Effect of repeated L-DOPA, bromocriptine, or lisuride administration on preproenkephalin-A and preproenkephalin-B mRNA levels in the striatum of the 6-hydroxydopamine-lesioned rat

Differential effects of opioid receptor antagonism on the anti-dyskinetic and anti-parkinsonian effects of sub-anesthetic ketamine treatment in a preclinical model

Sub-anesthetic ketamine treatment has been shown to be an effective therapy for treatment-resistant depression and chronic pain. Our group has previously shown that sub-anesthetic ketamine produces acute anti-parkinsonian, and acute anti-dyskinetic effects in preclinical models of Parkinson's disease (PD). Ketamine is a multifunctional drug and exerts effects through blockade of N-methyl-d-aspartate receptors but also through interaction with the opioid system. In this report, we provide detailed pharmacokinetic rodent data on ketamine and its main metabolites following an intraperitoneal injection, and second, we explore the pharmacodynamic properties of ketamine in a rodent PD model with respect to the opioid system, using naloxone, a pan-opioid receptor antagonist, in unilateral 6-hydroxydopamine-lesioned male rats, treated with 6 mg/kg levodopa (l-DOPA) to establish a model of l-DOPA-induced dyskinesia (LID). As previously reported, we showed that ketamine (20 mg/kg) is highly efficacious in reducing LID and now report that the magnitude of this effect is resistant to naloxone (3 and 5 mg/kg). The higher naloxone dose of 5 mg/kg, however, led to an extension of the time-course of the LID, indicating that opioid receptor activation, while not a prerequisite for the anti-dyskinetic effects of ketamine, still exerts an acute modulatory effect. In contrast to the mild modulatory effect on LID, we found that naloxone added to the anti-parkinsonian activity of ketamine, further reducing the akinetic phenotype. In conclusion, our data show opioid receptor blockade differentially modulates the acute anti-parkinsonian and anti-dyskinetic actions of ketamine, providing novel mechanistic information to support repurposing ketamine for individuals with LID.

Prenatal exposition to haloperidol: A preclinical narrative review

Pre-existing maternal mental disorders may affect the early interactions between mother and baby, impacting the child's psychoemotional development. The typical antipsychotic haloperidol can be used during pregnancy, even with some restrictions. Its prescription is not limited to psychotic disorders, but also to other psychiatric conditions of high incidence and prevalence in the woman's fertile period. The present review focused on the preclinical available data regarding the biological and behavioral implications of embryonic exposure to haloperidol. The understanding of the effects of psychotropic drugs during neurodevelopment is important for its clinical aspect since there is limited evidence regarding the risks of antipsychotic drug treatment in pregnant women and their children. Moreover, a better comprehension of the mechanistic events that can be affected by antipsychotic treatment during the critical period of neurodevelopment may offer insights into the pathophysiology of neurodevelopmental disorders. The findings presented in this review converge to the existence of several risks associated with prenatal exposure to such medication and emphasize the need for further studies regarding its dimensions.

Neurobiological and Pharmacological Perspectives of D3 Receptors in Parkinson’s Disease

The discovery of the D3 receptor (D3R) subtypes of dopamine (DA) has generated an understandable increase in interest in the field of neurological diseases, especially Parkinson’s disease (PD). Indeed, although DA replacement therapy with l-DOPA has provided an effective treatment for patients with PD, it is responsible for invalidating abnormal involuntary movements, known as L-DOPA-induced dyskinesia, which constitutes a serious limitation of the use of this therapy. Of particular interest is the finding that chronic l-DOPA treatment can trigger the expression of D1R–D3R heteromeric interactions in the dorsal striatum. The D3R is expressed in various tissues of the central nervous system, including the striatum. Compelling research has focused on striatal D3Rs in the context of PD and motor side effects, including dyskinesia, occurring with DA replacement therapy. Therefore, this review will briefly describe the basal ganglia (BG) and the DA transmission within these brain regions, before going into more detail with regard to the role of D3Rs in PD and their participation in the current treatments. Numerous studies have also highlighted specific interactions between D1Rs and D3Rs that could promote dyskinesia. Finally, this review will also address the possibility that D3Rs located outside of the BG may mediate some of the effects of DA replacement therapy.

The Multimodal Serotonergic Agent Vilazodone Inhibits L-DOPA-Induced Gene Regulation in Striatal Projection Neurons and Associated Dyskinesia in an Animal Model of Parkinson's Disease

Levodopa (L-DOPA) treatment in Parkinson's disease is limited by the emergence of L-DOPA-induced dyskinesia. Such dyskinesia is associated with aberrant gene regulation in neurons of the striatum, which is caused by abnormal dopamine release from serotonin terminals. Previous work showed that modulating the striatal serotonin innervation with selective serotonin reuptake inhibitors (SSRIs) or 5-HT1A receptor agonists could attenuate L-DOPA-induced dyskinesia. We investigated the effects of a novel serotonergic agent, vilazodone, which combines SSRI and 5-HT1A partial agonist properties, on L-DOPA-induced behavior and gene regulation in the striatum in an animal model of Parkinson's disease. After unilateral dopamine depletion by 6-hydroxydopamine (6-OHDA), rats received repeated L-DOPA treatment (5 mg/kg) alone or in combination with vilazodone (10 mg/kg) for 3 weeks. Gene regulation was then mapped throughout the striatum using in situ hybridization histochemistry. Vilazodone suppressed the development of L-DOPA-induced dyskinesia and turning behavior but did not interfere with the prokinetic effects of L-DOPA (forelimb stepping). L-DOPA treatment drastically increased the expression of dynorphin (direct pathway), 5-HT1B, and zif268 mRNA in the striatum ipsilateral to the lesion. These effects were inhibited by vilazodone. In contrast, vilazodone had no effect on enkephalin expression (indirect pathway) or on gene expression in the intact striatum. Thus, vilazodone inhibited L-DOPA-induced gene regulation selectively in the direct pathway of the dopamine-depleted striatum, molecular changes that are considered critical for L-DOPA-induced dyskinesia. These findings position vilazodone, an approved antidepressant, as a potential adjunct medication for the treatment of L-DOPA-induced motor side effects.

