Effects of Zinc, Mercury, or Lead on [3H]MK-801 and [3H]Fluorowillardiine Binding to Rat Synaptic Membranes.

Glutamate (Glu) is considered the most important excitatory amino acid neurotransmitter in the mammalian Central Nervous System. Zinc (Zn) is co-released with Glu during synaptic transmission and interacts with Glutamate receptors and transporters. We performed binding experiments using [3H]MK-801 (NMDA), and [3H]Fluorowillardine (AMPA) as ligands to study Zn-Glutamate interactions in rat cortical synaptic membranes. We also examined the effects of mercury and lead on NMDA or AMPA receptors. Zinc at 1 nM, significantly potentiates [3H]MK-801 binding. Lead inhibits [3H]MK-801 binding at micromolar concentrations. At millimolar concentrations, Hg also has a significant inhibitory effect. These effects are not reversed by Zn (1 nM). Zinc displaces the [3H]FW binding curve to the right. Lead (nM) and Hg (µM) inhibit [3H]FW binding. At certain concentrations, Zn reverses the effects of these metals on [3H]FW binding. These specific interactions serve to clarify the role of Zn, Hg, and Pb in physiological and pathological conditions.

Rats with different thresholds to clonic convulsions induced by DMCM differ in the binding of [3H]-MK-801 and [3H]-ouabain in the membranes of brain regions.

Considering the putative participation of N-methyl-D-aspartate (NMDA) receptors and the Na(+), K(+)-ATPase enzymes in the susceptibility to convulsions induced by the benzodiazepine inverse agonist methyl 6,7-dimethoxy-4-ethyl-ß-carboline-3-carboxylate (DMCM), the present study sought to determine if rats with high (HTR) and low (LTR) thresholds to clonic convulsions induced by DMCM differed in the following aspects: the binding of NMDA receptors by [(3)H]-MK-801, Na(+), K(+)-ATPase activity (K(+)-stimulated p-nitrophenylphosphatase) and high-affinity [(3)H]-ouabain binding to membranes from discrete brain regions. Compared to the HTR subgroup, the LTR subgroup presented a lower binding of [(3)H]-MK-801 in the hippocampus, frontal cortex and striatum. The subgroups did not differ in K(+)-p-nitrophenylphosphatase activity, but the LTR subgroup had a lower density of isozymes with a high-affinity to ouabain in the brainstem and in the frontal cortex and a lower affinity to ouabain in the hippocampus than the HTR subgroup. These results suggest that NMDA receptors and ouabain-sensitive Na(+), K(+)-ATPase isozymes may underlie the susceptibility to DMCM-induced convulsions.

A novel physiological property of snake bradykinin-potentiating peptides-reversion of MK-801 inhibition of nicotinic acetylcholine receptors.

The first naturally occurring angiotensin-converting enzyme (ACE) inhibitors described are pyroglutamyl proline-rich oligopeptides, found in the venom of the viper Bothrops jararaca, and named as bradykinin-potentiating peptides (BPPs). Biochemical and pharmacological properties of these peptides were essential for the development of Captopril, the first active site-directed inhibitor of ACE, currently used for the treatment of human hypertension. However, a number of data have suggested that the pharmacological activity of BPPs could not only be explained by their inhibitory action on enzymatic activity of somatic ACE. In fact, we showed recently that the strong and long-lasting anti-hypertensive effect of BPP-10c [

Interaction between glutamatergic-NMDA and cholinergic-muscarinic systems in classical fear conditioning.

A number of studies have suggested that the glutamatergic and cholinergic systems are both involved in learning and memory processes and that they interact in order to facilitate these processes. However, the role of M1-muscarinic receptors in mediating this interaction has not been elucidated. The aim of this study was to determine whether the concomitant administration of MK-801 (non-competitive NMDA antagonist) and dicyclomine (M1-muscarinic antagonist--DIC) in sub-effective doses impairs contextual fear conditioning (hippocampal-dependent task) and tone fear conditioning tasks (hippocampal-independent task). The results showed that concomitant pre-training administration of DIC (8.0 mg/kg) and MK-801 (0.07 mg/kg)--two sub-effectives doses for the contextual fear conditioning task--does impair the performance of animals on this task (as measured by freezing behavior time). Tone fear conditioning tasks were not affected by the drugs either administered separately or concurrently. The pre-training administration of sub-effective doses of MK-801 and DIC in combination impairs performance on contextual fear conditioning task (hippocampal-dependent), but not on tone fear conditioning task (hippocampal-independent). These data support the hypothesis that the interaction between glutamatergic and cholinergic systems in hippocampus-dependent learning and memory processes probably occurs through M1 receptor.

