MPTP-induced dopamine neuron degeneration and glia activation is potentiated in MDMA-pretreated mice

MDMA targets miR-124/MEKK3 via MALAT1 to promote Parkinson's disease progression

BACKGROUND

Parkinson's disease (PD) is a well-known neurodegenerative disease that is usually caused by the progressive loss of dopamine neurons and the formation of Lewy vesicles. 3,4-Methylenedioxymethamphetamine (MDMA) has been reported to cause damage to human substantia nigra neurons and an increased risk of PD, but the exact molecular mechanisms need further investigation.

METHODS

MPTP- and MPP+-induced PD cells and animal models were treated with Nissl staining to assess neuronal damage in the substantia nigra (SN) area; immunohistochemistry to detect TH expression in the SN; TUNEL staining to detect apoptosis in the SN area; Western blotting to detect the inflammatory factors NF-κB, TNF-α, IL-6 and mitogen-activated protein kinase kinase kinase 3 (MEKK3); Griess assay for NO; RT‒qPCR for metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) and miR-124 expression; Cell proliferation was assessed by CCK-8. Dual luciferase reporter genes were used to verify targeting relationships.

RESULTS

MDMA promoted MALAT1 expression, and knockdown of MALAT1 alleviated the MDMA-induced inhibition of SH-SY5Y cell proliferation, inflammation, NO release, SN neuronal injury, and TH expression inhibition. Both inhibition of miR-124 and overexpression of MEKK3 reversed the neuroprotective effects exhibited by knockdown of MALAT1.

CONCLUSION

MDMA promotes MALAT1 expression and inhibits the targeted downregulation of MEKK3 by miR-124, resulting in upregulation of the expression of MEKK3 and finally jointly promoting PD progression.

Inhibition of abnormal C/EBPβ/α-Syn signaling pathway through activation of Nrf2 ameliorates Parkinson's disease-like pathology

Parkinson's disease (PD) is characterized by the formation of Lewy bodies (LBs) in the brain. These LBs are primarily composed of α-Synuclein (α-Syn), which has aggregated. A recent report proposes that CCAAT/enhancer-binding proteins β (C/EBPβ) may act as an age-dependent transcription factor for α-Syn, thereby initiating PD pathologies by regulating its transcription. Potential therapeutic approaches to address PD could involve targeting the regulation of α-Syn by C/EBPβ. This study has revealed that Nrf2, also known as nuclear factor (erythroid-derived 2)-like 2 (NFE2L2), suppresses the transcription of C/EBPβ in SH-SY5Y cells when treated with MPP+ . To activate Nrf2, sulforaphane, an Nrf2 activator, was administered. Additionally, C/EBPβ was silenced using C/EBPβ-DNA/RNA heteroduplex oligonucleotide (HDO). Both approaches successfully reduced abnormal α-Syn expression in primary neurons treated with MPP+ . Furthermore, sustained activation of Nrf2 via its activator or inhibition of C/EBPβ using C/EBPβ-HDO resulted in a reduction of aberrant α-Syn expression, thus leading to an improvement in the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) in mouse models induced by 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) and those treated with preformed fibrils (PFFs). The data presented in this study illustrate that the activation of Nrf2 may provide a potential therapeutic strategy for PD by inhibiting the abnormal C/EBPβ/α-Syn signaling pathway.

Feruloylated oligosaccharides ameliorate MPTP-induced neurotoxicity in mice by activating ERK/CREB/BDNF/TrkB signalling pathway

BACKGROUND

Feruloylated oligosaccharides (FOs) are natural esterification products of ferulic acid and oligosaccharides.

STUDY DESIGN

In this study, we examined whether FOs contribute to the ensured survival of nigrostriatal dopamine neurons and inhibition of neuroinflammation in Parkinson's disease (PD).

METHODS

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg) was injected intraperitoneally into mice to establish a Parkinson's disease (PD) mouse model. FOs (15 and 30 mg/kg) were orally administered daily to the MPTP-treated mice. The rotarod test, balance beam test, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), quantitative PCR (qPCR), and western blot analyses were performed to examine the neuroprotective effects of FOs on MPTP-treated mice.

RESULTS

Our study indicated that FOs increased the survival of dopamine neurons in the substantia nigra pars compacta (SNc) of the MPTP-treated mice. The neuroprotective effects of FOs were accompanied by inhibited glial activation and reduced inflammatory cytokine production. The mechanistic experiments revealed that the neuroprotective effects of FOs might be mediated through the activation of the ERK/CREB/BDNF/TrkB signalling pathway.

CONCLUSION

This study provides new insights into the mechanism underlying the anti-neuroinflammatory effect of phytochemicals and may facilitate the development of dietary supplements for PD patients. Our results indicate that FOs can be used as potential modulators for the prevention and treatment of PD.

Role of Microglia in Psychostimulant Addiction

The use of psychostimulant drugs can modify brain function by inducing changes in the reward system, mainly due to alterations in dopaminergic and glutamatergic transmissions in the mesocorticolimbic pathway. However, the etiopathogenesis of addiction is a much more complex process. Previous data have suggested that microglia and other immune cells are involved in events associated with neuroplasticity and memory, which are phenomena that also occur in addiction. Nevertheless, how dependent is the development of addiction on the activity of these cells? Although the mechanisms are not known, some pathways may be involved. Recent data have shown psychoactive substances may act directly on immune cells, alter their functions and induce various inflammatory mediators that modulate synaptic activity. These could, in turn, be involved in the pathological alterations that occur in substance use disorder. Here, we extensively review the studies demonstrating how cocaine and amphetamines modulate microglial number, morphology, and function. We also describe the effect of these substances in the production of inflammatory mediators and a possible involvement of some molecular signaling pathways, such as the toll-like receptor 4. Although the literature in this field is scarce, this review compiles the knowledge on the neuroimmune axis that is involved in the pathogenesis of addiction, and suggests some pharmacological targets for the development of pharmacotherapy.

Suppression of abnormal α-synuclein expression by activation of BDNF transcription ameliorates Parkinson's disease-like pathology

Parkinson’s disease (PD) is characterized by the formation of Lewy bodies (LBs) in the brain. LBs are mainly composed of phosphorylated and aggregated α-synuclein (α-Syn). Thus, strategies to reduce the expression of α-Syn offer promising therapeutic avenues for PD. DNA/RNA heteroduplex oligonucleotides (HDOs) are a novel technology for gene silencing. Using an α-Syn-HDO that specifically targets α-Syn, we examined whether α-Syn-HDO attenuates pathological changes in the brain of mouse models of PD. Overexpression of α-Syn induced dopaminergic neuron degeneration through inhibition of cyclic AMP-responsive-element-binding protein (CREB) and activation of methyl CpG binding protein 2 (MeCP2), resulting in brain-derived neurotrophic factor (BDNF) downregulation. α-Syn-HDO exerted a more potent silencing effect on α-Syn than α-Syn-antisense oligonucleotides (ASOs). α-Syn-HDO attenuated abnormal α-Syn expression and ameliorated dopaminergic neuron degeneration via BDNF upregulation by activation of CREB and inhibition of MeCP2. These findings demonstrated that inhibition of α-Syn by α-Syn-HDO protected against dopaminergic neuron degeneration via activation of BDNF transcription. Therefore, α-Syn-HDO may serve as a new therapeutic agent for PD.

