Off-line consolidation of motor sequence learning results in greater integration within a cortico-striatal functional network.

The consolidation of motor sequence learning is known to depend on sleep. Work in our laboratory and others have shown that the striatum is associated with this off-line consolidation process. In this study, we aimed to quantify the sleep-dependent dynamic changes occurring at the network level using a measure of functional integration. We directly compared changes in connectivity before and after sleep or the simple passage of daytime. As predicted, the results revealed greater integration within the cortico-striatal network after sleep, but not an equivalent daytime period. Importantly, a similar pattern of results was also observed using a data-driven approach; the increase in integration being specific to a cortico-striatal network, but not to other known functional networks. These findings reveal, for the first time, a new signature of motor sequence consolidation: a greater between-regions interaction within the cortico-striatal system.

Brain plasticity related to the consolidation of motor sequence learning and motor adaptation.

This study aimed to investigate, through functional MRI (fMRI), the neuronal substrates associated with the consolidation process of two motor skills: motor sequence learning (MSL) and motor adaptation (MA). Four groups of young healthy individuals were assigned to either (i) a night/sleep condition, in which they were scanned while practicing a finger sequence learning task or an eight-target adaptation pointing task in the evening (test) and were scanned again 12 h later in the morning (retest) or (ii) a day/awake condition, in which they were scanned on the MSL or the MA tasks in the morning and were rescanned 12 h later in the evening. As expected and consistent with the behavioral results, the functional data revealed increased test-retest changes of activity in the striatum for the night/sleep group compared with the day/awake group in the MSL task. By contrast, the results of the MA task did not show any difference in test-retest activity between the night/sleep and day/awake groups. When the two MA task groups were combined, however, increased test-retest activity was found in lobule VI of the cerebellar cortex. Together, these findings highlight the presence of both functional and structural dissociations reflecting the off-line consolidation processes of MSL and MA. They suggest that MSL consolidation is sleep dependent and reflected by a differential increase of neural activity within the corticostriatal system, whereas MA consolidation necessitates either a period of daytime or sleep and is associated with increased neuronal activity within the corticocerebellar system.

Striatal Akt/GSK3 signaling pathway in the development of L-Dopa-induced dyskinesias in MPTP monkeys.

L-Dopa treatment, the gold standard therapy for Parkinson's disease, is hampered by motor complications such as dyskinesias. Recently, impairment of striatal Akt/GSK3 signaling was proposed to play a role in the mechanisms implicated in development of L-Dopa-induced dyskinesias in a rodent model of Parkinson's disease. The present experiment investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys, the effects on Akt/GSK3 of chronic L-Dopa treatment inducing dyskinesias compared to L-Dopa with CI-1041 (NMDA receptor antagonist) or a low dose of cabergoline (dopamine D2 receptor agonist) preventing dyskinesias. The extensive dopamine denervation induced by MPTP was associated with a decrease by about half of phosphorylated Akt(Ser473) levels in posterior caudate nucleus, anterior and posterior putamen; smaller changes were observed for phosphorylated Akt(Thr308) levels that did not reach statistical significance. Dopamine depletion reduced phosphorylated GSK3beta(Ser9) levels, mainly in posterior putamen whereas pGSK3beta(Tyr216) and pGSK3alpha(Ser21) were unchanged. In posterior caudate nucleus, anterior and posterior putamen of dyskinetic L-Dopa-treated MPTP monkeys, pAkt(Ser473) and pGSK3beta(Ser9) were elevated whereas L-Dopa+cabergoline treated MPTP monkeys without dyskinesias had lower values in posterior striatum as vehicle-treated MPTP monkeys. In non-dyskinetic MPTP monkeys treated with L-Dopa+CI-1041, putamen pAkt(Ser473) and pGSK3beta(Ser9) levels remained elevated as in dyskinetic monkeys while in posterior caudate nucleus, these levels were low as vehicle-treated and lower than L-Dopa treated MPTP monkeys. Extent of phosphorylation of Akt and GSK3beta in putamen correlated positively with dyskinesias scores of MPTP monkeys; these correlations were higher with dopaminergic drugs (L-Dopa, cabergoline) suggesting implication of additional mechanisms and/or signaling molecules in the NMDA antagonist antidyskinetic effect. In conclusion, our results showed that in MPTP monkeys, loss of striatal dopamine decreased Akt/GSK3 signaling and that increased phosphorylation of Akt and GSK3beta was associated with L-Dopa-induced dyskinesias.