Contribution of NMDA and non-NMDA receptors to in vivo glutamate-induced calpain activation in the rat striatum. Relation to neuronal damage.

Glutamate, the major excitatory neurotransmitter, can cause the death of neurons by a mechanism known as excitotoxicity. This is a calcium-dependent process and activation of the NMDA receptor subtype contributes mainly to neuronal damage, due to its high permeability to calcium. Activation of calpain, a calcium-dependent cysteine protease, has been implicated in necrotic excitotoxic neuronal death. We have investigated the contribution of NMDA and non-NMDA ionotropic receptors to calpain activation and neuronal death induced by the acute administration of glutamate into the rat striatum. Calpain activity was assessed by the cleavage of the cytoskeletal protein, alpha-spectrin. Caspase-3 activity was also studied because glutamate can also lead to apoptosis. Results show no caspase-3 activity, but a strong calpain activation involving both NMDA and non-NMDA receptors. Although neuronal damage is mediated mainly by the NMDA receptor subtype, it can not be attributed solely to calpain activity.

Bradykinin into amygdala induces thermal hyperalgesia in rats.

Bradykinin is one of the most potent endogenous algesic substances and its role in pain transmission has been intensively studied in the periphery. However, the action of this peptide in central structures involved in pain transmission remains unclear. Administration of bradykinin (0.25 nmol/site) into the right amygdala of adult male Wistar rats induced thermal hyperalgesia, evaluated in the paw-flick test. Bradykinin-induced hyperalgesia was abolished by co-administration with the B(2) receptor antagonist Hoe 140 (5 pmol/site), the NMDA antagonist MK-801 (5 nmol/site), the cyclooxygenase inhibitor indomethacin (10 nmol/site) and the glial metabolic inhibitor fluorocitrate (1 nmol/site). Since the intra-amygdala administration of bradykinin did not alter spontaneous locomotion in the open-field test, it is unlikely that the current described hyperalgesic effect of bradykinin is due to an unspecific action on motor activity. These findings provide evidence that bradykinin, through activation of amygdalar B(2) receptors induces hyperalgesia and that glutamatergic- and prostanoid-mediated mechanisms are involved in such effect.

Exercise affects glutamate receptors in postsynaptic densities from cortical mice brain.

Physical activity has been proposed as a behavior intervention that promotes mental health and some of the benefits induced by exercise have been related to the glutamatergic system. Indeed, glutamate is the most abundant excitatory neurotransmitter in brain. Thus, we evaluated if voluntary exercise in mice could modulate glutamatergic synapses at level of postsynaptic density (PSD). Through Western blot, we found that exercise during 1 month increased glutamatergic-related protein content in PSD from cortex of mice. Exercise increased the immunocontent of GluR1 (129%), SAP-97 (179%), GRIP-1 (129%), and in less extent, GluR2/3 (118%) and PSD-95 (112%) proteins. The overall content of NMDA subunits R1, R2A and R2B were not altered in mice that had exercised, however, the phosphorylated NMDA subunits, phospho-NMDAR1 (150%), and phospho-NMDAR2B (183%) showed a strong increase. Because exercise increased the content of phosphorylated forms of NMDA receptors, we evaluated the binding of MK-801, a specific ligand that binds to open NMDA channel. Exercise increased the binding of MK-801 in cortical cellular membranes in 51%. Altogether, our results point to a modulation of glutamatergic synapses by exercise with likely implications in the exercise-induced mental health.

Endobain E, a brain endogenous factor, is present and modulates NMDA receptor in ischemic conditions.