µ Opioid Receptor Agonism for L-DOPA-Induced Dyskinesia in Parkinson's Disease

Parkinson's disease (PD) is characterized by severe locomotor deficits and is commonly treated with the dopamine precursor L-DOPA, but its prolonged usage causes dyskinesias referred to as L-DOPA-induced dyskinesia (LID). Several studies in animal models of PD have suggested that dyskinesias are associated with a heightened opioid cotransmitter tone, observations that have led to the notion of a LID-related hyperactive opioid transmission that should be corrected by µ opioid receptor antagonists. Reports that both antagonists and agonists of the µ opioid receptor may alleviate LID severity in primate models of PD and LID, together with the failure of nonspecific antagonist to improve LID in pilot clinical trials in patients, raises doubt about the reliability of the available data on the opioid system in PD and LID. After in vitro characterization of the functional activity at the µ opioid receptor, we selected prototypical agonists, antagonists, and partial agonists at the µ opioid receptor. We then showed that both oral and discrete intracerebral administration of a µ receptor agonist, but not of an antagonist as long thought, ameliorated LIDs in the gold-standard bilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned female macaque model of PD and LID. The results call for a reappraisal of opioid pharmacology in the basal ganglia as well as for the development of brain nucleus-targeted µ opioid receptor agonists.SIGNIFICANCE STATEMENT µ opioid receptors have long been considered as a viable target for alleviating the severity of L-DOPA-induced hyperkinetic side effects, induced by the chronic treatment of Parkinson's disease motor symptoms with L-DOPA. Conflicting results between experimental parkinsonism and Parkinson's disease patients, however, dampened the enthusiasm for the target. Here we reappraise the pharmacology and then demonstrate that both oral and discrete intracerebral administration of a µ receptor agonist, but not of an antagonist as long thought, ameliorates LIDs in the gold-standard bilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned macaque model of Parkinson's disease, calling for a reappraisal of the opioid pharmacology as well as for the development of brain nucleus-targeted µ receptor agonists.

Selective Regulation of 5-HT1B Serotonin Receptor Expression in the Striatum by Dopamine Depletion and Repeated L-DOPA Treatment: Relationship to L-DOPA-Induced Dyskinesias

Dopamine and serotonin in the basal ganglia interact in a bidirectional manner. On the one hand, serotonin (5-HT) receptors regulate the effects of dopamine agonists on several levels, ranging from molecular signaling to behavior. These interactions include 5-HT receptor-mediated facilitation of dopamine receptor-induced gene regulation in striatal output pathways, which involves the 5-HT1B receptor and others. Conversely, there is evidence that dopamine action by psychostimulants regulates 5-HT1B receptor expression in the striatum. To further investigate the effects of dopamine and agonists on 5-HT receptors, we assessed the expression of 5-HT1B and other serotonin receptor subtypes in the striatum after unilateral dopamine depletion by 6-OHDA and subsequent treatment with L-DOPA (5 mg/kg; 4 weeks). Neither dopamine depletion nor L-DOPA treatment produced significant changes in 5-HT2C, 5-HT4, or 5-HT6 receptor expression in the striatum. In contrast, the 6-OHDA lesion caused a (modest) increase in 5-HT1B mRNA levels throughout the striatum. Moreover, repeated L-DOPA treatment markedly further elevated 5-HT1B expression in the dopamine-depleted striatum, an effect that was most robust in the sensorimotor striatum. A minor L-DOPA-induced increase in 5-HT1B expression was also seen in the intact striatum. These changes in 5-HT1B expression mimicked changes in the expression of neuropeptide markers (dynorphin, enkephalin mRNA) in striatal projection neurons. After repeated L-DOPA treatment, the severity of L-DOPA-induced dyskinesias and turning behavior was positively correlated with the increase in 5-HT1B expression in the associative, but not sensorimotor, striatum ipsilateral to the lesion, suggesting that associative striatal 5-HT1B receptors may play a role in L-DOPA-induced behavioral abnormalities.

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.

Characterization of a Multiple-Scan-Rate Voltammetric Waveform for Real-Time Detection of Met-Enkephalin

Opioid peptides are critically involved in a variety of physiological functions necessary for adaptation and survival, and as such, understanding the precise actions of endogenous opioid peptides will aid in identification of potential therapeutic strategies to treat a variety of disorders. However, few analytical tools are currently available that offer both the sensitivity and spatial resolution required to monitor peptidergic concentration fluctuations in situ on a time scale commensurate with that of neuronal communication. Our group has developed a multiple-scan-rate waveform to enable real-time voltammetric detection of tyrosine containing neuropeptides. Herein, we have evaluated the waveform parameters to increase sensitivity to methionine-enkephalin (M-ENK), an endogenous opioid neuropeptide implicated in pain, stress, and reward circuits. M-ENK dynamics were monitored in adrenal gland tissue, as well as in the dorsal striatum of anesthetized and freely behaving animals. The data reveal cofluctuations of catecholamine and M-ENK in both locations and provide measurements of M-ENK dynamics in the brain with subsecond temporal resolution. Importantly, this work also demonstrates how voltammetric waveforms can be customized to enhance detection of specific target analytes, broadly speaking.

The combination of the opioid glycopeptide MMP-2200 and a NMDA receptor antagonist reduced l-DOPA-induced dyskinesia and MMP-2200 by itself reduced dopamine receptor 2-like agonist-induced dyskinesia

Dopamine (DA)-replacement therapy utilizing l-DOPA is the gold standard symptomatic treatment for Parkinson's disease (PD). A critical complication of this therapy is the development of l-DOPA-induced dyskinesia (LID). The endogenous opioid peptides, including enkephalins and dynorphin, are co-transmitters of dopaminergic, GABAergic, and glutamatergic transmission in the direct and indirect striatal output pathways disrupted in PD, and alterations in expression levels of these peptides and their precursors have been implicated in LID genesis and expression. We have previously shown that the opioid glycopeptide drug MMP-2200 (a.k.a. Lactomorphin), a glycosylated derivative of Leu-enkephalin mediates potent behavioral effects in two rodent models of striatal DA depletion. In this study, the mixed mu-delta agonist MMP-2200 was investigated in standard preclinical rodent models of PD and of LID to evaluate its effects on abnormal involuntary movements (AIMs). MMP-2200 showed antiparkinsonian activity, while increasing l-DOPA-induced limb, axial, and oral (LAO) AIMs by ∼10%, and had no effect on dopamine receptor 1 (D1R)-induced LAO AIMs. In contrast, it markedly reduced dopamine receptor 2 (D2R)-like-induced LAO AIMs. The locomotor AIMs were reduced by MMP-2200 in all three conditions. The N-methyl-d-aspartate receptor (NMDAR) antagonist MK-801 has previously been shown to be anti-dyskinetic, but only at doses that induce parkinsonism. When MMP-2200 was co-administered with MK-801, MK-801-induced pro-parkinsonian activity was suppressed, while a robust anti-dyskinetic effect remained. In summary, the opioid glycopeptide MMP-2200 reduced AIMs induced by a D2R-like agonist, and MMP-2200 modified the effect of MK-801 to result in a potent reduction of l-DOPA-induced AIMs without induction of parkinsonism.

