Validation of a rodent model of Parkinson's Disease: evidence of a therapeutic window for oral Sinemet

Biochemical study of the effect of mesenchymal stem cells-derived exosome versus L-Dopa in experimentally induced Parkinson's disease in rats

Parkinson's disease (PD) is a chronic and ongoing neurological condition. Unfortunately, as the dopaminergic terminals continue to deteriorate, the effectiveness of anti-Parkinson therapy decreases. This study aimed to examine the effects of BM-MSCs-derived exosomes in rats induced with Parkinson's disease. The goal was to determine their potential for neurogenic repair and functional restoration. Forty male albino rats were divided into four groups: control (group I), PD (group II), PD-L-Dopa (group III), and PD-exosome (group IV). Motor tests, histopathological examinations, and immunohistochemistry for tyrosine hydroxylase were performed on brain tissue. The levels of α-synuclein, DJ-1, PARKIN, circRNA.2837, and microRNA-34b were measured in brain homogenates. Rotenone induced motor deficits and neuronal alterations. Groups (III) and (IV) showed improvement in motor function, histopathology, α-synuclein, PARKIN, and DJ-1 compared to group (II). Group (IV) showed improvement in microRNA-34b and circRNA.2837 compared to groups (III) and (II). MSC-derived exosomes showed a greater suppression of neurodegenerative disease (ND) compared to L-Dopa in Parkinson's patients.

Epalrestat improves motor symptoms by reducing oxidative stress and inflammation in the reserpine induced mouse model of Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting a large number of elderly people worldwide. The current therapies for PD are symptom-based; they do not provide a cure but improve the quality of life. Muscular dysfunction is the hallmark clinical feature of PD and oxidative stress and inflammation play a critical role in its pathogenesis. Epalrestat is used for the treatment of diabetic neuropathy and is known to improve antioxidative defense mechanisms in the CNS. Therefore, in this study, we investigated the role of Epalrestat in the reserpine induced mouse model of PD.

METHOD

We used Swiss Albino mice for the PD model and tested for akinesia/bradykinesia, muscular rigidity, palpebral ptosis, and tremor, as well as conducting swim and open field tests. Brain samples were used to determine oxidative stress parameters and infiltration of immune cells.

RESULTS

Epalrestat treatment significantly improved akinesia and bradykinesia, muscular dysfunctions, tremor level, and gait functions compared to the reserpine group. It also improved the latency in the swim test. Eplarestat significantly reduced lipid peroxidation and NO concentration in different brain tissues and increased the activity of antioxidative enzymes, glutathione, catalase, and superoxide dismutase. Furthermore, Epalrestat reduced neuroinflammation by reducing the number of infiltrating immune cells.

CONCLUSION

Eplarestat improves muscular dysfunction in PD by reducing oxidative stress and inflammation.

The Rodent Models of Dyskinesia and Their Behavioral Assessment

Dyskinesia, a major motor complication resulting from dopamine replacement treatment, manifests as involuntary hyperkinetic or dystonic movements. This condition poses a challenge to the treatment of Parkinson's disease. So far, several behavioral models based on rodent with dyskinesia have been established. These models have provided an important platform for evaluating the curative effect of drugs at the preclinical research level over the past two decades. However, there are differences in the modeling and behavioral testing procedures among various laboratories that adversely affect the rat and mouse models as credible experimental tools in this field. This article systematically reviews the history, the pros and cons, and the controversies surrounding rodent models of dyskinesia as well as their behavioral assessment protocols. A summary of factors that influence the behavioral assessment in the rodent dyskinesia models is also presented, including the degree of dopamine denervation, stereotaxic lesion sites, drug regimen, monitoring styles, priming effect, and individual and strain differences. Besides, recent breakthroughs like the genetic mouse models and the bilateral intoxication models for dyskinesia are also discussed.

[A study of combination treatment with nacom (levodopa + carbodope) and citicoline in the model of Parkinson disease in rats]

AIM

To evaluate the efficacy of the combined use of citicoline (neipilept) and levodopa/carbidopa (nakom) in the rotenone model of Parkinson's disease in rats.

MATERIAL AND METHODS

Rotenone was administrated during 14 days in dose 2 mg/kg/day subcutaneously. The duration of treatment was 7 days, intragastrically. Alteration of locomotor behavior components, muscular rigidity in resistance to passive flexion in the ankle joint and signs of extrapyramidal disorders were assessed.

RESULTS AND CONCLUSION

Combined therapy led to the decrease in muscle rigidity (the decrease of gibbosity in resistance to passive flexion in the ankle joint). There was a decrease in oligokinesia that emerged in higher vertical and horizontal locomotor activity of experimental animals, decrease in the time of head turning during climbing down the pole and total time of climbing down the pole. The combination of drugs had a more pronounced therapeutic effect on extrapyramidal disorders compared to monotherapy.

