dizocilpine-maleate and 5-7-dichlorokynurenic-acid

Stimulating the glycine(B) binding site on the N-methyl-d-aspartate ionotropic glutamate receptor (NMDAR) has been proposed as a novel mechanism for modulating behavioral effects of ethanol (EtOH) that are mediated via the NMDAR, including acute intoxication. Here, we pharmacologically interrogated this hypothesis in mice.. Effects of systemic injection of the glycine(B) agonist, d-serine, the GlyT-1 glycine transporter inhibitor, ALX-5407, and the glycine(B) antagonist, L-701,324, were tested for the effects on EtOH-induced ataxia, hypothermia, and loss of righting reflex (LORR) duration in C57BL/6J (B6) and 129S1/SvImJ (S1) inbred mice. Effects of the glycine(B) partial agonist, d-cycloserine (DCS), the GlyT-1 inhibitor, N-[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS), and the glycine(B) antagonist, 5,7-dichlorokynurenic (DCKA), on EtOH-induced LORR duration were also tested. Interaction effects on EtOH-induced LORR duration were examined via combined treatment with d-serine and ALX-5407, d-serine and MK-801, d-serine and L-701,324, as well as L-701,324 and ALX-5407, in B6 mice, and d-serine in GluN2A and PSD-95 knockout mice. The effect of dietary depletion of magnesium (Mg), an element that interacts with the glycine(B) site, was also tested.. Neither d-serine, DCS, ALX-5407, nor NFPS significantly affected EtOH intoxication on any of the measures or strains studied. L-701,324, but not DCKA, dose-dependently potentiated the ataxia-inducing effects of EtOH and increased EtOH-induced (but not pentobarbital-induced) LORR duration. d-serine did not have interactive effects on EtOH-induced LORR duration when combined with ALX-5407. The EtOH-potentiating effects of L-701,324, but not MK-801, on LORR duration were prevented by d-serine, but not ALX-5407. Mg depletion potentiated LORR duration in B6 mice and was lethal in a large proportion of S1 mice.. Glycine(B) site activation failed to produce the hypothesized reduction in EtOH intoxication across a range of measures and genetic strains, but blockade of the glycine(B) site potentiated EtOH intoxication. These data suggest endogenous activity at the glycine(B) opposes EtOH intoxication, but it may be difficult to pharmacologically augment this action, at least in nondependent subjects, perhaps because of physiological saturation of the glycine(B) site.

Topics: Alcoholic Intoxication; Animals; Ataxia; Cycloserine; Disease Models, Animal; Disks Large Homolog 4 Protein; Dizocilpine Maleate; Drug Therapy, Combination; Glycine Plasma Membrane Transport Proteins; Guanylate Kinases; Hypothermia; Kynurenic Acid; Magnesium; Male; Membrane Proteins; Mice; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Quinolones; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Reflex, Righting; Sarcosine; Serine

The feeding behaviour of the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa) is modulated by a number of molecules acting as neurotransmitters in other nervous systems. Here we present biochemical and functional evidence of the occurrence of putative NMDA receptors in Hydra tissues. Saturation experiments showed the presence of one population of binding sites with nanomolar affinity and low capacity for [3H]MK-801. Before equilibrium, [3H]MK-801 binding was increased by the agonists glutamate and glycine as well as by reduced glutathione (GSH). In vivo the glutamate receptor agonist NMDA markedly decreased the duration of the response to GSH. This effect was linearly related to ligand doses in the nanomolar concentration range and was counteracted by either the NMDAR-specific antagonist D-AP5 or by the d-serine antagonist DCKA. When NMDA concentration was increased to 10 or 100 microm, duration of the response to GSH was no longer affected unless the lectin concanavalin A, which prevents receptor desensitization in other systems, was added to the test medium. Simultaneous administration of ineffective doses of NMDA and strychnine, glycine or d-serine, an agonist at the glycine binding site of the NMDA receptor in vertebrate CNS, resulted in a strong reduction of response duration. Both D-AP5 and DCKA suppressed this effect. These results, together with the decrease in response duration produced by d-serine, support the hypothesis that NMDA-like glutamate receptors may occur in Hydra tissues where they are involved in modulation of the response to GSH with opposite actions to those of GABA and glycine.

Topics: 2-Amino-5-phosphonovalerate; Animals; Behavior, Animal; Binding Sites; Cell Membrane; Concanavalin A; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Feeding Behavior; Glutamic Acid; Glutathione; Glycine; Hydra; Kynurenic Acid; N-Methylaspartate; Receptors, N-Methyl-D-Aspartate; Serine; Strychnine

In our previous experiments, severe cellular damages and neuronal cell loss were observed following 24h of alcohol withdrawal in primary cultures of rat cortical neurones pre-treated with ethanol (50-200 mM) repeatedly for 3 days. Increased NMDA induced cytosolic calcium responses and excitotoxicity were also demonstrated in the ethanol pre-treated cultures. Thus, the enhancement in functions of NMDA receptors was supposed to be involved in the adaptive changes leading to the neurotoxic effect of alcohol-withdrawal. In this study, we investigated the effect of the 3-day repeated ethanol (100 mM) treatment on the function and subunit composition of the NMDA receptors. Here, we demonstrate that the maximal inhibitory effect of ethanol was significantly increased after ethanol pre-treatment. Similarly, the inhibitory activity of the NR2B subunit selective antagonists threo-ifenprodil, CP-101,606 and CI-1041 was also enhanced. On the contrary, the efficiency of the channel blocker agent MK-801 and the glycine-site selective antagonist 5,7-dichlorokynurenic acid was the same as in control cultures. According to these observations, a shift in subunit expression in favour for the NR2B subunit was suggested. Indeed, we provided evidence for increased expression of the NR2B and the C1 and C2' cassette containing splice variant forms of the NR1 subunit proteins in ethanol pre-treated cultures in further experiments using a flow cytometry based immunocytochemical method. These changes may constitute the basis of the increased NMDA receptor functions and subsequently the enhanced sensitivity of ethanol pre-treated cortical neurones to excitotoxic insults resulting in increased neuronal cell loss after ethanol withdrawal. Such alterations may play a role in the neuronal adaptation to ethanol as well as in the development of alcohol dependence, and might cause neuronal cell loss in certain areas of the brain during alcohol withdrawal.

