MPTP-induced hypoactivity in mice: reversal by L-dopa

Calcineurin inhibition protects against dopamine toxicity and attenuates behavioral decline in a Parkinson's disease model

BACKGROUND

Parkinson's disease (PD), a highly prevalent neuro-motor disorder is caused due to progressive loss of dopaminergic (DAergic) neurons at substantia nigra region of brain. This leads to depleted dopamine (DA) content at striatum, thus affecting the fine tuning of basal ganglia. In patients, this imbalance is manifested by akinesia, catalepsy and tremor. PD associated behavioral dysfunctions are frequently mitigated by l-DOPA (LD) therapy, a precursor for DA synthesis. Due to progressive neurodegeneration, LD eventually loses applicability in PD. Although DA is cytotoxic, it is unclear whether LD therapy can accelerate PD progression or not. LD itself does not lead to neurodegeneration in vivo, but previous reports demonstrate that LD treatment mediated excess DA can potentiate neurotoxicity when PD associated genetic or epigenetic aberrations are involved. So, minimizing DA toxicity during the therapy is an absolute necessity to halt or slowdown PD progression. The two major contributing factors associated with DA toxicity are: degradation by Monoamine oxidase and DAquinone (DAQ) formation.

RESULTS

Here, we report that apoptotic mitochondrial fragmentation via Calcineurin (CaN)-DRP1 axis is a common downstream event for both these initial cues, inhibiting which can protect cells from DA toxicity comprehensively. No protective effect is observed, in terms of cell survival when only PxIxIT domain of CaN is obstructed, demonstrating the importance to block DRP1-CaN axis specifically. Further, evaluation of the impact of DA exposure on PD progression in a mice model reveal that LD mediated behavioral recovery diminishes with time, mostly because of continued DAergic cell death and dendritic spine loss at striatum. CaN inhibition, alone or in combination with LD, offer long term behavioral protection. This protective effect is mediated specifically by hindering CaN-DRP1 axis, whereas inhibiting interaction between CaN and other substrates, including proteins involved in neuro-inflammation, remained ineffective when LD is co-administered.

CONCLUSIONS

In this study, we conclude that DA toxicity can be circumvented by CaN inhibition and it can mitigate PD related behavioral aberrations by protecting neuronal architecture at striatum. We propose that CaN inhibitors might extend the therapeutic efficacy of LD treatment.

Effect of l-Dopa in acute temozolomide-induced cognitive impairment in male mice: a possible antineuroinflammatory role

Temozolomide is used commonly in the treatment of some types of cancers, but it may also result in cognitive impairments such as memory deficits. l-Dopa, a well known medicine for the central nervous system, has been shown to have positive effects on some cognitive disorders. Here we sought to investigate the effect of l-Dopa on temozolomide-induced cognitive impairments. BALB/c mice were subjected to 3-days temozolomide and 6-days concomitant l-Dopa/benserazide administration in six groups (control, l-Dopa 25 mg/kg, l-Dopa 75 mg/kg, temozolomide, temozolomide + l-Dopa 25 mg/kg, and temozolomide + l-Dopa 75 mg/kg). Open field test, object location recognition, novel object recognition test, and shuttle-box test were carried out to determine the locomotor, anxiety-like behavior, and memory function of subjects. TNF-α and brain-derived neurotrophic factor (BDNF) gene expression in the hippocampus was measured by real-time PCR. Mice treated with temozolomide showed recognition memory impairment, along with hippocampal TNF-α and BDNF mRNA expression level raise, and detection of histological insults in hematoxylin and eosin hippocampal slides. Mice that received temozolomide + l-Dopa showed normal behavioral function and lower TNF-α and BDNF hippocampal mRNA expression levels, and histologically normal hippocampal CA1 region in comparison with mice in the temozolomide group. Our results provide evidence that l-Dopa prevents temozolomide-induced recognition memory deficit in mice at the acute phase probably via l-Dopa antineuroinflammatory effects.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

Exosomes derived from miR-188-3p-modified adipose-derived mesenchymal stem cells protect Parkinson's disease

Parkinson’s disease (PD) is the second-most common neurodegenerative disease after Alzheimer’s disease. The most important pathological feature of PD is the irreversible damage of dopamine neurons, which is related to autophagy and neuroinflammation in the substantia nigra. Previous studies found that the activation of NAcht Leucine-rich repeat Protein 3 (NLRP3) inflammasome/pyroptosis and cell division protein kinase 5 (CDK5)-mediated autophagy played an important role in PD. Bioinformatics analyses further predicted that microRNA (miR)-188-3p potentially targets NLRP3 and CDK5. Adipose-derived stem cell (ADSC)-derived exosomes were found to be excellent vectors for genetic therapy. We assessed the levels of injury, autophagy, and inflammasomes in 1-methyl-4-phenyl-1,2,4,5-tetrahydropyridine (MPTP)-induced PD mice models and neurotoxin 1-methyl-4-phenylpyridinium (MPP+)-induced cell models after treating them with miR-188-3p-enriched exosomes. miR-188-3p-enriched exosome treatment suppressed autophagy and pyroptosis, whereas increased proliferation via targeting CDK5 and NLRP3 in mice and MN9D cells. It was revealed that mir-188-3p could be a new therapeutic target for curing PD patients.

Pretreatment with Human Lactoferrin Had a Positive Effect on the Dynamics of Mouse Nigrostriatal System Recovery after Acute MPTP Exposure

We studied the effect of human lactoferrin (hLf) on degenerative changes in the nigrostriatal system and associated behavioral deficits in the animal model of Parkinson disease. Nigrostriatal dopaminergic injury was induced by single administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 40 mg/kg) to five-month-old C57Bl/6 mice. Behavioral disturbances were assessed in the open field and rotarod tests and by the stride length analysis. Structural deficits were assessed by the counts of tyrosine hydroxylase (TH)-immunoreactive neurons in the substantia nigra and optical density (OD) of TH-immunolabeled fibers in the striatum. Acute MPTP treatment induced long-term behavioral deficit and degenerative changes in the nigrostriatal system. Pretreatment with hLf prevented body weight loss and promoted recovery of motor functions and exploratory behavior. Importantly, OD of TH-positive fibers in the striatum of mice treated with hLf almost returned to normal, and the number of TH-positive cells in the substantia nigra significantly increased on day 28. These results indicate that hLf produces a neuroprotective effect and probably stimulates neuroregeneration under conditions of MPTP toxicity in our model. A relationship between behavioral deficits and nigrostriatal system disturbances at delayed terms after MPTP administration was found.

Genetic suppression of IKK2/NF-κB in astrocytes inhibits neuroinflammation and reduces neuronal loss in the MPTP-Probenecid model of Parkinson's disease

Neuroinflammatory activation of glia is considered a pathological hallmark of Parkinson's disease (PD) and is seen in both human PD patients and in animal models of PD; however, the relative contributions of these cell types, especially astrocytes, to the progression of disease is not fully understood. The transcription factor, nuclear factor kappa B (NFκB), is an important regulator of inflammatory gene expression in glia and is activated by multiple cellular stress signals through the kinase complex, IKK2. We sought to determine the role of NFκB in modulating inflammatory activation of astrocytes in a model of PD by generating a conditional knockout mouse (hGfapcre/Ikbk2^F/F) in which IKK2 is specifically deleted in astrocytes. Measurements of IKK2 revealed a 70% deletion rate of IKK2 within astrocytes, as compared to littermate controls (Ikbk2^F/F). Use of this mouse in a subacute, progressive model of PD through exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and probenecid (MPTPp) revealed significant protection in exposed mice to direct and progressive loss of dopaminergic neurons in the substantia nigra (SN). hGfapcre/Ikbk2^F/F mice were also protected against MPTPp-induced loss in motor activity, loss of striatal proteins, and genomic alterations in nigral NFκB gene expression, but were not protected from loss of striatal catecholamines. Neuroprotection in hGfapcre/Ikbk2^F/F mice was associated with inhibition of MPTPp-induced astrocytic expression of inflammatory genes and protection against nitrosative stress and apoptosis in neurons. These data indicate that deletion of IKK2 within astrocytes is neuroprotective in the MPTPp model of PD and suggests that reactive astrocytes directly contribute the potentiation of dopaminergic pathology.

