Biomedical subjects

S Urwyler

Publications and source records attributed to S Urwyler.

At least 19 recordsLinked to original sources

PubMed2001

Design, synthesis and preliminary evaluation of novel 3'-substituted carboxycyclopropylglycines as antagonists at group 2 metabotropic glutamate receptors.

Two novel 3'-substituted carboxycylopropylglycines, (2S,1'S,2'S,3'R)-2-(3'-xanthenylmethyl-2'-carboxycyclopropyl)glycine (8a) and (2S,1'S,2'S,3'R)-2-(3'-xanthenylethyl-2'-carboxycyclopropyl)glycine (8b), were synthesized and evaluated as mGluR ligands. Compound 8b showed to be a potent group II antagonist with submicromolar activity.

Animals↗

PubMed2001

Inorganic iron complexes derived from the nitric oxide donor nitroprusside: competitive N-methyl-D-aspartate receptor antagonists with nanomolar affinity.

Aquopentacyanoferrate(II), [Fe(II)H2O(CN)5]3-, is one of the photodegradation products of the vasodilator and nitric oxide donor nitroprusside. Earlier observations concerning the light dependence of N-methyl-D-aspartate (NMDA) receptor blockade by nitroprusside prompted us to examine the effects of this iron complex on the NMDA receptor. [Fe(II)H2O(CN)5]3- and two other related species, aminopentacyanoferrate(II) and aminopentacyanoferrate(III), were found to be highly potent, competitive, and selective NMDA receptor antagonists. In a binding assay for the transmitter recognition site on the NMDA receptor, these iron complexes displaced the radioligand [3H]CGP 39653 with nanomolar affinities. They did not displace radioligands labeling the channel ([3H]MK-801) or the glycine co-agonist ([3H]glycine) sites of the NMDA receptor, nor did they have any relevant affinities for a number of other neurotransmitter (alpha-adrenergic, 5-hydroxytryptamine, dopamine, opiate) receptors. The iron complexes blocked NMDA-induced depolarizations in rat cortical slices at submicromolar concentrations, whereas responses to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate were not affected. In another functional receptor assay (potentiation of [3H]MK-801 binding by glutamate under non-equilibrium conditions), Schild analysis demonstrated the competitive nature of the NMDA receptor antagonism. The pA2 values obtained from these experiments were similar to the pK(i) values derived from radioligand ([3H]CGP 39653) binding assays. To explain the high affinity and selectivity of these compounds for the NMDA receptor, a novel mechanism of antagonist-receptor interaction is proposed, involving a ligand exchange process in which a loosely bound species (here H2O or NH3) in the coordination sphere of the iron complex is replaced by a functional group of an amino acid side chain placed at the glutamate recognition site of the NMDA receptor, thereby hindering agonist binding.

2-Amino-5-phosphonovalerate↗

PubMed2001

Positive allosteric modulation of native and recombinant gamma-aminobutyric acid(B) receptors by 2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) and its aldehyde analog CGP13501.

The compounds CGP7930 [2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol] and its close analog CGP13501 were identified as positive modulators of gamma-aminobutyric acid(B) (GABA(B)) receptor function. They potentiate GABA-stimulated guanosine 5'-O-(3-[(35)S]thiotriphosphate) (GTP gamma[(35)S]) binding to membranes from a GABA(B(1b/2)) expressing Chinese hamster ovary (CHO) cell line at low micromolar concentrations and are ineffective in the absence of GABA. The structurally related compounds propofol and malonoben are inactive. Similar effects of CGP7930 are seen in a GTP gamma[(35)S] binding assay using a native GABA(B) receptor preparation (rat brain membranes). Receptor selectivity is demonstrated because no modulation of glutamate-induced GTP gamma[(35)S] binding is seen in a CHO cell line expressing the metabotropic glutamate receptor subtype 2. Dose-response curves with GABA in the presence of different fixed concentrations of CGP7930 reveal an increase of both the potency and maximal efficacy of GABA at the GABA(B(1b/2)) heteromer. Radioligand binding studies show that CGP7930 increases the affinity of agonists but acts at a site different from the agonist binding site. Agonist affinity is not modulated by CGP7930 at homomeric GABA(B(1b)) receptors. In addition to GTP gamma[(35)S] binding, we show that CGP7930 also has modulatory effects in cellular assays such as GABA(B) receptor-mediated activation of inwardly rectifying potassium channels in Xenopus laevis oocytes and Ca(2+) signaling in human embryonic kidney 293 cells. Furthermore, we show that CGP7930 enhances the inhibitory effect of L-baclofen on the oscillatory activity of cultured cortical neurons. This first demonstration of positive allosteric modulation at GABA(B) receptors may represent a novel means of therapeutic interference with the GABA-ergic system.