Topics: Animals; Animals, Newborn; Cells, Cultured; Cerebral Cortex; Culture Media, Serum-Free; Dizocilpine Maleate; Ethanol; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Hippocampus; Kynurenic Acid; N-Methylaspartate; Nerve Tissue Proteins; Neurons; Piperidines; Protein Subunits; Rats; Receptors, N-Methyl-D-Aspartate; RNA Splicing

N-methyl-D-aspartate receptor (NMDA-R) is an amino acid receptor and membrane calcium channel. NMDA-R is activated by binding of coagonists, L-glutamine and L-glycine. In the brain, calcium entry via NMDA-R activates type I nitric oxide synthase (NOS I). The kidney also contains NOS I and vasodilates in response to L-glycine. In this study, NMDA-R mRNA was demonstrated in rat kidney cortex by reverse transcriptase-PCR and cDNA sequencing. NMDA-R protein was demonstrated in kidney cortex by immunoblotting. To study the functional role of renal NMDA-R, renal hemodynamic effects of NMDA-R inhibition were assessed in rats using a blocker of the NMDA calcium channel (75 mg/kg MK-801 intraperitoneally) or an inhibitor of glycine binding to NMDA-R (30 mg/kg 5,7-dichlorokynurenic acid intraperitoneally). Renal blood flow was measured by perivascular pulse Doppler. GFR was measured by 3H-inulin clearance. Measurements were made before and during glycine infusion. Both NMDA-R antagonists caused renal vasoconstriction and attenuated the renal vasodilatory response to glycine infusion. These effects were not mediated by the renal nerves. The glycine response was not inhibited by aortic snare used to mimic the effects of NMDA-R inhibitors on basal renal blood flow. NMDA-R are expressed in kidney cortex, where they exert a tonic vasodilatory influence and may account for the vasodilatory response to glycine infusion.

Topics: Analysis of Variance; Animals; Dizocilpine Maleate; DNA, Complementary; Glomerular Filtration Rate; Glycine; Hemodynamics; Immunohistochemistry; Kidney Cortex; Kynurenic Acid; Male; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Renal Circulation; Reverse Transcriptase Polymerase Chain Reaction

The purpose of this study was to clarify the in vitro pharmacological profile and the in vivo activity of (3S)-7-chloro-3-[2-((1R)-1-carboxyethoxy)-4-aminomethylphenyl]aminocarbonylmethyl-1,3,4,5-tetrahydrobenz[c,d]indole-2-carboxylic acid hydrochloride (SM-31900). SM-31900 inhibited the binding of [3H]glycine and [3H]5,7-dichlorokynurenic acid, radioligands for the N-methyl-D-aspartate (NMDA) receptor glycine-binding site, to rat brain membranes in a competitive manner, with K(i) values of 11+/-2 and 1.0+/-0.1 nM, respectively, and completely prevented the binding of [3H]dizocilpine (MK-801), a radioligand for the NMDA receptor channel site. In cultures of rat cortical neurons, SM-31900 markedly prevented the neuronal cell death induced by transient exposure to glutamate, in a concentration-dependent manner. Its neuroprotective potency was much stronger than those of other glycine-binding site antagonists (4-trans-2-carboxy-5,7-dichloro-4-phenylaminocarbonylamino-1,2,3,4-tetrahydroquinoline (L-689,560), 5,7-dichlorokynurenic acid, and 7-chlorokynurenic acid). Furthermore, SM-31900 showed anticonvulsant activity when administered systemically, unlike other antagonists. These data indicate that SM-31900 is a systemically active antagonist with high affinity for the NMDA receptor glycine-binding site.

Topics: Aminoquinolines; Animals; Binding, Competitive; Brain; Cells, Cultured; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Antagonists; Fetus; Glutamic Acid; Indoles; Kynurenic Acid; Male; Neurons; Neuroprotective Agents; Neurotoxins; Radioligand Assay; Rats; Rats, Sprague-Dawley; Rats, Wistar; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Seizures

Numerous data indicate that noncompetitive and competitive N-methyl-D-aspartate (NMDA) receptor antagonists inhibit the development of physical dependence on opioids when these substances are administered together, and NMDA receptor antagonists are used at lower range of doses. Higher doses of these antagonists can enhance some opioid-induced effects. The present study extends these findings to the effects of NMDA/glycine (glycine(B)) site antagonists. Wistar rats were rendered dependent on morphine by implantation of morphine pellets. Both of the glycine(B) site antagonists used, 7-chloro-4-hydroxy-3-(3-phenoxy)-phenyl-2(H)-quinolone (L-701,324; 2.5 and 5.0 mg/kg) and 5,7-dichlorokynurenic acid (5,7-DCKA; 25, 50, and 100 mg/kg), suppressed the expression of morphine withdrawal syndrome estimated as wet dog shakes. Furthermore, L-701,324 (2.5 and 5 mg/kg), given twice a day during the development of morphine dependence, attenuated the development of morphine dependence, and the results were comparable to those obtained after administration of noncompetitive NMDA receptor antagonist - MK801 (0.1 mg/kg). Our data suggest that glycine(B) site antagonists may attenuate wet dog shakes (withdrawal) and the development of dependence, both being induced by chronic morphine administration in rats.

Topics: Animals; Behavior, Animal; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Implants; Excitatory Amino Acid Antagonists; Glycine Agents; Kynurenic Acid; Male; Morphine; Morphine Dependence; Naloxone; Narcotic Antagonists; Narcotics; Quinolones; Rats; Rats, Wistar; Receptors, Glycine; Substance Withdrawal Syndrome

