dizocilpine-maleate and homocysteic-acid

Mechanism of ictogenesis of D- and L-stereroisomers of homocysteic acid was studied in 12-day-old rats by means of antagonists of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. There was no qualitative difference between the two stereoisomers in generation of emprosthotonic (flexion) as well as generalized tonic-clonic seizures. Moderate differences were observed in the first, nonconvulsive effects of the two isomers. As generation of the two types of seizures is concerned, NMDA and AMPA participate in generalized tonic-clonic seizures whereas NMDA receptors play a dominant role in generation of flexion seizures.

Topics: 2-Amino-5-phosphonovalerate; Animals; Benzodiazepines; Dizocilpine Maleate; Homocysteine; Male; Quinoxalines; Rats, Wistar; Receptors, AMPA; Receptors, N-Methyl-D-Aspartate; Seizures; Stereoisomerism

Evidence corroborates the role of the anterior cingulate cortex (ACC) in the modulation of cognitive and emotional functions. Its involvement in the motivational-affective component of pain has been widely investigated using different methods to elucidate the specific role of different neurotransmitter systems. We used the peripheral noxious stimulus-induced vocalization algesimetric test to verify glutamatergic and GABAergic neurotransmission in the guinea pig ACC. Microinjection of homocysteic acid (DLH; 30 nmol) in the left guinea pig ACC increased the amplitude of vocalizations (pronociception) compared to controls injected with saline. Moreover, microinjection of MK-801 (3.6 nmol), an NMDA receptor antagonist, did not alter the amplitude of vocalizations, but its microinjection prior to DLH prevented the increase in vocalizations induced by this drug. Regarding the GABAergic system, blockade of GABAA receptors with bicuculline (1 nmol) increased the amplitude of vocalizations, while three different doses of the GABAA agonist muscimol (0.5, 1 and 2 nmol) did not influence nociceptive vocalization responses. Finally, a combination of MK-801 (3.6 nmol) and muscimol (1 nmol) reduced the amplitude of vocalizations (antinociception), suggesting that a combination of glutamate and GABA in the ACC modulates the expression of affective-motivational pain response. We suggest that activation of NMDA receptors or blockade of GABAergic neurotransmission promotes pronociception and that the antinociceptive effect of muscimol depends on the blockade of NMDA receptors.

Topics: Animals; Bicuculline; Dizocilpine Maleate; Dose-Response Relationship, Drug; Excitatory Amino Acid Agents; GABA Agents; gamma-Aminobutyric Acid; Glutamic Acid; Guinea Pigs; Gyrus Cinguli; Homocysteine; Male; Microinjections; Muscimol; Pain; Time Factors; Vocalization, Animal

Incubation of rat lymphocytes with homocysteine (HC) or homocysteic acid (HCA) was found to increase the stationary levels of free radicals in lymphocytes, the effect of both ligands being mediated by ionotropic receptors activated by N-methyl-D-aspactic acid (NMDA), the expression of which on rat lymphocyte membranes was earlier demonstrated. In agreement with these data, increase of free radicals in the lymphocyte cytoplasm is preceded by an increase in the intracellular calcium levels, activation of protein kinase C, nicotinamide adenine dinucleotide phosphate oxidase and/or nitric oxide synthase. Both HC and HCA increase the production of IFN-γ and TNF-α by lymphocytes and antagonist of NMDA receptors; MK-801 prevents this effect. The data presented show that rat lymphocyte membrane contains functionally active NMDA receptors, which regulate cytokine accumulation.

