The antioxidative property of green tea against iron-induced oxidative stress in rat brain

The antioxidative property of green tea against iron-induced oxidative stress was investigated in the rat brain both in vivo and in vivo. Incubation of brain homogenates at 37 degrees C for 4 hours in vitro increased the formation of Schiff base fluorescent products of malonaldehyde, an indicator of lipid peroxidation. Auto-oxidation (without exogenous iron) of brain homogenates was inhibited by green tea extract in a concentration-dependent manner. Moreover, incubation with iron (1 microM) elevated lipid peroxidation of brain homogenates after 4-hour incubation at 37 degrees C. Co-incubation with green tea extract dose-dependently inhibited the iron-induced elevation in lipid peroxidation. For the in vivo studies: ferrous citrate (iron, 4.2 nmoles) was infused intranigrally and induced degeneration of the nigrostriatal dopaminergic system of rat brain. An increase in lipid peroxidation in substantia nigra as well as a decrease in dopamine content in striatum was observed seven days after the iron infusion. Intranigral infusion of green tea extract alone did not increase, and in some cases, even decreased lipid peroxidation in substantia nigra. Co-infusion of green tea extract prevented oxidative injury induced by iron. Both iron-induced elevation in lipid peroxidation in substantia nigra and iron-induced decrease in dopamine content in striatum were suppressed. Oral administration of green tea extract for two weeks did not prevent the iron-induced oxidative injury in nigrostriatal dopaminergic system. Our results suggest that intranigral infusion of green tea extract appears to be nontoxic to the nigrostriatal dopaminergic system. Furthermore, the potent antioxidative action of green tea extract protects the nigrostriatal dopaminergic system from the iron-induced oxidative injury.     

Melatonin suppresses iron-induced neurodegeneration in rat brain

The antioxidative action of melatonin on iron-induced neurodegeneration in the nigrostriatal dopaminergic system was evaluated in vivo. Intranigral infusion of iron chronically degenerated the dopaminergic transmission of the nigrostriatal system. An increase in lipid peroxidation in the infused substantia nigra and reductions in dopamine levels and dopaminergic terminals in the ipsilateral striatum were observed 7 d after iron infusion. Whereas local infusion of melatonin (60 microg/microl, 1 microl) alone did not alter dopaminergic transmission, coinfusion of melatonin with iron suppressed iron-induced oxidative damages. Systemic infusion of melatonin via osmotic pumps had no effect on iron-induced neurodegeneration. However, repetitive intraperitoneal injections of melatonin (10 mg/kg) prevented iron-induced oxidative injuries. The ratio of glutathione (GSH)/oxidized glutathione (GSSG) was moderately increased in the lesioned substantia nigra of the melatonin-treated rats compared to that of the lesioned group in control rats. The antioxidative effect of melatonin was verified in cortical homogenates. Melatonin dose-dependently suppressed autoxidation and iron-induced lipid peroxidation. Melatonin was as effective as GSH and was less effective than Trolox (a water-soluble analogue of vitamin E) in inhibiting iron-elevated lipid peroxidation of brain homogenates. Our data suggest that melatonin is capable of at least partially preventing the iron-induced neurodegeneration in the nigrostriatal dopaminergic system.     

Coexistence of zinc and iron augmented oxidative injuries in the nigrostriatal dopaminergic system of SD rats

Clinical studies have demonstrated an excess of transition metals, including zinc and iron, in the substantia nigra (SN) of Parkinson's patients. In the present study, the neurotoxic effect of zinc was investigated using iron as a positive control. Addition of zinc or iron to brain homogenates increased lipid peroxidation. Zinc was less potent than iron in inducing lipid peroxidation. Coincubation with desferrioxamine prevented zinc- and iron-induced lipid peroxidation. Furthermore, glutathione (GSH), S-nitroso-N-acetylpenicillamine, or melatonin inhibited zinc-induced lipid peroxidation. The oxidative effect of zinc was further investigated in anesthetized rats. Seven days after intranigral infusion of zinc, lipid peroxidation was elevated in the infused SN, and dopamine content and tyrosine hydroxylase-positive axons were decreased in the ipsilateral striatum. Zinc was less potent than iron in inducing neurodegeneration in vivo. L-Buthionine-[S,R]-sulfoximine pretreatment (i.c.v.), which depletes cellular GSH levels, enhanced zinc-induced oxidative injuries in the nigrostriatal dopaminergic system. Moreover, simultaneous infusion of zinc and iron appeared to augment oxidative injuries in rat brain. Taken together, our results demonstrate that intranigral infusion of zinc caused degeneration of the nigrostriatal dopaminergic system in rat brain. Furthermore, coexistence of zinc and iron augmented oxidative injuries in rat brain. These findings indicate that both zinc and iron contribute to the etiology of Parkinsonism.     