1. Magnesium (Mg)-deficient rats develop a mechanical hyperalgesia which is reversed by a N-Methyl-D-Aspartate (NMDA) receptor antagonist. Given that functioning of this receptor-channel is modulated by Mg, we wondered whether facilitated activation of NMDA receptors in Mg deficiency state may in turn trigger a cascade of specific intracellular events present in persistent pain. Hence, we tested several antagonists of NMDA and non-NMDA receptors as well as compounds interfering with the functioning of intracellular second messengers for effects on hyperalgesia in Mg-deficient rats. 2. Hyperalgesic Mg-deficient rats were administered intrathecally (10 microl) or intraperitoneally with different antagonists. After drug injection, pain sensitivity was evaluated by assessing the vocalization threshold in response to a mechanical stimulus (paw pressure test) over 2 h. 3. Intrathecal administration of MgSO4 (1.6, 3.2, 4.8, 6.6 micromol) as well as NMDA receptor antagonists such as MK-801 (0.6, 6.0, 60 nmol), AP-5 (10.2, 40.6, 162.3 nmol) and DCKA (0.97, 9.7, 97 nmol) dose-dependently reversed the hyperalgesia. Chelerythrine chloride, a protein kinase C (PKC) inhibitor (1, 10.4, 104.2 nmol) and 7-NI, a specific nitric oxide (NO) synthase inhibitor (37.5, 75, 150 micromol x kg(-1), i.p.) induced an anti-hyperalgesic effect in a dose-dependent manner. SR-140333 (0.15, 1.5, 15 nmol) and SR-48968 (0.17, 1.7, 17 nmol), antagonists of neurokinin receptors, produced a significant, but moderate, increase in vocalization threshold. 4. These results demonstrate that Mg-deficiency induces a sensitization of nociceptive pathways in the spinal cord which involves NMDA and non-NMDA receptors. Furthermore, the data is consistent with an active role of PKC, NO and, to a lesser extent substance P in the intracellular mechanisms leading to hyperalgesia.

Topics: 2-Amino-5-phosphonovalerate; Alkaloids; Analgesics; Animals; Benzophenanthridines; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Hyperalgesia; Indazoles; Injections, Spinal; Kynurenic Acid; Magnesium Sulfate; Male; Neurons; Nitric Oxide Synthase; Pain Measurement; Phenanthridines; Protein Kinase C; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Spine

Changes to the binding properties of cortical N-methyl-D-aspartic acid (NMDA) and beta-adrenergic receptors have both been reported as potential indicators of antidepressant activity. In the present investigation we examined the effects of the noradrenaline reuptake inhibitor, reboxetine, the serotonin reuptake inhibitor, sertraline, alone and in combination on the binding properties of cortical NMDA receptors and cortical beta1-adrenoceptors following 14 days of treatment in the olfactory bulbectomized rat model of depression. A decrease in the potency of glycine to displace the strychnine insensitive glycine antagonist [3H] 5,7 dichlorokynurenic acid (5,7 DCKA) was observed in cortical homogenates of OB rats when compared to sham-operated controls. Similarly, treatment with the combination of reboxetine and sertraline for 14 days produced a decrease in the potency of glycine when compared to vehicle treated controls. By contrast neither olfactory bulbectomy or drug treatment significantly altered basal or glycine enhanced binding of the non-competitive NMDA antagonist [3H] MK-801 in cortical homogenates. Reboxetine alone, and in combination with sertraline, down-regulated [3H]-CGP 12177 (a selective beta-adrenoceptor antagonist) binding in both OB and sham-operated animals. The lack of a bulbectomy effect in the [3H] CGP-12177 binding assay, and the fact that olfactory bulbectomy and antidepressant treatments produce a similar change to the potency of glycine at the NMDA receptor, suggests that these tests do not provide a neurochemical marker for either the behavioral hyperactivity deficit or antidepressant response in the model.

Topics: Adrenergic beta-Antagonists; Adrenergic Uptake Inhibitors; Animals; Cerebral Cortex; Depressive Disorder; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Kynurenic Acid; Male; Morpholines; Neurons; Norepinephrine; Propanolamines; Rats; Rats, Sprague-Dawley; Reboxetine; Receptors, Adrenergic, beta-1; Receptors, N-Methyl-D-Aspartate; Serotonin; Sertraline

Quinolinic acid (QUIN) displaced binding of agonist and antagonist ligands for the N-methyl-D-aspartate (NMDA) receptor in rat brain synaptic membranes. Both QUIN and glutamic acid (GLU) potentiated binding of [3H]dizocilpine (MK-801) in the presence of glycine (GLY) alone, whereas the potentiation by QUIN was in a bell-shaped fashion in contrast to that by GLU. However, further addition of spermidine (SPD) induced bell-shaped potentiation by GLU as well as QUIN. The potentiation by QUIN was markedly deteriorated by the further addition of FeCl2 irrespective of the presence of GLY and SPD added. These results suggest that QUIN may potentiate [3H]MK-801 binding to the open NMDA channel in rat brain synaptic membranes through a mechanism different from that underlying the potentiation by GLU.

Topics: 2-Amino-5-phosphonovalerate; Allosteric Regulation; Animals; Binding Sites; Brain; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Ferrous Compounds; Glutamic Acid; Glycine; Inhibitory Concentration 50; Kynurenic Acid; Male; Quinolinic Acid; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Spermidine; Synaptic Membranes

We examined the effects of blockers of N-methyl-D-asparate (NMDA) and +/- -alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors on the maintenance of self-sustaining status epilepticus (SSSE) induced in rats by brief intermittent electrical stimulation of the perforant path (PPS). Blocking of NMDA receptor at the PCP site by MK-801 (0.5 mg/kg, i.p.) or ketamine (10 mg/kg, i.p.) as well as at the glycine allosteric site by intrahippocampal 5,7-dichlorokynurenic acid (5,7-DCK, 10 nmol), rapidly and irreversibly aborted both behavioral and electrographic manifestation of SSS. Intrahippocampal injection of the AMPA/kainate receptor blocker 6-cyano7-nitroquinixaline-3-dione (CNQX, 10 nmol) transiently suppressed seizures, which reappeared 4-5 h later. We suggest that the maintenance phase of SSSE depends on activation of NMDA receptors and that NMDA receptor blockers may be a promising class of compounds for the treatment of status epilepticus.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Animals; Anticonvulsants; Disease Models, Animal; Dizocilpine Maleate; Electric Stimulation; Excitatory Amino Acid Antagonists; Hippocampus; Ketamine; Kynurenic Acid; Male; Perforant Pathway; Rats; Rats, Wistar; Receptors, AMPA; Receptors, Kainic Acid; Receptors, N-Methyl-D-Aspartate; Status Epilepticus

Several studies have suggested that polyamines modulate the interaction of glycine with the NMDA receptor. We have further investigated the effects of polyamines using the NMDA receptor glycine site antagonist [(E)-3-(2-phenyl-2-carboxyethenyl)-4,6-dichloro-1H-indole-2-carbox ylic acid] ([3H]MDL 105,519). [3H]MDL 105,519 binding assays were performed using well washed membranes prepared from frozen rat brains. The polyamines spermine and spermidine increased the fraction of non-specific binding (determined by the addition of 1 mM glycine) in the [3H]MDL 105,519 binding assay from 40-60% when spermine or spermidine concentration was increased from 1 to 100 microM. Polyamine agonists spermine, spermidine and 1,5-(diethylamino)piperidine (30 microM) did not have a significant effect on displacement of [3H]MDL 105,519 binding by glycine or glycine site antagonists. Similarly, the polyamine antagonist arcaine did not have a significant effect on displacement of [3H]MDL 105,519 binding by glycine or glycine site antagonists. However, spermidine significantly depressed the potency of MDL 105,519 in displacing [3H]dizocilpine binding. These data suggest that [3H]MDL 105,519 may preferentially bind to a polyamine insensitive form of the NMDA receptor.

