Inhibitory effect of MK-801 on amantadine-induced dopamine release in the rat striatum

Amantadine in Treatment of Dysthymia-The Pilot Case Series Study

Dysthymia is a common chronic mood disorder in which isolated symptoms of depression persist for at least 2 years. Despite the many medications recommended for the treatment of dysthymia, no recommendations have yet been made for the treatment of patients who fail to achieve clinical improvement. This justifies attempts to identify second-line drugs for the treatment of dysthymia. In an open and naturalistic case study, five patients diagnosed with dysthymia in whom at least one antidepressant treatment was ineffective were treated with amantadine. In the age- and gender-matched external control group, patients were treated with sertraline at 100 mg/day. Depressive symptoms were assessed using HDRS-17. Two men and three women were treated with 100 mg amantadine for 3 months with 3-5 months follow-up. After 1 month of treatment with amantadine, a significant reduction in the intensity of depressive symptoms was achieved in all patients, and the clinical improvement increased over the next 2 months of treatment. No deterioration in well-being was observed in any patient after discontinuation of amantadine. The effect of amantadine treatment was comparable to that of sertraline treatment in patients with dysthymia who improved with this drug. The present study indicates that amantadine is an effective and well-tolerated drug in the treatment of dysthymia. Amantadine may be associated with a quick improvement in symptoms in the treatment of dysthymia. Treatment with this drug seems to be associated with good tolerability and persistency of the therapeutic effect after the discontinuation of the treatment.

Amantadine Revisited: A Contender for Initial Treatment in Parkinson's Disease?

The best practice for the initiation of symptomatic motor treatment for Parkinson's disease is an ongoing topic of debate. Fueled by interpretation of the results of the LEAP and MED Parkinson's disease studies, many practitioners opt for early initiation of levodopa formulations, avoiding dopamine agonists to circumvent potential deleterious side effects, namely impulse control disorder. Compared with levodopa, monoamine oxidase inhibitors may lack necessary potency. Ignored in this academic debate is another therapeutic option for patients with Parkinson's disease requiring treatment initiation: amantadine. Amantadine was first reported effective in the treatment of Parkinson's disease in 1969 and several studies were published in the 1970s supporting its efficacy. Currently, amantadine is mainly utilized as an add-on therapy to mitigate levodopa-related dyskinesia and, more recently, new long-acting amantadine formulations have been developed, with new indications to treat motor fluctuations. Amantadine has not been reported to cause dyskinesia and is rarely implicated in impulse control disorder.

Are ion channels potential therapeutic targets for Parkinson's disease?

Parkinson's disease (PD) is primarily associated with the progressive neurodegeneration of the dopaminergic neurons in the substantia nigra region of the brain. The resulting motor symptoms are managed with the help of dopamine replacement therapies. However, these therapeutics do not prevent the neurodegeneration underlying the disease and therefore lose their effectiveness in managing disease symptoms over time. Thus, there is an urgent need to develop newer therapeutics for the benefit of patients. The release of dopamine and the firing activity of substantia nigra neurons is regulated by several ion channels that act in concert. Dysregulations of these channels cause the aberrant movement of various ions in the intracellular milieu. This eventually leads to disruption of intracellular signalling cascades, alterations in cellular homeostasis, and bioenergetic deficits. Therefore, ion channels play a central role in driving the high vulnerability of dopaminergic neurons to degenerate during PD. Targeting ion channels offers an attractive mechanistic strategy to combat the process of neurodegeneration. In this review, we highlight the evidence pointing to the role of various ion channels in driving the PD processes. In addition, we also discuss the various drugs or compounds that target the ion channels and have shown neuroprotective potential in the in-vitro and in-vivo models of PD. We also discuss the current clinical status of various drugs targeting the ion channels in the context of PD.

Istradefylline - a first generation adenosine A2A antagonist for the treatment of Parkinson's disease

Introduction It is now accepted that Parkinson's disease (PD) is not simply due to dopaminergic dysfunction, and there is interest in developing non-dopaminergic approaches to disease management. Adenosine A_2A receptor antagonists represent a new way forward in the symptomatic treatment of PD.Areas covered In this narrative review, we summarize the literature supporting the utility of adenosine A_2A antagonists in PD with a specific focus on istradefylline, the most studied and only adenosine A_2A antagonist currently in clinical use.Expert opinion: At this time, the use of istradefylline in the treatment of PD is limited to the management of motor fluctuations as supported by the results of randomized clinical trials and evaluation by Japanese and USA regulatory authorities. The relatively complicated clinical development of istradefylline was based on classically designed studies conducted in PD patients with motor fluctuations on an optimized regimen of levodopa plus adjunctive dopaminergic medications. In animal models, there is consensus that a more robust effect of istradefylline in improving motor function is produced when combined with low or threshold doses of levodopa rather than with high doses that produce maximal dopaminergic improvement. Exploration of istradefylline as a 'levodopa sparing' strategy in earlier PD would seem warranted.