Zinc-induced apoptosis in substantia nigra of rat brain: neuroprotection by vitamin D3

Accumulation of transition metals has been suggested to be responsible for the deteriorated nigrostriatal dopaminergic system in Parkinson's patients. In the present study, the mechanism underlying the zinc-induced neurotoxicity was investigated in the nigrostriatal dopaminergic system in vivo. Our 6-methoxy-8-paratoluene sulfonamide quinoline fluorescence study showed zinc translocation in the infused nigral cells after intranigral infusion of zinc. Furthermore, lipid peroxidation in the zinc-infused substantia nigra was consistently elevated 4 h to 7 d after the infusion. At the same time, an abrupt increase in cytosolic cytochrome c content in the infused substantia nigra was observed 4 h after zinc infusion and gradually decreased to basal levels 7 d after infusion. Both TUNEL-positive neurons and DNA fragmentation, indicatives of apoptosis, were detected in the zinc-infused substantia nigra. Furthermore, striatal dopamine content was reduced 7 d after the infusion. In attempt to prevent zinc-induced neurotoxicity, vitamin D3 was systemically administered. Zinc-induced increases in lipid peroxidation and cytosolic cytochrome c in the infused substantia nigra were prevented by this treatment. Moreover, zinc-induced reduction in striatal dopamine content was attenuated after vitamin D3 treatment. Our in vivo data suggest that zinc-induced oxidative stress may result in apoptosis followed by reduced dopaminergic function in the nigrostriatal dopaminergic system. Furthermore, vitamin D3 prevented zinc-induced oxidative injuries in the rat brain.     

Differential effects of carboxyfullerene on MPP+/MPTP-induced neurotoxicity

The effects of carboxyfullerene on a well-known neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenyl-pyridinium (MPP+) were investigated. In chloral hydrate-anesthetized rats, cytosolic cytochrome c was elevated in the infused substantia nigra 4 h after an intranigral infusion of MPP+. Five days after local application of MPP+, lipid peroxidation (LP) was elevated in the infused substantia nigra. Furthermore, dopamine content and tyrosine hydroxylase (TH)-positive axons were reduced in the ipsilateral striatum. Concomitant intranigral infusion of carboxyfullerene abolished the elevation in cytochrome c and oxidative injuries induced by MPP+. In contrast, systemic application of carboxyfullerene did not prevent neurotoxicity induced by intraperitoneal injection of MPTP. In mice, systemic administration of MPTP induced a dose-dependent depletion in striatal dopamine content. Simultaneous injection of carboxyfullerene (10 mg/kg) actually potentiated MPTP-induced reduction in striatal dopamine content. Furthermore, systemic administration of carboxyfullerene (30 mg/kg) caused death in the MPTP-treated mice. An increase in the striatal MPP+ level and reduction in hepatic P450 level were observed in the carboxyfullerene co-treated mice. These data showed that systemic application of carboxyfullerene appears to potentiate MPTP-induced neurotoxicity while local carboxyfullerene has been suggested as a neuroprotective agent. Furthermore, an increase in striatal MPP+ level may contribute to the potentiation by carboxyfullerene of MPTP-induced neurotoxicity.     

