Intermittent Levodopa Research Articles

Zonisamide attenuates the severity of levodopa-induced dyskinesia via modulation of the striatal serotonergic system in a rat model of Parkinson's disease

Glutamate, GABA, acetylcholine, dopamine, and serotonin interact with each other to regulate the flow of neural information in the striatum. Serotonin type 1A receptor (5HT1A) is primarily expressed on glutamatergic nerve terminals, and 5HT1B is expressed on GABAergic medium spiny neurons (MSNs). Zonisamide (ZNS) reportedly improves the off period without worsening levodopa-induced dyskinesia (LID) in patients with advanced Parkinson's disease. In this study, LID model rats were prepared by administrating levodopa to unilaterally 6-OHDA-lesioned rats. We analyzed changes in serotonergic neurotransmission of LID model rats to elucidate the relationship between LID and the serotonergic system and pathomechanism of the anti-dyskinetic effects of ZNS. Abnormal involuntary movements (AIMs) were most severe in intermittently levodopa-treated rats but milder in rats intermittently medicated with levodopa and ZNS. Continuously levodopa-infused rats or intermittently ZNS-injected rats did not develop AIMs, and no differences in the expression of brain-derived neurotrophic factor, 5-HT transporter, 5HT1A, and 5HT1B mRNA between the lesioned striatum and normal side were observed. Expression of 5HT1B mRNA was elevated in the lesioned striatum of intermittently levodopa-treated rats, but this elevation was normalized by concomitant use of ZNS. The severity of AIMs was correlated with the ratio of 5HT1B to 5HT1A mRNA expression in the lesioned striatum, indicating that the anti-LID effect of ZNS is based on inhibition via 5HT1B receptors to direct pathway MSNs sensitized by intermittent levodopa treatment. Selectively acting serotonergic drugs, especially those that lower the 5HT1B to 5HT1A ratio, are promising new therapeutic agents to attenuate LID development.

From OFF to ON—Treating OFF Episodes in Parkinson’s Disease

In Parkinson’s disease (PD), OFF episodes continue to present a serious burden for patients, and their effective management remains a substantial unmet clinical need. Understanding of the pathophysiology of OFF episodes has advanced in recent years, providing valuable insights for improved treatments. OFF episodes generally appear 3–5 years after starting levodopa treatment, but can begin much earlier. They are characterized by motor symptoms (including tremor, rigidity, slowness, incoordination, and weakness) and are almost always associated with some non-motor symptoms (including psychological symptoms, pain, urinary problems, swallowing difficulties, and shortness of breath). In PD, higher doses of levodopa are associated with increased risk of motor and non-motor complications, which are notable limitations for longterm therapy. Their occurrence is associated with intermittent levodopa delivery and consequent fluctuating plasma levels. These issues can be offset using lower levodopa doses where possible, incremental dose increases, and combinations of levodopa with other pharmacological agents. OFF episodes in PD can be caused by gastroparesis and/or by Helicobacter pylori infection, which delays delivery of levodopa. These issues can be addressed using new formulations for continuous intrajejunal administration. In addition, pen injector, intranasal, and inhaled dosing systems have been studied and may provide relief via non-intestinal routes. Other approaches include deep-brain stimulation, which is effective but is restricted by costs and potential adverse events. This report presents the highlights of a satellite symposium held at the 14th International Conference on Alzheimer’s & Parkinson’s Diseases (AD/PD™ 2019), Lisbon, Portugal, which discussed the nature of OFF episodes in PD, associated risk factors and the potential of current and future treatments to effectively manage them and increase ON time.