Topics: Aminoquinolines; Animals; Binding Sites; Binding, Competitive; Brain; Cell Membrane; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glycine; Indoles; Kynurenic Acid; Polyamines; Rats; Receptors, N-Methyl-D-Aspartate; Spermidine; Spermine; Tritium

The aim of the study was to examine the effect of antagonists of the NMDA receptor on the parkinsonian-like muscle rigidity in rats. Reserpine and haloperidol increased the muscle resistance of the hind foot to passive movements, as well as the reflex electromyographic (EMG) activity in the gastroenemius and tibialis anterior muscles. MK-801 (0.32-1.28 mg/kg s.c.), an uncompetitive antagonist of the NMDA receptor, and L-701,324 (5-40 mg/kg i.p.), an antagonist of the glycine site, reduced the muscle tone and the reflex EMG activity enhanced by reserpine or haloperidol. AP-5 (2 and 5 micrograms/0.5 microliter), a competitive antagonist of the NMDA receptor, and 5,7-dichlorokynurenic acid (1.0-4.5 micrograms/0.5 microliter), the glycine site antagonist injected bilaterally into the rostral striatum, inhibited the muscle rigidity induced by haloperidol. In contrast, AP-5, injected alone bilaterally into the intermediate-caudal striatum induced muscle rigidity. The present results suggest that: (1) the inhibitory effect of the NMDA receptor antagonists on the parkinsonian-like muscle rigidity depends, at least partly, on their action on the rostral striatum; (2) the blockade of NMDA receptors in the intermediate-caudal striatum may reduce the beneficial impact of these compounds.

Topics: Animals; Corpus Striatum; Disease Models, Animal; Dizocilpine Maleate; Electromyography; Excitatory Amino Acid Antagonists; Haloperidol; Kynurenic Acid; Parkinson Disease; Quinolones; Rats; Receptors, N-Methyl-D-Aspartate; Reserpine

Field excitatory postsynaptic potentials (EPSPs) were recorded in the CA1 region of hippocampal slices from 12-18-day-old rats. The isolated N-methyl-D-aspartate (NMDA) receptor mediated field EPSP as well as the composite field EPSP of both NMDA and alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptor mediated components were obtained in low Mg2+ solutions with 10 microM or 1 microM of the AMPA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), respectively. The isolated AMPA receptor mediated field EPSP was obtained either in normal Mg2+ solution or in a low Mg2+ solution in the presence of the NMDA receptor antagonist D-2-amino-5-phosphonopentanoic acid. The waveforms of the field EPSPs were studied and the effect of long-term depression (LTD) on these waveforms was compared with the effects of several pharmacological agents that attenuate the synaptic efficacy. It was shown that LTD occurred without changes in the waveforms of isolated AMPA and NMDA EPSPs. Reducing the number of release sites by lowering the stimulus strength or reducing the probability of transmitter release by an adenosine agonist N6-cyclohexyl-adenosine both mimicked the LTD-induced changes. Partial blockade of the AMPA receptors was also without effect on the waveforms of isolated AMPA EPSPs. In contrast, partial blockade of the NMDA receptors in several different ways resulted in waveform changes. A similar result could be inferred from experiments using composite field EPSPs. The synaptic attenuation caused by a partial blockade of NMDA receptors therefore appears to differ mechanistically from that involved in LTD, arguing against a postsynaptic locus of the modification involved in LTD. However, directly testing for alterations in transmitter release using the open channel blocker of NMDA receptors MK-801 failed in revealing such presynaptic changes during LTD. Our results therefore suggest that LTD might be due to a coordinated pre- and postsynaptic change instead of distinct pre- or postsynaptic modifications.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Dizocilpine Maleate; Evoked Potentials; Excitatory Amino Acid Antagonists; Hippocampus; Kynurenic Acid; Male; Neuronal Plasticity; Neurotransmitter Agents; Rats; Rats, Sprague-Dawley; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Receptors, Presynaptic; Synapses

Topics: 2-Amino-5-phosphonovalerate; Animals; Binding, Competitive; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; gamma-Aminobutyric Acid; In Vitro Techniques; Kainic Acid; Kynurenic Acid; Male; Piperidines; Radioligand Assay; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

A stoichiometric analysis of N-methyl-D-aspartate (NMDA) receptor binding was conducted using [3H]dizocilpine, [3H]dichlorokynurenic acid and [3H]CGP39653, and membranes from various brain regions of rats. The ratio of the density of [3H]CGP39653 binding to [3H]dizocilpine binding was > 1 in frontal cortex and hippocampus, approximately 1 in striatum and spinal cord and < 1 in cerebellum. When [3H]dichlorokynurenic acid binding was compared with [3H]dizocilpine binding, the ratios were > 1 in frontal cortex, hippocampus and striatum, 3-4 in cerebellum, and approximately 2 in spinal cord. These observations suggest that a single channel complex may have more than one binding site for NMDA and/or glycine and that the stoichiometry between the binding domains of the NMDA receptor varies regionally.