Yokukansan, a Traditional Japanese Medicine, Enhances the L-DOPA-Induced Rotational Response in 6-Hydroxydopamine-Lesioned Rats: Possible Inhibition of COMT

The aim of the present study was to investigate the effects of the traditional Japanese medicine yokukansan (YKS) on the function of dopamine (DA) in the rat nigrostriatal system. Unilateral 6-hydroxydopamine lesions were produced in the rat nigrostriatal system. Despite a marked loss in the striatal immunoreactivity of tyrosine hydroxylase on the lesion side, striatal serotonin (5-HT) immunoreactivity was not affected. Treatment using L-3,4-dihydroxyphenylalanine (L-DOPA) in conjunction with benserazide for 15 d induced abnormal involuntary movements (AIMs) such as locomotive (rotational response), axial, forelimb, and orolingual movements in the lesioned rats. The L-DOPA-induced locomotive and axial, but not forelimb and orolingual, AIMs were significantly increased and prolonged by the pre-administration of YKS. We next investigated the effects of YKS on the production of DA from L-DOPA in 5-HT synthetic RIN 14B cells. RIN 14B cells produced DA and its metabolite, 3-methoxytyramine (3-MT), following L-DOPA treatment. YKS significantly augmented DA production and inhibited its metabolism to 3-MT in a manner similar to the catechol-O-methyltransferase (COMT) inhibitor entacapone. YKS and some alkaloids (corynoxeine: CX, geissoschizine methyl ether: GM) in Uncaria hook, a constituent herb of YKS, also inhibited COMT activity, indicating that the augmenting effect of YKS on L-DOPA-induced DA production in 5-HT synthetic cells was due to the inhibition of COMT by CX and GM. Our results suggest that YKS facilitates the DA supplemental effect of L-DOPA, and that COMT inhibition by CX and GM contributes, at least in part, to the effects of YKS.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Selective loss of bi-directional synaptic plasticity in the direct and indirect striatal output pathways accompanies generation of parkinsonism and l-DOPA induced dyskinesia in mouse models

Parkinsonian symptoms arise due to over-activity of the indirect striatal output pathway, and under-activity of the direct striatal output pathway. l-DOPA-induced dyskinesia (LID) is caused when the opposite circuitry problems are established, with the indirect pathway becoming underactive, and the direct pathway becoming over-active. Here, we define synaptic plasticity abnormalities in these pathways associated with parkinsonism, symptomatic benefits of l-DOPA, and LID. We applied spike-timing dependent plasticity protocols to cortico-striatal synapses in slices from 6-OHDA-lesioned mouse models of parkinsonism and LID, generated in BAC transgenic mice with eGFP targeting the direct or indirect output pathways, with and without l-DOPA present. In naïve mice, bidirectional synaptic plasticity, i.e. LTP and LTD, was induced, resulting in an EPSP amplitude change of approximately 50% in each direction in both striatal output pathways, as shown previously. In parkinsonism and dyskinesia, both pathways exhibited unidirectional plasticity, irrespective of stimulation paradigm. In parkinsonian animals, the indirect pathway only exhibited LTP (LTP protocol: 143.5±14.6%; LTD protocol 177.7±22.3% of baseline), whereas the direct pathway only showed LTD (LTP protocol: 74.3±4.0% and LTD protocol: 63.3±8.7%). A symptomatic dose of l-DOPA restored bidirectional plasticity on both pathways to levels comparable to naïve animals (Indirect pathway: LTP protocol: 124.4±22.0% and LTD protocol: 52.1±18.5% of baseline. Direct pathway: LTP protocol: 140.7±7.3% and LTD protocol: 58.4±6.0% of baseline). In dyskinesia, in the presence of l-DOPA, the indirect pathway exhibited only LTD (LTP protocol: 68.9±21.3% and LTD protocol 52.0±14.2% of baseline), whereas in the direct pathway, only LTP could be induced (LTP protocol: 156.6±13.2% and LTD protocol 166.7±15.8% of baseline). We conclude that normal motor control requires bidirectional plasticity of both striatal outputs, which underlies the symptomatic benefits of l-DOPA. Switching from bidirectional to unidirectional plasticity drives global changes in striatal pathway excitability, and underpins parkinsonism and dyskinesia.

RGS4 is involved in the generation of abnormal involuntary movements in the unilateral 6-OHDA-lesioned rat model of Parkinson's disease

Regulators of G-protein signalling (RGS) proteins are implicated in striatal G-protein coupled receptor (GPCR) sensitisation in the pathophysiology of l-DOPA-induced abnormal involuntary movements (AIMs), also known as dyskinesia (LID), in Parkinson's disease (PD). In this study, we investigated RGS protein subtype 4 in the expression of AIMs in the unilateral 6-hydroxydopamine (6-OHDA)-lesioned rat model of LID. The effects of RGS4 antisense brain infusion on the behavioural and molecular correlates of l-DOPA priming in 6-OHDA-lesioned rats were assessed. In situ hybridisation revealed that repeated l-DOPA/benserazide treatment caused an elevation of RGS4 mRNA levels in the striatum, predominantly in the lateral regions. The increased expression of RGS4 mRNA in the rostral striatum was found to positively correlate with the behavioural (AIM scores) and molecular (pre-proenkephalin B, PPE-B expression) markers of LID. We found that suppressing the elevation of RGS4 mRNA in the striatum by continuous infusion of RGS4 antisense oligonucleotides, via implanted osmotic mini-pumps, during l-DOPA priming, reduced the induction of AIMs. Moreover, ex vivo analyses of the rostral dorsolateral striatum showed that RGS4 antisense infusion attenuated l-DOPA-induced elevations of PPE-B mRNA and dopamine-stimulated [(35)S]GTPγS binding, a marker used for measuring dopamine receptor super-sensitivity. Taken together, these data suggest that (i) RGS4 proteins play an important pathophysiological role in the development and expression of LID and (ii) suppressing the elevation of RGS4 mRNA levels in l-DOPA priming attenuates the associated pathological changes in LID, dampening its physiological expression. Thus, modulating RGS4 proteins could prove beneficial in the treatment of dyskinesia in PD.

