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

Melatonin on sleep in Parkinson's disease: A randomized double blind placebo controlled trial

BACKGROUND

Sleep disturbances are one of the most common non-motor symptoms in Idiopathic Parkinson's Disease (IPD) patients. However, the effect of melatonin on sleep problems in Parkinson's disease patients is unclear.

AIMS AND OBJECTIVES

To study the effect of melatonin on sleep in IPD patients through subjective and objective assessment.

METHODS

Between August 2023 to February 2024, we conducted a randomized, double-blind, placebo-controlled trial on IPD patients. We randomized eligible subjects to melatonin (3 mg) (n = 43) or placebo (n = 43) for 8 weeks. The primary endpoint was sleep quality assessed through the Pittsburgh sleep quality index and daytime sleepiness using Epworth sleepiness scale. Secondary endpoints were polysomnographic sleep parameters, quality of life, motor and non-motor symptoms. Assessments were done at baseline and at the end of 8 weeks.

RESULTS

We screened 107 IPD patients and 86 patients were included in the study. Seventy three patients (melatonin, 35 and placebo, 38) completed the study. The mean change in Pittsburgh Sleep Quality Index (PSQI) score between the two groups was 1.87 (95 % CI: 1.5-2.1; p = 0.001) and Epworth Sleepiness Scale (ESS) score was 1.25 (95 % CI: 0.80-1.71; p = 0.001) favoring melatonin. The mean difference between the two groups for Non-Motor Symptoms Scale (NMSS) was 6.11 (95 % CI 5.27-6.92; p = 0.001), Parkinson's Disease Questionnaire (PDQ 39) 8.12 (95 % CI 6.97-9.50; p = 0.001) & Polysomnography (PSG) parameters [sleep latency 8.36 (95 % CI 4.38-12.34; p = 0.001) and total sleep time 14.51 (95 % CI 5.00-24.41; p = 0.005)] favoring melatonin. Side effects attributable to melatonin were minimal.

CONCLUSION

Melatonin is an effective and safe treatment option for sleep problems in PD patients, and beneficial effects on sleep quality are associated with improved non-motor symptoms and quality of life. We need to emphasize the fact that though we had statistically significant changes in our outcomes, it is not clear whether such changes would have real-life impact (meaningfulness) that would be relevant to licensing authorities or management as patients in our study are young, have short disease duration, have high use of anticholinergics and on modest levodopa equivalent dose. So, we are doubtful if this could be generalized to the typical PD population who are older, have longer disease duration and are on potentially sedating medications or not.

Melatonin alleviates arsenic-induced liver injury by regulating protein RKIP and enhancing antioxidant defencse mechanisms

Arsenic (As) is a highly toxic metal and one of the main factors in cancer development through oxidative stress and production of reactive oxygen species. Prior research has demonstrated melatonin's potential as a free radical scavenger. Raf kinase inhibitory protein (RKIP) is an important regulator of intracellular signaling pathways that has been linked to various types of cancer. The aim of this research was to explore the influence of melatonin's antioxidant properties on the expression of the protein RKIP and the antioxidant status of liver tissue in rats that were exposed to arsenic. Thirty two male Wistar rats were divided into four groups of eight, including control, melatonin-treated (20 mg/Kg of melatonin), sodium arsenite-treated (5.5 mg/Kg of sodium arsenite), and melatonin + sodium arsenite-treated groups (combination) for 4 weeks. The expression level of protein RKIP was measured by Western blot, and malondialdehyde (MDA) content of the liver as well as the activities of antioxidant enzymes were measured. The data analyzed using one-way ANOVA (significance level of p < 0.05) and GraphPad Prism (9) software. Sodium arsenite treatment led to a significant decrease in RKIP protein expression and antioxidant enzyme activity, and an increase in liver MDA levels (p < 0.001). Conversely, melatonin treatment in the combination group resulted in a significant increase in RKIP protein expression and antioxidant enzyme activity and a decrease in liver MDA levels (p < 0.05). These findings suggest that melatonin can attenuate oxidative damage caused by arsenic in liver cells by enhancing RKIP protein expression and antioxidant enzyme activity.

