Locomotor effects of amantadine in the mouse are not those of a typical glutamate antagonist

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.

A novel adenosine A(1) and A(2A) receptor antagonist ASP5854 ameliorates motor impairment in MPTP-treated marmosets: comparison with existing anti-Parkinson's disease drugs

Recent evidence indicates that adenosine A(2A) receptor antagonists hold therapeutic potential for the treatment of Parkinson's disease (PD). A study on the novel adenosine A(1) and A(2A) receptor dual antagonist 5-[5-amino-3-(4-fluorophenyl)pyrazin-2-yl]-1-isopropylpyridine-2(1H)-one (ASP5854) showed it to be effective in various rodents models of PD and cognition. In the present study, we further investigated the potential of ASP5854 as an anti-PD drug using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets, which is a highly predictive model of clinical efficacy in PD, and compared its effect with those of existing anti-PD drugs. ASP5854 significantly and dose-dependently improved the total motor disability score for 7h at doses higher than 1mg/kg, and significantly increased total locomotor activity at doses higher than 0.1mg/kg without adverse effects. l-3,4-Dihydroxyphenylalanine+benserazide and bromocriptine also significantly improved the motor disability score and the hypolocomotion caused by MPTP treatment in a dose-dependent fashion. This amelioration was significant at 32+8 and 10-32 mg/kg, respectively, although bromocriptine induced severe emesis. Trihexiphenidyl also significantly improved the total motor disability score at doses of 10-32 mg/kg; however, while a significant increase in the total locomotor activity was observed at 10mg/kg, the drug induced ataxia-like behavior at 32 mg/kg. On the other hand, neither selegiline nor amantadine improved the total motor disability and hypolocomotion. These data substantiate the evidence that the novel adenosine antagonist ASP5854 exerts comparable anti-PD activity with existing anti-PD drugs, which indicates that ASP5854 might have potential to ameliorate motor deficits in PD.

Behavioral effects of aminoadamantane class NMDA receptor antagonists on schedule-induced alcohol and self-administration of water in mice

RATIONALE

Aminoadamantanes represent a class of NMDA glutamate receptor antagonists that reduce alcohol consumption and may prevent alcohol-induced neuronal adaptations and side effects.

OBJECTIVE

Behavioral specificity of memantine and amantadine on alcohol drinking in a schedule-induced polydipsia (SIP) task was investigated in mice.

METHODS

Male C57BL/6J mice were food-deprived and divided into four groups: 5% alcohol SIP, water SIP, 1 h limited access regulatory water drinking, and a control group to determine if either drug altered ethanol drinking. Behavioral specificity of memantine (5, 10, and 25 mg/kg, ip) and amantadine (20, 40, and 60 mg/kg, ip) was determined by comparing alterations in alcohol or water consumption in SIP and regulatory water drinking. Drug effects on SIP drinking-specific measures (grams per kilogram consumption) were also compared to nondrinking measures (locomotion, head-entries for food, and lick efficiency).

RESULTS

Compared to saline, memantine reduced alcohol SIP drinking (10 and 25 mg/kg). Memantine increased locomotion during alcohol SIP (25 mg/kg) and during water SIP (5 and 25 mg/kg). In contrast, amantadine reduced both alcohol SIP (40 mg/kg) and water SIP (40 and 60 mg/kg). Both drugs reduced regulatory water consumption over the entire dose range tested. Blood alcohol concentrations indicated consumption of physiologically meaningful amounts of alcohol during SIP, and that changes in alcohol metabolism did not account for drug-induced reductions in alcohol drinking.

CONCLUSIONS

In addition to reducing alcohol drinking, both drugs had other behavioral effects that included reductions in regulatory drinking. These results suggest that the therapeutic utility of these drugs for ameliorating human alcohol addiction remains questionable.