Melatonin enhances L-DOPA therapeutic effects, helps to reduce its dose, and protects dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

L-3,4-dihydroxyphenylalanine (L-DOPA) reduces symptoms of Parkinson's disease (PD), but suffers from serious side effects on long-term use. Melatonin (10-30 mg/kg, 6 doses at 10 hr intervals) was investigated to potentiate L-DOPA therapeutic effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in mice. Striatal tyrosine hydroxylase (TH) immunoreactivity, TH, and phosphorylated ser 40 TH (p-TH) protein levels were assayed on 7th day. Nigral TH-positive neurons stereology was conducted on serial sections 2.8 mm from bregma rostrally to 3.74 mm caudally. MPTP caused 39% and 58% decrease, respectively, in striatal fibers and TH protein levels, but 2.5-fold increase in p-TH levels. About 35% TH neurons were lost between 360 and 600 μm from 940 μm of the entire nigra analyzed, but no neurons were lost between 250 μm rostrally and 220 μm caudally. When L-DOPA in small doses (5-8 mg/kg) failed to affect MPTP-induced akinesia or catalepsy, co-administration of melatonin with L-DOPA attenuated these behaviors. Melatonin administration significantly attenuated MPTP-induced loss in striatal TH fibers (82%), TH (62%) and p-TH protein (100%) levels, and nigral neurons (87-100%). Melatonin failed to attenuate MPTP-induced striatal dopamine depletion. L-DOPA administration (5 mg/kg, once 40 min prior to sacrifice, p.o.) in MPTP- and melatonin-treated mice caused significant increase in striatal dopamine (31%), as compared to L-DOPA and MPTP-treated mice. This was equivalent to 8 mg/kg L-DOPA administration in parkinsonian mouse. Therefore, prolonged, effective use of L-DOPA in PD with lesser side effects could be achieved by treating with 60% lower doses of L-DOPA along with melatonin.

Noradrenergic-Dopaminergic Interactions Due to DSP-4-MPTP Neurotoxin Treatments: Iron Connection

The investigations of noradrenergic lesions and dopaminergic lesions have established particular profiles of functional deficits and accompanying alterations of biomarkers in brain regions and circuits. In the present account, the focus of these lesions is directed toward the effects upon dopaminergic neurotransmission and expression that are associated with the movement disorders and psychosis-like behavior. In this context, it was established that noradrenergic denervation, through administration of the selective noradrenaline (NA) neurotoxin, DSP-4, should be performed prior to the depletion of dopamine (DA) with the selective neurotoxin, MPTP. Employing this regime, it was shown that (i) following DSP-4 (50 mg/kg) pretreatment of C57/Bl6 mice, both the functional and neurochemical (DA loss) effects of MPTP (2 × 20 and 2 × 40 mg/kg) were markedly exacerbated, and (ii) following postnatal iron (Fe(2+), 7.5 mg/kg, on postnatal days 19-12), pretreatment with DSP-4 followed by the lower 2 × 20 mg/kg MPTP dose induced even greater losses of motor behavior and striatal DA. As yet, the combination of NA-DA depletions, and even more so Fe(2+)-NA-DA depletion, has been considered to present a movement disorder aspect although studies exploring cognitive domains are lacking. With intrusion of iron overload into this formula, the likelihood of neuropsychiatric disorder, as well, unfolds.

Chronic administration of cholesterol oximes in mice increases transcription of cytoprotective genes and improves transcriptome alterations induced by alpha-synuclein overexpression in nigrostriatal dopaminergic neurons

Cholesterol-oximes TRO19622 and TRO40303 target outer mitochondrial membrane proteins and have beneficial effects in preclinical models of neurodegenerative diseases leading to their advancement to clinical trials. Dopaminergic neurons degenerate in Parkinson's disease (PD) and are prone to oxidative stress and mitochondrial dysfunction. In order to provide insights into the neuroprotective potential of TRO19622 and TRO40303 for dopaminergic neurons in vivo, we assessed their effects on gene expression in laser captured nigrostriatal dopaminergic neurons of wildtype mice and of mice that over-express alpha-synuclein, a protein involved in both familial and sporadic forms of PD (Thy1-aSyn mice). Young mice were fed the drugs in food pellets or a control diet from 1 to 4months of age, approximately 10months before the appearance of striatal dopamine loss in this model. Unbiased weighted gene co-expression network analysis (WGCNA) of transcriptional changes revealed effects of cholesterol oximes on transcripts related to mitochondria, cytoprotection and anti-oxidant response in wild-type and transgenic mice, including increased transcription of stress defense (e.g. Prdx1, Prdx2, Glrx2, Hspa9, Pink1, Drp1, Trak1) and dopamine-related (Th, Ddc, Gch1, Dat, Vmat2, Drd2, Chnr6a) genes. Even at this young age transgenic mice showed alterations in transcripts implicated in mitochondrial function and oxidative stress (e.g. Bcl-2, Bax, Casp3, Nos2), and both drugs normalized about 20% of these alterations. Young Thy1-aSyn mice exhibit motor deficits that differ from parkinsonism and are established before the onset of treatment; these deficits were not improved by cholesterol oximes. However, high doses of TRO40303 improved olfaction and produced the same effects as dopamine agonists on a challenging beam test, specifically an increase in footslips, an observation congruent with its effects on transcripts involved in dopamine synthesis. High doses of TRO19622 increased alpha-synuclein aggregates in the substantia nigra; this effect, not seen with TRO40303 was inconsistent and may represent a protective mechanism as in other neurodegenerative diseases. Overall, the results suggest that cholesterol oximes, while not improving early effects of alpha-synuclein overexpression on motor behavior or pathology, may ameliorate the function and resilience of dopaminergic neurons in vivo and support further studies of neuroprotection in models with dopaminergic cell loss.

Melatonin synergizes with low doses of L-DOPA to improve dendritic spine density in the mouse striatum in experimental Parkinsonism

The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), is the preferred drug for Parkinson's disease, but long-term treatment results in the drug-induced dyskinesias and other side effects. This study was undertaken to examine whether melatonin could potentiate low dose L-DOPA effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced experimental parkinsonism. Mice were treated with the parkinsonian neurotoxin, MPTP, and different doses of melatonin and low doses of L-DOPA. Behavior, striatal histology, and dopamine metabolism were evaluated on the 7th day. MPTP-induced striatal dopamine loss was not modified by melatonin administration (10-30 mg/kg; i.p. at 10-hr intervals, 6 times; or at 2-hr intervals, by day). However, low doses of L-DOPA (5 mg/kg, by oral gavage) administered alone or along with melatonin (10 mg/kg, i.p.) twice everyday for 2 days, 10 hr apart, after two doses of MPTP significantly attenuated striatal dopamine loss and provided improvements in both catalepsy and akinesia. Additionally, Golgi-impregnated striatal sections showed preservation of the medium spiny neurons, which have been damaged in MPTP-treated mouse. The results demonstrated that melatonin, but not L-DOPA, restored spine density and spine morphology of medium spiny neurons in the striatum and suggest that melatonin could be an ideal adjuvant to L-DOPA therapy in Parkinson's disease, and by the use of this neurohormone, it is possible to bring down the therapeutic doses of L-DOPA.

The yeast product Milmed enhances the effect of physical exercise on motor performance and dopamine neurochemistry recovery in MPTP-lesioned mice

Both clinical and laboratory studies have demonstrated that different types of physical exercise may alleviate Parkinsonism yet evidence for complete restoration of motor function and biomarker integrity are difficult to identify. MPTP (1 × 30 mg/kg, s.c., 4 groups) or saline (vehicle 1 × 5 ml/kg, s.c., 1 group) were administered in a single dose regime over three consecutive weeks on Fridays. Three MPTP groups were given four 30-min periods/week (Mondays to Thursdays), of these two groups, MPTP + Exer + M(i) and MPTP + Exer + M(ii); the former were introduced to exercise and Milmed (oral injection) on the week following the 1st MPTP injection and the latter on the Monday prior to the 1st injection of MPTP onwards. One MPTP group, MPTP + Exer, was given access to exercise (running wheels) from the week following the 1st MPTP injection onwards. The fourth MPTP group, MPTP-NoEx, and the Vehicle group were only given access to exercise on a single day each week (Wednesdays, exercise test) from the week following the 1st MPTP injection onwards. The exercise/exercise + Milmed regime was maintained for a further 9 weeks. It was observed that exercise by itself ameliorated MPTP-induced deficits regarding motor function and dopamine loss only partially whereas in the groups combining exercise with twice weekly dosages of Milmed the MPTP-induced deficits were abolished by the 10th week of the intervention. The three main conclusions that were drawn from correlational analyses of individual mice were: (i) that DA integrity was observed to be a direct function of ability to express running exercise in a treadmill wheel-running arrangement, and (ii) that DA integrity was observed to be a direct function of the capacity for motor performance as measured by spontaneous motor activity and subthreshold L-Dopa (5 mg/kg) induced activity in the motor activity test chambers, and (iii) that the extent to which running exercise in a running wheel was predictive of later motor performance in the activity test chambers was highly convincing.