Subthalamic 6-OHDA-induced lesion attenuates levodopa-induced dyskinesias in the rat model of Parkinson's disease

The subthalamic nucleus (STN) receives direct dopaminergic innervation from the substantia nigra pars compacta that degenerates in Parkinson's disease. The present study aimed to investigate the role of dopaminergic denervation of STN in the origin of levodopa-induced dyskinesias. Rats were distributed in four groups which were concomitantly lesioned with 6-OHDA or vehicle (sham) in the STN and in the medial forebrain bundle (MFB) as follows: a) MFB-sham plus STN-sham, b) MFB-sham plus STN-lesion, c) MFB-lesion plus STN-sham, and d) MFB-lesion plus STN-lesion. Four weeks after lesions, animals were treated with levodopa (6mg/kg with 15mg/kg benserazide i.p.) twice daily for 22 consecutive days. Abnormal involuntary movements were measured. In situ hybridization was performed measuring the expression of striatal preproenkephalin, preprodynorphin, STN cytochrome oxidase (CO) and nigral GAD67 mRNAs. STN 6-OHDA denervation did not induce dyskinesias in levodopa-treated MFB-sham animals but attenuated axial (p<0.05), limb (p<0.05) and orolingual (p<0.01) dyskinesias in rats with a concomitant lesion of the nigrostriatal pathway. The attenuation of dyskinesias was associated with a decrease in the ipsilateral STN CO mRNA levels (p<0.05). No significant differences between MFB-lesion plus STN-sham and MFB-lesion plus STN-lesion groups in the extent of STN dopaminergic denervation were observed. Moreover, intrasubthalamic microinfusion of dopamine in the MFB-lesion plus STN-lesion group triggered orolingual (p<0.01), but not axial or limb, dyskinesias. These results suggest that dopaminergic STN innervation influences the expression of levodopa-induced dyskinesias but also the existence of non dopaminergic-mediated mechanisms. STN noradrenergic depletion induced by 6-OHDA in the STN needs to be taken in account as a possible mechanism explaining the attenuation of dyskinesias in the combined lesion group.

Abnormal involuntary movement (AIM) expression following D2 dopamine agonist challenge is determined by the nature of prior dopamine receptor stimulation (priming) in 6-hydroxydopamine lesioned rats

Rats with unilateral 6-hydroxydopamine (6-OHDA) lesions show sensitization (priming) of rotational behavior upon repeated treatment with dopamine agonists. To relate these observations to dyskinesias exhibited by Parkinson's Disease patients, we assessed abnormal involuntary movements (AIMs) in 6-OHDA rats, which were primed with three injections of either the following: water, D1/D2 agonist apomorphine (Apo) (0.5mg/kg), D1 agonist SKF38393 (SKF) (10mg/kg) or D2 agonist quinpirole (Quin) (1 or 2.5mg/kg). The rats were challenged one week later with Quin (0.25mg/kg). Axial, limb, orolingual, locomotor, and grooming AIMs were scored (0-4) every 5min. Priming with water did not produce AIMs. Priming with Quin (1mg/kg) produced axial and locomotor AIMs, while priming with Apo, SKF or Quin (2.5mg/kg) produced axial, locomotor, limb, and grooming AIMs. The disparity in AIM profiles between Quin (1mg/kg) and (2.5mg/kg) was not the result of D1 receptor stimulation since there was little striatal Fos expression following the third priming injection with Quin (1 or 2.5mg/kg) compared to following SKF, which led to robust striatal Fos expression. Challenge with Quin (0.25mg/kg) essentially reproduced the categories of AIMs exhibited during priming, with no AIMs in water-primed 6-OHDA rats, mild, non-significant, axial and locomotor AIMs in Quin (1 and 2.5mg/kg)-primed 6-OHDA rats, and axial, limb, locomotor, and grooming AIMs in Apo- and SKF-primed 6-OHDA rats. These data suggest that the types of AIMs expressed following challenge with Quin depend on the dopamine receptor subtype and dose of dopamine agonist used during priming.

CNS penetration of the opioid glycopeptide MMP-2200: a microdialysis study

Endogenous opioid peptides enkephalin and dynorphin are major co-transmitters of striatofugal pathways of the basal ganglia. They are involved in the genesis of levodopa-induced dyskinesia and in the modulation of direct and indirect striatal output pathways that are disrupted in Parkinson's disease. One pharmacologic approach is to develop synthetic glycopeptides closely resembling endogenous peptides to restore their normal functions. Glycosylation promotes penetration of the blood-brain barrier. We investigated CNS penetration of the opioid glycopeptide MMP-2200, a mixed δ/μ-agonist based on leu-enkephalin, as measured by in vivo microdialysis and subsequent mass spectrometric analysis in awake, freely moving rats. The glycopeptide (10 mg/kg) reaches the dorsolateral striatum (DLS) rapidly after systemic (i.p.) administration and is stably detectable for the duration of the experiment (80 min). The detected level at the end of the experiment (around 250 pM) is about 10-fold higher than the level of the endogenous leu-enkephalin, measured simultaneously. This is one of the first studies to directly prove that glycosylation of an endogenous opioid peptide leads to excellent blood-brain barrier penetration after systemic injection, and explains robust behavioral effects seen in previous studies by measuring how much glycopeptide reaches the target structure, in this case the DLS.

Continuous dopaminergic stimulation: clinical aspects and experimental bases

In patients with Parkinson disease, pulsatile administration of dopaminergic drugs is associated with motor fluctuations and dyskinesias. By contrast, treatments that provide more continuous dopaminergic stimulation are associated with less intense motor complications. This can be achieved by using drugs with longer half-lives, delayed release formulations, and routes of administration that permit continuous delivery. The mechanisms by which different modes of dopaminergic treatment (pulsatile or continuous) determine the motor response are not fully understood. However, the use of experimental models of parkinsonism has helped understand the motor complications associated with pulsatile dopamine replacement. These studies have provided important insights into the biochemical and molecular changes in the basal ganglia in response to continuous stimulation. In addition, these models have facilitated the development of new treatments that may stabilize the motor response and the biochemical alterations in the basal ganglia to provide more efficient forms of continuous dopaminergic stimulation in patients with Parkinson disease.

