A peptide derived from the C-terminal region of acetylcholinesterase modulates extracellular concentrations of acetylcholinesterase in the rat substantia nigra

It is well established that acetylcholinesterase (AChE) has 'non-classical' functions independent of cholinergic transmission. A region of AChE distinct from the catalytic site may be responsible for these actions via a 14-residue peptide located between residues 586-599 at the C-terminus of human AChE. This AChE-peptide possesses a high amino acid sequence homology with a region of amyloid precursor protein and shares many biophysical and physiological characteristics. In this study, the effect of AChE-peptide (AEFHRWSSYMVHWK) on the extracellular levels of endogenous AChE was examined in rat substantia nigra in vitro. A chemiluminescent assay was used to continuously measure the soluble AChE concentration from tissue punches of the substantia nigra. Application of NMDA evoked an increase in extracellular AChE levels consistent with previous results obtained from in vivo models. AChE-peptide, when applied alone, had no effect on AChE release: however, when co-applied with NMDA, AChE-peptide reduced the effectiveness of NMDA to evoke release of AChE. These results indicate, in a region of the brain central to the aetiology of Parkinson's disease, that an AChE-peptide fragment derived from AChE displays a bioactivity that could involve regulation of Ca(2+) availability and hence the release of AChE.

Tissue transglutaminase catalyzes the formation of alpha-synuclein crosslinks in Parkinson's disease

In Parkinson's disease (PD), conformational changes in the alpha-synuclein monomer precede the formation of Lewy bodies. We examined postmortem PD and undiseased (control) substantia nigra for evidence of pathological crosslinking of alpha-synuclein by tissue transglutaminase (tTG) using immunohistochemistry, immunoprecipitation, and Western blot. Consistent with previous reports, we found that both tTG and its substrate-characteristic N(epsilon)-(gamma-glutamyl)-lysine crosslink are increased in PD nigral dopamine neurons. Furthermore, both the tTG protein and its substrate crosslink coprecipitated with alpha-synuclein in extracts of PD substantia nigra. Unexpectedly, the isodipeptide crosslink was detected in the alpha-synuclein monomer as well as in higher molecular mass oligomers of alpha-synuclein. Although the intramolecularly crosslinked alpha-synuclein monomer was present in control tissue, it was highly enriched in PD substantia nigra. Conversely, significantly less uncrosslinked alpha-synuclein remained in the postimmunoprecipitate lysate of PD tissue than in control. Crosslinked alpha-synuclein, formed at the expense of the total alpha-synuclein monomer, correlated with disease progression. These results demonstrate that much of the alpha-synuclein monomer in PD nigra is crosslinked by tTG and thus may be functionally impaired. This modification appears to be an early step in PD pathogenesis, preceding the aggregation of alpha-synuclein in Lewy bodies.

Mice deficient in dihydrolipoamide dehydrogenase show increased vulnerability to MPTP, malonate and 3-nitropropionic acid neurotoxicity

Altered energy metabolism, including reductions in activities of the key mitochondrial enzymes alpha-ketoglutarate dehydrogenase complex (KGDHC) and pyruvate dehydrogenase complex (PDHC), are characteristic of many neurodegenerative disorders including Alzheimer's Disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Dihydrolipoamide dehydrogenase is a critical subunit of KGDHC and PDHC. We tested whether mice that are deficient in dihydrolipoamide dehydrogenase (Dld+/-) show increased vulnerability to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), malonate and 3-nitropropionic acid (3-NP), which have been proposed for use in models of PD and HD. Administration of MPTP resulted in significantly greater depletion of tyrosine hydroxylase-positive neurons in the substantia nigra of Dld+/- mice than that seen in wild-type littermate controls. Striatal lesion volumes produced by malonate and 3-NP were significantly increased in Dld+/- mice. Studies of isolated brain mitochondria treated with 3-NP showed that both succinate-supported respiration and membrane potential were suppressed to a greater extent in Dld+/- mice. KGDHC activity was also found to be reduced in putamen from patients with HD. These findings provide further evidence that mitochondrial defects may contribute to the pathogenesis of neurodegenerative diseases.

