MPTP produces differential oxidative stress and antioxidative responses in the nigrostriatal and mesolimbic dopaminergic pathways

Extract from Nasco pomace loaded in nutriosomes exerts anti-inflammatory effects in the MPTP mouse model of Parkinson's disease

Neuroinflammation has recently emerged as a key event in Parkinson's disease (PD) pathophysiology and as a potential target for disease-modifying therapies. Plant-derived extracts, rich in bioactive phytochemicals with antioxidant properties, have shown potential in this regard. Yet their clinical utility is hampered by poor systemic availability and rapid metabolism. Recently, our group demonstrated that intragastric delivery of Nasco pomace extract via nutriosomes (NN), a novel nanoliposome formulation, contrasts the degeneration of nigrostriatal dopaminergic neurons in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In the present study, we investigated the impact of intragastric NN treatment on the reactivity of glial cells in the substantia nigra pars compacta (SNc) and caudate-putamen (CPu) of MPTP-treated mice. To this scope, in mice exposed to MPTP (20 mg/kg/day, × 4 days), we conducted immunohistochemistry analyses of glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA1) to assess the responsiveness of astrocytes and microglial cells, respectively. Additionally, we studied the co-localization of the pro-inflammatory interleukin (IL)-1β and tumor necrosis factor (TNF)-α with IBA1 to obtain insights into microglial phenotype. Immunohistochemical results showed that NN administration significantly mitigated astrogliosis and microgliosis in the CPu and SNc of mice receiving subacute MPTP treatment, with region-specific variations in anti-inflammatory efficacy. Remarkably, the CPu showed a heightened response to NN treatment, including a pronounced decrease in microglial IL-1β and TNF-α production. Altogether, these findings underscore the anti-inflammatory effects of NN treatment and provide a potential mechanism underlying the neuroprotective effects previously observed in a subacute MPTP mouse model of PD.

Iron accumulation in the ventral tegmental area in Parkinson's disease

Introduction

The ventral tegmental area (VTA) is less affected compared to substantia nigra pars compacta (SNc) in Parkinson's disease (PD). This study aimed to quantitatively evaluate iron content in the VTA across different stages of PD in order to help explain the selective loss of dopamine neurons in PD.

Methods

Quantitative susceptibility mapping (QSM) data were obtained from 101 PD patients, 35 idiopathic rapid eye movement sleep behavior disorder (RBD) patients, and 62 healthy controls (HCs). The mean QSM values in the VTA and SNc were calculated and compared among the groups.

Results

Both RBD and PD patients had increased iron values in the bilateral SNc compared with HCs. RBD and PD patients in the Hoehn-Yahr (H & Y) stage 1 did not show elevated iron values in the VTA, while PD patients with more than 1.5 H & Y staging had increased iron values in bilateral VTA compared to HCs.

Discussion

This study shows that there is no increased iron accumulation in the VTA during the prodromal and early clinical stages of PD, but iron deposition increases significantly as the disease becomes more severe.

Neuroprotective effect of NXP031 in the MPTP-induced Parkinson's disease model

Parkinson's disease (PD) is a neurodegenerative disease characterized by the progressive degeneration of dopaminergic neurons in the substantia nigra (SN). Oxidative stress has been identified as one of the major causes of nigrostriatal degeneration in PD. Ascorbic acid plays a role as an efficient antioxidant to protect cells from free radical damage, but it is easily oxidized and loses its antioxidant activity. To overcome this limitation, we have recently developed NXP031, a single-stranded DNA aptamer that binds to ascorbic acid with excellent specificity, reducing its oxidation and increasing its efficacy. This study investigated the neuroprotective effects of NXP031 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model. Acute degeneration of nigral dopaminergic neurons was induced by four consecutive treatments of MPTP (20 mg/kg) in male C57BL/6 J mice. NXP031 (Vitamin C/Aptamin C 200 mg/4 mg/kg) was administered intraperitoneally for 5 days following MPTP. We observed that the administration of NXP031 ameliorated MPTP-induced loss of dopaminergic neurons in the SN and exhibited improvement of MPTP-mediated motor impairment. We further found that NXP031 increased plasma ascorbic acid levels and inhibited microglia activation-induced neuroinflammation in the SN, which might contribute to the protective effects of NXP031 on nigrostriatal degeneration. Our findings suggest that NXP031 could be a potential therapeutic intervention in PD.

Acrolein-mediated alpha-synuclein pathology involvement in the early post-injury pathogenesis of mild blast-induced Parkinsonian neurodegeneration

Survivors of blast-induced traumatic brain injury (bTBI) have increased susceptibility to Parkinson's disease (PD), characterized by α-synuclein aggregation and the progressive degeneration of nigrostriatal dopaminergic neurons. Using an established bTBI rat model, we evaluated the changes of α-synuclein and tyrosine hydroxylase (TH), known hallmarks of PD, and acrolein, a reactive aldehyde and marker of oxidative stress, with the aim of revealing key pathways leading to PD post-bTBI. Indicated in both animal models of PD and TBI, acrolein is likely a point of pathogenic convergence. Here we show that after a single mild bTBI, acrolein is elevated up to a week, systemically in urine, and in whole brain tissue, specifically the substantia nigra and striatum. Acrolein elevation is accompanied by heightened α-synuclein oligomerization, dopaminergic dysregulation, and acrolein/α-synuclein interaction in the same brain regions. We further show that acrolein can directly modify and oligomerize α-synuclein in vitro. Taken together, our data suggests acrolein likely plays an important role in inducing PD pathology following bTBI by encouraging α-synuclein aggregation. These results are expected to advance our understanding of the long-term post-bTBI pathological changes leading to the development of PD, and suggest intervention targets to curtail such pathology.

Metabolism of Dopamine in Nucleus Accumbens Astrocytes Is Preserved in Aged Mice Exposed to MPTP

Parkinson disease (PD) is prevalent in elderly individuals and is characterized by selective degeneration of nigrostriatal dopamine (NSDA) neurons. Interestingly, not all dopamine (DA) neurons are affected equally by PD and aging, particularly mesolimbic (ML) DA neurons. Here, effects of aging were examined on presynaptic DA synthesis, reuptake, metabolism and neurotoxicant susceptibility of NSDA and mesolimbic dopamine (MLDA) neurons and astrocyte DA metabolism. There were no differences in phenotypic markers of DA synthesis, reuptake or metabolism in NSDA or MLDA neurons in aged mice, but MLDA neurons displayed lower DA stores. Astrocyte metabolism of DA to 3-methoxytyramine (3-MT) in the striatum was decreased in aged mice, but was maintained in the nucleus accumbens. Despite diminished DA vesicular storage capacity in MLDA neurons, susceptibility to acute neurotoxicant exposure was similar in young and aged mice. These results reveal an age- and neurotoxicant-induced impairment of DA metabolic activity in astrocytes surrounding susceptible NSDA neurons as opposed to maintenance of DA metabolism in astrocytes surrounding resistant MLDA neurons, and suggest a possible therapeutic target for PD.

