The non-NMDA glutamate receptor antagonist GYKI 52466 counteracts locomotor stimulation and anticataleptic activity induced by the NMDA antagonist dizocilpine

Summary The effects of the non-NMDA glutamate receptor antagonist GYKI 52466 (2.4 and 4.8 mg/kg, i.p.) on spontaneous locomotor activity and haloperidol-induced catalepsy (0.5 mg/kg, i.p.) were assessed in naive rats and in rats pretreated with the NMDA antagonist dizocilpine (0.08 mg/kg, i.p.). GYKI 52466 given alone did not alter locomotor activity and haloperidol-induced catalepsy, but significantly antagonized the dizocilpine-induced locomotor stimulation and counteracted the anti-cataleptic effects of dizocilpine on haloperidol-induced catalepsy. Thus blockade of non-NMDA glutamate receptors antagonized the behavioural stimulant effects of a NMDA receptor blockade. Correspondence to: W. Hauber at the above address     

Effects of MK-801, a non-competitive NMDA antagonist,on linguopharyngeal events in rats

The effects of MK-801 at doses from 0.005 to 1 mg/kg IP on linguopharyngeal events (protrusions, retrusions and swallows) were determined in rats to find out whether MK-801 resembles ketamine in its capacity to increase the frequency of recurrence of such events that we have demonstrated in previous studies. All rats receiving a dose of 0.05 mg/kg or higher showed an increase in linguopharyngeal event frequency within 5 min and this enhancement (3-fold from baseline level) was maintained for longer than 1 h. At the lowest dose of 5 µg/kg the effect lasted only very briefly. A general increase in motor behavior was also observed within 10 min of drug administration. More complex patterns of motor behavior, consisting of stereotypical head bobbing, paw movements reminiscent of walking activity, nystagmus, and ataxia were observed with doses of 0.25 mg/kg and higher. All rats showed a marked startle response at early stages post-injection and hypersensitivity to external stimuli such as noise or movement in the room. However, there was an absolute lack of coordinated avoidance responses normally associated with such startle responses or arousing stimuli.     

Influence of the non-competitive NMDA receptor antagonist MK-801 on 2-deoxy-D-glucose-induced hyperphagia in rats.

The effects of the glutamate N-methyl-D-aspartate (NMDA) receptor antagonist (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5, 10-imine (MK-801) on 2-deoxy-D-glucose-induced hyperphagia were investigated in rats. MK-801 significantly increased 2-deoxy-D-glucose-elicited eating. The facilitating effects of MK-801 on 2-deoxy-D-glucose-elicited feeding were not affected by coadministration of a nitric oxide (NO) precursor, L-arginine. Because NO synthase inhibitors inhibit 2-deoxy-D-glucose-induced hyperphagia and activation of the NMDA receptor leads to NO formation, our results suggest that blockade of the NMDA receptor increases 2-deoxy-D-glucose-induced hyperphagia, which is unrelated to inhibition of NO, and that NMDA receptors may play a role in satiety.     

The effect of antidepressant drugs on the locomotor hyperactivity induced by MK-801, a non-competitive NMDA receptor antagonist.

It was found earlier that imipramine, amitriptyline and citalopram enhanced the locomotor hyperactivity induced by MK-801, a non-competitive NMDA receptor antagonist, in rats. Now, three other antidepressants: (+)-oxaprotiline, an inhibitor of the uptake of noradrenaline, (-)-oxaprotiline, an enantiomer devoid of any effect on the uptake of noradrenaline and fluoxetine, an inhibitor of the uptake of 5-hydroxytryptamine, have been examined in male Wistar rats. All those antidepressants, given in a single dose, increased the MK-801-induced locomotor hyperactivity. That increase was completely antagonized by haloperidol and partly by SCH 23390 and (+/-)-sulpiride; prazosin was inactive. Repeated administration of antidepressants produced a similar but more potent (than acute one) enhancement of the action of MK-801. Also, in that case haloperidol and SCH 23390 produced the strongest antagonistic effect; (+/-)-sulpiride and prazosin had a distinctly less potent action. Another effect of MK-801, anticonvulsant activity (electroshock-induced convulsions), was not increased by the antidepressants studied. These results indicate that antidepressants with a different pharmacological profile, increased the MK-801-induced locomotor hyperactivity, this effect being probably indirectly mediated, at least in part, by a dopamine mechanism.     