We have isolated from rat cerebral cortex an endogenous Na(+), K(+)-ATPase inhibitor, termed endobain E, which modulates glutamatergic N-methyl-d-aspartate (NMDA) receptor. This endogenous factor allosterically decreases [(3)H]dizocilpine binding to NMDA receptor, most likely acting as a weak channel blocker. In the present study we investigated whether endobain E is present in the cerebral cortex of rats subjected to ischemia and modulates NMDA receptor exposed to the same conditions. Ischemia-reperfusion was carried out by bilateral occlusion of common carotid arteries followed by a 15-min reperfusion period. Elution profile of brain soluble fraction showed that endobain E is present in cerebral cortex of ischemia-reperfusion rats. On assaying its effect on synaptosomal membrane Na(+), K(+)-ATPase activity and [(3)H]dizocilpine binding to cerebral cortex membranes prepared from animals without treatment, it was found that the endogenous modulator isolated from ischemia-reperfusion rats was able to inhibit both enzyme activity and ligand binding. On the other hand, endobain E prepared from rats without treatment also decreased binding to cerebral cortex or hippocampal membranes obtained from animals exposed to ischemia-reperfusion. Since ischemia decreases tissue pH and NMDA receptor activity varies according to proton concentration, pH influence on endobain E effect was tested. Endobain E ( approximately 80 mg original tissue) decreased [(3)H]dizocilpine binding 25% at pH 7.4 or 8.0 but 90% at pH 6.5. These results demonstrate that endobain E is present and also able to modulate NMDA receptor in the short-term period that follows cerebral ischemia and that its effect depends on proton concentration, suggesting greater NMDA receptor modulation by endobain E at low pH, typical of ischemic tissues.

Chronic treatment with fluoxetine decreases seizure threshold in naïve but not in rats exposed to the learned helplessness paradigm: Correlation with the hippocampal glutamate release.

The proconvulsive effect of the new generation of antidepressants remains controversial. The authors investigated in naïve rats the effect of chronic treatment with fluoxetine (FLX) on the convulsive threshold and on two parameters of the hippocampal glutamatergic neurotransmission: the in vitro glutamate release and the binding of [3H] MK801 to NMDA receptors. While the acute treatment with FLX provoked no change either in seizure susceptibility or in the glutamate release, the chronic treatment decreased the convulsive threshold in coincidence with an increment in the in vitro glutamate release. No significant effects on the binding of [3H] MK801 to NMDA receptors were found to be attributable to the FLX treatment. We also assessed the effect of the chronic treatment with FLX on the seizure threshold in rats exposed to an experimental model of depression, the learned helplessness paradigm (LH). While a decrease in the K+-stimulated glutamate release was observed in non treated LH animals, when they were chronically injected with FLX, no changes in the epileptic susceptibility and no increments in the glutamate release were found. Our results indicate that chronic treatment with FLX decreases the epileptic threshold in naïve but not in LH rats and that this effect correlates with the levels of the hippocampal glutamate release.

Binding of [3H]MK-801 in subcellular fractions of Schistosoma mansoni: evidence for interaction with nicotinic receptors.

Several studies have suggested that l-glutamate is a putative neurotransmitter in Schistosoma mansoni. Recently, we detected the presence of low-affinity binding sites for [(3)H]kainic acid in the heterogeneous (P(1)) subcellular fraction of S. mansoni. In an attempt to characterize N-methyl-d-aspartate (NMDA) receptors in this worm, we performed binding assays with [(3)H]MK-801, a NMDA non-competitive antagonist, in the P(1) fraction of adult S. mansoni. In competition experiments, MK-801 (IC(50) approximately 200 microM) and ketamine (IC(50) approximately 500 microM) exhibited a low affinity for the sites labeled with [(3)H]MK-801. Along with the lack of modulation of this binding by glutamatergic agonists and antagonists and the absence of stereoselectivity for MK-801 isomers, these results suggest that [(3)H]MK-801 could label a site different from the classical NMDA receptor in S. mansoni. Based on the evidences that MK-801 interacts with mammalian muscle and central nervous system nicotinic receptors as a low-affinity noncompetitive antagonist, we have investigated the effects of MK-801 on the nicotine-induced flaccid paralysis of the worm, in vivo. The motility of S. mansoni was quantified by image analysis through a measure of displacement of the worm's extremities. In the presence of (-)-nicotine (10-100 microM), we observed an immediate paralysis of the worms, that was inhibited by 1mM MK-801. Besides nicotine, choline (10-50mM) was also able to inhibit the worm's motility. As a conclusion, we suggest that [(3)H]MK-801 binds to nicotinic receptors, and not NMDA receptors, in subcellular fractions of S. mansoni.

Stereoselective synthesis and preliminary evaluation of new D-3-heteroarylcarbonylalanines as ligands of the NMDA receptor.

New N-heteroarylcarbonylalanines of the D-series were stereoselectively prepared from enoates derived from D-mannitol. These compounds were active in binding and functional assays of the NMDA sub-type of glutamate receptors. A pyridine derivative inhibited MK801 binding, protected neurons from excitotoxic damage and blocked NMDA-induced currents in neurons. A thiophene derivative positively modulated the NMDA receptor, possibly through the allosteric glycine site.

The effect of endogenous modulator endobain E on NMDA receptor is interfered by Zn2+ but is independent of modulation by spermidine.