Amantadine: reappraisal of the timeless diamond-target updates and novel therapeutic potentials

The aim of the current review was to provide a new, in-depth insight into possible pharmacological targets of amantadine to pave the way to extending its therapeutic use to further indications beyond Parkinson's disease symptoms and viral infections. Considering amantadine's affinities in vitro and the expected concentration at targets at therapeutic doses in humans, the following primary targets seem to be most plausible: aromatic amino acids decarboxylase, glial-cell derived neurotrophic factor, sigma-1 receptors, phosphodiesterases, and nicotinic receptors. Further three targets could play a role to a lesser extent: NMDA receptors, 5-HT3 receptors, and potassium channels. Based on published clinical studies, traumatic brain injury, fatigue [e.g., in multiple sclerosis (MS)], and chorea in Huntington's disease should be regarded potential, encouraging indications. Preclinical investigations suggest amantadine's therapeutic potential in several further indications such as: depression, recovery after spinal cord injury, neuroprotection in MS, and cutaneous pain. Query in the database http://www.clinicaltrials.gov reveals research interest in several further indications: cancer, autism, cocaine abuse, MS, diabetes, attention deficit-hyperactivity disorder, obesity, and schizophrenia.

GABAergic and glutamatergic effects on nigrostriatal and mesolimbic dopamine release in the rat

In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal and mesolimbic system was systematically assessed after pharmacological challenge with GABAA receptor (R) and and N-methyl d-aspartate (NMDA)R agonists and antagonists. In these studies, [123I]iodobenzamide binding to the D2/3R was mesured in nucleus accumbens (NAC), caudateputamen (CP), substantia nigra/ventral tegmental area (SN/VTA), frontal (FC), motor (MC) and parietal cortex (PC) as well as anterior (aHIPP) and posterior hippocampus (pHIPP) with small animal SPECT in baseline and after injection of either the GABAAR agonist muscimol (1 mg/kg), the GABAAR antagonist bicuculline (1 mg/kg), the NMDAR agonist d-cycloserine (20 mg/kg) or the NMDAR antagonist amantadine (40 mg/kg). Muscimol reduced D2/3R binding in NAC, CP, SN/VTA, THAL and pHIPP, while, after amantadine, decreases were confined to NAC, CP and THAL. In contrast, d-cycloserine elevated D2/3R binding in NAC, SN/VTA, THAL, frontal cortex, motor cortex, PC, aHIPP and pHIPP, while, after bicuculline, increases were confined to CP and THAL. Taken together, similar actions on regional dopamine levels were exterted by the GABAAR agonist and the NMDAR antagonist on the one side and by the GABAAR antagonist and the NMDAR agonist on the other, with agonistic action, however, affecting more brain regions. Thereby, network analysis suggests different roles of GABAARs and NMDARs in the mediation of nigrostriatal, nigrothalamocortical and mesolimbocortical dopamine function.

Differential effects of D-cycloserine and amantadine on motor behavior and D2/3 receptor binding in the nigrostriatal and mesolimbic system of the adult rat

D-cycloserine (DCS) and amantadine (AMA) act as partial NMDA receptor (R) agonist and antagonist, respectively. In the present study, we compared the effects of DCS and AMA on dopamine D_2/3R binding in the brain of adult rats in relation to motor behavior. D_2/3R binding was determined with small animal SPECT in baseline and after challenge with DCS (20 mg/kg) or AMA (40 mg/kg) with [¹²³I]IBZM as radioligand. Immediately post-challenge, motor/exploratory behavior was assessed for 30 min in an open field. The regional binding potentials (ratios of the specifically bound compartments to the cerebellar reference region) were computed in baseline and post-challenge. DCS increased D_2/3R binding in nucleus accumbens, substantia nigra/ventral tegmental area, thalamus, frontal, motor and parietal cortex as well as anterodorsal and posterior hippocampus, whereas AMA decreased D_2/3R binding in nucleus accumbens, caudateputamen and thalamus. After DCS, ambulation and head-shoulder motility were decreased, while sitting was increased compared to vehicle and AMA. Moreover, DCS increased rearing relative to AMA. The regional elevations of D_2/3R binding after DCS reflect a reduction of available dopamine throughout the mesolimbocortical system. In contrast, the reductions of D_2/3R binding after AMA indicate increased dopamine in nucleus accumbens, caudateputamen and thalamus. Findings imply that, after DCS, nigrostriatal and mesolimbic dopamine levels are directly related to motor/exploratory activity, whereas an inverse relationship may be inferred for AMA.

Efficacy and safety of amantadine for the treatment of L-DOPA-induced dyskinesia

L-DOPA induced dyskinesias (LIDs) may affect up to 40% of Parkinson's disease (PD) and impact negatively health-related quality of life. Amantadine has demonstrated significant antidyskinetic effects in animal PD models and in randomized double-blind placebo-controlled trials (RCTs) in patients with PD. These effects are thought to be related to the blockade of NMDA receptors modulating cortico-striatal glutamatergic-dopaminergic interactions involved in the genesis of LIDs. There are three pharmaceutical forms of amantadine currently available in the market: an oral immediate-release (IR) formulation, which is widely available; an extended-release (ER) formulation (ADS-5102) which has been recently developed and approved by the FDA; and an intravenous infusion (IV) solution, which is not commonly used in clinical practice. RCTs with amantadine IR or ER, involving more than 650 patients have shown consistent and long-lasting reductions in LIDs. Interestingly, ADS-5102 not only reduced LIDs, but also reduced significantly at the same time the duration of daily OFF-time, a unique finding compared with other antiparkinsonian medications that usually reduce time spent OFF at the cost of worsening of LIDs. Amantadine IR might also have possible effects on other PD symptoms such as apathy or fatigue. The most common adverse reactions with amantadine are constipation, cardiovascular dysfunction including QT prolongation, orthostatic hypotension and edema, neuropsychiatric symptoms such as hallucinations, confusion and delirium, nausea and livedo reticularis. Corneal degeneration is rare but critical. In summary, amantadine immediate and extended-release are effective and safe for the treatment of LIDs.

