Dopamine D3 receptor ligand suppresses the expression of levodopa-induced dyskinesia in nonhuman primate model of parkinson's disease

Parkinson's disease (PD) is a complex multisystem, chronic and so far incurable disease with significant unmet medical needs. The incidence of PD increases with aging and the expected burden will continue to escalate with our aging population. Since its discovery in the 1961 levodopa has remained the gold standard pharmacotherapy for PD. However, the progressive nature of the neurodegenerative process in and beyond the nigrostriatal system causes a multitude of side effects, including levodopa-induced dyskinesia within 5 years of therapy. Attenuating dyskinesia has been a significant challenge in the clinical management of PD. We report on a small molecule that eliminates the expression of levodopa-induced dyskinesia and significantly improves PD-like symptoms. The lead compound PD13R we discovered is a dopamine D3 receptor partial agonist with high affinity and selectivity, orally active and with desirable drug-like properties. Future studies are aimed at developing this lead compound for treating PD patients with dyskinesia.

Mitochondrial oxidant stress mediates methamphetamine neurotoxicity in substantia nigra dopaminergic neurons

Methamphetamine abuse is associated with an increased risk of developing Parkinson's disease (PD). Recently, it was found that methamphetamine increases mitochondrial oxidant stress in substantia nigra pars compacta (SNc) dopaminergic neurons by releasing vesicular dopamine (DA) and stimulating mitochondrially-anchored monoamine oxidase (MAO). As mitochondrial oxidant stress is widely thought to be a driver of SNc degeneration in PD, these observations provide a potential explanation for the epidemiological linkage. To test this hypothesis, mice were administered methamphetamine (5 mg/kg) for 28 consecutive days with or without pretreatment with an irreversible MAO inhibitor. Chronic methamphetamine administration resulted in the degeneration of SNc dopaminergic neurons and this insult was blocked by pretreatment with a MAO inhibitor - confirming the linkage between methamphetamine, MAO and SNc degeneration. To determine if shorter bouts of consumption were as damaging, mice were given methamphetamine for two weeks and then studied. Methamphetamine treatment elevated both axonal and somatic mitochondrial oxidant stress in SNc dopaminergic neurons, was associated with a modest but significant increase in firing frequency, and caused degeneration after drug cessation. While axonal stress was sensitive to MAO inhibition, somatic stress was sensitive to Cav1 Ca2+ channel inhibition. Inhibiting either MAO or Cav1 Ca2+ channels after methamphetamine treatment attenuated subsequent SNc degeneration. Our results not only establish a mechanistic link between methamphetamine abuse and PD, they point to pharmacological strategies that could lessen PD risk for patients with a methamphetamine use disorder.

Dopamine D3 Receptor Modulates l-DOPA-Induced Dyskinesia by Targeting D1 Receptor-Mediated Striatal Signaling

The dopamine D3 receptor (D3R) belongs to the dopamine D2-like receptor family and is principally located in the ventral striatum. However, previous studies reported D3R overexpression in the dorsal striatum following l-DOPA treatment in parkinsonian animals. This fact has drawn attention in the importance of D3R in l-DOPA-induced dyskinesia (LID). Here, we used D3R knockout mice to assess the role of D3R in LID and rotational sensitization in the hemiparkinsonian model. Mice lacking D3R presented a reduction in dyskinesia without interfering with the antiparkinsonian l-DOPA effect and were accompanied by a reduction in the l-DOPA-induced rotations. Interestingly, deleting D3R attenuated important molecular markers in the D1R-neurons such as FosB, extracellular signal-regulated kinase, and histone-3 (H3)-activation. Colocalization studies in D1R-tomato and D2R-green fluorescent protein BAC-transgenic mice indicated that l-DOPA-induced D3R overexpression principally occurs in D1R-containing neurons although it is also present in the D2R-neurons. Moreover, D3R pharmacological blockade with PG01037 reduced dyskinesia and the molecular markers expressed in D1R-neurons. In addition, this antagonist further reduced dyskinetic symptoms in D1R heterozygous mice, indicating a direct interaction between D1R and D3R. Together, our results demonstrate that D3R modulates the development of dyskinesia by targeting D1R-mediated intracellular signaling and suggest that decreasing D3R activity may help to ameliorate LID.

Comparison of Neurotoxicity following Repeated Administration of L-Dopa, D-Dopa, and Dopamine to Embryonic Mesencephalic Dopamine Neurons in Cultures Derived from Fisher 344 and Sprague-Dawley Donors

Levodopa is the most efficacious and widely used symptomatic drug for Parkinson's disease (PD). There is currently, however, a great deal of interest focused on the possibility that levodopa-induced increases in dopamine (DA) turnover may increase oxidative damage derived from the breakdown of DA. Increased oxidative damage following levodopa may contribute to the progressive degeneration of remaining host nigral neurons as well as interfere with development and function of embryonic nigral neurons in neural grafting trials. There is abundant evidence that levodopa is toxic to embryonic nigral DA neurons in both cell culture and neural grafting models. These findings have prompted a number of studies on mechanisms of levodopa toxicity to identify effective means of ameliorating potential oxidative stress related to levodopa in PD. In the current study we have utilized cultures of embryonic nigral DA neurons to address the fundamental question of whether levodopa-induced toxicity is related to DA production or whether dopa itself contributes to cell death. We compared the degree of nigral DA cell death following chronic administration of: 1) levodopa (e.g.: l-dopa); 2) its less active stereoisomer d-dopa; and 3) DA. We examined the rank order of toxicity of these compounds in two species of rats, Fisher 344 (F344) and Sprague-Dawley (SD). Results indicate a toxicity profile of: DA > l-dopa > > d-dopa. In addition, although there was no difference in response of F344 and SD cultures to l-dopa, the SD cultures were significantly more susceptible to the neurotoxic effects of DA. Taken collectively, these results suggest that levodopa-induced toxicity is related primarily to DA production rather than oxidation of dopa to toxic metabolites, and that some strain related differences do exist.

Dopaminergic isoquinolines with hexahydrocyclopenta[ij]-isoquinolines as D2-like selective ligands

Dopamine receptors (DR) ligands are potential drug candidates for treating neurological disorders including schizophrenia or Parkinson's disease. Three series of isoquinolines: (E)-1-styryl-1,2,3,4-tetrahydroisoquinolines (series 1), 7-phenyl-1,2,3,7,8,8a-hexahydrocyclopenta[ij]-IQs (HCPIQs) (series 2) and (E)-1-(prop-1-en-1-yl)-1,2,3,4- tetrahydroisoquinolines (series 3), were prepared to determine their affinity for both D1 and D2-like DR. The effect of different substituents on the nitrogen atom (methyl or allyl), the dioxygenated function (methoxyl or catechol), the substituent at the β-position of the THIQ skeleton, and the presence or absence of the cyclopentane motif, were studied. We observed that the most active compounds in the three series (2c, 2e, 3a, 3c, 3e, 5c and 5e) possessed a high affinity for D2-like DR and these remarkable features: a catechol group in the IQ-ring and the N-substitution (methyl or allyl). The series showed the following trend to D2-RD affinity: HCPIQs > 1-styryl > 1-propenyl. Therefore, the substituent at the β-position of the THIQ and the cyclopentane ring also modulated this affinity. Among these dopaminergic isoquinolines, HCPIQs stood out for unexpected selectivity to D2-DR since the Ki D1/D2 ratio reached values of 2465, 1010 and 382 for compounds 3a, 3c and 3e, respectively. None of the most active THIQs in D2 DR displayed relevant cytotoxicity in human neutrophils and HUVEC. Finally, and in agreement with the experimental data, molecular modeling studies on DRs of the most characteristic ligands of the three series revealed stronger molecular interactions with D2 DR than with D1 DR, which further supports to the encountered enhanced selectivity to D2 DR.

Beneficial antioxidant properties of betaine against oxidative stress mediated by levodopa/benserazide in the brain of rats

The present study was designed to evaluate antioxidant effects of betaine in the brain following administration of levodopa and benserazide, which are routinely used in the treatment of Parkinson's disease. Sprague-Dawley male rats were divided into levodopa (LD), Betaine (Bet.), levodopa plus betaine (LD/Bet.), levodopa plus benserazide (LD/Ben.), levodopa plus betaine-benserazide (LD/Bet.-Ben.) and control groups. The experimental groups received LD 300 mg/kg, Bet. 1.5 % w/w of the total diet, Ben. 75 mg/kg and distilled water to controls for 10 consecutive days, orally. The concentration of plasma total homocysteine significantly increased in LD/Ben.-treated rats when compared to the other groups. Brain glutathione peroxidase (GPx) activity and glutathione content both elevated with betaine treatment in LD/Bet. and LD/Bet.-Ben groups. Superoxide dismutase activity was also higher in controls and betaine-treated rats in comparison with LD and LD/Ben. groups. Likewise, catalase activity significantly increased in control and betaine groups when compared to LD- and LD/Ben.-treated rats. In contrast, brain lipid peroxidation significantly increased in response to LD and LD/Ben.

TREATMENTS

Regarding metabolism of LD in peripheral tissues, serumic dopamine concentration significantly increased in LD-treated rats in comparison with LD/Ben. group. The present results show beneficial antioxidant and methyl donor properties of betaine versus oxidative stress and hyperhomocysteinemia induced by levodopa and benserazide in an animal model.