Characterization of Nasco grape pomace-loaded nutriosomes and their neuroprotective effects in the MPTP mouse model of Parkinson’s disease

Grape pomaces have recently received great attention for their richness in polyphenols, compounds known to exert anti-inflammatory and antioxidant effects. These pomaces, however, have low brain bioavailability when administered orally due to their extensive degradation in the gastrointestinal tract. To overcome this problem, Nasco pomace extract was incorporated into a novel nanovesicle system called nutriosomes, composed of phospholipids (S75) and water-soluble maltodextrin (Nutriose® FM06). Nutriosomes were small, homogeneously dispersed, had negative zeta potential, and were biocompatible with intestinal epithelial cells (Caco-2). Nasco pomace extract resulted rich in antioxidant polyphenols (gallic acid, catechin, epicatechin, procyanidin B2, and quercetin). To investigate the neuroprotective effect of Nasco pomace in the subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson’s disease (PD), Nasco nutriosomes or Nasco suspension was administered intragastrically and their neuroprotective effects were evaluated. Degeneration of nigro-striatal dopaminergic neurons induced by subacute MPTP treatment, the pathological hallmark of PD, was assessed through immunohistochemical evaluation of tyrosine hydroxylase (TH) in the caudate-putamen (CPu) and substantia nigra pars compacta (SNc), and the dopamine transporter (DAT) in CPu. Immunohistochemical analysis revealed that Nasco nutriosomes significantly prevented the reduction in TH- and DAT-positive fibres in CPu, and the number of TH-positive cells in SNc following subacute MPTP treatment, while Nasco suspension counteracted MPTP toxicity exclusively in SNc. Overall, these results highlight the therapeutic effects of Nasco pomace extract when administered in a nutriosome formulation in the subacute MPTP mouse model of PD and validate the effectiveness of the nutriosome preparation over suspension as an innovative nano-drug delivery system for in vivo administration.

MDMA related neuro-inflammation and adenosine receptors

3,4-methylenedioxymethamphetamine (MDMA) is a world-wide abused psychostimulant, which has the neurotoxic effects on dopaminergic and serotonergic neurons in both rodents and non-human primates. Adenosine acts as a neurotransmitter in the brain through the activation of four specific G-protein-coupled receptors and it acts as a neuromodulator of dopamine neurotransmission. Recent studies suggest that stimulation of adenosine receptors oppose many behavioral effects of methamphetamines. This review summarizes the specific cellular mechanisms involved in MDMA neuroinflammatory effects, along with the protective effects of adenosine receptors.

Neurotoxicity of MDMA: Main effects and mechanisms

Preclinical and clinical studies indicate that 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy'), in addition to having abuse potential, may elicit acute and persistent abnormalities of varying severity at the central level. Importantly, neurotoxic effects of MDMA have been demonstrated in experimental animals. Accordingly, central toxicity induced by MDMA may pose a serious harm for health, since MDMA is among the substances that are used for recreational purposes by young and adult people. This review provides a concise overview of recent findings from preclinical and clinical studies that evaluated the central effects of MDMA, and the mechanisms involved in the neurotoxicity induced by this amphetamine-related drug.

Activation of Antioxidant and Proteolytic Pathways in the Nigrostriatal Dopaminergic System After 3,4-Methylenedioxymethamphetamine Administration: Sex-Related Differences

3,4-Methylenedioxymethamphetamine (MDMA, “ecstasy”) is an amphetamine-related drug that may damage the dopaminergic nigrostriatal system. To investigate the mechanisms that sustain this toxic effect and ascertain their sex-dependence, we evaluated in the nigrostriatal system of MDMA-treated (4 × 20 mg/kg, 2 h apart) male and female mice the activity of superoxide dismutase (SOD), the gene expression of SOD type 1 and 2, together with SOD1/2 co-localization with tyrosine hydroxylase (TH)-positive neurons. In the same mice and brain areas, activity of glutathione peroxidase (GPx) and of β2/β5 subunits of the ubiquitin-proteasome system (UPS) were also evaluated. After MDMA, SOD1 increased in striatal TH-positive terminals, but not nigral neurons, of males and females, while SOD2 increased in striatal TH-positive terminals and nigral neurons of males only. Moreover, after MDMA, SOD1 gene expression increased in the midbrain of males and females, whereas SOD2 increased only in males. Finally, MDMA increased the SOD activity in the midbrain of females, without affecting GPx activity, decreased the β2/β5 activities in the striatum of males and the β2 activity in the midbrain of females. These results suggest that the mechanisms of MDMA-induced neurotoxic effects are sex-dependent and dopaminergic neurons of males could be more sensitive to SOD2- and UPS-mediated toxic effects.

The C-terminal domain of the heavy chain of tetanus toxin prevents the oxidative and nitrosative stress induced by acute toxicity of 1-methyl-4-phenylpyridinium, a rat model of Parkinson's disease

The recombinant carboxyl-terminal domain of the heavy chain of tetanus toxin (Hc-TeTx) exerts neuroprotective and neurorestorative effects on the dopaminergic system of animal models of Parkinson's disease (PD). The present study aimed to determine the effect of the Hc-TeTx fragment on the markers of oxidative stress and nitrosative stress generated by the acute toxicity of 1-methyl-4-phenylpyridinium (MPP⁺). For this purpose, the Hc-TeTx fragment was administered once a day in three 20 μg/kg consecutive injections into the grastrocnemius muscle of the rats, with an intra-striatal unilateral injection of 1 μL of MPP⁺ [10 μg/mL] then administered in order to cause a dopaminergic lesion. The results obtained show that the rats treated with Hc-TeTx plus MPP⁺ presented an increase in the expression of tyrosine hydroxylase (TH), a significantly greater decrease in the levels of the markers of oxidative stress, nitrosative stress, and neurodegeneration than that observed for the group injured with only MPP⁺. Moreover, it was observed that total superoxide dismutase (SOD) and copper/zinc SOD activity increased with the administration of Hc-TeTx. Finally, immunoreactivity levels were observed to decrease for the levels of 3-nitrotyrosine and the glial fibrillary acidic protein in the ipsilateral striatum of the rats treated with Hc-TeTx plus MPP⁺, in contrast with those lesioned with MPP⁺ alone. Our results demonstrate that the recombinant Hc-TeTx fragment may be a potent antioxidant and, therefore, could be suggested as a therapeutic tool against the dopaminergic neuronal impairment observed in the early stages of PD.

The CD200R1 microglial inhibitory receptor as a therapeutic target in the MPTP model of Parkinson's disease

Background

It is suggested that neuroinflammation, in which activated microglial cells play a relevant role, contributes to the development of Parkinson’s disease (PD). Consequently, the modulation of microglial activation is a potential therapeutic target to be taken into account to act against the dopaminergic neurodegeneration occurring in this neurological disorder. Several soluble and membrane-associated inhibitory mechanisms contribute to maintaining microglial cells in a quiescent/surveillant phenotype in physiological conditions. However, the presence of activated microglial cells in the brain in PD patients suggests that these mechanisms have been somehow overloaded. We focused our interest on one of the membrane-associated mechanisms, the CD200-CD200R1 ligand-receptor pair.