Topics: Animals; Benzophenanthridines; Calcium; Cell Membrane; Cytokines; Cytoplasm; Dizocilpine Maleate; Flow Cytometry; Fluorescence; Free Radicals; Homocysteine; Interferon-gamma; Lymphocytes; N-Methylaspartate; NADPH Oxidases; Nitric Oxide; Protein Kinase C; Rats; Receptors, N-Methyl-D-Aspartate; Tumor Necrosis Factor-alpha

Tonic immobility (TI) is an innate defensive behaviour elicited by physical restriction and postural inversion, and is characterised by a profound and temporary state of akinesis. Our previous studies demonstrated that glutamatergic stimulation of the dorsomedial/dorsolateral portion of periaqueductal gray matter (dPAG) decreases the duration of TI in guinea pigs (Cavia porcellus). Furthermore, evidence suggests that the anterior cingulate cortex (ACC) constitutes an important source of glutamate for the dPAG. Hence, in the current study, we investigated the effects of microinjection of the excitatory amino acid (EAA) agonist DL-homocysteic acid (DLH) and the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 into the ACC on the duration of TI in guinea pigs. We also assessed the effect of the NMDA receptor antagonist (MK-801) into the dorsal periaqueductal gray matter (dPAG) prior to DLH microinjection into the ACC on the TI duration in the guinea pig. Our results demonstrated that DLH microinjections into the ACC decreased the duration of TI. This effect was blocked by previous MK-801 microinjections into the ACC or into the dPAG. The MK-801 microinjections alone did not influence TI duration. These results provide the new insight that EAAs in the ACC can decrease the duration of TI. The mechanism seems to be dependent on the NMDA receptors present in the ACC and in the dPAG.

Topics: Analysis of Variance; Animals; Dizocilpine Maleate; Excitatory Amino Acid Antagonists; Guinea Pigs; Gyrus Cinguli; Homocysteine; Immobility Response, Tonic; Male; Microinjections; Periaqueductal Gray; Receptors, N-Methyl-D-Aspartate

Tonic immobility (TI) is an innate defensive behavior elicited by physical restriction and postural inversion, and is characterized by a profound and temporary state of motor inhibition. The participation of the periaqueductal gray matter (PAG) in TI modulation has previously been described. In addition, the excitatory amino acids (EAA) are important mediators involved in the adjustment of several defensive responses produced by PAG. In the present study, we investigated the effect of microinjection of the EAA agonist dl-homocysteic acid (DLH) and the N-methyl-d-aspartate (NMDA) receptor antagonist (MK-801) into the ventrolateral and dorsal PAG over the duration of TI in guinea pigs. Microinjection of 15 nmol/0.2 microl of DLH into the ventrolateral PAG (vlPAG) and 30 nmol/0.2 microl of DLH into the dorsal PAG (dPAG) promoted an increase and decrease in TI duration, respectively. These responses were blocked by prior microinjection of the NMDA receptor antagonist, MK-801 (3.6 nmol/0.2 microl) at the same site. Microinjection of MK-801 alone into the vlPAG and dPAG did not alter the duration of TI episodes. These results suggest that NMDA receptors are involved in the modulation of TI in both the vlPAG and dPAG. In addition, PAG excitatory amino acids modulate the TI response via columnar organization of the PAG. In this manner, the vlPAG facilitates TI modulation whereas dPAG has an inhibitory role in TI.

Topics: Analysis of Variance; Animals; Behavior, Animal; Dizocilpine Maleate; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Guinea Pigs; Homocysteine; Immobility Response, Tonic; Male; Microinjections; Periaqueductal Gray

