Evidence of oligodendrogliosis in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinsonism

AIMS

Mice and nonhuman primates administered with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) represent elective experimental models of Parkinsonism, in which degeneration of the nigrostriatal dopaminergic pathway is associated with prominent neuroinflammation, characterized by activated microglia and astrocytes in both substantia nigra (SN) and striatum. To date, it is unknown whether oligodendrocytes play a role in these events.

METHODS

We performed a detailed qualitative and quantitative analysis of oligodendrocyte-associated changes induced by acute and chronic MPTP treatment, in the SN and striatum of mice and macaques respectively. Oligodendrocytes were immunolabelled by cell-specific markers and analysed by confocal microscopy.

RESULTS

In both experimental models, MPTP treatment induces an increase in oligodendrocyte cell number and average size, as well as in the total area occupied by this cell type per tissue section, accompanied by evident morphological changes. This multifaceted array of changes, herein referred to as oligodendrogliosis, significantly correlates with the reduction in the level of dopaminergic innervation to the striatum.

CONCLUSIONS

This event, associated with early damage of the dopaminergic neurone axons and of the complex striatal circuits of which they are part, may result in an important, although neglected, aspect in the onset and progression of Parkinsonism.

Role of the Akt/GSK-3β/CRMP-2 pathway in axon degeneration of dopaminergic neurons resulting from MPP+ toxicity

Parkinson׳s disease (PD) is the most common neurodegenerative disease of the basal ganglia. Earlier reports suggest that the main pathological change in PD is due to apoptosis of dopaminergic neuronal soma in the substantia nigra (SN). The therapies for PD are also largely focused on the prevention of degeneration of the neuronal soma. However, these treatments can only provide temporary relief by delaying the progression of the disease and are therefore unable to prevent the long term neurodegeneration process. This limitation of the existing therapeutic treatment indicates that there may be other causes that either occur earlier or are independent of apoptosis of neuronal soma. Previous studies have shown that axon degeneration may play an important role in PD, and that this may occur at an early stage of the disease. Thus, preventing axon degeneration may be a potential new approach for therapeutic treatment for PD and future therapies can be useful if emphasis is given on the mechanisms of axon degeneration. It has been recognized that microtubule disassembly leads to axon degeneration because the depolymerized microtubules are more likely to be degraded. Previous studies have shown that glycogen synthase kinase-3β (GSK-3β)/collapsin response mediator protein 2 (CRMP-2) signaling pathway could be regulated by Akt for axonal-dendritic polarity. CRMP-2 is critical for specifying axon/dendrite fate possibly by promoting neurite elongation via microtubule assembly. However, whether Akt could regulate GSK-3β/CRMP-2 pathway and the possible effects of this regulation is unclear in dopaminergic axon degeneration induced by 1-methyl-4-phenylpyridiniumion (MPP+). In this study, we observe the degeneration of axon and neuronal soma by scanning electron microscope and tyrosine hydroxylase staining (TH) using a PD model in dopaminergic neurons in vitro. In addition to this, we detect the expression of total and phosphorylated form of Akt, GSK-3β and CRMP-2, as well as the axonal injury marker amyloid precursor protein (APP). From our studies, we observe that axon degeneration is a characteristic feature in the cascade of events that follow when neurons are induced by MPP+. This degeneration process occurs earlier in case of PD and is more severe than the degeneration of the neuronal soma and Akt/ GSK-3β/CRMP-2 pathway is involved in this process.

Causes and consequences of degeneration of the dorsal motor nucleus of the vagus nerve in Parkinson's disease

SIGNIFICANCE

Parkinson's disease (PD) is no longer considered merely a movement disorder caused by degeneration of dopamine neurons in the midbrain. It is now recognized as a widespread neuropathological syndrome accompanied by a variety of motor and nonmotor clinical symptoms. As such, any hypothesis concerning PD pathogenesis and pathophysiology must account for the entire spectrum of disease and not solely focus on the dopamine system.