Role of Dietary Supplements in the Management of Parkinson's Disease

The use of food supplements or functional food has significantly increased in the past decades, especially to compensate both the modern lifestyle and the food shortages of the industrialized countries. Despite food supplements are habitually intended to correct nutritional deficiencies or to support specific physiological functions, they are often combined with common drug therapies to improve the patient's health and/or mitigate the symptoms of many chronic diseases such as cardiovascular diseases, cystic fibrosis, cancer, liver and gastrointestinal diseases. In recent years, increased attentions are given to the patient's diet, and the use of food supplements and functional food rich in vitamins and antioxidants plays a very important role in the treatment and prevention of neurodegenerative diseases such as Parkinson's disease (PD). Natural compounds, phytochemicals, vitamins, and minerals can prevent, delay, or alleviate the clinical symptoms of PD in contrast to some of the main physiopathological mechanisms involved in the development of the disease, like oxidative stress, free radical formation, and neuroinflammation. The purpose of this review is to collect scientific evidences which support the use of specific biomolecules and biogenic elements commonly found in food supplements or functional food to improve the clinical framework of patients with PD.

Melatonin protects against behavioral deficits, dopamine loss and oxidative stress in homocysteine model of Parkinson's disease

AIM

Hyperhomocysteinemia and homocysteine (Hcy) mediated dopaminergic neurotoxicity is a matter of concern in the pathophysiology of Parkinson's disease (PD). Our previous study established the involvement of oxidative stress in the substantia nigra (SN) of Hcy rat model of PD; however, the role of antioxidants, such as melatonin, was not tested in this model.

MAIN METHODS

Melatonin (10, 20 and 30mg/kg, i.p.) was administered to rats injected with Hcy in right SN (1.0μmol in 2μl saline) to investigate its potency in attenuating the behavioral abnormalities, dopamine depletion and oxidative stress prompted by Hcy.

KEY FINDINGS

Treatment of melatonin protected against nigral dopamine loss and replenished the striatal dopamine loss that resulted in amelioration of rotational behavioral bias in Hcy denervated animals. Melatonin administration significantly improved mitochondrial complex-I activity and protected the SN neurons from the toxic insults of oxidative stress induced by Hcy. Amelioration of oxidative stress by melatonin in Hcy-infused SN was bought by dose-dependently scavenging of hydroxyl radicals, restoration of glutathione level and elevation in the activity of antioxidant enzymes.

SIGNIFICANCE

The observations bring into light the significant neuroprotective potentials of melatonin in Hcy model of PD which is attributed to the attenuation of oxidative stress in SN.

Anti-Oxidants in Parkinson's Disease Therapy: A Critical Point of View

Parkinson’s disease (PD) is a degenerative neurological syndrome, which is characterized by the preferential death of dopaminergic (DAergic) neurons in the Substantia Nigra. The pathogenesis of this disorder remains poorly understood and PD is still incurable. Current drug treatments are aimed primarily for the treatment of symptoms to improve the quality of life. Therefore, there is a need to find out new therapeutic strategies that not only provide symptomatic relief but also halt or reverse the neuronal damage hampering PD progression. Oxidative stress has been identified as one of the major contributors for the nigral loss in both sporadic and genetic forms of PD. In this review we first evaluate the current literature that links oxidative stress and mitochondrial dysfunction to PD. We then consider the results obtained through the treatment of animal models or PD patients with molecules that prevent oxidative stress or reduce mitochondrial dysfunction.

Inhibition of endoplasmic reticulum stress-activated IRE1α-TRAF2-caspase-12 apoptotic pathway is involved in the neuroprotective effects of telmisartan in the rotenone rat model of Parkinson's disease