Bilateral intracerebroventricular infusion of dl-homocysteic acid (DL-HCA) (600 nmol on each side) to immature 12-day-old rats induced generalized clonic-tonic seizures, recurring frequently for at least 90 min, with a high rate of survival. Electrographic recordings from sensorimotor cortex, hippocampus, and striatum demonstrated isolated spikes in the hippocampus and/or striatum as the first sign of dl-HCA action. Generalization of epileptic activity occurred during generalized clonic-tonic seizures, but electroclinical correlation was very low; dissociation between EEG pattern and motor phenomena was common. Seizures were accompanied by large decreases of cortical glucose and glycogen and by approximately 7- to 10-fold accumulation of lactate. ATP and phosphocreatine (PCr) levels remained unchanged even during longlasting (3 h) convulsions. Metabolite levels became normalized during the recovery period (24 h). The examination of the effect of selected antagonists of NMDA [AP7 (18.5 and 37 mg/kg, respectively), MK-801 (0.5 mg/kg)] and non-NMDA [NBQX (10, 15 and 30 mg/kg, respectively)] receptors revealed that seizures could be attenuated or prevented (depending on the dose employed) by antagonists of both NMDA and non-NMDA receptors, as evaluated not only according to the suppression of behavioral manifestations of seizures, but also in terms of the protection of metabolite changes accompanying seizures. All antagonists employed, when given alone in the same doses as those used for seizure protection, did not influence metabolite levels, with the exception of increased glucose concentrations. Furthermore, the pronounced anticonvulsant effect could be achieved by the combined treatment with low subthreshold doses of NMDA (AP7) and non-NMDA (NBQX) receptor antagonists, which may be of potential significance for a new approach to the treatment of epilepsy.

Topics: 2-Amino-5-phosphonovalerate; Age Factors; Animals; Cerebral Cortex; Disease Models, Animal; Dizocilpine Maleate; Electroencephalography; Energy Metabolism; Epilepsy; Excitatory Amino Acid Antagonists; Glucose; Homocysteine; Injections, Intraventricular; Male; Neuroprotective Agents; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Seizures

Hyperhomocysteinemia has been recognized as an independent risk factor for cerebral, coronary, and peripheral atherosclerosis. To examine the contribution of homocysteine (H[cys]) in the pathogenesis of vascular diseases, we sought to determine whether the H[cys] effect on vascular smooth muscle (VSMC) proliferation is mediated by a specific receptor/transporter or is due to an interaction with growth factors or cytokines. We show that H[cys] induced c-fos and c-myb and increased DNA synthesis and cell proliferation 12-fold in neural crest-derived VSMC (N-VSMC). The H[cys] effect on N-VSMC proliferation is inhibited by Mk-801, a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, a glutamate-gated calcium ion channel receptor, and CGS 19755, a competitive antagonist of NMDA-type glutamate receptor. H[cys] stimulates the synthesis of mass amounts of sn-1,2 diacylglycerol, and activates protein kinase C translocation from the nucleus and cytoplasm to cell membranes. Furthermore, protein kinase C inhibitors block the growth effect mediated by H[cys]. These findings indicate that H[cys]-mediated responses are coupled to diacylglycerol-dependent protein kinase C activation. Our results suggest that homocysteine activates a receptor/transporter-like factor in neural crest derived smooth muscle.

Topics: Aorta, Abdominal; Aorta, Thoracic; Cardiovascular Diseases; Cell Division; Diglycerides; Dizocilpine Maleate; DNA; Enzyme Activation; Excitatory Amino Acid Antagonists; Gene Expression Regulation; Genes, fos; Glutamic Acid; Homocysteine; Humans; Immunoblotting; Muscle, Smooth, Vascular; N-Methylaspartate; Oncogenes; Pipecolic Acids; Polymerase Chain Reaction; Precipitin Tests; Protein Kinase C; Receptors, N-Methyl-D-Aspartate; RNA

When rabbit retinas are exposed in vitro to specific excitatory amino acid receptor agonists certain GABAergic amacrine cells are activated to cause a release of GABA. The GABA that is not released can be detected by immunohistochemistry. Exposure of tissues to kainate or NMDA each caused a characteristic change in the GABA immunoreactivity. CNQX antagonised the kainate effect specifically while MK-801 counteracted the influence of NMDA. The effect produced by kainate was mimicked by domoic acid while the influence of homocysteic acid was identical with NMDA. Flupirtine alone did not influence the nature of the GABA immunoreactivity and so did not act as a kainate or NMDA agonist. However, flupirtine counteracted the influence produced by NMDA and homocysteic acid but had no effect on the kainate and domoic acid responses. Thus in this system flupirtine acts as an NMDA antagonist.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Aminopyridines; Animals; Dizocilpine Maleate; gamma-Aminobutyric Acid; Homocysteine; Immunohistochemistry; Kainic Acid; Rabbits; Receptors, N-Methyl-D-Aspartate; Retina