Effects of the noncompetitive NMDA receptor antagonist MK-801 on classical eyeblink conditioning in mice

N-methyl-D-aspartate (NMDA) receptors are involved in synaptic plasticity and play a critical role in learning and memory. We investigated the effects of the noncompetitive NMDA receptor antagonist (+)MK-801 on classical eyeblink conditioning of mice, using various interstimulus intervals between the conditioned stimulus (CS) and unconditioned stimulus (US). A tone was used for the CS and a periorbital shock was used for the US. In the delay paradigm, in which the US coterminated with the CS or started immediately after CS offset, the effect of (+)MK-801 (0.1mg/kg, i.p.) was a slight impairment in the acquisition of the conditioned response (CR). During subsequent CS-alone trials, the responses of (+)MK-801-injected mice were extinguished as easily as those of saline-injected mice. In the trace paradigm, (+)MK-801 impaired acquisition of the CR with a trace interval of 250 ms more than it did with a trace interval of 100 ms, and more than in the delay paradigm. (+)MK-801 injected after acquisition of 250-ms trace conditioning did not impair expression or extinction of the CR. These results suggest that NMDA receptors are involved in acquisition of the CR during longer trace interval conditioning more than during shorter trace interval conditioning or delay conditioning, and that their contribution to extinction is much smaller than their contribution to acquisition in mouse eyeblink conditioning.     

Interaction of GYKI 52466, a selective non-competitive antagonist of AMPA/kainate receptors, with conventional antiepileptic drugs in amygdala-kindled seizures in rats.

GYKI 52466 [1,4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine], a non-competitive AMPA/kainate receptor antagonist, administered i.p. at the dose of 5 mg/kg, exerted a significant anticonvulsant effect, as it decreased seizure and afterdischarge durations, being ineffective at 2 mg/kg. Subsequently, GYKI 52466 (2 mg/kg) was combined with antiepileptic drugs at doses ineffective in fully kindled rats. Co-administration of GYKI 52466 with clonazepam (0.003 mg/kg i.p.) resulted in a significant reduction of seizure severity (by 20%), seizure duration (by 31%) and afterdischarge duration (by 24%). Co-injection of GYKI 52466 with valproate (75 mg/kg i.p.) also resulted in the respective 8%, 16%, and 17% reductions of the three studied seizure parameters. No protection was observed when GYKI 52466 was co-administered with carbamazepine (20 mg/kg i.p.), phenobarbital (20 mg/kg i.p.), or diphenylhydantoin (40 mg/kg i.p.). Combinations of GYKI 524662 with antiepileptic drugs did not cause any significant motor (rotarod test) or long-term memory deficits (passive avoidance task). Only GYKI 52466 administered alone at 5 mg/kg, caused a significant impairment of retention in amygdala-kindled rats. The interaction at a pharmacokinetic level, at least in case of the combination of GYKI 52466 with valproate, can be excluded because GYKI 52466 did not interfere with the free plasma level of valproate. These results give further support to the idea of a potential clinical benefits of the combined treatment of AMPA/kainate receptor antagonists with some antiepileptic drugs.     

The NMDA receptor antagonist MK-801 increases morphine catalepsy and lethality.