Amantadine attenuates levodopa-induced dyskinesia in mice and rats preventing the accompanying rise in nigral GABA levels

Amantadine is the only drug marketed for treating levodopa-induced dyskinesia. However, its impact on basal ganglia circuitry in the dyskinetic brain, particularly on the activity of striatofugal pathways, has not been evaluated. We therefore used dual probe microdialysis to investigate the effect of amantadine on behavioral and neurochemical changes in the globus pallidus and substantia nigra reticulata of 6-hydroxydopamine hemi-lesioned dyskinetic mice and rats. Levodopa evoked abnormal involuntary movements (AIMs) in dyskinetic mice, and simultaneously elevated GABA release in substantia nigra reticulata (∼3-fold) but not globus pallidus. Glutamate levels were unaffected in both areas. Amantadine (40 mg/kg, i.p.), ineffective alone, attenuated (∼50%) AIMs expression and prevented the GABA rise. Moreover, it unraveled a facilitatory effect of levodopa on pallidal glutamate levels. Levodopa also evoked AIMs expression and a GABA surge (∼2-fold) selectively in the substantia nigra of dyskinetic rats. However, different from mice, glutamate levels rose simultaneously. Amantadine, ineffective alone, attenuated (∼50%) AIMs expression preventing amino acid increase and leaving unaffected pallidal glutamate. Overall, the data provide neurochemical evidence that levodopa-induced dyskinesia is accompanied by activation of the striato-nigral pathway in both mice and rats, and that the anti-dyskinetic effect of amantadine partly relies on the modulation of this pathway.

Effects of the novel glycopeptide opioid agonist MMP-2200 in preclinical models of Parkinson's disease

In Parkinson's disease (PD), the consequence of dopaminergic denervation is an imbalance in the activity of the direct and indirect striatofugal pathways, which include potentially important changes in opioid peptide expression and/or activity. The systemic administration of a novel glycosylated opioid peptide MMP-2200 (a.k.a. lactomorphin) was shown to have potent effects in two standard models of PD: 1) amphetamine-induced rotations in the hemi-Parkinsonian 6-hydroxydopamine (6-OHDA)-treated rat and 2) locomotion in the reserpine-treated rat. MMP-2200, an opioid mu and delta receptor agonist, reduced amphetamine-induced rotations in severely-lesioned hemi-Parkinsonian rats; this effect was fully blocked by naloxone, an opioid receptor antagonist. The selective δ-opioid receptor antagonist naltrindole only partially blocked the effect of MMP-2200. MMP-2200 alone did not induce rotations. This effect was also observed in a mild progressive rat 6-OHDA-lesion model. In animals treated with reserpine, profound akinesia was induced that was reversed with apomorphine. There was a prominent overshoot in animals that received apomorphine compared to non-reserpine treated animals, reflecting the well described phenomenon of dopamine supersensitivity indicating that apomorphine not only reversed akinesia but also induced hyper-kinesia. The opioid peptide MMP-2200 blocked the apomorphine-induced hyper-kinesia. This effect of MMP-2200 was prevented by pre-administration of naloxone. MMP-2200 had no effect in preventing the reserpine-induced akinesia, nor did it affect locomotion in control animals. Taken together, the results from these two models are consistent with the glycopeptide opioid agonist MMP-2200 having a potent effect on movements related to dopaminergic hyper-stimulation following striatal dopamine depletion that are best explained by a reduction in the downstream effects of dopamine agonists in these models.

Differential expression of FosB, c-Fos, and Zif268 in forebrain regions after acute or chronic L-DOPA treatment in a rat model of Parkinson's disease

A study was carried out to examine the effects of acute and chronic L-DOPA treatment on the distribution of the immediate-early gene (IEG) proteins (FosB, c-Fos, and Zif268) in forebrain regions in a unilateral 6-hydroxydopamine (6-OHDA) rat model of Parkinson's disease. During a course of chronic L-DOPA treatment (15 mg/day, 15 days), rats with a 6-OHDA lesion developed abnormal involuntary movements. Compared with the rats in the acute L-DOPA treatment group, those in the chronic treatment group had significantly more FosB-immunopositive cells in the anterior cingulate (Cg) and the dorsolateral caudate-putamen ipsilateral to the lesion and significantly fewer c-Fos-immunopositive cells in the Cg, the nucleus accumbens shell, and the basolateral nucleus of amygdala ipsilateral to the lesion. No significant difference was observed in the number of Zif268-immunopositive cells between the acute and chronic L-DOPA groups. In summary, differential expression of three IEG proteins was observed in the forebrain regions during a course of chronic L-DOPA treatment of 6-OHDA-treated hemiparkinsonian rats.

Phencyclidine (PCP)-induced disruption in cognitive performance is gender-specific and associated with a reduction in brain-derived neurotrophic factor (BDNF) in specific regions of the female rat brain

Phencyclidine (PCP), used to mimic certain aspects of schizophrenia, induces sexually dimorphic, cognitive deficits in rats. In this study, the effects of sub-chronic PCP on expression of brain-derived neurotrophic factor (BDNF), a neurotrophic factor implicated in the pathogenesis of schizophrenia, have been evaluated in male and female rats. Male and female hooded-Lister rats received vehicle or PCP (n=8 per group; 2 mg/kg i.p. twice daily for 7 days) and were tested in the attentional set shifting task prior to being sacrificed (6 weeks post-treatment). Levels of BDNF mRNA were measured in specific brain regions using in situ hybridisation. Male rats were less sensitive to PCP-induced deficits in the extra-dimensional shift stage of the attentional set shifting task compared to female rats. Quantitative analysis of brain regions demonstrated reduced BDNF levels in the medial prefrontal cortex (p<0.05), motor cortex (p<0.01), orbital cortex (p<0.01), olfactory bulb (p<0.05), retrosplenial cortex (p<0.001), frontal cortex (p<0.01), parietal cortex (p<0.01), CA1 (p<0.05) and polymorphic layer of dentate gyrus (p<0.05) of the hippocampus and the central (p<0.01), lateral (p<0.05) and basolateral (p<0.05) regions of the amygdaloid nucleus in female PCP-treated rats compared with controls. In contrast, BDNF was significantly reduced only in the orbital cortex and central amygdaloid region of male rats (p<0.05). Results suggest that blockade of NMDA receptors by sub-chronic PCP administration has a long-lasting down-regulatory effect on BDNF mRNA expression in the female rat brain which may underlie some of the behavioural deficits observed post PCP administration.

