Degeneration Of Dopaminergic Nerve Terminals Research Articles

Neuroprotective Effects of Anti-high Mobility Group Box-1 Monoclonal Antibody Against Methamphetamine-Induced Dopaminergic Neurotoxicity.

High mobility group box-1 (HMGB1) is a ubiquitous non-histone nuclear protein that plays a key role as a transcriptional activator, with its extracellular release provoking inflammation. Inflammatory responses are essential in methamphetamine (METH)-induced acute dopaminergic neurotoxicity. In the present study, we examined the effects of neutralizing anti-HMGB1 monoclonal antibody (mAb) on METH-induced dopaminergic neurotoxicity in mice. BALB/c mice received a single intravenous administration of anti-HMGB1 mAb prior to intraperitoneal injections of METH (4mg/kg × 2, at 2-h intervals). METH injections induced hyperthermia, an increase in plasma HMGB1 concentration, degeneration of dopaminergic nerve terminals, accumulation of microglia, and extracellular release of neuronal HMGB1 in the striatum. These METH-induced changes were significantly inhibited by intravenous administration of anti-HMGB1 mAb. In contrast, blood-brain barrier disruption occurred by METH injections was not suppressed. Our findings demonstrated the neuroprotective effects of anti-HMGB1 mAb against METH-induced dopaminergic neurotoxicity, suggesting that HMGB1 could play an initially important role in METH toxicity.

Protective Effect of Sauchinone on Methamphetamine-Induced Neurotoxicity in Mice

Sauchinone is a lignan isolated from Saururus chinensis known to suppress nitric oxide (NO) activity. Previous studies demonstrate that NO plays a key role in methamphetamine-induced neurotoxicity. Thus, we hypothesized that sauchinone could have a suppressive effect on the neurotoxicity induced by methamphetamine. Repeated injections of methamphetamine cause degeneration of dopaminergic nerve terminals, whereas sauchinone treatment significantly prevented this degeneration. Sauchinone treatment also inhibited the methamphetamine-induced activation of glia cells and the production of NO via a blockade of inducible NO synthase protein expression. Our results suggest that sauchinone can prevent methamphetamine-induced neurotoxicity through the suppression of NO production.

Cockayne Syndrome B Protects Against Methamphetamine-Enhanced Oxidative DNA Damage in Murine Fetal Brain and Postnatal Neurodevelopmental Deficits

Methamphetamine (METH) increases the oxidative DNA lesion 8-oxoguanine (8-oxoG) in fetal mouse brain, and causes postnatal motor coordination deficits after in utero exposure. Like oxoguanine glycosylase 1 (OGG1), the Cockayne syndrome B (CSB) protein is involved in the repair of oxidatively damaged DNA, although its function is unclear. Here we used CSB-deficient Csb(m/m) knockout mice to investigate the developmental role of DNA oxidation and CSB in METH-initiated neurodevelopmental deficits. METH (40 mg/kg intraperitoneally) administration to pregnant Csb females on gestational day 17 increased 8-oxoG levels in Csb(m/m) fetal brains (p < 0.05). CSB modulated 8-oxoG levels independent of OGG1 activity, as 8-oxoG incision activity in fetal nuclear extracts was identical in Csb(m/m) and Csb(+/+)mice. This CSB effect was evident despite 7.1-fold higher OGG1 activity in Csb(+/+) mice compared to outbred CD-1 mice. Female Csb(m/m) offspring exposed in utero to METH exhibited motor coordination deficits postnatally (p < 0.05). In utero METH exposure did not cause dopaminergic nerve terminal degeneration, in contrast to adult exposures. This is the first evidence that CSB protects the fetus from xenobiotic-enhanced DNA oxidation and postnatal functional deficits, suggesting that oxidatively damaged DNA is developmentally pathogenic, and that fetal CSB activity may modulate the risk of reactive oxygen species-mediated adverse developmental outcomes.