Exposure to mitochondrial genotoxins and dopaminergic neurodegeneration in Caenorhabditis elegans

Neurodegeneration has been correlated with mitochondrial DNA (mtDNA) damage and exposure to environmental toxins, but causation is unclear. We investigated the ability of several known environmental genotoxins and neurotoxins to cause mtDNA damage, mtDNA depletion, and neurodegeneration in Caenorhabditis elegans. We found that paraquat, cadmium chloride and aflatoxin B₁ caused more mitochondrial than nuclear DNA damage, and paraquat and aflatoxin B₁ also caused dopaminergic neurodegeneration. 6-hydroxydopamine (6-OHDA) caused similar levels of mitochondrial and nuclear DNA damage. To further test whether the neurodegeneration could be attributed to the observed mtDNA damage, C. elegans were exposed to repeated low-dose ultraviolet C radiation (UVC) that resulted in persistent mtDNA damage; this exposure also resulted in dopaminergic neurodegeneration. Damage to GABAergic neurons and pharyngeal muscle cells was not detected. We also found that fasting at the first larval stage was protective in dopaminergic neurons against 6-OHDA-induced neurodegeneration. Finally, we found that dopaminergic neurons in C. elegans are capable of regeneration after laser surgery. Our findings are consistent with a causal role for mitochondrial DNA damage in neurodegeneration, but also support non mtDNA-mediated mechanisms.

Nitric oxide synthase inhibition decreases l-DOPA-induced dyskinesia and the expression of striatal molecular markers in Pitx3(-/-) aphakia mice

Nitric oxide (NO), a gaseous messenger molecule synthesized by nitric oxide synthase (NOS), plays a pivotal role in integrating dopamine transmission in the basal ganglia and has been implicated in the pathogenesis of Parkinson disease (PD). To study the role of the nitrergic system in l-DOPA-induced dyskinesia (LID), we assessed the effect of the pharmacological manipulation of NO levels and NO/cyclic guanosine monophosphate (cGMP) signaling on LID in the Pitx3(-/-) aphakia mouse, a genetic model of PD. To evaluate the effect of decreased NO signaling on the development of LID, Pitx3(-/-) mice were chronically treated with l-DOPA and 7-nitroindazole (7-NI, a neuronal NOS inhibitor). To evaluate its effect on the expression of established LID, 7-NI was administered acutely to dyskinetic mice. The chronic 7-NI treatment attenuated the development of LID in the Pitx3(-/-) mice, and the sub-acute 7-NI treatment attenuated established dyskinesia without affecting the beneficial therapeutic effect of l-DOPA. Moreover, 7-NI significantly reduced FosB and pAcH3 expression in the acutely and chronically l-DOPA-treated mice. We also examined how increasing NO/cGMP signaling affects LID expression by acutely administering molsidomine (an NO donor) or zaprinast (a cGMP phosphodiesterase 5-PDE5 inhibitor) before l-DOPA in mice with established dyskinesia. Paradoxically, the administration of either of these drugs also significantly diminished the expression of established LID; however, the effect occurred at the expense of the antiparkinsonian l-DOPA properties. We demonstrate that targeting the NO/cGMP signaling pathway reduces dyskinetic behaviors and molecular markers, but only the 7-NI treatment preserved the antiparkinsonian effect of l-DOPA, indicating that NOS inhibitors represent a potential therapy to reduce LID.

Imaging of superoxide generation in the dopaminergic area of the brain in Parkinson's disease, using mito-TEMPO

We report a new methodology for direct visualization of superoxide production in the dopaminergic area of the brain in Parkinson's disease, based on the redox cycle of mito-TEMPO, a blood-brain barrier-, cell-, and mitochondria-penetrating nitroxide derivative with superoxide scavenging properties and T1 magnetic resonance imaging (MRI) contrast. The experiments were conducted on healthy and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. In healthy mice, the nitroxide-enhanced MRI signal was weak and short-lived (half-life ∼ 40 s; duration ∼ 80 s). The profile of the histograms indicated a high reducing activity of normal brain tissues against mito-TEMPO. In MPTP-treated mice, the nitroxide-enhanced MRI signal was strong and long-lived (half-life > 20 min; duration > 20 min), especially in the dopaminergic area of the brain. The histograms indicated a high oxidative activity in dopaminergic tissues of MPTP-treated mice. The results show directly, on intact mammals, that superoxide is a major inducer and/or mediator of neurodegenerative damage in Parkinson's disease. The high oxidative status of brain tissue in Parkinson's disease was also confirmed on isolated tissue specimens, using total reducing capacity assay and ROS/RNS assay.

3-O-demethylswertipunicoside inhibits MPP⁺-induced oxidative stress and apoptosis in PC12 cells

The 3-O-demethylswertipunicoside (3-ODS) is extracted from Swertia punicea. Recent study from our laboratory has demonstrated that the 3-ODS protects against oxidative toxicity and apoptosis in PC12 cells (Zhang, S.P., Du, X.G., Pu, X.P., 2010. Biol. Pharm. Bull. 33, 1529-1533). The aim of our study is to further investigate the neuroprotective mechanisms of 3-ODS in 1-methyl-4-phenylpyridinium (MPP(+))-induced neurotoxicity in PC12 cells. The results indicated that pre-treatment with 3-ODS significantly increased the cell viability compared with MPP(+) treatment. It also alleviated the oxidative stress by increasing superoxide dismutase (SOD) activity and decreasing malondialdehyde (MDA) level and reactive oxygen specise (ROS) production. Moreover, 3-ODS also attenuated MPP(+)-induced apoptosis by inhibiting Bax and Bcl-2 expressions, activating caspase-9, caspase-3, poly (ADP-ribose) polymerase-1 (PARP-1) cleavage, apoptosis-inducing factor (AIF) translocation and α-synuclein expression. These results suggest that 3-ODS might has applications as a complementary medicine for the treatment of Parkinson's disease (PD) or other neurodegenerative diseases.

RESP18 is involved in the cytotoxicity of dopaminergic neurotoxins in MN9D cells

RESP18 (Regulated endocrine-specific protein, 18 kDa) was first identified as a dopaminergic drugs-regulated intermediate pituitary transcript. RESP18 protein is a unique endoplasmic reticulum (ER) resident protein. Its functions in the brain especially in the nervous system disorders remain unknown. ER stress (ERS) has been proved to be one of the important pathogenesis of neurodegenerative diseases, including Parkinson's disease (PD). Here, we explored the association of RESP18 and ERS in cell models of PD. Dopaminergic neurotoxin 1-methyl-4-phenyl-pyridinium ion (MPP⁺), 6-hydroxydopamine (6-OHDA), and rotenone evoked dramatic MN9D cell death. The transcriptional expressions of RESP18 and two ERS markers--binding immunoglobulin protein/glucose-regulated protein 78 (BiP/GRP78) and CCAAT/enhancer-binding protein homologous protein (CHOP) manifested differential changes in MN9D cells treated with MPP⁺, 6-OHDA, and rotenone. The RESP18 protein levels increased in MPP⁺ and 6-OHDA-treated cells, but did not change in the cells treated with rotenone, while the protein levels of ER molecular chaperone heat shock protein 90 kDa beta member 1/glucose-regulated protein 94 (HSP90B1/GRP94) and BiP in the cells were up-regulated by MPP⁺ and 6-OHDA, respectively. Salubrinal, an ERS inhibitor, significantly reduced MPP⁺ and 6-OHDA-induced cell death. Moreover, ERS inducer--thapsigargin and tunicamycin, decreased the expression of RESP18, which is different from the changes of BiP, GRP94, and CHOP. Silencing RESP18 expression with Lenti-shRNA alleviated MPP⁺-induced cell death, while over-expression of RESP18 resulted in aggravated cell death induced by MPP⁺ and 6-OHDA. Taken together, our results suggest that RESP18 is involved in the cytotoxicity of dopaminergic neurotoxins.

The effect of adenosine A(2A) receptor antagonists on hydroxyl radical, dopamine, and glutamate in the striatum of rats with altered function of VMAT2

It has been shown that a decreased vesicular monoamine transporter (VMAT2) function and the disruption of dopamine (DA) storage is an early contributor to oxidative damage of dopamine neurons in Parkinson's disease (PD). In our previous study, we demonstrated that adenosine A(2A) receptor antagonists suppressed oxidative stress in 6-hydroxydopamine-treated rats suggesting that this effect may account for neuroprotective properties of drugs. In the present study, rats were injected with reserpine (10 mg/kg sc) and 18 h later the effect of the adenosine A(2A) receptor antagonists 8-(3-chlorostyryl)caffeine (CSC) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) on extracellular DA, glutamate and hydroxyl radical formation was studied in the rat striatum using in vivo microdialysis. By disrupting VMAT2 function, reserpine depleted DA stores, and increased glutamate and hydroxyl radical levels in the rat striatum. CSC (1 mg/kg) but not ZM 241385 (3 mg/kg) increased extracellular DA level and production of hydroxyl radical in reserpinised rats. Both antagonists decreased the reserpine-induced increase in extracellular glutamate. L-3,4-Dihydroxyphenylalanine (L-DOPA) (25 mg/kg) significantly enhanced extracellular DA, had no effect on reserpine-induced hydroxyl radical production and decreased extracellular glutamate concentration. CSC but not ZM 241385 given jointly with L-DOPA increased the effect of L-DOPA on extracellular DA and augmented the reserpine-induced hydroxyl radical production. CSC and ZM 241385 did not influence extracellular glutamate level, which was decreased by L-DOPA. It seems that by decreasing the MAO-dependent DA metabolism rate, CSC raised cytosolic DA and by DA autoxidation, it induced hydroxyl radical overproduction. Thus, the methylxanthine A(2A) receptor antagonists bearing properties of MAO-B inhibitor, like CSC, may cause a risk of oxidative stress resulting from dysfunctional DA storage mechanism in early PD.