A progressive mouse model of Parkinson's disease: the Thy1-aSyn ("Line 61") mice

Identification of mutations that cause rare familial forms of Parkinson's disease (PD) and subsequent studies of genetic risk factors for sporadic PD have led to an improved understanding of the pathological mechanisms that may cause nonfamilial PD. In particular, genetic and pathological studies strongly suggest that alpha-synuclein, albeit very rarely mutated in PD patients, plays a critical role in the vast majority of individuals with the sporadic form of the disease. We have extensively characterized a mouse model over-expressing full-length, human, wild-type alpha-synuclein under the Thy-1 promoter. We have also shown that this model reproduces many features of sporadic PD, including progressive changes in dopamine release and striatal content, alpha-synuclein pathology, deficits in motor and nonmotor functions that are affected in pre-manifest and manifest phases of PD, inflammation, and biochemical and molecular changes similar to those observed in PD. Preclinical studies have already demonstrated improvement with promising new drugs in this model, which provides an opportunity to test novel neuroprotective strategies during different phases of the disorder using endpoint measures with high power to detect drug effects.

Animal models of Parkinson's disease: a source of novel treatments and clues to the cause of the disease

Animal models of Parkinson's disease (PD) have proved highly effective in the discovery of novel treatments for motor symptoms of PD and in the search for clues to the underlying cause of the illness. Models based on specific pathogenic mechanisms may subsequently lead to the development of neuroprotective agents for PD that stop or slow disease progression. The array of available rodent models is large and ranges from acute pharmacological models, such as the reserpine- or haloperidol-treated rats that display one or more parkinsonian signs, to models exhibiting destruction of the dopaminergic nigro-striatal pathway, such as the classical 6-hydroxydopamine (6-OHDA) rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models. All of these have provided test beds in which new molecules for treating the motor symptoms of PD can be assessed. In addition, the emergence of abnormal involuntary movements (AIMs) with repeated treatment of 6-OHDA-lesioned rats with L-DOPA has allowed for examination of the mechanisms responsible for treatment-related dyskinesia in PD, and the detection of molecules able to prevent or reverse their appearance. Other toxin-based models of nigro-striatal tract degeneration include the systemic administration of the pesticides rotenone and paraquat, but whilst providing clues to disease pathogenesis, these are not so commonly used for drug development. The MPTP-treated primate model of PD, which closely mimics the clinical features of PD and in which all currently used anti-parkinsonian medications have been shown to be effective, is undoubtedly the most clinically-relevant of all available models. The MPTP-treated primate develops clear dyskinesia when repeatedly exposed to L-DOPA, and these parkinsonian animals have shown responses to novel dopaminergic agents that are highly predictive of their effect in man. Whether non-dopaminergic drugs show the same degree of predictability of response is a matter of debate. As our understanding of the pathogenesis of PD has improved, so new rodent models produced by agents mimicking these mechanisms, including proteasome inhibitors such as PSI, lactacystin and epoximycin or inflammogens like lipopolysaccharide (LPS) have been developed. A further generation of models aimed at mimicking the genetic causes of PD has also sprung up. Whilst these newer models have provided further clues to the disease pathology, they have so far been less commonly used for drug development. There is little doubt that the availability of experimental animal models of PD has dramatically altered dopaminergic drug treatment of the illness and the prevention and reversal of drug-related side effects that emerge with disease progression and chronic medication. However, so far, we have made little progress in moving into other pharmacological areas for the treatment of PD, and we have not developed models that reflect the progressive nature of the illness and its complexity in terms of the extent of pathology and biochemical change. Only when this occurs are we likely to make progress in developing agents to stop or slow the disease progression. The overarching question that draws all of these models together in the quest for better drug treatments for PD is how well do they recapitulate the human condition and how predictive are they of successful translation of drugs into the clinic? This article aims to clarify the current position and highlight the strengths and weaknesses of available models.

L-Dihydroxyphenylalanine modulates the steady-state expression of mouse striatal tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine and its metabolites in an MPTP mouse model of Parkinson's disease

AIMS

l-3,4-Dihydroxyphenylalanine (L-DOPA) is the most effective symptomatic treatment for Parkinson's disease (PD), but PD patients usually experience a successful response to L-DOPA therapy followed by a progressive loss of response. L-DOPA efficacy relies on its decarboxylation by aromatic l-amino acid decarboxylase (AAAD) to form dopamine (DA). So exogenous L-DOPA drives the reaction and AAAD becomes the rate limiting enzyme in the supply of DA. In turn, exogenous L-DOPA regulates the expression and activity of AAAD as well as the synthesis of DA and its metabolites, changes that may be linked to the efficacy and side-effects of L-DOPA.

MAIN METHODS

One-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse PD model was utilized to study the effects of L-DOPA on the steady-state level and activity of AAAD, tyrosine hydroxylase (TH), DA and the metabolites of DA. The MPTP and control mice were treated twice daily with PBS or with 100mg/kg of L-DOPA for 14days and the expression and activity of AAAD, the expression of TH and the levels of DA and its metabolites were determined 24h after L-DOPA or PBS treatment, when exogenous L-DOPA is eliminated.

KEY FINDINGS

In the MPTP model, L-DOPA reduced the steady-state expression and the activity of striatal AAAD by 52% and 50%, respectively, DA and metabolites were also significantly decreased.

SIGNIFICANCE

The outcome shows that while L-DOPA replenishes striatal DA it also down-regulates AAAD and the steady-state synthesis and metabolic capability of the dopaminergic system. These findings are important in the precipitation of L-DOPA induced side effects and the management of L-DOPA therapy.

The 5-HT(2A) Receptor Antagonist M100907 Produces Antiparkinsonian Effects and Decreases Striatal Glutamate

5-HT plays a regulatory role in voluntary movements of the basal ganglia and has a major impact on disorders of the basal ganglia such as Parkinson's disease (PD). Clinical studies have suggested that 5-HT(2) receptor antagonists may be useful in the treatment of the motor symptoms of PD. We hypothesized that 5-HT(2A) receptor antagonists may restore motor function by regulating glutamatergic activity in the striatum. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) exhibited decreased performance on the beam-walking apparatus. Peripheral administration of the 5-HT(2A) receptor antagonist M100907 improved performance of MPTP-treated mice on the beam-walking apparatus. In vivo microdialysis revealed an increase in striatal extracellular glutamate in MPTP-treated mice and local perfusion of M100907 into the dorsal striatum significantly decreased extracellular glutamate levels in saline and MPTP-treated mice. Our studies suggest that blockade of 5-HT(2A) receptors may represent a novel therapeutic target for the motor symptoms of PD.

Exercise alleviates Parkinsonism: clinical and laboratory evidence

The present review examines the putative benefits for individuals afflicted with Parkinsonism, whether in the clinical setting or in the animal laboratory, accruing from different exercise regimes. The tendency for patients with Parkinson's disease (PD) to express either normal or reduced exercise capacity appears regulated by factors such as fatigue, quality-of-life and disorder severity. The associations between physical exercise and risk for PD, the effects of exercise on idiopathic Parkinsonism and quality-of-life, the effects of exercise on animal laboratory models of Parkinsonism and dopamine (DA) loss following neurotoxic insults, and the effects of exercise on the DA precursor, L-Dopa, efficacy are examined. It would appear to be case that in view of the particular responsiveness of the dopaminergic neurons to exercise, the principle of 'use it or lose' may be of special applicability among PD patients.