RECENT ADVANCES

Based on its anatomy and the intrinsic properties of its neurons, the dorsal motor nucleus of the vagus nerve (DMV) is uniquely vulnerable to damage from PD. Fibers in the vagus nerve course throughout the gastrointestinal (GI) tract to and from the brainstem forming a close link between the peripheral and central nervous systems and a point of proximal contact between the environment and areas where PD pathology is believed to start. In addition, DMV neurons are under high levels of oxidative stress due to their high level of α-synuclein expression, fragile axons, and specific neuronal physiology. Moreover, several consequences of DMV damage, namely, GI dysfunction and unrestrained inflammation, may propagate a vicious cycle of injury affecting vulnerable brain regions.

CRITICAL ISSUES

Current evidence to suggest the vagal system plays a pivotal role in PD pathogenesis is circumstantial, but given the current state of the field, the time is ripe to obtain direct experimental evidence to better delineate it.

FUTURE DIRECTIONS

Better understanding of the DMV and vagus nerve may provide insight into PD pathogenesis and a neural highway with direct brain access that could be harnessed for novel therapeutic interventions.

Methamphetamine causes degeneration of dopamine cell bodies and terminals of the nigrostriatal pathway evidenced by silver staining

Methamphetamine is a widely abused illicit drug. Recent epidemiological studies showed that methamphetamine increases the risk for developing Parkinson's disease (PD) in agreement with animal studies showing dopaminergic neurotoxicity. We examined the effect of repeated low and medium doses vs single high dose of methamphetamine on degeneration of dopaminergic terminals and cell bodies. Mice were given methamphetamine in one of the following paradigms: three injections of 5 or 10 mg/kg at 3 h intervals or a single 30 mg/kg injection. The integrity of dopaminergic fibers and cell bodies was assessed at different time points after methamphetamine by tyrosine hydroxylase immunohistochemistry and silver staining. The 3 × 10 protocol yielded the highest loss of striatal dopaminergic terminals, followed by the 3 × 5 and 1 × 30. Some degenerating axons could be followed from the striatum to the substantia nigra pars compacta (SNpc). All protocols induced similar significant degeneration of dopaminergic neurons in the SNpc, evidenced by amino-cupric-silver-stained dopaminergic neurons. These neurons died by necrosis and apoptosis. Methamphetamine also killed striatal neurons. By using D1-Tmt/D2-GFP BAC transgenic mice, we observed that degenerating striatal neurons were equally distributed between direct and indirect medium spiny neurons. Despite the reduced number of dopaminergic neurons in the SNpc at 30 days after treatment, there was a partial time-dependent recovery of dopamine terminals beginning 3 days after treatment. Locomotor activity and motor coordination were robustly decreased 1-3 days after treatment, but recovered at later times along with dopaminergic terminals. These data provide direct evidence that methamphetamine causes long-lasting loss/degeneration of dopaminergic cell bodies in the SNpc, along with destruction of dopaminergic terminals in the striatum.

An alternative medical approach for the neuroprotective therapy to slow the progression of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by the core symptoms such as bradykinesia, resting tremor, rigidity and postural instability. Currently, pharmacotherapy and surgical approaches for the treatments of PD can only improve the neurological symptoms. Therefore, to search neuroprotective therapies using pharmacological and nonpharmacological approaches could be important to delay the progression of pathogenesis in PD. Coenzyme Q10 (CoQ10) is a component of the electron transport chain as well as an important antioxidant in mitochondrial and lipid membranes. The central role of CoQ10 in two areas implicated in the pathogenesis of PD, mitochondrial dysfunction and oxidative damages, suggest that it may be useful for treatment to slow the progression of PD. The neuroprotective effect of CoQ10 has been reported in several in vivo and in vitro models of neurodegenerative disorders. Although CoQ10 attenuated the toxin-induced reduction of dopamine content and tyrosine hydroxylase-immunoreactive neurons in the striatum of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model, it is still unknown how this nutrition affects the mitochondrial function. We demonstrated that oral administration of CoQ10 significantly attenuated the loss of dopaminergic nerve terminals induced by MPTP treatment. Furthermore, our experimental data indicate that an inhibition of mitochondrial cytochrome c release is one of the primary targets for CoQ10 and may lead to a potent neuroprotection.