Reduced 3,4-Methylenedioxymethamphetamine (MDMA, Ecstasy)-Initiated Oxidative DNA Damage and Neurodegeneration in Prostaglandin H Synthase-1 Knockout Mice

The neurodegenerative potential of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) and underlying mechanisms are under debate. Here, we show that MDMA is a substrate for CNS prostaglandin H synthase (PHS)-catalyzed bioactivation to a free radical intermediate that causes reactive oxygen species (ROS) formation and neurodegenerative oxidative DNA damage. In vitro PHS-1-catalyzed bioactivation of MDMA stereoselectively produced free radical intermediate formation and oxidative DNA damage that was blocked by the PHS inhibitor eicosatetraynoic acid. In vivo, MDMA stereoselectively caused gender-independent DNA oxidation and dopaminergic nerve terminal degeneration in several brain regions, dependent on regional PHS-1 levels. Conversely, MDMA-initiated striatal DNA oxidation, nerve terminal degeneration, and motor coordination deficits were reduced in PHS-1 +/- and -/- knockout mice in a gene dose-dependent fashion. These results confirm the neurodegenerative potential of MDMA and provide the first direct evidence for a novel molecular mechanism involving PHS-catalyzed formation of a neurotoxic MDMA free radical intermediate.

Oxoguanine Glycosylase 1 Protects Against Methamphetamine-Enhanced Fetal Brain Oxidative DNA Damage and Neurodevelopmental Deficits

In utero methamphetamine (METH) exposure enhances the oxidative DNA lesion 7,8-dihydro-8-oxoguanine (8-oxoG) in CD-1 fetal mouse brain, and causes long-term postnatal motor coordination deficits. Herein we used oxoguanine glycosylase 1 (ogg1) knock-out mice to determine the pathogenic roles of 8-oxoG and OGG1, which repairs 8-oxoG, in METH-initiated neurodevelopmental anomalies. Administration of METH (20 or 40 mg/kg) on gestational day 17 to pregnant +/- OGG1-deficient females caused a drug dose- and gene dose-dependent increase in 8-oxoG levels in OGG1-deficient fetal brains (p < 0.05). Female ogg1 knock-out offspring exposed in utero to high-dose METH exhibited gene dose-dependent enhanced motor coordination deficits for at least 12 weeks postnatally (p < 0.05). Contrary to METH-treated adult mice, METH-exposed CD-1 fetal brains did not exhibit altered apoptosis or DNA synthesis, and OGG1-deficient offspring exposed in utero to METH did not exhibit postnatal dopaminergic nerve terminal degeneration, suggesting different mechanisms. Enhanced 8-oxoG repair activity in fetal relative to adult organs suggests an important developmental protective role of OGG1 against in utero genotoxic stress. These observations provide the most direct evidence to date that 8-oxoG constitutes an embryopathic molecular lesion, and that functional fetal DNA repair protects against METH teratogenicity.

Amphetamine effects on brain protein structure and oxidative stress as revealed by FTIR microspectroscopy

Amphetamines are psychostimulants abused by man, that eventually leads to drug dependence. Amphetamine administration to rodents has been shown to provoke significant neurotoxicity involving dopaminergic nerve terminal degeneration. However, little information related to the effect of amphetamines on reactive oxygen species (ROS) production and neurotoxicity in brain is currently available. Herein we report the biochemical alterations of lipids and proteins in brain sections from amphetamine-treated rodents using infrared microspectroscopy, immunohistochemistry, and immunoblotting. The spectroscopic changes reveal for the first time the formation of beta-sheet-rich proteins in the cortex, but no significant protein alterations are visible in hippocampus region where hydroperoxide concentration is found to be lower relative to cortex. These result suggest that ROS generated by amphetamine-mediated oxidative stress induce formation beta-sheet-rich proteins which can be of amyloid beta-like character.