A brain endogenous factor, termed endobain E, allosterically decreases [3H]dizocilpine binding to NMDA receptor. Such effect depends on receptor activation by the coagonists glutamate and glycine and is interfered by channel blockers, suggesting its interaction with the inner surface of the associated channel. To further analyze endobain E effect on NMDA receptor, in the current study competitive [3H]dizocilpine binding assays to brain membranes were performed with Zn2+ to block the associated channel, as well as with spermidine (SPD), which exerts positive allosteric modulation of NMDA receptor. Partially or nonadditive effects on [3H]dizocilpine binding were recorded, respectively, in the presence of endobain E at a concentration that inhibits binding 25% plus IC25 Zn2+ or endobain E at a concentration that inhibits binding 50% plus IC50 Zn2+. With an endobain E concentration that decreases 25% ligand binding, SPD potentiated binding over a wide concentration range but failed to modify endobain E effect. Similarly, [3H]dizocilpine binding reduction over a wide endobain E concentration range remained unaltered by high SPD concentrations. Additive effects were observed with endobain E at a concentration that decreases binding 25% plus IC25 SPD site antagonists arcaine or ifenprodil. Zn2+ experiments indicated that endobain E effect is interfered by channel blockade produced by this ion. Although endobain E effect is dependent on NMDA receptor activation by glutamate and glycine, it proves independent of the positive modulation exerted by SPD. Thus the endogenous modulator seems not to interact at NMDA receptor polyamine site, favoring the hypothesis that endobain E binds inside the associated channel.

Ibogaine attenuation of morphine withdrawal in mice: role of glutamate N-methyl-D-aspartate receptors.

Ibogaine (IBO) is an alkaloid with putative antiaddictive properties, alleviating opiates dependence and withdrawal. The glutamate N-methyl-D-aspartate (NMDA) receptors have been implicated in the physiological basis of drug addiction; accordingly, IBO acts as a noncompetitive NMDA antagonist. The purpose of this study was to evaluate the effects of IBO on naloxone-induced withdrawal syndrome in morphine-dependent mice, focusing on the role of NMDA receptors. Jumping, a major behavioral expression of such withdrawal, was significantly (P<.01) inhibited by IBO (40 and 80 mg/kg, 64.2% and 96.9% inhibition, respectively) and MK-801 (0.15 and 0.30 mg/kg, 67.3% and 97.7%, respectively) given prior to naloxone. Coadministration of the lower doses of IBO (40 mg/kg) and MK-801 (0.15 mg/kg) results in 94.7% inhibition of jumping, comparable to the effects of higher doses of either IBO or MK-801. IBO and MK-801 also significantly inhibited NMDA-induced (99.0% and 71.0%, respectively) jumping when given 30 min (but not 24 h) prior to NMDA in nonaddictive mice. There were no significant differences in [3H]MK-801 binding to cortical membranes from naive animals, morphine-dependent animals, or morphine-dependent animals treated with IBO or MK-801. This study provides further evidence that IBO does have an inhibitory effect on opiate withdrawal symptoms and suggests that the complex process resulting in morphine withdrawal includes an IBO-sensitive functional and transitory alteration of NMDA receptor.

Differential and irreversible CNS ontogenic reduction in maximal MK-801 binding site number in the NMDA receptor after acute hypoxic hypoxia.

CNS exposure to hypoxia impairs excitatory and inhibitory neurotransmission. Our aim was to determine variations induced by normobaric acute hypoxic hypoxia (8% O(2) for 60 min) on the NMDA receptor complex, as well as their potential reversibility after normoxic recovery. To this end, [3H]MK-801 binding assays to a synaptic membrane fraction isolated from chick optic lobes were performed. Previous studies throughout development had disclosed a characteristic age-dependent pattern. Results at embryonic day (ED) 12 and 18 indicated two distinct MK-801 binding sites. Hypoxic treatment failed to alter either the high affinity site dissociation constant (K(d)) or its maximal binding capacity (B(max)), whereas the low affinity site B(max) was significantly decreased (50% and 30% at ED12 and 18, respectively), without alteration in its K(d) values. Hypoxic embryos restored for 48 h at ED12 to normoxic conditions displayed unchanged MK-801 binding reduction, unlike those treated likewise at ED18 whose values fully recovered control levels. To conclude, hypoxic treatment reduces low affinity MK-801 B(max) in the NMDA receptor which proves irreversible up to ED12. Such early neuronal vulnerability may be due to post-transcriptional changes, to endocytosis followed by receptor degradation, or alternatively to cell death.