Effect of Levodopa on Reward and Impulsivity in a Rat Model of Parkinson's Disease

The use of dopamine replacement therapies (DRT) in the treatment of Parkinson’s disease (PD) can lead to the development of dopamine dysregulation syndrome (DDS) and impulse control disorders (ICD), behavioral disturbances characterized by compulsive DRT self-medication and development of impulsive behaviors. However, the mechanisms behind these disturbances are poorly understood. In animal models of PD, the assessment of the rewarding properties of levodopa (LD), one of the most common drugs used in PD, has produced conflicting results, and its ability to promote increased impulsivity is still understudied. Moreover, it is unclear whether acute and chronic LD therapy differently affects reward and impulsivity. In this study we aimed at assessing, in an animal model of PD with bilateral mesostriatal and mesocorticolimbic degeneration, the behavioral effects of LD therapy regarding reward and impulsivity. Animals with either sham or 6-hydroxydopamine (6-OHDA)-induced bilateral lesions in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) were exposed to acute and chronic LD treatment. We used the conditioned place preference (CPP) paradigm to evaluate the rewarding effects of LD, whereas impulsive behavior was measured with the variable delay-to-signal (VDS) task. Correlation analyses between behavioral measurements of reward or impulsivity and lesion extent in SNc/VTA were performed to pinpoint possible anatomical links of LD-induced behavioral changes. We show that LD, particularly when administered chronically, caused the development of impulsive-like behaviors in 6-OHDA-lesioned animals in the VDS. However, neither acute or chronic LD administration had rewarding effects in 6-OHDA-lesioned animals in the CPP. Our results show that in a bilateral rat model of PD, LD leads to the development of impulsive behaviors, strengthening the association between DRT and DDS/ICD in PD.

The 1-Tosylpentan-3-one Protects against 6-Hydroxydopamine-Induced Neurotoxicity

Previous studies have demonstrated that the marine compound austrasulfone, isolated from the soft coral Cladiella australis, exerts a neuroprotective effect. The intermediate product in the synthesis of austrasulfone, dihydroaustrasulfone alcohol, attenuates several inflammatory responses. The present study uses in vitro and in vivo methods to investigate the neuroprotective effect of dihydroaustrasulfone alcohol-modified 1-tosylpentan-3-one (1T3O). Results from in vitro experiments show that 1T3O effectively inhibits 6-hydroxydopamine-induced (6-OHDA-induced) activation of both p38 mitogen-activated protein kinase (MAPK) and caspase-3 in SH-SY5Y cells; and enhances nuclear factor erythroid 2–related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) expression via phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling. Hoechst staining and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining results reveal that 1T3O significantly inhibits 6-OHDA-induced apoptosis. In addition, the addition of an Akt or HO-1 inhibitor decreases the protective effect of 1T3O. Thus, we hypothesize that the anti-apoptotic activity of 1T3O in neuronal cells is mediated through the regulation of the Akt and HO-1 signaling pathways. In vivo experiments show that 1T3O can reverse 6-OHDA-induced reduction in locomotor behavior ability in zebrafish larvae, and inhibit 6-OHDA-induced tumor necrosis factor-alpha (TNF-α) increase at the same time. According to our in vitro and in vivo results, we consider that 1T3O exerts its anti-apoptotic activities at SH-SY5Y cells after 6-OHDA challenges, probably via the regulation of anti-oxidative signaling pathways. Therefore, this compound may be a promising therapeutic agent for neurodegenerations.

Activation of PPAR gamma receptors reduces levodopa-induced dyskinesias in 6-OHDA-lesioned rats

Long-term administration of l-3,4-dihydroxyphenylalanine (levodopa), the mainstay treatment for Parkinson's disease (PD), is accompanied by fluctuations in its duration of action and motor complications (dyskinesia) that dramatically affect the quality of life of patients. Levodopa-induced dyskinesias (LID) can be modeled in rats with unilateral 6-OHDA lesions via chronic administration of levodopa, which causes increasingly severe axial, limb, and orofacial abnormal involuntary movements (AIMs) over time. In previous studies, we showed that the direct activation of CB1 cannabinoid receptors alleviated rat AIMs. Interestingly, elevation of the endocannabinoid anandamide by URB597 (URB), an inhibitor of endocannabinoid catabolism, produced an anti-dyskinetic response that was only partially mediated via CB1 receptors and required the concomitant blockade of transient receptor potential vanilloid type-1 (TRPV1) channels by capsazepine (CPZ) (Morgese et al., 2007). In this study, we showed that the stimulation of peroxisome proliferator-activated receptors (PPAR), a family of transcription factors activated by anandamide, contributes to the anti-dyskinetic effects of URB+CPZ, and that the direct activation of the PPARγ subtype by rosiglitazone (RGZ) alleviates levodopa-induced AIMs in 6-OHDA rats. AIM reduction was associated with an attenuation of levodopa-induced increase of dynorphin, zif-268, and of ERK phosphorylation in the denervated striatum. RGZ treatment did not decrease striatal levodopa and dopamine bioavailability, nor did it affect levodopa anti-parkinsonian activity. Collectively, these data indicate that PPARγ may represent a new pharmacological target for the treatment of LID.

Optogenetic inactivation of the subthalamic nucleus improves forelimb akinesia in a rat model of Parkinson disease

BACKGROUND

The inhibition of neuronal activity by electrical deep brain stimulation is one of the mechanisms explaining the therapeutic effects in patients with Parkinson disease (PD) but cannot specifically activate or inactivate different types of neurons. Recently, a new technology based on optogenetics has been developed to modulate the activity of specific neurons. However, the therapeutic effects of optical inactivation in the subthalamic nucleus (STN) have not been fully investigated.

OBJECTIVE

To perform various behavioral tests to evaluate changes in motor functions in a PD rat model after optogene expression and, unlike previous studies, to assess the therapeutic effects of direct optogenetic inactivation in the STN.

METHODS

6-Hydroxydopamine-induced hemiparkinsonian rats received injections of hSynapsin1-NpHR-YFP adeno-associated virus or an equivalent volume of phosphate-buffered saline. Three weeks after injection of adeno-associated virus or phosphate-buffered saline, the optic fiber was implanted into the ipsilateral STN. A stepping test, a cylinder test, and an apomorphine-induced rotation test were performed in 3 sequential steps: during light-off state, during light stimulation, and again during light-off state.

