Different functional basal ganglia subcircuits associated with anti-akinetic and dyskinesiogenic effects of antiparkinsonian therapies

Subthalamic nucleus high frequency stimulation (STN-HFS) efficiently alleviates l-DOPA-sensitive parkinsonian motor symptoms, but has no direct beneficial action on l-DOPA-induced dyskinesias (LID). Here, we provide evidence that anti-akinetic STN-HFS or dyskinesiogenic l-DOPA similarly reversed the dopamine lesion-induced increases in gene expression of cytochrome oxidase subunit I (CoI), a metabolic marker of neuronal activity, in the globus pallidus, STN and substantia nigra pars reticulata (SNr) in rats. In contrast, in entopeduncular nucleus (EP), STN-HFS did not modify the lesion-induced increase in CoI mRNA levels, whereas l-DOPA induced a marked decrease versus control. Combining the two treatments did not reveal significant interaction. Interestingly, CoI gene expression in EP but not in SNr was inversely correlated with striatal preprodynorphin mRNA level, a LID marker. This work suggests the existence of two functional basal ganglia subcircuits: the one, including STN and SNr, involved in antiparkinsonian action, and the other, including EP, preferentially involved in LID.     

Nociceptive Response to <Emphasis Type="SmallCaps">l</Emphasis>-DOPA-Induced Dyskinesia in Hemiparkinsonian Rats

Non-motor symptoms are increasingly identified to present clinical and diagnostic importance for Parkinson’s disease (PD). The multifactorial origin of pain in PD makes this symptom of great complexity. The dopamine precursor, l-DOPA (l-3,4-dihydroxyphenylalanine), the classic therapy for PD, seems to be effective in pain threshold; however, there are no studies correlating l-DOPA-induced dyskinesia (LID) and nociception development in experimental Parkinsonism. Here, we first investigated nociceptive responses in a 6-hydroxydopamine (6-OHDA)-lesioned rat model of Parkinson’s disease to a hind paw-induced persistent inflammation. Further, the effect of l-DOPA on nociception behavior at different times of treatment was investigated. Pain threshold was determined using von Frey and Hot Plate/Tail Flick tests. Dyskinesia was measured by abnormal involuntary movements (AIMs) induced by l-DOPA administration. This data is consistent to show that 6-OHDA-lesioned rats had reduced nociceptive thresholds compared to non-lesioned rats. Additionally, when these rats were exposed to a persistent inflammatory challenge, we observed increased hypernociceptive responses, namely hyperalgesia. l-DOPA treatment alleviated pain responses on days 1 and 7 of treatment, but not on day 15. During that period, we observed an inverse relationship between LID and nociception threshold in these rats, with a high LID rate corresponding to a reduced nociception threshold. Interestingly, pain responses resulting from CFA-induced inflammation were significantly enhanced during established dyskinesia. These data suggest a pro-algesic effect of l-DOPA-induced dyskinesia, which is confirmed by the correlation founded here between AIMs and nociceptive indexes. In conclusion, our results are consistent with the notion that central dopaminergic mechanism is directly involved in nociceptive responses in Parkinsonism condition.     

Effect of entacapone on plasma homocysteine levels in Parkinson’s disease patients

Peripheral metabolism of l-DOPA via enzyme catechol-O-methyltransferase (COMT) is one of the possible sources of homocysteine (HCY). The aim of this study was to assess plasma HCY levels in l-DOPA-treated Parkinson’s disease (PD) patients and its influence by adding the inhibitor COMT (entacapone). Patients were divided into two groups: (1) patients long term treated with l-DOPA but were naïve to entacapone, (2) l-DOPA naïve patients, in whom a combined treatment with l-DOPA and entacapone was started. The HCY levels were higher in Group 1 than in Group 2. No statistically significant changes of HCY concentrations were found in both patient groups after adding entacapone to their l-DOPA treatments. Results of this study confirm that patients treated with l-DOPA for a long term have increased plasma HCY concentrations. We believe combined l-DOPA and entacapone therapy could be a possible protective mechanism against hyperhomocysteinemia in early PD.     

l-Theanine Prevents Long-Term Affective and Cognitive Side Effects of Adolescent Δ-9-Tetrahydrocannabinol Exposure and Blocks Associated Molecular and Neuronal Abnormalities in the Mesocorticolimbic Circuitry