Effects of 5-aminolevulinic acid on the glutamatergic neurotransmission.

The haem precursor 5-aminolevulinic acid (ALA) has been proposed to be involved in the neurological dysfunctions presented by patients with acute porphyrias. The effects of ALA on the [3H]glutamate and [3H]MK-801 (dizocilpine) binding to rat cortical membranes and on [3H]glutamate uptake by rat astrocyte cultures were evaluated in the present study in order to elucidate the interaction of ALA with the glutamatergic system and its possible contribution to the in vivo excitatory properties of ALA. ALA (0-1mM) did not affect the binding of 100 nM [3H]glutamate, nor the equilibrium binding constants (K(d) and B(max)) of this neurotransmitter in rat or human cortical membranes. The binding of the NMDA-channel blocker, [3H]MK-801, was not affected by ALA (0-10mM) either. ALA (0-3mM) dose-dependently inhibited glutamate uptake by astrocyte cultures. ALA significantly reduced both the K(m) and V(max) of glutamate uptake indicating an uncompetitive inhibition. The inhibitory effect was irreversible and apparently related to the selective inhibition of the GLT-1 (EAAT2) subtype of glutamate transporter. The finding that ALA significantly increased astrocyte lipoperoxidation in astrocytes incubated under these conditions suggests that the inhibitory effect of ALA might be related to an oxidative damage of the transporter. We propose that the inhibition of glutamate uptake may underlie ALA-induced convulsions.

Resistance to ethanol sensitization is associated with increased NMDA receptor binding in specific brain areas.

Co-administration of N-methyl-D-aspartate (NMDA) receptor antagonists is known to block the development of behavioral sensitization to ethanol and other psychostimulants. Since ethanol sensitization in mice does not occur uniformly in all treated animals, the present study examined the possibility that NMDA receptor binding would be selectively altered in mice susceptible to ethanol sensitization. Mice received 2.4 g/kg ethanol or saline i.p. daily for 21 days and were sacrificed 24 h later. No differences in [3H]dizocilpine ([3H](+)MK-801) binding were found between sensitized and vehicle-treated mice in any of the brain regions analyzed. However, ethanol-treated mice that did not develop sensitization showed significantly higher binding in the nucleus accumbens core (+32% and +40% compared to controls and ethanol-sensitized mice, respectively; P<0.04) and the prefrontal cortex (+15% and +22%; P<0.02). In a separate experiment, sensitization resistant mice challenged with 0.25 mg/kg (+)MK 801 showed significantly less motor activation than saline-treated or ethanol-sensitized mice. These results point to a clear association between elevated NMDA receptor binding in specific brain regions and resistance to ethanol sensitization.

Age-related changes in the N-methyl-D-aspartate receptor binding sites within the human basal ganglia.

The present study examined the regional differences in dopamine transporter binding sites and NMDA receptor complex binding based on autoradiographic images obtained in postmortem sections of human normal brain tissues. In middle-aged control tissues, high and comparable levels of [(3)H]CFT binding were observed in the caudate nucleus, putamen, and accumbens nucleus without significant alteration along the rostrocaudal axis and ventral and dorsal parts of these nuclei. In aging normal brain tissues, dopamine binding sites for [(3)H]CFT were significantly reduced in the caudate nucleus, putamen, and accumbens nucleus. l-[(3)H]Glutamate, [(3)H]MK-801, and [(3)H]glycine binding to the NMDA receptor complex was lower in aging brain tissues than in middle-aged controls. Significant correlation did occur between age and [(3)H]CFT binding and between age and l-[(3)H]glutamate, [(3)H]MK-801, and [(3)H]glycine binding sites. These results demonstrate that the basal ganglia have age-associated reductions in dopamine transporter uptake and NMDA receptors. These data support hypoactive activity of the NMDA receptor complex system with advancing age. The dopamine transporter uptake and NMDA receptors appear to be vulnerable to the aging process in the basal ganglia.

[3H]dizocilpine binding to N-methyl-D-aspartate (NMDA) receptor is modulated by an endogenous Na+, K+-ATPase inhibitor. Comparison with ouabain.