High-frequency stimulation of both zona incerta and subthalamic nucleus induces a similar normalization of basal ganglia metabolic activity in experimental parkinsonism

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) alleviates dramatically motor symptoms in Parkinson's disease, and recently it has been suggested that zona incerta (ZI) stimulation might be as beneficial to patients. We used in situ cytochrome oxidase (CoI) mRNA hybridization to investigate and compare the effects of HFS of the STN and the ZI on metabolic activity of the STN, globus pallidus (GP), and substantia nigra reticulata (SNr) in normal rats as well as in rats with 6-hydroxydopamine (6-OHDA) lesion, an animal model of Parkinson's disease. In normal rats, HFS of the STN, as well as of the ZI, induced a significant decrease in CoI mRNA expression within the STN and SNr but an increase within the GP. In 6-OHDA rats, HFS of the STN reversed dopamine denervation-induced changes in the expression of CoI mRNA in the STN, SNr, and GP. Similar results were obtained with HFS of the ZI except for the STN, which showed only a trend toward normalization. These data suggest that the ZI, as well as the STN, are implicated in the functional mechanism of HFS supporting the involvement of GABA transmission for the reduction of neuronal activity in the basal ganglia output structures.

Chronic intoxication with 3-nitropropionic acid in rats induces the loss of striatal dopamine terminals without affecting nigral cell viability

3-Nitropropionic acid (3NP) is a succinate dehydrogenase inhibitor allowing the generation of animal models of Huntington's disease. In the present study, we found that a 5-day continuous chronic infusion of 3NP produces loss of [3H]mazindol binding and tyrosine hydroxylase (TH) immunoreactivity in the striatal area of degeneration. This loss of dopamine terminals was not due to a loss of nigral neurons since the expression of TH as well as the number of TH-expressing neurons remained unaltered in the substantia nigra of rats treated by 3NP. This suggests that the 3NP-induced dopamine terminal loss is secondarily related to the striatal degeneration andlor to a direct effect of 3NP on striatal terminals and not to a primary effect on nigral cells.

Ritanserin counteracts both rat vacuous chewing movements and nigro-striatal tyrosine hydroxylase-immunostaining alterations induced by haloperidol

The effect of subchronic co-administration of ritanserin (1.5 mg/kg, i.p., twice a day) and haloperidol (1 mg/kg, i.p., twice a day) on rat vacuous chewing movements and on tyrosine hydroxylase-immunostaining was investigated. Ritanserin significantly reduced rat vacuous chewing movements observed following 2, 3 and 4 weeks of haloperidol administration and after 5 days of haloperidol withdrawal. Furthermore, ritanserin prevented the reduction of striatal tyrosine hydroxylase-immunostaining and the shrinkage of nigral dopaminergic cell bodies induced by haloperidol. The present results indicate that ritanserin may possess protective properties on both dopaminergic nigro-striatal neuron alterations and vacuous chewing movements induced by haloperidol, and provide further evidence indicating a possible association between these two haloperidol-induced effects.

CEP11004, a novel inhibitor of the mixed lineage kinases, suppresses apoptotic death in dopamine neurons of the substantia nigra induced by 6-hydroxydopamine

There is much evidence that the kinase cascade which leads to the phosphorylation of c-jun plays an important signaling role in the mediation of programmed cell death. We have previously shown that c-jun is phosphorylated in a model of induced apoptotic death in dopamine neurons of the substantia nigra in vivo. To determine the generality and functional significance of this response, we have examined c-jun phosphorylation and the effect on cell death of a novel mixed lineage kinase inhibitor, CEP11004, in the 6-hydroxydopamine model of induced apoptotic death in dopamine neurons. We found that expression of total c-jun and Ser73-phosphorylated c-jun is increased in this model and both colocalize with apoptotic morphology. CEP11004 suppresses apoptotic death to levels of 44 and 58% of control values at doses of 1.0 and 3.0 mg/kg, respectively. It also suppresses, to approximately equal levels, the number of profiles positive for the activated form of capase 9. CEP11004 markedly suppresses striatal dopaminergic fiber loss in these models, to only 22% of control levels. We conclude that c-jun phosphorylation is a general feature of apoptosis in living dopamine neurons and that the mixed lineage kinases play a functional role as up-stream mediators of cell death in these neurons.

Dendritic spinules in rat nigral neurons revealed by acetylcholinesterase immunocytochemistry and serial sections of the dendritic spine heads

Dendritic spinules of rat nigral neurons were visualized at electron microscopic level by acetylcholinesterase immunocytochemistry and serial sections of the nigral dendrites. The spinules (at least 150 nm in length and 10-20 nm in width) which protruded from the spine heads are found in extracellular space in the neuropil and particularly between nerve terminals of the presynaptic neurons and fine glial processes. The nigral spinules are, however, not observed as invaginated processes in the nerve terminals. The dendritic spinule may be endowed with synaptic plasticity and metabolic exchange between nerve terminals and glial processes.