Angeli's salt induces neurotoxicity in dopaminergic neurons in vivo and in vitro

In this study, we investigated the hypothesis that the pro-oxidative properties of Angeli's salt (AS), a nitroxyl anion (HNO/NO -) releasing compound, cause neurotoxicity in dopaminergic neurons. The pro-oxidative properties were demonstrated in vitro by measuring hydroxylation products of salicylate and peroxidation of lipids under various redox conditions. AS (0-1000 μM) released high amounts of hydroxylating species in a concentration dependent manner. AS also increased lipid peroxidation in brain homogenates at concentrations below 100 μM, while inhibiting it at 1000 μM concentration. The AS induced pro-oxidative effects were completely suppressed by copper (II), which converts nitroxyl anion to nitric oxide, as well as by a potent nitroxyl anion scavenger glutathione. Neurotoxicity towards dopaminergic neurons was tested in rat nigrostriatal dopaminergic system in vivo and by using primary mesencephalic dopaminergic neuronal cultures in vitro . Intranigral infusion of AS (0-400 nmol) caused neurotoxicity reflected as a dose dependent decrease of striatal dopamine seven days after treatment. The effect of the 100 nmol dose was more pronounced when measured 50 days after the infusion. Neurotoxicity was also confirmed as a decrease of tyrosine hydroxylase positive neurons in the substantia nigra. Neither sulphononoate, a close structural analog of AS, nor sodiumnitrite caused changes in striatal dopamine, thus reflecting lack of neurotoxicity. In primary dopaminergic neuronal cultures AS reduced [ 3 H] dopamine uptake with concentrations over 200 μM confirming neurotoxicity. In line with the quite low efficacy to increase lipid peroxidation in vitro , infusion of AS into substantia nigra did not cause increased formation of fluorescent products of lipid peroxidation. These results support the hypothesis that AS derived species oxidize critical thiol groups, rather than membrane lipids, potentially leading to protein oxidation/dysfunction and demonstrated neurotoxicity. These findings may have pathophysiological relevance in case of excess formation of nitroxyl anion.     

Effect of Buthionine Sulfoximine, a Synthesis Inhibitor of the Antioxidant Glutathione, on the Murine Nigrostriatal Neurons

Abstract: This study analyzed the effects of acute systemic treatment with buthionine sulfoximine (BSO), a synthesis inhibitor of the antioxidant reduced glutathione (GSH), on dopaminergic neurons of the murine nigrostriatal pathway. Part 1 of the study established a dose-response curve and the temporal pattern of GSH loss and recovery in the substantia nigra and striatum following acute BSO treatment. Part 2 of the study determined the effect of acute BSO treatment on the morphology and biochemistry of nigrostriatal neurons. We found that decreases in GSH levels had profound morphological effects, including decreased catecholamine fluorescence per cell, increased levels of lipid peroxidation and lipofuscin accumulation, and increased numbers of dystrophic axons in dopaminergic neurons of the nigrostriatal pathway. However, no measurable effects were observed in biochemical levels of either dopamine or its metabolites. These changes mimic those that have been reported to occur in the nigrostriatal system of rodents with advancing age. Our data suggest that reduction of GSH via BSO treatment results in the same types of nigrostriatal degenerative effects that occur during the aging process and consequently is a good model system for examining the role of GSH in protecting this area of the brain against the harmful effects of age-related oxidative stress.     

Semichronic Inhibition of Glutathione Reductase Promotes Oxidative Damage to Proteins and Induces both Transcription and Translation of Tyrosine Hydroxylase in the Nigrostriatal System

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.     

Semichronic inhibition of glutathione reductase promotes oxidative damage to proteins and induces both transcription and translation of tyrosine hydroxylase in the nigrostriatal system

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.     

Genetic vitamin E deficiency does not affect MPTP susceptibility in the mouse brain

Oxidative stress is involved in the degeneration of the nigrostriatal dopaminergic system in Parkinson's disease (PD). Vitamin E (alpha-tocopherol) is a potent antioxidant in the cell membrane that can trap free radicals and prohibit lipid peroxidation. The retention and secretion of vitamin E are regulated by alpha-tocopherol transfer protein (TTP) in the brain and liver. Dysfunction of TTP results in systemic deficiency of vitamin E in humans and mice, and increased oxidative stress in mouse brain. In this study, we investigated the effect of vitamin E deficiency in PD development by generating an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD using TTP knockout (TTP-/-) mice. Vitamin E concentration in the brains of TTP+/- mice was half that in TTP+/+ mice, and in TTP-/- mice, was undetectable. MPTP treatment tended to decrease striatal dopamine, but the effect was comparable and not significant in any of the three genotypes. Furthermore, the extent of loss of dopaminergic cell bodies in the substantia nigra did not differ among the groups. One the other hand, oral administration of vitamin E resulted in the partial protection of striatal dopaminergic terminals against MPTP toxicity. Our results suggest that vitamin E does not play a major protective role in MPTP-induced nigrostriatal dopaminergic neurodegeneration in the brain.     

