physiological levels of melatonin in forestalling oxidative damage in the brain is currently being tested.

EPC-K1, a hydroxyl radical scavenger, prevents 6-hydroxydopamine-induced dopamine depletion in the mouse striatum by up-regulation of catalase activity

We examined the effect of pretreatment with EPC-K1, a potent hydroxyl radical scavenger, on 6-hydroxydopamine (6-OHDA)-induced reduction of dopamine (DA) and its metabolites in the mouse striatum. EPC-K1 was mixed with diet (0.2%, wt/wt) for 1 or 2 weeks, and then 6-OHDA (60 microg in 2 microl of saline solution) was injected intracereberoventricularly. Mice continued to be fed EPC-K1-containing diet for another one week before they were sacrificed. The concentrations of DA and its metabolites in the striatum were measured by high performance liquid chromatography. 6-OHDA reduced the level of DA and its metabolites in the striatum. Pretreatment with EPC-K1 for 2 weeks, but not for 1 week, abrogated the neurotoxic effect of 6-OHDA on striatal concentrations of DA and its metabolites. Measurement of striatal concentrations of thiobarbituric acid reactive substances, glutathione, and malonaldehyde plus 4-hydroxynonenal, and the activities of superoxide dismutase and catalase in EPC-K1 treated mice showed an increase in catalase activity after 2 weeks of such treatment. No other changes in anti-oxidants levels were noted. Our results suggest that EPC-K1 counteracts the neurotoxicity of 6-OHDA by increasing catalase activities.

Melatonin increases striatal dopaminergic function in 6-OHDA-lesioned rats

The purpose of this study was to assess the in vivo effects of melatonin, as an antioxidant, on striatal dopaminergic function in rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the striatum. Compared with sham-operated controls and expressed as a ratio relative to the contralateral side, there was an increase in the lipid peroxidation product malondialdehyde (MDA, 142%) and a significant reduction in tyrosine hydroxylase (TH) enzyme activity (28%) and dopamine (DA, 32%) and its metabolite dihydroxyphenylacetic acid (DOPAC, 50%) 2 weeks after 6-OHDA injection. Melatonin treatment almost completely restored MDA levels to normal, suggesting the in vivo action of melatonin as an antioxidant. In parallel, partial, but statistically significant recovery of striatal dopaminergic function, including TH enzyme activity and DA levels, also occurred following melatonin treatment. Taken together with our previous reports showing behavioral and histochemical effects of melatonin on the nigrostriatal dopaminergic system, the present results strongly support the hypothesis that melatonin, as an antioxidant, may have beneficial effects on therapeutic approaches for the treatment of oxidative stress-induced neurodegenerative disease such as Parkinson's disease (PD).