Chronic adolescent exposure to Δ-9-tetrahydrocannabinol (THC) is linked to elevated neuropsychiatric risk and induces neuronal, molecular and behavioral abnormalities resembling neuropsychiatric endophenotypes. Previous evidence has revealed that the mesocorticolimbic circuitry, including the prefrontal cortex (PFC) and mesolimbic dopamine (DA) pathway are particularly susceptible to THC-induced pathologic alterations, including dysregulation of DAergic activity states, loss of PFC GABAergic inhibitory control and affective and cognitive abnormalities. There are currently limited pharmacological intervention strategies capable of preventing THC-induced neuropathological adaptations. l-Theanine is an amino acid analog of l-glutamate and l-glutamine derived from various plant sources, including green tea leaves. l-Theanine has previously been shown to modulate levels of GABA, DA, and glutamate in various neural regions and to possess neuroprotective properties. Using a preclinical model of adolescent THC exposure in male rats, we report that l-theanine pretreatment before adolescent THC exposure is capable of preventing long-term, THC-induced dysregulation of both PFC and VTA DAergic activity states, a neuroprotective effect that persists into adulthood. In addition, pretreatment with l-theanine blocked THC-induced downregulation of local GSK-3 (glycogen synthase kinase 3) and Akt signaling pathways directly in the PFC, two biomarkers previously associated with cannabis-related psychiatric risk and subcortical DAergic dysregulation. Finally, l-theanine powerfully blocked the development of both affective and cognitive abnormalities commonly associated with adolescent THC exposure, further demonstrating functional and long-term neuroprotective effects of l-theanine in the mesocorticolimbic system.SIGNIFICANCE STATEMENT With the increasing trend of cannabis legalization and consumption during adolescence, it is essential to expand knowledge on the potential effects of adolescent cannabis exposure on brain development and identify potential pharmacological strategies to minimize Δ-9-tetrahydrocannabinol (THC)-induced neuropathology. Previous evidence demonstrates that adolescent THC exposure induces long-lasting affective and cognitive abnormalities, mesocorticolimbic dysregulation, and schizophrenia-like molecular biomarkers that persist into adulthood. We demonstrate for the first time that l-theanine, an amino acid analog of l-glutamate and l-glutamine, is capable of preventing long-term THC side effects. l-Theanine prevented the development of THC-induced behavioral aberrations, blocked cortical downregulation of local GSK-3 (glycogen synthase kinase 3) and Akt signaling pathways, and normalized dysregulation of both PFC and VTA DAergic activity, demonstrating powerful and functional neuroprotective effects against THC-induced developmental neuropathology.     

1-Benzyl-1,2,3,4-tetrahydroisoquinoline,an Endogenous Neurotoxic Compound,Disturbs the Behavioral and Biochemical Effects of l-DOPA: In Vivo and Ex Vivo Studies in the Rat

Environmental factors and endogenously produced toxins, such as 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ), are considered to be involved in the pathogenesis of Parkinson’s disease (PD). In this study, we investigated the impact of single and multiple 1BnTIQ (25 and 50 mg/kg i.p.) administration on l-DOPA-induced changes in the rate of dopamine and serotonin metabolism in the rat brain. Additionally, using in vivo microdialysis, we measured the impact of acute and multiple 1BnTIQ administrations on l-DOPA-induced dopamine release in the striatum. These data were compared with results from behavioral tests in which we measured the effect of 1BnTIQ and l-DOPA on locomotor activity. Finally, we determined the effect of the repeated administration of 1BnTIQ on the l-DOPA-induced elevation of caspase-3 activity in the hippocampus. An ex vivo neurochemical study indicated that both acute and chronic 1BnTIQ injections strongly inhibited l-DOPA-induced increases in the concentration of dopamine and all of its metabolites in dopaminergic structures. In contrast, in vivo microdialysis studies suggested that the differences in 1BnTIQ’s effects are dependent on the type of treatment. A single dose of 1BnTIQ intensified the elevation of dopamine release induced by l-DOPA administration (~1,300 %; P < 0.01), while multiple administrations of 1BnTIQ significantly enhanced the basal dopamine levels while partially diminishing the effects of l-DOPA injection (~200 %; P < 0.01). Additionally, we found that chronic administration of 1BnTIQ completely blocked the l-DOPA-induced increase in caspase-3 activity in the hippocampus. These findings indicate that both acute and chronic administrations of 1BnTIQ disturbs the behavioral and biochemical effects of l-DOPA in the rat. The data presented from ex vivo and in vivo studies clearly suggest that 1BnTIQ’s effects may be connected with the inhibition of DAT and/or COMT activity in the brain. Furthermore, elevated endogenous levels of 1BnTIQ may pose a serious risk in PD patients undergoing l-DOPA therapy.     