Interactions between excitatory amino acids and opioids were examined by studying the ability of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 to affect morphine catalepsy and lethality. MK-801 (0.3 mg/kg) reduced the ED50 for morphine-induced catalepsy from approximately 30 mg/kg to less than 10 mg/kg, and reduced the LD50 for morphine from approximately 100 mg/kg to approximately 10 mg/kg. Lower doses of MK-801 did not affect morphine catalepsy or lethality. MK-801, in the absence of morphine, produced no catalepsy or lethality at doses up to 3.0 mg/kg; at 0.3 mg/kg MK-801 caused weaving, body rolling and ataxis, as previously described, while at 3.0 mg/kg animals appeared to lose muscle tone, becoming limp. These results demonstrate that blockade of NMDA receptors can dramatically potentiate morphine catalepsy and lethality, and suggest a potential dangerous interaction with opioids in the clinical use of NMDA receptor antagonists.     

Rapid quantification of the non-competitive NMDA antagonist MK-801 in canine cerebrospinal fluid and plasma by capillary gas chromatography-nitrogen phosphorus detection

A facile and sensitive method utilizing solid-phase cartridge extraction and capillary gas chromatography (GC) with nitrogen phosphorus detection was validated for the determination of MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine maleate], a non-competitive NMDA receptor antagonist, in dog cerebrospinal fluid (CSF) and plasma. Clonidine hydrochloride was used as the internal standard (ISTD), after evaluation of several ISTD candidates. Separations were performed with an intermediate polarity fused silica capillary column, yielding typical retention times of 3.20 min for MK-801 and 4.90 min for ISTD. Plasma and CSF samples were extracted with 100 mg Bond Elut C(18) TCA Copyright cartridges to yield methanolic eluates that were evaporatively enriched before reconstitution in anhydrous ethanol prior to injection. The standard curve was validated from 1 to 100,000 ng/ml for CSF, and from 0.1 to 1,000 ng/ml for plasma. Chromatograms from naive plasma and CSF exhibited no endogenous interfering peaks. The efficiency of extraction recovery was >94%, and the intra-assay and inter-assay precision was within 9% relative standard deviation (%R.S.D.) for both fluids. MK-801 and ISTD were stable in the injection solvent at 22 degrees C for at least 48 h. The assay was applied to the toxocologic study of intrathecal MK-801 administration in the dog.     

The NMDA receptor antagonist MK-801 has a dissociative effect on seizure activity of hippocampal-kindled cats.

This study assessed the behavioral and electrographic effects of (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine maleate (MK-801) (0.1 and 0.5 mg/kg, IP), a noncompetitive antagonist of the NMDA receptors, in hippocampal (HIP)-kindled cats. MK-801 at a higher dose significantly reduced the afterdischarge duration, but not the behavioral seizure stage, of HIP-kindled seizures. This anticonvulsant effect occurred in association with the appearance of severe behavioral toxicity and paradoxical worsening of background electroencephalogram characterized by profound spike and wave discharges. The present data suggest the dissociative effect of MK-801 on seizure activity and limitations of its clinical utility as an antiepileptic agent.     

The anticonflict effect of MK-801, an NMDA antagonist: investigation by punishment procedure in mice

The NMDA antagonist MK-801 at 0.3 mg/kg, i.p. increased the punished response under a MULT VI 1.5/FR 5-punishment schedule of food reinforcement in mice. Furthermore, although neither MK-801 (0.1 mg/kg, i.p.) nor diazepam (0.25 mg/kg, s.c.) was without effect when separately administered, a significant increase in the punished response appeared after the combined administration of these two drugs. The present results suggest that MK-801 not only shows an anticonflict effect, but also enhances the anticonflict effect of benzodiazepine anxiolytics in mice.     

Development of both conditioning and sensitization of the behavioral activating effects of amphetamine is blocked by the non-competitive NMDA receptor antagonist,MK-801