Microtubule alterations occur early in experimental parkinsonism and the microtubule stabilizer epothilone D is neuroprotective

The role of microtubule (MT) dysfunction in Parkinson's disease is emerging. It is still unknown whether it is a cause or a consequence of neurodegeneration. Our objective was to assess whether alterations of MT stability precede or follow axonal transport impairment and neurite degeneration in experimental parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in C57Bl mice. MPTP induced a time- and dose-dependent increase in fibres with altered mitochondria distribution, and early changes in cytoskeletal proteins and MT stability. Indeed, we observed significant increases in neuron-specific βIII tubulin and enrichment of deTyr tubulin in dopaminergic neurons. Finally, we showed that repeated daily administrations of the MT stabilizer Epothilone D rescued MT defects and attenuated nigrostriatal degeneration induced by MPTP. These data suggest that alteration of ΜΤs is an early event specifically associated with dopaminergic neuron degeneration. Pharmacological stabilization of MTs may be a viable strategy for the management of parkinsonism.

Glial-mediated inflammation underlying parkinsonism

The interest in studying neuroimmune interactions is increasing in the scientific community, and for many researchers, immunity is becoming a crucial factor in the understanding of the physiology of the normal brain as well as the biology underlying neurodegenerative diseases. Mounting data over the last two decades point toward immune and inflammatory alterations as important mediators of the progressive dopaminergic degeneration in Parkinson's disease. The purpose of this review is to address, under a historical perspective, as well as in the light of recent reports, the glial-mediated inflammatory and immune responses that occur in Parkinsonism. In line with this, this review also evaluates and highlights available anti-inflammatory drugs and putative targets for Parkinson's disease therapy for the near future.

DLP1-dependent mitochondrial fragmentation mediates 1-methyl-4-phenylpyridinium toxicity in neurons: implications for Parkinson's disease

Selective degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) can be modeled by the administration of the neurotoxin 1-methyl-4-phenylpyridinium (MPP(+) ). Because abnormal mitochondrial dynamics are increasingly implicated in the pathogenesis of PD, in this study, we investigated the effect of MPP(+) on mitochondrial dynamics and assessed temporal and causal relationship with other toxic effects induced by MPP(+) in neuronal cells. In SH-SY5Y cells, MPP(+) causes a rapid increase in mitochondrial fragmentation followed by a second wave of increase in mitochondrial fragmentation, along with increased DLP1 expression and mitochondrial translocation. Genetic inactivation of DLP1 completely blocks MPP(+) -induced mitochondrial fragmentation. Notably, this approach partially rescues MPP(+) -induced decline in ATP levels and ATP/ADP ratio and increased [Ca(2+) ](i) and almost completely prevents increased reactive oxygen species production, loss of mitochondrial membrane potential, enhanced autophagy and cell death, suggesting that mitochondria fragmentation is an upstream event that mediates MPP(+) -induced toxicity. On the other hand, thiol antioxidant N-acetylcysteine or glutamate receptor antagonist D-AP5 also partially alleviates MPP(+) -induced mitochondrial fragmentation, suggesting a vicious spiral of events contributes to MPP(+) -induced toxicity. We further validated our findings in primary rat midbrain dopaminergic neurons that 0.5 μm MPP(+) induced mitochondrial fragmentation only in tyrosine hydroxylase (TH)-positive dopaminergic neurons in a similar pattern to that in SH-SY5Y cells but had no effects on these mitochondrial parameters in TH-negative neurons. Overall, these findings suggest that DLP1-dependent mitochondrial fragmentation plays a crucial role in mediating MPP(+) -induced mitochondria abnormalities and cellular dysfunction and may represent a novel therapeutic target for PD.