Allosteric Regulation↗

PubMed2000

Ca(2+) requirement for high-affinity gamma-aminobutyric acid (GABA) binding at GABA(B) receptors: involvement of serine 269 of the GABA(B)R1 subunit.

The gamma-aminobutyric acid (GABA) receptor type B (GABA(B)R) is constituted of at least two homologous proteins, GABA(B)R1 and GABA(B)R2. These proteins share sequence and structural similarity with metabotropic glutamate and Ca(2+)-sensing receptors, both of which are sensitive to Ca(2+). Using rat brain membranes, we report here that the affinity of GABA and 3-aminopropylphosphinic acid for the GABA(B)R receptor is decreased by a factor >10 in the absence of Ca(2+). Such a large effect of Ca(2+) is not observed with baclofen or the antagonists CGP64213 and CGP56999A. In contrast to baclofen, the potency of GABA in stimulating GTPgammaS binding in rat brain membranes is also decreased by a factor >10 upon Ca(2+) removal. The potency for Ca(2+) in regulating GABA affinity was 37 microM. In cells expressing GABA(B)R1, the potency of GABA, but not of baclofen, in displacing bound (125)I-CGP64213 was similarly decreased in the absence of Ca(2+). To identify residues that are responsible for the Ca(2+) effect, the pharmacological profile and the Ca(2+) sensitivity of a series of GABA(B)R1 mutants were examined. The mutation of Ser269 into Ala was found to decrease the affinity of GABA, but not of baclofen, and the GABA affinity was found not to be affected upon Ca(2+) removal. Finally, the effect of Ca(2+) on the GABA(B) receptor function is no longer observed in cells coexpressing this GABA(B)R1-S269A mutant and the wild-type GABA(B)R2. Taken together, these results show that Ser269, which is conserved in the GABA(B)R1 protein from Caenorhabditis elegans to mammals, is critical for the Ca(2+)-effect on the heteromeric GABA(B) receptor.

Amino Acid Sequence↗

PubMed1999

2-Methyl-6-(phenylethynyl)-pyridine (MPEP), a potent, selective and systemically active mGlu5 receptor antagonist.

In the present paper we describe 2-methyl-6-(phenylethynyl)-pyridine (MPEP) as a potent, selective and systemically active antagonist for the metabotropic glutamate receptor subtype 5 (mGlu5). At the human mGlu5a receptor expressed in recombinant cells, MPEP completely inhibited quisqualate-stimulated phosphoinositide (PI) hydrolysis with an IC50 value of 36 nM while having no agonist or antagonist activities at cells expressing the human mGlu1b receptor at concentrations up to 30 microM. When tested at group II and III receptors, MPEP did not show agonist or antagonist activity at 100 microM on human mGlu2, -3, -4a, -7b, and -8a receptors nor at 10 microM on the human mGlu6 receptor. Electrophysiological recordings in Xenopus laevis oocytes demonstrated no significant effect at 100 microM on human NMDA (NMDA1A/2A), rat AMPA (Glu3-(flop)) and human kainate (Glu6-(IYQ)) receptor subtypes nor at 10 microM on the human NMDA1A/2B receptor. In rat neonatal brain slices, MPEP inhibited DHPG-stimulated PI hydrolysis with a potency and selectivity similar to that observed on human mGlu receptors. Furthermore, in extracellular recordings in the CA1 area of the hippocampus in anesthetized rats, the microiontophoretic application of DHPG induced neuronal firing that was blocked when MPEP was administered by iontophoretic or intravenous routes. Excitations induced by microiontophoretic application of AMPA were not affected.