Intranigral iron infusion in the rat

Iron is known to induce lipid perocidation and recent evidence indicates that both iron and lipid peroxidation are elevated in the substantia nigra in Parkinson's disease (PD). To test whether excess intranigral iron induces lipid peroxidation, we infused an iron citrate solution (0.63 nmol in 0.25 μL) into the rat substantia nigra and measured nigral thiobarbituric acid reactive products at 1-h, 1-d, 1-wk, and 1-mo postinfusion. In a separate group of iron-infused animals, histologic analysis within the substantia nigra through 1-mo postinfusion was accomplished by thionine- and iron-staining, with concurrent assessment of striatal neurochemical markers. Concentrations of nigral thiobarbituric acid reactive products were significantly elevated at 1 h and 1 d in iron-infused animals compared to vehicle-infused and unoperated animals, with a return to control values by 1 wk. Similarly, striatal dopamine turnover was acutely elevated, suggesting damage to dopaminergic neurons, which was confirmed histologically. Although iron-staining within the iron diffusionary area was increased through the postinfusion month, there was an apparent progression of the cellular character of staining from predominantly neuronal to reactive glial and finally to oligodendroglial by 1 mo postinfusion. this progression of cellular iron-staining may indicate a shifting of infused iron to a more bound unreactive form, thus explaining only an acute elevation in lipid peroxidation through 1 d following intranigral iron infusion. The data indicate that damage to nigral neurons induced by iron infusion is transciently associated with a marker of oxidative damage and supports the possibility that iron-induced oxidative stress contributes to the pathogenesis of PD.     

Antioxidant Effects of SelegilIne in Oxidative Stress Induced by Iron Neonatal Treatment in Rats

Increased levels of iron in specific brain regions have been reported in neurodegenerative disorders. It has been postulated that iron exerts its deleterious effects on the nervous system by inducing oxidative damage. In a previous study, we have shown that iron administered during a particular period of the neonatal life induces oxidative damage in brain regions in adult rats. The aim of the present study was to evaluate the possible protective effect of selegiline, a monoamino-oxidase B (MAO-B) inhibitor used in pharmacotherapy of Parkinson’s disease, against iron-induced oxidative stress in the brain. Results have shown that selegiline (1.0 and 10.0 mg/kg), when administered early in life was able to protect the substantia nigra as well as the hippocampus against iron-induced oxidative stress, without affecting striatum. When selegiline (10.0 mg/kg) was administered in the adult life to iron-treated rats, oxidative stress was reduced only in the substantia nigra.     

Neuroprotective Effects of Baicalein on Acrolein-induced Neurotoxicity in the Nigrostriatal Dopaminergic System of Rat Brain

Elevated levels of acrolein, an α,β-unsaturated aldehyde are detected in the brain of patients with Parkinson’s disease (PD). In the present study, the neuroprotective effect of baicalein (a phenolic flavonoid in the dried root of Scutellaria baicalensis Georgi) on acrolein-induced neurodegeneration of nigrostriatal dopaminergic system was investigated using local infusion of acrolein in the substantia nigra (SN) of rat brain. Systemic administration of baicalein (30 mg/kg, i.p.) significantly attenuated acrolein-induced elevations in 4-hydroxy-2-noneal (a product of lipid peroxidation), N-(3-formyl-3,4-dehydropiperidino)lysine (a biomarker of acrolein-conjugated proteins), and heme-oxygenase-1 levels (a redox-regulated protein) in the infused SN, indicating that baicalein inhibited acrolein-induced oxidative stress and protein conjugation. Furthermore, baicalein reduced acrolein-induced elevations in glial fibrillary acidic protein (a biomarker of activated astrocytes), ED-1 (a biomarker of activated microglia), and mature cathepsin B levels (a cysteine lysosomal protease), suggesting that baicalein attenuated acrolein-induced neuroinflammation. Moreover, baicalein attenuated acrolein-induced caspase 1 activation (a pro-inflammatory caspase) and interleukin-1β levels, indicating that baicalein prevented acrolein-induced inflammasome activation. In addition, baicalein significantly attenuated acrolein-induced caspase 3 activation (a biomarker of apoptosis) as well as acrolein-induced elevation in receptor interacting protein kinase (RIPK) 3 levels (an initiator of necroptosis), indicating that baicalein attenuated apoptosis and necroptosis. At the same time, baicalein mitigated acrolein-induced reduction in dopamine levels in the striatum ipsilateral to acrolein-infused SN. In conclusion, our data suggest that baicalein is neuroprotective via inhibiting oxidative stress, protein conjugation, and inflammation. Furthermore, baicalein prevents acrolein-induced program cell deaths, suggesting that baicalein is therapeutically useful for slowing PD progression.     