Levodopa/Benserazide PLGA Microsphere Prevents L-Dopa–Induced Dyskinesia via Lower β-Arrestin2 in 6-Hydroxydopamine Parkinson’s Rats

Prolonged pulsatile administration of Levodopa (L-dopa) can generate L-dopa–induced dyskinesia (LID). Numerous research has reported that continuous dopamine delivery (CDD) was useful in reducing the severity of LID. 6-OHDA lesioned rats were divided into two groups to receive intermittent L-dopa stimulation (L-dopa/benserazide) or Levodopa/benserazide PLGA microsphere (LBPM) for 3 weeks. rAAV (recombinant adeno-associated virus) vector was used to overexpress and ablation of β-arrestin2. We found that LBPM developed less AIM severity compared with standard L-dopa administration, whereas selective deletion of β-arrestin2 in striatum neurons dramatically enhanced the severity of dyskinesia by LBPM. On the contrary, the effects of LBPM in terms of ALO AIM were further relieved by β-arrestin2 overexpression. Furthermore, no significant change in motor behavior was seen either in inhibition or overexpression of β-arrestin2. In short, our experiments provided evidence that LBPM’s prevention of LID behavior was likely due to β-arrestin2, suggesting that a therapy modulating β-arrestin2 may offer a more efficient anti-dyskinetic method with a low risk of untoward effects.

Levodopa/Benserazide Loaded Microspheres Alleviate L-dopa Induced Dyskinesia through Preventing the Over-Expression of D1R/Shp-2/ERK1/2 Signaling Pathway in a Rat Model of Parkinson's Disease.

Background: The long-term intermittent Levodopa (L-dopa) stimulation contributes to an aberrant activation of D1 receptor (D1R) mediated extracellular signal-regulated kinases1/2 (ERK1/2) in the striatal medium spiny neurons, resulting in the occurrence of L-dopa induced dyskinesia (LID). Recently, a novel signaling pathway, D1R/Shp-2/ERK1/2, was proposed to be required for the occurrence of LID. Here we designed the study in which two different methods of L-dopa delivery [continuous dopamine stimulation (CDS) vs. intermittent dopamine stimulation] were used to further identify: (1) the role of D1R/Shp-2/ERK1/2 signaling pathway in the occurrence of LID; (2) whether CDS alleviated LID though preventing the over-expression of the D1R/Shp-2/ERK1/2 signaling pathway.Methods: 6-OHDA-lesioned rat models of Parkinson's disease (PD) were randomly divided into two groups to receive intermittent L-dopa stimulation (L-dopa/benserazide standard group, LS group) or CDS (L-dopa/benserazide loaded microspheres, LBM group) for 21 days. Dyskinesia and anti-parkinsonian effect were compared between the two groups through the AIMs assessment and cylinder test. The critical protein changes in the D1R/Shp-2/ERK1/2 signaling pathway were compared between the two groups through Western blotting.Results: Intermittent L-dopa administration induced serious dyskinetic movements in the 6-OHDA-lesioned rats, and the anti-parkinsonian effect of L-dopa was gradually counteracted by the occurrence of dyskinesia. Intermittent L-dopa administration enhanced the expression of membrane D1R, and induced a robust increase of phosphorylation of Shp-2, Src, DARPP-32, and ERK1/2 in the 6-OHDA-lesioned striatum. In contrast, CDS played a dose-dependent anti-parkinsonian role, without inducing such apparent dyskinetic movements. Moreover, CDS induced no change of membrane D1R expression or phosphorylation of Shp-2, Src, DARPP-32, and ERK1/2 in the 6-OHDA-lesioned striatum.Conclusion: The aberrant activation of D1R/Shp-2 complex was evidenced to be required for the D1R mediating ERK1/2 phosphorylation and the occurrence of LID. CDS effectively prevented the overexpression of D1R/Shp-2/ERK1/2 signaling pathway, resulting in the reduction of LID in 6-OHDA-lesioned rats model of PD.

Zonisamide ameliorates levodopa-induced dyskinesia and reduces expression of striatal genes in Parkinson model rats

To investigate the difference in results according to the mode of levodopa administration and the effect of zonisamide (ZNS), we analyzed the mRNA expression of dopaminergic and non-dopaminergic receptors in the striatum of Parkinson model rats in relation to the development of levodopa-induced dyskinesia (LID). Unilateral Parkinson model rats were subdivided into 4 groups and treated as follows: no medication (group N), continuous levodopa infusion (group C), intermittent levodopa injection (group I), and intermittent levodopa and ZNS injection (group Z). Two weeks after the treatment, LID was observed in group I and Z, but less severe in group Z. The level of both D1 and D2 receptor mRNAs was elevated in groups I and Z, but only D2 receptor mRNA expression was elevated in group C. Adenosine A2A receptor mRNA showed increased expression only in group I. The level of endocannabinoid CB1 receptor mRNA was elevated in groups N, C, and I, but not in group Z. Intermittent injection of levodopa caused LID, in association with elevated expression of D1 and A2A receptors. ZNS ameliorated the development of LID and inhibited up-regulation of A2A and CB1 receptors. Modulation of these receptors may lead to therapeutic approaches for dyskinesia.