The TrkB-positive dopaminergic neurons are less sensitive to MPTP insult in the substantia nigra of adult C57/BL mice

Tyrosine kinase receptors TrkB and TrkC mediate neuroprotective effects of the brain-derived neurotrophic factor (BDNF) and neurotrophins in the dopaminergic nigro-striatal system, but it is obscure about their responses or expression changes in the injured substantia nigra under Parkinson's disease. In present study, immunofluorescence, Fluoro-Jade staining and laser scanning confocal microscopy were applied to investigate distribution and changes of TrkB and TrkC in the dopamine neurons of the substantia nigra by comparison of control and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. It revealed that TrkB and TrkC-immunoreactivities were substantially localized in cytoplasm and cell membrane of the substantia nigra neurons of control adults. While neurons double-labeled with tyrosine hydroxylase (TH)/TrkB, or TH/TrkC were distributed in a large numbers in the substantia nigra of controls, they apparently went down at 36.2-65.7% of normal level, respectively following MPTP insult. In MPTP model, cell apoptosis or degeneration of nigral neurons were confirmed by caspase-3 and Fluoro-Jade staining. More interestingly, TH/TrkB-positive neurons survived more in cell numbers in comparison with that of TH/TrkC-positive ones in the MPTP model. This study has indicated that TrkB-containing dopamine neurons are less sensitive in the substantia nigra of MPTP mouse model, suggesting that specific organization of Trks may be involved in neuronal vulnerability to MPTP insult, and BDNF-TrkB signaling may play more important role in protecting dopamine neurons and exhibit therapeutic potential for Parkinson's disease.

The effects of salsolinol on the mucosal mast cells in the rat gut

Mast cells in the gastrointestinal tract have been found in close spatial contact with the regulatory cells of gastrointestinal motility: interstitial cells of Cajal (ICC) and myenteric neurons, suggesting their functional interaction. Because of the regulatory role of mast cells even the slight damage or change in activity of these cells may cause considerable disorder of the gut motility. The catechol isoquinoline derivatives are endogenous compounds present in the mammalian brain and the representative one is referred to as salsolinol. Increased salsolinol levels are detected in the cerebrospinal fluid of Parkinson's disease patients. Gastrointestinal dysmotility in those patients has been associated with peripheral action of salsolinol. The aim of this study was to evaluate effects of exogenous salsolinol on mast cells in the gastrointestinal tract of rats. Male Wistar rats (n = 8) were injected intraperitoneally with salsolinol (50 mg/kg/day) for 3 weeks and the equal group served as a control. On the last day the animals were sacrificed, stomachs, small and large intestines were removed, and paraffin embedded specimens were prepared. Slides were toluidine blue stained and the total number and percentage of degranulated mast cells in gastric antral, duodenal and ascending colon wall were assessed by image analysis. The number of mast cells in the gastrointestinal wall was decreased in the salsolinol group compared to the control--in the stomach 98.7 +/- 53.3 vs. 156.7 +/- 45.8, in the duodenum 2.6 +/- 2.1 vs. 7.83 +/- 7.8 and in colon 12.8 +/- 14 vs. 10.7 +/- 17.1 (salsolinol treated vs. control group). Carried out examinations showed the destructive action of salsolinol on the mast cells in all segments examined of gastrointestinal tract.

The sigma-1 antagonist BMY-14802 inhibits L-DOPA-induced abnormal involuntary movements by a WAY-100635-sensitive mechanism

RATIONALE

Levodopa (L-DOPA), the gold standard treatment for Parkinson's disease (PD), eventually causes L-DOPA-induced dyskinesia (LID) in up to 80% of patients. In the 6-hydroxydopamine (6-OHDA) rat model of PD, L-DOPA induces a similar phenomenon, which has been termed abnormal involuntary movement (AIM). We previously demonstrated that BMY-14802 suppresses AIM expression in this model.

OBJECTIVES

Although BMY-14802 is widely used as a sigma-1 antagonist, it is also an agonist at serotonin (5-HT) 1A and adrenergic alpha-1 receptors. The current study was conducted to determine which of these mechanisms underlies BMY-14802's AIM-suppressing effect. This characterization included testing the 5-HT1A agonist buspirone and multiple sigma agents. When these studies implicated a 5-HT1A mechanism, we subsequently undertook a pharmacological reversal study, evaluating whether the 5-HT1A antagonist WAY-100635 counteracted BMY-14802's AIM-suppressing effects.

RESULTS

Buspirone dose-dependently suppressed AIM, supporting past findings. However, no AIM-suppressing effects were produced by drugs with effects at sigma receptors, including BD-1047, finasteride, SM-21, DTG, trans-dehydroandrosterone (DHEA), carbetapentane, and opipramol. Finally, we show for the first time that the AIM-suppressing effect of BMY-14802 was dose-dependently prevented by WAY-100635 but not by the alpha-1 antagonist prazosin.

CONCLUSIONS

BMY-14802 exerts its AIM-suppressing effects via a 5-HT1A agonist mechanism, similar to buspirone. Other 5-HT1A agonists have failed clinical trials, possibly due to submicromolar affinity at other receptors, including D2, which may exacerbate PD symptoms. BMY-14802 is a promising candidate for clinical trials due to its extremely low affinity for the D2 receptor and lack of extrapyramidal effects during prior clinical trials for schizophrenia.

Effects of intranasally applied dopamine on behavioral asymmetries in rats with unilateral 6-hydroxydopamine lesions of the nigro-striatal tract

Due to its lipophobic properties, dopamine is unable to cross the blood-brain barrier following systemic application. However, recently it has been demonstrated that, when applied directly via the nasal passages in the rat, dopamine exerts neurochemical and behavioural action, including increases of dopamine in striatal subregions, antidepressive-like action, and increased behavioral activity. These effects could potentially be mediated by exogenous dopamine acting as a direct agonist at postsynaptic dopamine receptors. However, it is also possible that intranasally applied dopamine acts indirectly via the modulation of the activity of dopaminergic cell bodies. To approach this question, the present study used rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal tract, as these lesions lead to pharmacologically stimulated behavioural asymmetries which are specific for direct and indirect dopamine agonists. We found that 7 days of repeated treatment with intranasal dopamine induced a sensitization of the turning response to amphetamine, but not to apomorphine. Furthermore, intranasal dopamine dose-dependently increased the use of the forepaw ipsilateral to the 6-OHDA-lesioned side of the brain. These results suggest that intranasally administered dopamine acts via an indirect mechanism of action, putatively by increasing the release of endogenous dopamine in the brain.

PACAP38 increases vesicular monoamine transporter 2 (VMAT2) expression and attenuates methamphetamine toxicity

Pituitary adenylyl cyclase activating polypeptide, 38 amino acids (PACAP38) is a brain-gut peptide with diverse physiological functions and is neuroprotective in several models of neurological disease. In this study, we show that systemic administration of PACAP38, which is transported across the blood-brain barrier, greatly reduces the neurotoxicity of methamphetamine (METH). Mice treated with PACAP38 exhibited an attenuation of striatal dopamine loss after METH exposure as well as greatly reduced markers of oxidative stress. PACAP38 treatment also prevented striatal neuroinflammation after METH administration as measured by overexpression of glial fibrillary acidic protein (GFAP), an indicator of astrogliosis, and glucose transporter 5 (GLUT5), a marker of microgliosis. In PACAP38 treated mice, the observed protective effects were not due to an altered thermal response to METH. Since the mice were not challenged with METH until 28 days after PACAP38 treatment, this suggests the neuroprotective effects are mediated by regulation of gene expression. At the time of METH administration, PACAP38 treated animals exhibited a preferential increase in the expression and function of the vesicular monoamine transporter (VMAT2). Genetic reduction of VMAT2 has been shown to increase the neurotoxicity of METH, thus we propose that the increased expression of VMAT2 may underlie the protective actions of PACAP38 against METH. The ability of PACAP38 to increase VMAT2 expression suggests that PACAP38 signaling pathways may constitute a novel therapeutic approach to treat and prevent disorders of dopamine storage.