Methods

The acute MPTP experimental mouse model of PD was used to study the temporal pattern of mRNA expression of CD200 and CD200R1 in the context of MPTP-induced dopaminergic neurodegeneration and neuroinflammation. Dopaminergic damage was assessed by tyrosine hydroxylase (TH) immunoreactivity, and neuroinflammation was evaluated by the mRNA expression of inflammatory markers and IBA1 and GFAP immunohistochemistry. The effect of the modulation of the CD200-CD200R1 system on MPTP-induced damage was determined by using a CD200R1 agonist or CD200 KO mice.

Results

MPTP administration resulted in a progressive decrease in TH-positive fibres in the striatum and TH-positive neurons in the substantia nigra pars compacta, which were accompanied by transient astrogliosis, microgliosis and expression of pro- and anti-inflammatory markers. CD200 mRNA levels rapidly decreased in the ventral midbrain after MPTP treatment, while a transient decrease of CD200R1 mRNA expression was repeatedly observed in this brain area at earlier and later phases. By contrast, a transient increase in CD200R1 expression was observed in striatum. The administration of a CD200R1 agonist resulted in the inhibition of MPTP-induced dopaminergic neurodegeneration, while microglial cells showed signs of earlier activation in CD200-deficient mice.

Conclusions

Collectively, these findings provide evidence for a correlation between CD200-CD200R1 alterations, glial activation and neuronal loss. CD200R1 stimulation reduces MPTP-induced loss of dopaminergic neurons, and CD200 deficiency results in earlier microglial activation, suggesting that the potentiation of CD200R1 signalling is a possible approach to controlling neuroinflammation and neuronal death in PD.

In utero exposure to dexamethasone causes a persistent and age-dependent exacerbation of the neurotoxic effects and glia activation induced by MDMA in dopaminergic brain regions of C57BL/6J mice

Clinical and preclinical evidence indicates that prenatal exposure to glucocorticoids may induce detrimental effects in the offspring, including reduction in fetal growth and alterations in the CNS. On this basis, the present study investigated whether in utero exposure to high levels of glucocorticoids is a risk factor that may lead to an exacerbation of the central noxious effects induced by psychoactive drugs consumed later in life. To this end, pregnant C57BL6/J dams were treated with dexamethasone (DEX, 0.05 mg/kg per day) from gestational day 14 until delivery. Thereafter, the male offspring were evaluated to ascertain the magnitude of dopaminergic damage, astrogliosis and microgliosis elicited in the nigrostriatal tract by the amphetamine-related drug 3,4--methylenedioxymethamphetamine (MDMA, 4 × 20 mg/kg, 2 h apart, sacrificed 48 h later) administered at either adolescence or adulthood. Immunohistochemistry was performed in the substantia nigra pars compacta (SNc) and striatum, to evaluate dopaminergic degeneration by measuring tyrosine hydroxylase (TH), as well as astrogliosis and microgliosis by measuring glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (IBA-1), respectively. Moreover, immunohistochemistry was used to ascertain the co-localization of IBA-1 with either the pro-inflammatory interleukin (IL) IL-1β or the anti-inflammatory IL IL-10, in order to determine the microglial phenotype. In utero administration of DEX induced dopaminergic damage by decreasing the density of TH-positive fibers in the striatum, although only in adult mice. MDMA administration induced dopaminergic damage and glia activation in the nigrostriatal tract of adolescent and adult mice. Mice exposed to DEX in utero and treated with MDMA later in life showed a more pronounced loss of dopaminergic neurons (adolescent mice) and astrogliosis (adolescent and adult mice) in the SNc, compared with control mice. These results suggest that prenatal exposure to glucocorticoids may induce an age-dependent and persistent increase in the susceptibility to central toxicity of amphetamine-related drugs used later in life.

Classic and evolving animal models in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor and non-motor symptoms. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and deficiency of dopamine in the striatal region. The primary objective in PD research is to understand the pathogenesis, targets, and development of therapeutic interventions to control the progress of the disease. The anatomical and physiological resemblances between humans and animals gathered the researcher's attention towards the use of animals in PD research. Due to varying age of onset, symptoms, and progression rate, PD becomes heterogeneous which demands the variety of animal models to study diverse features of the disease. Parkinson is a multifactorial disorder, selection of models become important as not a single model shows all the biochemical features of the disease. Currently, conventional pharmacological, neurotoxin-induced, genetically modified and cellular models are available for PD research, but none of them recapitulate all the biochemical characteristics of the disease. In this review, we included the updated knowledge on the main features of currently available in vivo and in vitro models as well as their strengths and weaknesses.

Breathing new life into neurotoxic-based monkey models of Parkinson's disease to study the complex biological interplay between serotonin and dopamine

Numerous clinical studies have shown that the serotonergic system also degenerates in patients with Parkinson's disease. The causal role of this impairment in Parkinson's symptomatology and the response to treatment remains to be refined, in particular thanks to approaches allowing the two components DA and 5-HT to be isolated if possible. We have developed a macaque monkey model of Parkinson's disease exhibiting a double lesion (dopaminergic and serotonergic) thanks to the sequential use of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and MDMA (3,4-methylenedioxy-N-methamphetamine) (or MDMA prior MPTP). We characterized this monkey model by multimodal imaging (PET, positron emission tomography with several radiotracers; DTI, diffusion tensor imaging), behavioral assessments (parkinsonism, dyskinesia, neuropsychiatric-like behavior) and post-mortem analysis (with DA and 5-HT markers). When administrated after MPTP, MDMA damaged the 5-HT presynaptic system without affecting the remaining DA neurons. The lesion of 5-HT fibers induced by MDMA altered rigidity and prevented dyskinesia and neuropsychiatric-like symptoms induced by levodopa therapy in MPTP-treated animals. Interestingly also, prior MDMA administration aggravates the parkinsonian deficits and associated DA injury. Dystonic postures, action tremor and global spontaneous activities were significantly affected. All together, these data clearly indicate that late or early lesions of the 5-HT system have a differential impact on parkinsonian symptoms in the macaque model of Parkinson's disease. Whether MDMA has an impact on neuropsychiatric-like symptoms such as apathy, anxiety, depression remains to be addressed. Despite its limitations, this toxin-based double-lesioned monkey model takes on its full meaning and provides material for the experimental study of the heterogeneity of patients.

Neuroprotection or Neurotoxicity of Illicit Drugs on Parkinson's Disease

Parkinson's Disease (PD) is currently the most rapid growing neurodegenerative disease and over the past generation, its global burden has more than doubled. The onset of PD can arise due to environmental, sporadic or genetic factors. Nevertheless, most PD cases have an unknown etiology. Chemicals, such as the anthropogenic pollutant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amphetamine-type stimulants, have been associated with the onset of PD. Conversely, cannabinoids have been associated with the treatment of the symptoms'. PD and medical cannabis is currently under the spotlight, and research to find its benefits on PD is on-going worldwide. However, the described clinical applications and safety of pharmacotherapy with cannabis products are yet to be fully supported by scientific evidence. Furthermore, the novel psychoactive substances are currently a popular alternative to classical drugs of abuse, representing an unknown health hazard for young adults who may develop PD later in their lifetime. This review addresses the neurotoxic and neuroprotective impact of illicit substance consumption in PD, presenting clinical evidence and molecular and cellular mechanisms of this association. This research area is utterly important for contemporary society since illicit drugs' legalization is under discussion which may have consequences both for the onset of PD and for the treatment of its symptoms.