Loss of striatal dopaminergic terminals during the early stage in response to MPTP injection in C57BL/6 mice

The molecular mechanisms underlying MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced dopaminergic (DAergic) neuronal death in vivo are still not fully understood. To investigate the selective DAergic neurotoxicity, we have developed an immunological technique to isolate DAergic synaptosomes from mouse striatal tissues using an antibody against 20 amino acid residues in the extracellular second loop of dopamine transporter (DAT). The DAT protein level in the isolated DAergic synaptosomes was markedly decreased at 16 h after a single injection of 30 mg/kg MPTP, but not in striatal homogenate and crude synaptosomes fraction. GBR-12909, a dopamine uptake inhibitor, completely reversed the MPTP-induced decrease of DAT protein in the DAergic synaptosomes. These results suggest that the isolated DAergic synaptosomes can be useful to identify mechanisms of loss of the nerve terminals.

Microtubule dysfunction precedes transport impairment and mitochondria damage in MPP+ -induced neurodegeneration

Dysfunction of the microtubule (MT) system is an emerging theme in the pathogenesis of Parkinson's disease. This study was designed to investigate the putative role of MT dysfunction in dopaminergic neuron death induced by the neurotoxin 1-methyl-4-phenylpiridinium (MPP(+)). In nerve growth factor-differentiated PC12 cells, we have analyzed post-translational modifications of tubulin known to be associated with differently dynamic MTs and show that MPP(+) causes a selective loss of dynamic MTs and a concomitant enrichment of stable MTs. Through a direct live cell imaging approach, we show a significant reduction of MT dynamics following exposure to MPP(+) and a reorientation of MTs. Furthermore, these alterations precede the impairment of intracellular transport as revealed by changes in mitochondria movements along neurites and their accumulation into varicosities. We have also analyzed activation of caspase 3 and mitochondrial injury, well-known alterations induced by MPP(+), and found that they are noticeable only when MT dysfunction is already established. These data provide the first evidence that axonal transport impairment and mitochondrial damage might be a consequence of MT dysfunction in MPP(+) -induced neurodegeneration, lending support to the concept that alterations of MT organization and dynamics could play a pivotal role in neuronal death in Parkinson's disease.

Kinetics of microglial activation and degeneration of dopamine-containing neurons in a rat model of Parkinson disease induced by 6-hydroxydopamine

In both Parkinson disease and in animal models of Parkinson disease, there is a microglial reaction in addition to the loss of dopaminergic neurons in the ventral midbrain. To determine the pathological role of this microglial reaction, we analyzed the kinetics of microglial activation and dopaminergic cell death induced in rats with the neurotoxin 6-hydroxydopamine. As early as Day 1 after the injection, there was a decline in the motor performance of the 6-hydroxydopamine-lesioned rats that correlated with a reduction of dopaminergic innervation of the contralateral striatum. Loss of dopaminergic neurons in the ventral midbrain developed a few days later and seemed to follow a specific temporospatial pattern. Degenerating neurons and activated microglia were seen only in areas in which dopaminergic cells were no longer observed, suggesting that the loss of the dopaminergic phenotype preceded the degenerative process. In sham-lesioned rats, there was a transient activation of microglia in the vicinity of the needle tract without any cell degeneration. This chronology of events supports the hypothesis that microglial activation is a secondary rather than primary phenomenon in dopaminergic cell degeneration induced by 6-hydroxydopamine.

Adenosine A(2A) receptors in Parkinson's disease treatment

Latest results on the action of adenosine A(2A) receptor antagonists indicate their potential therapeutic usefulness in the treatment of Parkinson's disease. Basal ganglia possess high levels of adenosine A(2A) receptors, mainly on the external surfaces of neurons located at the indirect tracts between the striatum, globus pallidus, and substantia nigra. Experiments with animal models of Parkinson's disease indicate that adenosine A(2A) receptors are strongly involved in the regulation of the central nervous system. Co-localization of adenosine A(2A) and dopaminergic D2 receptors in striatum creates a milieu for antagonistic interaction between adenosine and dopamine. The experimental data prove that the best improvement of mobility in patients with Parkinson's disease could be achieved with simultaneous activation of dopaminergic D2 receptors and inhibition of adenosine A(2A) receptors. In animal models of Parkinson's disease, the use of selective antagonists of adenosine A(2A) receptors, such as istradefylline, led to the reversibility of movement dysfunction. These compounds might improve mobility during both monotherapy and co-administration with L-DOPA and dopamine receptor agonists. The use of adenosine A(2A) receptor antagonists in combination therapy enables the reduction of the L-DOPA doses, as well as a reduction of side effects. In combination therapy, the adenosine A(2A) receptor antagonists might be used in both moderate and advanced stages of Parkinson's disease. The long-lasting administration of adenosine A(2A) receptor antagonists does not decrease the patient response and does not cause side effects typical of L-DOPA therapy. It was demonstrated in various animal models that inhibition of adenosine A(2A) receptors not only decreases the movement disturbance, but also reveals a neuroprotective activity, which might impede or stop the progression of the disease. Recently, clinical trials were completed on the use of istradefylline (KW-6002), an inhibitor of adenosine A(2A) receptors, as an anti-Parkinson drug.