Dual motor response to l-dopa and nociceptin/orphanin FQ receptor antagonists in 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) treated mice: Paradoxical inhibition is relieved by D(2)/D(3) receptor blockade

Motor activity of mice acutely treated with the parkinsonian toxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) was monitored for 6 days using behavioral tests which provide complementary information on motor function: the bar, reaction time, drag, stair climbing, grip, rotarod and footprinting tests. These tests consistently disclosed a prolonged motor impairment characterized by akinesia, bradykinesia, speed reduction, loss of coordination and gait patterns. This impairment was associated with approximately 60% loss of striatal dopamine terminals, as revealed by tyrosine hydroxylase immunohistochemistry, and was attenuated by dopaminergic drugs. Indeed, the dopamine precursor, l-dopa (1-10 mg/kg), and the D(3)/D(2) receptor agonist pramipexole (0.0001-0.001 mg/kg) promoted stepping activity in the drag test (a test for akinesia/bradykinesia). The novel nociceptin/orphanin FQ receptor (NOP) antagonist 1-[1-(cyclooctylmethyl)-1,2,3,6-tetrahydro-5-(hydroxymethyl)-4-pyridinyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (Trap-101, 0.001-0.1 mg/kg), an analogue of 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397), also promoted stepping and synergistically or additively (depending on test) attenuated parkinsonism when combined to dopamine agonists. High doses of l-dopa (100 mg/kg), pramipexole (0.1 mg/kg), Trap-101 and J-113397 (1 mg/kg), however, failed to modulate stepping, worsening immobility time and/or rotarod performance. Low doses of amisulpride (0.1 mg/kg) reversed motor inhibition induced by l-dopa and J-113397, suggesting involvement of D(2)/D(3) receptors. This study brings further evidence for a dopamine-dependent motor phenotype in MPTP-treated mice reinforcing the view that this model can be predictive of symptomatic antiparkinsonian activity provided the appropriate test is used. Moreover, it offers mechanistic interpretation to clinical reports of paradoxical worsening of parkinsonism following l-dopa. Finally, it confirms that NOP receptor antagonists may be proven effective in reversing parkinsonism when administered alone or in combination with dopamine agonists.

5-HT2A receptor antagonists improve motor impairments in the MPTP mouse model of Parkinson's disease

Clinical observations have suggested that ritanserin, a 5-HT(2A/C) receptor antagonist may reduce motor deficits in persons with Parkinson's Disease (PD). To better understand the potential antiparkinsonian actions of ritanserin, we compared the effects of ritanserin with the selective 5-HT(2A) receptor antagonist M100907 and the selective 5-HT(2C) receptor antagonist SB 206553 on motor impairments in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP-treated mice exhibited decreased performance on the beam-walking apparatus. These motor deficits were reversed by acute treatment with L-3,4-dihydroxyphenylalanine (levodopa). Both the mixed 5-HT(2A/C) antagonist ritanserin and the selective 5-HT(2A) antagonist M100907 improved motor performance on the beam-walking apparatus. In contrast, SB 206553 was ineffective in improving the motor deficits in MPTP-treated mice. These data suggest that 5-HT(2A) receptor antagonists may represent a novel approach to ameliorate motor symptoms of Parkinson's disease.

Physical exercise attenuates MPTP-induced deficits in mice

Two experiments were performed to investigate the effects of physical exercise upon the hypokinesia induced by two different types of MPTP administration to C57/BL6 mice. In the first, mice were administered either the standard MPTP dose (2 × 20 or 2 × 40 mg/kg, 24-h interval) or vehicle (saline, 5 ml/kg); and over the following 3 weeks were given daily 30-min period of wheel running exercise over five consecutive days/week or placed in a cage in close proximity to the running wheels. Spontaneous motor activity testing in motor activity test chambers indicated that exercise attenuated the hypokinesic effects of both doses of MPTP upon spontaneous activity or subthreshold L: -Dopa-induced activity. In the second experiment, mice were either given wheel running activity on four consecutive days (30-min period) or placed in a cage nearby and on the fifth day, following motor activity testing over 60 min, injected with either MPTP (1 × 40 mg/kg) or vehicle. An identical procedure was maintained over the following 4 weeks with the exception that neither MPTP nor vehicle was injected after the fifth week. The animals were left alone (without either exercise or MPTP) and tested after 2- and 4-week intervals. Weekly exercise blocked, almost completely, the progressive development of severe hypokinesia in the MPTP mice and partially restored normal levels of activity after administration of subthreshold L: -Dopa, despite the total absence of exercise following the fifth week. In both experiments, MPTP-induced loss of dopamine was attenuated by the respective regime of physical exercise with dopamine integrity more effectively preserved in the first experiment. The present findings are discussed in the context of physical exercise influences upon general plasticity and neuroreparative propensities as well as those specific for the nigrostriatal pathway.

Aging and alpha-synuclein affect synaptic plasticity in the dentate gyrus

Although intracellular accumulation of alpha-synuclein (alpha-syn) is a characteristic pathological change in Parkinson's disease, Lewy body dementia and Alzheimer's disease, the normal function of this presynaptic protein is still unknown. To assess the contribution of alpha-syn to synaptic plasticity as well as to age-related synaptic degeneration in mice, we compared adult and aged mice overexpressing mutated (A30P) human alpha-syn with their nontransgenic littermates using behavioral tests and electrophysiological measures in the dentate gyrus. We found decreased basal synaptic transmission and paired-pulse facilitation in the perforant path-dentate granule cell synapses of aged mice. In addition, alpha-syn accumulation in aged A30P mice but not in aged wild-type mice led to long-term depression of synaptic transmission after a stimulation protocol that normally induces long-term potentiation. These findings suggest that overexpression of mutated alpha-syn exacerbates the aging process and leads to impaired synaptic plasticity.

The hyperactive syndrome: metanalysis of genetic alterations, pharmacological treatments and brain lesions which increase locomotor activity

The large number of transgenic mice realized thus far with different purposes allows addressing new questions, such as which animals, over the entire set of transgenic animals, show a specific behavioural abnormality. In the present study, we have used a metanalytical approach to organize a database of genetic modifications, brain lesions and pharmacological interventions that increase locomotor activity in animal models. To further understand the resulting data set, we have organized a second database of the alterations (genetic, pharmacological or brain lesions) that reduce locomotor activity. Using this approach, we estimated that 1.56% of the genes in the genome yield to hyperactivity and 0.75% of genes produce hypoactivity when altered. These genes have been classified into genes for neurotransmitter systems, hormonal, metabolic systems, ion channels, structural proteins, transcription factors, second messengers and growth factors. Finally, two additional classes included animals with neurodegeneration and inner ear abnormalities. The analysis of the database revealed several unexpected findings. First, the genes that, when mutated, induce hyperactive behaviour do not pertain to a single neurotransmitter system. In fact, alterations in most neurotransmitter systems can give rise to a hyperactive phenotype. In contrast, fewer changes can decrease locomotor activity. Specifically, genetic and pharmacological alterations that enhance the dopamine, orexin, histamine, cannabinoids systems or that antagonize the cholinergic system induce an increase in locomotor activity. Similarly, imbalances in the two main neurotransmitters of the nervous system, GABA and glutamate usually result in hyperactive behaviour. It is remarkable that no genetic alterations pertaining to the GABA system have been reported to reduce locomotor behaviour. Other neurotransmitters, such as norepinephrine and serotonin, have a more complex influence. For instance, a decrease in norepinephrine synthesis usually results in hypoactive behaviour. However, a chronic increase in norepinephrine may result in hypoactivity too. Similarly, changes in both directions of serotonin levels may reduce locomotor activity, whereas alterations in specific serotonin receptors can induce hyperactivity. The lesion of at least 12 different brain regions can increase locomotor activity too. Comparatively, few focal lesions decrease locomotor activity. Finally, a large number of toxic events can increase locomotor activity, particularly if delivered during the prepuberal time window. These data show that there is a net imbalance in the number of altered genes/brain lesions/toxics that induce hyperactivity versus hypoactive behaviour. Although some of these data may be explained in terms of the activating role of subcortical systems (such as catecholamines), the larger number of alterations that induce hyperactivity suggests a different scenario. Specifically, we hypothesize (i) the existence of a control system that continuously inhibit a basally hyperactive locomotor tone and (ii) that this control system is highly vulnerable (intrinsic fragility) to any change in the genetic asset or to any toxic/drug delivered during prepuberal stages. Brain lesion studies suggest that the putative control system is located along an axis that connects the olfactory bulb and the enthorhinal cortex (enthorhinal-hippocampal-septal-prefrontal cortex-olfactory bulb axis). We suggest that the increased locomotor activity in many psychiatric diseases may derive from the interference with the development of this brain axis during a specific postnatal time window.

Functional consequences of iron overload in catecholaminergic interactions: the Youdim factor

The influence of postnatal iron overload upon implications of the functional and interactive role of dopaminergic and noradrenergic pathways that contribute to the expressions of movement disorder and psychotic behaviours in mice was studied in a series of experiments. (1) Postnatal iron overload at doses of 7.5 mg/kg (administered on Days 10-12 post partum) and above, invariably induced a behavioural syndrome consisting of an initial (1st 20-40 min of a 60-min test session) hypoactivity followed by a later (final 20 min of a 60-min test session) hyperactivity, when the mice were tested at adult ages (age 60 days or more). (2) Following postnatal iron overload, subchronic treatment with the neuroleptic compounds, clozapine and haloperidol, dose-dependently reversed the initial hypoactivity and later hyperactivity induced by the metal. Furthermore, DA D(2) receptor supersensitivity (as assessed using the apomorphine-induced behaviour test) was directly and positively correlated with iron concentrations in the basal ganglia. (3) Brain noradrenaline (NA) denervation, using the selective NA neurotoxin, DSP4, prior to administration of the selective DA neurotoxin, MPTP, exacerbated both the functional (hypokinesia) and neurochemical (DA depletion) effects of the latter neurotoxin. Treatment with L-Dopa restored motor activity only in the animals that had not undergone NA denervation. These findings suggest an essential neonatal iron overload, termed "the Youdim factor", directing a DA-NA interactive component in co-morbid disorders of nigrostriatal-limbic brain regions.