Zonisamide ameliorates levodopa-induced dyskinesia and reduces expression of striatal genes in Parkinson model rats

To investigate the difference in results according to the mode of levodopa administration and the effect of zonisamide (ZNS), we analyzed the mRNA expression of dopaminergic and non-dopaminergic receptors in the striatum of Parkinson model rats in relation to the development of levodopa-induced dyskinesia (LID). Unilateral Parkinson model rats were subdivided into 4 groups and treated as follows: no medication (group N), continuous levodopa infusion (group C), intermittent levodopa injection (group I), and intermittent levodopa and ZNS injection (group Z). Two weeks after the treatment, LID was observed in group I and Z, but less severe in group Z. The level of both D1 and D2 receptor mRNAs was elevated in groups I and Z, but only D2 receptor mRNA expression was elevated in group C. Adenosine A2A receptor mRNA showed increased expression only in group I. The level of endocannabinoid CB1 receptor mRNA was elevated in groups N, C, and I, but not in group Z. Intermittent injection of levodopa caused LID, in association with elevated expression of D1 and A2A receptors. ZNS ameliorated the development of LID and inhibited up-regulation of A2A and CB1 receptors. Modulation of these receptors may lead to therapeutic approaches for dyskinesia.

Differential induction of dyskinesia and inflammatory responses by intermittent versus continuous L-DOPA delivery in the 6-OHDA model of Parkinson's disease.

Differential induction of dyskinesia and inflammatory responses by intermittent versus continuous L-DOPA delivery in the 6-OHDA model of Parkinson's disease.

Differential induction of dyskinesia and inflammatory responses by intermittent versus continuous L-DOPA delivery in the 6-OHDA model of Parkinson's disease

Differential induction of dyskinesia and inflammatory responses by intermittent versus continuous L-DOPA delivery in the 6-OHDA model of Parkinson's disease

Dyskinesias do not develop after chronic intermittent levodopa therapy in clinically hemiparkinsonian rhesus monkeys

The stable 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced hemiparkinsonian (HP) rhesus monkey model of Parkinson’s disease (PD) has been frequently used to test preclinical experimental therapeutics targeted to treat patients with advanced PD who suffer from motor fluctuations and drug-induced dyskinesias. We retrospectively analyzed data from 17 stable HP rhesus monkeys treated long-term with chronic intermittent dosing of levodopa (LD) in an attempt to induce choreoathetoid and dystonic dyskinesias. Rhesus monkeys in stable HP state for greater than 6 months as confirmed by multiple blinded behavioral ratings and 18F-dopa Positron Emission Tomography (PET) were treated with optimal doses of LD to provide maximal amelioration of unilateral clinical parkinsonism without any adverse effects. Thereafter, each animal was given chronic intermittent daily challenge with doses of LD up to 700 mg/day orally or with 300 mg/kg/day parenteral injections. LD treatments failed to induce choreoathetoid and dystonic dyskinesias in these animals despite chronic intermittent high dose administration. These results suggest that the stable strictly unilateral HP rhesus monkey model of PD may not be a suitable animal model to test experimental therapeutics targeted against dyskinesias, and that bilateral parkinsonian rhesus models that readily demonstrate drug-induced dyskinesias and clinically relevant motor fluctuations are more appropriate for preclinical experimental testing of therapies designed to treat patients with advanced PD.