Some molecular mechanisms of dopaminergic and glutamatergic dysfunctioning in Parkinson’s disease

Parkinson’s disease (PD) is a chronic progressive neurodegenerative disorder with a considerable socioeconomic burden. The pathomechanism of PD clearly involves the synergistic interaction of dopaminergic and glutamatergic dysfunctioning, including maladaptive corticostriatal synaptoplasticity. Most of the available treatment options have the aim of restoration of the physiological dopaminergic activity. Currently, the most widely used treatment is l-3,4-dihydroxyphenylalanine (l-DOPA), which leads to the best symptomatic relief in PD. However, the long-term use of l-DOPA results in abnormal involuntary movements in almost all cases, the development of these dyskinetic movements also involving maladaptive corticostriatal synaptoplasticity. Perhaps chronic l-DOPA treatment has neurotoxic effects as well, but it has not yet been proved in clinical studies. Another important group of dopamine replacement therapy (DRT)-related side-effects consists of disinhibitory psychopathologies. Recent studies revealed that genetic polymorphisms affecting certain dopaminergic and glutamatergic receptors serve as independent risk factors for the development of these pathological conditions in PD patients. The available scientific data demonstrate that alterations in the kynurenine pathway of the tryptophan metabolism can be observed in PD and these alterations may contribute to the disease pathogenesis and to the occurrence of DRT-related side-effects. Therapeutic strategies that target the restoration of the kynurenine metabolism could therefore hold promise.     

Cholinergic manipulation of motor disability and l-DOPA-induced dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets

Anti-cholinergic drugs are used in the treatment of Parkinson’s disease (PD) and they can improve motor disability in some patients and may alter the expression of dyskinesia. We report the effects of anti-cholinergic and pro-cholinergic agents administered alone and combined with l-DOPA, on motor function in 1-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets. Administration of atropine to MPTP-treated marmosets, not previously exposed to l-DOPA, improved motor disability but this did not occur with other centrally acting anti-cholinergics. Motor disability was worsened by centrally acting pro-cholinergics. However, neither peripherally acting anti- nor pro-cholinergics produced any effect on motor disability or dyskinesia. In MPTP-treated marmosets previously primed with l-DOPA to exhibit dyskinesia, acute l-DOPA challenge induced both chorea and dystonia. In these animals, centrally acting anti-cholinergics including atropine and trihexyphenidyl reversed motor deficits, but induced chorea. Combined with l-DOPA, both centrally and peripherally acting anti-cholinergics reduced peak locomotor activity and produced more chorea than dystonia compared to l-DOPA alone. Centrally acting pro-cholinergics decreased locomotor activity, worsened motor disability and induced dystonia. Co-administered with l-DOPA, pro-cholinergics reduced locomotor activity and decreased chorea while increasing dystonia compared with l-DOPA alone. In conclusion, anti-cholinergics can increase chorea with and without l-DOPA but improve motor disability. Pro-cholinergics decrease the proportion of chorea when combined with l-DOPA, increase motor disability and antagonise l-DOPA’s effectiveness. These data suggest that there may be a case for revisiting the use of anti-cholinergic drugs in the treatment of PD.     