Absence of Ret Signaling in Mice Causes Progressive and Late Degeneration of the Nigrostriatal System

Support of ageing neurons by endogenous neurotrophic factors such as glial cell line–derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) may determine whether the neurons resist or succumb to neurodegeneration. GDNF has been tested in clinical trials for the treatment of Parkinson disease (PD), a common neurodegenerative disorder characterized by the loss of midbrain dopaminergic (DA) neurons. BDNF modulates nigrostriatal functions and rescues DA neurons in PD animal models. The physiological roles of GDNF and BDNF signaling in the adult nigrostriatal DA system are unknown. We generated mice with regionally selective ablations of the genes encoding the receptors for GDNF (Ret) and BDNF (TrkB). We find that Ret, but not TrkB, ablation causes progressive and adult-onset loss of DA neurons specifically in the substantia nigra pars compacta, degeneration of DA nerve terminals in striatum, and pronounced glial activation. These findings establish Ret as a critical regulator of long-term maintenance of the nigrostriatal DA system and suggest conditional Ret mutants as useful tools for gaining insights into the molecular mechanisms involved in the development of PD.

Methamphetamine-enhanced embryonic oxidative DNA damage and neurodevelopmental deficits

Methamphetamine (METH) causes dopaminergic nerve terminal degeneration and functional deficits in adult mice, but its neurodevelopmental effects are unclear. We investigated METH-initiated oxidative DNA damage in brain during the embryonic and fetal periods, and the postnatal histological and functional consequences. Pregnant CD-1 mice were treated with a single dose of METH (20 or 40 mg/kg ip) or its saline vehicle on Gestational Day 14 or 17. METH enhanced conceptal DNA oxidation, determined by 8-oxoguanine formation, in brain and liver by at least 2-fold at 1 h ( P < 0.05), and more so in some fetal brains at 4 h. After birth, motor coordination on the rotarod apparatus in the METH-exposed offspring was impaired for at least 12 weeks ( P < 0.05). Unlike in adults, this postnatal functional deficit in offspring exposed in utero to METH was not associated with degeneration of striatal dopaminergic nerve terminals at 12 weeks of age determined by tyrosine hydroxylase staining, suggesting a novel pathological mechanism in utero. This is the first evidence of oxidative DNA damage in embryonic and fetal brain caused by amphetamines, leading to long-term postnatal neurodevelopmental deficits via a mechanism different from that underlying the neurodegeneration observed in METH-exposed adults.

Effects of monoamine oxidase inhibitors on the diethyldithiocarbamate-induced enhancement of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity in C57BL/6 mice.

Diethyldithiocarbamate (DDC) is known to potentiate the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The aims of the present study were to provide biochemical, pathological and behavioral evidence for the degeneration of dopamine (DA) neurons in C57BL/6 strain mice treated simultaneously with DDC and MPTP, and to evaluate the effects of monoamine oxidase (MAO) inhibitors on DDC-enhanced MPTP toxicity. DDC (400 mg/kg)+ MPTP (30 mg/kg) treatment decreased significantly the levels of striatal DA and its metabolites and induced bradykinesia. In mice treated with DDC+MPTP, degenerative areas were found in striatum, substantia nigra and tuberculum olfactorium by assessment of the binding of [125I]RTI-121, a DA transporter ligand. Pretreatment with a MAO-B inhibitor selegiline prior to the administration of DDC and MPTP completely inhibited the decrease in the levels of DA and its metabolites, bradykinesia and degeneration of dopaminergic nerve terminals. In contrast, the protective action of clorgyline was not clearly observed in this model system.

Obesity exacerbates chemically induced neurodegeneration

Obesity is a major risk factor associated with a variety of human disorders. While its involvement in disorders such as diabetes, coronary heart disease and cancer have been well characterized, it remains to be determined if obesity has a detrimental effect on the nervous system. To address this issue we determined whether obesity serves as a risk factor for neurotoxicity. Model neurotoxicants, methamphetamine (METH) and kainic acid (KA), which are known to cause selective neurodegeneration of anatomically distinct areas of the brain, were evaluated using an animal model of obesity, the ob/ob mouse. Administration of METH and KA resulted in mortality among ob/ob mice but not among their lean littermates. While METH caused dopaminergic nerve terminal degeneration as indicated by decreased striatal dopamine (49%) and tyrosine hydroxylase protein (68%), as well as an increase in glial fibrillary acidic protein by 313% in the lean mice, these effects were exacerbated under the obese condition (96%, 86% and 602%, respectively). Similarly, a dosage of KA that did not increase glial fibrillary acidic protein in lean mice increased the hippocampal content of this protein (93%) in ob/ob mice. KA treatment resulted in extensive neuronal degeneration as determined by Fluoro-Jade B staining, decreased hippocampal microtubule-associated protein-2 immunoreactivity and increased reactive gliosis in ob/ob mice. The neurotoxic outcome in ob/ob mice remained exacerbated even when lean and ob/ob mice were dosed with METH or KA based only on a lean body mass. Administration of METH or KA resulted in up-regulation of the mitochondrial uncoupling protein-2 to a greater extent in the ob/ob mice, an effect known to reduce ATP yield and facilitate oxidative stress and mitochondrial dysfunction. These events may underlie the enhanced neurotoxicity seen in the obese mice. In summary, our results implicate obesity as a risk factor associated with chemical- and possibly disease-induced neurodegeneration.