Behavioral findings suggest that the effects of neostriatal glutamate and ascorbate are opposed to those of neostriatal dopamine. Recent evidence also indicates that glutamate and ascorbate are linked via a carrier-mediated heteroexchange process, suggesting that ascorbate may act through the glutamate system to influence behavior. In order to assess glutamate-ascorbate interactions and their influence on the behavioral output of the basal ganglia, glutamate and homocysteic acid (a glutamate reuptake blocker) as well as NMDA antagonists were infused into the neostriatum of freely moving rats while extracellular neostriatal ascorbate was monitored via electrochemically modified carbon-fiber electrodes. Neostriatal 3,4-dihydroxyphenylacetic acid (DOPAC), a major dopamine metabolite, also was recorded in order to assess the dependency of any drug effect on the nigrostriatal dopamine system. Intraneostriatal infusions of L-glutamate (1 micrograms/microliters), but not L-homocysteic acid (30 micrograms/microliters), elevated extracellular neostriatal ascorbate levels. Neither of these drugs had any effect on neostriatal DOPAC or overt behavioral activity. Intraneostriatal infusion of the noncompetitive NMDA antagonist dizocilpine (MK-801; 3 micrograms/microliters) or the competitive NMDA antagonist 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonene (CPPene; 5 micrograms/microliters) decreased neostriatal ascorbate but had no effect on neostriatal DOPAC. Both dizocilpine and CPPene activated behavior in intact and sham-lesioned animals as well as in animals with near-total depletions of neostriatal dopamine following a 6-hydroxydopamine lesion. When administered systemically, however, dizocilpine (1.0 mg/kg) significantly increased neostriatal DOPAC. This effect appears to be regulated via midbrain NMDA receptors, in that this effect was completely abolished by electrolytic lesions of the substantia nigra pars reticulata.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Ascorbic Acid; Dizocilpine Maleate; Glutamates; Glutamic Acid; Homocysteine; Infusions, Parenteral; Male; Motor Activity; Neostriatum; Oxidopamine; Piperazines; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Stereotyped Behavior

L-Homocysteic acid (L-HCA) is a sulfated amino acid which is present in mammalian striatum and is a putative excitatory striatal neurotransmitter. In the present study we examined the histologic and neurochemical effects of L-HCA induced striatal lesions to determine how closely changes resemble those of Huntington's disease (HD). Increasing doses of L-HCA injected into the anterior striatum resulted in dose-dependent reductions in both substance P-like immunoreactivity (SP-LI) and gamma-aminobutyric acid (GABA) while there was a relative sparing of both somatostatin-like immunoreactivity (SS-LI) and neuropeptide Y-like immunoreactivity (NPY-LI). Immunocytochemical studies showed a relative sparing of NADPH-diaphorase neurons (which colocalize with SS and NPY) within regions in which there was a significant depletion of enkephalin stained neurons. The lesions were blocked by pretreatment with MK-801, a systemically effective non-competitive antagonist of N-methyl-D-aspartate (NMDA) receptors or coinjection of equimolar concentrations of 2-amino-5-phosphonovalerate (APV). These findings are similar to those produced with the NMDA agonist quinolinic acid, and suggest that other endogenous NMDA agonists, such as L-HCA, could be potential excitotoxins in HD.