Neurotransmission systems in Parkinson’s disease

Parkinson’s disease (PD) is histologically characterized by the accumulation of α-synuclein particles, known as Lewy bodies. The second most common neurodegenerative disorder, PD is widely known because of the typical motor manifestations of active tremor, rigidity, and postural instability, while several prodromal non-motor symptoms including REM sleep behavior disorders, depression, autonomic disturbances, and cognitive decline are being more extensively recognized. Motor symptoms most commonly arise from synucleinopathy of nigrostriatal pathway. Glutamatergic, γ-aminobutyric acid (GABA)ergic, cholinergic, serotoninergic, and endocannabinoid neurotransmission systems are not spared from the global cerebral neurodegenerative assault. Wide intrabasal and extrabasal of the basal ganglia provide enough justification to evaluate network circuits disturbance of these neurotransmission systems in PD. In this comprehensive review, English literature in PubMed, Science direct, EMBASE, and Web of Science databases were perused. Characteristics of dopaminergic and non-dopaminergic systems, disturbance of these neurotransmitter systems in the pathophysiology of PD, and their treatment applications are discussed.

URB597 and the Cannabinoid WIN55,212-2 Reduce Behavioral and Neurochemical Deficits Induced by MPTP in Mice: Possible Role of Redox Modulation and NMDA Receptors

Several physiological events in the brain are regulated by the endocannabinoid system (ECS). While synthetic cannabinoid receptor (CBr) agonists such as WIN55,212-2 act directly on CBr, agents like URB597, a fatty acid amide hydrolase (FAAH) inhibitor, induce a more "physiological" activation of CBr by increasing the endogenous levels of the endocannabinoid anandamide (AEA). Herein, we compared the pre- and post-treatment efficacy of URB597 and WIN55,212-2 on different endpoints evaluated in the toxic model produced by the mitochondrial toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice. MPTP (40 mg/kg, s.c., single injection) decreased locomotor activity, depleted the striatal and nigral levels of dopamine (DA), augmented the levels of lipid peroxidation and protein carbonylation in both regions, decreased the striatal protein levels of tyrosine hydroxylase, and increased the striatal protein content of the subunit 1 (NR1) of the N-methyl-D-aspartate receptor (NMDAr). Both URB597 (0.3 mg/kg, i.p., once a day) and WIN55,212-2 (10 μg/kg, i.p., twice a day), administered for five consecutive days, either before or after the MPTP injection, prevented the alterations elicited by MPTP and downregulated NMDAr. Our results support a modulatory role of the ECS on the toxic profile exerted by MPTP in mice via the stimulation of antioxidant activity and the induction of NMDAr downregulation and hypofunction, and favor the stimulation of CBr as an effective experimental therapeutic strategy.

Low Levels of Prohibitin in Substantia Nigra Makes Dopaminergic Neurons Vulnerable in Parkinson's Disease

Since substantia nigra (SN) and ventral tegmental area (VTA) dopaminergic neurons are, respectively, susceptible or largely unaffected in Parkinson's disease (PD), we searched for protein(s) that regulates this differential sensitivity. Differentially, expressed proteins in SN and VTA were investigated employing two-directional gel electrophoresis- matrix-assisted laser desorption ionization time of flight (MALDI-TOF-TOF) analyses. Prohibitin, which is involved in mitochondrial integrity, was validated using immunoblot, qRT-PCR, and immunohistochemistry in normal mice as well as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-model, PD postmortem human brains, and PD cybrids. In prohibitin over-expression, differentiated SH-SY5Y neurons were investigated for their susceptibility to PD neurotoxin, 1-methyl-4-phenyl-pyridnium (MPP⁺). Prohibitin, Hsc73, and Cu-Zn superoxide dismutase (Cu-Zn SOD) were highly expressed in VTA, whereas heat shock protein A8 (HSPA8) and 14-3-3ζ/δ were 2-fold more in SN. Prohibitin level was transiently increased in SN but unaltered in VTA on the third day of MPTP-induced mice, whereas in PD human brains, prohibitin was depleted in both these regions. Parallel to mouse SN, an enhanced prohibitin expression was found in human PD cybrids. In MPP⁺-induced cellular model of PD, reduction in prohibitin level was found to be associated with a loss in its binding with Ndufs3, a mitochondrial complex I protein partner. Prohibitin over-expression resisted MPP⁺-induced neuronal death by restoring mitochondrial membrane potential, preventing reactive oxygen species generation and cytochrome c release into cytosol. These protective phenomena exerted by prohibitin over-expression altogether hinder caspase 3 activation induced by MPP⁺. These results imply that prohibitin is an important negotiator protein that regulates dopaminergic cell death in SN and their protection in VTA in PD.

Loss of dopaminergic neurons occurs in the ventral tegmental area and hypothalamus of rats following chronic stress: Possible pathogenetic loci for depression involved in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by loss of dopaminergic (DA) neurons in the nigrostriatal and mesolimbic pathways including ventral tegmental area (VTA). Although several factors for the neuronal loss have been suggested, most of the PD cases are sporadic and idiopathic. In our previous study, we demonstrated the first evidence that solely chronic restraint stress (RS) induced the DA neuronal loss in the substantia nigra (SN). In this study, we further investigated whether chronic stress could affect other major DA systems, VTA and tuberoinfundibular system (TIDA), by using immunohistochemical and in situ hybridization techniques. The present study showed that, in the VTA, tyrosine hydroxylase (TH) immunoreactive neurons decreased by 9.8% at 2nd week, 19.2% at 4th week, 39.5% at 8th week, and 40.6% at 16th week during chronic RS as compared to control. Similarly, in the TIDA, the TH neurons decreased by 10.9% at 2nd week, 38.2% at 4th week, 56.3% at 8th week, and 57.1% at 16th week. The in situ hybridization results consistently demonstrated decreases in Th mRNA expressing cells in the VTA and TIDA in a comparable time dependent manner. Thus, exposure to chronic stress may simultaneously induce multiple neuronal loss of DA systems.

Chronic restraint stress triggers dopaminergic and noradrenergic neurodegeneration: Possible role of chronic stress in the onset of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and, to a lesser extent, in the noradrenergic neurons of the locus coeruleus (LC). Most cases of PD are idiopathic and sporadic and are believed to be the result of both environmental and genetic factors. Here, to the best of our knowledge, we report the first evidence that chronic restraint stress (8h/day, 5days/week) substantially reduces nigral DA and LC noradrenergic neuronal cell numbers in rats. Loss of DA neurons in the SNpc was evident after 2weeks of stress and progressed in a time-dependent manner, reaching up to 61% at 16weeks. This reduction was accompanied by robust microglial activation and oxidative stress and was marked by nitrotyrosine in the SNpc and LC of the midbrain. These results indicate that chronic stress triggers DA and noradrenergic neurodegeneration by increasing oxidative stress, and that activated microglia in the substantia nigra and LC may play an important role in modulating the neurotoxic effects of oxidative stress. Taken together, these data suggest that exposure to chronic stress triggers DA and noradrenergic neurodegeneration, which is a cause of PD.

Antioxidant Formulae, Shengmai San, and LingGuiZhuGanTang, Prevent MPTP Induced Brain Dysfunction and Oxidative Damage in Mice

The present study was designed to evaluate the preventive effect of antioxidative traditional oriental medicine formulae, Shengmai San (SMS) and LingGuiZhuGanTang (LGZGT), against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (i.p 30 mg·kg⁻¹ for 5 consecutive days) induced neurotoxicity. In in vitro antioxidant assays measured with Trolox and butyl hydroxyl toluene as reference antioxidant revealed that SMS has higher scavenging potential against hydroxyl radical than superoxide anion radical, but LGZGT was the reverse. The neuroprotective effect of SMS and LGZGT against MPTP was evaluated in mice by behavioral, biochemical, and immunohistochemical studies. In the behavioral study, both SMS and LGZGT significantly reversed the locomotive impairment induced by MPTP. Simultaneously, both formulae significantly prevented the MPTP induced dopaminergic neuron loss assessed by tyrosine hydroxylase in the midbrain. Both SMS and LGZGT significantly attenuated the elevated lipid peroxidation and protein carbonyls levels by MPTP. The DNA damage induced by MPTP was also prevented by both formulae. Although a little difference in the protective functions was observed between the two formulae, such as in DNA damage and behavioral studies, the results indicate that both SMS and LGZGT with antioxidant property act as a good candidate applicable for the antioxidant based complementary therapies of neurodegenerative diseases.