Noradrenergic modulation of the motor response induced by long-term levodopa administration in Parkinsonian rats

A decrease in noradrenergic activity in Parkinson's disease might play a critical role in long-term motor complications associated with chronic dopaminergic replacement. Using the rat model of parkinsonism with an additional noradrenergic degeneration induced by the N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) toxin we evaluated whether the circling motor activity and dose-failure episodes induced by levodopa (L-DOPA) differ between single (6-OHDA) and double (6-OHDA + DSP-4) denervated animals challenged with a single daily dose of L-DOPA. While single-lesioned animals showed a sensitization-desensitization turning response with a significant increase on day 15 and a decrease on day 22, in double-lesioned animals, the turning activity was maximal from day 1 and did not decay on day 22. Double-lesioned rats exhibited significantly higher number of turns on days 15 and 22 and a significantly lower percentage of dose-failure episodes during treatment. Noradrenergic denervation appears to be associated with prolonged long-term dopaminergic sensitization. This type of response appears to be comparable to that in the clinical setting with intermittent L-DOPA administration where no desensitization occurs once the abnormal response is established.

Chronic intermittent L‐DOPA treatment induces changes in dopamine release

3,4-Dihydroxyphenyl-l-alanine (l-DOPA)-induced dyskinesia often develops as a side effect of chronic l-DOPA therapy. This study was undertaken to investigate dopamine (DA) release upon l-DOPA treatment. Chronoamperometric measurements were performed in unilaterally DA-depleted rats, chronically treated with l-DOPA, resulting in dyskinetic and non-dyskinetic animals. Normal and lesioned l-DOPA naïve animals were used as controls. Potassium-evoked DA releases were significantly reduced in intact sides of animals undertaken chronic l-DOPA treatment, independent on dyskinetic behavior. Acute l-DOPA further attenuated the amplitude of the DA release in the control sides. In DA-depleted striata, no difference was found in potassium-evoked DA releases, and acute l-DOPA did not affect the amplitude. While immunoreactivity to serotonin uptake transporter was higher in lesioned striata of animals displaying dyskinetic behavior, no correlation could be documented between serotonin transporter-positive nerve fiber density and the amplitude of released DA. In conclusions, the amplitude of potassium-evoked DA release is attenuated in intact striatum after chronic intermittent l-DOPA treatment. No change in amplitude was found in DA-denervated sides of either dyskinetic or non-dyskinetic animals, while release kinetics were changed. This indicates the importance of studying DA release dynamics for the understanding of both beneficial and adverse effects of l-DOPA replacement therapy.

Intermittent l-DOPA treatment differentially alters synaptotagmin 4 and 7 gene expression in the striatum of hemiparkinsonian rats

Long-term use of l-DOPA in Parkinson's disease (PD) is frequently associated with side effects that are reflected in changed neurotransmitter/neuropeptide secretion in basal ganglia. These side effects could be connected with synaptotagmins (syts) because syts are involved in regulation of membrane trafficking. We have previously reported that acute l-DOPA treatment upregulated the expression of Syt 4 and Syt 7 mRNAs in hypersensitive striatum of 6-OHDA rat model for PD. Here we investigate whether intermittent l-DOPA treatment that produces behavior sensitization affects the Syt 1, Syt 2, Syt 4, Syt 7 and Syt 10 mRNAs in striatum of 6-OHDA rats killed 4 and 12 h after the last l-DOPA injection. We verified behavioral sensitization by increased intensity of contralateral turning. 6-OHDA lesion caused Syt 2 mRNA downregulation and Syt 10 mRNA upregulation in striatum, but failed to alter Syt 4, Syt 7 and Syt 1 mRNAs. Acute l-DOPA induced an increase of Syt 4 and Syt 7 mRNAs in the denervated striatum leaving the levels of Syt 1, Syt 2 and Syt 10 mRNAs unaffected. Intermittent l-DOPA treatment did not alter Syt 1, Syt 2 and Syt 10 mRNA striatal levels, suggesting that 6-OHDA-induced Syt 2 and Syt 10 mRNA changes reflect a persistent striatal abnormality caused by dopamine depletion. On contrary, intermittent l-DOPA treatment downregulated Syt 4 mRNA and prolonged the elevation of Syt 7 mRNA in the denervated striatum. We conclude that Syt 4 and Syt 7 might be specifically involved in striatal plasticity caused by repeated l-DOPA administration that accompanies sensitization.