Involvement of the sigma 1 receptor in the modulation of dopaminergic transmission by amantadine

Pharmacological effects of amantadine on dopaminergic transmission are proposed to result from an uncompetitive antagonism at glutamate N-methyl-D-aspartate (NMDA) receptors. However, our previous studies examining amantadine-mediated dopamine receptor regulation in the rat striatum revealed a discrepancy from a direct interference with glutamate transmission. Preliminary in vitro binding data from the literature suggested the interaction of amantadine with the sigma1 receptor. Therefore, we have now further characterized the pharmacological properties of amantadine and memantine at this receptor and investigated its involvement in the modulation of striatal dopaminergic transmission. Our binding studies using [3H]-(+)SKF-10,047 indicated that amantadine and memantine behave as ligands of the sigma(1) receptor in rat forebrain homogenates (Ki values of 7.44 +/- 0.82 and 2.60 +/- 0.62 microm, respectively). In NG108-15 neuroblastoma cells, both drugs (amantadine (100 microm) and memantine (10 microm)) potentiated the bradykinin-induced mobilization of intracellular Ca2+, mimicking the effect of the sigma1 receptor agonist PRE-084 (1 microm). Finally, we previously showed that in striatal membranes from amantadine-treated rats, the functional coupling of dopamine receptors with G-proteins was enhanced. Similarly, PRE-084 dose-dependently increased the [35S]GTPgammaS binding induced by dopamine (Emax 28 and 26% of basal, 0.3 and 1 mg/kg PRE-084, respectively). By contrast, BD1047, which is without effect on its own, antagonized the effects of amantadine and PRE-084. Together, these data demonstrate that aminoadamantanes behave as sigma1 receptor agonists, and confirm an involvement of this receptor in modulating dopamine receptors exerted by therapeutically relevant concentrations of amantadine.

Distinct effects of amantadine and memantine on dopaminergic transmission in the rat striatum

Striatal glutamatergic inputs are known to participate in the modulation of dopaminergic transmission. Accordingly, the non-competitive N-methyl-D-aspartate receptor antagonists memantine and amantadine increase striatal dopamine levels, the latter being widely used in Parkinson's disease therapy. Based on our previous work revealing increased function of dopamine receptors and dopamine transporter after amantadine treatment, we studied the effects of repeated memantine administration on dopaminergic neurotransmission. On rat striatal membranes, dopamine-stimulated [(35)S]GTPgammaS binding was significantly reduced (20%) after 2 days injection with memantine (20 mg/kg per day, i.p.) but not after longer treatments (4 or 7 days). Evaluation of [(3)H]SCH 23390 and [(3)H]spiperone specific bindings only revealed a significant increase in D1 receptor density after 4 or 7 days treatment. Finally, none of these treatments were found to change the activity of the neuronal dopamine transporter in striatal synaptosomes. This shows that amantadine and memantine differentially affect striatal dopaminergic transmission, which could indicate that these two related aminoadamantanes display distinct pharmacodynamic properties.

Hypersensitivity of dopamine transmission in the rat striatum after treatment with the NMDA receptor antagonist amantadine

Amantadine, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist known to increase dopamine synthesis and release in the striatum, is frequently associated with L-DOPA in the treatment of Parkinson's disease. However, the biochemical mechanisms involved in the effect of amantadine and the consequences of its repetitive administration on the modulation of striatal dopamine transmission still need to be clarified. We have investigated the effects of short-term amantadine treatments on the expression of dopamine receptors and the functional coupling to G proteins in rat striatal membranes. Dopamine-induced stimulation of guanosine 5'-[gamma-35S]triphosphate ([35S]GTPgammaS) binding was significantly enhanced (40%) in striatum homogenates from rats treated for 4 days with amantadine (40 mg/kg, i.p.) compared to vehicle-treated animals. This effect was specific for dopamine receptors and was transient as no significant modifications were observed when animals were treated for either 2 or 7 days. Administration of amantadine did not directly affect the animal behaviour. However, treated animals exhibited hypersensitive dopamine transmission since rats treated for 4 days showed exacerbated responses to a single apomorphine administration (enhanced locomotor activity and reduced stereotypy). Since the effects of amantadine administration differ from those usually observed with direct dopamine receptor agonists or other NMDA receptor antagonists, we suggest that multiple biochemical mechanisms contribute to the modulation of dopamine transmission by amantadine.