Contribution of night and day sleep vs. simple passage of time to the consolidation of motor sequence and visuomotor adaptation learning.

There is increasing evidence supporting the notion that the contribution of sleep to consolidation of motor skills depends on the nature of the task used in practice. We compared the role of three post-training conditions in the expression of delayed gains on two different motor skill learning tasks: finger tapping sequence learning (FTSL) and visuomotor adaptation (VMA). Subjects in the DaySleep and ImmDaySleep conditions were trained in the morning and at noon, respectively, afforded a 90-min nap early in the afternoon and were re-tested 12 h post-training. In the NightSleep condition, subjects were trained in the evening on either of the two learning paradigms and re-tested 12 h later following sleep, while subjects in the NoSleep condition underwent their training session in the morning and were re-tested 12 h later without any intervening sleep. The results of the FTSL task revealed that post-training sleep (day-time nap or night-time sleep) significantly promoted the expression of delayed gains at 12 h post-training, especially if sleep was afforded immediately after training. In the VMA task, however, there were no significant differences in the gains expressed at 12 h post-training in the three conditions. These findings suggest that "off-line" performance gains reflecting consolidation processes in the FTSL task benefit from sleep, even a short nap, while the simple passage of time is as effective as time in sleep for consolidation of VMA to occur. They also imply that procedural memory consolidation processes differ depending on the nature of task demands.

Motor sequence learning increases sleep spindles and fast frequencies in post-training sleep.

STUDY OBJECTIVES: To investigate polysomnographic (PSG) sleep and NREM sleep characteristics, including sleep spindles and spectral activity involved in offline consolidation of a motor sequence learning task. DESIGN: Counterbalanced within-subject design. SETTING: Three weekly visits to the sleep laboratory. PARTICIPANTS: Fourteen healthy participants aged between 20 and 30 years (8 women). INTERVENTIONS: Motor sequence learning (MSL) task or motor control (CTRL) task before sleep. MEASUREMENTS AND RESULTS: Subjects were trained on either the MSL or CTRL task in the evening and retested 12 hours later the following morning on the same task after a night of PSG sleep recording. Total number and duration of sleep spindles and spectral power between 0.5 and 24 Hz were quantified during NREM sleep. After performing the MSL task, subjects exhibited a large increase in number and duration of sleep spindles compared to after the CTRL task. Higher sigma (sigma; 13 Hz) and beta (beta; 18-20 Hz) spectral power during the post-training night's sleep were also observed after the MSL task. CONCLUSIONS: These results provide evidence that sleep spindles are involved in the offline consolidation of a new sequence of finger movements known to be sleep dependent. Moreover, they expand on prior findings by showing that changes in NREM sleep following motor learning are specific to consolidation (and learning), and not to nonspecific motor activity. Finally, these data demonstrate, for the first time, higher fast rhythms (beta frequencies) during sleep after motor learning.

Normalization of GABAA receptor specific binding in the substantia nigra reticulata and the prevention of L-dopa-induced dyskinesias in MPTP parkinsonian monkeys.