Topics: 2-Amino-5-phosphonovalerate; Animals; Brain; Brain Chemistry; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; In Vitro Techniques; Kinetics; Kynurenic Acid; Male; Nerve Tissue Proteins; Radioligand Assay; Rats; Rats, Inbred F344; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate

We have recently demonstrated that a single administration of m-chlorophenylpiperazine (m-CPP, a preferential 5-HT2C receptor agonist) produces tolerance to its stimulatory effect on adrenocorticotropic hormone (ACTH) concentrations when challenged 24 h later with the same dose of m-CPP. In the present study, we studied the effects of pretreatment with various N-methyl-D-aspartate (NMDA) receptor antagonists on development of tolerance to m-CPP's stimulatory effect on ACTH concentrations. Pretreatment with various NMDA receptor antagonists such as 5.7-dichlorokynurenic acid (1.0 mg/kg), 3-amino-1-hydroxy 2-pyrrolidone (1.0 mg/kg), dizocilpine (0.1 mg/kg) and ifenprodil (1.0 mg/kg) injected 30 min before the first injection of m-CPP (2.5 mg/kg) blocked development of tolerance to m-CPP's stimulatory effect on ACTH concentrations in rats injected 24 h later with the same dose (2.5 mg/kg) of m-CPP. These findings suggest that tolerance to postsynaptic 5-HT2C receptor-mediated response is initiated though stimulation of NMDA receptor complex and, furthermore, demonstrate a functional interaction between the 5-HT and glutamate systems.

Topics: Adrenocorticotropic Hormone; Animals; Dimethyl Sulfoxide; Dizocilpine Maleate; Drug Tolerance; Kynurenic Acid; Male; Phencyclidine; Piperazines; Piperidines; Pyrrolidinones; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Serotonin Receptor Agonists

We have previously reported that enhanced glycine release is produced by epidural spinal cord stimulation, a clinical method for treating neuropathic pain. Our current hypothesis is that glycine administered intrathecally reduces neuropathic pain as measured by the Randall-Selitto method. Neuropathic rats created by unilateral partial ligation of the sciatic nerve were treated with intrathecal infusion of glycine, strychnine, MK-801, or 5,7-DKA at 0.1 mumol, or artificial CSF for 2 hours at a rate of 10 microliters/min. Force required to produce the pain response was significantly increased after glycine administration and reduced using strychnine, a specific glycine receptor (Gly l) antagonist. Strychnine blocked the response to glycine when infused together. Administration of the non-specific NMDA receptor MK-801 antagonist and 5,7-DKA, a specific glycine-NMDA receptor (Gly 2) antagonist, however, failed to block the response to glycine. Our results provide evidence for the use of glycine and related compounds to treat neuropathic pain.

Topics: Animals; Cerebrospinal Fluid; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glycine; Glycine Agents; Injections, Spinal; Kynurenic Acid; Male; Mechanoreceptors; Neuralgia; Nociceptors; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Strychnine; Transcutaneous Electric Nerve Stimulation

The cytotoxicity induced by the transient expression of functional N-methyl-D-aspartate (NMDA) receptors has been examined with the use of a luciferase reporter assay in Chinese hamster ovary cells. Various NMDA receptor antagonists, in a dose-dependent manner, prevented a loss of luciferase activity 24 to 48 hr post-transfection of either the NR1/NR2A or NR1/ NR2B subunit receptor configurations, likely correlating to the time required to express functionally these receptors. Both glutamate and NMDA were potently cytotoxic to transfected cells previously protected by antagonists. The novel ifenprodil analog (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol (CP101,606-27) protected cells expressing NR1/NR2B, but not those cells expressing either NR1/NR2A or, putatively, NR1/NR2A/NR2B. Decreased cytotoxicity was observed when a mutated NR1 subunit (N616R) with reduced Ca++ permeability was used in coexpression studies with NR2A or NR2B. In contrast to our results with NR1/NR2A or NR1/NR2B, cells expressing NR1/NR2C did not perish. Our studies suggest that expression of functional NMDA receptors in non-neuronal cells leads to a form of excitotoxicity similar to that observed in mammalian neurons in vitro.

Topics: Animals; Calcium; Cell Survival; CHO Cells; Cricetinae; Dizocilpine Maleate; Kynurenic Acid; L-Lactate Dehydrogenase; Luciferases; Pipecolic Acids; Piperidines; Receptors, N-Methyl-D-Aspartate; Transfection

Ethanol, acutely, is a potent inhibitor of the function of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. After chronic exposure of animals to ethanol, however, the NMDA receptor in brain is upregulated. This upregulation is associated with the occurrence of ethanol withdrawal seizures. When cultured cerebellar granule neurons are exposed chronically to ethanol, the resulting upregulation of NMDA receptor function renders the cells more susceptible to glutamate-induced neurotoxicity. The present studies show that chronic ethanol exposure produces an increase in NMDA receptor number in the cells, measured by ligand binding to intact cells. Glutamate-induced excitotoxicity, both in control and ethanol-exposed cells, is blocked by the same NMDA receptor antagonists previously shown to block ethanol withdrawal seizures in animals. In addition, glutamate neurotoxicity is blocked by acute (2-hr) pretreatment of cells with ganglioside GM1 or by chronic (3 days) treatment with the ganglioside. Acute ganglioside treatment does not interfere with the initial rise in intracellular calcium caused by glutamate, whereas this response is downregulated after chronic ganglioside treatment. These results suggest that therapeutic agents can be developed to block both ethanol withdrawal signs and the neuronal damage that accompanies ethanol withdrawal. Furthermore, chronic ganglioside treatment during ethanol exposure has the potential to prevent changes in the NMDA receptor that lead to withdrawal seizures and enhanced susceptibility to excitotoxicity.

Topics: Alcohol Withdrawal Delirium; Alcoholism; Animals; Animals, Newborn; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Female; G(M1) Ganglioside; Glutamic Acid; Kynurenic Acid; Neurons; Pipecolic Acids; Rats; Receptors, N-Methyl-D-Aspartate; Synaptic Transmission; Up-Regulation