Levodopa-induced hyperactivity in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The present study examines the motor responses of 10- to 12-month-old, male C57 mice that were either given intraperitoneal (IP) injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 30 mg/kg per day) or vehicle for 10 consecutive days, followed by IP injections of levodopa (200 mg/kg) plus carbidopa (25 mg/kg). Five days of MPTP exposure resulted in the Straub tail phenomenon and pronounced hypokinesia. However, during the next 5 days, motor activity returned to baseline, even with continued MPTP treatment. After 10 to 14 days of rest, all mice were then treated with levodopa/carbidopa twice daily for multiple, consecutive days. However, only the previously MPTP-treated animals became hyperkinetic, as compared to levodopa-treated control animals that were not previously exposed to MPTP. Abnormal activity included scratching, running, gnawing, and jumping movements. Hyperactivity lasted for approximately 2 hours after each levodopa injection and then returned to baseline, but the amount of hyperkinesia increased with additional days of levodopa treatment, even though the daily levodopa dose was not changed. These results demonstrate that levodopa can cause reproducible hyperactivity in mice that were previously exposed to MPTP.

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

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

Postnatal iron overload destroys NA-DA functional interactions

C57/BL6 mice were administered either postnatal iron (Fe(2+) 7.5 mg/kg, on postnatal days 10-12) or vehicle, followed by administration of either DSP4 (50 mg/kg, s.c., 30 min after injection of zimeldine, 20 mg/kg, s.c.) or vehicle (saline) at 63 days of age. Three weeks later, iron/vehicle treated, DSP4/vehicle treated mice were injected with either a low dose of MPTP (2 x 20 mg/kg, with a 24-hr interval between injections) or vehicle. Behaviour testing took place a further three weeks (spontaneous behaviour and L-Dopa induced) and two weeks (clonidine-L-Dopa induced) later. Postnatal iron administration exacerbated the bradykinesia induced by MPTP and virtually abolished all spontaneous motor activity in NA-denervated mice that were MPTP-treated. Postnatal iron administration reduced markedly the restoration of motor activity by suprathreshold L-Dopa (20 mg/kg) following a 60-min habituation to the test chambers. Pretreatment with DSP4 effectively eliminated the restorative effect of L-Dopa in the MPTP mice. The synergistic effects of co-administration of clinidine (1 mg/kg) with a subthreshold dose of L-Dopa (5 mg/kg) in elevating the motor activity of MPTP mice were reduced markedly by postnatal iron administration, as well as by pretreatment with DSP4. NA-denervation by DSP4, after postnatal iron treatment, totally abolished the activity-elevating effects of the alpha-adrenoceptor agonist + DA-precursor combination in MPTP mice, and virtually eliminated these effects in saline (non-MPTP) mice. Postnatal iron administration caused enduring higher levels of total iron content in all the groups with an increased level in mice treated with DSP4 followed by MPTP. These divergent findings confirm the direct influence of NA innervation upon dopaminergic functional expression and indicate a permanent vulnerability both in the noradrenergic and dopaminergic pathways following the postnatal infliction of an iron overload.

Pitx3 deficiency in mice affects cholinergic modulation of GABAergic synapses in the nucleus accumbens

We investigated to what extent Pitx3 deficiency, causing hyperdopaminergic transmission in the nucleus accumbens microcircuitry, may lead to developmental changes. First, spontaneous firing activity of cholinergic interneurons in the nucleus accumbens was recorded in vitro. Firing patterns in the Pitx3-deficient mice were more variable and intrinsically different from those observed in wild-type mice. Next, to test whether the irregular firing patterns observed in mutant mice affected the endogenous nicotinic modulation of the GABAergic input of medium spiny neurons, we recorded spontaneous GABAergic inputs to these cells before and after the application of the nicotinic receptor blocker mecamylamine. Effects of mecamylamine were found in slices of either genotype, but in a rather inconsistent manner. Possibly this was attributable to heterogeneity in firing of nearby cholinergic interneurons. Thus paired recordings of cholinergic interneurons and medium spiny neurons were performed to more precisely control the experimental conditions of the cholinergic modulation of GABAergic synaptic transmission. We found that controlling action potential firing in cholinergic neurons leads to a conditional increase in GABAergic input frequency in wild-type mice but not in Pitx3-deficient mice. We conclude that Pitx3-deficient mice have neural adaptations at the level of the nucleus accumbens microcircuitry that in turn may have behavioral consequences. It is discussed to what extent dopamine release in the nucleus accumbens may be a long-term gating mechanism leading to alterations in cholinergic transmission in the nucleus accumbens, in line with previously reported neural adaptations found as consequences of repeated drug treatment in rodents.

Locomotor activity and evoked dopamine release are reduced in mice overexpressing A30P-mutated human alpha-synuclein

We have generated a transgenic mouse line overexpressing mutated human A30P alpha-synuclein under the control of the prion-related protein promoter. Immunohistology revealed mutated human A30P alpha-synuclein protein in numerous brain areas, but no gross morphological changes, Lewy bodies, or loss of dopaminergic cell bodies. The transgenic mice displayed decreased locomotion, impaired motor coordination, and balance. In vivo voltammetry showed that A30P mice responded to longer stimulation of the ascending dopaminergic pathways with less dopamine release in striatum and had a slower rate of dopamine decline after repeated stimulations or after alpha-methyl-p-tyrosine-HCl treatment. However, dopamine re-uptake or transporter levels were similar in transgenic and control mice. Our data provide evidence that overexpression of mutated human A30P alpha-synuclein in mice leads to a reduced size of the dopamine storage pool. This is in agreement with the previously postulated involvement of alpha-synuclein in the turnover of transmitter vesicles and may explain the observed motor deficits in A30P mice.

Influence of noradrenaline denervation on MPTP-induced deficits in mice

C57/BL6 mice were administered either DSP4 (50 mg/kg, s.c., 30 min after injection of zimeldine, 20 mg/kg, s.c.) or vehicle (saline) at 63 days of age. Three weeks later, one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered MPTP (2 x 40 mg/kg, s.c., 24 hours between injections; the High dose groups), one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered MPTP (2 x 20 mg/kg, s.c., 24 hours between injections; the Low dose groups), and one group (n = 10) of DSP4-treated and one group of vehicle-treated mice were administered vehicle. Three weeks later, all six groups were tested in motor activity test chambers, followed by injections of L-Dopa (20 mg/kg, s.c.), and then tested over a further 360 min in the activity test chambers. It was found that pretreatment with the selective NA neurotoxin, DSP4, deteriorated markedly the dose-dependent motor activity deficits observed in the vehicle pretreated MPTP treated mice. These 'ultra-deficits' in the spontaneous motor behaviour of MPTP-treated mice were observed over all three parameters: locomotion, rearing and total activity, and were restricted to the 1(st) and 2(nd) 20-min periods. Administration of L-Dopa (20 mg/kg) following the 60-min testing of spontaneous behaviour restored the motor activity of Vehicle + MPTP treated mice (neither the Vehicle + MPTP-Low nor the Vehicle + MPTP-High groups differed from the Vehicle-Vehicle group, here) but failed to do so in the DSP4 pretreated mice. Here, a dose-dependent deficit of L-Dopa-induced motor activity (over all three parameters) was obtained thereby offering further evidence of an 'ultra-deficit' of function due to previous denervation of the NA terminals. The present findings support the notion that severe damage to the locus coeruleus noradrenergic system, through systemic DSP4, disrupts the facilitatory influence on the nigrostriatal DA system, and interferes with the ability of the nigrostriatal pathway to compensate for or recover from marked injury, MPTP treatment.