RESULTS

Stepping tests revealed that optical inhibition of the STN significantly improved 6-hydroxydopamine-induced forelimb akinesia. PD motor signs, as assessed by cylinder and apomorphine tests, were not affected by optical inhibition. Immunofluorescence revealed that halorhodopsin was highly expressed and colocalized with vesicular glutamate transporter 2 in the STN.

CONCLUSION

Optogenetic inhibition in the STN may be effective in improving contralateral forelimb akinesia but not in changing forelimb preference or reducing dopaminergic receptor supersensitivity. These findings are useful as a basis for future studies on optogenetics in PD.

The combination of oral L-DOPA/rimonabant for effective dyskinesia treatment and cytological preservation in a rat model of Parkinson's disease and L-DOPA-induced dyskinesia

Parkinson's disease is the second most prevalent neurodegenerative disease in the world. Its treatment is limited so far to the management of parkinsonian symptoms with L-DOPA (LD). The long-term use of LD is limited by the development of L-DOPA-induced dyskinesias and dystonia. However, recent studies have suggested that pharmacological targeting of the endocannabinoid system may potentially provide a valuable therapeutic tool to suppress these motor alterations. In the present study, we have explored the behavioral (L-DOPA-induced dyskinesias severity) and cytological (substantia nigra compacta neurons and striatum neuropil preservation) effects of the oral coadministration of LD and rimonabant, a selective antagonist of CB1 receptors, in the 6-hydroxydopamine rat model of Parkinson's disease. Oral coadministration of LD (30 mg/kg) and rimonabant (1 mg/kg) significantly decreased abnormal involuntary movements and dystonia, possibly through the conservation of some functional tyrosine hydroxylase-immunoreactive dopaminergic cells, which in turn translates into a well-preserved neuropil of a less denervated striatum. Our results provide anatomical evidence that long-term coadministration of LD with cannabinoid antagonist-based therapy may not only alleviate specific motor symptoms but also delay/arrest the degeneration of striatal and substantia nigra compacta cells.

L-DOPA improves visuo-motor coordination in stable Parkinson's disease patients

The visuo-motor coordination of 26 stable, treated, Parkinson's disease (PD) patients with average Hoehn and Yahr rating of 1.75+/-0.6, was assessed by use of several tracing and tracking tests before and 30min after ingestion of the mid-day levodopa (L-DOPA) dose. Significant improvement was found in all aspects of visuo-motor coordination 30min after drug intake. This included the ability to control the direction and velocity of hand-movement, and the capacity to persist in tracking. A subgroup of 12 patients was tested 30min and 1h after L-DOPA intake. A continuing (but small) improvement in directional and velocity control could still be seen an hour after drug intake, while tracking persistence remained unchanged with respect to the preceding test. We conclude that changes in executional capabilities can be documented in "stable" PD patients, consequent to L-DOPA intake, when high-level skills, such as visuo-motor coordination, are tested.

Anti-dyskinetic mechanisms of amantadine and dextromethorphan in the 6-OHDA rat model of Parkinson's disease: role of NMDA vs. 5-HT1A receptors

Amantadine and dextromethorphan suppress levodopa (L-DOPA)-induced dyskinesia (LID) in patients with Parkinson's disease (PD) and abnormal involuntary movements (AIMs) in the unilateral 6-hydroxydopamine (6-OHDA) rat model. These effects have been attributed to N-methyl-d-aspartate (NMDA) antagonism. However, amantadine and dextromethorphan are also thought to block serotonin (5-HT) uptake and cause 5-HT overflow, leading to stimulation of 5-HT(1A) receptors, which has been shown to reduce LID. We undertook a study in 6-OHDA rats to determine whether the anti-dyskinetic effects of these two compounds are mediated by NMDA antagonism and/or 5-HT(1A) agonism. In addition, we assessed the sensorimotor effects of these drugs using the Vibrissae-Stimulated Forelimb Placement and Cylinder tests. Our data show that the AIM-suppressing effect of amantadine was not affected by the 5-HT(1A) antagonist WAY-100635, but was partially reversed by the NMDA agonist d-cycloserine. Conversely, the AIM-suppressing effect of dextromethorphan was prevented by WAY-100635 but not by d-cycloserine. Neither amantadine nor dextromethorphan affected the therapeutic effects of L-DOPA in sensorimotor tests. We conclude that the anti-dyskinetic effect of amantadine is partially dependent on NMDA antagonism, while dextromethorphan suppresses AIMs via indirect 5-HT(1A) agonism. Combined with previous work from our group, our results support the investigation of 5-HT(1A) agonists as pharmacotherapies for LID in PD patients.

Cranial and related sensorimotor impairments in rodent models of Parkinson's disease

In Parkinson's disease both limb and cranial sensorimotor functions are impaired, leading to a profound diminished quality of life for many patients. Toxin and genetic animal models of Parkinson's disease are likely essential for understanding the pathology associated with these impairments as well as for the development and testing of potential therapeutics. Here we describe useful novel and established behavioral outcome measures for assessing limb and cranial sensorimotor functions in toxin and genetic models of parkinsonism in rats and mice.