GSTpi expression in MPTP-induced dopaminergic neurodegeneration of C57BL/6 mouse midbrain and striatum

MPTP-induced dopaminergic neurotoxicity involves major biochemical processes such as oxidative stress and impaired energy metabolism, leading to a significant reduction in the number of nigrostriatal dopaminergic neurons. Glutathione S-transferase pi (GSTpi) is a phase II detoxifying enzyme that provides protection of cells from injury by toxic chemicals and products of oxidative stress. In humans, polymorphisms of GSTP1 affect substrate selectivity and stability increasing the susceptibility to parkinsonism-inducing effects of environmental toxins. Given the ability of MPTP to increase the levels of reactive oxygen species and the link between altered redox potential and the expression and activity of GSTpi, we investigated the effect of MPTP on GSTpi cellular concentration in an in vivo model of Parkinson's disease. The present study demonstrates that GSTpi is actively expressed in both substantia nigra pars compacta and striatum of C57BL/6 mice brain, mostly in oligodendrocytes and astrocytes. After systemic administration of MPTP, GSTpi expression is significantly increased in glial cells in the vicinity of dopaminergic neurons cell bodies and fibers. The results suggest that GSTpi expression may be part of the mechanism underlying the ability of glial cells to elicit protection against the mechanisms involved in MPTP-induced neuronal death.

1-Methyl-4-phenylpyridinium affects fast axonal transport by activation of caspase and protein kinase C

Parkinson's disease (PD), a late-onset condition characterized by dysfunction and loss of dopaminergic neurons in the substantia nigra, has both sporadic and neurotoxic forms. Neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and its metabolite 1-methyl-4-phenylpyridinium (MPP+) induce PD symptoms and recapitulate major pathological hallmarks of PD in human and animal models. Both sporadic and MPP+-induced forms of PD proceed through a "dying-back" pattern of neuronal degeneration in affected neurons, characterized by early loss of synaptic terminals and axonopathy. However, axonal and synaptic-specific effects of MPP+ are poorly understood. Using isolated squid axoplasm, we show that MPP+ produces significant alterations in fast axonal transport (FAT) through activation of a caspase and a previously undescribed protein kinase C (PKCdelta) isoform. Specifically, MPP+ increased cytoplasmic dynein-dependent retrograde FAT and reduced kinesin-1-mediated anterograde FAT. Significantly, MPP+ effects were independent of both nuclear activities and ATP production. Consistent with its effects on FAT, MPP+ injection in presynaptic domains led to a dramatic reduction in the number of membranous profiles. Changes in availability of synaptic and neurotrophin-signaling components represent axonal and synaptic-specific effects of MPP+ that would produce a dying-back pathology. Our results identify a critical neuronal process affected by MPP+ and suggest that alterations in vesicle trafficking represent a primary event in PD pathogenesis. We propose that PD and other neurodegenerative diseases exhibiting dying-back neuropathology represent a previously undescribed category of neurological diseases characterized by dysfunction of vesicle transport and associated with the loss of synaptic function.