Telmisartan, one unique angiotensin II type 1 receptor blocker, has been attracting attention due to its putative peroxisome proliferator-activated receptor (PPAR)-γ or β/δ actions. Recently, telmisartan has been reported to exert neuroprotective effects in animal models of Parkinson's disease (PD). However, the underlying mechanisms have not been fully clarified. Recently, accumulating evidence has shown that endoplasmic reticulum (ER) stress plays a crucial role in rotenone-induced neuronal apoptosis. Additionally, studies have revealed that inositol-requiring enzyme/endonuclease 1α (IRE1α) is necessary and sufficient to trigger ER stress. In the present study, we aimed to determine whether ER stress-activated IRE1α-mediated apoptotic pathway is involved in the neuroprotection of telmisartan in the rotenone rats of PD and explore the possible involvement of PPAR-β/δ activation. The catalepsy tests were performed to test the catalepsy symptom. The dopamine content and α-synuclein expression were ascertained through high-performance liquid chromatography and immunohistochemistry, respectively. The expression of IRE1α, TNF receptor associated factor 2 (TRAF2), caspase-12 and PPAR-β/δ was detected by western blot. Neuronal apoptosis was assessed by TUNEL and immunohistochemistry. Our results show that telmisartan ameliorated the catalepsy symptom and attenuated dopamine depletion as well as α-synuclein accumulation. Moreover, telmisartan decreased ER stress-mediated neuronal apoptosis. Furthermore, telmisartan inhibited IRE1α-TRAF2-caspase-12 apoptotic signaling pathway. Additionally, telmisartan activated PPAR β/δ, implying that PPAR-β/δ activation properties of telmisartan are possibly or partially involved in the neuroprotective effects. In conclusion, our findings suggest that suppressing ER stress-activated IRE1α-TRAF2-caspase-12 apoptotic pathway is involved in the neuroprotective effects of telmisartan in the rotenone rats of PD.

Effect of melatonin on sleep disorders in a monkey model of Parkinson's disease

OBJECTIVES

To evaluate and compare the effects of melatonin and levodopa (L-dopa) on sleep disorders in a monkey model of Parkinson's disease.

MATERIALS AND METHODS

The daytime and nighttime sleep patterns of four macaques that were rendered parkinsonian by administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were recorded using polysomnography in four conditions: at baseline, during the parkinsonian condition; after administration of L-dopa, and after administration of a combination of melatonin with L-dopa.

RESULTS

It was confirmed that MPTP intoxication induces sleep disorders, with sleep episodes during daytime and sleep fragmentation at nighttime. L-dopa treatment significantly reduced the awake time during the night and tended to improve all other sleep parameters, albeit not significantly. In comparison to the parkinsonian condition, combined treatment with melatonin and L-dopa significantly increased total sleep time and sleep efficiency, and reduced the time spent awake during the night in all animals. A significant decrease in sleep latencies was also observed in three out of four animals. Compared with L-dopa alone, combined treatment with melatonin and L-dopa significantly improved all these sleep parameters in two animals. On the other hand, combined treatment had no effect on sleep architecture and daytime sleep.

CONCLUSION

These data demonstrated, for the first time, objective improvement on sleep parameters of melatonin treatment in MPTP-intoxicated monkeys, showing that melatonin treatment has a real therapeutic potential to treat sleep disturbances in people with Parkinson's disease.

Melatonin is protective against 6-hydroxydopamine-induced oxidative stress in a hemiparkinsonian rat model

Melatonin is known to reduce detrimental effects of free radicals by stimulating antioxidant enzymes; however, its role has not been studied in 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease (PD). Therefore, we aimed to elucidate the effects of melatonin on motor activity and oxidative stress parameters in 6-OHDA-induced rat model of PD. Three-month-old male Wistar rats were divided into 5 groups: vehicle (V), melatonin-treated (M), 6-OHDA-injected (6-OHDA), 6-OHDA-injected + melatonin-treated (6-OHDA-Mel), and melatonin-treated + 6-OHDA-injected (Mel-6-OHDA) group. Melatonin was administered intraperitoneally at a dose of 10 mg/kg/day for 30 days in M and Mel-6-OHDA groups, for 7 days in 6-OHDA-Mel group. Rats received a unilateral stereotaxic injection of 6-OHDA into the right medial forebrain bundle. The 6-OHDA-Mel group started receiving melatonin when experimental PD was created and the treatment was continued for 7 days. In the Mel-6-OHDA group, experimental PD was created on the 23rd day of melatonin treatment and continued for the remaining 7 days. Locomotor activity decreased in 6-OHDA group compared with that in vehicle group; however, melatonin treatment did not improve this impairment. 6-OHDA injection caused an obvious reduction in tyrosine-hydroxylase-positive dopaminergic neuron viability as determined by immunohistochemistry. Melatonin supplementation decreased dopaminergic neuron death in 6-OHDA-Mel and Mel-6-OHDA groups compared with that in 6-OHDA group. Biochemical analysis confirmed the beneficial effects of melatonin displaying higher superoxide dismutase, catalase, and glutathione peroxidase activities and lower lipid peroxidation in substantia nigra samples in comparison to non-treated 6-OHDA group. Starting melatonin treatment before creating experimental PD was more effective on observed changes.