L-Dopa therapy in Parkinson's disease (PD) is counfounded by the development of involuntary movements such as L-Dopa-induced dyskinesias (LIDs). In this study GABA(A) receptor autoradiography was assessed using [(3)H]flunitrazepam binding to the benzodiazepine site of the GABA(A) receptor and [(35)S]t-butylbicyclophosphorothionate (TBPS) binding to the chloride channel of GABA(A) receptors in the substantia nigra reticulata (SNr) and subthalamic nucleus (STN). L-Dopa-treated parkinsonian monkeys experiencing LIDs were compared to animals in which LIDs was prevented by adjunct treatments with CI-1041, a selective antagonist of the NR1A/2B subtype of NMDA receptor, or low doses of the dopamine D2 receptor agonist, cabergoline. Our results demonstrated a decrease of GABA(A) receptor specific binding in the posterior part of the SNr in dyskinetic monkeys compared to nondyskinetic animals, while no modulation has been observed in the STN. These results provide evidence for the first time that pharmacological treatments preventing LIDs in nonhuman primate model of PD are associated with normalization of GABA(A) receptor-mediated signalling in the SNr.

mGluR5 metabotropic glutamate receptors and dyskinesias in MPTP monkeys.

Modulation of excessive glutamatergic transmission within the basal ganglia is considered as an alternative approach to reduce l-Dopa-induced dyskinesias (LIDs) in Parkinson's disease (PD). In this study receptor binding autoradiography of [3H]MPEP, a metabotropic glutamate receptor 5 (mGluR5) selective radioligand, was used to investigate possible changes in mGluR5 in the basal ganglia of l-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs was prevented by adjunct treatments. LIDs were associated with an increase of mGluR5 specific binding in the posterior putamen and pallidum (+41% and +56%) compared to controls. By contrast, prevention of dyskinesias was associated with an important decrease of mGluR5 specific binding in these areas (-37% and -48%) compared with dyskinetic animals. Moreover, an upregulation (+34%) of mGluR5 receptor binding was seen in the anterior caudate nucleus of saline treated MPTP monkeys. This study is the first to provide evidence that enhanced mGluR5 specific binding in the posterior putamen and pallidum may contribute to the pathogenesis of LIDs in PD.

Basal ganglia group II metabotropic glutamate receptors specific binding in non-human primate model of L-Dopa-induced dyskinesias.

L-Dopa-induced dyskinesias (LIDs), the disabling abnormal involuntary movements induced by chronic use of L-Dopa, limit the quality of life in Parkinson's disease (PD) patients. Modulation of group II metabotropic glutamate receptors (mGluR2/3) in the basal ganglia, a brain region critically involved in motor control, is considered as an alternative approach in therapy of PD. In this study, receptor binding autoradiography of [3H]LY341495, a mGluR2/3 selective radioligand, was used to investigate possible changes in mGluR2/3 in the basal ganglia of L-Dopa-treated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys having developed LIDs compared to animals in which LIDs were prevented by adjunct treatments with CI-1041, a selective antagonist of the NR1A/2B subtype of NMDA receptor, or low doses of the dopamine D2 receptor agonist, cabergoline. Our study is the first to provide evidence of: (1) the similar localization of [3H]LY341495 specific binding to mGluR2/3 in the primate basal ganglia as compared to receptor distribution measured by immunohistochemistry in human and rat as well as this ligand binding in intact rat brain; (2) no change of [3H]LY341495 specific binding in basal ganglia after nigrostriatal denervation by MPTP; and (3) a widespread reduction of [(3)H]LY341495 specific binding to mGluR2/3 in the caudate nucleus (-17% to -31%), putamen (-12% to -45%) and globus pallidus (-56 to -59%) of non-dyskinetic animals treated with L-Dopa+cabergoline as compared to controls, MPTP monkeys treated with saline, L-Dopa alone (dyskinetic) or L-Dopa+CI-1041 (non-dyskinetic). This study is the first to propose a close interaction between mGluR2/3 and dopamine D2 receptors activation in the basal ganglia.

Prevention of dyskinesia by an NMDA receptor antagonist in MPTP monkeys: effect on adenosine A2A receptors.