Neuroprotective effect of Valeriana wallichii rhizome extract against the neurotoxin MPTP in C57BL/6 mice

Oxidative stress and inflammation are some of the contributing factors for dopaminergic neurodegeneration in Parkinson's disease (PD). Though Valeriana wallichii D.C. is known for its nervine activities its effect against PD is yet to be studied. This is the first report on the antioxidant and anti-inflammatory effect of V. wallichii rhizome extract (VWE) in MPTP induced PD mice. GC-MS analysis of VWE indicated the presence of phytoconstituents like isovaleric acid and acacetin. PD induced mice were treated orally with three different doses (50, 100 and 200mg/kg body weight (BW)) of VWE for 14 days and their behavioural changes were studied on days 0, 8, 13 and 21. The levels of striatal dopamine, mid brain tyrosine hydroxylase positive (TH(+)) cell count, TH protein expression, reactive oxygen species (ROS), lipid peroxidation (LPO), antioxidants and inflammatory cytokines were analysed. Mid brain glial fibrillary acidic protein (GFAP) expression was assessed by immunohistochemistry and western blotting. Also mid brain histopathological analysis was performed. VWE treatment significantly recuperated the altered behavioural test scores, striatal dopamine levels, mid brain TH(+) cell count and TH protein levels, increased GFAP expression and the histopathological changes observed in PD mice. Similarly, diminished levels of antioxidants, elevated levels of ROS, LPO and inflammatory cytokines were also significantly ameliorated following VWE treatment. The effective dose of VWE was found to be 200mg/kg BW. Conclusively, V. wallichii rhizome extract has the potential to mitigate oxidative stress and inflammatory damage in PD.

Gender-specific brain regional variation of neurons, endogenous estrogen, neuroinflammation and glial cells during rotenone-induced mouse model of Parkinson's disease

Rotenone (RT) produces reactive oxygen species (ROS) by inhibiting the mitochondrial electron transport chain; causing dopaminergic (DA) cell death in the substantia nigra (SN) and simulates other models of induced Parkinson's disease (PD). There is a sincere dearth of knowledge regarding the status of glial cells, neuroprotective estrogen and the status of neuroinflammatory TNF-α in the different brain regions in either sex during healthy, as well as during PD conditions. In the present study of RT-induced mouse model of PD, we have selected the frontal cortex (FC), hippocampus (HC) and SN from either sex of Swiss albino mice as these are the major regions involved during PD pathogenesis. During non pathogenic conditions, the ROS-scavenging enzyme activity varied among the brain regions and also in between genders. The number of DOPA decarboxylase-positive cells, astrocytes and microglia was similar in the respective regions of the brain in both the sexes. The level of proinflammatory cytokine TNF-α was same in the respective FC and HC in either sex except that of SN. The expression level of estrogen and its receptors varied among the three brain regions. During RT treatment, ROS-scavenging enzyme activities increased, DOPA decarboxylase-positive neurons and fibers in DA as well as in norepinephrinergic (NE) systems become degenerated, number of astrocytes decreased and microglial cells increased in those specific brain regions in either of the sexes except in the SN region of males where astrocyte number remained unaltered and microglial cell percentage decreased. TNF-α increased in the FC and SN but remained unaltered in the HC of both sexes. Estradiol level decreased in the HC and SN but the level unevenly varied in the FC. Similarly, the estrogen bound and nuclear-cytosolic receptor α and β also varied differentially among the brain regions of the two sexes. Therefore our present study depicts that there exists a clear variation of neuronal and astroglial cell population, estrogen and its receptor levels in different brain regions of both the sexes during control and RT-treated pathogenic condition and these variations have major implication in PD pathogenesis and progression.

The herbicide glyphosate causes behavioral changes and alterations in dopaminergic markers in male Sprague-Dawley rat

Glyphosate (Glyph) is the active ingredient of several herbicide formulations. Reports of Glyph exposure in humans and animal models suggest that it may be neurotoxic. To evaluate the effects of Glyph on the nervous system, male Sprague-Dawley rats were given six intraperitoneal injections of 50, 100, or 150 mg Glyph/kg BW over 2 weeks (three injections/week). We assessed dopaminergic markers and their association with locomotor activity. Repeated exposure to Glyph caused hypoactivity immediately after each injection, and it was also apparent 2 days after the last injection in rats exposed to the highest dose. Glyph did not decrease monoamines, tyrosine hydroxylase (TH), or mesencephalic TH+ cells when measured 2 or 16 days after the last Glyph injection. In contrast, Glyph decreased specific binding to D1 dopamine (DA) receptors in the nucleus accumbens (NAcc) when measured 2 days after the last Glyph injection. Microdialysis experiments showed that a systemic injection of 150 mg Glyph/kg BW decreased basal extracellular DA levels and high-potassium-induced DA release in striatum. Glyph did not affect the extracellular concentrations of 3,4-dihydroxyphenylacetic acid or homovanillic acid. These results indicate that repeated Glyph exposure results in hypoactivity accompanied by decreases in specific binding to D1-DA receptors in the NAcc, and that acute exposure to Glyph has evident effects on striatal DA levels. Additional experiments are necessary in order to unveil the specific targets of Glyph on dopaminergic system, and whether Glyph could be affecting other neurotransmitter systems involved in motor control.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.

Neuroprotective effects of puerarin on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induced Parkinson's disease model in mice

Puerarin, an active component of Pueraria montana var. lobata (Willd.) Sanjappa & Pradeep is well-known for its anti-oxidative and neuroprotective activities. Although anti-Parkinson's disease activity of puerarin was reported in both of in vivo and in vitro model, detailed mechanisms are not clarified. In this study, we addressed that puerarin attenuated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced behavioral deficits, dopaminergic neuronal degeneration and dopamine depletion. Puerarin administration enhanced glutathione (GSH) activity, glial cell line-derived neurotrophic factor (GDNF) expression and PI3K/Akt pathway activation, which might ameliorate MPTP injection-induced progressive elevation of reactive oxygen species (ROS) formation in mice. In addition to the effect on ROS, puerarin ameliorated MPTP-reduced lysosome-associated membrane protein type 2A (Lamp 2A) expression. Taken together, our data demonstrate that puerarin attenuates MPTP-induced dopaminergic neuronal degeneration via modulating GDNF expression, PI3K/Akt pathway and GSH activation, which subsequently ameliorate MPTP-induced ROS formation and decrease of Lamp 2A expression.