The anticonvulsant felbamate may act as an N-methyl-D-aspartate (NMDA) receptor antagonist, but the mechanism of block has not been fully characterized. We sought to identify the sites at which felbamate exerts its NMDA receptor blocking action using radioligand binding to rat forebrain membranes and whole-cell voltage clamp and single-channel recordings from cultured rat hippocampal neurons. Equilibrium binding isotherms for [3H]dizocilpine, a channel blocking ligand, were obtained in the presence of saturating glutamate and glycine. At a concentration of 1 mM, felbamate competitively inhibited specific [3H]dizocilpine binding, indicating that felbamate interacts with the channel blocking site. At a higher concentration (3 mM), felbamate also reduced the maximal saturation binding, demonstrating an additional allosteric action. The dissociation constant (Kb), estimated from fits to the binding isotherms, was 0.7-1.1 mM. It has been proposed that felbamate block of NMDA receptors occurs via competitive glycine site antagonism. However, the slowing of [3H]dizocilpine dissociation by felbamate, unlike the slowing produced by 7-chlorokynurenic acid, was not reversed by increasing the glycine concentration. In addition, felbamate did not reduce specific binding of [3H]5,7-dichlorokynurenic acid, a glycine site ligand. In whole-cell voltage clamp recordings of NMDA receptor currents, its blocking time constant (69 +/- 0.4 msec) was substantially faster than the dissociation time constant of glycine (390 +/- 23 msec), whereas the time constant for 5,7-dichlorokynurenic acid (390 +/- 20 msec) was similar. These observations indicate that felbamate block of NMDA receptors does not occur by an action at the glycine site.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Anticonvulsants; Cells, Cultured; Dizocilpine Maleate; Felbamate; Kynurenic Acid; Membrane Potentials; Phenylcarbamates; Propylene Glycols; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Tritium

Chronic antidepressant treatment results in adaptation of the NMDA receptor complex in the rodent cortex. This adaptation consists of a reduction in the potency of glycine to displace [3H]5,7-dichlorokynurenic acid from strychnine-insensitive glycine receptors and a reduction in high affinity, glycine-displaceable [3H]CGP-39653 binding to glutamate receptors. We hypothesized that dysfunction of NMDA receptors might occur in frontal cortices from human suicide victims. We now report that the proportion of high affinity, glycine displaceable [3H]CGP-39653 binding to glutamate receptors is reduced from 45 +/- 5% in controls to 27 +/- 6% in age- and post-mortem interval-matched suicide victims. In contrast, neither the potency nor the maximum efficacy of glycine to inhibit [3H]CGP-39653 binding is altered in the frontal cortex of suicide victims compared to controls. Moreover, neither the potency of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding to the strychnine-insensitive glycine receptor nor the specific binding of [3H]5,7-dichlorokynurenic acid binding differed in suicide victims compared to controls. Likewise, neither basal nor glycine- or glutamate enhanced non-equilibrium binding of [3H]dizocilpine was altered in the frontal cortex of suicide victims compared to controls. These data represent the first demonstration supporting the hypothesis that glutamatergic dysfunction is involved in psychopathology underlying suicide and, potentially in human major depression.

Topics: 2-Amino-5-phosphonovalerate; Adult; Dizocilpine Maleate; Female; Frontal Lobe; Humans; In Vitro Techniques; Kynurenic Acid; Male; Middle Aged; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Suicide

Expression of the NR-1 subunit in Xenopus oocytes produces channels that respond to glutamate and are blocked by competitive and noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptor. Ionic conductances through these channels are increased by coexpression with NR-2 receptor subunits. We have characterized the pharmacological properties of NMDA receptors assembled from combinations of subunits expressed in transfected cells, to determine the minimum subunit requirements for binding of competitive glutamate antagonists, glycine antagonists, and channel-blocking agents, as detected by ligand-binding experiments. Expression of NR-1a alone produced glycine antagonist binding, whereas the combination of NR-1a and NR-2A was needed to produce binding sites for glutamate antagonists and channel-blocking agents. These results suggest that functional NMDA receptors assemble from these subunits. However, differences in the pharmacological effects of NMDA and polyamines show that not all characteristics of native NMDA receptors are reproduced by this combination of subunits.

Topics: Binding Sites; Cells, Cultured; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Glutamates; Glutamic Acid; Glycine; Humans; Ion Channels; Kynurenic Acid; Receptors, N-Methyl-D-Aspartate; Transfection

The ligand preferences of recombinant NR1 homomeric and NR1-NR2 heteromeric NMDA receptors were examined by homogenate binding assay. The binding affinities for most ligands were similar to those reported for native NMDA receptors. The order of affinity for [3H]glutamate was NR1-NR2B > NR1-NR2A approximately NR1-NR2D > NR1-NR2C > NR1. NMDA had approximately equal affinity for all heteromeric types (Ki approximately 5 microM), but the competitive antagonists CGS 19755 (cis-4-(phosphonomethyl)piperidine-2-carboxylic acid) and CGP 39653 (D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid) displayed the affinity order NR1-NR2A > NR1-NR2B > NR1-NR2D > NR1-NR2C. Binding of [3H]CGP 39653 could only be detected at the NR1-NR2A receptor type (Kd approximately 6 nM). The glycine site antagonist [3H]5,7-dichlorokynurenate bound with good affinity to all recombinant receptors (Kd approximately 50-100 nM), while glycine exhibited an affinity order of NR1-NR2C >> NR1 = NR1-NR2B = NR1-NR2D > NR1-NR2A. The channel-site ligand [3H]MK 801 ((+)-5-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate) showed the affinity ranking NR1-NR2A = NR1-NR2B >> NR1 > NR1-NR2C = NR1-NR2D. Thus the ligand binding affinities of recombinant NMDA receptors is dependent on their subunit composition. The NR1-NR2A, NR1-NR2B, NR1-NR2C and NR1-NR2D receptors may account for the antagonist-preferring, agonist-preferring, cerebellar, and medial thalamic subtypes of native NMDA receptors, respectively.

Topics: 2-Amino-5-phosphonovalerate; Animals; Autoradiography; Binding Sites; Binding, Competitive; Brain; Cloning, Molecular; Dizocilpine Maleate; DNA; Glutamic Acid; Ion Channels; Kinetics; Kynurenic Acid; Ligands; Rats; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Recombinant Proteins