Adenosine A2A receptors, dopamine D2 receptors and their interactions in Parkinson's disease

Future therapies in Parkinson's disease may substantially build on the existence of intra-membrane receptor-receptor interactions in DA receptor containing heteromeric receptor complexes. The A(2A)/D(2) heteromer is of substantial interest in view of its specific location in cortico-striatal glutamate terminals and in striato-pallidal GABA neurons. Antagonistic A(2A)/D(2) receptor interactions in this heteromer demonstrated at the cellular level, and at the level of the striato-pallidal GABA neuron and at the network level made it possible to suggest A(2A) antagonists as anti-parkinsonian drugs. The major mechanism is an enhancement of D(2) signaling leading to attenuation of hypokinesia, tremor, and rigidity in models of Parkinson's disease with inspiring results in two clinical trials. Other interactions are antagonism at the level of the adenylyl cyclase; heterologous sensitization at the A(2A) activated adenylyl cyclase by persistent D(2) activation and a compensatory up-regulation of A(2A) receptors in response to intermittent Levodopa treatment. An increased dominance of A(2A) homomers over D(2) homomers and A(2A)/D(2) heteromers after intermittent Levodopa treatment may therefore contribute to development of Levodopa induced dyskinesias and to the wearing off of the therapeutic actions of Levodopa giving additional therapeutic roles of A(2A) antagonists. Their neuroprotective actions may involve an increase in the retrograde trophic signaling in the nigro-striatal DA system.

Differential gene expression analysis in treatment of Parkinson's disease using the moduli space of triangles

The long-term utility of levodopa (l-dopa) treatmentagainst PD is known to be limited by its subsequentinduction of dyskinesia (l-dopa-induced dyskinesia orLID). Up to now, few treatment strategies have been iden-tified to reverse LID and restore l-dopa efficacy in dyski-netic patients. Among various mechanisms, l-dopasensitization (priming) may play an important role inthe development and maintenance of LID. Disregulationof dopamine (DA) synthesis, release and clearance ofextracellular DA (due to DA neuronal death and conse-quent ectopic synthesis and release by 5-HT terminals)is thought to lead to exaggerated fluctuations in the syn-aptic DA concentrations and consequent neurobiologicalalterations during chronic intermittent l-dopa treatment.These fluctuations, in turn, induce long-term, synapticalterations in the striatum and other brain areas compris-ing the basal ganglia. Previous studies have shown thatlong-term sensitization to cocaine can be reversed byinjecting a dopamine receptor agonist, followed by a 5-HT2 or 5-HT3 antagonist approximately 3.5 hours later[1,2]. To the extent that cocaine addiction may share sim-ilar neurobiological mechanisms with LID, it is reasona-ble to examine a regimen of the DA agonist pergolidefollowed by the 5-HT2 antagonist ketanserin at the peakof acute withdrawal over a treatment period and reversesensitization to l-dopa. Based on our previous finding thatthis specific drug combination regimen can reverse previ-ously-established behavioral and molecular markers ofcocaine or methamphetamine sensitization in rats [3], wedetermined the striatal mRNA expression profiles associ-ated with l-dopa-induced dyskinesia in rats and itsreversal by the pergolide-ketanserin regimen. 6-Hydroxy-dopamine (6-OHDA)-lesioned rats were treated with l-dopa twice a day for 21 days (days 1 – 21) to induceabnormal involuntary movements (AIM), a model of LID.Subsequently, they were treated subcutaneously once aday for 2 weeks with one of the following. Group Areceived pergolide followed by ketanserin; Group Breceived pergolide followed by saline; Group C, the con-trol group, received saline on both occasions. The expres-sion levels of mRNA were measured for 27,342 genes. Thenormalized values provide triplets of positive numbers D= { (

The effect of subchronic, intermittent l-DOPA treatment on neuronal nitric oxide synthase and soluble guanylyl cyclase expression and activity in the striatum and midbrain of normal and MPTP-treated mice