MK-801 inhibits L-DOPA-induced abnormal involuntary movements only at doses that worsen parkinsonism

Amantadine and dextromethorphan suppress levodopa (L-DOPA)-induced dyskinesia in Parkinson's disease patients and abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA) rat model. These medications have been hypothesized to exert their therapeutic effects by a noncompetitive N-methyl-D-aspartate (NMDA) antagonist mechanism, but they also have known serotonin (5-HT) indirect agonist effects that could suppress AIMs. This raised the possibility that NMDA antagonists lacking 5-HTergic effects would not have the anti-dyskinetic action predicted by previous investigators. To test this hypothesis, we investigated MK-801, the most widely-studied NMDA antagonist. We found that chronic low-dose MK-801 (0.1 mg/kg) had no effect on development of AIMs or contraversive rotation. In addition, in L-DOPA-primed rats, low-dose MK-801 (0.1 mg/kg) had no effect on expression of AIMs, contraversive rotation, or sensorimotor function. Conversely, higher doses of MK-801 (0.2-0.3 mg/kg) suppressed expression of AIMs. However, as we show for the first time, anti-dyskinetic doses of MK-801 also suppressed L-DOPA-induced contralateral rotation and impaired sensorimotor function, likely due to non-specific interference of MK-801 with L-DOPA-induced behavior. We conclude that noncompetitive NMDA antagonists are unlikely to suppress dyskinesia clinically without worsening parkinsonism.

Improvement of postural adjustment steps in hemiparkinsonian rats chronically treated with caffeine is mediated by concurrent blockade of A1 and A2A adenosine receptors

Chronic treatment with the non-selective adenosine receptor antagonist caffeine produces full recovery of the contralateral adjusting steps in hemiparkinsonian rats. In order to disclose which adenosine receptor subtype mediates this effect, a group of hemiparkinsonian rats (n=9) was treated with caffeine (5.15 mumol/kg/day), or equimolar doses of selective A1 (DPCPX) or A2A (ZM 241385) adenosine receptor antagonists, administered in a counterbalanced order over periods of 3 weeks, interspersed with equivalent washout intervals. Treatment with ZM 241385 caused full recovery (102+/-6%) of the contralateral forepaw stepping, while the maximal effect of DPCPX was only 73+/-7% of that produced by caffeine. The maximal effect of caffeine and ZM 241385 remained stable throughout the treatment period. The response to DPCPX showed more fluctuations, but tolerance did not develop. Stepping improvement was significantly faster with DPCPX than with ZM 241385, while caffeine had intermediate values. Stepping decrease after treatment interruption was faster with ZM 241385 than with caffeine, while DPCPX had intermediate values. In other experiments with the same rats, addition of the A2AR agonist CGS 21680 (5.15 mumol/kg) or the A1R agonist CCPA (2.71 mumol/kg) during the second week of caffeine treatment reversed the improvement of contralateral stepping by 59+/-4% and 30+/-3%, respectively. The combined treatment with CGS 21680 and CCPA caused complete reversal of the contralateral stepping recovery afforded by caffeine, which was more than additive (114+/-5%) compared with the sum of the maximal inhibition produced by either agonist administered alone (89+/-4%). In all cases, after interrupting the adenosine agonists, the effect of caffeine was fully restored. None of the aforementioned treatments induced significant changes in the stepping of the ipsilateral forepaw. Collectively, these results suggest that the improvement of postural adjustments induced by chronic treatment with low doses of caffeine in hemiparkinsonian rats is mediated by concurrent blockade of A1 and A2A adenosine receptors, with a larger involvement of the latter.

Dopamine D2-receptor activation elicits akinesia, rigidity, catalepsy, and tremor in mice expressing hypersensitive {alpha}4 nicotinic receptors via a cholinergic-dependent mechanism

Recent studies suggest that high-affinity neuronal nicotinic acetylcholine receptors (nAChRs) containing alpha4 and beta2 subunits (alpha4beta2*) functionally interact with G-protein-coupled dopamine (DA) D(2) receptors in basal ganglia. We hypothesized that if a functional interaction between these receptors exists, then mice expressing an M2 point mutation (Leu9'Ala) rendering alpha4 nAChRs hypersensitive to ACh may exhibit altered sensitivity to a D(2)-receptor agonist. When challenged with the D(2)R agonist, quinpirole (0.5-10 mg/kg), Leu9'Ala mice, but not wild-type (WT) littermates, developed severe, reversible motor impairment characterized by rigidity, catalepsy, akinesia, and tremor. While striatal DA tissue content, baseline release, and quinpirole-induced DA depletion did not differ between Leu9'Ala and WT mice, quinpirole dramatically increased activity of cholinergic striatal interneurons only in mutant animals, as measured by increased c-Fos expression in choline acetyltransferase (ChAT)-positive interneurons. Highlighting the importance of the cholinergic system in this mouse model, inhibiting the effects of ACh by blocking muscarinic receptors, or by selectively activating hypersensitive nAChRs with nicotine, rescued motor symptoms. This novel mouse model mimics the imbalance between striatal DA/ACh function associated with severe motor impairment in disorders such as Parkinson's disease, and the data suggest that a D(2)R-alpha4*-nAChR functional interaction regulates cholinergic interneuron activity.

The nociceptin/orphanin FQ receptor antagonist J-113397 and L-DOPA additively attenuate experimental parkinsonism through overinhibition of the nigrothalamic pathway

By using a battery of behavioral tests, we showed that nociceptin/orphanin FQ receptor (NOP receptor) antagonists attenuated parkinsonian-like symptoms in 6-hydroxydopamine hemilesioned rats (Marti et al., 2005). We now present evidence that coadministration of the NOP receptor antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H benzimidazol-2-one (J-113397) and L-DOPA to 6-hydroxydopamine hemilesioned rats produced an additive attenuation of parkinsonism. To investigate the neurobiological substrates underlying this interaction, in vivo microdialysis was used in combination with behavioral measurements (bar test). J-113397 and L-DOPA alone reduced the time on bars (i.e., attenuated akinesia) and elevated GABA release selectively in the lesioned substantia nigra reticulata. J-113397 also reduced nigral glutamate levels, whereas L-DOPA was ineffective. J-113397 and L-DOPA coadministration produced additive antiakinetic effect, which was associated with additive increase in nigral GABA release but no additional reductions in glutamate levels. To investigate whether the increase in nigral GABA release could translate to changes in nigrothalamic transmission, GABA release was monitored in the ventromedial thalamus (one of the main target areas of the nigrothalamic projections). J-113397 and L-DOPA decreased thalamic GABA release and attenuated akinesia, their combination resulting in a more profound effect. These actions were prevented by perfusing the voltage-dependent Na+ channel blocker tetrodotoxin or the GABA(A) receptor antagonist bicuculline in the substantia nigra reticulata. These data demonstrate that J-113397 and L-DOPA exert their antiparkinsonian action through overinhibition of nigrothalamic transmission and suggest that NOP receptor antagonists may be useful as an adjunct to L-DOPA therapy for Parkinson's disease.