The effects of an antagonist at the strychnine insensitive glycine site (5,7-dichlorokynurenic acid, i.c.v.), and of noncompetitive (MK-801, i.p.) and competitive (CGP 37849, i.p.; CGP 39551, i.p.; AP-7, i.c.v.) NMDA antagonists were compared with diazepam (i.p.) in two animal models of anxiety (the open field exploratory behavior of non-habituated rats, and the Vogel conflict test). All drugs when applied in appropriate doses increased punished drinking in the Vogel test, without producing any significant changes in free drinking and the stimulus threshold at their lowest anticonflict doses. The effective doses were as follows: diazepam 1.5 and 2.5 mg/kg; MK-801 0.005 and 0.01 mg/kg; CGP 39551 5.0 and 20.0 mg/kg; CGP 37849 1.0 and 2.5 mg/kg; 5,7-dichlorokynurenic acid 5.0 microgram (i.c.v.); AP-7 0.5 microgram (i.c.v.). In the open field diazepam (0.05 mg/kg), MK-801 (0.1 mg/kg), CGP 37849 (0.01, 0.1, 1.0 mg/kg), and AP-7 2.5 micrograms (i.c.v.) significantly increased exploratory activity in the central sectors of the open field (anti-neophobic reaction), without changing motor activity of the rat. MK-801 at the highest tested dose of 0.2 mg/kg significantly stimulated animal locomotor activity. CGP 37849 in the largest dose examined (10 mg/kg) significantly depressed the motor behavior of rats. Overall, it appeared that different NMDA antagonists showed an anxiolytic-like profile, similar to that of the benzodiazepine diazepam. Among different NMDA receptor complex antagonists studied, CGP 37849 was characterized by the largest distinction between the doses showing an anxiolytic-like action in the open field test, and changing rat motor behavior.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anxiety; Behavior, Animal; Conflict, Psychological; Diazepam; Dizocilpine Maleate; Drinking; Electroshock; Exploratory Behavior; Injections, Intraventricular; Kynurenic Acid; Male; Motor Activity; Rats; Rats, Wistar; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate

Immobilization stress in water for 3 h was effective in inducing significant potentiation of [3H](+)-5-methyl-10,11-dihydro-5H- dibenzo [a,d] cyclohepten-5,10-imine ([3H]MK-801) binding 5 days after the stressful manipulation in rat hypothalamus and cerebellum when determined before equilibrium in the absence of any added agonists, in addition to resulting in marked reduction of rearing behaviors of animals. However, the stressful manipulation failed to modulate the [3H]MK-801 binding in other central regions examined, and binding of either [3H]DL-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid or [3H]kainic acid was not significantly affected in all brain structures studied 5 days after the stress application. In contrast, the stressful procedures potentiated binding of both L-[3H]glutamic ([3H]Glu) and [3H]DL-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic ([3H]CGP-39653) acids in the hypothalamus and cerebellum 5 days later, without affecting binding of [3H]-glycine and 5,7-dichloro[3H]kynurenic acid. The systemic administration of corticosterone mimicked the stress manipulation at doses of 5-50 mg/kg in terms of inducing significant enhancement of binding of both [3H]Glu and [3H]CGP-39653 in the hypothalamus and cerebellum when determined 5 days after the single administration. The translation inhibitor cycloheximide was effective in preventing the stress-induced potentiation of [3H]Glu binding in the cerebellum, without altering that in the hypothalamus. Furthermore, the stressful handling significantly increased the densities of [3H]Glu binding sites in the hypothalamus and cerebellum, with the affinities being unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Amino-5-phosphonovalerate; Adrenal Cortex Hormones; Animals; Autoradiography; Behavior, Animal; Brain Chemistry; Cerebellum; Corpus Striatum; Cycloheximide; Dizocilpine Maleate; Dose-Response Relationship, Drug; Glycine; Hypothalamus; Kynurenic Acid; Male; N-Methylaspartate; Rats; Rats, Wistar; Stress, Physiological; Tritium

The effect of glycine on the intracellular free Ca2+ concentration ([Ca2+])i response to N-methyl-D-aspartate (NMDA) was examined in small groups of cerebellar granule cells loaded with fura 2. NMDA alone evoked a long-lasting monophasic [Ca2+]i plateau, which was abolished by removal of extracellular Ca2+, or addition of the NMDA channel antagonist dizocilpine or the glycine site antagonist 5,7-dichlorokynurenic acid, virtually unaffected by the L-type Ca2+ channel antagonist (-)-PN 202 791, and greatly, though variably, potentiated by addition of glycine. In the presence of glycine the response to NMDA was clearly biphasic. However, there was no consistent relationship between the magnitudes of the peak and plateau phases of the response, and their temporal relationship was also highly variable. The potentiation seen with exogenous glycine was highly dependent on plating density, which may be the result of higher levels of endogenous glycine in more dense cultures. Our results provide an explanation of the inconsistent findings previously reported by different groups on the potentiation of the [Ca2+]i response to NMDA by exogenous glycine.

Topics: Animals; Calcium; Calcium Channel Agonists; Cells, Cultured; Cerebellum; Dizocilpine Maleate; Glycine; Kynurenic Acid; Nicotinic Acids; Oxadiazoles; Rats; Receptors, N-Methyl-D-Aspartate

Chronic (14 daily injections) treatment of mice with the prototypic tricyclic antidepressant imipramine significantly alters ligand binding to the N-methyl-D-aspartate (NMDA) receptor complex. These effects were compared to a chronic regimen of 1-aminocyclopropanecarboxylic acid, a high-affinity partial agonist at strychnine-insensitive glycine receptors which mimics the effects of imipramine in preclinical models predictive of antidepressant action. Changes in the NMDA receptor complex after chronic, but not acute treatment with imipramine were manifested as: 1) a reduction in the potency of glycine to inhibit [3H]5,7-dichlorokynurenic acid binding to strychnine-insensitive glycine receptors; 2) a decrease in the proportion of high-affinity glycine sites inhibiting [3H]CGP 39653 binding to NMDA receptors; and 3) a decrease in basal [3H]MK-801 binding (under nonequilibrium conditions) to sites within NMDA receptor-coupled cation channels which was reversible by the addition of glutamate. These effects were observed in cerebral cortex, but not in hippocampus, striatum or basal forebrain. Chronic treatment with 1-aminocyclopropanecarboxylic acid resulted in changes which paralleled those of imipramine on ligand binding to the NMDA receptor complex, but the reduction in basal [3H]MK-801 binding did not achieve statistical significance. These findings indicate that adaptive changes in the NMDA receptor complex could be a feature common to chronic treatment with structurally unrelated antidepressants.