Altered behavioural and neurochemical profile of L-DOPA following deuterium substitutions in the molecule

In Parkinson's disease patients, a prolonged half-life of dopamine formed from l-DOPA may reduce the risk of developing l-DOPA-induced side-effects. Deuterium substitutions in the l-DOPA molecule are expected to yield dopamine with an altered half-life because C–D bonds are more stable than C–H bonds. Therefore we tested, in the rat, the neurochemical and behavioral effects of different types of l-DOPA with deuterium substitutions at the α-carbon and/or the β-carbon. By means of microdialysis, we found that l-DOPA with 3 deuterium substitutions (D3-l-DOPA) enhanced dopamine output in the striatum more effectively than l-DOPA and all the other deuterium variants. Moreover, D3-l-DOPA produced a more pronounced stimulation of locomotor activity in reserpinized rats compared to conventional l-DOPA. In contrast β,β-D2-l-DOPA was less effective than l-DOPA in raising striatal dopamine levels and was ineffective at restoring locomotor activity in reserpinized rats. These results demonstrate that the introduction of deuterium at different positions in the l-DOPA molecule dramatically changes its behavioral and neurochemical profile and suggest that l-DOPA treatment of Parkinson's disease may be improved in this way.     

Assessment of Symptomatic and Neuroprotective Efficacy of Mucuna Pruriens Seed Extract in Rodent Model of Parkinson’s Disease

Mucuna pruriens (MP) has long been used in Indian traditional medicine as support in the treatment of Parkinson’s disease. However, no systematic preclinical studies that aimed at evaluating the efficacy of this substance are available to date. This study undertook an extensive evaluation of the antiparkinsonian effects of an extract of MP seeds known to contain, among other components, 12.5% l-dihydroxyphenylalanine (l-DOPA), as compared to equivalent doses of l-DOPA. Moreover, the neuroprotective efficacy of MP and its potential rewarding effects were evaluated. The results obtained reveal how an acute administration of MP extract at a dose of 16 mg/kg (containing 2 mg/kg of l-DOPA) consistently antagonized the deficit in latency of step initiation and adjusting step induced by a unilateral 6-hydroxydopamine lesion, whereas l-DOPA was equally effective only at the doses of 6 mg/kg. At the same dosage, MP significantly improved the placement of the forelimb in vibrissae-evoked forelimb placing, suggesting a significant antagonistic activity on both motor and sensory-motor deficits. The effects of MP extract were moreover investigated by means of the turning behavior test and in the induction of abnormal involuntary movements (AIMs) after either acute or subchronic administration. MP extract acutely induced a significantly higher contralateral turning behavior than l-DOPA (6 mg/kg) when administered at a dose of 48 mg/kg containing 6 mg/kg of l-DOPA. On subchronic administration, both MP extract (48 mg/kg) and l-DOPA (6 mg/kg) induced sensitization of contralateral turning behavior; however, l-DOPA alone induced a concomitant sensitization in AIMs suggesting that the dyskinetic potential of MP is lower than that of l-DOPA. MP (48 mg/kg) was also effective in antagonizing tremulous jaw movements induced by tacrine, a validated test reproducing parkinsonian tremor. Furthermore, MP induced no compartment preference in the place preference test, indicating the lack of components characterized by rewarding effects in the extract. Finally, in a subchronic mice model of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine hydrochloride (MPTP)-induced dopamine neuron degeneration, MP extract did not prove capable of preventing either tyrosine hydroxylase decrease induced by MPTP or astroglial or microglial activation as assessed by means of GFAP and CD11b immunohistochemistry, supporting the absence of neuroprotective effects by MP. Characterization MP extract strongly supports its antiparkinsonian activity.     

Acute l-DOPA Effect on Hydroxyl Radical- and DOPAC-Levels in Striatal Microdialysates of Parkinsonian Rats

The object of the current study was to determine the effect of l-3,4-dihydroxyphenylalanine (l-DOPA) on the in vivo striatal microdialysate levels of the respective dopamine and serotonin metabolites 3,4-dihydroxyphenlalanine (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) and hydroxyl radical level (HO^?; 2,3- and 2,5-dihydroxybenzoic acid, 2,3- and 2,5-DHBA) in adult rats made parkinsonian by treatment at 3 days after birth with the neurotoxin 6-hydroxydopamine (6-OHDA; 66.7 μg, base form, on each side; desipramine pretreatment, 1 h). Using HPLC/ED we found that in 6-OHDA-lesioned rats the basal striatal extraneuronal level of DOPAC was dramatically reduced and constituted only ~4.5% of referenced value (intact rats). Conversely, the striatal microdialysate level of 5-HIAA was elevated 2-fold in 6-OHDA-lesioned rats. Acute l-DOPA (60 mg/kg i.p.; S-carbidopa pretreatment, 12.5 mg/kg i.p., 30 min) produced a rapid rise in the extraneuronal DOPAC in both tested groups but to a much greater extent in intact rats (P < 0.05). Levels of HO^? (spin-trap products of salicylate, 2,3- and 2,5-DHBA) were elevated 2-fold in 6-OHDA-lesioned rats. However, l-DOPA did not enhance HO^? production; acute 6-OHDOPA treatment (60 mg/kg i.p.) also did not alter HO^? production. In summary, l-DOPA, an effective drug in ameliorating PD symptoms, did not acutely pose a risk for HO^? generation in parkinsonian rats. We conclude that l-DOPA is not likely to generate reactive oxygen species in humans nor is l-DOPA likely to accelerate PD in humans.     