Initial treatment of Parkinson's disease in 2016: The 2000 consensus conference revisited

In 2000, a French consensus conference proposed guidelines for the treatment of Parkinson's disease (PD). Since then, new drugs have been concocted, new studies have been published and clinicians have become aware of some drug-induced adverse effects that were little known in the past. This has led us to reconsider the recommendations published 16 years ago. Thus, the aim of the present review is to present the recent data related to the different medications and non-pharmacological approaches available for PD, with a special focus on early-stage PD. Levodopa (LD), dopamine agonists (DAs), catechol-O-methyltransferase inhibitors (COMT-Is), anticholinergics, monoamine oxidase inhibitors (MAOB-Is) and amantadine have been considered, and their efficacy and safety for both motor as well as non-motor aspects are reported here. This has led to our proposal for a revised therapeutic strategy for the initiation of treatment in newly diagnosed PD patients, based on the available literature and the relative benefits/side effects balance.

Safety overview of FDA-approved medications for the treatment of the motor symptoms of Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is among the most common of the neurodegenerative disorders. Treatment is primarily focused on correcting neurotransmitter imbalances. Several classes of medication are available for this purpose.

AREAS COVERED

A Medline search was performed to gather information about the safety of the medications approved for the treatment of the motor symptoms of PD. This was supplemented with additional articles obtained from online sources and information provided by the FDA and the manufacturers. The focus of this review is the side-effect and safety profiles of carbidopa/levodopa, dopamine agonists, selective monoamine oxidase inhibitors, catechol-o-methyltransferase inhibitors, anticholinergics and amantadine.

EXPERT OPINION

Though serious side-effects may occur, as a group, the medications used for the treatment of PD motor symptoms tend to produce side-effects that are mild to moderate in nature, and that primarily reflect the focus on dopaminergic therapies. Care plans for Parkinson's patients should be approached based on the needs of the individual as disease presentation, lifestyle, level of disability, concurrent disease states and the presence of non-motor symptoms make each case unique. Patients and caregivers must have realistic expectations about the use of PD medications.

Amantadine ameliorates dopamine-releasing deficits and behavioral deficits in rats after fluid percussion injury

Aims

To investigate the role of dopamine in cognitive and motor learning skill deficits after a traumatic brain injury (TBI), we investigated dopamine release and behavioral changes at a series of time points after fluid percussion injury, and explored the potential of amantadine hydrochloride as a chronic treatment to provide behavioral recovery.

Materials and Methods

In this study, we sequentially investigated dopamine release at the striatum and behavioral changes at 1, 2, 4, 6, and 8 weeks after fluid percussion injury. Rats subjected to 6-Pa cerebral cortical fluid percussion injury were treated by using subcutaneous infusion pumps filled with either saline (sham group) or amantadine hydrochloride, with a releasing rate of 3.6mg/kg/hour for 8 weeks. The dopamine-releasing conditions and metabolism were analyzed sequentially by fast scan cyclic voltammetry (FSCV) and high-pressure liquid chromatography (HPLC). Novel object recognition (NOR) and fixed-speed rotarod (FSRR) behavioral tests were used to determine treatment effects on cognitive and motor deficits after injury.

Results

Sequential dopamine-release deficits were revealed in 6-Pa-fluid-percussion cerebral cortical injured animals. The reuptake rate (tau value) of dopamine in injured animals was prolonged, but the tau value became close to the value for the control group after amantadine therapy. Cognitive and motor learning impairments were shown evidenced by the NOR and FSRR behavioral tests after injury. Chronic amantadine therapy reversed dopamine-release deficits, and behavioral impairment after fluid percussion injuries were ameliorated in the rats treated by using amantadine-pumping infusion.

Conclusion

Chronic treatment with amantadine hydrochloride can ameliorate dopamine-release deficits as well as cognitive and motor deficits caused by cerebral fluid-percussion injury.

Amantadine improves gait in PD patients with STN stimulation

In advanced Parkinson's disease (PD), axial symptoms such as speech, gait, and balance impairment often become levodopa-unresponsive and they are difficult to manage, even in patients with subthalamic nucleus deep brain stimulation (STN-DBS). We anecdotally observed that oral administration of amantadine was very effective in treating both residual and stimulation-induced axial symptoms after bilateral STN-DBS in one PD patient. Therefore, we conducted a prospective multicenter observational study to evaluate the effects of amantadine on speech, gait and balance in PD patients with STN-DBS and incomplete axial benefit. Primary outcomes were changes in speech (UPDRS III, item 18), gait (item 29) and postural stability (item 30) with amantadine treatment compared to baseline. Secondary outcome was the patients' subjective scoring of axial symptoms with amantadine compared to baseline. Forty-six PD patients with STN-DBS were enrolled in the study and followed for 10.35 ± 8.21 months (median: 9.00; range: 1-31). The mean daily dose of amantadine was 273.44 ± 47.49 mg. Gait scores significantly improved (from 1.51 ± 0.89 to 1.11 ± 0.92, P = 0.015) with amantadine treatment, whereas postural stability and speech scores were similar before and after treatment. Thirty-five (76.1%) patients reported subjective improvement in speech, gait or balance with amantadine, whereas thirty (65.2%) patients reported improvement in gait and balance. In conclusion, our data suggest that amantadine may have new beneficial effects on axial symptoms in PD patients with STN-DBS.