Analysis of cellular, transgenic and human models of Huntington's disease reveals tyrosine hydroxylase alterations and substantia nigra neuropathology

Huntington's disease (HD) is a progressive, autosomal dominant neurodegenerative disorder that is pathologically characterized by a striatal-specific degeneration. Aberrant dopamine neurotransmission has been proposed as a mechanism underlying the movement disorder of HD. We report that the enzymatic activity of tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine biosynthesis, is decreased in a transgenic mouse model of HD. In addition, mutant huntingtin was found to disrupt transcription of TH and dopamine beta-hydroxylase (DbetaH) promoter reporter constructs. In situ hybridization revealed extensive loss of TH mRNA and decreased dopaminergic cell size in human HD substantia nigra. TH-immunoreactive protein was reduced in human grade 4 HD substantia nigra by 32% compared to age-matched controls. These findings implicate abnormalities in dopamine neurotransmission in HD and may provide new insights into targets for pharmacotherapy.

Time-course of the expression of inflammatory cytokines and matrix metalloproteinases in the striatum and mesencephalon of mice injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a dopaminergic neurotoxin

Injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice results in a retrograde nigrostriatal dopaminergic pathway denervation and subsequent tissue reorganization. Since the role of inflammatory mediators after MPTP remains unclear, proinflammatory cytokine and matrix metalloproteinase (MMP) expression were evaluated by comparative RT-PCR during denervation and tissue reorganization following a single-dose of MPTP (40 mg/kg, s.c.) in young (8-week-old) mice. The time-course of denervation/reorganization was assessed through [(3)H]GBR-12935 binding on dopamine transporter and tyrosine hydroxylase immunohistochemistry. In the striatum, TNF-alpha, IL-1alpha, IL-1beta, IL-6 and MMP-9 mRNA expression peaked on day 1. In the ventral mesencephalon, cytokines (TNF-alpha, IL-1alpha, IL-1beta) and MMP-9 mRNA expression peaked on day 3. During tissue reorganization (day 6 through 16), the only change observed in the striatum consisted of IL-1alpha mRNA and protein overexpression together with MMP-2 downregulation. Whereas the early expression of proinflammatory cytokines and MMP might participate in the retrograde nigrostriatal denervation, the late component of IL-1alpha expression suggests a possible role for this cytokine in the subsequent striatal reorganization.

COX-2-deficient mice are less prone to MPTP-neurotoxicity than wild-type mice

The primary lesion in Parkinson's disease is the death of dopaminergic neurons in the substantia nigra. The role of cyclooxygenase (COX)-2 in the etiology of Parkinson's disease was explored using COX-2 gene knockout mice. Mortality after injection of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP, a chemical known to cause parkinsonism in humans) in heterozygous COX-2-deficient mice was lower than that in wild-type mice. The number of tyrosine hydroxylase immunoreactive neurons in the substantia nigra pars compacta of MPTP-treated wild-type mice declined to a greater extent than in heterozygous mice. Inhibition of COX-2 protein expression decreased the lesion caused by MPTP and protected the dopaminergic neurons in substantia nigra pars compacta. This result suggested that inhibition of COX-2 has potential therapeutic implications.

Microglial activation and tyrosine hydroxylase immunoreactivity in the substantia nigral region following transient focal ischemia in rats

The temporal profiles of the changes of dopaminergic cells and microglial activation induced by transient cerebral ischemia were investigated in the substantia nigra pars compacta (SNc) located outside ischemic areas of rat brain. Transient cerebral ischemia was induced by intraluminal occlusion of the right middle cerebral artery for 2 h and reperfusion was continued for 1, 2, 3, 4, 7, 10, 14, 28, 60, and 120 days. Dopaminergic cells immunostained with tyrosine hydroxylase (TH)-antibody in the ipsilateral SNc were significantly decreased at 7 days post-ischemia compared with those in the contralateral side (P<0.05). However, at 60 and 120 days, there were no significant differences between ipsilateral and contralateral side of the SNc. Unlike the TH immunoreactivity, activated microglial cells immunostained with OX-42 antibody were significantly increased at 2 and 3 days and then decreased gradually until 10 days post-ischemia. Activated microglial cells were increased at 2 weeks post-ischemia, and this pattern remained until 60 days. These results suggest that the transient changes of TH-immunoreactive cells in the SNc caused by transient focal ischemia are correlated with a biphasic microglial cell activation response.