Recovery of experimental Parkinson's disease with the melatonin analogues ML-23 and S-20928 in a chronic, bilateral 6-OHDA model: a new mechanism involving antagonism of the melatonin receptor

Over the past 10 years, there has been a resurgence of interest in examining the role of melatonin in health and disease. While the brunt of research in this area has portrayed melatonin in a favorable light, there is a growing body of evidence suggesting that melatonin may possess adverse effects contributing to the development of various neuropsychiatric disease states. In preclinical models of Parkinson's disease (PD), melatonin has been shown to enhance the severity of this condition while its antagonism, using constant light or pinealectomy, facilitates recovery. To test this hypothesis further, the present study employed the melatonin analogues ML-23 and S-20928 in a post-6-OHDA injection regime to determine whether they may have a favorable effect on the symptoms of this more chronic model of PD. When ML-23 was injected I.P. in a dose of 3 mg/kg twice daily for 3.5 days after 6-OHDA, significant improvement in motor function and regulatory deficits was observed. Similarly, the injection of S-20928 in a 1 mg/kg dose (I.P.), in the same regimen, facilitated modest improvement in motor function and regulatory deficits while the larger dose enhanced the severity of behavioural deficits and produced severe side effects causing deterioration in condition during the course of drug administration. ML-23 administration totally abolished the 6-OHDA-induced mortality, which accompanies dopamine (DA) degeneration, while S-20928 had no effect on this parameter. These results suggest that some melatonin analogues can aid in recovery from DA depleting lesions after DA degeneration has commenced and the recovery is not attributable to the antioxidative properties of this hormone. While the exact mechanism by which ML-23 and S-20928 are exerting their therapeutic effect is unclear, it is possible that antagonism of melatonin receptors may play some role and this should be considered when assessing the potential of melatonin analogues for treatment of human neuropsychiatric disorders.

The therapeutic effects of dopamine replacement therapy and its psychiatric side effects are mediated by pineal function

There are reports that melatonin secretion from the pineal gland gradually diminishes with advancing age. It has been suggested that various forms of neuropsychiatric disease, in particular, Parkinson's disease (PD), is consequentially related to this decrease by virtue of increased oxidative stress which enhances the process of dopamine (DA) degeneration. There is, however, considerable disagreement on this theme as very little is generally known about the role of the pineal gland in the aetiology and treatment of PD. To assess the role of the pineal gland in PD and in dopamine replacement therapy (DART), the effect of three anti-Parkinsonian drugs on motor and psychiatric function was assessed in normal, pinealectomized (PX) and DA deficient, PX rats. In the first study, rats underwent PX or sham operation and were then injected (IP) with Amantadine (30 or 50 mg/kg), Bromocriptine (5 or 10 mg/kg) or L-Dopa (30 or 60 mg/kg plus 50 mg/kg of R-044602) 3-8 weeks after surgery. Open field performance and motor reflex tests were assessed during the light and dark phases of the L/D cycle. In a second study, clinically effective doses of Bromocriptine (10 mg/kg) and L-Dopa (30 and 100 mg/kg with 50 mg/kg R-044602) were injected into depleted, PX or sham operated rats. In study I, sham operated and PX rats responded differently to Bromocriptine and L-Dopa, while Amantadine did not differentially effect motor performance in the two groups. In study II, 6-OHDA induced degeneration of the nigro-striatal system abolished the effects of Bromocriptine and dramatically altered the effects of L-Dopa seen in study I, in sham operated versus PX rats. DART significantly altered emotionality, as measured by escape attempts, agitation and rage in sham operated animals, compared to PX rats. DA deficiency abolished the tendency to escape in all groups except those treated with 100mg/kg of L-Dopa. Conversely, agitation and rage scores were greater after 100 mg/kg of L-Dopa, in rats with intact pineal function, than in PX rats. These results provide compelling evidence that altered pineal function plays a major role in the aetiology of PD, the therapeutic effect of anti-Parkinsonian drugs and in the psychiatric side effects of DART.

Influence of polychlorinated biphenyls and turning preference on striatal dopamine metabolism

Male BALB/c mice, assessed for spontaneous nocturnal rotation that has been linked with functional differences in striatal dopamine (DA) content, were divided into right (R), left (L), and no turning preference (NP) groups. Both total turning activity and turning in the preferred direction were greatest in the R mice. To determine whether turning preference influences the response to exposure to an environmental toxicant known to reduce striatal DA function, striatal tissues from R, L, or NP mice were exposed to polychlorinated biphenyls (PCBs). In vitro exposure of striata from these mice to varying concentrations of PCBs for 4 h concentration-dependently decreased tissue DA content and increased the concentrations of DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the media, a phenomenon already observed, although of smaller magnitude, with rat tissues. These effects were independent of the turning preference of the mice. Although the DA content initially did not differ among the striatal tissue from R, L, and NP mice, following 4 h of incubation in control medium (without PCBs), there was significantly greater DA content in striata from R mice in comparison to that from either L or NP mice. This difference was also apparent after 6 h of incubation, and it was not due to differences in DA turnover or cytotoxicity. Rather, the greater DA content in the striata of R mice was due to increased DA synthesis, since tyrosine hydroxylase (TH) activity was greater in striata from R mice than in striata from either L or NP mice. These differences in striatal DA synthesis, if present in vivo, may explain the observed greater nocturnal turning activity of the R mice. Additionally, the in vitro analyses suggest that striata from R mice have differential responses to stress compared with striata from L or NP mice. With regard to the effects of PCBs, however, it appears that (1) striata derived from mice with different turning preference are equally sensitive to this dopaminergic toxicant and (2) mice appear more sensitive to PCBs than rats.

Grid performance test to measure behavioral impairment in the MPTP-treated-mouse model of parkinsonism

Behavioral impairments in mice following administration of the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) require large depletions in striatal dopamine content and are often transient. In this paper, we describe a simple and inexpensive test that measures long-term behavioral deficits in mice treated with moderate doses of MPTP. These measures are significantly correlated with the loss of striatal dopamine and immunoreactivity of the dopamine transporter, vesicular monoamine transporter and tyrosine hydroxylase. In addition, behavioral impairments on the measures were reversed following L-DOPA administration. Employment of this test will allow for more efficacious use of mice in PD research, as well as provide more sensitive measures of behavioral improvement following potential therapeutic or neuroprotective interventions.

Effect of postnatal iron administration on MPTP-induced behavioral deficits and neurotoxicity: behavioral enhancement by L-Dopa-MK-801 co-administration

Two experiments were performed to investigate the interactive effects of postnatal iron administration and adult MPTP treatment upon the function of C57 Bl/6 mice tested at adult age and to ascertain the possible ameliatory effects of a subthreshold dose of L-Dopa co-administered with different doses of the uncompetitive glutamate antagonist, MK-801. Experiment I indicated that postnatal iron induced marked deficits (hypoactivity), initially, in all three parameters of motor activity at the 5.0 and 7.5 mg/kg doses, and to a lesser extent at the 2.5 mg/kg dose. Later combination with MPTP (2x40 mg/kg) potentiated severely these deficits. During the final period of testing a marked hyperactivity was obtained for the two higher dose groups; this effect was abolished in mice administered MPTP. Experiment II indicated that the deficits in motor activity parameters induced by postnatal iron at 7.5 mg/kg were alleviated in a dose-related manner by the co-administration of the uncompetitive glutamate antagonist, MK-801, with a subthreshold dose of L-Dopa. Postnatal iron (7.5 mg/kg) administration followed by low doses of MPTP (2x20 mg/kg) 3 months later virtually abolished all motor activity. The combination of these compounds increased also the motor activity of mice treated with MPTP (2x20 mg/kg) or mice treated with the combination of postnatal iron and MPTP. The combination of MK-801 with L-Dopa increased locomotor (0.3 mg/kg), rearing (0.1 and 0.3 mg/kg) and total activity (0.3 mg/kg) of iron-treated mice during the initial, hypoactive 30-min period of testing. Locomotor activity (0.1 mg/kg) of MPTP-treated mice was increased too during this period. During the final 30-min period of testing all three parameters of activity (locomotion, 0.3 mg/kg; rearing and total activity, 0.1 and 0.3 mg/kg) were enhanced in the iron-treated mice, locomotion (0.1 mg/kg) and rearing (0.1 mg/kg) in the iron plus MPTP treated mice and only locomotion (0.1 mg/kg) in the MPTP-treated mice. In control mice (vehicle+saline), the higher doses of MK-801 (0.1 and 0.3 mg/kg) enhanced both locomotor and total activity. Analyses of total iron concentration in the frontal cortex and basal ganglia of Fe(2+) and vehicle treated mice indicated that marked elevations basal ganglia iron levels of the 5.0 and 7.5 mg/kg groups, later injected either saline or MPTP, were obtained (Experiment I). In Experiment II, iron concentrations in the basal ganglia were elevated in both the Fe(2+)-sal and Fe(2+)-MPTP groups to 170 and 177% of Veh.-sal values, respectively. There was a significant increase in the frontal cortex of iron-treated mice later administered either saline or MPTP (2x40 mg/kg) in Experiment I as well as in those given iron followed by MPTP (2x20mg/kg) in Experiment II. The implications of iron overload in parkinsonism seem confirmed by the interactive effects of postnatal administration of the metal followed by adult MPTP treatment upon motor activity and the activity-enhancing effects of co-administration of L-Dopa with MK-801.