Amphetamine-induced rotation in the transplanted hemi-parkinsonian rat--response to pharmacological modulation

The transplantation of dopamine rich foetal tissue into Parkinson's disease patients holds much promise as a therapeutic strategy. The functional efficiency of transplantation is often tested experimentally, by grafting rat derived embryonic ventral mesencephalon tissue suspensions into the denervated striatum of hemi-parkinsonian rats that were previously rendered dyskinetic with L-DOPA. The survival and integration of the grafts in rats can be assessed by a variety of behavioural tests, however amphetamine-induced rotations remain one of the most widely used and robust measures. In this test, dopamine released from the transplant typically drives net rotation in the contralateral direction, in contrast to the ipsilateral rotational bias seen post-lesion. It is unknown what contribution other neurotransmitter systems may make to this response. In this study we monitored amphetamine-induced rotation in transplanted rats that were co-administered a second pharmacological challenge with agents known to affect dopamine-mediated behavioural responses in this model. Both D₁ and D₂ receptor antagonism (by SCH23390 and raclopride respectively) reduced the rotational response. However the cannabinoid CB1 agonist WIN55,212-2 and α₁ and α₂ adrenergic receptor antagonist yohimbine had no effect on rotation. Interestingly, glutamatergic antagonists reduced (MTEP) or even reversed (MK-801) total net rotations. The serotoninergic 5-HT(1A) and 5-HT(1B) agonists (8-OH-DPAT and CP94253 respectively) altered the temporal profile of the rotational behaviour supporting a regulatory role. Although dopamine clearly drives the motor response, this data implicates both 5-HT and glutamate systems in its regulation.

Amantadine in the treatment of pathological gambling: a case report

Despite almost a decade of intense research, effective treatment strategies for Pathological Gambling (PG) remain very challenging. This paper details a case report suggesting that the treatment of PG may benefit from the use of the non-specific glutamate blocker amantadine. The drug was well-tolerated and effective, leading to a 43-64% reduction in severity of gambling symptoms (as measured with G-SAS). Our result is discussed in the context of the glutamatergic hypothesis of addiction and in light of previous observations on the potential impact of glutamatergic agents in the treatment of PG. The role of the dopaminergic system, and its interaction with the glutamatergic system, is also explored. Further studies are required to define the true benefits of amantadine for the treatment of PG.

The noradrenaline transporter as site of action for the anti-Parkinson drug amantadine

Amantadine is an established antiparkinsonian drug with a still unclear molecular site of action. In vivo studies on rodents, in vitro studies on tissue of rodents as well as binding studies on post mortem human tissue implicate monoamine transporters and NMDA receptors. In order to re-examine its action at human variants of these proteins on intact cells we established cells stably expressing the human NR1/2A NMDA-receptor, noradrenaline transporter (NAT) or dopamine transporter (DAT) and tested the activity of amantadine in patch-clamp, uptake, release, and cytotoxicity experiments. Amantadine was less potent in blockade of NMDA-induced inward currents than in blockade of noradrenaline uptake and in induction of inward currents in NAT expressing cells. It was 30 times more potent in blocking uptake in NAT- than in DAT cells. Amantadine induced NAT-mediated release at concentrations of 10-100 μM in superfusion experiments and blocked NAT-mediated cytotoxicity of the parkinsonism inducing neurotoxin 1-methyl-4-phenyl-pyridinium (MPP(+)) at concentrations of 30-300 μM, whereas 300-1000 μM amantadine was necessary to block NMDA-receptor mediated cytotoxicity. Similar to amphetamine, amantadine was inactive at α(2A)-adrenergic receptors and induced reverse noradrenaline transport by NAT albeit with smaller effect size. Thus, amantadine acted as "amphetamine-like releaser" with selectivity for the noradrenergic system. These findings and differences with memantine, which had been reported as less efficient antiparkinsonian drug than amantadine but in our hands was significantly more potent at the NMDA-receptor, suggest contributions from a noradrenergic mechanism in the antiparkinsonian action of amantadine.

The potent inhibitory effect of tipepidine on marble-burying behavior in mice

Our previous study revealed that centrally acting non-narcotic antitussives inhibited G-protein-coupled inwardly rectifying K(+) (GIRK) channel currents in brain neurons, and that the tipepidine antitussives had a novel antidepressive-like effect on rats. Furthermore, the antitussives revealed multiplexed ameliorating actions on intractable brain disease models. This study evaluated the therapeutic potential of tipepidine in obsessive-compulsive disorder (OCD) subjects using marble-burying behavior (MBB) tests in mice. In fact, OCD is classified as an anxiety disorder characterized by obsession or compulsion. Although selective 5-HT reuptake inhibitors (SSRIs) are considered first choice agents for the pharmacological treatment of OCD, 50% of patients with OCD failed to respond to SSRIs. The burying of harmless objects such as marbles by mice might reflect the formation of compulsive behavior. The results show that tipepidine reduced MBB in a dose-dependent manner. The effect of tipepidine was significant even at a dosage as small as 5 mg/kg. The tipepidine at 10 mg/kg s.c. nearly abolished MBB without reducing the locomotor activity in mice. It is particularly interesting that the dopamine D₂ antagonist or 5-HT(1A) antagonist partly inhibited the effect of tipepidine on MBB. The results suggest that tipepidine has more of a potent inhibitory effect on MBB, compared with known drugs used for the treatment of OCD, and that the tipepidine action mechanism might differ from that of known drugs.