The protective role of plasmalogens in iron-induced lipid peroxidation

The role of plasmalogens in iron-induced lipid peroxidation was investigated in two liposomal systems. The first consisted of total brain phospholipids with and without plasmalogens, and the second of phosphatidylethanolamine/phosphatidylcholine liposomes with either diacyl- or alkenylacyl-phosphatidylethanolamine. By measuring thiobarbituric acid reactive substances, oxygen consumption, fatty acids and aldehydes, we show that plasmalogens effectively protect polyunsaturated fatty acids from oxidative damage, and that the vinyl ether function of plasmalogens is consumed simultaneously. Furthermore, the lack of lag phase, the increased antioxidant efficiency with time, and the experiments with lipid- and water-soluble azo compounds, indicate that plasmalogens probably interfere with the propagation rather than the initiation of lipid peroxidation, and that the antioxidative effect cannot be related to iron chelation.     

Time Course Changes in the Dopaminergic Nigrostriatal System Following Transection of the Medial Forebrain Bundle: Detection of Oxidatively Modified Proteins in Substantia Nigra

Abstract: We studied the time course of oxidatively modified proteins in the nigrostriatal dopaminergic system following transection of the medial forebrain bundle by quantifying the number of carbonyl groups coupled to striatal and nigral protein homogenates, an index of metal-catalyzed oxidations. We found a striking effect of axotomy on the number of oxidatively modified proteins in the substantia nigra but not in the striatum within the first 5 days postlesion. This effect was correlated with the neurochemical activity of the dopaminergic and serotoninergic systems in the substantia nigra, which suggests a role of dopamine- and serotonin-derived radical oxygen species in the oxidative stress detected in this brain area. We then searched for the type of cell death in the substantia nigra following axotomy. The fragmentation pattern obtained by agarose gel electrophoresis of DNA isolated from nigral tissue was indicative of cell death being entirely necrotic. In fact, no evidence of apoptosis was detected at any postlesion time as revealed by TdT-mediated dUTP-biotin nick end-labeling (TUNEL) staining. The course of necrotic cell death in the substantia nigra coincided with the maximal levels of oxidatively modified proteins in the substantia nigra, suggesting a link between oxidative stress and nerve cell death and also coinciding with the neurochemical activity of both dopaminergic and serotoninergic systems.     

Hemoglobin and iron-evoked oxidative stress in the brain: protection by bile pigments, manganese and S-nitrosoglutathione

In the present in vitro and in vivo study we investigated the pro-oxidant effects of hemoglobin, as well as the antioxidant effects of its metabolites, in the brain. Incubation of rat brain homogenates with hemoglobin (0-10 μM) but not hemin induced lipid peroxidation up to 24 h (EC₅₀ = 1.2 μM). Hemoglobin's effects were similar to ferrous ion (EC₅₀ = 1.7 μM) and were blocked by the chelating agent deferoxamine (IC₅₀ = 0.5 μM) and a nitric oxide-releasing compound S-nitrosoglutathione (IC₅₀ = 40 μM). However, metabolites of hemoglobin — biliverdin and bilirubin — inhibited brain lipid peroxidation induced by cell disruption and hemoglobin (biliverdin IC₅₀ = 12-30 and bilirubin IC₅₀ = 75-170 μM). Biliverdin's antioxidative effects in spontaneous and iron-evoked lipid peroxidation were further augmented by maganese (2 μM) since manganese is an antioxidative transition metal and conjugates with bile pigments. Intrastriatal infusion of hemoglobin (0-24 nmol) produced slight, but significant 20-22% decreases in striatal dopamine levels. Whereas, intrastriatal infusion of ferrous citrate (0-24 nmol) dose-dependently induced a greater 66% depletion of striatal dopamine which was preceded by an acute increase of lipid peroxidation. In conclusion, contrary to the in vitro results hemoglobin is far less neurotoxic than ferrous ions in the brain. It is speculated that hemoglobin may be partially detoxified by heme oxygenase and biliverdin reductase to its antioxidative metabolites in the brain. However, in head trauma and stroke, massive bleeding could significantly produce iron-mediated oxidative stress and neurodegeneration which could be minimized by endogenous antioxidants such as biliverdin, bilirubin, manganese and S-nitrosoglutathione.     