Quantitative RT-PCR reveals a ubiquitous but preferentially neural expression of the KIS gene in rat and human

KIS is the only known protein kinase that possesses an RNA recognition motif. This original structure indicates a role for KIS in the maturation of RNAs possibly by phosphorylating and regulating the activities of RNA associated factors. Another function of KIS has recently been unravelled--it negatively regulates the cdk inhibitor p27Kip1 and thus promotes cell cycle progression through G1. In order to explore the functional expression of this kinase, we quantified its mRNA in a wide range of rat and human tissues, during development and in tumors. In both species, the highest level of KIS gene expression was in adult neural tissues. Interestingly, within the adult rat brain, KIS mRNA is enriched in several areas including the substantia nigra compacta and nuclei of the brain stem. Furthermore, KIS gene expression increases dramatically during brain development. Altogether our results point to a ubiquitous function for KIS together with a particular implication during neural differentiation or in the function of mature neural cells. No dysregulation of KIS gene expression was detected in human tumors from breast, bladder, prostate, liver and kidney origins. On the other hand, the KIS gene was overexpressed in NF1-associated plexiform neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs) as compared to dermal neurofibroma which suggests a possible implication of KIS in the genesis of NF1-associated tumors.

Normal nigrostriatal innervation but dopamine dysfunction in mice carrying hypomorphic tyrosine hydroxylase alleles

We investigated the use of the mouse tyrosine hydroxylase (TH) gene to drive knock-in constructs in catecholaminergic neurons. Two targeting constructs representing truncated forms of either of the BMP receptors ALK-2 or BMPR-II preceded by an internal ribosome entry site (IRES) were introduced into the 3' untranslated region of TH. An frt-flanked neomycin-resistance (neo(r)) cassette was placed in the 3' end of the targeting constructs. Mice homozygous for the knock-in alleles showed various degrees of hypokinetic behavior, depending mainly on whether the neo(r) cassette was removed. In situ hybridization and immunohistochemistry showed that TH mRNA and protein were variously down-regulated in these mouse strains. Reduced levels of dopamine and noradrenalin were found in several brain areas. However, number and morphology of neurons in substantia nigra and their projections to striatum appeared normal in the neo(r)-positive TH hypomorphic mice as examined by markers for L-aromatic amino acid decarboxylase and the dopamine transporter. Elimination of the neo(r) cassette from the knock-in alleles partially restored TH and dopamine levels. The present neo(r)-positive TH hypomorphic mice show that nigrostriatal innervation develops independently of TH and should find use as a model for conditions of reduced catecholamine synthesis, as seen in, for example, L-dihydroxyphenylalanine-responsive dystonia/infantile parkinsonism.

Inhibition of calpains prevents neuronal and behavioral deficits in an MPTP mouse model of Parkinson's disease

The molecular mechanisms mediating degeneration of midbrain dopamine neurons in Parkinson's disease (PD) are poorly understood. Here, we provide evidence to support a role for the involvement of the calcium-dependent proteases, calpains, in the loss of dopamine neurons in a mouse model of PD. We show that administration of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes an increase in calpain-mediated proteolysis in nigral dopamine neurons in vivo. Inhibition of calpain proteolysis using either a calpain inhibitor (MDL-28170) or adenovirus-mediated overexpression of the endogenous calpain inhibitor protein, calpastatin, significantly attenuated MPTP-induced loss of nigral dopamine neurons. Commensurate with this neuroprotection, MPTP-induced locomotor deficits were abolished, and markers of striatal postsynaptic activity were normalized in calpain inhibitor-treated mice. However, behavioral improvements in MPTP-treated, calpain inhibited mice did not correlate with restored levels of striatal dopamine. These results suggest that protection against nigral neuron degeneration in PD may be sufficient to facilitate normalized locomotor activity without necessitating striatal reinnervation. Immunohistochemical analyses of postmortem midbrain tissues from human PD cases also displayed evidence of increased calpain-related proteolytic activity that was not evident in age-matched control subjects. Taken together, our findings provide a potentially novel correlation between calpain proteolytic activity in an MPTP model of PD and the etiology of neuronal loss in PD in humans.