Effects of glutamate-related drugs on marble-burying behavior in mice: implications for obsessive-compulsive disorder

Clinical evidence demonstrates altered glutamatergic neurotransmission in patients suffering from obsessive-compulsive disorder (OCD). We examined the effects of glutamate-related drugs on marble-burying behavior, which is an animal model of OCD. The uncompetitive N-methyl-d-aspartate (NMDA) antagonists memantine (10 mg/kg, i.p.) and amantadine (30 mg/kg, i.p.) significantly inhibited marble-burying behavior without affecting locomotor activity in mice. Similarly, the uncompetitive NMDA receptor antagonist 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine hydrogen maleate (MK-801, 0.3 mg/kg, i.p.) inhibited marble-burying behavior. However, MK-801 at the same dose markedly increased locomotor activity. By contrast, the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) and the glutamate release inhibitor riluzole showed no effect on marble-burying behavior and significant suppression of locomotor activity. MK-801 (0.3 mg/kg, i.p.) and memantine (10 mg/kg, i.p.) significantly disrupted prepulse inhibition as an operational measure of sensorimotor gating. By contrast, amantadine (30 mg/kg, i.p.) did not affect prepulse inhibition. These findings suggest that amantadine could be a useful drug for the treatment of OCD.

Subjective and cardiovascular effects of cocaine during treatment with amantadine and baclofen in combination

This study assessed the subjective and cardiovascular effects of relevant doses of cocaine administration during steady-state treatment of the combination of amantadine and baclofen compared to placebo. Participants included 8 healthy, male, cocaine-dependent, non-treatment-seeking individuals (age=36.6+/-5.9; 75% African American, 25% Caucasian; using cocaine for an average of 15.3+/-6.5 years). Data were collected prior to and following double-blind intravenous administration of 0 mg, 20 mg, and 40 mg of cocaine. Data were collected at baseline, following 5 days of treatment with placebo, and again following 5 days of treatment with a combination of amantadine 100 mg t.i.d. and baclofen 30 mg t.i.d. counterbalanced for order of medication and placebo in a cross-over design. Results showed no significant alterations to cardiovascular variables (heart rate, systolic and diastolic blood pressure) from treatment using combination medication or placebo in the presence of cocaine. Self-rated "desire" for cocaine was significantly lower during cocaine administrations while participants were receiving treatment with amantadine-baclofen compared to infusions while taking placebo medication, although there was no difference in the intensity of cocaine-induced euphoria, or reduction in the likelihood to use cocaine if given access. Study findings support the safety of the amantadine-baclofen combination treatment for cocaine dependence.

Modulation of human motor cortex excitability by single doses of amantadine

Amantadine-sulfate has been used for several decades to treat acute influenza A, Parkinson's disease (PD), and acute or chronic drug-induced dyskinesia. Several mechanisms of actions detected in vivo/in vitro including N-methyl-D-aspartate (NMDA)-receptor antagonism, blockage of potassium channels, dopamine receptor agonism, enhancement of noradrenergic release, and anticholinergic effects have been described. We used transcranial magnetic stimulation (TMS) to evaluate the effect of single doses of amantadine on human motor cortex excitability in normal subjects. Using a double-blind, placebo-controlled, crossover study design, motor thresholds, recruitment curves, cortical stimulation-induced silent period (CSP), short intracortical inhibition (ICI), intracortical facilitation (ICF), and late inhibition (L-ICI) in 14 healthy subjects were investigated after oral doses of 50 and 100 mg amantadine with single and paired pulse TMS paradigms. Spinal cord excitability was investigated by distal latencies and M-amplitudes of the abductor digiti minimi muscle. After intake of amantadine, a significant dose-dependent decrease of ICF was noticed as well as a significant increase of L-ICI as compared to placebo. The effect on ICF and L-ICI significantly correlated with amantadine serum levels. ICI was slightly increased after amantadine intake, but the effect failed to be significant. Furthermore, amantadine had no significant effects on motor thresholds, MEP recruitment curves, CSP, or peripheral excitability. In conclusion, a low dose of amantadine is sufficient in modulating human motor cortex excitability. The decrease of ICF and increase of L-ICI may reflect glutamatergic modulation or a polysynaptic interaction of glutamatergic and GABA-ergic circuits. Although amantadine has several mechanisms of action, the NMDA-receptor antagonism seems to be the most relevant effect on cortical excitability. As L-ICI can be influenced by this type of drug, it may be an interesting parameter for studies of motor learning and use-dependent plasticity.

Effect of Amantadine on Depressive Symptoms in Chronic Hepatitis C Patients Treated with Pegylated Interferon

OBJECTIVE

Assess the effect of amantadine on depressive symptoms during interferon alfa therapy for hepatitis C virus infection.

METHODS

We performed a randomized, controlled trial with 14 hepatitis C virus-infected patients, treated with pegylated interferon alfa-2a 180 microg/wk plus ribavirin 1.200 mg/d. Eight patients were randomized to receive amantadine 200 mg/d, and 6 other individuals were randomized to control group without amantadine. Severity of depression and anxiety was measured using the Hospital Anxiety and Depression Scale, before starting re-treatment, and 4, 12, and 24 weeks after immunotherapy with pegylated interferon alfa-2a. Evaluations were performed by psychiatrists blinded in reference to the state of amantadine treatment. Friedman chi(2) test for repeated measures and Mann-Whitney test for nonparametric data were used to assess significant differences.