The non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, MK-801, has been shown to block the development of sensitization of the behavioral activating effects of amphetamine. Three experiments were designed to determine in rats whether MK-801 had its effects through interference with long-term changes underlying sensitization, per se, or through interference with the development of conditioning of the drug effect to the environment where the drug was given. In experiment 1, conditioning was promoted by explicitly pairing amphetamine (1.5 mg/kg, IP) with the testing environment. In experiment 2, a random-pairing procedure was used to eliminate the possibility of association between the drug and a specific context. Experiment 3 was carried out to assess the duration of the blockade of sensitization by MK-801. The effect of MK-801 (0.25 mg/kg, IP) during amphetamine pre-exposure was studied in tests for conditioning (following saline injections, experiment 1) and in tests for sensitization (following 0.75 mg/kg amphetamine, experiments 1, 2 and 3). It was found in experiment 1 that MK-801 given with amphetamine during the amphetamine pre-exposure phase blocked the development of both conditioning activity and environment-specific sensitization to amphetamine. The results of experiment 2, showing that sensitization to amphetamine was blocked by MK-801 even when conditioning was prevented, suggest that the two effects of MK-801 are independent, and may implicate different sites of action. Experiment 3 showed that the blockade of sensitization by MK-801 was evident in tests made 10 days after pre-exposure to amphetamine, supporting the view that MK-801 interferes with long-term changes underlying sensitization to amphetamine.     

A novel NMDA antagonist, MK-801, impairs performance in a hippocampal-dependent spatial learning task

N-Methyl-d-aspartate (NMDA) receptors have been implicated with the triggering of long-term potentiation, a currently studied physiological model of learning and memory. The compound (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate (MK-801) has recently been classified as a potent and selective NMDA antagonist acting at the associated ion channel. After determination of the highest intraperitoneal dose of MK-801 at which increases in activity (measured in photocell activity cages and 3-arm maze) were not observed (0.2 mg/kg), rats that had been previously trained to obtain food pellets in an 8-arm radial maze up to criterion were tested with 0.1 and 0.2 mg/kg doses. Dose-related decreases in "efficiency" in the task were found. The present findings support the suggestion that NMDA antagonists cause impairments in "working memory" and also support the status of long-term potentiation as a physiological model of memory.     

Effect of the NMDA antagonist MK-801 on MPTP-induced parkinsonism in the monkey

Current evidence suggests that the motor symptoms of parkinsonism are due to abnormal overactivity of the medial segment of the globus pallidus, brought about by overactivity of the subthalamic nucleus, from which it receives an excitatory amino acid-mediated projection. The possibility exits, therefore, that excitatory amino acid antagonists might have an anti-parkinson effect by normalising medial pallidal activity. The NMDA antagonist MK-801 was administered i.m. to a single cynomolgus monkey with parkinsonism induced by the neurotoxin MPTP. In fact, MK-801 exacerbated the symptoms of parkinsonism. When administered after a therapeutic dose of L-DOPA it antagonised the anti-parkinson action of L-DOPA. The results suggest that any potential anti-parkinson action of excitatory amino acid antagonists will depend upon an action at non-NMDA sites. The administration of the selective neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to produce a primate model of Parkinson's disease is well-documented (Burns, Markey, Phillips & Chiuch, 1984; Crossman, 1987; Langston, Forno, Rebert & Irwin, 1984). Intravenous injection of MPTP, titrated judiciously over a period of several weeks, can produce a stable manifestation of the motor disability seen in the idiopathic disease of man, with a remarkable correspondence of both symptoms and pathology. Additionally, primates rendered parkinsonian by MPTP respond well to L-DOPA treatment. As in human Parkinson's disease, long-term L-DOPA therapy of MPTP-induced parkinsonism tends to be complicated by the emergence of choreiform movements and dystonic postures (Boyce, Clarke, Luquin, Peggs, Robertson, Mitchell, Sambrook & Crossman, 1989; Clarke, Sambrook, Mitchell & Crossman, 1987).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of the NMDA antagonist MK-801 on latent inhibition of fear conditioning

N-methyl-d-aspartate (NMDA) receptors seem to play a central role in learning and memory processes involved in Latent Inhibition (LI). In fact, MK-801, a non-competitive NMDA receptor antagonist, has proved its effectiveness as a drug for attenuating LI when administered before or after stimulus preexposure and conditioning stages. This paper presents three experiments designed to analyze the effect of MK-801 on LI when the drug is administered before (Experiment 1A) or after (Experiment 1B) preexposure and conditioning stages with a conditioned emotional response procedure. Additionally, we analyze the effect of the drug when it was administered before preexposure, before conditioning or before both phases (Experiment 2). The results show that the effect of the drug varied as a function of the dose (with only the highest dose being effective), the moment of administration (with only the drug administered before the experimental treatments being effective), and the phase of procedure (reducing LI when the drug was administered only at preexposure, and disrupting fear conditioning when administered at conditioning). These differences may be due to several factors ranging from the role played by NMDA receptors in the processing of stimuli of different sensorial modalities to the molecular processes triggered by drug administration.     