Sustained improvement of motor function in hemiparkinsonian rats chronically treated with low doses of caffeine or trihexyphenidyl

The effects of chronic oral treatment with low doses of caffeine (1-3 mg/kg) and trihexyphenidyl (0.1-0.2 mg/kg) were tested on hemiparkinsonian rats, which received the following treatments in a counterbalanced order: vehicle, caffeine, trihexyphenidyl, and caffeine plus trihexyphenidyl. Three preclinical models were used: the stepping test, the cylinder test, and the staircase test. Compared to pre-lesion values, the forepaw contralateral to the dopamine-denervated side showed impaired stepping, fewer wall contacts in the cylinder test, and fewer pellets retrieved in the staircase test. In the stepping test both doses of caffeine produced a complete recovery of motor function (100%), whereas the effect of trihexyphenidyl was less intense (77-80%). In this same test the maximal effect of drugs did not develop tolerance during 2-3 weeks, and was completely reversible after drug cessation. In the cylinder test only the wall contacts performed simultaneously with both forepaws were significantly increased by caffeine (3 mg/kg) and trihexyphenidyl (0.2 mg/kg), and this effect was also reversible. In the staircase test none of the treatments improved food pellet retrieval with the contralateral forepaw. Altogether, these results show that chronic treatment with caffeine, at doses similar to daily human consumption, produces a sustained improvement in the use of the contralateral forelimb in unilaterally 6-hydroxydopamine denervated rats, without the development of tolerance. Although the combined administration of caffeine plus trihexyphenidyl showed no synergism in these models, the results suggest that low doses of caffeine (1-3 mg/kg/day) could be of therapeutic value for the reversal of motor symptoms in parkinsonian patients.

Behavioral effects of dopaminergic agonists in transgenic mice overexpressing human wildtype alpha-synuclein

Overexpression of alpha-synuclein causes familial Parkinson's disease and abnormal aggregates of the protein are present in sporadic cases of the disease. We have examined the behavioral effects of direct and indirect dopaminergic agonists in transgenic mice expressing human alpha-synuclein under the Thy-1 promoter (Thy1-aSyn, alpha-synuclein overexpressor), which exhibit progressive impairments in behavioral tests sensitive to nigrostriatal dopamine dysfunction. Male Thy1-aSyn and wild-type mice received vehicle, benserazide/L-DOPA (25 mg/kg, i.p.), high (2 mg/kg, s.c.) and low doses (0.125, 0.25, 0.5 mg/kg, s.c.) of apomorphine, and amphetamine (5 mg/kg, i.p.), beginning at 3 months of age, and were tested on the challenging beam, spontaneous activity, pole test, and gait. l-DOPA had a paradoxical effect and worsened the deficits in Thy1-aSyn mice compared with controls, whereas the high dose of apomorphine only produced few deficits above those already present in Thy1-aSyn. In contrast to wild-type mice, Thy1-aSyn mice did not show amphetamine-induced stereotypies. The results indicate that chronic overexpression of alpha-synuclein led to abnormal pharmacological responses in mice.

Dopamine-independent locomotor actions of amphetamines in a novel acute mouse model of Parkinson disease

Brain dopamine is critically involved in movement control, and its deficiency is the primary cause of motor symptoms in Parkinson disease. Here we report development of an animal model of acute severe dopamine deficiency by using mice lacking the dopamine transporter. In the absence of transporter-mediated recycling mechanisms, dopamine levels become entirely dependent on de novo synthesis. Acute pharmacological inhibition of dopamine synthesis in these mice induces transient elimination of striatal dopamine accompanied by the development of a striking behavioral phenotype manifested as severe akinesia, rigidity, tremor, and ptosis. This phenotype can be reversed by administration of the dopamine precursor, L-DOPA, or by nonselective dopamine agonists. Surprisingly, several amphetamine derivatives were also effective in reversing these behavioral abnormalities in a dopamine-independent manner. Identification of dopamine transporter- and dopamine-independent locomotor actions of amphetamines suggests a novel paradigm in the search for prospective anti-Parkinsonian drugs.

Identification of dopamine transporter- and dopamine- independent locomotor actions of amphetamines suggests a novel paradigm in the search for prospective anti-Parkinsonian drugs.