Effects of acute administration of DA agonists on locomotor activity: MPTP versus neonatal intracerebroventricular 6-OHDA treatment

The effects of several dopamine (DA) receptor agonists upon locomotor activity on adult MPTP-treated mice and postnatal 6-hydroxydopamine- (6-OHDA-) treated rats were assessed in ten experiments. C57 BL/6 mice were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 2 x 40 mg/kg, s.c., 24-hr interval between injections) at 5-months-age, while 1-day-old male Wistar rat pups were given intracisternal 6-OHDA (50 mg, once following desipramine, 25 mg/kg). MPTP-treated mice were tested 4-5 weeks following MPTP injections whereas neonatal 6-OHDA rats were tested at 3-months-age. Locomotor activity was measured in respective activity test chambers following acute administration of DA receptor agonists. In MPTP-treated mice, apomorphine failed to elevate locomotor activity but instead further exacerbated (1.0 and 3.0 mg/kg, s.c.) the hypokinesia of these animals while inducing marked increases in control mice. Cabergoline (0.3 mg/kg, s.c.) and bromocriptine (3.0 mg/kg, s.c.) caused dose-specific elevations of locomotion in MPTP and control mice but suppressed activity at the highest doses. Quinpirole (0.2 mg/kg) and 7-hydroxydipropylaminotetralin (7-OH-DPAT; 300 nmole/kg) increased locomotion in hypokinesic MPTP-treated mice; in control mice, activity was elevated by quinpirole (0.2 and 0.7 mg/kg) and 7-OH-DPAT (100 and 300 nmole/kg), while higher doses suppressed activity. Neither SKF 38393 (1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol) nor FCE 23884 [4-(9,10-didehydro-6-methylergolin-8 beta-yl) methyl-piperazine-2,6-dione] affected locomotor activity. Apomorphine (0.3, 1.0 and 2.0 mg/kg), bromocriptine (3.0 mg/kg) and cabergoline (1.0 mg/kg) stimulated locomotion in sham-operated rats, and to a greater extent in the 6-OHDA-treated rats. Higher dose cabergoline (3.0 mg/kg) induced increased activity of similar extent in sham controls and 6-OHDA treated rats. Activity-enhancing effects of quinpirole (0.2, 0.7 and 2.1 mg/kg) in sham rats were attenuated in 6-OHDA treated rats. Both SKF 38393 (10 mg/kg) and FCE 23884 (0.3 and 1.0 mg/kg) induced locomotor activity increases in 6-OHDA, but not sham, rats. Finally, 7-OH-DPAT (1200 mg/kg) enhanced activity in 6-OHDA rats vs. shams. The effects of the DA agonists are discussed with regard to the putative antihypokinesic effects in MPTP mice and DA-receptor supersensitivity effects in neonatal 6-OHDA rats, pertaining to their more-or-less selective subreceptor profiles.

Behavioral phenotyping of the MPTP mouse model of Parkinson's disease

In mice, the systemical or intracranial application of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can lead to severe damage to the nigrostriatal dopaminergic system. This can result in a variety of symptoms concerning motor control resembling those in human Parkinson's disease, such as akinesia, rigidity, tremor, gait and posture disturbances. The aim of this work is to review a variety of behavioral paradigms for these and other symptoms, which have been used to characterize behavioral changes in mice after MPTP treatment. Main results are summarized, and general influential factors as well as potential problems in the experimental procedures are discussed, which should be taken into account when conducting behavioral analyses in mice with parkinsonian symptoms. Since there is reliable evidence (e.g. from strain comparisons) that the susceptibility of the nigrostriatal pathway to neurodegeneration is probably genetically influenced, relevant genes can be expected to be identified in the future. Therefore, the points discussed here will be useful not only for further applications in the MPTP mouse model, but also more generally for the behavioral characterization of future mouse models of PD, e.g. mice with a manipulation of genes relevant to the function of the basal ganglia.

The frissonnant mutant mouse, a model of dopamino-sensitive, inherited motor syndrome

The frissonnant (fri) mutation is an autosomic recessive mutation which spontaneously appeared in the stock of C3H mice. fri mutant mice have locomotor instability and rapid tremor. Since tremor ceases when mutant mice have sleep or are anaesthetized, and because of their obvious stereotyped motor behavior, these mice could represent an inherited Parkinsonian syndrome. We show here that the fri/fri mouse fulfills two out of the three criteria required to validate an experimental model of human disease, that is isomorphism, homology and predictivity. Indeed, fri/fri mice present an important motor deficit accompanying visible tremor and stereotypies. They display some memory deficits as in human Parkinson's desease. l-Dopa and apomorphine (dopaminergic agonists), ropinirole (selective D2 agonist), and selegiline (an monoamino-oxidase B [MAO-B] inhibitor) improve their clinical status. However, neither anatomopathological evidence of nigrostriatal lesion, nor decrease in tyrosine hydroxylase production could be seen.

Neonatal iron potentiates adult MPTP-induced neurodegenerative and functional deficits

The interactive effects of neonatal iron and adult MPTP treatment groups of C57 Bl/6 mice were studied through adminustration of iron (Fe(2+)) 7.5mg/kg b.w., p.o. or vehicle (saline) on days 10-12 post partum, followed at 3months of age by administration of either MPTP (2x20 or 2x40mg/kg, s.c.) or saline. Neonatal iron administration to mice-induced hypoactivity during the first 20-min period of testing and hyperactivity during the 3rd and final 20-min period for all three parameters of motor activity tested at 4months of age. MPTP treatment caused a dose-related hypokinesia throughout the 3x20-min test periods; in the mice that received both neonatal iron and MPTP severe deficits of motor activity (akinesia) were obtained. Iron treatment impaired the ability of mice to habituate to the novel testing environment and later administration of MPTP potentiated the impairment markedly. Neurochemical analyses of striatal and frontal cortical dopamine (DA) and DA metabolites demonstrated that the depletions were potentiated under conditions of combined neonatal iron and adult MPTP. The analysis of total iron content (µg/g) in brain regions indicated notably elevated levels in the basal ganglia, but not in the frontal cortex, of mice administered Fe(2+). Iron-overload combined with MPTP treatment induced functional and neurochemical deficits with interactive consequences beyond a mere additive effect that may have implications for the neurodegenerative process in parkinsonism.

Co-administration of memantine and amantadine with sub/suprathreshold doses of L-Dopa restores motor behaviour of MPTP-treated mice

The antiparkinsonian effects of the uncompetitive NMDA antagonists, memantine, amantadine and MK-801, in combination with an acute subthreshold dose of L-Dopa (5 mg/kg) in drug-naive MPTP-treated mice or a suprathreshold dose (20 mg/kg) in L-Dopa tolerant MPTP-treated mice were investigated. In the former case, memantine (locomotion: 3 mg/kg; rearing: 1 mg/kg) and amantadine (locomotion and rearing: 10 mg/kg) injected 60 min before the subthreshold dose of L-Dopa (5 mg/kg), each induced an antiparkinsonian action in hypokinesic MPTP-treated mice that consisted of dose-specific, as opposed to dose-related, elevations of locomotion and rearing behaviour. At the same time, higher doses of memantine reduced further the rearing (10 and 30 mg/kg) and locomotor (30mg/kg) behaviour of the MPTP-treated mice. MK-801 plus L-Dopa elevated locomotion (0.1 mg/kg) but reduced rearing at the 0.3 mg/kg dose. In control, saline-treated mice, memantine (3, 10 and 30 mg/kg) and MK-801 (0.1 and 0.3 mg/kg) increased locomotor behaviour but decreased rearing behaviour, while amantadine produced no effects. Memantine increased locomotor (1 and 3 mg/kg, s.c.; 1 mg/kg dose restored activity) and rearing (0.3 and 3 mg/kg) activity in the L-Dopa tolerant MPTP-treated mice, whereas amantadine (3 and 10 mg/kg) restored both locomotor (30 mg/kg significantly increased locomotion but did not restore the activity level) and rearing (3 mg/kg only) activity. MK-801 (0.1 and 0.3 mg/kg, s.c.) also increased significantly locomotor activity of L-Dopa-tolerant MPTP mice although the antikinetic action was not reversed, thereby precluding a restorative effect of the compound. These results, demonstrating both a synergistic and a restorative effect of the NMDA antagonists in coadministration with L-Dopa, demonstrate a putative antiparkinson action by these compounds in a functional animal model that incorporates the "wearing-off" complications of L-Dopa administration in the disorder.