Gender Differences in Neurodegeneration, Neuroinflammation and Na+-Ca2+ Exchangers in the Female A53T Transgenic Mouse Model of Parkinson's Disease

Twelve-month-old male mice expressing the human A53T variant of α-synuclein (A53T) develop dopamine neuron degeneration, neuroinflammation, and motor deficits, along with dysfunctions of the mitochondrial Na⁺-Ca²⁺ exchanger (NCX) isoforms 1 (NCX1) and 3 (NCX3) in the nigrostriatal system. Since gender is thought to play a role in the etiology of Parkinson's disease (PD), we characterized neurochemical and behavioral alterations in 12-month-old female A53T transgenic mice. We investigated the presence of dopaminergic degeneration, astrogliosis and microgliosis using immunohistochemistry for tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule-1 (IBA-1) in both the substantia nigra pars compacta (SNc) and striatum. In the same regions, we also evaluated the co-localization of NCX1 in cells positive for IBA-1 and the co-localization of NCX3 in TH-positive neurons and fibers. Furthermore, in both male and female mice, we performed motor (beam walking and pole tests) and memory [novel object recognition (NOR) and spontaneous alternation] tasks, together with tests to evaluate peripheral deficits (olfactory and stool collection tests). Female A53T transgenic mice displayed degeneration of nigral dopaminergic neurons, but neither microgliosis nor astrogliosis in the SNc and striatum. Moreover, female A53T transgenic mice displayed co-localization between NCX1 and IBA-1 positive cells in the striatum but not SNc, whereas NCX3 did not co-localize with either TH-positive terminals or neuronal bodies in the nigrostriatal system. Furthermore, female A53T transgenic mice showed increased crossing time in the beam walking test, but no impairments in the pole or memory tests, and in tests that evaluated peripheral deficits, whereas male A53T transgenic mice displayed motor, memory and peripheral deficits. Immunohistochemical and behavioral results obtained here in the female mice differ from those previously observed in males, and suggest a dissimilar influence of NCX1 and NCX3 on dopaminergic function in female and male A53T transgenic mice, strengthening the validity of these mice as a model for studying the etiological factors of PD.

Neuronal and peripheral damages induced by synthetic psychoactive substances: an update of recent findings from human and animal studies

Preclinical and clinical studies indicate that synthetic psychoactive substances, in addition to having abuse potential, may elicit toxic effects of varying severity at the peripheral and central levels. Nowadays, toxicity induced by synthetic psychoactive substances poses a serious harm for health, since recreational use of these substances is on the rise among young and adult people. The present review summarizes recent findings on the peripheral and central toxicity elicited by “old” and “new” synthetic psychoactive substances in humans and experimental animals, focusing on amphetamine derivatives, hallucinogen and dissociative drugs and synthetic cannabinoids.

Effects of MDMA on neuroplasticity, amyloid burden and phospho-tau expression in APPswe/PS1dE9 mice

BACKGROUND

3,4-Methylenedioxymethamphetamine (MDMA) is still one of the most consumed drugs by adolescents. Its abuse is related with cognitive impairment, which seems due to maladaptive plasticity and neural stress. In turn, new hypotheses suggest that Alzheimer's disease (AD) may be promoted by neural stressors.

AIMS AND METHODS

To test if there is an increase in vulnerability to AD after chronic MDMA consumption, we investigated the effects of this drug on recognition memory and its neurotoxic and neuroplastic effects in a transgenic mouse model of presymptomatic familiar AD (APP/PS1 dE9, Tg).

RESULTS

MDMA-treated animals showed recognition memory deficits, regardless of genotype, which were accompanied by changes in plasticity markers. Tg mice showed an impaired expression of Arc compared with wild-type animals, but exposure to MDMA induced an increase in the expression of this factor of the same percentage in both genotypes. However, the expression of c-fos, BDNF and p-CREB was not significantly altered by MDMA treatment in Tg mice. Although Tg mice had higher free choline levels than wild-type mice (about 123%), MDMA did not modify these levels in any case, ruling out any specific effect of this drug on the acetylcholine pathway. MDMA treatment significantly increased the presence of cortical amyloid plaques, as well as Aβ40, Aβ42 and secreted APPβ levels in Tg mice. These plaques were accompanied by increased tau phosphorylation (S199), which does not seem to occur via the canonic pathway involving AKT, CDK5 or GSK3β.

CONCLUSIONS

The present results support previous evidences that MDMA can contribute to the amyloid cascade.

Lack of Rhes Increases MDMA-Induced Neuroinflammation and Dopamine Neuron Degeneration: Role of Gender and Age

Ras homolog enriched in striatum (Rhes) is a protein that exerts important physiological functions and modulates psychostimulant drug effects. On this basis, the object of this study was to assess 3,4-methylenedioxymethamphetamine (MDMA) effects on microglial (CD11b) and astroglial (GFAP) activation and on dopamine neuron degeneration (TH) in wild-type (WT) and Rhes knockout (KO) male and female mice of different ages. Motor activity was also evaluated. Adult (3 months) MDMA-treated mice displayed an increase in GFAP-positive cells in striatum (STR), whereas the substantia nigra pars compacta (SNc) was affected only in male mice. In these mice, the increase of CD11b was more extensive including STR, SNc, motor cortex (CTX), ventral tegmental area (VTA), and nucleus accumbens (NAc). MDMA administration also affected TH immunoreactivity in both STR and SNc of male but not female WT and Rhes KO mice. In middle-aged mice (12 months), MDMA administration further increased GFAP and CD11b and decreased TH immunoreactivity in STR and SNc of all mice. Finally, MDMA induced a higher increase of motor activity in adult Rhes KO male, but not female mice. The results show that Rhes protein plays an important role on MDMA-mediated neuroinflammation and neurodegeneration dependent on gender and age, and confirm the important role of Rhes protein in neuroinflammatory and neurodegenerative processes.

Increased iNOS and Nitrosative Stress in Dopaminergic Neurons of MDMA-Exposed Rats

Several mechanisms underlying 3,4-Methylenedioxy-N-methylamphetamine (MDMA) neurotoxicity have been proposed, including neurochemical alterations and excitotoxicity mediated by reactive oxygen species (ROS), nitric oxide (NO), and reactive nitrogen species (RNS). However, ROS, NO, and RNS sources in the brain are not fully known. We aimed to investigate possible alterations in the expression of the ROS producer NOX enzymes (NOX2, NOX1, and NOX4), NO generators (iNOS, eNOS, and nNOS), markers of oxidative (8-hydroxy-2'-deoxyguanosine, 8OHdG), and nitrosative (3-nitrotyrosine, NT) stress, as well as the colocalization between cells positive for the dopamine transporter (DT1) and cells expressing the neuronal nuclei (NeuN) marker, in the frontal cortex of rats receiving saline or MDMA, sacrificed 6 h, 16 h, or 24 h after its administration. MDMA did not affect NOX2, NOX1, and NOX4 immunoreactivity, whereas iNOS expression was enhanced. The number of NT-positive cells was increased in MDMA-exposed animals, whereas no differences were detected in 8OHdG expression among experimental groups. MDMA and NT markers colocalized with DT1 positive cells. DT1 immunostaining was found in NeuN-positive stained cells. Virtually no colocalization was observed with microglia and astrocytes. Moreover, MDMA immunostaining was not found in NOX2-positive cells. Our results suggest that iNOS-derived nitrosative stress, but not NOX enzymes, may have a crucial role in the pathogenesis of MDMA-induced neurotoxicity, highlighting the specificity of different enzymatic systems in the development of neuropathological alterations induced by the abuse of this psychoactive compound.