We have investigated the effects of low (10 mg/kg) and high (100 mg/kg) doses of l-DOPA on the expression and activity of neuronal nitric oxide synthase (nNOS) and guanylyl cyclase (GC) in the striatum and midbrain of mice. l-DOPA was administered subchronically for 11 days (beginning 3 days after last MPTP/NaCl injection) or for 14 days (with dosing started immediately following the last MPTP/NaCl injection). Adult mice received three intraperitoneal (i.p.) injections of physiological saline or MPTP at 2 h intervals (total dose of 40 mg/kg). Normal and MPTP-injected mice were treated twice a day for 11 or 14 days with low (10/2.5 mg/kg bw) or high (100/25 mg/kg bw) doses of l-DOPA/benserazide. The present study indicates that several days of treatment with l-DOPA does not affect MPTP-activation of the nNOS/sGC/cGMP pathway or the neurodegenerative processes that occur in the striatum and midbrain of mice. In normal mice, l-DOPA upregulates the expression and activity of nNOS and GC to levels found in MPTP-injected mice. Due to upregulation of nNOS and GC, cGMP levels in the mouse striatum and midbrain are also elevated, however, significantly lower in mice administrated with low dose of l-DOPA. In both investigated brain regions of normal mice cGMP-dependent PDEs activities were elevated after low dose administration of l-DOPA, but no change in PDEs activities has been detected in MPTP and high l-DOPA-injected mice as compared to control values. The enhancement of nNOS mRNA and GCβ1 mRNA levels were generated by both doses of l-DOPA, given in a time-dependent fashion. l-DOPA-injected for 11 or 14 days caused a decrease in TH protein levels in the striatum and midbrain, respectively; this result was noted irrespective of dose. l-DOPA therapy did not prevent the MPTP-induced decrease in TH protein levels in either investigated brain region.

2.265 The effect of subchronic, intermittent L-DOPA treatment on nNOS and sCG expression and activity in the striatum and midbrain of normal and MPTP-treated mice

2.265 The effect of subchronic, intermittent L-DOPA treatment on nNOS and sCG expression and activity in the striatum and midbrain of normal and MPTP-treated mice

Effect of antisense FosB and CREB on the expression of prodynorphin gene in rats with Levodopa-induced dyskinesias

The effects of antisense FosB and CREB intra-striatum injection on the expression of prodynorphin (PDyn) gene in striatal neurons of Levodopa-induced dyskinesias (LID) rats with Parkinson disease (PD) were explored. PD model in rats was established by 6-OHDA microinjection stereotaxically. The rats were treated with chronic intermittent Levodopa celiac injection for 28 days to get the LID rats. Antisense FosB and cAMP response element-binding protein (CREB) were injected into striatum of all rats respectively. In situ hybridization was used to measure the changes in the expression of PDyn mRNA in striatum and behavior changes were observed. The results showed after administration of antisense FosB, abnormal involuntary movement (AIM) was decreased and the expression of PDyn mRNA in striatum was increased in LID rats as compared with sense FosB group (P<0.01, respectively). As compared with the control group, the expression of PDyn mRNA in striatum was decreased by antisense CREB-treated LID group (P<0.01) and compared with sense CREB treated LID group, antisense CREB-treated LID group showed no changes in AIM scores and the expressions of PDyn mRNA (both P>0.05). In conclusion, FosB protein, which replaced the CREG, could regulate the expression of PDyn mRNA and play critical role in the pathogenesis of LID.

Contribution of D1 receptor stimulation to the development of levodopa-induced dyskinesias in 6-hydroxydopamine-lesioned rats