Role of dopamine D3 and serotonin 5-HT 1A receptors in L: -DOPA-induced dyskinesias and effects of sarizotan in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease

Sarizotan, a 5-HT(1A) agonist with additional affinity for D(3) and D(4) receptors, has been demonstrated to have anti-dyskinetic effects. The mechanism by which these effects occur is not clear. Using unilateral 6-hydroxydopamine-lesioned rats that received chronic intraperitoneal (ip) administration of L: -3,4-dihydroxyphenylalanine (L: -DOPA) we investigated the involvement of D(3) and 5-HT(1A) receptors in the effects of sarizotan on contraversive circling and abnormal involuntary movements (AIMs). Before sensitization by chronic L: -DOPA treatment (12.5 with 3.25 mg/kg benserazide ip, twice daily for 21 days), no effect of the selective D(3) agonist, PD128907 (1 or 3 mg/kg ip), or the selective D(3) antagonist, GR103691 (0.5 or 1.5 mg/kg ip), was observed. Treatment with sarizotan (1 or 5 mg/kg ip) dose-dependently inhibited the L: -DOPA-induced contraversive turning and AIMs. In co-treatment with the 5-HT(1A) antagonist, WAY100635 (1 mg/kg ip), sarizotan failed to affect this behaviour, confirming the prominent 5-HT(1A) receptor-mediated mechanism of action. In the presence of PD128907 (3 mg/kg ip), the effects of sarizotan on contraversive turning, locomotive dyskinesia and axial dystonia, but not on orolingual and forelimb dyskinesia, were blocked. On its own, PD128907 had no effect on the behavioural effects of L: -DOPA except that it tended to reduce orolingual and forelimb dyskinesia. GR103691 had no effect on its own or in combination with sarizotan. These data identify an involvement of D(3) receptors in the action of sarizotan on some, but not all L: -DOPA-induced motor side effects. This selective involvement is in contrast to the more general involvement of 5-HT(1A) receptors in the anti-dyskinetic effects of sarizotan.

Basal Ganglia circuits underlying the pathophysiology of levodopa-induced dyskinesia

Involuntary movements or dyskinesia, represent a debilitating complication of levodopa therapy for Parkinson's disease. Dyskinesia is, ultimately, experienced by the vast majority of the patients. Despite the importance of this problem, little was known about the cause of dyskinesia, a situation that has dramatically evolved in the last few years with a focus upon the molecular and signaling changes induced by chronic levodopa treatment. Departing from this, we here review the progress made in functional anatomy and neuroimaging that have had a tremendous impact on our understanding of the anatomo-functional organization of the basal ganglia in Parkinsonism and dyskinetic states, notably the demonstration that dyskinesia are linked to a pathological processing of limbic and cognitive information.

Deletion of adenosine A₁ or A(₂A) receptors reduces L-3,4-dihydroxyphenylalanine-induced dyskinesia in a model of Parkinson's disease

Adenosine A(₂A) receptor antagonism provides a promising approach to developing nondopaminergic therapy for Parkinson's disease (PD). Clinical trials of A(₂A) antagonists have targeted PD patients with L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID) in an effort to improve parkinsonian symptoms. The role of adenosine in the development of LID is little known, especially regarding its actions via A₁ receptors. We aimed to examine the effects of genetic deletion and pharmacological blockade of A₁ and/or A(₂A) receptors on the development of LID, on the induction of molecular markers of LID including striatal preprodynorphin and preproenkephalin (PPE), and on the integrity of dopaminergic nigrostriatal neurons in hemiparkinsonian mice. Following a unilateral 6-hydroxydopamine lesion A₁, A(₂A) and double A₁-A(₂A) knockout (KO) and wild-type littermate mice, and mice pretreated with caffeine (an antagonist of both A₁ and A(₂A) receptors) or saline were treated daily for 18-21 days with a low dose of L-DOPA. Total abnormal involuntary movements (AIMs, a measure of LID) were significantly attenuated (p<0.05) in A₁ and A(₂A) KOs, but not in A₁-A(₂A) KOs and caffeine-pretreated mice. An elevation of PPE mRNA ipsilateral to the lesion in WT mice was reduced in all KO mice. In addition, neuronal integrity assessed by striatal dopamine content was similar in all KOs and caffeine-pretreated mice following 6-hydroxydopamine lesioning. Our findings raise the possibility that A₁ or A(₂A) receptors blockade might also confer a disease-modifying benefit of reduced risk of disabling LID, whereas the effect of their combined inactivation is less clear.

From the cell to the clinic: a comparative review of the partial D₂/D₃receptor agonist and α2-adrenoceptor antagonist, piribedil, in the treatment of Parkinson's disease

Though L-3,4-dihydroxyphenylalanine (L-DOPA) is universally employed for alleviation of motor dysfunction in Parkinson's disease (PD), it is poorly-effective against co-morbid symptoms like cognitive impairment and depression. Further, it elicits dyskinesia, its pharmacokinetics are highly variable, and efficacy wanes upon long-term administration. Accordingly, "dopaminergic agonists" are increasingly employed both as adjuncts to L-DOPA and as monotherapy. While all recognize dopamine D(2) receptors, they display contrasting patterns of interaction with other classes of monoaminergic receptor. For example, pramipexole and ropinirole are high efficacy agonists at D(2) and D(3) receptors, while pergolide recognizes D(1), D(2) and D(3) receptors and a broad suite of serotonergic receptors. Interestingly, several antiparkinson drugs display modest efficacy at D(2) receptors. Of these, piribedil displays the unique cellular signature of: 1), signal-specific partial agonist actions at dopamine D(2)and D(3) receptors; 2), antagonist properties at α(2)-adrenoceptors and 3), minimal interaction with serotonergic receptors. Dopamine-deprived striatal D(2) receptors are supersensitive in PD, so partial agonism is sufficient for relief of motor dysfunction while limiting undesirable effects due to "over-dosage" of "normosensitive" D(2) receptors elsewhere. Further, α(2)-adrenoceptor antagonism reinforces adrenergic, dopaminergic and cholinergic transmission to favourably influence motor function, cognition, mood and the integrity of dopaminergic neurones. In reviewing the above issues, the present paper focuses on the distinctive cellular, preclinical and therapeutic profile of piribedil, comparisons to pramipexole, ropinirole and pergolide, and the core triad of symptoms that characterises PD-motor dysfunction, depressed mood and cognitive impairment. The article concludes by highlighting perspectives for clarifying the mechanisms of action of piribedil and other antiparkinson agents, and for optimizing their clinical exploitation.