The human tyrosine hydroxylase gene promoter

13.329 kilobases of the single copy human tyrosine hydroxylase (hTH) gene were isolated from a genomic library. The 5' flanking 11 kilobases fused to the reporter green fluorescent protein (GFP) drove high level expression in TH+ cells of the substantia nigra of embryonic and adult transgenic mice as determined by double label fluorescence microscopy. To provide a basis for future analysis of polymorphisms and structure-function studies, the previously unreported distal 10.5 kilobases of the hTH promoter were sequenced with an average coverage of 20-fold, the remainder with 4-fold coverage. Sequence features identified included four perfect matches to the bicoid binding element (BBE, consensus: BBTAATCYV) all of which exhibited specific binding by electrophoretic mobility shift assay (EMSA). Comparison to published sequences of mouse and rat TH promoters revealed five areas of exceptional homology shared by these species in the upstream TH promoter region -2 kb to -9 kb relative to the transcription start site. Within these conserved regions (CRs I-V), potential recognition sites for NR4A2 (Nurr1), HNF-3beta, HOXA4, and HOXA5 were shared across human, mouse, and rat TH promoters.

Tyrosine hydroxylase mRNA and protein are down-regulated by chronic clozapine in both the mesocorticolimbic and the nigrostriatal systems

The dopaminergic system is one of the most important targets for pharmacological treatment of schizophrenia. Despite substantial work on mechanisms of action, it is not clear which dopaminergic pathways mediate the therapeutic effects of antipsychotic drugs. It has been shown that chronic clozapine, an atypical antipsychotic, decreases dopamine levels in the mesocorticolimbic system but not in the nigrostriatal system. Because tyrosine hydroxylase is the rate-limiting enzyme in the biosynthesis of dopamine, we studied the effect of chronic clozapine in both dopaminergic systems. We demonstrated a decrease of tyrosine hydroxylase mRNA not only in the ventral tegmental area but also in the substantia nigra, the cell body areas of the mesocorticolimbic and the nigrostriatal systems, respectively. The reduced tyrosine hydroxylase mRNA level in these areas is accompanied by an ample reduction in the tyrosine hydroxylase protein level in their corresponding axonal terminal fields, the nucleus accumbens and the striatum. There was thus discordance between the clozapine-induced decrease of tyrosine hydroxylase mRNA and protein and the absence of an effect on dopamine levels in the nigrostriatal system. It has been suggested that reduced levels of dopamine in the mesocorticolimbic system are required for the antipsychotic effect of the drug. Therefore, the modulation of tyrosine hydroxylase gene expression by clozapine in the mesocorticolimbic system might be necessary for its antipsychotic effect; this effect might be of relevance when considering new atypical agents.

Motor dysfunction and gliosis with preserved dopaminergic markers in human alpha-synuclein A30P transgenic mice

Alpha-synuclein is a major component of Lewy bodies (LBs) in the substantia nigra and cortex in Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and in glial inclusions in multiple systems atrophy (MSA). Mutations in alpha-synuclein have been associated with autosomal dominant forms of PD. We investigated the clinical and neuropathological effects of overexpression of human alpha-synuclein, alpha-synuclein A30P, and alpha-synuclein A53T under the control of the hamster prion protein (PrP) promoter; 5-15x endogenous levels of protein expression were achieved with widespread neuronal, including nigral, transgene expression. High expression of alpha-synuclein A30P in the Tg5093 line was associated with a progressive motor disorder with rigidity, dystonia, gait impairment, and tremor. Histological analysis of this line showed aberrant expression of the protein in cell soma and progressive CNS gliosis, but no discrete Lewy body-like alpha-synuclein inclusions could be identified. Biochemical analysis demonstrated alpha-synuclein fragmentation. Despite strong expression of the transgene in the nigra, there was no specific deterioration of the nigrostriatal dopaminergic system as assessed by quantitation of nigral tyrosine hydroxylase (TH) containing neurons, striatal TH immunoreactivity, dopamine levels, or dopamine receptor number and function. Lower expressing lines had no specific behavioral or histopathological phenotype. Thus, high expression of mutant human alpha-synuclein resulted in a progressive motor and widespread CNS gliotic phenotype independent of dopaminergic dysfunction in the Tg5093 line.