RESULTS

From baseline to follow-up, no significant increase in mean Hospital Anxiety and Depression Scale scores of depressive symptoms were seen in amantadine group (P = 0.142), meanwhile there was a statistical increase of depression scores in the control group (P = 0.001).

CONCLUSIONS

Our randomized pilot study, though small, clearly indicates that interferon alfa-induced depressive symptoms can be prevented by the use of amantadine. However, double-blind placebo-controlled trials with a higher sample size are required to confirm these preliminary findings.

Dopamine and NMDA systems modulate long-term nociception in the rat anterior cingulate cortex

The anterior cingulate cortex (ACC) plays a key role in pain processing. It has been reported that increased activity of glutamatergic projections into the ACC intensifies nociception; whereas dopaminergic projections inhibit it. The aim of this study was to evaluate the role of dopaminergic and NMDA systems of the ACC in the modulation of long-term nociception elicited by sciatic denervation in the rat. Score, onset and incidence of long-term nociception were measured by the autotomy behavior. The effects of a single microinjection into the ACC of different doses of dopamine (100 nM, 100 microM and 100 mM), a NMDA receptor antagonist (MK801 200 nM and 9.34 mM) and amantadine, a dopamine agonist and NMDA receptor antagonist (10, 100 and 1000 microM) were tested on long-term nociception. Dopamine diminished autotomy behavior in an inverse dose-dependent manner, with dopamine 100 nM as most effective concentration. MK801 and amantadine elicited a significant reduction on autotomy score. Prior injections of D1 and D2 receptor antagonists blocked the antinociceptive effects of amantadine on long-term nociceptive behavior. The present study suggests an interaction between dopaminergic and glutamatergic systems within the ACC in the genesis and maintenance of long-term nociception.

Levetiracetam Potentiates the Antidyskinetic Action of Amantadine in the 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-Lesioned Primate Model of Parkinson's Disease

Levetiracetam (LEV) (Keppra; UCB Pharma, Brussels, Belgium) has recently been reported to have antidyskinetic activity against levodopa (L-DOPA)-induced dyskinesia in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmoset and macaque models of Parkinson's disease. Amantadine is frequently used as adjunctive therapy for L-DOPA-induced dyskinesia, but adverse effects limit its clinical utility. The current study was designed to investigate whether LEV can potentiate the antidyskinetic action of amantadine. The antiparkinsonian and antidyskinetic effects of LEV (13 and 60 mg/kg) and amantadine (0.01, 0.03, 0.1, and 0.3 mg/kg), administered alone and in combination, were assessed in the MPTP-lesioned marmoset model of L-DOPA-induced dyskinesia (n = 12). LEV (60 mg/kg) and amantadine (0.3 mg/kg) administered alone significantly reduced l-DOPA-induced dyskinesia without compromising the antiparkinsonian action of l-DOPA. Lower doses were without any significant effects. The combination of LEV (60 mg/kg) and amantadine (0.01, 0.03, 0.1, and 0.3 mg/kg) significantly decreased dyskinesia severity, without compromising the antiparkinsonian action of L-DOPA, more efficaciously than LEV or amantadine monotherapy. These results support the concept that normalization of different pathophysiological mechanisms (i.e., altered synchronization between neurons and enhanced N-methyl-D-aspartate transmission) has a greater efficacy. Combined LEV/amantadine therapy might be useful as an adjunct to L-DOPA to treat dyskinetic side effects and to expand the population of Parkinson's disease patients who benefit from treatment with amantadine alone.

Siah-1 facilitates ubiquitination and degradation of synphilin-1

Parkinson's disease is a common neurodegenerative disorder characterized by loss of dopaminergic neurons and appearance of Lewy bodies, cytoplasmic inclusions that are highly enriched with ubiquitin. Synphilin-1, alpha-synuclein, and Parkin represent the major components of Lewy bodies and are involved in the pathogenesis of Parkinson's disease. Synphilin-1 is an alpha-synuclein-binding protein that is ubiquitinated by Parkin. Recently, a mutation in the synphilin-1 gene has been reported in patients with sporadic Parkinson's disease. Although synphilin-1 localizes close to synaptic vesicles, its function remains unknown. To investigate the proteins that interact with synphilin-1, the present study performed a yeast two-hybrid screening and identified a novel interacting protein, Siah-1 ubiquitin ligase. Synphilin-1 and Siah-1 proteins were endogenously expressed in the central nervous system and were found to coimmunoprecipitate each other in rat brain homogenate. Confocal microscopic analysis revealed colocalization of both proteins in cells. Siah-1 was found to interact with the N terminus of synphilin-1 through its substrate-binding domain and to specifically ubiquitinate synphilin-1 via its RING finger domain. Siah-1 facilitated synphilin-1 degradation via the ubiquitin-proteasome pathway more efficiently than Parkin. Siah-1 was found to not facilitate ubiquitination and degradation of wild type or mutant alpha-synuclein. Synphilin-1 inhibited high K+-induced dopamine release from PC12 cells. Siah-1 was found to abrogate the inhibitory effects of synphilin-1 on dopamine release. Such findings suggest that Siah-1 might play a role in regulation of synphilin-1 function.