Topics: 2-Amino-5-phosphonovalerate; Animals; Corpus Striatum; Dibenzocycloheptenes; Dizocilpine Maleate; Dose-Response Relationship, Drug; gamma-Aminobutyric Acid; Homocysteine; Immunohistochemistry; Male; Neuropeptide Y; Rats; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Somatostatin; Substance P

Rat brain synaptosomal membranes that are depleted of endogenous excitatory amino acids cannot bind [(+)-5-methyl-10, 11-dihydro-5H-dibenzo(a,d]cyclohept-5,10-imine maleate] ([3H]MK-801). However, they do so upon the restoration of excitatory amino acid agonists such as L-glutamate. [3H]MK-801 provides a molecular probe which is specific for a binding site located within the ionophore of the N-methyl-D-aspartate-type excitatory amino acid receptor, [3H]MK-801 does not bind to non-N-methyl-D-aspartate excitatory amino acid receptors. Exploiting [3H]MK-801 binding as a quantitative measure of agonist activity with respect to ability of inducing the open channel conformation, the present study demonstrates that L-homocysteate is an agonist almost equivalent to L-glutamate in terms of efficacy (maximal N-methyl-D-aspartate response) as well as potency (EC50). The effect of L-homocysteate was dose-dependent, stereospecific (L-homocysteate greater than DL-homocysteate greater than D-homocysteate), suppressible by the N-methyl-D-aspartate-selective competitive antagonist (+/-)-3(2-carboxy-piperazine-4-yl)propyl-l-phosphonate, and potentiated by the N-methyl-D-aspartate-selective "allosteric" modulator glycine. The demonstrated inactivity of L-homocysteine (and virtually all naturally occurring, non-acidic amino acids) implies that the omega-sulphonic acid moiety is an acceptable substitute for the omega carboxyl group for activating the N-methyl-D-aspartate receptor. While the potency of L-homocysteate at N-methyl-D-aspartate receptors was by a factor of only 1.6 smaller than that of L-glutamate, the affinity of L-homocysteate for kainate-type excitatory amino acid receptors was approximately four-fold lower than that of L-glutamate.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 2-Amino-5-phosphonovalerate; Animals; Dizocilpine Maleate; Homocysteine; In Vitro Techniques; Ion Channels; Kinetics; Male; Piperazines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Receptors, Phencyclidine; Stereoisomerism; Stimulation, Chemical

The actions of the stereoisomers of homocysteic acid (HCA) were characterized at N-methyl-D-aspartate (NMDA)-type receptors which mediate excitatory amino acid-evoked [3H]acetylcholine ([3H]ACh) release from striatal cholinergic interneurons. Like NMDA, L-HCA and D-HCA evoked the release of [3H]ACh formed from [3H]choline in striatal slices. The concentration-response curve for L-HCA was virtually superimposable on that for NMDA, yielding an equal EC50 value (56.1 microM) and maximal response. However, D-HCA was weaker, with an EC50 value of 81.1 microM, and an apparently smaller maximal response. L-HCA-evoked [3H]ACh release was inhibited by the same categories of compounds which inhibit NMDA-evoked [3H]ACh release: the divalent ion Mg2+ (IC50 = 25.8 microM); competitive NMDA antagonists 2-amino-7-phosphonoheptanoate (IC50 = 51.2 microM) and 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (IC50 = 20.1 microM); and the dissociative anesthetics tiletamine (IC50 = 0.59 microM) and MK-801 (IC50 = 0.087 microM). Like NMDA, L-HCA produced a tachyphylaxis in this system. Tachyphylaxis to NMDA resulted in a decrease response to L-HCA, and conversely, tachyphylaxis to L-HCA resulted in a decrease response to NMDA. The results suggest that L-HCA is an agonist at the NMDA-type receptor and may represent an endogenous ligand for this excitatory amino acid receptor.

Topics: 2-Amino-5-phosphonovalerate; Acetylcholine; Amino Acids; Animals; Choline; Corpus Striatum; Dibenzocycloheptenes; Dizocilpine Maleate; Homocysteine; Interneurons; Magnesium; Male; Piperazines; Rats; Rats, Inbred Strains; Receptors, N-Methyl-D-Aspartate; Receptors, Neurotransmitter; Stereoisomerism; Tachyphylaxis; Tiletamine