Direct binding and functional coupling of alpha-synuclein to the dopamine transporters accelerate dopamine-induced apoptosis.

Mutations in alpha-synuclein, a protein highly enriched in presynaptic terminals, have been implicated in the expression of familial forms of Parkinson's disease (PD) whereas native alpha-synuclein is a major component of intraneuronal inclusion bodies characteristic of PD and other neurodegenerative disorders. Although overexpression of human alpha-synuclein induces dopaminergic nerve terminal degeneration, the molecular mechanism by which alpha-synuclein contributes to the degeneration of these pathways remains enigmatic. We report here that alpha-synuclein complexes with the presynaptic human dopamine transporter (hDAT) in both neurons and cotransfected cells through the direct binding of the non-A beta amyloid component of alpha-synuclein to the carboxyl-terminal tail of the hDAT. alpha-Synuclein--hDAT complex formation facilitates the membrane clustering of the DAT, thereby accelerating cellular dopamine uptake and dopamine-induced cellular apoptosis. Since the selective vulnerability of dopaminergic neurons in PD has been ascribed in part to oxidative stress as a result of the cellular overaccumulation of dopamine or dopamine-like molecules by the presynaptic DAT, these data provide mechanistic insight into the mode by which the activity of these two proteins may give rise to this process.

Long-term induction of Fos-related antigen-2 after methamphetamine-, methylenedioxymethamphetamine-, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- and trimethyltin-induced brain injury

A long-term induction of Fos-related antigens has been shown in neurons after brain injury, suggesting that Fos-related antigens are involved in enhancing the transcription of genes related to the process of regeneration and repair. In the present study, we report that levels of Fos-related antigen-2 are elevated in several models of chemically induced brain injury. Trimethyltin, which causes degeneration of neurons primarily in the hippocampus and other limbic regions, results in a five-fold induction of Fos-related antigen-2 immunoreactivity in neurons in the pyramidal and dentate layers of the hippocampus starting at seven days post-treatment and persisting for 60 days. Methamphetamine and methylenedioxymethamphetamine, agents which cause degeneration of dopaminergic nerve terminals in the striatum of the mouse, cause an increase in Fos-related antigen-2 immunoreactivity which begins at three days post-treatment and returns to basal levels by days 5 and 15, respectively. Treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine elevated levels of Fos-related antigen-2 in the mouse striatum at three days post-treatment. This abbreviated time-course of Fos-related antigen-2 induction is consistent with less severe insult (terminal damage) relative to trimethyltin (cell death), but induction occurs during the period of regeneration and repair in both models. Dexfenfluramine, a non-neurotoxic amphetamine, does not induce Fos-related antigen-2 expression. Decreasing core temperature of the mouse, which blocks amphetamine-induced neurotoxicity, also blocks Fos-related antigen-2 induction. In summary, Fos-related antigen-2 is induced in models of both cell death and terminal degeneration, suggesting that this transcription factor may serve as a universal signal transduction molecule involved in the regulation of genes related to regeneration and repair in the CNS.