Amantadine increases L-DOPA-derived extracellular dopamine in the striatum of 6-hydroxydopamine-lesioned rats

We investigated the effect of amantadine on L-DOPA-derived extracellular dopamine (DA) levels and aromatic L-amino acid decarboxylase (AADC) activity in the striatum of rats with nigrostriatal dopaminergic denervation by 6-hydroxydopamine (6-OHDA). Pretreatment with 30 mg/kg amantadine increased the cumulative amount of extracellular DA in the striatum of 6-OHDA-lesioned rats treated with 10 mg/kg benserazide and 50 mg/kg L-DOPA to 250% of that without amantadine (P<0.01). Under pretreatment with 10 mg/kg benserazide, AADC activity after 30 mg/kg amantadine administration was reduced to 43% of controls (P<0.01). Amantadine-induced increase in L-DOPA-derived extracellular DA provides the basis for the clinical usefulness of amantadine in combination with L-DOPA. However, the effect of amantadine on L-DOPA-derived extracellular DA may not be caused by changes in AADC activity.

Amantadine in Parkinson's disease

BACKGROUND

Although levodopa is the most common drug prescribed to relieve the symptoms of Parkinson's disease it is associated with motor and psychiatric side-effects. Consequently, interest has turned to alternative drugs with improved side-effect profiles to replace or augment levodopa. Amantadine, originally used as an antiviral drug, has been shown to improve the symptoms of Parkinson's disease.

OBJECTIVES

To compare the efficacy and safety of amantadine therapy (monotherapy or adjuvant therapy) versus placebo in treating people with Parkinson's disease.

SEARCH STRATEGY

Electronic searches of The Cochrane Controlled Trials Register (The Cochrane Library Issue 3, 2001), MEDLINE (1966-2001), EMBASE (1974-2001), SCISEARCH (1974-2001), BIOSIS (1993-2001), GEROLIT (1979-2001), OLDMEDLINE (1957-1965), LILACS (1982-2001), MedCarib (17th Century - 2001), PASCAL (1973-2001), JICST-EPLUS (1985-2001), RUSSMED (1973-2001), DISSERTATION ABSTRACTS (2000-2001), SIGLE (1980-2001), ISI-ISTP (1990-2001), Aslib Index to Theses (2001), Clinicaltrials.gov (2001), metaRegister of Controlled Trials (2001), NIDRR (2001) and NRR (2001) were conducted. Grey literature was hand searched and the reference lists of identified studies and reviews examined. The manufacturers of amantadine were contacted.

SELECTION CRITERIA

Randomised controlled trials comparing amantadine with placebo in the treatment of patients with a clinical diagnosis of idiopathic Parkinson's disease.

DATA COLLECTION AND ANALYSIS

Data was abstracted independently by NC and KD onto standardised forms and disagreements were resolved by discussion.

MAIN RESULTS

Six randomised controlled trials were found comparing amantadine monotherapy or adjuvant therapy with placebo in the treatment of idiopathic Parkinson's disease. Five examined amantadine as adjuvant therapy with optimal levels of levodopa or anticholinergics and one examined amantadine as an adjuvant therapy with minimum tolerated levels of anticholinergics or as a monotherapy. Five were double-blind cross-over studies and one was a double-blind parallel group study. In total they examined 215 patients. The parallel group study allowed the randomisation codes to be broken and allowed patients in the placebo group to then receive amantadine. This could have led to bias. One study did not present the results of the placebo arm of the trial, hence we could not determine the difference between the two treatment groups. Two cross-over studies presented the results of the combined data from both treatment and placebo arms. The risk of carry-over effect into the second arm meant that these results could not be analysed. The final two studies presented at least some of their data from the end of the first arm of the trials. However only means were given, without standard deviations, so we could not determine the statistical significance of any difference between the amantadine and placebo groups. Although the authors did report on the side-effects from amantadine (such as livido recticularis, dry mouth and blurred vision), they state that none of them were severe.

REVIEWER'S CONCLUSIONS

A considerable amount of evidence on the effectiveness of amantadine has accrued from non-controlled trials, often in patients with Parkinsonian conditions other than idiopathic Parkinson's disease. However, rigorous analysis of the six randomised controlled trials of amantadine reveals insufficient evidence of its efficacy and safety in the treatment of idiopathic Parkinson's disease.

Increased dopamine uptake in striatal synaptosomes after treatment of rats with amantadine

The aim of the present study was to investigate the effect of short- and long-term treatments with amantadine on the activity of the neuronal dopamine transporter (DAT) in the rat striatum. For this purpose, the [3H]dopamine uptake was measured in striatal synaptosomes prepared from rats treated for 2, 7 and 14 days with amantadine (40 mg/kg; i.p.). After 7 days of treatment, amantadine increased the apparent V(max) by 30% without modification of the apparent K(m) of dopamine uptake whereas no change in these parameters was observed after 2 and 14 days treatment. Binding assays conducted with [3H]GBR-12935 on membranes prepared from animals treated with amantadine revealed no difference in the density and the affinity of striatal DAT binding sites as compared to control. This indicates that the increased dopamine uptake was not reflecting a modification at the level of the DAT expression. The activity of the DAT is regulated by phosphorylation and one may propose that ionotropic glutamate receptors present on presynaptic terminals directly modulate this phosphorylation. An indirect mechanism would involve presynaptic dopamine receptors that control the activity of the DAT in response to the increased dopamine concentration in the synaptic cleft.