H2O2: a dynamic neuromodulator

Increasing evidence implicates hydrogen peroxide (H(2)O(2)) as an intracellular and intercellular signaling molecule that can influence processes from embryonic development to cell death. Most research has focused on relatively slow signaling, on the order of minutes to days, via second messenger cascades. However, H(2)O(2) can also mediate subsecond signaling via ion channel activation. This rapid signaling has been examined most thoroughly in the nigrostriatal dopamine (DA) pathway, which plays a key role in facilitating movement mediated by the basal ganglia. In DA neurons of the substantia nigra, endogenously generated H(2)O(2) activates ATP-sensitive K(+) (K-ATP) channels that inhibit DA neuron firing. In the striatum, H(2)O(2) generated downstream from glutamatergic AMPA receptor activation in medium spiny neurons acts as a diffusible messenger that inhibits axonal DA release, also via K-ATP channels. The source of dynamically generated H(2)O(2) is mitochondrial respiration; thus, H(2)O(2) provides a novel link between activity and metabolism via K-ATP channels. Additional targets of H(2)O(2) include transient receptor potential (TRP) channels. In contrast to the inhibitory effect of H(2)O(2) acting via K-ATP channels, TRP channel activation is excitatory. This review describes emerging roles of H(2)O(2) as a signaling agent in the nigrostriatal pathway and basal ganglia neurons.

Increased iron levels correlate with the selective nigral dopaminergic neuron degeneration in Parkinson's disease

The staging of Lewy-related pathology in sporadic Parkinson's disease (PD) reveals that many brain nuclei are affected in PD during different stages, except the ventral tegmental area (VTA), which is close related to the substantia nigra (SN) and enriched in dopamine (DA) neurons. Why DA neurons are selectively degenerated in the SN of PD is far from known. In the present study, we observed that the number of tyrosine hydroxylase immunoreactive neurons decreased and iron-staining positive cells increased in the SN, but not in the VTA, in the chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated PD mice. Increased expression of divalent metal transporter 1 and decreased expression of ferroportin 1 might associate with this increased nigral iron levels. Lipofuscin granular aggregations and upregulation of alpha-synuclein (α-synuclein) were also observed only in the SN. These results suggest that increased iron levels associate with the selective degeneration of DA neurons in the SN. The intracellular regulation mechanisms for the iron transporters may be different in the SN and VTA under the same conditions. Moreover, the lipofuscin granular aggregations and upregulation of α-synuclein were also involved in the selective degeneration of dopaminergic neurons in the SN.

Selective neuronal vulnerability to oxidative stress in the brain

Oxidative stress (OS), caused by the imbalance between the generation and detoxification of reactive oxygen and nitrogen species (ROS/RNS), plays an important role in brain aging, neurodegenerative diseases, and other related adverse conditions, such as ischemia. While ROS/RNS serve as signaling molecules at physiological levels, an excessive amount of these molecules leads to oxidative modification and, therefore, dysfunction of proteins, nucleic acids, and lipids. The response of neurons to this pervasive stress, however, is not uniform in the brain. While many brain neurons can cope with a rise in OS, there are select populations of neurons in the brain that are vulnerable. Because of their selective vulnerability, these neurons are usually the first to exhibit functional decline and cell death during normal aging, or in age-associated neurodegenerative diseases, such as Alzheimer's disease. Understanding the molecular and cellular mechanisms of selective neuronal vulnerability (SNV) to OS is important in the development of future intervention approaches to protect such vulnerable neurons from the stresses of the aging process and the pathological states that lead to neurodegeneration. In this review, the currently known molecular and cellular factors that contribute to SNV to OS are summarized. Included among the major underlying factors are high intrinsic OS, high demand for ROS/RNS-based signaling, low ATP production, mitochondrial dysfunction, and high inflammatory response in vulnerable neurons. The contribution to the selective vulnerability of neurons to OS by other intrinsic or extrinsic factors, such as deficient DNA damage repair, low calcium-buffering capacity, and glutamate excitotoxicity, are also discussed.

Ethanol and acetaldehyde action on central dopamine systems: mechanisms, modulation, and relationship to stress

There has been a great deal of activity in recent years in the study of the direct effects of ethanol on the dopamine reward system originating in the ventral tegmental area (VTA). In addition, recent evidence suggests that acetaldehyde formed from ethanol in the brain or periphery may be a crucial factor in the central effects of ethanol. This critical review examines the actions of ethanol and acetaldehyde on neurons of the VTA and the possible interactions with stress, with a focus on electrophysiological studies in vivo and in vitro. Ethanol has specific effects on dopamine neurons and there is recent evidence that some of the in vivo and in vitro effects of ethanol are mediated by acetaldehyde. Stress has some analogous actions on neuronal activity in the VTA, and the interactions between the effects of stress and alcohol on VTA neurons may be a factor in ethanol-seeking behavior. Taken together, the evidence suggests that stress may contribute to the activating effects of ethanol on dopamine VTA neurons, that at least some actions of ethanol on dopamine VTA neurons are mediated by acetaldehyde, and that the interaction between stress and alcohol could play a role in susceptibility to alcoholism. The link between acetaldehyde and ethanol actions on brain reward pathways may provide a new avenue for the development of agents to reduce alcohol craving.

Crucial role of acetaldehyde in alcohol activation of the mesolimbic dopamine system

Ethyl alcohol (EtOH), the main psychoactive ingredient of alcoholic drinks, is widely considered responsible for alcohol abuse and alcoholism through its positive motivational properties, which depend, at least partially, on the activation of the mesolimbic dopaminergic system. On the other hand, acetaldehyde (ACD), EtOH's first metabolite, has been classically considered aversive and useful in the pharmacologic therapy of alcoholics. Here we show that EtOH-derived ACD is necessary for EtOH-induced place preference, a preclinical test with high predictive validity for reward liability. We also found that ACD is essential for EtOH-increased microdialysate dopamine (DA) levels in the nucleus accumbens (NAcc), and that this effect is mimicked by ACD administration to the intraventral tegmental area (VTA). Furthermore, in vitro, ACD enhances VTA DA neuronal firing. Coherently, EtOH-stimulating properties on DA neurons are prevented by pharmacologic blockade of local catalase: the main metabolic step for biotransformation of EtOH into ACD in the central nervous system. These results provide in vivo and in vitro evidence for a key role of ACD in EtOH motivational properties and its activation of the mesolimbic DA system. Additionally, these observations suggest that ACD, by increasing VTA DA neuronal activity, would oppose its well-known peripherally originating aversive properties. These findings could help in devising new effective pharmacologic therapies in alcoholism.

Glycyrrhizin Attenuates MPTP Neurotoxicity in Mouse and MPP-Induced Cell Death in PC12 Cells

The present study examined the inhibitory effect of licorice compounds glycyrrhizin and a metabolite 18beta-glycyrrhetinic acid on the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the mouse and on the 1-methyl-4-phenylpyridinium (MPP(+))-induced cell death in differentiated PC12 cells. MPTP treatment increased the activities of total superoxide dismutase, catalase and glutathione peroxidase and the levels of malondialdehyde and carbonyls in the brain compared to control mouse brain. Co-administration of glycyrrhizin (16.8 mg/kg) attenuated the MPTP effect on the enzyme activities and formation of tissue peroxidation products. In vitro assay, licorice compounds attenuated the MPP(+)-induced cell death and caspase-3 activation in PC12 cells. Glycyrrhizin up to 100microM significantly attenuated the toxicity of MPP(+). Meanwhile, 18beta-glycyrrhetinic acid showed a maximum inhibitory effect at 10microM; beyond this concentration the inhibitory effect declined. Glycyrrhizin and 18beta-glycyrrhetinic acid attenuated the hydrogen peroxide- or nitrogen species-induced cell death. Results from this study indicate that glycyrrhizin may attenuate brain tissue damage in mice treated with MPTP through inhibitory effect on oxidative tissue damage. Glycyrrhizin and 18beta-glycyrrhetinic acid may reduce the MPP(+) toxicity in PC12 cells by suppressing caspase-3 activation. The effect seems to be ascribed to the antioxidant effect.