Counteraction by Nitric Oxide Synthase Inhibitor of Neurochemical Alterations of Dopaminergic System in 6-OHDA-Lesioned Rats Under l-DOPA Treatment

Nitric oxide synthase inhibitors reduce l-3, (Del-Bel et al., Cell Mol Neurobiol 25(2):371–392, 2005) 4-dihydroxyphenylalanine (l-DOPA)-induced abnormal motor effects subsequent to depletion of dopaminergic neurons in rodents and non-human primates. The present study used quantitative high-performance liquid chromatography to analyze, for the first time, dopamine metabolism in striatum of rats in order to elucidate the mechanism of action of the nitric oxide synthase inhibitors. Adult male Wistar rats received unilateral microinjection of saline (sham) or 6-hydroxydopamine (6-OHDA-lesioned) in the medial forebrain bundle. Past 3 weeks, rats were treated during 21 days with l-DOPA/benserazide (30 mg/kg/7.5 mg/kg, respectively, daily). On the 22nd day rats received an intraperitoneal (i.p.) injection of either vehicle or 7-nitroindazole, a preferential neuronal nitric oxide synthase inhibitor before l-DOPA. Abnormal involuntary movements and rotarod test were assessed as behavioral correlate of motor responses. Lesion intensity was evaluated through tyrosine hydroxylase immunohystochemical reaction. Dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and an extent of dopamine striatal tissue levels/dopamine metabolism were measured in the striatum. Lesion with 6-OHDA decreased dopamine, DOPAC, and DOPAC/dopamine ratio in the lesioned striatum. l-DOPA treatment induced abnormal involuntary movements and increased DOPAC/dopamine ratio (nearly five times) in the lesioned striatum. l-DOPA-induced dyskinesia was mitigated by 7-nitroindazole, which also decreased dopamine turnover, dopamine and DOPAC levels. Our results revealed an almost two times increase in dopamine content in the non-lesioned striatum of 6-OHDA-lesioned rats. Reduction of striatal DOPAC/dopamine ratio in dyskinetic rats may suggest an increase in the dopamine availability. Our data confirm contribution of nitrergic transmission in the pathogenesis of l-DOPA-induced dyskinesia with potential utilization of nitric oxide synthase inhibitors for treatment.     

l-DOPA exacerbates amphetamine-induced dopamine depletion

Administration ofl-DOPA to Parkinson patients has been suggested to exacerbate “functional denervation” of the nigrostriatal system. Therefore, experiments were conducted to determine ifl-DOPA combined with the DOPA decarboxylase inhibitor, Ro4-4602 (benserazide hydrochloride) would potentiate amphetamine-induced neurotoxicity. Mice received two injections of saline or benserazide +l-DOPA (25.0 or 100.0 mg/kg) interspersed with four injections of amphetamine (15.0 mg/kg) at 2-h intervals. Significant depletion of striatal dopamine, DOPAC, and HVA was evident 1 wk following amphetamine administered with or without 25.0 mg/kgl-DOPA+benserazide, whereas 100.0 mg/kgl-DOPA+benserazide potentiated amphetamine-induced depletion of striatal dopamine (17 vs 28% of control values). This enhanced toxicity may be consequent to increased dopamine turnover followingl-DOPA (360 vs 231%), a situation akin to that observed in compromised dopaminergic nigrostriatal systems of parkinsonian patients. Furthermore, striatal 5-HT was not altered by amphetamine alone, whereas concurrent administration ofl-DOPA/benserazide depleted 5-HT to 82% of control values. No changes were evident in the frontal cortex following amphetamine with or without concurrentl-DOPA/benserazide; however,l-DOPA/benserazide administered alone reduced 5-HT and 5-HT turnover to 58% of control values.     