Rapid-onset dystonia-parkinsonism: Linkage to chromosome 19q13

Rapid-onset dystonia-parkinsonism (RPD) is an autosomal dominant movement disorder characterized by sudden onset of persistent dystonia and parkinsonism, generally during adolescence or early adulthood. Symptoms evolve over hours or days, and generally stabilize within a few weeks, with slow or no progression. Other features include little or no response to L-dopa, and low levels of homovanillic acid in the central nervous system. Neuroimaging studies indicate no degeneration of dopaminergic nerve terminals in RDP, suggesting that this disorder results from a functional deficit, as in dystonia, rather than neuronal loss, as in Parkinson's disease. We studied 81 members of two midwestern US families with RDP, 16 of whom exhibited classic features of RDP. We found significant evidence for linkage in these two families to markers on chromosome 19q13, with the highest multipoint LOD score at D19S198 (z = 5.77 at theta = 0.0). The flanking markers D19S587 and D19S900 define a candidate region of approximately 8 cM. Although RDP itself is a rare condition, it is important because it has clinical and biochemical similarities to both Parkinson's disease and dystonia. Identification of the genetic defect in RDP holds promise for understanding the underlying disease processes of both of these more common diseases.

Protective effects of MK-801 on methamphetamine-induced depletion of dopaminergic and serotonergic terminals and striatal astrocytic response: an immunohistochemical study.

It has been shown previously that methamphetamine induces dopaminergic nerve terminal degeneration, serotonin depletion and striatal reactive astrogliosis, and that the noncompetitive N-methyl-D-aspartate (NMDA) antagonist MK-801 can block methamphetamine (MA)-induced depletion of dopamine and serotonin and reduction in activity of their synthetic enzymes. In this study, immunohistochemistry was used to evaluate the effect of MK-801 on methamphetamine-induced neuropathological alterations of dopaminergic and serotonergic terminals and striatal astrocytic responses. Adult male rats were treated with methamphetamine (4 injections of 10 mg/kg at 2 hour intervals) in conjunction with MK-801 which was administered 15 min before each methamphetamine administration at doses of 1 mg/kg or 2 mg/kg. Brains were examined three days following treatment. MK-801 administration prevented methamphetamine-induced depletion of 5-hydroxytryptophan (5-HT) terminals in the forebrain and depletion of tyrosine hydroxylase-positive dopaminergic terminals and astrocytic response in the neostriatum in most animals. These results support the concept that excitatory amino acids acting through an NMDA receptor are involved in methamphetamine-induced neuronal damage on dopaminergic and serotonergic terminal fields. A minor depletion of TH-positive terminals and astrogliosis in the neostriatum was seen in three of nine MA-MK-801-treated animals. This indicates that the protective effects of MK-801 on MA-induced dopaminergic terminal degeneration varies among animals with complete protection in most animals and partial protection in the others using the present doses and dosing regimen.

The effects of amfonelic acid, a dopamine uptake inhibitor, on methamphetamine-induced dopaminergic terminal degeneration and astrocytic response in rat striatum

Administration of methamphetamine (MA) induces degeneration of dopaminergic nerve terminals and astrogliosis, such as hypertrophy and an increase in apparent number, in the neostriatum. In this experiment adult rats were treated with MA (10 mg/kg, i.p.) 4 times in one day at 2 h intervals. Amfonelic acid (AFA), a dopamine reuptake inhibitor, was administered (20 mg/kg, i.p.) at the same time the last MA dose was given. Three days later, dopaminergic terminals and astrocytes were examined immunohistochemically and the contents of striatal dopamine and its metabolites were analyzed by HPLC. The results showed that MA-induced the typical depletion of dopaminergic terminals, reduction of dopamine content and astrogliosis in the neostriatum. AFA treatment completely prevented the effects of MA on the dopaminergic system, both morphologically and biochemically. However, the reaction of astrocytes remained in the region where the most severe depletion dopaminergic terminals was seen in MA treated animals (ventral-lateral portion of neostriatum). The results support the concept that the dopamine transporter is involved in MA-induced dopaminergic nerve terminal degeneration. The results also indicate that blocking the dopamine transporter cannot completely prevent the reaction of astrocytes in the neostriatum, which indicates that the astrocytic reaction can be induced by factors other than degeneration of dopaminergic terminals in this region. Based on these and other data, it is hypothesized that MA may cause degeneration of corticostriatal glutamate pathways and this effect may be responsible for the astrogliosis in MA-AFA treated animals.