Melatonin enhances L-DOPA therapeutic effects, helps to reduce its dose, and protects dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

L-3,4-dihydroxyphenylalanine (L-DOPA) reduces symptoms of Parkinson's disease (PD), but suffers from serious side effects on long-term use. Melatonin (10-30 mg/kg, 6 doses at 10 hr intervals) was investigated to potentiate L-DOPA therapeutic effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in mice. Striatal tyrosine hydroxylase (TH) immunoreactivity, TH, and phosphorylated ser 40 TH (p-TH) protein levels were assayed on 7th day. Nigral TH-positive neurons stereology was conducted on serial sections 2.8 mm from bregma rostrally to 3.74 mm caudally. MPTP caused 39% and 58% decrease, respectively, in striatal fibers and TH protein levels, but 2.5-fold increase in p-TH levels. About 35% TH neurons were lost between 360 and 600 μm from 940 μm of the entire nigra analyzed, but no neurons were lost between 250 μm rostrally and 220 μm caudally. When L-DOPA in small doses (5-8 mg/kg) failed to affect MPTP-induced akinesia or catalepsy, co-administration of melatonin with L-DOPA attenuated these behaviors. Melatonin administration significantly attenuated MPTP-induced loss in striatal TH fibers (82%), TH (62%) and p-TH protein (100%) levels, and nigral neurons (87-100%). Melatonin failed to attenuate MPTP-induced striatal dopamine depletion. L-DOPA administration (5 mg/kg, once 40 min prior to sacrifice, p.o.) in MPTP- and melatonin-treated mice caused significant increase in striatal dopamine (31%), as compared to L-DOPA and MPTP-treated mice. This was equivalent to 8 mg/kg L-DOPA administration in parkinsonian mouse. Therefore, prolonged, effective use of L-DOPA in PD with lesser side effects could be achieved by treating with 60% lower doses of L-DOPA along with melatonin.

Melatonin synergizes with low doses of L-DOPA to improve dendritic spine density in the mouse striatum in experimental Parkinsonism

The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), is the preferred drug for Parkinson's disease, but long-term treatment results in the drug-induced dyskinesias and other side effects. This study was undertaken to examine whether melatonin could potentiate low dose L-DOPA effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced experimental parkinsonism. Mice were treated with the parkinsonian neurotoxin, MPTP, and different doses of melatonin and low doses of L-DOPA. Behavior, striatal histology, and dopamine metabolism were evaluated on the 7th day. MPTP-induced striatal dopamine loss was not modified by melatonin administration (10-30 mg/kg; i.p. at 10-hr intervals, 6 times; or at 2-hr intervals, by day). However, low doses of L-DOPA (5 mg/kg, by oral gavage) administered alone or along with melatonin (10 mg/kg, i.p.) twice everyday for 2 days, 10 hr apart, after two doses of MPTP significantly attenuated striatal dopamine loss and provided improvements in both catalepsy and akinesia. Additionally, Golgi-impregnated striatal sections showed preservation of the medium spiny neurons, which have been damaged in MPTP-treated mouse. The results demonstrated that melatonin, but not L-DOPA, restored spine density and spine morphology of medium spiny neurons in the striatum and suggest that melatonin could be an ideal adjuvant to L-DOPA therapy in Parkinson's disease, and by the use of this neurohormone, it is possible to bring down the therapeutic doses of L-DOPA.