Postsynaptic Serine Racemase Regulates NMDA Receptor Function

d-serine is the primary NMDAR coagonist at mature forebrain synapses and is synthesized by the enzyme serine racemase (SR). However, our understanding of the mechanisms regulating the availability of synaptic d-serine remains limited. Though early studies suggested d-serine is synthesized and released from astrocytes, more recent studies have demonstrated a predominantly neuronal localization of SR. More specifically, recent work intriguingly suggests that SR may be found at the postsynaptic density, yet the functional implications of postsynaptic SR on synaptic transmission are not yet known. Here, we show an age-dependent dendritic and postsynaptic localization of SR and d-serine by immunohistochemistry and electron microscopy in mouse CA1 pyramidal neurons. In addition, using a single-neuron genetic approach in SR conditional KO mice from both sexes, we demonstrate a cell-autonomous role for SR in regulating synaptic NMDAR function at Schaffer collateral (CA3)-CA1 synapses. Importantly, single-neuron genetic deletion of SR resulted in the elimination of LTP at 1 month of age, which could be rescued by exogenous d-serine. Interestingly, there was a restoration of LTP by 2 months of age that was associated with an upregulation of synaptic GluN2B. Our findings support a cell-autonomous role for postsynaptic neuronal SR in regulating synaptic NMDAR function and suggests a possible autocrine mode of d-serine action.SIGNIFICANCE STATEMENT NMDARs are key regulators of neurodevelopment and synaptic plasticity and are unique in their requirement for binding of a coagonist, which is d-serine at most forebrain synapses. However, our understanding of the mechanisms regulating synaptic d-serine availability remains limited. d-serine is synthesized in the brain by the neuronal enzyme serine racemase (SR). Here, we show dendritic and postsynaptic localization of SR and d-serine in CA1 pyramidal neurons. In addition, using single-neuron genetic deletion of SR, we establish a role of postsynaptic SR in regulating NMDAR function. These results support an autocrine mode of d-serine action at synapses.     

Effect of nicotine on l-dopa-induced dyskinesia in animal models of Parkinson’s disease: a systematic review and meta-analysis

l-dopa-induced dyskinesias (LIDs) are abnormal involuntary movements (AIM) that develop with long-term l-dopa therapy for Parkinson’s disease (PD). In this study, we used these tools to describe the efficacy of nicotine reduced LID in animal models of PD. Studies were identified by electronic searching of six online databases up to September of 2013 to identify preclinical trials involving nicotine for LID in animal model. Data were extracted for AIM compared with LID animals. Pre-specified subgroup analysis was carried out according to method of model, gender, anesthetic used, and species. Combined standardized mean difference (SMD) estimates and 95 % confidence intervals (CIs) were calculated using a random-effects model. Eleven studies involving 181 animals which described the effect of nicotine on LID were included in the meta-analysis. Nicotine was efficacious in reducing total AIM compared with control group (SMD ?3.77, 95 % CI ?5.30 to ?2.23, P < 0.00001). Meanwhile, four studies showed certain effects of nicotine for improving the axial AIM (SMD ?2.21, 95 % CI ?4.17 to ?0.24, P = 0.03); oral AIM and forelimb AIM were obvious improved in six studies in the nicotine group (SMD ?3.00, 95 % CI ?4.55 to ?1.44, P = 0.0002; SMD ?2.52, 95 % CI ?3.52 to ?1.53, P < 0.00001, respectively). We conclude that nicotine appears to have efficacy in animal models of LID. Large randomized clinical trials testing the effect of nicotine in PD patients with LID are warranted.     