Preclinical Evaluation of CHF3381 as a Novel Antiepileptic Agent

CHF3381 [n-(2-indanyl)-glycinamide hydrochloride] has been selected on the basis of a screening program as the compound displaying the highest anticonvulsant activity in the maximal electroshock seizure (MES) test and the best therapeutic index with reference to the rotarod test in mice and rats. In this study, the antiepileptic activity and the behavioural toxicity of CHF3381 were characterised in multiple model systems. CHF3381 effectively prevented MES-induced convulsions when administered i.p. (ED50, 24 mg/kg and 7.5 mg/kg) or p.o. (ED50, 21 mg/kg and 21 mg/kg) in both mice and rats, respectively. The time course of oral anti-MES activity in the rat was related to the brain concentration profile of unchanged CHF3381. Interestingly, the brain drug levels were about 4-5 times higher than in plasma. CHF3381 was very effective in mice against picrotoxin-, and i.c.v. N-methyl-D-aspartate (NMDA)-induced hind limb tonic extension (ED50 Approximately/=10 mg/kg), but was a weaker antagonist of 4-amynopyridine- and bicuculline-induced tonic seizures (ED50 approximately/=100 mg/kg), and ineffective against pentylentetrazole- and picrotoxin-induced clonic seizures. CHF3381 antagonised the behavioural effects and lethality of i.p. administered NMDA (ED50 = 57 mg/kg p.o.), indicating that the compound may act as a functional NMDA antagonist. In keeping with this idea, CHF3381 weakly displaced [(3)H]-TCP from binding to NMDA receptor channels (Ki, 8.8 microM). In the rat amygdala kindling model, CHF3381 was more efficient against kindling development than against kindled seizures (minimally active dose = 80 vs. 120 mg/kg i.p). Furthermore, it significantly increased the seizure threshold in kindled rats at relatively low doses (40 mg/kg i.p.). In contrast with MK-801-induced hyperactivity, CHF3381 moderately reduced the spontaneous locomotor activity in mice at anticonvulsant doses. Toxic effects on motor performance (rotarod test) were found at high doses only (TD50 approximately/= 300 mg/kg p.o., congruent with 100 mg/kg i.p. in both mice and rats). Furthermore, CHF3381 did not impair passive avoidance and Morris water maze responding in the therapeutic range of doses. Finally, the development of tolerance after repeated doses was negligible. These data indicate that CHF3381 exerts anticonvulsant and antiepileptogenic effects in various seizure models and possesses good therapeutic window, with scarce propensity to cause neurological side-effects.

Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist--a review of preclinical data

N-methyl-D-aspartate (NMDA) receptor antagonists have therapeutic potential in numerous CNS disorders ranging from acute neurodegeneration (e.g. stroke and trauma), chronic neurodegeneration (e.g. Parkinson's disease, Alzheimer's disease, Huntington's disease, ALS) to symptomatic treatment (e.g. epilepsy, Parkinson's disease, drug dependence, depression, anxiety and chronic pain). However, many NMDA receptor antagonists also produce highly undesirable side effects at doses within their putative therapeutic range. This has unfortunately led to the conclusion that NMDA receptor antagonism is not a valid therapeutic approach. However, memantine is clearly an uncompetitive NMDA receptor antagonist at therapeutic concentrations achieved in the treatment of dementia and is essentially devoid of such side effects at doses within the therapeutic range. This has been attributed to memantine's moderate potency and associated rapid, strongly voltage-dependent blocking kinetics. The aim of this review is to summarise preclinical data on memantine supporting its mechanism of action and promising profile in animal models of chronic neurodegenerative diseases. The ultimate purpose is to provide evidence that it is indeed possible to develop clinically well tolerated NMDA receptor antagonists, a fact reflected in the recent interest of several pharmaceutical companies in developing compounds with similar properties to memantine.