Globus pallidus plays a critical role in neurotrophic factor induced functional improvements in hemiparkinsonian monkeys

This study was designed to test the hypothesis that the integrity of the globus pallidus (GP) is critical for neurotrophic factor, such as glial-derived neurotrophic factor (GDNF), induced functional changes in rhesus macaques with MPTP-induced parkinsonism, because our previous studies demonstrated that the GP was one of the most affected areas as assessed by the levels of dopamine (DA) and its metabolites. A group of eight hemiparkinsonian monkeys with pallidal lesions, which positively responsed to intraventricular (ICV) injections of GDNF prior to the lesions, and a group of eight hemiparkinsonian monkeys without pallidal lesions, were treated with GDNF after a long washout period after the initial ICV infusions of GDNF. Significant behavioral improvements were only seen in the monkeys without pallidal lesions that received GDNF. Monkeys with pallidal lesions failed to exhibit any behavioral improvement even though they had elevated nigral DA levels. The results suggest that the GP is critical for neurotrophic factor induced functional changes in PD monkeys.

Protective effects of metallothionein against dopamine quinone-induced dopaminergic neurotoxicity

Dopamine (DA) quinone as DA neuron-specific oxidative stress conjugates with cysteine residues in functional proteins to form quinoproteins. Here, we examined the effects of cysteine-rich metal-binding proteins, metallothionein (MT)-1 and -2, on DA quinone-induced neurotoxicity. MT quenched DA semiquinones in vitro. In dopaminergic cells, DA exposure increased quinoproteins and decreased cell viability; these were ameliorated by pretreatment with MT-inducer zinc. Repeated L-DOPA administration markedly elevated striatal quinoprotein levels and reduced the DA nerve terminals specifically on the lesioned side in MT-knockout parkinsonian mice, but not in wild-type mice. Our results suggested that intrinsic MT protects against L-DOPA-induced DA quinone neurotoxicity in parkinsonian mice by its quinone-quenching property.

Gene expression profiling of MPP+-treated MN9D cells: A mechanism of toxicity study

Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of midbrain dopaminergic neurons with unknown etiology. MPP+ (1-methyl-4-phenylpyridinium) is the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces Parkinson's-like syndromes in humans and animals. MPTP/MPP+ treatment produces selective dopaminergic neuronal degeneration, therefore, these agents are commonly used to study the pathogenesis of PD. However, the mechanisms of their toxicity have not been elucidated. In order to gain insights into MPP+-induced neurotoxicity, a gene expression microarray study was performed using a midbrain-derived dopaminergic neuronal cell line, MN9D. Utilizing a two-color reference design, Agilent mouse oligonucleotide microarrays were used to examine relative gene expression changes in MN9D cells treated with 40microM MPP+ compared with controls. Bioinformatics tools were used for data evaluation. Briefly, raw data were imported into the NCTR ArrayTrack database, normalized using a Lowess method and data quality was assessed. The Student's t-test was used to determine significant changes in gene expression (set as p<0.05, fold change >1.5). Gene Ontology for Function Analysis (GOFFA) and Ingenuity Pathway Analysis were employed to analyze the functions and roles of significant genes in biological processes. Of the 51 significant genes identified, 44 were present in the GOFFA or Ingenuity database. These data indicate that multiple pathways are involved in the underlying mechanisms of MPP+-induced neurotoxicity, including apoptosis, oxidative stress, iron binding, cellular metabolism, and signal transduction. These data also indicate that MPP+-induced toxicity shares common molecular mechanisms with the pathogenesis of PD and further pathway analyses will be conducted to explore these mechanisms.

Pharmacological inhibition of neuronal NADPH oxidase protects against 1-methyl-4-phenylpyridinium (MPP+)-induced oxidative stress and apoptosis in mesencephalic dopaminergic neuronal cells

Oxidative stress is widely recognized as a key mediator of degenerative processes in Parkinson's disease (PD). Recently, we demonstrated that the dopaminergic toxin MPP+ initiates oxidative stress to cause caspase-3-dependent apoptotic cell death in mesencephalic dopaminergic neuronal (N27) cells. In this study, we determined the source of reactive oxygen species (ROS) produced during MPP+-induced apoptotic cell death. In addition to mitochondria, plasma membrane NADPH oxidase is considered a major producer of ROS inside the cell. Here, we show that N27 neuronal cells express key NADPH oxidase subunits gp91phox and p67phox. We used structurally diverse NADPH oxidase inhibitors, aminoethyl-benzenesulfonylfluoride (AEBSF, 100-1000microM), apocynin (100-1000microM), and diphenylene iodonium (DPI, 3-30microM), to inhibit intrinsic NADPH oxidase activity in N27 cells. Flow cytometric analysis using the ROS-sensitive dye hydroethidine revealed that AEBSF blocked 300microM MPP+-induced ROS production for over 45min in N27 cells, in a dose-dependent manner. Further treatment with DPI, apocynin, and SOD also blocked MPP+-induced ROS production. In Sytox cell death assays, co-treatment with AEBSF, apocynin, or DPI for 24h significantly suppressed MPP+-induced cytotoxic cell death. Similarly, co-treatment with these inhibitors also significantly attenuated MPP+-induced increases in caspase-3 enzymatic activity. Furthermore, quantitative DNA fragmentation ELISA assays revealed that AEBSF, DPI, and apocynin rescue N27 cells from MPP+-induced apoptotic cell death. Together, these results indicate for the first time that intracellular ROS generated by NAPDH oxidase are present within the mesencephalic neuronal cells, and are a key determinant of MPP+-mediated dopaminergic degeneration in in vitro models of dopaminergic degeneration. This study supports a critical role of NADPH oxidase in the oxidative damage in PD; targeting this enzyme may lead to novel therapies for PD.

Glutathione prevented dopamine-induced apoptosis of melanocytes and its signaling

BACKGROUND

Dopamine (DA), a monoamine neurotransmitter, is a well-known neurotoxin and plays an etiologic role in neurodegenerative disorders such as Parkinson's disease. DA exerts its toxic effect by generation of reactive oxygen species and quinone product. Vitiligo, a depigmentary disorder of the skin and hair characterized by selective destruction of melanocytes, has been reported to show increased levels of DA with onset and progression of the disease.

OBJECTIVE

The aim of this study is to investigate the cytotoxic effect of DA on melanocytes and to search for protective antioxidants against DA-induced toxicity. In addition, molecular mechanism of cell death was also investigated.

METHODS

Cells were treated with DA and cell viabilities were measured by crystal violet staining method. To investigate the cytoprotective activity of various antioxidants, vitamin C, vitamin E, Trolox, quercetin, N-acetylcysteine (NAC) and l-glutathione (GSH) were used. To study cytoprotective effects of NAC and GSH, Mel-Ab cells and cultured normal human melanocytes were pretreated with NAC or GSH, then DA solution was added. DA-induced apoptosis and activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) were also observed by flow cytometric analysis and Western blotting.

RESULTS

The viability of DA-treated Mel-Ab cells significantly decreased in a dose-dependent manner while keratinocytes were much more resistant to DA-toxicity, which was a consistent finding with the selective melanocyte loss observed in vitiligo. Among various antioxidants used in this study, only thiol-containing antioxidants such as NAC or GSH inhibited both JNK and p38 MAPK activation and apoptosis, indicating the unique protective capacity of thiol compounds. Cultured normal human melanocytes were also susceptible to DA and thiol compounds were very efficiently protective against DA-induced cytotoxicity.

CONCLUSION

DA-induced apoptosis and cytoprotective effect of thiol compounds shown in this study could be a clue to understand pathogenesis of viltigo and provide a new therapeutic strategy.

The partial 5-HT1A agonist buspirone reduces the expression and development of l-DOPA-induced dyskinesia in rats and improves l-DOPA efficacy

Dopamine (DA) replacement therapy with l-DOPA remains the standard pharmacotherapy for Parkinson's disease (PD). Unfortunately, chronic l-DOPA treatment is accompanied by development of motor fluctuations and l-DOPA-induced dyskinesia (LID). While serotonin (5-HT)(1A) agonists acutely reduce these complications, their prophylactic and long-term effects are not well-delineated. To test this, male Sprague-Dawley rats received unilateral 6-hydroxydopamine (6-OHDA) lesions. In experiment 1, l-DOPA-primed rats were pre-treated with Vehicle (0.9% NaCl), various doses of the partial 5-HT(1A) agonist, buspirone (0.25, 1.0 or 2.5 mg/kg, ip) or buspirone (2.5 mg/kg, ip)+the 5-HT(1A) antagonist, WAY100635 (0.5 mg/kg, ip) 5 min prior to l-DOPA (12 mg/kg+15 mg/kg benserazide, ip). Rats were tested for LID using the abnormal involuntary movements (AIMs) scale and motor performance using the forepaw adjusting steps test (FAS). In experiment 2, l-DOPA-naïve rats received co-administration of l-DOPA+buspirone (1.0 or 2.5 mg/kg, ip) for 2 weeks. AIMs and FAS were measured throughout. In l-DOPA-primed rats, buspirone dose-dependently reduced LID and improved l-DOPA-related motor performance due to action at the 5-HT(1A) receptor. In l-DOPA-naïve rats, buspirone delayed LID development while improving l-DOPA's anti-parkinsonian efficacy indicating the potential long-term benefits of 5-HT(1A) agonists for reduction of l-DOPA-related side effects.