Continuous administration of rotigotine to MPTP-treated common marmosets enhances anti-parkinsonian activity and reduces dyskinesia induction

Rotigotine is a novel, non-ergoline dopamine D₃/D₂/D₁-receptor agonist for the treatment of Parkinson's disease that can be continuously delivered by the transdermal route to provide stable plasma levels. Continuous drug delivery should reduce the risk of dyskinesia induction in comparison to pulsatile dopaminergic treatment. Thus the aim of the study was to compare the reversal of motor disability and induction of dyskinesia produced by continuous compared to pulsatile rotigotine administration in MPTP-treated common marmosets. The study also investigated whether pulsatile or continuous rotigotine administration in combination with l-DOPA prevented l-DOPA-induced dyskinesia. Animals were treated for 28 days with vehicle or pulsatile (twice daily) or continuous delivery of rotigotine (via an osmotic minipump). Subsequently, l-DOPA was then co-administered for a further 28 days. Animals were assessed for locomotor activity, motor disability and dyskinesia induction. The study showed that both continuous and pulsatile administration of rotigotine improved motor deficits and normalized motor function in MPTP-treated monkeys. However, continuous rotigotine delivery reduced dyskinesia expression compared to pulsatile treatment. Both pulsatile and continuous rotigotine administration produced less dyskinesia than administration of l-DOPA alone. The addition of l-DOPA to either pulsatile or continuous rotigotine treatment resulted in the induction of marked dyskinesia similar to that produced by treatment with l-DOPA alone. These data further support the hypothesis that continuous delivery of a dopaminergic agent reduces the risk of dyskinesia induction. However, continuous rotigotine administration did not prevent l-DOPA from inducing dyskinesia suggesting that l-DOPA may induce dyskinesia by mechanisms different from dopamine agonist drugs.     

l-Deprenyl induces aromaticl-amino acid decarboxylase (AADC) mRNA in the rat substantia nigra and ventral tegmentum

l-Deprenyl is a complex drug, and number of mechanisms have been proposed to explain its effects. These include blockade of dopamine metabolism, amplification of dopamine responses, induction of superoxide dismutase or delaying apoptosis. Usingin situ hybridization techniques, we have shown thatl-deprenyl (5–10 mg/kg intraperitoneally, killed after 24 h) increases aromaticl-amino acid decarboxylase (AADC) mRNA levels in rat substantia nigraventral tegmental area. In human brain tissue, AADC is present at low levels, suggesting a possible rate-limiting role in monoamine synthesis. This is particularly important in parkinsonian patients, since the therapeutic efficacy ofl-DOPA is attributed to its enzymatic decarboxylation to dopamine. The present findings support that one of the effects ofl-deprenyl may be to facilitate the decarboxylation ofl-DOPA by increasing the availability of AADC.     

Effect of Adenosine A2A Receptor Antagonists on l-DOPA-Induced Hydroxyl Radical Formation in Rat Striatum

A_2A adenosine receptor antagonists have been proposed as a new therapy for Parkinson’s disease (PD). Since oxidative stress plays an important role in the pathogenesis of PD, we studied the effect of the selective A_2A adenosine receptor antagonists 8-(3-chlorostyryl)caffeine (CSC) and 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM 241385) on l-3,4-dihydroxyphenylalanine (l-DOPA)-induced hydroxyl radical generation using in vivo microdialysis in the striatum of freely moving rats. l-DOPA (100 mg/kg; in the presence of benserazide, 50 mg/kg) given acutely or repeatedly for 14 days generated a high level of hydroxyl radicals, measured by HPLC with electrochemical detection, as the product of their reaction with p-hydroxybenzoic acid (PBA). CSC (1 mg/kg) and ZM 241385 (3 mg/kg) decreased haloperidol (0.5 mg/kg)-induced catalepsy, while at low doses of 0.1 and 0.3 mg/kg, respectively, they did not display an effect. CSC (1 and 5 mg/kg) and ZM 241385 (3 and 9 mg/kg) given acutely, or CSC (1 mg/kg) and ZM 241385 (3 mg/kg) given repeatedly, increased the production of hydroxyl radicals in dialysates from rat striatum. Both acute and repeated administration of CSC (0.1 and 1 mg/kg) and ZM 241385 (3 mg/kg) decreased l-DOPA-induced generation of hydroxyl radicals. However, a high single dose of either CSC (5 mg/kg) and ZM 241385 (9 mg/kg) markedly potentiated the effect of l-DOPA on hydroxyl radical production. The increase in hydroxyl radical production by acute and chronic injection of CSC and ZM 241385 may be related to the increased release of dopamine (DA) and its metabolism in striatal dialysates. Similarly, increased DA release following a single high dose of CSC or ZM 241385 appears to be responsible for augmentation of l-DOPA-induced hydroxyl radical formation. Conversely, the inhibition of l-DOPA-induced production of hydroxyl radical by single and repeated low doses of CSC or repeated low doses of ZM 241385 may be related to reduced DA metabolism. Summing up, A_2A antagonists, used as a supplement of l-DOPA therapy, depending on the dose used, may have a beneficial or adverse effect on ongoing neurodegenerative processes and accompanying oxidative stress.     