Adenosine A(2A) receptors (A(2A)R) have received increasing attention for the treatment of L-DOPA-induced dyskinesias in Parkinson disease. In the present study, A(2A)R messenger RNA (mRNA) and receptor-specific binding in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys were studied after treatment with L-DOPA and a selective NR1A/2B NMDA receptor antagonist, CI-1041. Four MPTP monkeys received L-DOPA/benserazide and all developed dyskinesias, whereas among the four MPTP monkeys who additionally received CI-1041, only one developed mild dyskinesias. Four normal monkeys and four MPTP-treated monkeys were also studied. All MPTP monkeys had similar striatal dopamine (DA) denervation. A(2A)R mRNA levels, measured by in situ hybridization, were increased in the rostral lateral caudate and putamen of saline-treated MPTP monkeys as well as in the caudal lateral and medial putamen when compared with those of controls. A(2A)R mRNA levels remained elevated in the rostral caudate and putamen of L-DOPA-treated MPTP monkeys when compared with those of controls. A(2A)R mRNA levels of L-DOPA + CI-1041-treated monkeys were at control levels and decreased in the lateral rostral caudate and caudal putamen when compared with those of L-DOPA-treated and saline-treated MPTP monkeys respectively. No change was measured in the caudal medial putamen and caudate nucleus. A(2A)Rs labeled by autoradiography with [(3)H]SCH-58261 had lower level in the L-DOPA + CI-1041-treated MPTP monkeys compared with saline- or L-DOPA-treated MPTP and control monkeys in the rostral lateral and medial caudate and the putamen. No effect of lesion or L-DOPA treatment was measured on [(3)H]SCH-58261-specific binding. These findings suggest that blockade of NMDA receptors could prevent the development of dyskinesias by altering A(2A)Rs.

Postmortem brain fatty acid profile of levodopa-treated Parkinson disease patients and parkinsonian monkeys.

Fatty acids play a critical role in brain function but their specific role in the pathophysiology of Parkinson disease (PD) and levodopa-induced motor complications is still unknown. From a therapeutic standpoint, it is important to determine the relation between brain fatty acids and PD because the brain fatty acid content depends on nutritional intake, a readily manipulable environmental factor. Here, we report a postmortem analysis of fatty acid profile by gas chromatography in the brain cortex of human patients (12 PD patients and nine Controls) as well as in the brain cortex of monkeys (four controls, five drug-naive MPTP monkeys and seven levodopa-treated MPTP monkeys). Brain fatty acid profile of cerebral cortex tissue was similar between PD patients and Controls and was not correlated with age of death, delay to autopsy or brain pH. Levodopa administration in MPTP monkeys increased arachidonic acid content (+7%; P < 0 .05) but decreased docosahexaenoic acid concentration (-15%; P < 0.05) and total n-3:n-6 polyunsaturated fatty acids ratio (-27%; P < 0.01) compared to drug-naive MPTP animals. Interestingly, PD patients who experienced motor complications to levodopa had higher arachidonic acid concentrations in the cortex compared to Controls (+13.6%; P < 0.05) and to levodopa-treated PD patients devoid of motor complications (+14.4%; P < 0.05). Furthermore, PD patients who took an above-median cumulative dose of levodopa had a higher relative amount of saturated fatty acids but lower monounsaturated fatty acids in their brain cortex (P < 0.01). These results suggest that changes in brain fatty acid relative concentrations are associated with levodopa treatment in PD patients and in a non-human primate model of parkinsonism.

Prevention of levodopa-induced dyskinesias by a selective NR1A/2B N-methyl-D-aspartate receptor antagonist in parkinsonian monkeys: implication of preproenkephalin.