Acetaldehyde mediates alcohol activation of the mesolimbic dopamine system

Ethanol (EtOH), the main psychoactive ingredient of alcoholic drinks, is widely considered to be responsible for alcohol abuse and alcoholism through its positive motivational properties, which depend, at least partially, on the activation of the mesolimbic dopaminergic system. However, acetaldehyde (ACD), the first metabolite of EtOH, has been classically considered to be aversive and useful in the pharmacological therapy of alcoholics. Here we show that EtOH-derived ACD is necessary for EtOH-induced place preference, a pre-clinical test with high predictive validity for reward liability. We also found that ACD is essential for EtOH-increased microdialysate dopamine (DA) levels in the rat nucleus accumbens and that this effect is mimicked by intra-ventral tegmental area (VTA) ACD administration. Furthermore, in vitro, ACD enhances VTA DA neuronal firing through action on two ionic currents: reduction of the A-type K+ current and activation of the hyperpolarization-activated inward current. EtOH-stimulating properties on DA neurons are prevented by pharmacological blockade of local catalase, the main metabolic step for biotransformation of EtOH into ACD in the central nervous system. These results provide in-vivo and in-vitro evidence for a key role of ACD in the motivational properties of EtOH and its activation of the mesolimbic DA system. Additionally, these observations suggest that ACD, by increasing VTA DA neuronal activity, would oppose its well-known peripherally originating aversive properties. Careful consideration of these findings could help in devising new effective pharmacological therapies aimed at reducing EtOH intake in alcoholics.

Neuroprotective effect of hydrogen peroxide on an in vitro model of brain ischaemia

BACKGROUND AND PURPOSE

Reactive oxygen species (ROS) have been postulated to play a crucial role in the pathogenesis of ischaemia-reperfusion injury. Among these, hydrogen peroxide (H(2)O(2)) is known to be a toxic compound responsible for free-radical-dependent neuronal damage. In recent years, however, the 'bad reputation' of H(2)O(2) and other ROS molecules has changed. The aim of this study was to assess the protective role of H(2)O(2) and modification in its endogenous production on the electrophysiological and morphological changes induced by oxygen/glucose deprivation (OGD) on CA1 hippocampal neurons.

EXPERIMENTAL APPROACH

Neuroprotective effects of exogenous and endogenous H(2)O(2) were determined using extracellular electrophysiological recordings of field excitatory post synaptic potentials (fEPSPs) and morphological studies in a hippocampal slice preparation. In vitro OGD was delivered by switching to an artificial cerebrospinal fluid solution with no glucose and with oxygen replaced by nitrogen.

KEY RESULTS

Neuroprotection against in vitro OGD was observed in slices treated with H(2)O(2) (3 mM). The rescuing action of H(2)O(2) was mediated by catalase as pre-treatment with the catalase inhibitor 3-amino-1,2,4-triazole blocked this effect. More interestingly, we showed that an increase of the endogenous levels of H(2)O(2), due to a combination of an inhibitor of the glutathione peroxidase enzyme and addition of Cu,Zn-superoxide dismutase in the tissue bath, prevented the OGD-induced irreversible depression of fEPSPs.

CONCLUSIONS AND IMPLICATIONS

Taken together, our results suggest new possible strategies to lessen the damage produced by a transient brain ischaemia by increasing the endogenous tissue level of H(2)O(2).

MPTP-treated mice: long-lasting loss of nigral TH-ir neurons but not paradoxical sleep alterations

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model is widely used for studying Parkinson's disease. A previous study in our laboratory showed that MPTP-treated mice presented an increase in paradoxical sleep (PS) throughout the sleep/wakefulness cycle. However, many researchers have reported a behavioural and dopaminergic neuron recovery process which appears some time after MPTP treatment. Hence, in a first step, we decided to study tyrosine hydroxylase-immunoreactive (TH-ir) neuron loss in the nigrostriatal pathway 7, 15, 40 and 60 days after MPTP injection. We then studied S/W in MPTP-treated mice 20 days and 40 days after MPTP injection. Our results showed that MPTP-treated mice presented a 30% reduction in the number of TH-ir neurons in the substantia nigra and a 50% decrease in striatal TH staining, compared with saline-treated mice. These nigrostriatal pathway alterations are stable until 60 days post-MPTP treatment. The PS increase observed in our previous study was also observed in the present work 20 days after MPTP treatment but not after 40 days. The present results demonstrated that TH-ir neuronal loss in MPTP mice is quite stable until 60 days, whereas PS alterations are not. This finding suggests that there is no correlation between the dopaminergic neuronal loss and PS alteration in MPTP-treated mice. Hence, other neurotransmission systems may be involved in PS amount variations in MPTP mice and it is possible that the PS increase is accounted for by a homeostatic process, following a hypothetical reduction in this sleep state.

17β-Estradiol reduces nitrotyrosine immunoreactivity and increases SOD1 and SOD2 immunoreactivity in nigral neurons in male mice following MPTP insult

Emerging evidence suggests the beneficial effects of estrogen on Parkinson's disease (PD), yet the mechanisms of action implicated remain elusive. While experimental evidence suggests that estrogen possesses potent antioxidative properties, it is still unknown whether the hormone exhibits a neuroprotection in a PD animal model through its antioxidant activities. This study therefore investigated the effects of 17beta-estradiol (E2) on the immunoreactivity of nigral neurons and glia for nitrotyrosine (NT, a stable marker for oxidative stress), Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. Adult male mice were treated with E2 or vehicle for 11 days during which they were injected with MPTP or saline on the sixth day. The brains were collected on day 11 and quantitative immunohistochemistry was used to assess the number of NT-, SOD1- and SOD2-immunoreactive (IR) cells in the substantia nigra pars compacta (SNpc). In saline-treated group, E2 decreased NT-IR neuronal number and raised SOD1 and SOD2 expression in neurons and glia in the SNpc. MPTP induced a significant increase in the number of NT- and SOD2-IR neurons, but decreased the number of SOD1-IR neurons. MPTP also triggered a significant increase of SOD2- and SOD1-IR glial number. E2 pretreatment in MPTP mice reduced the number of NT-IR neurons, increased the number of SOD1- and SOD2-IR neurons, but did not alter the MPTP effect on glia immunoreactive to either SOD. Stimulation of SOD1 and SOD2 expression in nigral neurons suggests that E2 provides neuroprotection against MPTP-induced oxidative stress, partly through its ability to act as an antioxidant.