Do Tardive Dyskinesia and l-Dopa Induced Dyskinesia Share Common Genetic Risk Factors? An Exploratory Study

Tardive dyskinesia (TD) in schizophrenia patients treated with antipsychotic medications and l-dopa induced dyskinesia (LID) among Parkinson's disease (PD) affected individuals share similar clinical features. Both conditions are induced by chronic exposure to drugs that target dopaminergic receptors (antagonists in TD and agonists in LID) and cause pulsatile and nonphysiological stimulation of these receptors. We hypothesized that the two motor adverse effects partially share genetic risk factors such that certain genetic variants exert a pleiotropic effect, influencing susceptibility to TD as well as to LID. In this pilot study, we focused on 21 TD-associated SNPs, previously reported in TD genome-wide association studies or in candidate gene studies. By applying logistic regression and controlling for relevant clinical risk factors, we studied the association of the SNPs with LID vulnerability in two independent pharmacogenetic samples. We included a Jewish Israeli sample of 203 PD patients treated with l-dopa for a minimum of 3 years and evaluated the existence or absence of LID (LID+?=?128; LID??=?75). An Italian sample was composed of early LID developers (within the first 3 years of treatment, N?=?187) contrasted with non-early LID developers (after 7 years or more of treatment, N?=?203). None of the studied SNPs were significantly associated with LID susceptibility in the two samples. Therefore, we were unable to obtain proof of concept for our initial hypothesis of an overlapping contribution of genetic risk factors to TD and LID. Further studies in larger samples are required to reach definitive conclusions.     

The effect of piribedil on l-DOPA-induced dyskinesias in a rat model of Parkinson’s disease: differential role of α2 adrenergic mechanisms

Piribedil is a non-ergoline, dopamine D₂/D₃ receptor agonist with α₂ adrenoceptor antagonist properties that has been used in the treatment of Parkinson’s disease (PD). Noradrenergic neurotransmission may be involved in the pathogenesis of dyskinesias induced by chronic treatment with l-DOPA (3,4-dihydroxyphenylalanine, levodopa), but its role in the in vivo action of piribedil or on different subclasses of abnormal involuntary movements (AIMs) remains unclear. The aims of this study were therefore (1) to investigate the anti-dyskinetic effects of piribedil on l-DOPA-induced contralateral turning behaviour, locomotive dyskinesias (LD), axial dystonia (AD), orolingual dyskinesia (OD) and forelimb dyskinesia (FD) and (2) to compare these effects to the α₂ adrenoceptor antagonist, idazoxan, or the α₂ adrenoceptor agonist, clonidine. Rats were unilaterally lesioned with 6-hydroxydopamine (6-OHDA) and injected intraperitoneally twice daily with l-DOPA methylester (12.5 mg/kg) and benserazide (3.25 mg/kg). After 3 weeks, the effects of piribedil (5, 15, 40 mg/kg), clonidine (0.15 mg/kg), idazoxan (10 mg/kg) and combinations of these drugs were scored during 2 h. Pre-treatment with 5 and 40 mg/kg, but not 15 mg/kg, of piribedil reduced turning behaviour and AD, OD and FD, but piribedil increased LD at the 40 mg/kg doses compared to the l-DOPA group. Idazoxan induced similar effects as piribedil (40 mg/kg), except that it had no effect on LD. Idazoxan blocked the effect of piribedil on AD and FD. Clonidine reduced all AIMs except OD, possibly because of its sedative effect. Clonidine blocked the effect of piribedil on AD, OD and FD. These data suggest a differential involvement of α₂ adrenergic receptors in the action of piribedil on different subclasses of l-DOPA-induced dyskinesias.