Effects of MAO inhibitors upon MPTP mice chronically treated with suprathreshold doses of L-dopa

Groups of mice were administered either saline or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (2 X 40 mg / kg, s.c., separated by a 24-hour interval) 4-6 weeks prior to behavioural testing. At testing, all the MPTP-injected mice were repeatedly administered L-dopa (20 mg / kg, s.c., five times each week, Monday-Friday), by applying a procedure that induced a severe reduction of motor activity parameters from Day 1 to Day 25. Control (uninjected mice) received only saline and were retained only for neurochemical analysis. In each of three experiments, following the reduction of the activity-stimulating effects of L-dopa by repeated administration, a restorative effect of different monoamine oxidase (MAO) inhibitors was tested by co-administration of the test compounds (irreversible MAO-B inhibitor, reversible MAO-A inhibitors, or irreversible MAO-A / mixed MAO inhibitors) with L-dopa (20 mg / kg). In each case the MAO inhibitor was injected 60 min prior to L-dopa. L-Deprenyl (3 or 10 mg / kg, s.c.), in combination with L-dopa, reinstated locomotion and total activity, but not rearing, dose-dependently, in L-dopa-tolerant mice. The reversible MAO-A inhibitors, amiflamine and alpha-ethyltryptamine, in combination with L-dopa, reinstated locomotion and total activity, leaving rearing unaffected; Ro 41-1049 (3 mg / kg, s.c.) restored all three parameters of activity; locomotor activity was restored by all three doses (1, 3, and 10 mg / kg, s.c.). On the other hand, neither the irreversible MAO-A inhibitor, clorgyline, nor the mixed MAO inhibitor, phenelzine, produced any directly effective restorative increments. Neurochemical analysis confirmed the severe striatal dopamine depletion of MPTP-treated mice. These results demonstrate a synergistic and restorative action of combining certain MAO inhibitors, namely the reversible MAO-A inhibitors, with the suprathreshold dose of L-dopa in MPTP-treated, L-dopa-tolerant mice.

MPTP-induced deficits in motor activity: neuroprotective effects of the spintrapping agent, alpha-phenyl-tert-butyl-nitrone (PBN)

In Experiment 1, groups of mice were administered either saline or MPTP (2 x 30 mg/kg, s.c., separated by a 24-hr interval) 30 min after being injected either PBN (15, 50 or 150 mg/kg, s.c., low, medium and high doses, respectively) or L-Deprenyl (0.25 or 10.0 mg/kg, s.c., low and high doses, respectively), the reference compound used, or saline. Tests of spontaneous motor activity 14 days later indicated that the MPTP-induced hypokinesia for locomotion and rearing was alleviated by prior administration with PBN (50 or 150 mg/kg) or L-Deprenyl (10.0 mg/kg); lower doses of PBN (15 mg/kg) and L-Deprenyl (0.25 mg/kg) did not affect the MPTP-induced deficits. Dopamine (DA) concentrations in the striatum confirmed a more severe loss of DA in the MPTP, PBN (15) + MPTP and Deprenyl(0.25) + MPTP groups than in the control group. Significant protection of DA was observed in the PBN(50) + MPTP, PBN(150) + MPTP and Deprenyl(10) + MPTP groups that did not exhibit an hypokinetic behaviour. In Experiment 2, the effects of repeated treatment with PBN (50 mg/kg, s.c. over 12 days), post-MPTP, were studied in aged (15-month-old) and young (3-month-old) mice. Subchronic administration of PBN increased substantially the motor activity of old and young mice that had received MPTP. Aged control (saline) mice showed an activity deficit compared to young control mice; this deficit was abolished by repeated PBN treatment. The results suggest that moderate-to-high doses of PBN whether injected in a single dose prior to MPTP or subchronically following MPTP injections may afford protective effects against both the functional changes and DA-loss caused by MPTP treatment, possibly through an antioxidant mechanism.

Restoration and putative protection in Parkinsonism

Synergistic antiparkinsonian actions of different classes of putative therapeutic agents co-administered with a subthreshold dose of L-3,4-dihydroxyphenylalanine (L-Dopa) (5 mg/kg) in drug-naive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as well as the restorative actions of those compounds in suprathreshold L-Dopa-tolerant MPTP-treated mice subjected to "wearing-off" of L-Dopa efficacy were assessed in a series of experiments. The classes of compounds studied included the noncompetitive NMDA antagonists, memantine, amantadine and MK-801, the anticonvulsive and putative anticonvulsive agents, lamotrigine, FCE 26743, phenytoin, the monoamine oxidase inhibitors, L-Deprenyl, amiflamine, alpha-ethyltryptamine, clorgyline and guanfacine. In this final case, the restorative effects of clonidine and guanfacine were antagonized by the alpha(2)-adrenoceptor antagonist, yohimbine, but not the alpha(1)-adrenoceptor antagonist, prazosin. Within each class of potentially therapeutic agents a differential restorative efficacy was obtained, but the combination of different doses of apomorphine with clonidine failed to restore motor activity. Finally, the neuroprotective actions of acute and subchronic administration of the nitrone spin-trapping compound, alpha-phenyl-tert-butyl nitrone upon the spontaneous motor behaviour and striatal dopamine concentrations of MPTP-treated mice was examined.

Strain-dependent recovery of open-field behavior and striatal dopamine deficiency in the mouse MPTP model of Parkinson's disease

The neurotoxin MPTP can damage dopamine systems in the brains of rodents, cats, or monkeys, and is therefore widely used to model degenerative processes that underlie human Parkinson's disease. Here, we investigated the relationships between behavioral and neurochemical effects of systemic MPTP treatment in C57Bl/6 and Balb/c mice. Initially, different doses of MPTP were used to determine which of them might be useful to establish severe striatal dopamine depletions. These data showed that four injections of 20mg/kg at two hour intervals, were more efficient than 10 or 15mg/kg per injection. However, this dose was not usable due to its severe lethality in females. In contrast, 4x 15mg/kg had a low risk of lethality and led to substantial dopamine depletions, which were more severe in the neostriatum than the ventral striatum, and more severe in C57 than in Balb mice. In the first open field test, which was performed two hours after the last injection, this treatment led to severe behavioral inactivation in all parameters taken (distance and speed of locomotion, peripheral activity, frequency and duration of rearing). This effect was seen in both strains and gender. Thereafter, recovery differed between strains, since Balb mice, which had sustained the smaller lesions, had completely recovered on the subsequent day, whereas similar recovery took longer in C57 mice. On the fourth day, all groups appeared largely normal; however, the measure of rearing behavior still showed a deficit in C57 mice. This deficit on day 4 was correlated with neostriatal dopamine depletion; that is, the larger the lesion, the less the number and duration of rearings. Interestingly, these relationships were also observed with respect to ventral striatal dopamine damage, which was correlated with the rearing deficit not only on day 4, but also on day 1. These data will be discussed with respect to mechanisms of toxicity, functional recovery, and the function of striatal dopamine systems.

Paraquat elicited neurobehavioral syndrome caused by dopaminergic neuron loss

The herbicide paraquat, bearing structural similarity to the known dopaminergic neurotoxicant MPTP, has been suggested as a potential etiologic factor in Parkinson's disease. Consideration of paraquat as a candidate neurotoxicant requires demonstration that systemic delivery produces substantia nigra dopaminergic neuron loss and the attendant neurobehavioral syndrome reflecting depletion of dopamine terminals within the striatum. To address these issues paraquat was administered systemically into adult C57 bl/6 mice, ambulatory behavior monitored, substantia nigra dopamine neuron number and striatal dopamine terminal density quantified. The data indicate that paraquat like MPTP elicits a dose-dependent decrease in substantia nigra dopaminergic neurons assessed by a Fluoro-gold prelabeling method, a decline in striatal dopamine nerve terminal density assessed by measurement of tyrosine hydroxylase immunoreactivity; and neurobehavioral syndrome characterized by reduced ambulatory activity. Taken together, these data suggest that systemically absorbed paraquat crosses the blood-brain barrier to cause destruction of dopamine neurons in the substantia nigra, consequent reduction of dopaminergic innervation of the striatum and a neurobehavioral syndrome similar to the well characterized and bona fide dopaminergic toxin MPTP.