Rhes Counteracts Dopamine Neuron Degeneration and Neuroinflammation Depending on Gender and Age

We have recently shown that male Rhes knockout (KO) mice develop a mild form of spontaneous Parkinson’s disease (PD)-like phenotype, characterized by motor impairment and a decrease in nigrostriatal dopamine (DA) neurons. Experimental evidence has implicated neuroinflammation in PD progression, and the presence of activated glial cells has been correlated with DA neuron degeneration. Despite this, several factors, such as gender, have been found to affect DAergic neuron degeneration and influence neuroinflammation, explaining the differences between men and women in the etiology of PD. On these basis, we studied age and gender differences in DA neuron degeneration and gliosis in the nigrostriatal system of adult (3-month-old) and middle aged (12-month-old) male and female Rhes wild-type (WT) and KO mice. Through immunohistochemistry, tyrosine hydroxylase (TH), microglial (complement type 3 receptor [CD11b]) and astroglial (glial fibrillary acid protein [GFAP]) increase, were evaluated. Adult male Rhes KO mice showed a decrease in TH and an increase in CD11b, both in the caudate putamen (CPu) and substantia nigra pars compacta (SNc), and an increase in GFAP in the CPu. In contrast, adult female Rhes KO mice showed only a decrease in TH in the SNc, whereas no modifications to the levels of GFAP and CD11b were observed in the CPu or SNc. Middle aged male Rhes KO mice showed a decrease in TH in the CPu and SNc, and an increase in GFAP and CD11b in the SNc. Middle aged female Rhes KO mice showed a decrease in TH in the CPu and SNc and an increase in CD11b only in the CPu, but no modifications to GFAP levels. The more marked DA neuron degeneration and neuroinflammation in male compared with female Rhes KO mice, while confirming the role of Rhes as an important protein for DA neuron survival, gives support to Rhes KO mice as a valuable preclinical model for studying the vulnerability factors of DA neuron degeneration as in PD.

Repeated Administration of 3,4-Methylenedioxymethamphetamine (MDMA) Elevates the Levels of Neuronal Nitric Oxide Synthase in the Nigrostriatal System: Possible Relevance to Neurotoxicity

Previous studies have consistently demonstrated that the amphetamine-related drug 3,4-methylenedioxymethamphetamine (MDMA) induces dopaminergic damage in the mouse brain, and that this effect is most marked in the nigrostriatal system. Moreover, it has been suggested that the overproduction of nitric oxide (NO) may participate in the dopaminergic damage induced by MDMA. To further elucidate this issue, we evaluated the levels of the enzyme nitric oxide synthase (nNOS), which catalyzes the production of NO, in mice treated with regimens of MDMA that induce progressive and persistent neurotoxicity in the dopaminergic nigrostriatal system. Mice received 14, 28, or 36 administrations of MDMA (10 mg/kg i.p.), twice a day/twice a week, and were sacrificed at different time-points after treatment discontinuation. Thereafter, the number of nNOS-positive neurons was quantified by immunohistochemistry in the caudate-putamen (CPu) and substantia nigra pars compacta (SNc). MDMA elevated the numbers of nNOS-positive neurons in the CPu of mice that received 28 or 36 drug administrations. This effect was still detectable at 3 months after treatment discontinuation. Moreover, MDMA elevated the numbers of nNOS-positive neurons in the SNc. However, this effect occurred only in mice that received 28 drug administrations and were sacrificed 3 days after treatment discontinuation. These results are in line with the hypothesis that activation of the NO cascade participates in the toxic effects induced by MDMA in the dopaminergic nigrostriatal system. Moreover, they suggest that activation of the NO cascade induces toxic effects that are more marked in striatal terminals, compared with nigral neurons.

Neurochemical and Neurotoxic Effects of MDMA (Ecstasy) and Caffeine After Chronic Combined Administration in Mice

MDMA (3,4-methylenedioxymethamphetamine) is a psychostimulant popular as a recreational drug because of its effect on mood and social interactions. MDMA acts at dopamine (DA) transporter (DAT) and serotonin (5-HT) transporter (SERT) and is known to induce damage of dopamine and serotonin neurons. MDMA is often ingested with caffeine. Caffeine as a non-selective adenosine A1/A2A receptor antagonist affects dopaminergic and serotonergic transmissions. The aim of the present study was to determine the changes in DA and 5-HT release in the mouse striatum induced by MDMA and caffeine after their chronic administration. To find out whether caffeine aggravates MDMA neurotoxicity, the content of DA and 5-HT, density of brain DAT and SERT, and oxidative damage of nuclear DNA were determined. Furthermore, the effect of caffeine on MDMA-induced changes in striatal dynorphin and enkephalin and on behavior was assessed. The DA and 5-HT release was determined with in vivo microdialysis, and the monoamine contents were measured by HPLC with electrochemical detection. DNA damage was assayed with the alkaline comet assay. DAT and SERT densities were determined by immunohistochemistry, while prodynorphin (PDYN) and proenkephalin were determined by quantitative PCR reactions. The behavioral changes were measured by the open-field (OF) test and novel object recognition (NOR) test. Caffeine potentiated MDMA-induced DA release while inhibiting 5-HT release in the mouse striatum. Caffeine also exacerbated the oxidative damage of nuclear DNA induced by MDMA but diminished DAT decrease in the striatum and worsened a decrease in SERT density produced by MDMA in the frontal cortex. Neither the striatal PDYN expression, increased by MDMA, nor exploratory and locomotor activities of mice, decreased by MDMA, were affected by caffeine. The exploration of novel object in the NOR test was diminished by MDMA and caffeine. Our data provide evidence that long-term caffeine administration has a powerful influence on functions of dopaminergic and serotonergic neurons in the mouse brain and on neurotoxic effects evoked by MDMA.

In vivo imaging of early signs of dopaminergic neuronal death in an animal model of Parkinson's disease

The Parkinson's disease (PD) evolves over an extended period of time with the onset occurring long before clinical signs begin to manifest. Characterization of the molecular events underlying the PD onset is instrumental for the development of diagnostic markers and preventive treatments, progress in this field is hindered by technical limitations. We applied an imaging approach to demonstrate the activation of Nrf2 transcription factor as a hallmark of neurodegeneration in neurotoxin-driven models of PD. In dopaminergic SK-N-BE neuroblastoma cells, Nrf2 activation was detected in cells committed to die as proven by time lapse microscopy; in the substantia nigra pars compacta area of the mouse brain, the Nrf2 activation preceded dopaminergic neurodegeneration as demonstrated by in vivo and ex vivo optical imaging, a finding confirmed by co-localization experiments carried out by immunohistochemistry. Collectively, our results identify the Nrf2 signaling as an early marker of neurodegeneration, anticipating dopaminergic neurodegeneration and motor deficits.