Temporal mRNA profiles of inflammatory mediators in the murine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). With the exception of a few rare familial forms of the disease, the precise molecular mechanisms underlying PD are unknown. Inflammation is a common finding in the PD brain, but due to the limitation of postmortem analysis its relationship to disease progression cannot be established. However, studies using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD have also identified inflammatory responses in the nigrostriatal pathway that precede neuronal degeneration in the SNpc. To assess the pathological relevance of these inflammatory responses and to identify candidate genes that might contribute to neuronal vulnerability, we used quantitative reverse-transcription polymerase chain reaction (qRT-PCR) to measure mRNA levels of 11 cytokine and chemokine encoding genes in the striatum of MPTP-sensitive (C57BL/6J) and MPTP-insensitive (Swiss Webster, SWR) mice following administration of MPTP. The mRNA levels of all 11 genes changed following MPTP treatment, indicating the presence of inflammatory responses in both strains. Furthermore, of the 11 genes examined only 3, interleukin 6 (Il-6), macrophage inflammatory protein 1 alpha/CC chemokine ligand 3 (Mip-1alpha/Ccl3) and macrophage inflammatory protein 1 beta/CC chemokine ligand 4 (Mip-1beta/Ccl4), were differentially regulated between C57BL/6J and SWR mice. In both mouse strains, the level of monocyte chemoattractant protein 1/CC chemokine ligand 2 (Mcp-1/Ccl2) mRNA was the first to increase following MPTP administration, and might represent a key initiating component of the inflammatory response. Using Mcp-1/Ccl2 knockout mice backcrossed onto a C57BL/6J background we found that MPTP-stimulated Mip-1alpha/Ccl3 and Mip-1beta/Ccl4 mRNA expression was significantly lower in the knockout mice; suggesting that Mcp-1/Ccl2 contributes to MPTP-enhanced expression of Mip-1alpha/Ccl3 and Mip-1beta/Ccl4. However, stereological analysis of SNpc neuronal loss in Mcp-1/Ccl2 knockout and wild-type mice showed no differences. These findings suggest that it is the ability of dopaminergic SNpc neurons to survive an inflammatory insult, rather than genetically determined differences in the inflammatory response itself, that underlie the molecular basis of MPTP resistance.

Chemokines in the MPTP model of Parkinson’s disease: Absence of CCL2 and its receptor CCR2 does not protect against striatal neurodegeneration

Recent studies have invoked inflammation as a major contributor to the pathogenesis of Parkinson's disease (PD). We determined the role of members of the chemokine system, key inflammatory mediators, in PD pathogenesis. In the MPTP model of murine PD, several chemokines, including CC chemokine ligand 2 (CCL2, Monocyte Chemoattractant Protein-1) and CCL3 (Macrophage Inflammatory Protein-1alpha), were upregulated in the striatum and the ventral midbrain. Astrocytes were the predominant source of CCL2 and CCL3 in the striatum and the substantia nigra, and dopaminergic neurons in the substantia nigra constitutively expressed these two chemokines. MPTP treatment resulted in decreased CCL2 expression and increased CCL3 expression in the surviving dopaminergic neurons. Because we found that CCL2 induced production of TNF-alpha in microglial cells, a cytokine known to play a detrimental role in PD, we anticipated that deletion of the genes encoding CCL2 and CCR2, its major receptor, would confer a protective phenotype. However, MPTP-induced striatal dopamine depletion was comparable in double knockout and wild-type mice. Our results demonstrate that chemokines such as CCL2 are induced following MPTP treatment, but that at least within the context of this PD model, the absence of CCL2 and CCR2 does not protect against striatal dopamine loss.

Cellular distribution of interleukin-1α-immunoreactivity after MPTP intoxication in mice