Antioxidant responses and lipid peroxidation following intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in rats: increased susceptibility of olfactory bulb

We evaluated an alternative method to investigate a possible involvement of environmental toxins in the pathology of Parkinson's disease (PD). There is considerable evidence supporting the role of oxidative stress in the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin largely used to modeling PD in primates and rodents. We have recently demonstrated that rats treated with intranasal (i.n.) infusion of MPTP suffer from progressive signs of PD that are correlated with time-dependent degeneration in dopaminergic neurons. In the present study, we investigated the time-dependent (2 h to 7 days) effect of a single i.n. administration of MPTP (0.1 mg/nostril) on the glutathione-related antioxidant status and lipid peroxidation (TBARS) in the adult Wistar rat brain. The effects were more pronounced in the olfactory bulb at 6 h after i.n. MPTP administration, as indicated by an increase in TBARS and total glutathione (GSH-t) levels, and also in the gamma-glutamyl transpeptidase (GGT) activity. Increased levels of TBARS, GSH-t and GGT activity were also observed at 6 h post-MPTP infusion in some structures (e.g. striatum, hippocampus and prefrontal cortex). No difference regarding glutathione reductase activity was observed in any of the brain structures analyzed, while a marked decrease in glutathione peroxidase activity was specifically observed in the substantia nigra 7 days after MPTP treatment. These results demonstrate that a single i.n. infusion of MPTP in rats induces significant alterations in the brain antioxidant status and lipid peroxidation, reinforcing the notion that the olfactory system represents a particularly sensitive route for the transport of neurotoxins into the central nervous system that may be related to the etiology of PD.

H2O2 signaling in the nigrostriatal dopamine pathway via ATP-sensitive potassium channels: issues and answers

The role of reactive oxygen species (ROS) as signaling agents is increasingly appreciated. Studies of ROS functions in the central nervous system, however, are only in their infancy. Using fast-scan cyclic voltammetry and fluorescence imaging in brain slices, the authors discovered that hydrogen peroxide (H2O2) is an endogenous regulator of dopamine release in the dorsal striatum. Given the key role of dopamine in motor, reward, and cognitive pathways, regulation by H2O2 has implications for normal dopamine function, as well as for dysfunction of dopamine transmission. In this review, data are summarized to show that H2O2 is a diffusible messenger in the striatum, generated downstream from glutamate receptor activation, and an intracellular signal in dopamine neurons of the substantia nigra, generated during normal pacemaker activity. The mechanism by which H2O2 inhibits dopamine release and dopamine cell activity is activation of ATP-sensitive K+ (KATP) channels. Characteristics of the neuronal and glial antioxidant networks required to permit H2O2 signaling, yet prevent oxidative damage, are also considered. Lastly, estimates of physiological H2O2 levels are discussed, and strengths and limitations of currently available methods for H2O2 detection, including fluorescence imaging using dichlorofluorescein (DCF) and the next generation of fluorescent probes, are considered.

Dopaminergic neurons reduced to silence by oxidative stress: an early step in the death cascade in Parkinson's disease?

Parkinson's disease (PD) is a common neurodegenerative disorder that is most often sporadic, but in some cases it can be inherited as a simple Mendelian trait. The most important pathological feature of the disease is the death of brainstem dopaminergic neurons in the substantia nigra, which leads to characteristic motor symptoms. The etiology of PD remains unknown, but mitochondrial dysfunction and oxidative stress may contribute actively to the underlying pathomechanism. New studies suggest that K(ATP) channel activation may represent a downstream effector of these two cellular anomalies.

Endogenous hydrogen peroxide regulates the excitability of midbrain dopamine neurons via ATP-sensitive potassium channels

ATP-sensitive K+ (K(ATP)) channels link metabolic state to cell excitability. Here, we examined regulation of K(ATP) channels in substantia nigra dopamine neurons by hydrogen peroxide (H2O2), which is produced in all cells during aerobic metabolism. Blockade of K(ATP) channels by glibenclamide (100 nM) or depletion of intracellular H2O2 by including catalase, a peroxidase enzyme, in the patch pipette increased the spontaneous firing rate of all dopamine neurons tested in guinea pig midbrain slices. Using fluorescence imaging with dichlorofluorescein to visualize intracellular H2O2, we found that moderate increases in H2O2 during partial inhibition of glutathione (GSH) peroxidase by mercaptosuccinate (0.1-0.3 mM) had no effect on dopamine neuron firing rate. However, with greater GSH inhibition (1 mM mercaptosuccinate) or application of exogenous H2O2, 50% of recorded cells showed K(ATP) channel-dependent hyperpolarization. Responsive cells also hyperpolarized with diazoxide, a selective opener for K(ATP) channels containing sulfonylurea receptor SUR1 subunits, but not with cromakalim, a selective opener for SUR2-based channels, indicating that SUR1-based K(ATP) channels conveyed enhanced sensitivity to elevated H2O2. In contrast, when endogenous H2O2 levels were increased after inhibition of catalase, the predominant peroxidase in the substantia nigra, with 3-amino-1,2,4-triazole (1 mM), all dopamine neurons responded with glibenclamide-reversible hyperpolarization. Fluorescence imaging of H2O2 indicated that catalase inhibition rapidly amplified intracellular H2O2, whereas inhibition of GSH peroxidase, a predominantly glial enzyme, caused a slower, smaller increase, especially in nonresponsive cells. Thus, endogenous H2O2 modulates neuronal activity via K(ATP) channel opening, thereby enhancing the reciprocal relationship between metabolism and excitability.

Molecular mechanism of the neurotrophic effect of GDNF on DA neurons: role of protein kinase CK2

Glial cell line-derived neurotrophic factor (GDNF) is suggested as a specific neurotrophic factor for midbrain dopamine (DA) neurons, but the molecular mechanism underlying the neuroprotective action of GDNF is not well known. In the present study, we have shown that GDNF increased protein kinase CK2 activity in rat substantia nigra (SN) in a dose-dependent and time-dependent manner. This effect is prevented by prior treatment of the receptor Ret blocker K-252b. Immunostaining results also revealed that CK2 is expressed in TH-positive neurons in mesencephalon culture. Transfection of the wildtype CK2alpha DNA increased, whereas transfection of the catalytically inactive CK2alphaA156 mutant DNA decreased CK2 activity in the SN. CK2alphaA156 mutant DNA also antagonized the enhancing effect of GDNF on CK2 activity. It also antagonized the enhancing effects of GDNF on tyrosine hydroxylase (TH) protein level in the SN, DA turnover in the striatum and rotarod performance in rats. Further, CK2alpha wildtype DNA increased, whereas CK2alphaA156 mutant DNA decreased TH activity in the SN without altering the TH protein level. On the other hand, the DA neuron toxin 1-methyl-4-phenylpyridinium iodide (MPP+) markedly decreased the number of TH-positive neurons and TH protein level in the SN, decreased DA level in the striatum and impaired rotarod performance in rats. Over-expression of the CK2alpha wildtype DNA partially, but significantly, prevented the deteriorating effect of MPP+ on these measures. Prior administration of MPP+ also antagonized the enhancing effect of GDNF on CK2 activity. These results together suggest that the CK2 signaling pathway contributes to the neuroprotective action of GDNF on DA neurons.

Protective role of hydrogen peroxide in oxygen-deprived dopaminergic neurones of the rat substantia nigra

Hydrogen peroxide (H2O2) is a reactive oxygen species, responsible for cytotoxic damage through the formation of hydroxyl radicals. Dopamine (DA) neurones of the substantia nigra pars compacta (SNc) are highly sensitive to metabolic stress, and they typically respond to energy deprivation with membrane hyperpolarization, mainly through opening of ATP-dependent K+ channels. Accordingly, H2O2 (3 mM) induced a tolbutamide-sensitive outward current in DA neurones. Conversely, in a hypoxic medium, H2O2 reverted membrane hyperpolarization, which is associated with oxygen deprivation in DA neurones, restored their action potential firing, and reduced the hypoxia-mediated outward current in a concentration-dependent manner, between 0.1 and 3 mM (IC50 0.6+/-0.1 mM). Notably, H2O2 did not counteract membrane hyperpolarization associated with hypoglycaemia, moreover, when catalase was inhibited with 3-amino-1,2,4-triazole (3-AT; 30 mM), H2O2 did not reduce hypoxia-mediated outward current. The counteracting action of H2O2 on hypoxia-mediated effects was further confirmed by single-unit extracellular recordings of presumed DA neurones in acute midbrain slices preparations, using a planar multi-electrode array device. Whilst a prolonged period of hypoxia (40 min) caused firing suppression, which did not recover after perfusion in normoxic conditions, the presence of H2O2 (3 mM) during this prolonged hypoxic period rescued most of the neurones from irreversible firing inhibition. Accordingly, morphological studies showed that H2O2 counteracts the cytochrome c release provoked by prolonged hypoxic treatment. Taken together, our data suggest that H2O2 prevents the metabolic stress of DA neurones induced by hypoxia by serving as a supplementary source of molecular oxygen, through its degradation by catalase.