Topics: 2-Amino-5-phosphonovalerate; Amino Acids; Amino Acids, Cyclic; Animals; Brain; Dizocilpine Maleate; Drug Administration Schedule; Glycine; Imipramine; In Vitro Techniques; Kynurenic Acid; Male; Mice; Receptors, N-Methyl-D-Aspartate

Antagonists at the N-methyl-D-aspartate (NMDA) receptor site share a number of properties including anticonvulsant and anxiolytic-like behaviors. In the social interaction and elevated plus maze assay, two non-conditioned paradigms predictive of anxiolytic activity, the NMDA antagonists 5,7 DCKA, CPP and MK-801, as well as diazepam, all significantly increased both social interaction time and open arm exploration time, respectively. Likewise, in the Cook and Davidson conditioned conflict paradigm, the NMDA antagonists 5,7 dichlorokynurenic acid (DCKA; 100 and 173 mg/kg), (+-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP; 10 mg/kg), dizolcipine (MK-801; 0.03 mg/kg) and the benzodiazepine, diazepam (3-30 mg/kg) significantly disinhibited conflict responding. In addition, administration of 5,7 DCKA did not result in a generalization to a MK-801 discriminative cue in a drug discrimination paradigm. In general, antagonism at the NMDA receptor complex results in anxiolytic-like behavior in rodents. In particular, selective antagonism at the strychnine-insensitive glycine modulatory site (5,7 DCKA) may represent a new and novel class of compounds with potential therapeutic efficacy in anxiety without some of the side effects associated with other NMDA antagonists.

Topics: Analysis of Variance; Animals; Anti-Anxiety Agents; Behavior, Animal; Conflict, Psychological; Diazepam; Discrimination Learning; Dizocilpine Maleate; Glycine; Kynurenic Acid; Male; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Social Behavior

Felbamate (2-phenyl-1,3-propanediol dicarbamate) is a novel agent effective against maximal electroshock, pentylenetetrazol and other chemically induced seizures in mice and rats. Felbamate has been proposed as a novel anticonvulsant for the treatment of generalized tonic-clonic and complex partial seizures. In addition, felbamate has been shown to have neuroprotectant effects (in vitro and in vivo) in neonate models of cerebral ischemia. However, few existing studies have contributed to the elucidation of the mechanism of anticonvulsant and neuroprotectant action of felbamate. Because glycinergic mechanisms have been demonstrated to be involved with seizure disorders and neuroprotection, we investigated the binding interaction of felbamate with strychnine-insensitive glycine receptors and compared these findings with brain and plasma levels of felbamate after drug treatment. Inhibition of [3H]5,7-dichlorokynurenic acid (a high-affinity glycine receptor antagonist) binding by felbamate (IC50 = 374 microM) corresponded well with peak felbamate concentrations found in brain (683 and 759 microM) and plasma (679 and 807 microM) 8 hr after 300 (i.p.) or 500 mg/kg (p.o.) doses, respectively. Chemically diverse anticonvulsants tested and MK 801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclohepten-5,10-imine maleate] did not modulate [3H]5,7-dichlorokynurenic acid binding. Additional studies have shown that felbamate does not interact with other sites associated with the N-methyl-D-aspartate receptor complex. Thus, the data presented in this report strongly indicate a mechanism of action for felbamate through strychnine-insensitive glycine receptor interaction.

Topics: Animals; Anticonvulsants; Brain; Dizocilpine Maleate; Felbamate; Female; In Vitro Techniques; Kynurenic Acid; Male; Neurons; Phenylcarbamates; Propylene Glycols; Rats; Rats, Sprague-Dawley; Receptors, Glycine; Receptors, Neurotransmitter; Strychnine

The effects of the excitatory amino acid (EAA) receptor antagonists MK-801 (non-competitive NMDA receptor antagonist), DNQX (competitive non-NMDA receptor antagonist) and 5,7-DCKA (antagonist of glycine site of NMDA receptor) have been examined on the naloxone (4 mg/kg, i.p.)-precipitated withdrawal jumping behaviour in morphine-dependent mice. The results indicate that withdrawal jumping behaviour in morphine-dependent mice was attenuated by all three EAA receptor antagonists, MK-801, DNQX and 5,7-DCKA. However, MK-801, DNQX and 5,7-DCKA inhibited the jumping behaviour in a relatively narrow dose range.

Topics: Animals; Behavior, Animal; Dizocilpine Maleate; Glycine; Kynurenic Acid; Male; Mice; Morphine Dependence; Naloxone; Quinoxalines; Receptors, Amino Acid; Receptors, Glycine; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Substance Withdrawal Syndrome

Pre-weaning rat pups emit ultrasonic vocalizations when removed from the litter. These 'separation-induced vocalizations' (SIV) are suppressed by classical benzodiazepine anxiolytics and by non-benzodiazepine anxiolytics which lack muscle relaxant and sedative properties. The present study used the SIV model to assess potential anxiolytic properties of compounds which target different sites associated with the NMDA receptor complex. Comparison was made to drugs which affect benzodiazepine or serotonin (5-HT) receptors. Muscle relaxant potential was assessed using 'TIP' (time on an inclined plane), the amount of time a pup was able to retain its position on a steeply inclined surface. Mephenesin, a centrally acting muscle relaxant, significantly suppressed TIP but not SIV. The benzodiazepine agonist diazepam suppressed both SIV and TIP, whereas the 5-HT1A partial agonists, buspirone and MDL 73,005EF, suppressed SIV without affecting TIP. The 5-HT2 antagonist MDL 11,939 suppressed TIP but not SIV, whereas neither measure was affected by the 5-HT3 antagonist MDL 73,147EF. SIV was suppressed by NMDA antagonists including those acting at the glutamate recognition site (D,L-amino-phosphonovaleric acid (AP5) and MDL 100,453) or at the ion channel (MK-801), or by the strychnine-insensitive glycine antagonist 5,7-dichlorokynurenic acid (5,7-DCKA). TIP was suppressed even more potently by AP5, MDL 100,453 and MK-801, whereas 5,7-DCKA was inactive on this measure. Thus, antagonists acting at different sites present on the glutamate recognition site exhibit potential anxiolytic activity, but the glycine antagonist was unusual in its lack of prominent muscle relaxant side effects.

Topics: 2-Amino-5-phosphonovalerate; Animals; Anti-Anxiety Agents; Anxiety, Separation; Behavior, Animal; Buspirone; Diazepam; Dioxins; Dizocilpine Maleate; Dose-Response Relationship, Drug; Indoles; Kynurenic Acid; Maternal Deprivation; Mephenesin; Piperidines; Quinolizines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Serotonin; Serotonin Antagonists; Spiro Compounds; Valine; Vocalization, Animal