Dyskinesias represent a troublesome complication of l-DOPA therapy in Parkinson's disease patients. However, the pathogenesis of l-DOPA-induced dyskinesia (LID) remains to be determined. The clinical fact that pallidotomy has a striking anti-dyskinesic effect provides evidence that the medial globus pallidus (MGP) plays a crucial role in the development of LID. We have shown that intermittent l-DOPA treatment induced hypertrophy of MGP with dyskinesias in 6-hydroxydopamine (OHDA)-lesioned hemiparkinsonian rats. The hypertrophy resulted from enlargement of axon terminals of the direct pathway (GABAergic projection from the striatum to MGP). This observation implies that pallidotomy has ameliorative effects on LID, since the procedure breaks down the enlargement. Striatal neurons in the direct pathway express dopamine D 1 receptors. Taken together, our results strongly suggest that abnormal stimulation of striatal D 1 receptors by l-DOPA-derived dopamine is a primary cause of hypertrophy of MGP and probably LID. To prove the hypothesis, we examined the motor behavior and neuropathological changes in MGP of 6-OHDA-lesioned rats intermittently treated (twice daily for 14 days) with saline, SKF38393 (D 1 agonist), quinpirole (D 2 agonist) and l-DOPA (D 1 and D 2 agonist). Dyskinesia was induced markedly by SKF38393 and l-DOPA in 6-OHDA-lesioned rats, but minimally by quinpirole. Treatment with SKF38393 and l-DOPA caused hypertrophy of MGP in the lesioned side of 6-OHDA-lesioned rats, although quinpirole treatment had no effect on the MGP volume. Enlargement of axon terminals in MGP of the lesioned side was observed in 6-OHDA-lesioned rats treated with SKF38393 and l-DOPA, but such a change did not occur in 6-OHDA-lesioned rats treated with quinpirole. These results suggest that dopamine D 1 receptor stimulation is essential to induce hypertrophy of MGP and LID.

Expression of dyskinetic movements and turning behaviour in subchronic l-DOPA 6-hydroxydopamine-treated rats is influenced by the testing environment

Sensitisation in contralateral turning behaviour and induction of abnormal involuntary movements (AIMs) after subchronic intermittent l-DOPA were compared for their predictive validity as model of parkinsonian dyskinetic movements. l-DOPA treatment produced sensitisation in turning behaviour in 6-hydroxydopamine-lesioned rats, when animals were evaluated in hemispherical bowls but not in cages. In contrast, sensitisation in AIMs was obtained both in hemispherical bowls and cages. Results provide evidence that the choice of the environment used in evaluation of AIMs and turning behaviour is of crucial importance.

Vesicular monoamine transporter-2 and aromatic l-amino acid decarboxylase gene therapy prevents development of motor complications in parkinsonian rats after chronic intermittent l-3,4-dihydroxyphenylalanine administration

Motor complications after chronic l-3,4-dihydroxyphenylalanine ( l-DOPA) therapy occur partly because of the sensitization to dopaminergic agents resulting from pulsatile dopaminergic stimulation. The loss of presynaptic storage contributes to short duration of action by dopamine. Vesicular monoamine transporter-2 (VMAT-2) controls intraneuronal dopamine storage by packaging dopamine into synaptic vesicles, thereby allowing exocytotic release of dopamine. Using primary fibroblast doubly transduced with VMAT-2 and aromatic l-amino acid decarboxylase (AADC) genes, we previously demonstrated the beneficial effects of such double gene transduction in the production, storage, and gradual release of dopamine in vitro and in vivo. In this study, we further evaluate the effect of achieving sustained level of dopamine within the striata by VMAT-2 gene on behavioral response of parkinsonian rats after chronic intermittent l-DOPA administration. Primary fibroblast (PF) cells were genetically modified with AADC and VMAT-2 genes. We grafted primary fibroblast cells, PF with AADC (PFAADC), or doubly transduced PF with AADC and VMAT-2 (PFVMAA) ( n = 6 for each group) into parkinsonian rat striata and administered l-DOPA (25 mg/kg/day) intermittently for 4 weeks. For behavioral study, we employed a model of akinesia using forepaw adjusting steps (FAS) that have been well characterized to reflect the effect of the lesion and the antiparkinsonian effect of dopaminergic drugs and transplants. The duration of FAS response to l-DOPA was sustained for a longer duration in rats grafted with PFVMAA cells than in those grafted with either control cells or cells with AADC alone. In PFVMAA-grafted animals, prolonged duration of FAS responses to l-DOPA was sustained even 6 weeks after discontinuation of 4-week intermittent l-DOPA treatment. These findings suggest that the restoration of dopamine storage capacity could enhance the efficacy of l-DOPA therapy and attenuate the motor fluctuations that result from chronic intermittent l-DOPA administration. The gene therapy expressing AADC and VMAT-2 along with systemic l-DOPA therapy could provide a novel treatment strategy to prevent motor fluctuations.