Brain antioxidant systems in human methamphetamine users

Animal data suggest that the widely abused psychostimulant methamphetamine can damage brain dopamine neurones by causing dopamine-dependent oxidative stress; however, the relevance to human methamphetamine users is unclear. We measured levels of key antioxidant defences [reduced (GSH) and oxidized (GSSG) glutathione, six major GSH system enzymes, copper-zinc superoxide dismutase (CuZnSOD), uric acid] that are often altered after exposure to oxidative stress, in autopsied brain of human methamphetamine users and matched controls. Changes in the total (n = 20) methamphetamine group were limited to the dopamine-rich caudate (the striatal subdivision with the most severe dopamine loss) in which only activity of CuZnSOD (+ 14%) and GSSG levels (+ 58%) were changed. In the six methamphetamine users with severe (- 72 to - 97%) caudate dopamine loss, caudate CuZnSOD activity (+ 20%) and uric acid levels (+ 63%) were increased with a trend for decreased (- 35%) GSH concentration. Our data suggest that brain levels of many antioxidant systems are preserved in methamphetamine users and that GSH depletion, commonly observed during severe oxidative stress, might occur only with severe dopamine loss. Increased CuZnSOD and uric acid might reflect compensatory responses to oxidative stress. Future studies are necessary to establish whether these changes are associated with oxidative brain damage in human methamphetamine users.

Chronic administration of rotenone increases levels of nitric oxide and lipid peroxidation products in rat brain

The complex I inhibitor rotenone is a neurotoxin that has been proposed to induce Parkinson-like degeneration. As the mechanisms of rotenone toxicity are not fully understood, the present study addresses the question of whether rotenone induces NO production and lipid peroxidation-like products, that is, thiobarbituric acid reactive substances (TBARS). Rotenone at a dose of 1.5 mg kg(-1) i.p. was administered to rats daily for 10, 20, 30, and 60 days, and NO and TBARS were measured in the frontal cortex and in the striatum. On the 1st and 10th day, there were no increases in NO and TBARS levels, after 20 days, the NO and TBARS levels were increased in the striatum. After 30 and 60 days, NO and TBARS levels were increased in striatum and frontal cortex. Behaviorally, on days 30 and 60, the rats exhibited akinesia and rigidity in the catalepsy test. These results show that chronic administration of rotenone over a long period is capable of increasing NO and TBARS in the cortex and striatum and mimics Parkinson's disease (PD)-like behavioral symptoms that are akinesia and rigidity in rats.

Neuroprotective Effects of a Novel Poly(ADP-Ribose) Polymerase-1 Inhibitor, 2-{3-[4-(4-Chlorophenyl)-1-piperazinyl] propyl}-4(3H)-quinazolinone (FR255595), in an in Vitro Model of Cell Death and in Mouse 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine Model of Parkinson's Disease

The massive activation of poly(ADP-ribose) polymerase-1 (PARP-1) by DNA-damaging stimuli, such as exposure to reactive oxygen species (ROS), can lead to cell injury via severe, irreversible depletion of the NAD and ATP pool, and PARP-1 inhibitors have been expected to rescue neurons from degeneration in a number of disease models. We have recently identified 2-[3-[4-(4-chlorophenyl)-1-piperazinyl] propyl]-4(3H)-quinazolinone (FR255595) as a novel and potent PARP-1 inhibitor through structure-based drug design and high-throughput screening. This compound potently inhibited PARP activity with an IC(50) value of 11 nM and was orally active and highly brain penetrable. Here, we show that prevention of PARP activation by FR255595 protects against both ROS-induced cells injury in vitro and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigrostriatal dopaminergic damage in an in vivo Parkinson's disease (PD) model. In cell death models in vitro, exposure of hydrogen peroxide induced cell death with PARP overactivation in PC12 cells and SH-SY5Y cells, and pre- and post-treatment with FR255595 (10(-9)-10(-5) M) significantly reduced PARP activation and cell death. In mouse MPTP model, MPTP (20 mg/kg i.p.) intoxication lead to PARP activation and cell damage in the nigrostriatal dopaminergic pathway, which was significantly ameliorated by oral administration of FR255595 (10-32 mg/kg), both in the substantia nigra and in the striatum via marked reduction of PARP activation, even with delayed treatment. These findings clearly indicate that the novel PARP-1 inhibitor FR255595 exerts neuroprotective effect through its potent PARP-1 inhibitory actions in PD model, suggesting that the drug could be an attractive candidate for several neurodegenerative disorders, including PD.

Effect of 6-hydroxydopamine on striatal GDNF and nigral GFRα1 and RET mRNAs in the adult rat

Exogenous GDNF as well as vectors containing the gene for this trophic factor has been shown to be neuroprotective in animal models of Parkinson's disease. We therefore investigated whether changes in striatal GDNF protein and nigral mRNA levels of its co-receptors GFRalpha1 and RET occur in response to lesions of dopamine (DA) neurons and examined the temporal profile of these changes as they relate to the loss of dopaminergic markers. Rats were lesioned with 6-hydroxydopamine and sacrificed 3 h to 60 days post-infusion. DA tissue levels in the striatum and tyrosine hydroxylase immunoreactivity in the substantia nigra (SN) and ventral tegmental area (VTA) were used to determine the size of the lesions. GDNF protein was measured in the striatum using radioimmunocytochemistry. In situ hybridization was used to determine alterations in the mRNAs of RET and GFRalpha1 in the SN and VTA. We observed no persistent changes in GDNF protein in the striatum in response to 6-hydroxydopamine over the 60-day observation period, suggesting that compensatory changes in this trophic factor do not occur in response to injury. Dramatic decreases in RET and GFRalpha1 were observed in both SN and VTA that were generally correlated with the loss of TH protein and striatal DA content, strongly suggesting that these receptors are located on DA neurons and that the protective effect of GDNF reflects a direct action of the trophic factor on these neurons.