Enkephalin is reported to play an important role in the pathophysiology of levodopa (LD) -induced dyskinesias. The present study investigated the effect of chronic treatment with a selective NR1A/2B N-methyl-D-aspartate (NMDA) receptor antagonist, CI-1041, on the expression of preproenkephalin-A (PPE-A) in brains of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) -treated monkeys in relation to the development of LD-induced dyskinesias. Four MPTP-monkeys received LD/benserazide alone; they all developed dyskinesias. Four other MPTP-monkeys received LD/benserazide plus CI-1041; only one of them developed mild dyskinesias at the end of the fourth week of treatment. Four normal monkeys and four saline-treated MPTP monkeys were also included. MPTP-treated monkeys had extensive and similar striatal dopamine denervation. An increase of PPE-A mRNA levels assayed by in situ hybridization was observed in the lateral putamen (rostral and caudal) and caudate nucleus (rostral) of saline-treated MPTP monkeys compared to controls, whereas no change or a small increase was observed in their medial parts. Striatal PPE-A mRNA levels remained elevated in LD-treated MPTP monkeys, whereas cotreatment with CI-1041 brought them back to control values. These findings suggest that chronic blockade of striatal NR1A/2B NMDA receptors with CI-1041 normalizes PPE-A mRNA expression and prevents the development of LD-induced dyskinesias in an animal model of Parkinson disease.

Naltrexone in the short-term decreases antiparkinsonian response to l-Dopa and in the long-term increases dyskinesias in drug-naïve parkinsonian monkeys.

Nigrostriatal dopaminergic denervation and levodopa therapy in animal models and in parkinsonian patients are associated with an enhanced opioid transmission in the striatum. The functional role of this increase has always been a subject of debate. In this study two groups of drug-naïve macaque monkeys with MPTP-induced parkinsonism were treated daily, during four weeks, with l-Dopa alone or l-Dopa plus naltrexone, a non-selective opioid receptor antagonist. The improvement of parkinsonism in all animals treated with l-Dopa alone was clearly displayed from the first day of treatment. By contrast, naltrexone co-treatment blocked the antiparkinsonian action of l-Dopa for 7-14 days. As soon as the therapeutical action of l-Dopa appeared in naltrexone-treated monkeys, the magnitude and duration of the antiparkinsonian response were similar in both groups. Furthermore, in animals treated with l-Dopa plus naltrexone the beginning of the therapeutical effect of l-Dopa was accompanied by the appearance of dyskinesias. In this group, the severity of dyskinesias during the third and fourth weeks of treatment was significantly higher than the group treated with l-Dopa alone. The results of the present study demonstrate that in de novo MPTP parkinsonian monkeys antagonizing the action of opioid receptors worsens the motor response to l-Dopa.

Relevance of the MPTP primate model in the study of dyskinesia priming mechanisms.

For nearly 20 years, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) primate model has allowed great strides to be made in our understanding of the maladaptive changes underlying the levodopa-related motor response complications occurring in most parkinsonian patients. Studies indicate that sustained dopamine D2 receptor occupancy can prevent and reverse existing dyskinesias. Recent experiments in levodopa-treated MPTP animals, co-administered either a threshold dose of cabergoline or a glutamate NMDA NR2B-selective antagonist (CI-1041), have afforded protection against dyskinesia, perhaps through presynaptic inhibition of glutamate release and blockade of supersensitive postsynaptic NMDA receptors in the striatum, respectively. Some of the biochemical events that have correlated with dyskinesias, namely upregulated GABA(A) receptors in the internal pallidum, rise in pre-proenkephalin-A gene expression in the striatum, and upregulated striatal glutamate ionotropic receptors and adenosine A(2a) receptors, may be counteracted by these preventive strategies.

Effect of a selective glutamate antagonist on L-dopa-induced dyskinesias in drug-naive parkinsonian monkeys.