Calcium-permeable AMPA receptors are involved in the induction and expression of l-DOPA-induced dyskinesia in Parkinson's disease

Overactivity of striatal alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors is implicated in the pathophysiology of L-DOPA-induced dyskinesia (LID) in Parkinson's disease (PD). In this study, we evaluated the behavioural and molecular effects of acute and chronic blockade of Ca(2+)-permeable AMPA receptors in animal models of PD and LID. The acute effects of the Ca(2+)-permeable AMPA receptor antagonist 1-trimethylammonio-5-(1-adamantane-methylammoniopentane) dibromide hydrobromide (IEM 1460) on abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat and LID in the MPTP-lesioned non-human primate were assessed. Subsequently, the effects of chronic treatment of 6-OHDA-lesioned rats with vehicle, L-DOPA/benserazide (6/15 mg/kg, i.p.) + vehicle or L-DOPA + IEM 1460 (3 mg/kg, i.p.) on behavioural and molecular correlates of priming for LID were evaluated. In the 6-OHDA-lesioned rat and MPTP-lesioned non-human primate, acute treatment with IEM 1460 (1-3 mg/kg) dose-dependently reduced LID without adverse effects on motor performance. Chronic co-treatment for 21 days with IEM 1460 reduced the induction of AIMs by L-DOPA in the 6-OHDA-lesioned rat without affecting peak rotarod performance, and attenuated AIMs score by 75% following l-DOPA challenge (p < 0.05). Chronic IEM 1460 treatment reversed L-DOPA-induced up-regulation of pre-proenkephalin-A, and normalised pre-proenkephalin-B mRNA expression in the lateral striatum, indicating an inhibition of both behavioural and molecular correlates of priming. These data suggest that Ca(2+)-permeable AMPA receptors are critically involved in both the induction and subsequent expression of LID, and represent a potential target for anti-dyskinetic therapies.

Metabotropic glutamate mGluR5 receptor blockade opposes abnormal involuntary movements and the increases in glutamic acid decarboxylase mRNA levels induced by l-DOPA in striatal neurons of 6-hydroxydopamine-lesioned rats

The present study examined the effect of a subchronic systemic administration of the glutamate metabotropic mGluR5 receptor antagonist MPEP on l-DOPA-induced dyskinesias and striatal gene expression in adult rats with a unilateral 6-OHDA lesion of dopamine neurons. The daily systemic administration of l-DOPA for 2 weeks induced a gradual increase in limb dyskinesia and axial dystonia. The subchronic systemic co-administration of MPEP reduced the severity of limb dyskinesia and axial dystonia over the whole duration of l-DOPA treatment. Subchronic l-DOPA administration was paralleled by a significant increase in mRNA levels of the two isoforms of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD67 and GAD65) and preprodynorphin (PPD). Single cell analysis on emulsion radioautographs indicated that l-DOPA-induced increases in GAD67 occurred predominantly in preproenkephalin-unlabeled striatonigral and, to a lesser extent, in preproenkephalin-labeled striatopallidal neurons. MPEP completely reversed the effects of l-DOPA on GAD67 and reduced the increases in GAD65 and PPD mRNA levels in striatonigral neurons. MPEP also reversed the small l-DOPA-induced increase in GAD67 mRNA levels in striatopallidal neurons. Altogether, the findings support the idea that the relative efficacy of mGluR5 receptor antagonists to oppose l-DOPA-induced abnormal involuntary movements involves an ability to oppose increases in GAD gene expression and GABA-mediated signaling in striatonigral and striatopallidal neurons. The results also confirm the potential usefulness of antagonists of mGluR5 receptors as adjuncts in the treatment of l-DOPA-induced dyskinesia in patients with Parkinson's disease.

Effect of acute and chronic physical exercise on patients with periodic leg movements

PURPOSE

Nonpharmacological interventions may lead to an improvement in sleep quality. The objective of our study was to evaluate the effects of acute intensive exercise and chronic exercise on sleep patterns in patients with periodic leg movements (PLM).

METHODS

The study involved acute and chronic exercise. The acute intensive exercise group consisted of 22 volunteers who underwent a maximum effort test and a polysomnography (PSG) on the same night. The chronic exercise group included 11 patients who performed 72 physical training sessions undergoing three PSG studies on the night of sessions 1, 36, and 72. Blood samples were collected from both acute and chronic groups for beta-endorphin dosage.

RESULTS

Our results showed that both forms of physical exercise lowered PLM levels. The acute physical exercise increased sleep efficiency, rapid eye movement (REM) sleep, and reduced wake after sleep onset, whereas the chronic physical exercise increased sleep efficiency, REM sleep, and reduced sleep latency. We also found a significant negative correlation between beta-endorphin release after acute intensive exercise and PLM levels (r = -0.63).

CONCLUSION

Physical exercise may improve sleep patterns and reduce PLM levels. The correlation between beta-endorphin release after acute intensive exercise and PLM levels might be associated with the impact physical exercise has on the opiodergic system. We suggest that physical exercise may be a useful nonpharmacological treatment for PLM.

Increased vulnerability to 6-hydroxydopamine lesion and reduced development of dyskinesias in mice lacking CB1 cannabinoid receptors

Motor impairment, dopamine (DA) neuronal activity and proenkephalin (PENK) gene expression in the caudate-putamen (CPu) were measured in 6-OHDA-lesioned and treated (L-DOPA+benserazide) CB1 KO and WT mice. A lesion induced by 6-OHDA produced more severe motor deterioration in CB1 KO mice accompanied by more loss of DA neurons and increased PENK gene expression in the CPu. Oxidative/nitrosative and neuroinflammatory parameters were estimated in the CPu and cingulate cortex (Cg). CB1 KO mice exhibited higher MDA levels and iNOS protein expression in the CPu and Cg compared to WT mice. Treatment with L-DOPA+benserazide (12 weeks) resulted in less severe dyskinesias in CB1 KO than in WT mice. The results revealed that the lack of cannabinoid CB1 receptors increased the severity of motor impairment and DA lesion, and reduced L-DOPA-induced dyskinesias. These results suggest that activation of CB1 receptors offers neuroprotection against dopaminergic lesion and the development of L-DOPA-induced dyskinesias.