Dynamic Changes in the Nigrostriatal Pathway in the MPTP Mouse Model of Parkinson's Disease

The characteristic brain pathology and motor and nonmotor symptoms of Parkinson's disease (PD) are well established. However, the details regarding the causes of the disease and its course are much less clear. Animal models have significantly enriched our current understanding of the progression of this disease. Among various neurotoxin-based models of PD, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model is the most commonly studied model. Here, we provide an overview of the dynamic changes in the nigrostriatal pathway in the MPTP mouse model of PD. Pathophysiological events, such as reductions in the striatal dopamine (DA) concentrations and levels of the tyrosine hydroxylase (TH) protein, depletion of TH-positive nerve fibers, a decrease in the number of TH-positive neurons in the substantia nigra pars compacta (SNpc), and glial activation, are addressed. This article will assist with the development of interventions or therapeutic strategies for PD.

Progression and Persistence of Neurotoxicity Induced by MDMA in Dopaminergic Regions of the Mouse Brain and Association with Noradrenergic, GABAergic, and Serotonergic Damage

The amphetamine-related drug 3,4-methylenedioxymethamphetamine (MDMA) is known to induce neurotoxic damage in dopaminergic regions of the mouse brain. In order to characterize how the number of administrations influenced the severity of MDMA-induced dopaminergic damage and to describe the localization and persistence of this damage, we evaluated the changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) in different regions of the mouse brain. Moreover, we investigated whether dopaminergic damage was associated with noradrenergic, GABAergic, and serotonergic damage, by evaluating the changes in noradrenaline transporter (NET), glutamic acid decarboxylase-67 (GAD-67), and serotonin transporter (SERT). Mice received 14, 28, or 36 MDMA administrations (10 mg/kg twice a week) and were sacrificed at different time points (postnatal days 85, 110, 138, or 214) for immunohistochemical evaluation. Mice receiving 28 administrations showed reduced levels of DAT-positive fibers in caudate-putamen (CPu) and medial prefrontal cortex (mPFC) and reduced levels of TH-positive nigral neurons. These mice also displayed increased NET-positive hippocampal fibers, reduced GAD-67-positive neurons in CPu and hippocampus, and reduced GAD-67-positive fibers in mPFC. Similar effects of MDMA on DAT, TH, and GAD-67 were found in mice receiving 36 administrations, which also displayed reduced levels of striatal, cortical, and hippocampal TH-immunoreactive fibers. The reductions in dopaminergic markers and GAD-67 persisted at 3 months after MDMA discontinuation. Finally, MDMA never modified the levels of SERT. These results provide further insight into the localization and persistence of MDMA-induced dopaminergic damage and show that this effect may associate with GABAergic but not noradrenergic or serotonergic damage.

Effect of crowding, temperature and age on glia activation and dopaminergic neurotoxicity induced by MDMA in the mouse brain

3,4-methylenedyoxymethamphetamine (MDMA or "ecstasy"), a recreational drug of abuse, can induce glia activation and dopaminergic neurotoxicity. Since MDMA is often consumed in crowded environments featuring high temperatures, we studied how these factors influenced glia activation and dopaminergic neurotoxicity induced by MDMA. C57BL/6J adolescent (4 weeks old) and adult (12 weeks old) mice received MDMA (4×20mg/kg) in different conditions: 1) while kept 1, 5, or 10×cage at room temperature (21°C); 2) while kept 5×cage at either room (21°C) or high (27°C) temperature. After the last MDMA administration, immunohistochemistry was performed in the caudate-putamen for CD11b and GFAP, to mark microglia and astroglia, and in the substantia nigra pars compacta for tyrosine hydroxylase, to mark dopaminergic neurons. MDMA induced glia activation and dopaminergic neurotoxicity, compared with vehicle administration. Crowding (5 or 10 mice×cage) amplified MDMA-induced glia activation (in adult and adolescent mice) and dopaminergic neurotoxicity (in adolescent mice). Conversely, exposure to a high environmental temperature (27°C) potentiated MDMA-induced glia activation in adult and adolescent mice kept 5×cage, but not dopaminergic neurotoxicity. Crowding and exposure to a high environmental temperature amplified MDMA-induced hyperthermia, and a positive correlation between body temperature and activation of either microglia or astroglia was found in adult and adolescent mice. These results provide further evidence that the administration setting influences the noxious effects of MDMA in the mouse brain. However, while crowding amplifies both glia activation and dopaminergic neurotoxicity, a high environmental temperature exacerbates glia activation only.

Adolescent exposure to MDMA induces dopaminergic toxicity in substantia nigra and potentiates the amyloid plaque deposition in the striatum of APPswe/PS1dE9 mice

MDMA is one of the most used drugs by adolescents and its consumption has been associated with many psychobiological problems, among them psychomotor problems. Moreover, some authors described that early exposure to MDMA may render the dopaminergic neurons more vulnerable to the effects of future neurotoxic insults. Alzheimer disease (AD) is the main cause of dementia in the elderly and a percentage of the patients have predisposition to suffer nigrostriatal alterations, developing extrapyramidal signs. Nigrostriatal dysfunction in the brain of aged APPswe/PS1dE9 (APP/PS1), a mouse model of familiar AD (FAD), has also been described. The aim of the present study was to investigate the consequences of adolescent exposure to MDMA in APP/PS1 mice, on nigrostriatal function on early adulthood. We used a MDMA schedule simulating weekend binge abuse of this substance. Our MDMA schedule produced a genotype-independent decrease in dopaminergic neurons in the substantia nigra that remained at least 3months. Shortly after the injury, wild-type animals showed a decrease in the locomotor activity and apparent DA depletion in striatum, however in the APP/PS1 mice neither the locomotor activity nor the DA levels were modified, but a reduction in dopamine transporter (DAT) expression and a higher levels of oxidative stress were observed. We found that these disturbances are age-related characteristics that this APP/PS1 mice develops spontaneously much later. Therefore, MDMA administration seems to anticipate the striatal dopaminergic dysfunction in this FAD model. The most important outcome lies in a potentiation, by MDMA, of the amyloid beta deposition in the striatum.

Protection effect of piperine and piperlonguminine from Piper longum L. alkaloids against rotenone-induced neuronal injury

Currently available treatment approaches for Parkinson׳s disease (PD) are limited in terms of variety and efficacy. Piper longum L. (PLL; Piperaceae) is used in traditional medicine in Asia and the Pacific Islands, with demonstrated anti-inflammatory and antioxidant activities in preclinical studies, and alkaloid extracts of PLL have shown protective effects in PD models. The present study investigated the mechanistic basis for the observed protective effects of PLL. Rats treated with PLL-derived alkaloids showed improvement in rotenone-induced motor deficits, while reactive oxygen species (ROS) production was decreased, mitochondrial membrane potential was stabilized, and the opening of the mitochondrial permeability transition pore (mPTP)-which is involved in ROS production-was inhibited. In addition, rotenone-induced apoptosis was abrogated in the presence of these alkaloids, while a pretreatment stimulated autophagy, likely mitigating neuronal injury by the removal of damaged mitochondria. These findings provide novel insight into the neuroprotective function of PLL as well as evidence in favor of its use in PD treatment. This article is part of a Special Issue entitled SI: Neuroprotection.

The Small GTP-Binding Protein Rhes Influences Nigrostriatal-Dependent Motor Behavior During Aging

BACKGROUND

Here we aimed to evaluate: (1) Rhes mRNA expression in mouse midbrain, (2) the effect of Rhes deletion on the number of dopamine neurons, (3) nigrostriatal-sensitive behavior during aging in knockout mice.

METHODS

Radioactive in situ hybridization was assessed in adult mice. The beam-walking test was executed in 3-, 6- and 12-month-old mice. Immunohistochemistry of midbrain tyrosine hydroxylase (TH)-positive neurons was performed in 6- and 12-month-old mice.