Neurotoxic effects of chronic restraint stress in the striatum of methamphetamine-exposed rats

RATIONALE

Stress is a common experience in drug abusers. Methamphetamine (METH) is an abused psychostimulant that damages dopamine and serotonin terminals through pro-oxidant mechanisms and glutamate-mediated excitotoxicity. Both METH and stress increase dopamine and glutamate release in the striatum. Since dopamine inhibits striatal glutamate release and METH depletes dopamine, stress-induced glutamate release may be disinhibited after METH exposure.

OBJECTIVE

We examined if repeated stress would worsen excitotoxic damage to the striatum after METH pretreatment.

MATERIALS AND METHODS

In vivo microdialysis was used to examine stress-induced striatal glutamate release in rats pre-exposed to METH (7.5 mg/kg x 4 injections) or saline. The effects on striatal DA, serotonin, DAT, SERT, and spectrin proteolysis produced by chronic restraint stress (CRS, 6 h/day for 21 days) in the presence or absence of corticosterone synthesis inhibition by metyrapone (50 mg/kg) beginning 7 days after METH were also examined.

RESULTS

Stress-induced glutamate release was augmented in rats pre-exposed to METH. CRS 7 days after METH enhanced METH-induced DAT depletions from 23 to 44% in the nonstressed versus stressed rats, respectively. Striatal SERT and serotonin tissue content were decreased by 51 and 36%, respectively, in rats exposed to both METH and CRS but was unchanged by either treatment alone. Spectrin proteolysis was increased by 53% in rats treated with both METH and CRS but was unaffected by either treatment alone. Metyrapone blocked the effects of CRS on METH-induced depletions of SERT but not DAT.

CONCLUSIONS

Exposure to chronic stress depleted striatal dopamine and serotonin terminal markers possibly through excitotoxic mechanisms in METH-treated rats.

Lamotrigine is neuroprotective in the energy deficiency model of MPTP intoxicated mice

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) inhibits the mitochondrial complex I of the respiratory chain. This results in ATP and ion homeostasis disturbances, which lead to selective death of the substantia nigra dopaminergic neurons. Well known as a Parkinson's disease model, the MPTP animal model also provides a potential paradigm of the energy deficiencies found in childhood. In these conditions, anticonvulsants may provide neuroprotection by limiting cellular energy consumption. We tested valproate, topiramate and lamotrigine in the MPTP mouse model. Dopamine transporter (DAT) density was assessed by quantitative autoradiography, tyrosine hydroxylase (TH) was evaluated by immunohistochemistry and dopamine (DA) levels by HPLC-ED whereas neuronal apoptosis was monitored through active caspase-3. Expectedly, the DAT density, TH immunoreactive neurons and DA content in the MPTP group were respectively reduced to 51%, 40% and 26% versus control animals. Unlike valproate and topiramate, lamotrigine provided a significant neuroprotection against MPTP in maintaining these levels at 99%, 74% and 58% respectively and reducing the induced apoptosis. Altogether, the data indicate that lamotrigine limits dopaminergic neuronal death in the substantia nigra and promotes striatal dendrites sprouting. Lamotrigine, a widely used and well-tolerated molecule in young patients, could represent a valuable adjuvant therapy in various energy deficiency conditions during childhood.

Attenuation of methamphetamine-induced nigrostriatal dopaminergic neurotoxicity in mice by lipopolysaccharide pretreatment

Immunological activation has been proposed to play a role in methamphetamine-induced dopaminergic terminal damage. In this study, we examined the roles of lipopolysaccharide, a pro-inflammatory and inflammatory factor, treatment in modulating the methamphetamine-induced nigrostriatal dopamine neurotoxicity. Lipopolysaccharide pretreatment did not affect the basal body temperature or methamphetamine-elicited hyperthermia three days later. Such systemic lipopolysaccharide treatment mitigated methamphetamine-induced striatal dopamine and 3,4-dihydroxyphenylacetic acid depletions in a dose-dependent manner. As the most potent dose (1 mg/kg) of lipopolysaccharide was administered two weeks, one day before or after the methamphetamine dosing regimen, methamphetamine-induced striatal dopamine and 3,4-dihydroxyphenylacetic acid depletions remained unaltered. Moreover, systemic lipopolysaccharide pretreatment (1 mg/kg) attenuated local methamphetamine infusion-produced dopamine and 3,4-dihydroxyphenylacetic acid depletions in the striatum, indicating that the protective effect of lipopolysaccharide is less likely due to interrupted peripheral distribution or metabolism of methamphetamine. We concluded a critical time window for systemic lipopolysaccharide pretreatment in exerting effective protection against methamphetamine-induced nigrostriatal dopamine neurotoxicity.

Attenuation of 1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine induced nigrostriatal toxicity in mice by N-acetyl cysteine

The present study was designed to investigate the effects of N-acetyl cysteine (NAC), an antioxidant on 1-methyl 4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) induced neurotoxicity in the nigrostriatal dopaminergic system of mice. MPTP treatment caused 80% decrease of the dopamine levels in the striatum of C57BL/ 6J mice. A marked increase in the extent of lipid peroxidation, superoxide dismutase (SOD) and g-glutamyl transpeptidase (g-GTP) was seen, while a significant decrease in the levels of glutathione (GSH), total thiols and glutathione peroxidase (GPx) activity was observed in the substantia nigra pars compacta (SNpc) of MPTP treated animals. As compared to control animals, Co-administration of NAC with MPTP restored the depleted dopamine, GSH, total tissue thiol levels and GPx activity in SNpc of treated mice brain. Moreover, NAC treatment also provided protection against lipid peroxidation and superoxide dismutase activity. The results of present study suggested that NAC attenuates MPTP neurotoxicity in mice brain and this protection by the NAC might be contributing to the regeneration of GSH, a major antioxidant.

Anaerobic glycolysis protection against 1-methy-4-phenylpyridinium (MPP+) toxicity in C6 glioma cells

The neurotoxin 1-methy-4-phenylpyridinium (MPP(+)) is used for its' capacity to induce Parkinsonism through its inhibitory effects on mitochondrial complex I. This inhibition disrupts cellular energy formation and aerobic glycolysis. The objective of this study was to demonstrate that the toxic effect of mitochondrial aerobic pathway inhibition with MPP(+ )can be reduced by stimulating anaerobic glycolysis using glucose supplementation. In this study, C6 Glioma cell viability was examined in the presence of different concentrations of MPP alone and with the addition of glucose. The results obtained indicate that there was a significant increase (P < 0.001) in cell viability in cells treated with glucose and MPP(+ )verses cells treated with MPP(+ )alone. Fluorometric analysis using 100 microM Rhodamine 123 indicated mitochondrial membrane potential was not restored in MPP(+ )treated cells with glucose; however, normal cell viability was confirmed using 2 microg/ml Fluorescein diacetate. This dual fluorescence indicated mitochondrial damage from MPP(+ )while glucose augmented cell survival. Further confirmation of cell survival upon damage to the mitochondria was evident in TUNEL staining. Positive staining was prominent only in MPP(+) treatment groups alone, while control and co-treated groups exhibited little to no TUNEL staining. ATP measurements of all MPP(+) treated groups exhibited a significant (P < 0.001) decrease verses control. Groups co-treated with MPP(+ )and glucose revealed a significant increase (250 microM group: P < 0.001) in ATP. It was concluded from this study that glucose supplementation was able to sustain cellular viability and ATP production through anaerobic glycolysis despite the inhibitory effect of MPP(+ )on aerobic glycolysis.

Impairment in consolidation of learned place preference following dopaminergic neurotoxicity in mice is ameliorated by N-acetylcysteine but not D1 and D2 dopamine receptor agonists

Some of the major concerns related to methamphetamine (METH) abuse are the neuronal damage inflicted at dopamine (DA) nerve terminals and the cognitive deficits observed in human METH abusers. We have shown that a high dose of METH selectively depleted dopaminergic markers in striatum, frontal cortex and amygdala of Swiss Webster mice, and impaired learned place preference. In this study, we investigated whether deficits in consolidation of place learning, as a consequence of METH neurotoxicity, underlie the underperformance of cocaine conditioned place preference (CPP). Administration of METH (5 mg/kg x 3) to Swiss Webster mice decreased striatal tyrosine hydroxylase (TH) immunoreactive neurons and significantly increased glial fibrillary acidic protein (GFAP) expression, confirming the neurotoxic potential of METH in mice. This treatment significantly attenuated the establishment of cocaine (15 mg/kg) CPP compared to control. To investigate whether manipulation of the consolidation phase improves learned place preference, mice were trained by cocaine and received daily post-training injections of DA receptor agonists or N-acetylcysteine (NAC). As memory consolidation occurs shortly after training, drugs were administered either immediately or 2 h post-training. Immediate post-training administration of the D1 DA receptor agonist SKF38393 (5, 10, and 20 mg/kg) or the D2 DA receptor agonist quinpirole (0.25, 0.5, and 1.0 mg/kg) did not improve the establishment of CPP following METH neurotoxicity. However, immediate but not delayed NAC administration (50 and 100 mg/kg) enhanced cocaine CPP following METH neurotoxicity and had no effect on control CPP. The levels of the reduced form of glutathione (GSH) in striatum, amygdala, hippocampus and frontal cortex were significantly lower in METH-treated mice compared to control during the period of CPP training. Acute and repeated administration of NAC to METH-treated mice restored the decreased brain GSH but had no effect on controls. Results suggest that METH-induced dopaminergic neurotoxicity is associated with impairment of consolidation of learned place preference, and that this impairment is improved by immediate post-training administration of the glutathione precursor NAC and not by D1 or D2 DA receptor agonists. Restoration of brain glutathione levels immediately post-training may facilitate the consolidation process.