An intermittent, controlled-rate, slow progressive degeneration model of Parkinson's disease: antiparkinson effects of Sinemet and protective effects of methylphenidate

The causes of nigrostriatal neuron degeneration in Parkinson's disease (PD) are not known, but it has been suggested that exogenous or endogenous factors or neurotoxins may play a role. The degree of vulnerability to neurotoxins or other potential mediators of nigral dopamine cell death is thought to be important in understanding Parkinson's disease. In most animal models, the rate of terminal degeneration and corresponding functional impairment is too rapid to investigate effectively either cell vulnerability or the potential benefits of some neuroprotective treatments. In the present study, a new model of Parkinson's disease is described that might help in addressing the issue of nigral cell vulnerability and to evaluate interventions with clinical potential. 6-Hydroxydopamine (6-OHDA) was infused in escalating, intrastriatal doses over several weeks. Control animals received multiple infusions of vehicle at the same volume. Behavioral testing was carried out between each infusion, including forelimb-use and somatosensory function. A symptomatic threshold was established for each animal, indicating the amount of neurotoxin required to induce a stable deficit. Oral administration of L-DOPA (Sinemet) ameliorated limb-use asymmetries acutely. An immunocytochemical assay for tyrosine hydroxylase, a dopamine cell marker, revealed a partial loss of immunoreactive cells in the substantia nigra. Animals that were co-administered methylphenidate (MPH), a dopamine transport inhibitor, along with the 6-OHDA were spared from the behavioral and neurochemical effects of 6-OHDA, despite receiving more than twice as much neurotoxin as controls. These data suggest that establishing a symptomatic threshold preclinically may help researchers evaluate potential treatments and model individual and group resistance to nigrostriatal insults.

A model of L-DOPA-induced dyskinesia in 6-hydroxydopamine lesioned mice: relation to motor and cellular parameters of nigrostriatal function

L-DOPA-induced dyskinesia is a major complication of L-DOPA pharmacotherapy in Parkinson's disease, and is thought to depend on abnormal cell signaling in the basal ganglia. In this study, we have addressed the possibility to model L-DOPA-induced dyskinesia in the mouse at both the behavioral and the molecular level. C57BL/6 mice sustained unilateral injections of 6-hydroxydopamine (6-OHDA) either in the medial forebrain bundle (MFB) or in the sensorimotor part of the striatum. Both types of lesion produced a similar degree of forelimb akinesia on the contralateral side of the body. The lowest dose of L-DOPA that could significantly relieve this akinetic deficit (i.e., 6 mg/kg) did not differ between MFB and intrastriatal lesions. The L-DOPA threshold dose for the induction of dyskinesia did however differ between the two lesion types. A daily dose of 6 mg/kg L-DOPA caused MFB lesioned mice to develop abnormal movements affecting orofacial, trunk, and forelimb muscles on the side contralateral to the lesion, whereas a daily dose of 18 mg/kg was required to produce comparable dyskinetic effects in the intrastriatally lesioned animals. The development of abnormal movements was accompanied by a striatal induction of DeltaFosB-like proteins and prodynorphin mRNA, that is, molecular markers that are associated with L-DOPA-induced dyskinesia in both rats and nonhuman primates. We conclude that 6-OHDA lesioned mice exhibit behavioral and cellular features of akinesia and L-DOPA-induced dyskinesia that are similar to those previously characterized in rats. The mouse model of L-DOPA-induced dyskinesia will provide a useful tool to study the molecular determinants of this movement disorder in transgenic mice strains.

A pulmonary formulation of L-dopa enhances its effectiveness in a rat model of Parkinson's disease

The efficacy of oral L-dopa becomes problematic with the progression of Parkinson's disease, due in large part to a lost ability to accommodate L-dopa's inherently poor pharmacokinetics. Pulmonary delivery represents a novel approach to reducing this problem. L-dopa was formulated into inhalable (Alkermes AIR) particles, and its pharmacokinetics and pharmacodynamics compared with those of an oral formulation. Pulmonary administration of L-dopa (2 mg) to rats resulted in a rapid elevation of plasma levels (C(max) = 4.8 +/- 1.10 microg/ml at 2 min), whereas oral administration of L-dopa produced a much delayed and lower C(max) (1.8 +/- 0.40 microg/ml at 30 min). In a rat model of Parkinson's disease (unilateral 6-hydroxydopamine lesion), the pulmonary formulation of L-dopa (0.5-2.0 mg) yielded more rapid and robust elevations in striatal L-dopa, dopamine, and dihydroxyphenylacetic acid levels, as well as 2.5 to 3.7 times as many c-fos-expressing striatal neurons. Moreover, motor function was significantly improved by 10 min after administration, with peak improvements occurring within 15 to 30 min. In contrast, considerably higher doses (6.8-10 mg) of orally administered L-dopa took over three times longer to produce similar effects. These results suggest that an inhalable formulation of l-dopa has superior pharmacokinetic properties and may provide patients with a more effective form of rescue therapy as well as being a reliable adjuvant or replacement for first-line oral therapy.

Pharmacological validation of behavioural measures of akinesia and dyskinesia in a rat model of Parkinson's disease

In an attempt to define clinically relevant models of akinesia and dyskinesia in 6-hydroxydopamine (6-OHDA)-lesioned rats, we have examined the effects of drugs with high (L-DOPA) vs. low (bromocriptine) dyskinesiogenic potential in Parkinson's disease on three types of motor performance, namely: (i) abnormal involuntary movements (AIMs) (ii) rotational behaviour, and (iii) spontaneous forelimb use (cylinder test). Rats with unilateral 6-OHDA lesions received single daily i.p. injections of L-DOPA or bromocriptine at therapeutic doses. During 3 weeks of treatment, L-DOPA but not bromocriptine induced increasingly severe AIMs affecting the limb, trunk and orofacial region. Rotational behaviour was induced to a much higher extent by bromocriptine than L-DOPA. In the cylinder test, the two drugs initially improved the performance of the parkinsonian limb to a similar extent. However, L-DOPA-treated animals showed declining levels of performance in this test because the drug-induced AIMs interfered with physiological limb use, and gradually replaced all normal motor activities. L-DOPA-induced axial, limb and orolingual AIM scores were significantly reduced by the acute administration of compounds that have antidyskinetic efficacy in parkinsonian patients and/or nonhuman primates (-91%, yohimbine 10 mg/kg; -19%, naloxone 4-8 mg/kg; -37%, 5-methoxy 5-N,N-dimethyl-tryptamine 2 mg/kg; -30%, clozapine 8 mg/kg; -50%, amantadine 40 mg/kg). L-DOPA-induced rotation was, however, not affected. The present results demonstrate that 6-OHDA-lesioned rats do exhibit motor deficits that share essential functional similarities with parkinsonian akinesia or dyskinesia. Such deficits can be quantified using novel and relatively simple testing procedures, whereas rotometry cannot discriminate between dyskinetic and antiakinetic effects of antiparkinsonian treatments.