Serotonin innervation of Lurcher mutant mice: basic data and manipulation with a combination of amantadine, thiamine and L-tryptophan

The Lurcher (Lc/+) mutant mouse is characterized by a considerable atrophy of the cerebellum due to a massive loss of cerebellar Purkinje and granule cells, as well as of neurons from the inferior olivary nucleus. In this study the effects of a therapeutic combination of amantadine, thiamine and L-tryptophan on the serotonin (5-HT) innervation was assessed in Lurcher mice by autoradiography, using [3H]citalopram to label 5-HT transporters. In wild type mice as well as in both saline-treated and drug-treated Lurcher mutants, [3H]citalopram binding remained unchanged in forebrain and brainstem regions. In the cerebellum, labelling of deep cerebellar nuclei (CBnuc) was about twofold higher than in the cortex (CBctx). In saline-treated Lurcher mutants compared to wild type mice, the densities of [3H]citalopram were 98% higher in CBctx, and 180% higher in CBnuc. In CBctx of drug-treated Lurcher mutants, transporter densities were 89% higher than in the wild type, but did not differ from the saline-treated Lurcher. In the CBnuc of the drug-treated Lurcher mutants, [3H]citalopram binding was 50% higher than in the saline-treated Lurcher group, and 320% higher than in wild type mice. The results show that 5-HT transporters, already upregulated in the CBnuc of Lurcher mutant mice, can be further increased by a pharmacological treatment, possibly altering the availability of 5-HT in some of its target areas.

Antiparkinsonian actions of glutamate antagonists--alone and with L-DOPA: a review of evidence and suggestions for possible mechanisms

There has been much speculation of late as to whether antagonists of glutamate receptors can be used to combat the motor difficulties of Parkinson's disease, either as monotherapy, or as polytherapy to boost the effects of conventional L-DOPA treatment. The latter seems to be the more practical approach and the therapeutic implications of such treatment have been discussed in some detail. However, the mechanisms by which glutamate antagonists potentiate the antiparkinsonian actions of L-DOPA, remain cryptic. In this review we have explored the evidence and considered the practicality of using NMDA and non-NMDA receptor blockers to treat parkinsonism, as well as focusing on the ways in which the behavioural synergy between dopamine and glutamate systems could conceivably arise at the cellular level. Particular attention has been paid to the differential interaction between glutamate antagonists and postsynaptic dopamine D1 and D2 receptory mechanisms, since these are currently believed to reflect the activity of the two major basal ganglia output circuits: the so-called direct pathway to the substantia nigra and the indirect pathway to the globus pallidus. Finally, we have considered the new proposal, that inhibiting glutamate transmission in the basal ganglia accelerates the enzymic conversion of L-DOPA to dopamine at presynaptic sites.

6-Hydroxydopamine lesion of locus coeruleus and the antiparkinsonian potential of NMDA-receptor antagonists in rats

Behavioral and neurochemical effects after bilateral 6-hydroxy-dopamine locus coeruleus- (LC) lesion were examined in rats and compared to sham-lesioned controls. Behavior after treatment with the antiakinetic drugs dizocilpine, amantadine, memantine or L-DOPA as well as joint treatment of these drugs with haloperidol were tested in an open field with holeboard and in an experimental chamber. Under saline spontaneous activity (open field with holeboard) and sniffing (experimental chamber) were reduced after lesion. Injection of the proparkinsonian drug haloperidol decreased sniffing in all rats but to a greater extent in LC-lesioned rats. In combination with haloperidol none of the tested drugs could completely compensate for the motor deficits induced by the lesion. Neurochemical data revealed a reduced content of noradrenaline in the prefrontal cortex and in the posterior striatum of LC-lesioned rats. These results indicate that loss of LC neurons intensifies parkinsonian symptoms induced by blockade of dopamine D2-receptors, and lowers the antiakinetic potential of dizocilpine, amantadine, memantine or L-DOPA.