Effect of MPTP on Dopamine Metabolism in Ames Dwarf Mice

Hypopituitary dwarf mice exhibit a heightened antioxidative capacity and live extensively longer than age-matched controls. Importantly, dwarf mice resist peripheral oxidative stress induced by paraquat, and behaviorally, they maintain cognitive function and locomotor activity at levels above those observed in old wild-type animals. We assessed monoaminergic neurotransmitters in nigrostriatal tract and cerebellum after the administration of the dopaminergic neurotoxin, MPTP. There was no significant change in mitochondrial monoamine oxidase (MAO)-B and total MAO activity in the substantia nigra and nucleus caudatus putamen of wild-type and dwarf mice. Coenzymes Q-9 and Q-10 were present in similar quantities, as were dopamine, norepinephrine, and serotonin levels in the cerebellum and nigrostriatal tract. MPTP set off tremor, hind limb abduction, and straub tail behavior and induced significant dopamine depletion in the striatum of both dwarf and normal mice. This study shows that the MAO activity and the coenzyme content of dwarf mice are similar to those of their wild-type controls and hence susceptible to MPTP-induced toxicity.     

Regional lipid peroxidation in rat brain in vitro: Possible role of endogenous iron

Lipoperoxidative capacity of various brain areas of aging rats was examined in vitro using the thiobarbituric acid test. Significant regional differences in the generation of lipid peroxides were found in freshly prepared homogenates from different areas of brain incubated under air. Incubation under oxygen resulted in marked stimulation of lipid peroxidation, with highest increases in hypothalamus (144%). Addition of exogenous Fe²⁺ and ascorbic acid resulted in stimulation of lipid peroxidation ranging from 10-fold in cortex to 20-fold in hypothalamus homogenates during incubation in air. A linear relationship was found between endogenous iron content in brain regions and their ability to produce lipid peroxides in vitro under oxygen for all areas except striatum. Several iron chelating agents effectively inhibited lipid peroxidation under hyperbaric oxygen whereas oxygenfree radical scavengers, as well as catalase and superoxide dismutase were not effective. It is concluded that regional differences in lipoperoxidative capacity of brain areas in vitro are in part governed by local endogenous iron content and may indicate regional susceptibility to oxidative damage.     

Responsiveness of nigral neurons to the stimulation of striatal dopaminergic receptors in the rat

The microinfusion of low doses of apomorphine into the striatum of anesthetized rats depressed the electrical activity of the neurons of the substantia nigra pars compacta while the infusion of bromocriptine had an excitatory or inhibitory effect. These data suggest that:1) the action of the two dopamine agonists on the striato-nigral pathway is different; 2) the striatum might contain dopaminergic receptors located on cells projecting to the substantia nigra with different roles in the feedback regulation of the latter; 3) the inhibitory action of systemically injected apomorphine is not simply due to a stimulation of dopamine “autoreceptors” but also to an action mediated by fibers descending from the striatum to the substantia nigra.     

Effects of cypermethrin on monoamine transporters,xenobiotic metabolizing enzymes and lipid peroxidation in the rat nigrostriatal system

Abstract

Long-term exposure to cypermethrin induces the nigrostriatal dopaminergic neurodegeneration in adult rats and its pre-exposure in the critical periods of brain development enhances the susceptibility during adulthood. Monoamine transporters, xenobiotic metabolizing enzymes and oxidative stress play critical roles in the nigrostriatal dopaminergic neurodegeneration. The study was undertaken to investigate the effects of cypermethrin on DAT, VMAT 2, CYP2E1, GST Ya, GST Yc and GSTA4-4 expressions, CYP2E1 and GST activities and lipid peroxidation in the nigrostriatal system of adult rats with/without post-natal exposure to cypermethrin. Cypermethrin reduced VMAT 2 and increased CYP2E1 expressions without causing significant change in DAT. Although GSTA4-4 mRNA expression and lipid peroxidation were increased, no significant changes were observed in GST Ya and GST Yc expressions and total GST activity. The results obtained demonstrate that long-term exposure to cypermethrin modulates VMAT 2, CYP2E1, GSTA4-4 expressions and lipid peroxidation, which could contribute to the nigrostriatal dopaminergic neurodegeneration.