Striatal alterations of secretogranin-1, somatostatin, prodynorphin, and cholecystokinin peptides in an experimental mouse model of Parkinson disease

The principal causative pathology of Parkinson disease is the progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta projecting to the striatum in the brain. The information regarding the expression of neuropeptides in parkinsonism is very limited. Here we have elucidated striatal neuropeptide mechanisms in experimental parkinsonism using the unilateral 6-hydroxydopamine model to degenerate dopamine neurons. A thoroughly controlled sample preparation technique together with a peptidomics approach and targeted neuropeptide sequence collections enabled sensitive detection, identification, and relative quantitation of a great number of endogenous neuropeptides. Previously not recognized alterations in neuropeptide levels were identified in the unilateral lesioned mice with or without subchronic 3,4-dihydroxy-L-phenylalanine administration, the conventional treatment of Parkinson disease. Several of these peptides originated from the same precursor such as secretogranin-1, somatostatin, prodynorphin, and cholecystokinin. Disease-related biotransformation of precursors into individual peptides was observed in the experimental model of Parkinson disease. Several previously unreported potentially biologically active peptides were also identified from the striatal samples. This study provides further evidence that neuropeptides take part in mediating the central nervous system failure associated with Parkinson disease.

Intermittent Dopaminergic stimulation causes behavioral sensitization in the addicted brain and parkinsonism

The gold standard therapy for Parkinson's disease (PD) consists in chronic administration of pulses of the dopamine (DA) precursor l-dihydroxyphenylalanine (l-DOPA). Although the main brain area which is DA-deficient is the dorsal striatum (more the putamen than the caudate nucleus), other DA-innervated brain regions (i.e., the ventral striatum and other limbic areas) are affected by systemic administration of l-DOPA. While such a therapy produces an increase in synaptic and nonsynaptic DA, which replace the neurotransmitter deficiency, peaks of extracellular DA in the course of disease progression produce abnormal involuntary movements related to behavioral sensitization. Methamphetamine (METH), a widely abused drug, is known to produce behavioral sensitization, related to DA release (more in the ventral than dorsal striatum as well as other limbic regions). The present review discusses the overlapping between these treatments, based on pulses of DA stimulation with an emphasis on the class of DA receptors; signal transduction pathways; rearranged expression of neurotransmitters, cotransmitters, and their receptors coupled with ultrastructural changes. In fact, all these levels of synaptic plasticity show a surprising homology following these treatments, posing the mechanisms of behavioral sensitization during DA-replacement therapy in PD very close to the neurobiological mechanisms operating during METH abuse. In line with this view is the growing evidence of addictive behaviors in PD patients during the course of DA-replacement therapy.

Implanted reuptake-deficient or wild-type dopaminergic neurons improve ON L-dopa dyskinesias without OFF-dyskinesias in a rat model of Parkinson's disease

OFF-L-dopa dyskinesias have been a surprising side-effect of intrastriatal foetal ventral mesencephalic transplantation in patients with Parkinson's disease. It has been proposed that excessive and unregulated dopaminergic stimulation of host post-synaptic striatal neurons by the grafts could be responsible for these dyskinesias. To address this issue we transplanted foetal dopaminergic neurons from mice lacking the dopamine transporter (DATKO) or from wild-type mice, into a rat model of Parkinson's disease and L-dopa-induced dyskinesias. Both wild-type and DATKO grafts reinnervated the host striatum to a similar extent, but DATKO grafts produced a greater and more diffuse increase in extra-cellular striatal dopamine levels. Interestingly, grafts containing wild-type dopaminergic neurons improved parkinsonian signs to a similar extent as DATKO grafts, but provided a more complete reduction of L-dopa induced dyskinesias. Neither DATKO nor wild-type grafts induced OFF-L-dopa dyskinesias. Behavioural and receptor autoradiography analyses demonstrated that DATKO grafts induced a greater normalization of striatal dopaminergic receptor supersensitivity than wild-type grafts. Both graft types induced a similar downregulation and normalization of PEnk and fosb/Deltafosb in striatal neurons. In summary, DATKO grafts causing high and diffuse extra-cellular dompamine levels do not per se alter graft-induced recovery or produce OFF-L-dopa dyskinesias. Wild-type dopaminergic neurons appear to be the most effective neuronal type to restore function and reduce L-dopa-induced dyskinesias.

Dopamine depletion and subsequent treatment with L-DOPA, but not the long-lived dopamine agonist pergolide, enhances activity of the Akt pathway in the rat striatum

Dysregulation of signaling pathways is believed to contribute to Parkinson's disease pathology and l-DOPA-induced motor complications. Long-lived dopamine (DA) agonists are less likely to cause motor complications by virtue of continuous stimulation of DA receptors. In this study, we compared the effects of the unilateral 6-hydroxydopamine lesion and subsequent treatment with l-DOPA and DA agonist pergolide on signaling pathways in rats. Pergolide caused less pronounced behavioral sensitization than l-DOPA (25 mg/kg, i.p., 10 days), particularly at lower dose (0.5 and 0.25 mg/kg, i.p.). Pergolide, but not l-DOPA, reversed lesion-induced up-regulation of preproenkephalin and did not up-regulate preprodynorphine or DA D3 receptor in the lesioned hemisphere. Pergolide was as effective as l-DOPA in reversing the lesion-induced elevation of ERK2 phosphorylation in response to acute apomorphine administration (0.05 mg/kg, s.c.). Chronic l-DOPA significantly elevated the level of Akt phosphorylation at both Thr(308) and Ser(473) and concentration of phosphorylated GSK3alpha, whereas pergolide suppressed the lesion- and/or challenge-induced supersensitive Akt responses. The data indicate that l-DOPA, unlike pergolide, exacerbates imbalances in the Akt pathway caused by the loss of DA. The results support the hypothesis that the Akt pathway is involved in long-term actions of l-DOPA and may be linked to l-DOPA-induced dyskinesia.