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.

Therapeutic potential of melatonin and its analogs in Parkinson's disease: focus on sleep and neuroprotection

Sleep disorders constitute major nonmotor features of Parkinson's disease (PD) that have a substantial effect on patients' quality of life and can be related to the progression of the neurodegenerative disease. They can also serve as preclinical markers for PD, as it is the case for rapid eye movement (REM)-associated sleep behavior disorder (RBD). Although the etiology of sleep disorders in PD remains undefined, the assessment of the components of the circadian system, including melatonin secretion, could give therapeutically valuable insight on their pathophysiopathology. Melatonin is a regulator of the sleep/wake cycle and also acts as an effective antioxidant and mitochondrial function protector. A reduction in the expression of melatonin MT(1) and MT(2) receptors has been documented in the substantia nigra of PD patients. The efficacy of melatonin for preventing neuronal cell death and for ameliorating PD symptoms has been demonstrated in animal models of PD employing neurotoxins. A small number of controlled trials indicate that melatonin is useful in treating disturbed sleep in PD, in particular RBD. Whether melatonin and the recently developed melatonergic agents (ramelteon, tasimelteon, agomelatine) have therapeutic potential in PD is also discussed.

Melatonin protects against neurobehavioral and mitochondrial deficits in a chronic mouse model of Parkinson's disease

Neuronal oxidative stress and mitochondrial dysfunction have been implicated in Parkinson's disease. Melatonin is a natural antioxidant and free radical scavenger that has been shown to effectively reduce cellular oxidative stress and protect mitochondrial functions in vitro. However, whether melatonin is capable of slowing down the neurodegenerative process in animal models of Parkinson's disease remains controversial. In this research, we examined long-term melatonin treatment on striatal mitochondrial and dopaminergic functions and on animal locomotor performance in a chronic mouse model of Parkinson's disease originally established in our laboratory by gradually treating C57BL/6 mice with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (15 mg/kg, s.c.) and probenecid (250 mg/kg, i.p.) over five weeks. We report here that when the chronic Parkinsonian mice were pre-treated and continuously treated with melatonin (5mg/kg/day, i.p.) for 18 weeks, the defects of mitochondrial respiration, ATP and antioxidant enzyme levels detected in the striatum of chronic Parkinson's mice were fully preempted. Meanwhile, the striatal dopaminergic and locomotor deficits seen in the chronic Parkinson's mice were partially and significantly forestalled. These results imply that long-term melatonin is not only mitochondrial protective but also moderately neuronal protective in the chronic Parkinson's mice. Melatonin may potentially be effective for slowing down the progression of idiopathic Parkinson's disease and for reducing oxidative stress and respiratory chain inhibition in other mitochondrial disorders.

Ebselen effects on MPTP-induced neurotoxicity

We evaluated the effect of ebselen on human SH-SY5Y dopaminergic neuronal cells and determined whether ebselen, a glutathione peroxidase-mimetic, protected against MPTP-induced dopamine depletion in mice. Ebselen (10-100 microM) inhibited the proliferation of SH-SY5Y cells dose-dependently. Ebselen did not induce any behavioral changes and did not block MPTP-induced tremor and akinesia. Ebselen had no effect on the monoamine oxidase activity and did not protect against MPTP-induced dopamine depletion in striatum.

Circulating Melatonin Levels: Possible Link Between Parkinson’s Disease and Cancer Risk?

Lower rates of cancer mortality/incidence in patients with Parkinson's disease (PD) have given rise to speculations about risk or preventative factors common to both diseases, including life-style factors (such as smoking) and genetic susceptibility. Melatonin, a hormone known for its sleep regulatory effects, may play an important role in carcinogenesis as suggested by substantial laboratory and less direct epidemiologic evidence. Particularly, a reduction in melatonin, such as experienced by persons who are exposed to light at night, appears to increase cancer risk. Variations in melatonin levels have been linked to PD in several different ways. Some studies show higher morning melatonin levels in PD patients than in healthy controls. One could speculate that the sleep disorders that affect almost two thirds of those suffering from PD and can precede PD motor symptoms by several years may be associated with variations in melatonin levels. Moreover, in animal models, interventions that increase the bioavailability of melatonin appears to increase the severity of parkinsonian symptoms, whereas reduction in melatonin by pinealectomy or exposure to bright light can enhance recovery from parkinsonisms symptoms. Finally, preliminary epidemiological evidence suggests that longer years of working night shifts is associated with a reduced risk of PD among participants of the Nurses' Health Study (NHS), whereas longer hours of sleep appear to increase their risk. In sum, while lower melatonin concentrations may predict a higher cancer risk, there is also some evidence that they may be associated with a lower risk of PD. We therefore hypothesize that elevated circulating melatonin levels in PD patients may contribute to their lower cancer rates.