Attenuation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity by the novel selective dopamine D3-receptor partial agonist FAUC 329 predominantly in the nucleus accumbens of mice

We previously synthesised a novel dopamine (DA) partial agonist FAUC 329 with high affinity and selectivity for the DA D(3) receptor. This is the first in vivo study to investigate the protective effects of FAUC 329 in a MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model of Parkinson's disease. Adult male C57bl/6 mice were injected with FAUC 329 (0, 0.1, 0.5, 0.75, or 1 mg/kg) 30 min before MPTP (2 x 30 mg/kg, 4 hr apart). One week later, accumbal and striatal tissue was processed for DA and metabolite HPLC determination as well as immunohistochemical analysis of DA transporter positive neurons in the substantia nigra pars compacta and ventral tegmental area was carried out. FAUC 329 showed a significant attenuation of MPTP-induced DA reduction in the nucleus accumbens (0.5, 0.75 and 1 mg/kg) in a dose-dependent manner. FAUC 329 (0.75 mg/kg) partly protected against DA depletion in the dorsal striatum as well as protected against loss of DA transporter immunoreactivity in the substantia nigra pars compacta. The highest dose of FAUC 329 (1 mg/kg), however, showed a non-significant tendency to augment the MPTP-induced striatal DA reduction. The protective effect of FAUC 329 against MPTP-induced DA depletion was most pronounced in the nucleus accumbens and appears to be linked to the preferential abundance of D(3) receptors in this region. Targeting the mesolimbic DA system may have implications for improvement of impaired motor behaviour and particularly non-motor functions related to the nucleus accumbens.

Genetic or pharmacological iron chelation prevents MPTP-induced neurotoxicity in vivo: a novel therapy for Parkinson's disease

Studies on postmortem brains from Parkinson's patients reveal elevated iron in the substantia nigra (SN). Selective cell death in this brain region is associated with oxidative stress, which may be exacerbated by the presence of excess iron. Whether iron plays a causative role in cell death, however, is controversial. Here, we explore the effects of iron chelation via either transgenic expression of the iron binding protein ferritin or oral administration of the bioavailable metal chelator clioquinol (CQ) on susceptibility to the Parkinson's-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrapyridine (MPTP). Reduction in reactive iron by either genetic or pharmacological means was found to be well tolerated in animals in our studies and to result in protection against the toxin, suggesting that iron chelation may be an effective therapy for prevention and treatment of the disease.

Brain antioxidant regulation in mammals and anoxia-tolerant reptiles: balanced for neuroprotection and neuromodulation

Reactive oxygen species (ROS) generated by mitochondrial respiration and other processes are often viewed as hazardous substances. Indeed, oxidative stress, defined as an imbalance between oxidant production and antioxidant protection, has been linked to several neurological disorders, including cerebral ischemia-reperfusion and Parkinson's disease. Consequently, cells and organisms have evolved specialized antioxidant defenses to balance ROS production and prevent oxidative damage. Research in our laboratory has shown that neuronal levels of ascorbate, a low molecular weight antioxidant, are ten-fold higher than those in much less metabolically active glial cells. Ascorbate levels are also selectively elevated in the CNS of anoxia-tolerant reptiles compared to mammals; moreover, plasma and CSF ascorbate concentrations increase markedly in cold-adapted turtles and in hibernating squirrels. Levels of the related antioxidant, glutathione, vary much less between neurons and glia or among species. An added dimension to the role of the antioxidant network comes from recent evidence that ROS can act as neuromodulators. One example is modulation of dopamine release by endogenous hydrogen peroxide, which we describe here for several mammalian species. Together, these data indicate adaptations that prevent oxidative stress and suggest a particularly important role for ascorbate. Moreover, they show that the antioxidant network must be balanced precisely to provide functional levels of ROS, as well as neuroprotection.

Protective effect of melatonin in a chronic experimental model of Parkinson's disease

Parkinson's disease is a chronic condition characterized by cell death of dopaminergic neurons mainly in the substantia nigra. Among the several experimental models used in mice for the study of Parkinson's disease 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- (MPTP-) induced parkinsonism is perhaps the most commonly used. This neurotoxin has classically been applied acutely or sub-acutely to animals. In this paper we use a chronic experimental model for the study of Parkinson's disease where a low dose (15 mg/kg bw) of MPTP was administered during 35 days to mice to induce nigral cell death in a non-acute way thus emulating the chronic condition of the disease in humans. Free radical damage has been implicated in the origin of this degeneration. We found that the antioxidant melatonin (500 microg/kg bw) prevents cell death as well as the damage induced by chronic administration of MPTP measured as number of nigral cells, tyrosine hydroxylase levels, and several ultra-structural features. Melatonin, which easily passes the blood-brain barrier and lacks of any relevant side-effect, is proposed as a potential therapy agent to prevent the disease and/or its progression.

Melatonin attenuates MPP+-induced neurodegeneration and glutathione impairment in the nigrostriatal dopaminergic pathway

In this study we selected a rat model of Parkinson's disease (PD) by using intrastriatal infusion of the 1-methyl-4-phenyl-pyridinium ion (MPP+) to investigate the neuroprotective action of melatonin and its inhibitory activity on MPP+-impaired glutathione (GSH) system in the nigrostriatal system. Results show that MPP+ caused not only a severe neuronal injury in the striatum and in the ipsilateral substantia nigra (SN), but it also induced a significant decrease in GSH levels and an increase in the GSSG/GSH ratio 3 days after intrastriatal MPP+ infusion. Intraperitoneal co-administration of melatonin (10 mg/kg, five times) significantly attenuated MPP+-induced nigrostriatal neurotoxicity and GSH impairment. Depletion of cytosolic GSH by L-buthionine sulfoximine (BSO) did not cause neuronal damage by itself. It, however, when co-administrated with MPP+, potentiated the GSH reduction in the striatum, without aggravating nigrostriatal neurodegeneration induced by MPP+. Moreover, the MPP+-caused neuronal damage was positively correlated with a rising ratio of GSSG/GSH, but not with a drop of GSH. These results suggest that the MPP+-triggered oxidative stress may play a more important role than the loss of the antioxidant GSH in determining neuronal injury. Interestingly, the neuronal damage and oxidative stress elicited by co-treatment of BSO with MPP+ were effectively reduced by melatonin. Our results hence provide direct evidence showing that melatonin attenuates MPP+-induced nigrostriatal dopaminergic injury by its ability to impede the increase of GSSG/GSH ratio; therefore melatonin may have therapeutic implications in PD.

Sub-chronic treatment with classical but not atypical antipsychotics produces morphological changes in rat nigro-striatal dopaminergic neurons directly related to "early onset" vacuous chewing

In the present work, we investigated if an impairment of dopaminergic neurons after subchronic haloperidol treatment might be a possible physiopathologic substrate of the "early onset" vacuous chewing movements (VCMs) in rats. For this purpose, different antipsychotics were used to analyse a possible relationship between VCMs development and morphological alterations of tyrosine-hydroxylase-immunostained (TH-IM) neurons. Rats treated twice a day with haloperidol displayed a significant increase of VCMs that was both time- (2-4 weeks) and dose (0.1-1 mg/kg) dependent. Immunocytochemical analysis showed a shrinkage of TH-IM cell bodies in substantia nigra pars compacta and reticulata and a reduction of TH-immunostaining in the striatum of haloperidol treated rats with the arising of VCMs. No differences were observed in TH-IM neurons of ventral tegmental area and nucleus accumbens vs. control rats. The atypical antipsychotics risperidone (2 mg/kg, twice a day), amisulpride (20 mg/kg, twice a day) and clozapine (10 mg/kg, twice a day) did not produce any nigro-striatal morphological changes or VCMs. TH-IM nigro-striatal neuron morphological alterations and VCMs were still present after three days of withdrawal in rats treated for four weeks with haloperidol (1 mg/kg). Both the main morphological changes and the behavioural correlate disappeared after three weeks of withdrawal. These results suggest that haloperidol induces a morphological impairment of the dopaminergic nigro-striatal neurons which is directly associated with the arising, permanency and disappearance of VCMs in rats.