Biphasic mechanism of the toxicity induced by 1-methyl-4-phenylpyridinium ion (MPP+) as revealed by dynamic changes in glucose metabolism in rat brain slices

1-Methyl-4-phenylpyridinium (MPP+) is a well-known neurotoxin which causes a clinical syndrome similar to Parkinson's disease. The classical mechanism of MPP+ toxicity involves its entry into cells through the dopamine transporter (DAT) to inhibit aerobic glucose metabolism, while recent studies suggest that an oxidative mechanism may contribute to the toxicity of MPP+. However, it has not been adequately determined what role these two mechanisms play in the development of neurotoxicity after MPP+ loading in the brain. To clarify this issue, MPP+ was added directly to fresh rat brain slices and the dynamic changes in the cerebral glucose metabolic rate (CMRglc) produced by MPP+ were serially and two-dimensionally measured using the dynamic positron autoradiography technique with [(18)F]2-fluoro-2-deoxy-D-glucose as a tracer. MPP+ dose-dependently increased CMRglc in each of the brain regions examined, reflecting enhanced glycolysis compensating for the decrease in aerobic metabolism. Treatment with DAT inhibitor GBR 12909 significantly attenuated the enhanced glycolysis induced by 10 microM MPP+ in the striatum. Treatment with free radical spin trap alpha-phenyl-N-tert-butylnitrone (PBN) significantly attenuated the enhancement of glycolysis induced by 100 microM MPP+ in all brain regions. These results suggest that the mechanism of the toxicity of MPP+ is biphasic and consists of a DAT-mediated mechanism selective for dopaminergic regions at a lower concentration of MPP+ (10 microM), and an oxidative mechanism that occurs at a higher concentration of MPP+ (100 microM) and is not restricted to dopaminergic regions.

How reliable is the behavioural evaluation of dyskinesia in animal models of Parkinson's disease?

In spite of the current availability of several pharmacological therapies for the treatment of Parkinson's disease, side effects are invariably manifested during long-term treatment. Dyskinesia, wearing-off and on-off are among the most disabling side effects produced by the dopamine precursor L-dihydroxyphenylalanine and, to a lesser degree, by other pharmacological treatments based on dopamine receptor agonism. Evaluation of the side effects, in particular dyskinesia, produced by antiparkinsonian drug treatments, therefore represents a critical issue in drug validation prior to a clinical trial. Moreover, a reliable model of dyskinesia is a fundamental requirement for the study of the as yet unknown mechanisms at the basis of this severely disabling side effect. The present review aims to provide a critical evaluation of the validity, reliability and utility of animal models of dyskinesia. In the first part of this review, we present a brief overview of the different models of Parkinson's disease focusing on those utilized for the evaluation of dyskinetic movements, then proceed to critically examine the turning behaviour model in an attempt to assess the way in which it has influenced the evaluation of drugs utilized in the treatment of Parkinson's disease. Subsequently, the various models of dyskinesia are reviewed and conclusions are drawn as to how the environment in which experiments are performed can influence the behaviour observed.

Calcitriol protects against the dopamine- and serotonin-depleting effects of neurotoxic doses of methamphetamine

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in brain dopamine (DA) and serotonin (5-HT) content. Calcitriol, the active metabolite of vitamin D, has potent effects on brain cells, both in vitro and in vivo, including the ability to upregulate trophic factors and protect against various lesions. The present experiments were designed to examine the ability of calcitriol to protect against METH-induced reductions in striatal and nucleus accumbens levels of DA and 5-HT. Male Fischer-344 rats were administered vehicle or calcitriol (1 microg/kg, s.c.) once a day for eight consecutive days. After the seventh day of treatment the animals were given METH (5 mg/kg, s.c.) or saline four times in 1 day at 2-h intervals. Seven days later the striata and accumbens were harvested from the animals for high-performance liquid chromatography (HPLC) analysis of monoamines and metabolites. In animals treated with vehicle and METH, there were significant reductions in DA, 5-HT, and their metabolites in both the striatum and accumbens. In animals treated with calcitriol and METH, the magnitude of the METH-induced reductions in DA, 5-HT, and metabolites was substantially and significantly attenuated. The calcitriol treatments did not reduce the hyperthermia associated with multiple injections of METH, indicating that the neuroprotective effects of calcitriol are not due to the prevention of increases in body temperature. These results suggest that calcitriol can provide significant protection against the DA- and 5-HT-depleting effects of neurotoxic doses of METH.

Methamphetamine-induced selective dopaminergic neurotoxicity is accompanied by an increase in striatal nitrate in the mouse

Exposure to high doses of methamphetamine (METH), a major drug of abuse, may cause neuronal damage. Previous studies have implicated the role of peroxynitrite, produced by nitric oxide (NO) and reactive oxygen species, in dopaminergic neurotoxicity produced by METH in mice. The present article was undertaken to investigate if a neurotoxic regimen of METH is associated with changes in tissue levels of nitrate and nitrite, which are the stable products of NO. Administration of METH (5 mg/kg x 3) to Swiss Webster mice resulted in marked depletion of dopamine (DA) and DA transporter (DAT) binding sites but no change in 5-hydroxytryptamine (5-HT) and 5-HT transporter (5-HTT) binding sites in the striatum, amygdala, frontal cortex, and hippocampus, suggesting that METH causes selective neurotoxicity to DA nerve terminals. The concentration of nitrate in the striatum was increased by about two-fold after METH administration; however, no changes in nitrate concentration were detected in other brain regions that endured dopaminergic neurotoxicity. These findings suggest that (a) a neurotoxic regimen of METH produces selective increase in NO in the striatum, which may generate toxic species such as peroxynitrite, and (b) toxins other than NO-related derivatives may mediate dopaminergic neurotoxicity in the amygdala and frontal cortex.

Fluoxetine as a potential pharmacotherapy for methamphetamine dependence: studies in mice

The monoamine transporters are the main targets of psychostimulant drugs, including methamphetamine (METH) and cocaine. Interestingly, the rewarding effects of cocaine are retained in dopamine transporter (DAT) knockout (KO) mice, while serotonin transporter (SERT) and DAT double KO mice do not exhibit conditioned place preference (CPP) to cocaine. These data suggest that SERT inhibition decreases the rewarding effects of psychostimulants. To further test this hypothesis, in the present study, we investigated the effects of intraperitoneal (i.p.) injections of 20 mg/kg fluoxetine, a selective serotonin reuptake inhibitor (SSRI), on 2 mg/kg METH (i.p.) CPP and locomotor sensitization to 1 mg/kg METH (i.p.) in C57BL/6J mice. Fluoxetine treatment before both the conditioning and preference tests abolished METH CPP. A two-way analysis of variance (ANOVA) revealed that METH CPP tended to be lower in mice pretreated with fluoxetine before the preference test than in control mice pretreated with saline before the preference test. Furthermore, pretreatment with fluoxetine had inhibitory effects on METH-induced locomotor sensitization. These results suggest that fluoxetine, a widely used medication for depression, may be also a useful tool for treating METH dependence.

Fine ultrastructure and biochemistry of PC12 cells: a comparative approach to understand neurotoxicity

The PC12 cell line is commonly used as a tool to understand the biochemical mechanisms underlying the physiology and degeneration of central dopamine neurons. Despite the broad use of this cell line, there are a number of points differing between PC12 cells and dopamine neurons in vivo which are missed out when translating in vitro data into in vivo systems. This led us to compare the PC12 cells with central dopamine neurons, aiming at those features which are predictors of in vivo physiology and degeneration of central dopamine neurons. We carried out this comparison, either in baseline conditions, following releasing or neurotoxic stimuli (i.e. acute or chronic methamphetamine), to end up with therapeutic agents which are suspected to produce neurotoxicity (l-DOPA). Although the neurotransmitter pattern of PC12 cells is close to dopamine neurons, ultrastructural morphometry demonstrates that, in baseline conditions, PC12 cells possess very low vesicles density, which parallels low catecholamine levels. Again, compartmentalization of secretory elements in PC12 cells is already pronounced in baseline conditions, while it is only slightly affected following catecholamine-releasing stimuli. This low flexibility is caused by the low ability of PC12 cells to compensate for sustained catecholamine release, due both to non-sufficient dopamine synthesis and poor dopamine storage mechanisms. This contrasts markedly with dopamine-containing neurons in vivo lending substance to opposite findings between these compartments concerning the sensitivity to a number of neurotoxins.