Screening of novel pentacyclo-undecylamines for neuroprotective activity

A novel series of pentacyclo-undecylamines with 8-benzylamino-8,11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane (NGP1-01) as the lead compound was synthesised and screened for neuroprotective activity in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) parkinsonian mouse model. We hypothesise that these compounds may attenuate excitotoxic neuronal cell death mediated through the NMDA receptor (similar to memantine), and through calcium channel block. The pentacyclo-undecylamines (300 mg/kg) were administered to C57BL/6 mice 30 min before intraperitoneal (i.p.) MPTP administration (35 mg/kg). Striatal dopamine, 3,4-hydroxyphenylacetic acid (DOPAC), and homovanillic acid levels were analysed 10 days later by means of HPLC with electrochemical detection. Increased levels of DOPAC and homovanillic acid were observed when some of the test compounds were administered together with MPTP (compared to animals receiving only MPTP). One compound in the series, 8-phenylethylamino-8,11-oxapentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane, attenuated MPTP-induced striatal dopamine depletion when compared to animals treated with MPTP only (p<0.05).

Rescue of dying neurons by (R)-deprenyl in the MPTP-mouse model of Parkinson's disease does not include restoration of neostriatal dopamine

Chronic (8- to 10-week) administration of the selective, potent, and irreversible monoamine oxidase B inhibitor (R)-deprenyl has been shown to increase the tyrosine hydroxylase immunoreactivity in the substantia nigra of mice that had been treated three days earlier with a neurotoxic dose of the parkinsonian-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). This reported rescuing of lesioned nigrostriatal cell bodies by (R)-deprenyl prompted us to investigate if this (R)-deprenyl treatment also could restore neostriatal dopamine levels that are depleted by MPTP. The results of these experiments show that long term (8 or 10 weeks) treatment with (R)-deprenyl beginning three days post MPTP administration did not result in restoration of depleted neostriatal dopamine levels in C57BL/6 mice. We conclude that, although (R)-deprenyl may rescue MPTP-injured nigrostriatal neurons, it does not lead to functional recovery of these neurons as measured by the restoration of neostriatal dopamine levels.

Selective inhibition of MAO-B through chronic low-dose (R)-deprenyl treatment in C57BL/6 mice has no effect on basal neostriatal dopamine levels

C. Thiffault, L. Lamarre-Théroux, R. Quirion, and J. Poirier (1997, Mol. Brain Res. 44: 238-244) recently reported that chronic treatment of young (12 week old) C57BL/6 mice with (R)-deprenyl, a mechanism-based inactivator of monoamine oxidase B (MAO-B), leads to a more than fourfold increase in neostriatal dopamine levels. Such an effect could complicate the interpretation of results obtained from mechanistic studies designed to evaluate the putative neuroprotective effects of (R)-deprenyl in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mice. In contrast to the results of Thiffault et al., we have found that neostriatal dopamine levels in mature (32 week old) C57BL/6 mice were unaltered by chronic (R)-deprenyl treatment even though brain monoamine oxidase B activity was reduced by more than 80%. Neostriatal dopamine levels also were unaltered in both young and mature mice when the (R)-deprenyl treatment period was doubled compared to that reported by Thiffault et al. Consequently, studies on the putative neuroprotective properties of (R)-deprenyl in MPTP-lesioned mice are unlikely to be complicated by the possibility that inhibition of MAO-B alone will lead to an increase in neostriatal dopamine levels.