Stimulation of basal and L-DOPA-induced motor activity by glutamate antagonists in animal models of Parkinson's disease

In parkinsonism, glutamate pathways within the basal ganglia become overactive, leading to the suggestion that glutamate antagonists might possess antiparkinsonian qualities. This report examines the motor properties of antagonists of NMDA and AMPA-type glutamate receptors, as well as some inhibitors of glutamate release, in animal models of idiopathic Parkinson's disease. High affinity NMDA open-channel blockers (e.g. MK 801, phencyclidine), are highly potent antagonists with inconsistent antiakinetic and strong myorelaxant activity. Other compounds are better tolerated and are capable of relieving immobility and muscular rigidity by themselves (e.g. 1-aminoadamantanes, polyamine site antagonists, kappa agonists, riluzole). Yet others do not restore movements alone (e.g. dextromethorphan, ketamine), but may interact with and strengthen the antiparkinsonian action of L-DOPA (e.g. competitive NMDA and AMPA antagonists, lamotrigine). They may do this by potentiating dopaminergic behaviours mediated by D1 or D2 receptors, or by some other mechanism.

Aminoadamantanes as NMDA receptor antagonists and antiparkinsonian agents--preclinical studies

Aminoadamantanes such as 1-aminoadamantane (amantadine) and 1-amino-3,5-dimethyladamantane (memantine) are N-methyl-D-aspartate (NMDA) receptor antagonists which show antiparkinsonian-like activity in animal models and in Parkinson's patients. The issue of whether NMDA antagonism plays a role in the symptomatological antiparkinsonian activity of amantadine and memantine is addressed by comparing: behaviourally effective doses, serum/brain levels, and their potency as NMDA receptor antagonists. In the case of memantine, blockade of NMDA receptors is probably the only mechanism responsible for antiparkinsonian activity, whereas for amantadine the situation is clearly far more complex. There are a number of differences between memantine and amantadine both in vitro and in vivo, and although NMDA receptor antagonism certainly participates in the antiparkinsonian activity of amantadine, other effects, some of which are elusive, also play a role. Moreover, it has been suggested that the pathomechanism of Parkinson's disease involves excitotoxic processes and that treatment with NMDA receptor antagonists might also slow the progression of neurodegeneration. If this claim is true, such an effect could be achieved with amantadine and memantine which show neuroprotective activity in animals at therapeutically relevant doses.

Memantine induces heat shock protein HSP70 in the posterior cingulate cortex, retrosplenial cortex and dentate gyrus of rat brain

High-affinity N-methyl-D-aspartate (NMDA) receptor antagonists like MK-801 are known to induce the heat shock protein, HSP70, in the posterior cingulate cortex and retrosplenial cortex of rat brain. Memantine, which is a low affinity uncompetitive NMDA receptor antagonist, has been used in the treatment of Parkinson's disease in Europe. The faster kinetics of memantine in blocking and unblocking the NMDA receptor-operated ion channel as opposed to high-affinity NMDA antagonists like MK-801 has been thought to account for the safety of memantine. The present study evaluated the neurotoxic potential of memantine and amantadine using the induction of HSP70 immunoreactivity in rat brain. Memantine (25, 50, 75 mg/kg) induced HSP70 in the posterior cingulate, retrosplenial cortex and dentate gyrus of rat brain. In contrast, amantadine (50, 100, 200 mg/kg) did not induce HSP70 in the rat brain. These results suggest that memantine has an antagonistic effect at NMDA receptor in vivo, and raises the possibility that high doses of memantine may cause neuronal damage similar to those observed with other high-affinity NMDA receptor antagonists.