Endothelial proliferation and increased blood-brain barrier permeability in the basal ganglia in a rat model of 3,4-dihydroxyphenyl-L-alanine-induced dyskinesia

3,4-Dihydroxyphenyl-L-alanine (L-DOPA)-induced dyskinesia is associated with molecular and synaptic plasticity in the basal ganglia, but the occurrence of structural remodeling through cell genesis has not been explored. In this study, rats with 6-hydroxydopamine lesions received injections of the thymidine analog 5-bromo-2'-deoxyuridine (BrdU) concomitantly with L-DOPA for 2 weeks. A large number of BrdU-positive cells were found in the striatum and its output structures (globus pallidus, entopeduncular nucleus, and substantia nigra pars reticulata) in L-DOPA-treated rats that had developed dyskinesia. The vast majority (60-80%) of the newborn cells stained positively for endothelial markers. This endothelial proliferation was associated with an upregulation of immature endothelial markers (nestin) and a downregulation of endothelial barrier antigen on blood vessel walls. In addition, dyskinetic rats exhibited a significant increase in total blood vessel length and a visible extravasation of serum albumin in the two structures in which endothelial proliferation was most pronounced (substantia nigra pars reticulata and entopeduncular nucleus). The present study provides the first evidence of angiogenesis and blood-brain barrier dysfunction in an experimental model of L-DOPA-induced dyskinesia. These microvascular changes are likely to affect the kinetics of L-DOPA entry into the brain, favoring the occurrence of motor complications.

Interleukin-1beta mediates GDNF up-regulation upon dopaminergic injury in ventral midbrain cell cultures

We recently proposed the involvement of diffusible modulators in signalling astrocytes to increase glial cell line-derived neurotrophic factor (GDNF) expression after selective dopaminergic injury by H2O2 or L-DOPA. Here we report that interleukin-1beta (IL-1beta) is involved in this crosstalk between injured neurons and astrocytes. IL-1beta was detected only in the media from challenged neuron-glia cultures. Exogenous IL-1beta did not change GDNF protein levels in astrocyte cultures, and diminished GDNF levels in neuron-glia cultures. This decrease was not due to cell loss, as assessed by the MTT assay and immunocytochemistry. Neither H2O2 nor L-DOPA induced microglia proliferation or appeared to change its activation state. The IL-1 receptor antagonist (IL-1ra) prevented GDNF up-regulation in challenged cultures, showing that IL-1beta is involved in the signalling between injured neurons and astrocytes. Since IL-1ra decreased the number of dopaminergic neurons in H2O2-treated cultures, we propose that IL-1 has a neuroprotective role in this system involving GDNF up-regulation.

Caenorhabditis elegans MPP+ model of Parkinson's disease for high-throughput drug screenings

The neurotoxin MPTP and its active metabolite MPP+ cause Parkinson's disease (PD)-like symptoms in vertebrates by selectively destroying dopaminergic neurons in the substantia nigra. MPTP/MPP+ models have been established in rodents to screen for pharmacologically active compounds. In addition to being costly and time consuming, these animal models are not suitable for large scale testings using compound libraries. We present a novel MPP+-based model for high-throughput screenings using the nematode Caenorhabditis elegans. Incubation of C. elegans with MPTP or its active metabolite MPP+ resulted in strong symptomatic defects including reduced mobility and increased lethality, and is correlated with a specific degeneration of the dopaminergic neurons. The phenotypic consequences of MPTP/MPP+ treatments were recorded using automated hardware and software for quantification. Incubation of C. elegans with a variety of pharmacologically active components used in PD treatment reduced the MPP+-induced defects. Our data suggest that the C. elegans MPTP/MPP+ model can be used for the quantitative evaluation of anti-PD drugs.

In 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-Treated Primates, the Selective 5-Hydroxytryptamine 1a Agonist (R)-(+)-8-OHDPAT Inhibits Levodopa-Induced Dyskinesia but Only with\ Increased Motor Disability

5-Hydroxytryptamine 1a (5-HT(1a)) receptor agonists, such as sarizotan and tandospirone, are reported to reduce levodopa-induced dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated macaques and in Parkinson's disease without worsening motor disability. However, these compounds are not specific for 5-HT(1a) receptors and also possess dopamine antagonist actions. We now report on the effects of (2R)-(+)-8-hydroxy-2-(di-n-propylamino)tetralin [(R)-(+)-8-OHDPAT], a selective 5-HT(1a) agonist lacking dopaminergic activity, on motor disability and dyskinesia (chorea and dystonia) in levodopa-primed MPTP-treated common marmosets. Administration of (R)-(+)-8-OHDPAT (0.2, 0.6, and 2.0 mg/kg s.c), in conjunction with levodopa/carbidopa (12.5 mg/kg each p.o.) to levodopa-primed animals, dose-dependently reduced levodopa-induced chorea but did not affect dystonic movements. However, (R)-(+)-8-OHDPAT treatment also reduced locomotor activity and the reversal of motor disability. Administration of (R)-(+)-8-OHDPAT alone had no effects of motor behaviors. The effects of (R)-(+)-8-OHDPAT on levodopa-induced motor behaviors were antagonized by the 5-HT(1a) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide maleate (WAY-100635) (1.0 mg/kg s.c.). Administration of (R)-(+)-8-OHDPAT (0.6 mg/kg s.c.) also reduced chorea produced by the administration of the D(2)/D(3) dopamine receptor agonist pramipexole (0.06 mg/kg p.o.) to levodopa-primed MPTP-treated animals. However, again the increase in locomotor activity and reversal of motor disability produced by pramipexole were also inhibited. These data suggest that selective 5-HT(1a) agonists do not provide an effective means of suppressing levodopa-induced dyskinesia, except with worsening of parkinsonism.

Evaluation of acute antiapoptotic effects of Li+ in neuronal cell cultures

Li(+) exerts protective effect against several neurotoxins in neuronal cell preparations. Here we examined the antiapoptotic effects of GSK3beta in cerebellar granule neurons (CGNs) in the presence of several neurotoxins. Acute treatment with Li(+) protected neurons against nocodazole and serum/potassium (S/K) deprivation, but were ineffective against kainic acid and MPP(+). Li(+) 5 mM also decreased caspase-3 activation induced by nocodazole and S/K deprivation as measured by Ac-DEVD-p-nitroaniline and the breakdown of alpha-spectrin. All the neurotoxins used in the present study activated GSK3beta, evaluated with a specific antibody phospho-GSK-3beta (Ser9) by Western-blot and immunocytochemistry and were always inhibited by Li(+) 5 mM. Our results implicate Li(+) in the regulation of apoptosis mediated by caspase activation (Type I). Furthermore inhibition of GSK3beta by acute treatment with Li(+) 5 mM is not an indicator of neuroprotection. The acute antiapoptotic function of Li(+) is discussed in terms of its inhibition of Type I pathway, the intrinsic (mitochondrial) apoptotic pathway in cerebellar granule cells.

Mechanisms of methamphetamine-induced dopaminergic neurotoxicity

Methamphetamine (METH) is a powerful stimulant of abuse with potent addictive and neurotoxic properties. More than 2.5 decades ago, METH-induced damage to dopaminergic neurons was described. Since then, numerous advancements have been made in the search for the underlying mechanisms whereby METH causes these persistent dopaminergic deficits. Although our understanding of these mechanisms remains incomplete, combinations of various complex processes have been described around a central theme involving reactive species, such as reactive oxygen and/or nitrogen species (ROS and RNS, respectively). For example, METH-induced hyperthermia, aberrant dopamine(DA), or glutamate transmission; or mitochondrial disruption leads to the generation of reactive species with neurotoxic consequences. This review will describe the current understanding of how high-dose METH administration leads to the production of these toxic reactive species and consequent permanent dopaminergic deficits.

Protection by GDNF and Other Trophic Factors Against the Dopamine-Depleting Effects of Neurotoxic Doses of Methamphetamine

Repeated methamphetamine (METH) administration to animals can result in long-lasting decreases in striatal dopamine (DA) content. It has previously been shown that glial cell line-derived neurotrophic factor (GDNF) can reduce the DA-depleting effects of neurotoxic doses of METH. However, there are several other trophic factors that are protective against dopaminergic toxins. Thus, the present experiments further investigated the protective effect of GDNF as well as the protective effects of several other trophic factors. Male Fischer-344 rats were given an intracerebral injection of trophic factor (2-10 microg) 1 day before METH (5 mg/kg, s.c., 4 injections at 2-h intervals). Seven days later DA levels in the striatum were measured using high-performance liquid chromatography (HPLC). Initial experiments indicated that only intrastriatal GDNF, and not intranigral GDNF, was protective. Thereafter, all other trophic factors were administered into the striatum. Members of the GDNF family (GDNF, neurturin, and artemin) all provided significant protection against the DA-depleting effects of METH, with GDNF providing the greatest protection. Brain-derived neurotrophic factor, neurotrophin-3, acidic fibroblast growth factor, basic fibroblast growth factor, ciliary neurotrophic factor, transforming growth factor-alpha (TGF-alpha), heregulin beta1 (HRG-beta1), and amphiregulin (AR) provided no significant protection at the doses examined. These results suggest that the GDNF family of trophic factors can provide significant protection against the DA-depleting effects of neurotoxic doses of METH.