The NMDA receptor antagonist dizocilpine (MK-801) stereoselectively inhibits morphine-induced place preference conditioning in mice

The effect of the non-competitive NMDA receptor antagonist dizocilpine (MK-801) on conditioned place preference induced by morphine was studied in mice. As expected, morphine (1–8 mg/kg, IP) elicited a significant preference for the drug-paired compartment. Pretreatment of mice with (+)-dizocilpine (0.1 and 0.2 mg/kg, IP), the more active dizocilpine enantiomer, dose-dependently reversed the conditioned place preference produced by morphine (4 mg/kg, IP), whereas (–)-dizocilpine (0.2 mg/kg, IP) did not modify morphine-induced effects. In contrast, both enantiomers of dizocilpine (at a dose of 0.2 mg/kg, IP) elicited a conditioned place preference. These data suggest that (1) NMDA receptors play a role in morphine-induced place preference, and (2) dizocilpine-reinforcing properties in the place preference paradigm do not seem to be dependent on NMDA receptor blockade.     

Behavioural interaction between the NMDA antagonist MK-801 and the dopaminergic antagonist haloperidol: support for a balance model

One hundred and four male Sprague-Dawley rats were divided into three experiments. The first two experiments were to assess the effect of different MK-801 doses (0.1-0.3 mg/kg) and combinations of MK-801/ haloperidol (0.3/0.1-0.5 mg/kg) on locomotor behaviour. The animals from the third experiment were administered either saline, MK-801 (0.3 mg/kg), haloperidol (0.5 mg/kg) or MK-801/haloperidol (0.3/0.5 mg/kg). Locomotor activity measurements showed that the NMDA antagonist MK-801 induced a dose-dependent hyperactivity, while haloperidol, the D-2 dopamine receptor antagonist, induced hypoactivity. Significantly the highest doses of combined MK-801/haloperidol treatment (0.3/0.5 mg/kg) showed behavioural equivalence to the saline animals in both total locomotion, locomotion patterns and within-session habituation. Thus, the behavioural effects of each drug given alone were cancelled when the drugs were given together. This cancellation effect could not be ascribed to direct drug interference effects on dopamine metabolism since the ex vivo biochemical data revealed that the combined MK-801/haloperidol (0.3/0.5 mg/kg) treatment increased dopamine metabolism to the same extent as haloperidol given alone. None of the drug treatments, however, had any effect on brain serotonin metabolism. Serum measurement indicated that dopamine, homovanillic acid, 3,4-dihydroxyphenyl-acetic acid, 5-hydroxyindole-3-acetic acid, norepinephrine and corticosterone were not differentially affected by the drug treatment. Haloperidol-treated animals, however, had higher serum serotonin concentration than saline-treated animals. Taken together, these results support the hypothesis that the effect of MK-801 on behaviour is independent of biochemical changes in dopaminergic neuro transmission per se. Rather, the present results support the hypothesis of a glutamatergic-dopaminergic balance which when disturbed leads to behavioural changes along an excitatory-inhibitory behavioural gradient.     