Alterations of striatal glutamate receptors are believed to be responsible, at least in part, for the pathogenesis of L-dopa-induced dyskinesias (LID). To evaluate whether co-administration of CI-1041, a novel NMDA receptor antagonist selective for the NR1A/NR2B subtype, with L-dopa might prevent the appearance of this side effect, eight de novo parkinsonian monkeys were treated chronically orally with either L-dopa alone or L-dopa plus CI-1041 (n= 4 for each group). After 4 weeks of treatment with L-dopa alone, all four animals developed moderate dyskinesias either choreic or dystonic in nature. CI-1041 co-treatment completely prevented the induction of dyskinesias in three animals and only one monkey developed mild dyskinesias at the end of the fourth week of treatment in the L-dopa + CI-1041 group. The magnitude and duration of the antiparkinsonian action of L-dopa was similar in both groups. These results suggest that selective NMDA receptor antagonism may be interesting for managing LID in Parkinson's disease patients.

Motor-learning impairment by amantadine in healthy volunteers.

NMDA receptor antagonists impair learning and memory in animal models, presumably by inhibiting long-term potentiation in the motor cortex. Human studies are limited and restricted by the paucity of safe NMDA antagonists. Here, we investigated the contribution of glutamatergic neurotransmission to the capacity of acquiring motor-adaptation learning in humans. In a double-blind design, 200 mg of amantadine (a low-affinity NMDA receptor channel blocker) or a matching placebo were given orally to groups of 14 and 13 human healthy young volunteers, respectively. Blood samples were collected 3 h after treatment to assay plasma concentrations, and the subjects were then tested using a motor-adaptation paradigm consisting of an eight-target-pointing task. To rule out drug-related generalized impairments such sedation, tests measuring motor dexterity and attention were also administered pre- and post-treatment. Comparison of the mean performance levels on the motor-adaptation task revealed that subjects in the amantadine group performed at a lower level than those in the placebo group, but this difference did not reach significance. Interestingly, however, despite plasma amantadine concentrations being relatively low, ranging from 2.09 to 4.74 microM (mean=3.3 microM), they nevertheless correlated negatively with motor learning. Furthermore, when the amantadine group was divided into low-performance and high-performance subgroups, subjects in the former subgroup displayed mean amantadine concentrations 36% higher than the latter subgroup, and performed significantly worser than the placebo group. No change in performance was found on the motor-dexterity and attention tests. Altogether, our results lend support to the hypothesis that normal NMDA receptor function is necessary for the acquisition of motor adaptation.

Chronic treatment with small doses of cabergoline prevents dopa-induced dyskinesias in parkinsonian monkeys.

Levodopa continues to be the most effective agent for the symptomatic treatment of Parkinson's disease (PD). But over time, initial benefits decline in efficacy because of a rise in adverse effects such as dyskinesias. The pathophysiology of levodopa-induced dyskinesias (LID) is not completely understood, but it appears to result from deficient regulation by dopamine of corticostriatal glutamatergic inputs leading to a cascade of neurochemical changes in the striatum and the output pathways. In the present study, we examined if the addition of small doses of cabergoline (a long-acting D(2) receptor agonist) to levodopa could prevent LID. The major hypothesis is that sustained activation of postsynaptic D(2) receptors on medium spiny neurons even by small doses of cabergoline could prevent or reduce LID. The minor hypothesis, and the more controversial of the two, is that the long-acting stimulation by small doses of cabergoline could diminish the release of glutamate by the corticostriatal pathway and prevent LID. Eight MPTP-treated monkeys with a long-standing and stable parkinsonian syndrome and having never received dopaminergic agents were used. Two groups of four were treated for 1 month with levodopa/benserazide administered orally (100 mg/25 mg). The second group received in addition a threshold dose of cabergoline (dose ranging from 0.015 to 0.035 mg/kg, SC). During the treatment, we observed LID in the levodopa group but not in the group receiving levodopa+cabergoline. Furthermore, the combination produced a comparable antiparkinsonian effect in terms of quality but prolonged the duration (by 1 to 2 hours) and increased the locomotion (mean for 2 weeks congruent with 104%). Our data suggest that a small dose of a long-acting D(2) agonist combined with high doses of levodopa could be preventive of LID in patients with PD and could be an alternative to using antiglutamatergic agents for this purpose.