In young rodents, peripheral injection of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) results in a dopaminergic nigrostriatal denervation (during the first week after injection), followed by a spontaneous dopaminergic reinnervation. Sprouting from residual neurons has been proposed to account for this event. It has been shown that an inflammatory process takes place during striatal dopaminergic denervation but its consequences remain controversial. Some clues notably indicate that interleukin (IL)-1alpha may participate in MPTP-induced inflammation and promote recovery. We therefore studied the immunohistochemical localization of IL-1alpha expression in the striatum and ventral mesencephalon at different times (1, 3, 6, 16, and 30 days) after MPTP injection in mice. IL-1alpha-immunoreactivity (ir) was observed in striatum, substantia nigra pars compacta, and ventral tegmental area. Apart from a few localization in mesencephalic activated microglia, IL-1alpha was almost exclusively found in activated astrocytes. However, in the striatal parenchyma, another component of IL-1alpha-ir colocalized with tyrosine hydroxylase (TH)-ir, a marker for dopaminergic neurons. Moreover, some parenchymal TH-positive axons were also found to express the growth cone-associated protein (GAP)-43, a marker for axonal growth cones. In the striatum, IL-1alpha-ir was also detected in a non-astrocytic perivascular component, with a distribution similar to GAP-43-ir. IL-1alpha could thus directly or indirectly influence striatal reorganization after MPTP.

Interleukine-1beta and interleukine-6 levels in striatum and other brain structures after MPTP treatment: influence of behavioral lateralization

MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) induces diminution of the dopamine in nigrostriatal pathway and cognitive deficits in mice. MPTP treatment also increases pro-inflammatory cytokine production in substantia nigra and striatum. Since, pro-inflammatory cytokines influence striatal dopamine content and provoke cognitive impairments, the cognitive defects induced by MPTP may be partly due to brain cytokine induction in other structures than nigrostriatal pathway. Furthermore, behavioral lateralization, as assessed by paw preference, influences cytokine production at the periphery and in the central nervous system. Behavioral lateralization may thus influence brain cytokine levels after MPTP. In order to address these issues, mice selected for paw preference were injected with 25 mg/kg MPTP i.p. for five consecutive days after which striatal dopamine and DOPAC contents were measured by HPLC and IL-1beta and IL-6 quantified by ELISA in the striatum, cerebral cortex, hippocampus and hypothalamus. The results showed that MPTP treatment induced dramatic loss of DA in striatum, simultaneously, IL-6 levels decreased in the striatum and increased in hippocampus and hypothalamus, while IL-1beta levels decreased in the striatum, cerebral cortex and hippocampus. Interestingly, striatal dopamine turnover under basal conditions as well as striatal IL-1beta and IL-6 levels under basal conditions and after MPTP depended on behavioral lateralization. Left pawed mice showed a higher decrease in dopamine turnover and lower cytokine levels as compared to right pawed animals. Behavioral lateralization also influenced IL-6 hippocampal levels under basal conditions and IL-1beta cortical levels after MPTP. From these results, it can be concluded that MPTP-induced cognitive defects are accompanied by an alteration of pro-inflammatory cytokine levels in brain structures other than those involved in the nigrostriatal pathway. In addition, MPTP-induced dopamine decrease is influenced by behavioral lateralization, possibly through an effect on brain cytokine levels.

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.

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

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

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

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

Dopamine D3 receptor as a therapeutic target for antipsychotic and antiparkinsonian drugs

The cloning of the gene for the D3 receptor and subsequent identification of its distribution in brain and pharmacology allowed for serious consideration of the possibility that it might be a target for drugs used to treat schizophrenia and Parkinson's disease (PD). That is because it is highly expressed in limbic regions of the brain, exhibits low expression in motor divisions, and has pharmacologic similarity to the D2 receptor. Thus, antipsychotics that were presumed to block D2 receptors also had high affinity for the D3 receptor. Dopamine agonists used to treat the clinical symptoms of PD also have high affinity for the D3 receptor, and two D3 receptor-preferring agonists were found to be effective for treatment of PD. Many compounds achieving high potency and selectivity are now available, but few have reached clinical testing. Recent findings with respect to the anatomy of this receptor in human brain, altered expression in schizophrenia and PD, and biological models to study its function support the proposal that it is a target for development of drugs to alleviate symptoms in neuropsychiatric and neurologic disorders. Because of distinct aspects of regulation of the D3 receptor, it represents a unique target for therapeutic intervention in schizophrenia without high potential for unintended side effects such as tardive dyskinesia. It may also be that D3 receptor agonists can provide neuroprotective effects in PD and can modify clinical symptoms that D2 receptor-preferring agonists cannot provide.