An endogenous Na+, K+-ATPase inhibitor termed endobain E has been isolated from rat brain which shares several biological properties with ouabain. This cardiac glycoside possesses neurotoxic properties attributable to Na+, K+-ATPase inhibition, which leads to NMDA receptor activation, thus supporting the concept that Na+/K+ gradient impairment has a critical impact on such receptor function. To evaluate potential direct effects of endobain E and ouabain on NMDA receptors, we assayed [3H]dizocilpine binding employing a system which excludes ionic gradient participation. Brain membranes thoroughly washed and stored as pellets ('non-resuspended' membranes) or after resuspension in sucrose ('resuspended' membranes) were employed. Membrane samples were incubated with 4 or 10 nM ligand with or without added endobain E or ouabain, in the presence of different glutamate plus glycine combinations, with or without spermidine. [3H]dizocilpine basal binding and Na+, K+- and Mg2+-ATPase activities proved very similar in 'non-resuspended' or 'resuspended' membranes. Endobain E decreased [3H]dizocilpine binding to 'resuspended' membranes in a concentration-dependent manner, attaining roughly 50% binding inhibition with the highest endobain E concentration assayed. Among tested conditions, only in 'resuspended' membranes, with 4 nM ligand and with 1x10(-8) M glutamate plus 1x10(-5) M glycine, was [3H]dizocilpine binding enhanced roughly +24% by ouabain (1 mM). After Triton X-100 membrane treatment, which drastically reduces Na+, K+-ATPase activity, the effect of ouabain on binding was lost whereas that of endobain E remained unaltered. Results indicate that not only membrane preparation but also treatment and storage are crucial to observe direct endobain E and ouabain effects on NMDA receptor, which are not attributable to changes in Na+, K+-ATPase activity or to Na+/K+ equilibrium alteration.

Effect of dithiol chelating agents on [3H]MK-801 and [3H]glutamate binding to synaptic plasma membranes.

2,3-Dimercaptopropanol (BAL- British Anti-Lewesite) is a dithiol chelating agent used for the treatment of heavy metal poisoning, however, BAL can produce neurotoxic effects in a variety of situations. Based on the low therapeutic efficiency of BAL other dithiols were developed and DMSA (meso-2,3-dimercaptosuccinic acid) and DMPS (2,3-dimercaptopropane-1-sulfonic acid) are becoming used for treatments of humans exposed to heavy metals. In the present investigation the effect of dithiols in the glutamatergic system was examined. The results showed that BAL inhibited [3H]MK-801 and [3H]glutamate binding in a concentration-dependent manner. At 100 microM BAL and DMSA caused a significantly inhibition of [3H]MK-801 binding to brain membranes (p < 0.05 by Duncan's multiple range test). BAL at 100 microM caused an inhibition of 40% on [3H]glutamate binding. DMPS and DMSA had no significant effect on [3H]glutamate binding. Dithiotreitol (DTT), abolished the inhibitory effect of BAL on [3H]MK-801 binding. The protection exerted by DTT suggests that BAL inhibit [3H]MK-801 binding by interacting with cysteinyl residues that are important for redox modulation of receptor responses. ZnCl2 inhibited [3H]glutamate and [3H]MK-801 binding to brain synaptic membrane; nevertheless, the inhibitory effect was slight more accentuated for [3H]MK-801 than [3H]glutamate binding (p < 0.05). The inhibition caused by 10 microM ZnCl2 on [3H]MK-801 binding was attenuated by BAL. The findings present in this study may provide the evidence that BAL affect the glutamatergic system and these effects can contributed to explain, at least in part, why BAL, in contrast to DMPS and DMSA is neurotoxic.

Effects of an adenosine analogue administration on the striatal NMDA receptors in an experimental model of epilepsy.

Specific [3H]-MK801 binding to rat NMDA receptors following the administration of the convulsant drug 3-mercaptopropionic acid (MP) and the adenosine analogue cyclopentyladenosine (CPA) was studied in striatal membrane fractions. MP administration (150 mg/kg, i.p.) caused an increase of 53% and 82% in [3H]-MK801 binding during seizure and the postseizure period respectively. Administration of CPA (2 mg/kg, i.p.) raised [3H]-MK801 binding by 72%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 64%, was observed. Saturation results indicate that receptor sites increased their maximal binding capacity (Bmax) in all treatments while the apparent dissociation constant (Kd) remained unchanged. MP administration brought about an increase of 52% and 42% in [3H]-MK801 binding sites during seizure and postseizure respectively. Administration of CPA raised receptor density by 75%. When CPA was administered 30 min before MP and rats sacrificed at seizure (CPA + MPc), an increase of 62%, was observed. These results show that striatal NMDA receptors have a selective role in seizure activity in the basal ganglia and that the adenosine analogue administration may modify [3H]-MK801 binding in a way similar to that of the convulsant drug.