Cytotoxicity of chloral-derived β-carbolines is not specific towards neuronal nor dopaminergic cells

beta-Carbolines structurally related to the selective dopaminergic neurotoxin 1-methyl-4- phenylpyridinium (MPP(+)) may contribute to dopaminergic neurodegeneration in Parkinson's disease. The chloral-derived mammalian alkaloid derivative 1-trichloromethyl-1,2,3,4-tetrahydro-beta-carboline (TaClo) is formed endogenously by a Pictet-Spengler condensation from the biogenic amine tryptamine (Ta) and the hypnotic aldehyde chloral (Clo). Here we examine the dopaminergic toxicity of TaClo and related compounds by testing their differential cytotoxicities in dopaminergic SH-SY5Y and non-dopaminergic murine Neuro2A neuroblastoma cell lines as well as in heterologous expression systems of the dopamine transporter (DAT) using both HEK-293 and Neuro2A cells. All TaClo derivatives showed significant cytotoxicity in all cell lines after 72 hours with the following rank order of toxic potency: 1-Tribromomethyl-1,2,3,4-tetrahydro-beta-carboline (TaBro) > TaClo > MPP(+) > 1,2,3,4-tetrahydro-beta-carboline (THbetaC) > 2[N]-methyl-TaClo > 2[N]-methyl-THbetaC. In contrast to MPP(+), there was no selectivity towards dopaminergic cells or cells ectopically expressing the DAT in vitro. Our results suggest that TaClo and related analogs are strong cytotoxins without selectivity towards dopaminergic cells.

Iron contributes to dopamine-induced toxicity in oligodendrocyte progenitors

Iron is potentially toxic to oligodendrocyte progenitors due to its high intracellular levels and its ability to catalyse oxidant-producing reactions. Oxidative stress resulting from a hypoxic-ischaemic insult has been implicated in death of oligodendrocyte progenitors that occurs in the hypomyelinating disorder periventricular leucomalacia. Ischaemic insults induce the release of various neurotransmitters, including dopamine (DA), and we previously showed that DA is toxic to cultured oligodendrocytes, by inducing oxidative stress and apoptosis. Therefore, we investigated the role of iron in DA-induced cell death in oligodendrocyte progenitors. Intracellular iron levels were altered using an iron chelator, deferoxamine (DFO), and supplementation with ferrous sulphate (FeSO(4)). Addition of FeSO(4) to cultures increased DA-induced toxicity as assessed by mitochondrial dehydrogenase activity and cellular release of lactate dehydrogenase. Furthermore, FeSO(4) increased expression of the stress protein heme oxygenase-1 (HO-1), nuclear condensation and caspase-3 activation. In contrast, preincubation with DFO reduced these events as well as cleavage of alpha-spectrin, a caspase-3 substrate. In addition, FeSO(4) reversed the protective effect of DFO on DA-induced cytotoxicity, HO-1 expression and caspase-3 activation. These results indicate that elevated levels of free iron contribute to DA-induced toxicity in oligodendrocyte progenitors.

Synthetic bovine proline-rich-polypeptides generate hydroxyl radicals and fail to protect dopaminergic neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurotoxicity in mice

Proline-rich-polypeptides (PRPs) isolated from bovine hypothalamus have been shown to render protection against neuronal injury of the brain and spinal cord. We examined two PRPs containing 15 and 10 amino acid residues (PRP-1 and PRP-4 synthetic polypeptide) for their effect, if any, on dopaminergic neuronal damage caused by the parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Effects of these PRPs on hydroxyl radical ((*)OH) generation in a Fenton-like reaction as well as from isolated mitochondria were monitored, employing a sensitive salicylate hydroxylation procedure. Balb/c mice treated (i.p., twice, 16 h apart) with MPTP (30 mg/kg) or PRP-1 (1.6 mg/kg), but not PRP-4 (1.6 mg/kg) showed significant loss of striatal dopamine and norepinephrine as assayed by an HPLC-electrochemical procedure. Pretreatment with the PRPs, 30 min prior to the neurotoxin administration failed to attenuate MPTP-induced striatal dopamine or norepinephrine depletion, but significantly attenuated the MPTP-induced decrease in dopamine turnover. A significant increase in the generation of (*)OH by the PRPs in a Fenton-like reaction or from isolated mitochondria suggests their pro-oxidant action, and explains their failure to protect against MPTP-induced parkinsonism in mice.

Estrogen, Testosterone, and Methamphetamine Toxicity

The gonadal steroid hormone, estrogen, can diminish the degree of striatal dopamine depletion resulting from methamphetamine. In this article, we describe the conditions of this estrogen neuroprotection as well as the potential for estrogen and testosterone to enhance methamphetamine-induced neurodegeneration of the nigrostriatal dopaminergic system. When administered prior to a neurotoxic regimen of methamphetamine, estrogen significantly decreases the amount of striatal dopamine depletion in intact or gonadectomized female, but not male, mice. This capacity for estrogen to function as a neuroprotectant can occur quite rapidly, at 30 min prior to methamphetamine administration, and with relatively low doses of estrogen (1 microg estradiol benzoate). Estrogen remains an effective neuroprotectant in neonatally gonadectomized female mice treated with testosterone, but not in female mice that were gonadectomized prior to puberty. Nor does estrogen demonstrate any beneficial effects when administered after methamphetamine. Recent data have indicated some conditions where gonadal steroids can increase the extent of striatal neurodegeneration in response to methamphetamine. Specifically, when some existing perturbation is present in the nigrostriatal dopaminergic system, treatment with estrogen enhances the extent of striatal dopamine depletion to methamphetamine. Similarly, increased striatal dopamine depletion to methamphetamine is observed in gonadectomized male mice treated with testosterone.

Differential protection against MPTP or methamphetamine toxicity in dopamine neurons by deletion of ppN/OFQ expression

Nociceptin (N/OFQ) is an endogenous neuropeptide that plays a role in the behavioral deficits associated with Parkinson's disease (PD). The purpose of the present study was to characterize the protective effects of prepro (pp)N/OFQ gene deletion against two dopamine toxins, MPTP and methamphetamine (METH). Results demonstrate that ppN/OFQ gene deletion attenuates the loss of both the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc) and loss of TH and vesicular monoamine transporter-2 (VMAT) immunoreactivity in the caudate putamen (CPu) of MPTP-treated mice. This protection was unaffected by age or gender, although, when loss of TH exceeded 90% in 5-6 month-old mice, the protective effect was greatly diminished. In contrast, METH administration preferentially damaged dopaminergic terminals in the CPu with little effect on dopamine neurons in the SNpc, an effect not reversed by ppN/OFQ gene deletion. To determine if N/OFQ and MPP+ act directly and synergistically on dopamine neurons, differentiated SH-SY5Y cells were incubated with N/OFQ and/or MPP+. N/OFQ did not increase MPP+-mediated cell loss, suggesting an indirect action of N/OFQ. These studies demonstrate that inhibition of the endogenous N/OFQ system may represent a new therapeutic target for prevention of neuronal loss associated with PD.

The copper chelator, D-penicillamine, does not attenuate MPTP induced dopamine depletion in mice

In MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and 6-hydroxydopamine induced dopaminergic neurotoxicity and Parkinson's disease iron accumulates in substantia nigra pars compacta which has been suggested to participate in oxidative stress induced neurodegeneration. Pretreatment with iron chelators desferal, clioquinol, VK-28 and M30 are neuroprotective in both models. To determine the specificity of chelation neuroprotective activity we have examined the effect of D-penicillamine, a relatively specific copper chelator, in the mice model of MPTP-induced dopamine depletion. Our studies show that D-penicillamine, employed for removal of copper in Wilson disease is relatively weak in preventing dopaminergic neurotoxicity induced by MPTP, as compared to iron chelators previously studied. The results indicate that for prevention of MPTP-induced dopamine depletion and dopamine neurodegeneration, iron rather than copper chelation may be more effective and specific.

7-Ketocholesterol enhances 1-methyl-4-phenylpyridinium-induced mitochondrial dysfunction and cell death in PC12 cells

The present study investigated the promoting effect of oxysterol 7-ketocholesterol against the cytotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in differentiated PC12 cells. 7-Ketocholesterol significantly enhanced the MPP(+)-induced nuclear damage, decrease in the mitochondrial transmembrane potential, cytosolic accumulation of cytochrome c, activation of caspase-3, increase in the formation of reactive oxygen species and depletion of GSH. N-Acetylcysteine, ascorbate, trolox, carboxy-PTIO and Mn-TBAP reduced the cytotoxic effect of MPP(+) in the presence of 7-ketocholesterol. The results indicate that 7-ketocholesterol shows a synergistic effect against the cytotoxic effect of MPP(+). 7-Ketocholesterol may enhance the MPP(+)-induced viability loss in PC12 cells by promoting the mitochondrial membrane permeability change, release of cytochrome c and subsequent activation of caspase-3, which is associated with the increased formation of reactive oxygen species and depletion of GSH. The findings suggest that 7-ketocholesterol as a promoting agent for the formation of mitochondrial permeability transition may enhance the toxic neuronal cell injury.

Contralateral prefrontal projections in gerbils mature abnormally after early methamphetamine trauma and isolated rearing

As previously shown, a miswiring of ipsilateral prefrontal projections after methamphetamine (MA) intoxication and/or isolated rearing (IR) may serve as a model of so-called "dysconnection" in human schizophrenia. We here find that deep prefrontal projections to contralateral targets were drastically reduced by both MA and IR alone, but remained equally dense if both impairments cumulated. Projections from superficial layers were not altered by MA and/or IR. These findings confirm that the normal intercortical integration of information is compromised in this animal model of schizophrenia.