Complex motor disturbances in a sequential double lesion rat model of striatonigral degeneration (multiple system atrophy)

This study characterizes paw reaching, stepping and balance abnormalities in a double lesion rat model of striatonigral degeneration, the core pathology underlying levodopa unresponsive parkinsonism associated with multiple system atrophy. Extensive unilateral nigral or striatal lesions induced by 6-hydroxydopamine or quinolinic acid, respectively, produced a similarly marked contralateral paw reaching deficit without further deterioration following a secondary (complementary) lesion of ipsilateral striatum or substantia nigra. Contralateral stepping rates were reduced by unilateral 6-hydroxydopamine lesions without further deterioration following the secondary striatal lesion. In contrast, initial unilateral striatal quinolinic acid injections induced bilateral stepping deficits that significantly worsened contralaterally following the secondary nigral lesion. Contralateral sidefalling rates were significantly increased following primary nigral and striatal lesions. Secondary nigral but not secondary striatal lesions worsened contralateral sidefalling rates. Histological studies revealed subtotal (>90%) depletion of dopaminergic neurons in substantia nigra pars compacta and variable degrees of striatal degeneration depending on the lesion sequence. Animals pre-lesioned with 6-hydroxydopamine showed significantly larger residual striatal surface areas following the secondary striatal quinolinic acid lesion compared to animals with primary striatal quinolinic acid lesions (P<0.001). These findings are in line with previous experimental studies demonstrating that striatal dopamine depletion confers neuroprotection against subsequent excitotoxic injury. Whether loss of dopaminergic neurons protects against the striatal disease process occurring in multiple system atrophy (Parkinson-type) remains to be elucidated. In summary, this is the first experimental study to investigate spontaneous motor behaviour in a unilateral double lesion rat model. Our observations are consistent with a complex interaction of nigral and striatal lesions producing distinct behavioural and histological changes depending on the lesion sequence. Tests of forelimb akinesia and complex motor behaviour appear to provide a reliable tool that will be helpful for monitoring the effects of interventional strategies such as embryonic neuronal transplantation in the rat model of striatonigral degeneration.

Effect of acute L-Dopa pretreatment on apomorphine-induced rotational behavior in a rat model of Parkinson's disease

Currently, reduction of apomorphine-induced rotational behavior in the 6-hydroxydopamine (6-OHDA) lesioned rat is the most utilized drug-induced paradigm for assessing functional efficacy in a rat model of Parkinson's disease (PD). Any clinically predictive animal model of PD should include a positive response to l-dopa, the standard pharmacotherapy for PD. However, the acute interaction between L-dopa and apomorphine has never been studied to determine if L-dopa pretreatment could reduce apomorphine-induced rotational behavior in a 6-OHDA lesioned rat. The present study was designed to explore whether, indeed, pretreatment with subrotational doses of L-dopa could inhibit apomorphine-induced rotations. The data indicate that L-dopa significantly reduced apomorphine-induced rotational behavior only at one dose (5.0 mg/kg) for 12 min. Based on these and other data, it is concluded that although the apomorphine-induced rotational paradigm may continue to be utilized as one additional indicator of efficacy in the 6-OHDA rat model of PD, it is not in itself a completely valid functional assay.

Progress in direct striatal delivery of L-dopa via gene therapy for treatment of Parkinson's disease using recombinant adeno-associated viral vectors

Viral vectors have recently been used successfully to transfer genes and express different proteins in the brain. This review discusses the requirements to consider human clinical trials in which recombinant adeno-associated virus vectors are used to transfer the genes necessary to produce l-dihydroxyphenylalanine (l-dopa) directly into the striatum of Parkinson's patients. Preclinical data that apply to the criteria defined as prerequisite for clinical trials are discussed. Thus, in animal models using recombinant adeno-associated virus vectors it has been demonstrated that l-dopa can be synthesized in the striatum after in vivo transduction. In addition, these l-dopa levels are sufficient to affect behavior in a dopamine-deficient animal model, the expression is extremely long-lasting, and the ability to transcriptionally regulate tyrosine hydroxylase has been demonstrated but not fully characterized. However, while immune responses to recombinant adeno-associated virus infection in the periphery have been studied, direct assessment of the potential immune response in the brain has not been sufficiently defined. Therefore, the rationale for delivering l-dopa directly to the striatum to treat Parkinson's disease is sound and the preclinical data are promising but all the issues surrounding this strategy are not resolved.