RESULTS

Rhes mRNA is expressed in TH-positive neurons of SNpc and the ventral tegmental area. Moreover, lack of Rhes leads to roughly a 20% loss of nigral TH-positive neurons in both 6- and 12-month-old mutants, when compared with their age-matched controls. Finally, lack of Rhes triggers subtle alterations in motor performance and coordination during aging.

CONCLUSIONS

Our findings indicate a fine-tuning role of Rhes in regulating the number of TH-positive neurons of the substantia nigra and nigrostriatal-sensitive motor behavior during aging.

Amphetamine-related drugs neurotoxicity in humans and in experimental animals: Main mechanisms

Amphetamine-related drugs, such as 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH), are popular recreational psychostimulants. Several preclinical studies have demonstrated that, besides having the potential for abuse, amphetamine-related drugs may also elicit neurotoxic and neuroinflammatory effects. The neurotoxic potentials of MDMA and METH to dopaminergic and serotonergic neurons have been clearly demonstrated in both rodents and non-human primates. This review summarizes the species-specific cellular and molecular mechanisms involved in MDMA and METH-mediated neurotoxic and neuroinflammatory effects, along with the most important behavioral changes elicited by these substances in experimental animals and humans. Emphasis is placed on the neuropsychological and neurological consequences associated with the neuronal damage. Moreover, we point out the gap in our knowledge and the need for developing appropriate therapeutic strategies to manage the neurological problems associated with amphetamine-related drug abuse.

CX3CR1 Disruption Differentially Influences Dopaminergic Neuron Degeneration in Parkinsonian Mice Depending on the Neurotoxin and Route of Administration

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons accompanied by an inflammatory reaction. The neuron-derived chemokine fractalkine (CX3CL1) is an exclusive ligand for the receptor CX3CR1 expressed on microglia. The CX3CL1/CX3CR1 signaling is important for sustaining microglial activity. Using a recently developed PD model, in which the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxin is delivered intranasally, we hypothesized that CX3CR1 could play a role in neurotoxicity and glial activation. For this, we used CX3CR1 knock-in mice and compared results with those obtained using the classical PD models through intraperitonal MPTP or intrastriatal 6-hydroxydopamine (6-OHDA). The striatum from all genotypes (CX3CR1(+/+), CX3CR1(+/GFP) and CX3CR1-deficient mice) showed a significant dopaminergic depletion after intranasal MPTP inoculation. In contrast to that, we could not see differences in the number of dopaminergic neurons in the substantia nigra of CX3CR1-deficient animals. Similarly, after 6-OHDA infusion, the CX3CR1 deletion decreased the amphetamine-induced turning behavior observed in CX3CR1(+/GFP) mice. After the 6-OHDA inoculation, a minor dopaminergic neuronal loss was observed in the substantia nigra from CX3CR1-deficient mice. Distinctly, a more extensive neuronal cell loss was observed in the substantia nigra after the intraperitoneal MPTP injection in CX3CR1 disrupted animals, corroborating previous results. Intranasal and intraperitoneal MPTP inoculation induced a similar microgliosis in CX3CR1-deficient mice but a dissimilar change in the astrocyte proliferation in the substantia nigra. Nigral astrocyte proliferation was observed only after intraperitoneal MPTP inoculation. In conclusion, intranasal MPTP and 6-OHDA lesion in CX3CR1-deficient mice yield no nigral dopaminergic neuron loss, linked to the absence of astroglial proliferation.

Animal models of Parkinson's disease: An updated overview

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology, besides a minority of genetic cases, is still largely unknown. Animal models have contributed to elucidate PD etiology and pathogenesis, as well as its cellular and molecular mechanisms, leading to the general hypothesis that this neurological disorder is due to complex interactions between environmental and genetic factors. However, the full understanding of PD is still very far from being achieved, and new potential treatments need to be tested to further improve patients' quality of life and, possibly, slow down the neurodegenerative process. In this context, animal models of PD are required to address all these issues. "Classic" models are based on neurotoxins that selectively target catecholaminergic neurons (such as 6-hydroxydopamine, 1-methyl-1,2,3,6-tetrahydropiridine, agricultural pesticides, etc.), while more recent models employ genetic manipulations that either introduce mutations similar to those find in familial cases of PD (α-synuclein, DJ-1, PINK1, Parkin, etc.) or selectively disrupt nigrostriatal neurons (MitoPark, Pitx3, Nurr1, etc.). Each one of these models has its own advantages and limitations, thus some are better suited for studying PD pathogenesis, while others are more pertinent to test therapeutic treatments. Here, we provide a critical and updated review of the most used PD models.

Lesion of the locus coeruleus aggravates dopaminergic neuron degeneration by modulating microglial function in mouse models of Parkinson׳s disease

The degeneration of noradrenergic neurons in the locus coeruleus (LC) commonly occurs in patients with Parkinson's disease (PD), which is characterized by a selective injury of dopaminergic neurons in the substantia nigra (SN). The pathological impact of the LC on the SN in the disease is unknown. In the present study, we used a noradrenergic toxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4), to deplete noradrenaline (NA) derived from the LC to explore its influence on degeneration or injury of dopaminergic neurons in the SN in mouse model produced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or lipopolysaccharide (LPS). Our results demonstrated that lesion of the LC could change microglial function in the brain, which led to enhanced or prolonged expression of pro-inflammatory cytokines, diminished neurotrophic factors, and weakened ability of anti-oxidation in the SN. The in vitro experiments further confirmed that NA could reduce the inflammatory reaction of microglia. The selective injury of dopaminergic neurons by inflammation, however, was due to the inflammation in different brain regions rather than the depletion of NA. Our results indicate that the lesion in the LC is an important factor in promoting dopaminergic neuron degeneration by impacting the function of microglia in the midbrain.

Neonatal chlorpyrifos exposure induces loss of dopaminergic neurons in young adult rats

Increasing epidemiological and toxicological evidence suggests that pesticides and other environmental exposures may be associated with the development of Parkinson's disease (PD). Chlorpyrifos (CPF) is a widely used organophosphorous pesticide with developmental neurotoxicity. Its neurotoxicity, notably on the monoamine system, suggests that exposure of CPF may induce dopaminergic neuronal injury. We investigated whether neonatal exposure to CPF contributes to initiation and progression of dopaminergic neurotoxicity and explored the possible underlying mechanisms. The newborn rats were administrated 5 mg/kg CPF subcutaneously from postnatal day (PND) 11 to PND 14 daily. The effect of CPF on dopaminergic neurons, microglia, astrocyte, nuclear factor-κB (NF-κB) p. 65 and p. 38 mitogen-activated protein kinase (MAPK) signaling pathways was analyzed in the substantia nigra of rats at 12h, 24h, 72 h, 16d and 46 d after exposure. CPF-treated rats exhibited significant reduction of dopaminergic neurons at 16d and 46 d after exposure, and a significant increase in the expression of microglia and astrocytes in the substantia nigra after CPF exposure. Intense activation of NF-κB p. 65 and p. 38 MAPK inflammatory signaling pathways was observed. Our findings indicate that neonatal exposure to CPF may induce long-term dopaminergic neuronal damage in the substantia nigra mediated by the activation of inflammatory response via NF-κB p. 65 and p. 38 MAPK pathways in the nigrostriatal system.