Age-related microglial activation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration in C57BL/6 mice

Microglial activation was investigated in the brains of young (3 months old) and older (9-12 months old) mice following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Tyrosine hydroxylase (TH)-positive neuronal loss differed significantly between young and older mice. Importantly, the two groups clearly demonstrated a distinct microglial activation pattern. In young mice which showed TH neuronal loss at 1 day (33.4%), 3 days (45.1%), 7 days (47.1%) and 14 days (46.9%), microglial activation was first observed at 1 day, with lesser activation at 3 days and none shown later than 7 days. In contrast, in older mice which showed TH neuronal loss at 1 day (49.6%), 3 days (56.1%), 7 days (71.7%) and 14 days (72.1%), microglial activation occurred at 1 day, further intensified at 3-7 days, and was largely abated by 14 days. The double immunohistochemistry further demonstrated that the activated microglia surrounded dopaminergic neurons in older mice at 7 days, which was sharply in contrast to the young mice which were devoid of massive microglial activation in the SN later than 3 days after MPTP treatment. The present study suggests that age-related microglial activation in the SN may be relevant to the higher susceptibility to MPTP neurotoxicity in older mice.

Up-regulation of inducible nitric oxide synthase in the substantia nigra by lipopolysaccharide causes microglial activation and neurodegeneration

The present study was designed to examine whether expression of iNOS was involved in LPS-induced neurodegeneration in rat substantia nigra (SN) and to study the role of NO in the loss of the SN dopaminergic neurons. In Western blot analysis, iNOS was induced in the SN after injection of LPS in a time- and dose-dependent manner. Immunofluorescence and immunohistochemical analyses revealed that the iNOS is located in a fully activated microglia with the characteristic amoeboid morphology. Furthermore, LPS-induced loss of dopaminergic neurons was significantly inhibited by the administration of L-N(G)-nitroarginine, a selective inhibitor of NOS, and the glucocorticoid dexamethasone. These inhibiting agents for iNOS reduced LPS-induced microglial activation, suggesting that NO has a role in inflammatory-mediated microglial activation. These results demonstrate that LPS induces the expression of iNOS in activated microglia in the SN, and that NO and/or its metabolites may play a crucial role in inflammation-mediated degeneration of dopaminergic neurons.

The role of oxidative stress in paraquat-induced neurotoxicity in rats: protection by non peptidyl superoxide dismutase mimetic

Herbicides, including paraquat, may produce neurodegenerative effect when given both peripherally and into the brain though the pathophysiological mechanism is still unknown. Microinfusion of paraquat into the Substantia Nigra (50 microg) produced increased motor activity, jumping and circling opposite to the injection site, associated with ECoG desynchronization, high voltage epileptogenic spikes, and with neuropathological effects. These effects were accompanied by increase of malondialdehyde (MDA) levels in the Substantia Nigra, suggesting that paraquat was able to induce oxidative stress when injected directly into the rat brain. Pre-treatment of rats with M40401, a non peptidyl superoxide dismutase (SOD) mimetic given directly into the Substantia Nigra or i.p. prevented both behavioural, electrocorticogram and neuropathological effects and MDA elevation. Taken together, these results demonstrate that paraquat produces brain damage via abnormal formation of oxygen free radicals and that this effect may be counteracted by novel SOD mimetics.

Additive Neuroprotective Effects of Creatine and a Cyclooxygenase 2 Inhibitor Against Dopamine Depletion in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP) Mouse Model of Parkinson's Disease

There is evidence that both inflammatory mechanisms and mitochondrial dysfunction contribute to Parkinson's disease (PD) pathogenesis. We investigated whether the cyclooxygenase 2 (COX-2) inhibitor rofecoxib either alone or in combination with creatine could exert neuroprotective effects in the 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine model of PD in mice. Both rofecoxib and creatine administered alone protected against striatal dopamine depletions and loss of substantia nigra tyrosine hydroxylase immunoreactive neurons. Administration of rofecoxib with creatine produced significant additive neuroprotective effects against dopamine depletions. These results suggest that a combination of a COX-2 inhibitor with creatine might be a useful neuroprotective strategy for PD.