The effect of the NMDA receptor antagonist, MK-801, on the course and outcome of kindling

A rapid kindling procedure was used to distinguish between the anticonvulsant activity of drugs and their ability to retard the kindling process. MK-801 is a specific ligand at the phencyclidine (PCP) recognition site, and acts as a noncompetitive antagonist of NMDA-type glutamate/aspartate receptors. Intraperitoneal injections of MK-801 (0.5-4.0 mg/kg IP) significantly reduced the cumulated effect of 12 2-hr kindling stimulations, as determined from behavioral measures of seizure activity in immediately ensuing 24-hr drug-free kindling sessions; however, the corresponding electrographic effects did not reach significance. MK-801 also showed significant anticonvulsant activity when injected in fully kindled rats. Higher doses tested were accompanied by locomotor and postural effects. The anticonvulsant benzodiazepine, clonazepam, formulated with a proprietary diluent (as Rivotril, Roche), injected in anticonvulsant doses during the first 12 kindling sessions (0.64 mg/kg IP, repeated after 9 hr) did not significantly affect the course of subsequent sessions of drug-free kindling. Systemic injections of kynurenic acid (300-600 mg/kg IP 4 hours), a nonspecific antagonist of glutamate receptors in vitro, were without significant anticonvulsant or antikindling activity. Activity of NMDA-sensitive glutamate/aspartate receptors associated with the PCP recognition site may induce lasting facilitation of neural transmission; this facilitation may be responsible for the remote propagation and progressive enhancement of seizure activity kindled in the amygdala. The facilitatory process appears to be antagonised by MK-801.     

Modifications of the behavioral profile of non-competitive NMDA receptor antagonists, memantine, amantadine and (+)MK-801 after chronic administration

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists show antiparkinsonian-like activity in animal models, and possess neuroprotective properties. However they also induce a number of behavioral side effects in rodents at higher doses; these include learning impairment, hyperlocomotion, and ataxia. The present study focused on the possible development of tolerance, or sensitization, to any of these effects after sustained administration, either by repeated injection or continuous infusion. When memantine or (+)MK-801 (20 and 0.31 mg/kg/day respectively) were either infused or repeatedly injected for 14 days, tolerance was observed to their learning impairing effect at high doses, in a passive avoidance test. Tolerance to their ataxic effect developed after repeated administration ((+)MK-801 and memantine), or after infusion (memantine). Sensitization to the locomotor stimulation was seen following repetitive injections of memantine for 14 days, but not seen with (+)MK-801. In animals with an unilateral 6-OHDA lesion of the nigrostriatal system, acute administration of memantine caused ipsilateral rotations, which were augmented following 14 days of infusion. The potency of amantadine to antagonize neuroleptic-induced catalepsy was unchanged following either infusion or repeated injections. The various acute effects of non-competitive NMDA receptor antagonists were modified differently by sustained treatment (i.e. tolerance to learning impairment and ataxia; sensitization to memantine's locomotor stimulation). The anti-cataleptic activity of amantadine remained unaltered. However, differences between drugs and the two treatment regimens (i.e. repetitive versus continuous treatments) were apparent.     

The non-competitive NMDA receptor antagonist (+)MK-801 counteracts the long-lasting attenuation of the hypothermic response induced by acute doses of 8-OH-DPAT in the rat

The effects of acute doses of 8-hydroxy 2-(di-n-dipropylamino)tetralin (8-OH-DPAT) on the hypothermic response, induced by a challenge dose of 8-OH-DPAT, were examined in rats. Acute doses of 8-OH-DPAT (1.0 or 0.5 mg/kg, s.c.) significantly attenuated the hypothermic response induced by 8-OH-DPAT (0.05 mg/kg, s.c.). The response to 8-OH-DPAT was almost abolished between 4 hr and 4 days and the attenuation of the response lasted for 21 days. On day 28 the response had returned to the control level. The non-competitive (N-methyl- -aspartate) (NMDA) receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)cyclohepten-5,10-imine [(+)MK-801], blocked this long-lasting attenuation of the 8-OH-DPAT-induced hypothermic response. Given on its own, (+)MK-801 did not reduce body temperature, at the doses used in the experiments but the drug did block the acute effects of 8-OH-DPAT, at the same doses which blocked the attenuation of the hypothermic response. The present data suggest that stimulation of glutamate NMDA receptors may underlie the long-lasting effect of acute injections of 8-OH-DPAT.