Monoamine reuptake inhibitors in Parkinson's disease

The motor manifestations of Parkinson's disease (PD) are secondary to a dopamine deficiency in the striatum. However, the degenerative process in PD is not limited to the dopaminergic system and also affects serotonergic and noradrenergic neurons. Because they can increase monoamine levels throughout the brain, monoamine reuptake inhibitors (MAUIs) represent potential therapeutic agents in PD. However, they are seldom used in clinical practice other than as antidepressants and wake-promoting agents. This review article summarises all of the available literature on use of 50 MAUIs in PD. The compounds are divided according to their relative potency for each of the monoamine transporters. Despite wide discrepancy in the methodology of the studies reviewed, the following conclusions can be drawn: (1) selective serotonin transporter (SERT), selective noradrenaline transporter (NET), and dual SERT/NET inhibitors are effective against PD depression; (2) selective dopamine transporter (DAT) and dual DAT/NET inhibitors exert an anti-Parkinsonian effect when administered as monotherapy but do not enhance the anti-Parkinsonian actions of L-3,4-dihydroxyphenylalanine (L-DOPA); (3) dual DAT/SERT inhibitors might enhance the anti-Parkinsonian actions of L-DOPA without worsening dyskinesia; (4) triple DAT/NET/SERT inhibitors might exert an anti-Parkinsonian action as monotherapy and might enhance the anti-Parkinsonian effects of L-DOPA, though at the expense of worsening dyskinesia.

Anti-neuroinflammatory effects of DPTP, a novel synthetic clovamide derivative in in vitro and in vivo model of neuroinflammation

Neuroinflammation is one of the critical pathological mechanisms influencing various neurodegenerative disorders. Most of the neurodegenerative diseases involve over-activation of microglial cells contributing to the demise of neurons. The objective of the current study is to evaluate the anti-inflammatory effect of novel synthetic clovamide derivative on the suppression of microglial activation in an in vitro and in vivo model of neuroinflammation. We have used lipopolysaccharide (LPS) to induce an inflammatory response in murine BV-2 microglial cells. Molecular tools like immunocytochemistry and immunoblotting were used to study the activity of novel synthetic clovamide derivative to inhibit inflammation induced by LPS in microglial cells. In in vivo experiments, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxicated mouse model of neuroinflammation was developed to investigate the anti-neuroinflammatory effects of DPTP [3-(3,4-Dihydroxy-phenyl)-2-[4-(3-trifluoromethylphenyl)-but-2-enoylamino]-propionic acid methyl ester]. DPTP was observed to reduce the proinflammatory response in BV-2 cells induced by LPS. Further investigation revealed that DPTP attenuated phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), which was accompanied by a decrease in nuclear translocation of nuclear factor-κB (NF-κB) in LPS-treated BV2 microglia. Moreover, prophylactic treatment with DPTP (20mg/kg) for 7 days suppressed MPTP induced glial activation and behavioral impairment. Overall, our findings suggested that, DPTP exerts anti-neuroinflammatory effects against activated microglia in an in vitro and in vivo model and hence might be a promising therapeutic agent for alleviating the evolvement of neurodegenerative diseases associated with microglial activation.

Parkinson's disease: animal models and dopaminergic cell vulnerability

Parkinson's disease (PD) is a neurodegenerative disorder that affects about 1.5% of the global population over 65 years of age. A hallmark feature of PD is the degeneration of the dopamine (DA) neurons in the substantia nigra pars compacta (SNc) and the consequent striatal DA deficiency. Yet, the pathogenesis of PD remains unclear. Despite tremendous growth in recent years in our knowledge of the molecular basis of PD and the molecular pathways of cell death, important questions remain, such as: (1) why are SNc cells especially vulnerable; (2) which mechanisms underlie progressive SNc cell loss; and (3) what do Lewy bodies or α-synuclein reveal about disease progression. Understanding the variable vulnerability of the dopaminergic neurons from the midbrain and the mechanisms whereby pathology becomes widespread are some of the primary objectives of research in PD. Animal models are the best tools to study the pathogenesis of PD. The identification of PD-related genes has led to the development of genetic PD models as an alternative to the classical toxin-based ones, but does the dopaminergic neuronal loss in actual animal models adequately recapitulate that of the human disease? The selection of a particular animal model is very important for the specific goals of the different experiments. In this review, we provide a summary of our current knowledge about the different in vivo models of PD that are used in relation to the vulnerability of the dopaminergic neurons in the midbrain in the pathogenesis of PD.

MDMA administration during adolescence exacerbates MPTP-induced cognitive impairment and neuroinflammation in the hippocampus and prefrontal cortex

RATIONALE

We have recently shown that chronic exposure to 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") of adolescent mice exacerbates dopamine neurotoxicity and neuroinflammatory effects elicited by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the substantia nigra and striatum at adulthood.

OBJECTIVES

The present study investigated whether the amplification of MPTP effects by previous treatment with MDMA extends to the limbic and cortical regions and consequently affects cognitive performance.

METHODS

Mice received MDMA (10 mg/kg, twice a day/twice a week) for 9 weeks, followed by MPTP (20 mg/kg × 4 administrations), starting 2 weeks after MDMA discontinuation. Complement type 3 receptor (CD11b) and glial fibrillary acidic protein (GFAP) were evaluated by immunohistochemistry in both the hippocampus and the medial prefrontal cortex (mPFC) to measure microglia and astroglia activation. These neurochemical evaluations were paired with an assessment of cognitive performance by means of the novel object recognition (NOR) and spontaneous alternation tasks.

RESULTS

MPTP administration to MDMA-pretreated mice elicited a stronger activation of CD11b and GFAP in both the hippocampus and the mPFC compared with either substance administered alone. Furthermore, NOR performance was lower in MDMA-pretreated mice administered MPTP compared with mice that received either substance alone.

CONCLUSIONS

These results demonstrate that MDMA-MPTP negative interactions extend to the limbic and cortical regions and may result in cognitive impairment, providing further evidence that exposure to MDMA may amplify the effects of later neurotoxic insults.

Elevation of striatal urate in experimental models of Parkinson's disease: a compensatory mechanism triggered by dopaminergic nigrostriatal degeneration?

Epidemiological studies have indicated an inverse association between high uricemia and incidence of Parkinson's disease (PD). To investigate the link between endogenous urate and neurotoxic changes involving the dopaminergic nigrostriatal system, this study evaluated the modifications in the striatal urate levels in two models of PD. To this end, a partial dopaminergic degeneration was induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice, while a severe dopaminergic degeneration was elicited by unilateral medial forebrain bundle infusion of 6-hydroxydopamine (6-OHDA) in rats. Urate levels were measured by in vivo microdialysis at 7 or 14 days from toxin exposure. The results obtained demonstrated higher urate levels in the dopamine-denervated striatum of 6-OHDA-lesioned rats compared with the intact striatum. Moreover, an inverse correlation between urate and dopamine levels was observed in the same area. In contrast, only a trend to significant increase in striatal urate was observed in MPTP-treated mice. These results demonstrate that a damage to the dopaminergic nigrostriatal system elevates the striatal levels of urate, and suggest that this could be an endogenous compensatory mechanism to attenuate dopaminergic neurodegeneration. This finding may be important in light of the epidemiological and preclinical evidences that indicate a link between urate and development of PD.