Evidence for dopamine-derived hydroxyl radical formation in the nigrostriatal system in response to axotomy

We have evaluated the ability of the injured nigrostriatal dopaminergic system to produce highly reactive hydroxyl radicals ((*)OH) by the electrochemical detection of salicylate hydroxylation. Unilateral transection of the medial forebrain bundle transiently increased the formation of (*)OH in substantia nigra (SN) but not in striatum during the first 48 h postlesion, when most relevant changes in terms of oxidatively modified proteins take place. Short-term adaptive axotomy-induced changes in substantia nigra included downregulation of nigral tyrosine hydroxylase (TH) and dopamine transporter (DAT) mRNA expression and more intense TH immunoreactivity. Maintained inhibition of monoamine oxidase activity with deprenyl totally prevented the axotomy-induced formation of (*)OH, thus demonstrating the dopaminergic nature of these radicals. In contrast, deprenyl treatment, which is associated with a diminution in free radical production, failed to delay the onset of dopaminergic degeneration. This observation highlights the importance of being extremely cautious when analyzing parameters of oxidative stress and extrapolating them as a primary cause of cell death in the context of neurodegeneration. Long-term adaptive changes included a dramatic downregulation of DAT mRNA expression along with a moderate decrease in TH mRNA levels in SN. We anticipate a key regulatory role of the DAT to maximally optimize dopaminergic transmission in the synaptic cleft under conditions of degeneration.

Long-term striatal overexpression of GDNF selectively downregulates tyrosine hydroxylase in the intact nigrostriatal dopamine system

Sustained neurotrophic factor treatment in neurodegenerative disorders such as Parkinson's disease is likely to affect both degenerating and intact neurons. To investigate the effect of long-term glial cell line-derived neurotrophic factor (GDNF) overexpression on intact nigrostriatal dopamine neurons, we injected a recombinant lentiviral vector encoding GDNF, or green fluorescent protein, in the right striatum of young adult rats. Thirteen months after viral injection GDNF levels were 4.5 ng/mg tissue in the striatum and 0.9 ng/mg in the substantia nigra as measured by ELISA, representing a 25-100-fold increase above control vector- or nontransduced tissue. GDNF overexpression significantly reduced tyrosine hydroxylase mRNA levels (by 39-72%) in the substantia nigra and ventral tegmental area neurons, and the optical density of tyrosine hydroxylase-immunoreactive innervation in the striatum was reduced by 25-52% with the most prominent reductions appearing caudally. No significant reduction was seen in striatal vesicular monoamine transporter 2-immunoreactivity or [3H]mazindole binding autoradiography to dopamine uptake sites, two other presynaptic markers in dopamine axon terminals. The striatal D1 and D2 receptor binding as determined by [3H]SCH23390 and [3H]spiperone binding, respectively, was unaltered relative to the intact side in both treatment groups. Preproenkephalin mRNA levels in postsynaptic striatal neurons, which increase upon removal of striatal dopamine, were also unaffected by the GDNF treatment. Taken together our findings indicate that sustained GDNF administration to intact nigrostriatal dopamine neurons selectively reduces tyrosine hydroxylase expression, without altering striatal dopamine transmission to the extent that compensatory changes in several other components related to dopamine storage and signalling occur.

Tyrosine phosphatase inhibition enhances neurotrophin potency and rescues nigrostriatal neurons in adult rats

Neurotrophic factors regulate a variety of cellular processes, including neuronal survival during development and after injury. For instance, brain-derived neurotrophic factor (BDNF) can prevent the death of dopaminergic substantia nigra neurons in rats. Most neurotrophic factor receptors, such as TrkB for BDNF, are tyrosine kinases whose signaling is terminated by protein tyrosine phosphatases (PTPs). We tested the idea that inhibition of PTPs, and thus potentially enhancement of the efficiency of endogenous trophic factors and their receptors, would lead to increased neuronal survival. After a 2-week infusion of the small PTP inhibitor molecule peroxovanadium (pVa, pervanadate) close to the substantia nigra of adult rats, up to 66% of axotomized substantia nigra neurons had survived, compared to only 33% in control rats infused with PBS. PVa most likely affected TrkB and/or downstream signaling molecules, as ineffective doses of BDNF and pVa had a synergistic effect when given simultaneously, rescuing 82% of the neurons. PVa stimulated tyrosine hydroxylase (TH) expression in the noninjured substantia nigra but did not prevent axotomy-induced loss of TH. These results raise the possibility that PTP inhibition can prevent neuronal death by enhancing neurotrophic factor signaling pathways in the adult mammalian nervous system, identifies an important role for PTPs in neuronal functioning, and points to a novel small molecule treatment approach for neurologic disorders