Incomplete nigrostriatal dopaminergic cell loss and partial reductions in striatal dopamine produce akinesia, rigidity, tremor and cognitive deficits in middle-aged rats

The present study was conducted to determine if the full array of parkinsonian symptoms could be detected in rats with nigrostriatal cell loss and striatal dopamine depletions similar to levels reported in the clinical setting, and to determine if older rats exhibit more robust parkinsonian deficits than younger rats. Young (2 months old) and middle-aged (12 months old) rats received bilateral striatal infusions of 6-OHDA, over the next 3 months they were assessed with a battery of behavioral tests, and then dopaminergic nigrostriatal cells and striatal dopamine and DOPAC levels were quantified. The results of the present study suggest that: (1) the full array of parkinsonian symptoms (i.e. akinesia, rigidity, tremor and visuospatial cognitive deficits) can be quantified in rats with incomplete nigrostriatal dopaminergic cell loss and partial reductions in striatal dopamine levels (2) parkinsonian symptoms were more evident in middle-aged rats with 6-OHDA infusions, and (3) there was evidence of substantial neuroplasticity in the older rats, but regardless of the age of the animal, endogenous compensatory mechanisms were unable to maintain striatal dopamine levels after rapid, lesion-induced nigrostriatal cell loss. These results suggest that using older rats with nigrostriatal dopaminergic cell loss and reductions in striatal dopamine levels similar to those in the clinical condition, and measuring behavioral deficits analogous to parkinsonian symptoms, might increase the predictive validity of pre-clinical rodent models.

Therapeutic Potential of a Polymer-Encapsulated L-Dopa and Dopamine-Producing Cell Line in Rodent and Primate Models of Parkinson's Disease

Encapsulation of cells within polymer membranes prior to transplantation provides a novel means of achieving continuous, site-specific delivery of therapeutic molecules to the CNS. The use of encapsulated dopamine-secreting cells that can be transplanted directly into the striatum has particular appeal for the treatment of Parkinson's disease. This article provides a brief and timely review of the progress that has been made over the past decade using encapsulated PC12 cells as a means of delivering dopamine and l-DOPA to the striatum in rodent and primate models of Parkinson's disease. The polymer membranes are well tolerated and biocompatible. Encapsulated PC12 cells survive in vivo for up to 6 mo, they release dopamine into the surrounding host striatum, and they clearly improve behavioral function in both dopamine-depleted rodents and primates. Although these results are promising, fundamental issues remain concerning the extent of dopamine diffusion from the polymer membranes and the number of devices needed for behavioral improvement, and the duration and consistency of cell viability and device output. Nevertheless, this technology appears to be a promising means of avoiding many of the practical, societal, and ethical issues that have been associated with other transplantation approaches.

Rats with partial striatal dopamine depletions exhibit robust and long-lasting behavioral deficits in a simple fixed-ratio bar-pressing task

It is widely accepted that enduring parkinsonian symptoms are only evident if there are few remaining dopaminergic neurons in the substantia nigra and dopamine levels in the basal ganglia are very low [26,41]. In the present study, partial dopamine depletions were produced by infusing 6-OHDA bilaterally into the ventrolateral striatum as previously described [11,12,44]. Consistent with previous studies, behavioral deficits were detectable in rats with partial lesions with a simple fixed-ratio bar-pressing task. The present study demonstrated that these behavioral deficits were long-lasting, and that the sensitivity of this bar-pressing task could be increased by manipulating the level of difficulty of the task-higher fixed ratios were more sensitive to partial dopamine depletions. Deficits in rats with partial dopamine depletions could also be detected using non-automated neurological tests of parkinsonian symptoms developed for rats with severe unilateral dopamine depletions, but these deficits were transient and not as robust as those detected with the bar-pressing task. Oral Sinemet (L-DOPA:carbidopa) did not attenuate behavioral deficits related to partial dopamine depletions in this simple fixed-ratio bar-pressing task, but the present results suggest that Parkinson's patients might be identifiable earlier in the disease process, at a time when they could benefit from treatment with neuroprotective/neurotrophic agents. In addition, the results of the present study demonstrate that robust behavioral deficits may emerge with age. Mild dopamine depletions that were not detectable behaviorally at the time of the insult became clearly evident 10 months after the lesion with this bar-pressing task, and this may represent a more clinically relevant rodent model of Parkinson's disease.

Somatic delivery of catecholamines in the striatum attenuate parkinsonian symptoms and widen the therapeutic window of oral sinemet in rats

Guidelines for clinical transplantation studies for Parkinson's disease emphasize that transplants should be considered as an adjunct to systemic L-DOPA, yet few preclinical studies have specifically assessed the potential of transplants as an adjunct to the clinical gold standard treatment. The objectives of the present study were to determine if encapsulated PC12 cells implanted in rats with severe unilateral dopamine depletions: (i) have a direct therapeutic effect on measures of parkinsonian symptoms; and/or (ii) increase the therapeutic window of oral sinemet in this model. Rats with severe unilateral dopamine depletions received striatal implants of encapsulated PC12 cells producing dopamine and L-DOPA. These rats were tested on a battery of behavioral measures of parkinsonian symptoms, at a range of doses of oral sinemet (0, 12, 24, and 36 mg/kg). Stereotypies/dyskinesias were also quantified after high doses of oral sinemet (36 and 50 mg/kg). The results confirm that parkinsonian symptoms can be quantified in rats with severe dopamine depletions, and the validity and clinical relevance of these measures are supported by the fact that the clinical gold standard treatment, oral sinemet, attenuates these parkinsonian symptoms. Somatic delivery of dopamine and L-DOPA, directly to the dopamine-depleted striatum, also attenuates parkinsonian symptoms. In fact, the magnitude of the therapeutic effect produced by continuous, site-specific, somatic delivery of dopamine and L-DOPA was larger than the effect produced by acute, systemic, oral sinemet. The beneficial effects of oral sinemet and striatal implants of catecholamine-producing devices were additive, but there were no adverse effects related to striatal catecholamine-producing devices, and these devices did not increase the adverse effects related to oral sinemet. Therefore, striatal implants of catecholamine-producing devices have direct therapeutic effects which are fairly robust, and they widen the therapeutic window of oral sinemet.