Effects of (S)-ketamine on striatal dopamine: a [11C]raclopride PET study of a model psychosis in humans

Administration of the N-methyl-D-aspartate (NMDA) antagonist S-ketamine in normals produces a psychosis-like syndrome including several positive and negative symptoms of schizophrenic disorders (Abi-Saab WM, D'Souza DC, Moghaddam B, Krystal JH. The NMDA antagonist model for schizophrenia: promise and pitfalls. Pharmacopsychiatry 1998;31:104-109). Given the clinical efficacy of dopamine (DA) D2 receptor antagonists in the treatment of positive symptoms, it is conceivable that S-ketamine-induced psychotic symptoms are partially due to a secondary activation of dopaminergic systems. To date, animal and human studies of the effects of NMDA antagonists on striatal DA levels have been inconsistent. The present study used positron emission tomography (PET) to determine whether a psychotomimetic dose of S-ketamine decreases the in vivo binding of [11C]raclopride to striatal DA D2 receptors in humans (n = 8). S-ketamine elicited a psychosis-like syndrome, including alterations in mood, cognitive disturbances, hallucinations and ego-disorders. S-ketamine decreased [11C]raclopride binding potential (BP) significantly in the ventral striatum (-17.5%) followed by the caudate nucleus (-14.3%) and putamen (-13.6%), indicating an increase in striatal DA concentration. The change in raclopride BP in the ventral striatum correlated with heightened mood ranging from euphoria to grandiosity. These results provide evidence that the glutamatergic NMDA receptor may contribute to psychotic symptom formation via modulation of the DA system.

Stimulation of dopa decarboxylase activity in striatum of healthy human brain secondary to NMDA receptor antagonism with a low dose of amantadine

The efficacy of amantadine in alleviating motor symptoms of Parkinson's disease may be mediated in part by stimulation of cerebral dopa decarboxylase (DDC) activity, secondary to antagonism of N-methyl-D-aspartate (NMDA) type glutamate receptors. We tested the specific hypothesis that amantadine increases the decarboxylation rate of 6-[(18)F]fluoro-L-DOPA (FDOPA), an exogenous substrate for DDC, in healthy human brain. Radioactivity concentrations in brain tissue of neurologically normal volunteers (n = 5) injected intravenously with FDOPA ( approximately 4.5 mCi) were recorded by positron emission tomography (PET) for 120 min, first in a baseline condition, and again following three consecutive days of treatment with amantadine (100 mg/day, p.o.). Data from four telencephalic regions of interest containing appreciable DDC activity were analyzed with the tissue slope-intercept plot, using cerebellar cortex as the reference tissue, to estimate a coefficient of in situ FDOPA decarboxylation (k(3)(r), min(-1)). Mean estimates of k(3)(r) were increased following amantadine treatment in caudate nucleus (+12%), putamen (+28%), ventral striatum (+27%), and frontal cortex (+9%). For an initial confidence level of 95%, paired one-sided Student's t-tests with Bonferroni correction for multiple comparisons revealed a statistically significant drug effect in ventral striatum. Present results are consistent with stimulation of DDC activity in striatum of healthy human brain secondary to NMDA receptor antagonism with a low dose of amantadine, and suggest that this response is an important mechanism underlying the anti-parkinsonian properties of amantadine. Nonetheless, PET studies in parkinsonian patients using higher, clinically effective doses of amantadine may reveal more pronounced enhancements of cerebral DDC activity.

Effects of cocaine, nicotine, dizocipline and alcohol on mice locomotor activity: cocaine-alcohol cross-sensitization involves upregulation of striatal dopamine transporter binding sites

We investigated if repeated administration of cocaine, nicotine, dizocipline (MK-801) and alcohol yields behavioral cross-sensitization between these agents. Swiss Webster mice received in their home cage one of the following intraperitoneal (i. p.) injections for 5 consecutive days: (a) saline, (b) cocaine (20 mg/kg), (c) nicotine (0.5 mg/kg), (d) MK-801 (0.3 mg/kg) and (e) ethanol (2.0 g/kg). After a 10-day drug free period, each group (n=30) was divided into three subgroups (n=10) and received challenge injections of either cocaine, nicotine or MK-801. The horizontal and vertical movements of the mice were recorded in locomotor activity cages (test cage). Among the various drugs tested, only the cocaine and ethanol experienced mice developed sensitization to a challenge injection of cocaine; MK-801 pretreated mice showed a sensitized response only to a challenge injection of MK-801. In a second experiment, mice in their home cages received (a) saline, (b) cocaine (20 mg/kg) or (c) ethanol (2.0 g/kg) for 5 days, and challenged with an i.p. ethanol injection (2.0 g/kg) after a 10-day drug free period. Both, cocaine and ethanol experienced mice developed marked sensitization to ethanol challenge compared with the saline experienced mice. Assessment of the densities of striatal dopamine transporter (DAT) sites (by [3H]mazindol binding) 11 days after the extinction of repeated treatment with either cocaine or ethanol revealed a significant increase (71-108%) in the number of DAT binding sites. Thus, among the various psychostimulants investigated in the present study cross-sensitization between cocaine and ethanol was only observed. The behavioral sensitization we measured was primarily 'drug-dependent', rather than 'context-dependent', because animals were exposed to the test cage only once. The finding that cocaine- and ethanol-induced behavioral sensitization is associated with upregulation of striatal DAT binding sites supports the hypothesis that similar neural substrates are involved in the psychomotor/rewarding effects of cocaine and alcohol.