Animals↗

PubMed1999

(R,S)-4-phosphonophenylglycine, a potent and selective group III metabotropic glutamate receptor agonist, is anticonvulsive and neuroprotective in vivo.

Group III metabotropic glutamate receptors (mGluRs) are thought to modulate neurotoxicity of excitatory amino acids, via mechanisms of presynaptic inhibition, such as regulation of neurotransmitter release. Here, we describe (R,S)-4-phosphonophenylglycine (PPG) as a novel, potent, and selective agonist for group III mGluRs. In recombinant cell lines expressing the human receptors hmGluR4a, hmGluR6, hmGluR7b, or hmGluR8a, EC50 values for (R,S)-PPG of 5.2 +/- 0.7 microM, 4.7 +/- 0.9 microM, 185 +/- 42 microM, and 0.2 +/- 0.1 microM, respectively, were measured. The compound showed EC50 and IC50 values of >/=200 microM at group I and II hmGluRs and was inactive at cloned human N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate, and kainate receptors (>300 microM). On the other hand, it showed micromolar affinity for a Ca2+/Cl--dependent L-glutamate binding site in rat brain, similar to other phosphono-substituted amino acids like L-2-amino-4-phosphonobutyrate. In cultured cortical neurons, (R, S)-PPG provided protection against a toxic pulse of N-methyl-D-aspartate (EC50 = 12 microM), which was reversed by the group III mGluR antagonist (R,S)-alpha-methylserine-O-phosphate but not by the group II antagonist (2S)-alpha-ethylglutamate. Moreover, (R,S)-PPG protected against N-methyl-D-aspartate- and quinolinic acid-induced striatal lesions in rats and was anticonvulsive in the maximal electroshock model in mice. In contrast to the group III mGluR agonists L-2-amino-4-phosphonobutyrate and L-serine-O-phosphate, (R,S)-PPG showed no proconvulsive effects (2200 nmol i.c.v.). These data provide novel in vivo evidence for group III mGluRs as attractive targets for neuroprotective and anticonvulsive therapy. Also, (R,S)-PPG represents an attractive tool to analyze the roles of group III mGluRs in nervous system physiology and pathology.

Animals↗

PubMed1996

SDZ PSD 958, a novel D1 receptor antagonist with potential limbic selectivity.

SDZ PSD 958, a novel benzo[g]quinoxaline derivative exhibits the properties of a potent orally active selective D1 receptor antagonist. It has high affinity for D1-like receptors (D1, D5; pKi = 9.7-9.8) labelled by [3H]SCH23390 and is at least 400 fold less active at D2-like receptors (i.e. D2, D4) labelled by [3H]spiperone. Effects in functional tests are consistent with D1 receptor antagonist properties. SDZ PSD 958 inhibited apomorphine-induced rearing in mice and prevented prolongation of novelty-induced locomotion in rats elicited by the selective D1 receptor agonist CY 208-243. By contrast, SDZ PSD 958 did not induce catalepsy and only weakly inhibited apomorphine-induced stereotyped gnawing in rats. This suggests that SDZ PSD 958 preferentially inhibits responses mediated by dopamine systems innervating the limbic system.

Acetylcholine↗

PubMed1996

SDZ GLC 756, a novel octahydrobenzo[g]quinoline derivative exerts opposing effects on dopamine D1 and D2 receptors.

SDZ GLC-756, a novel octahydrobenzo[g]quinoline derivative, is equipotent in displacing [3H]SCH23390 from dopamine D1 receptors and [3H]205-501 from dopamine D2 receptor binding sites. It blocks dopamine sensitive adenylate cyclase with the same potency as SCH23390, indicating antagonist properties at dopamine D1 receptors. On the other hand, SDZ GLC 756 inhibits electrically evoked acetylcholine release from rat striatal slices with the same potency as the selective dopamine D2 receptor agonist bromocriptine. This effect is blocked by spiperone suggesting that it is mediated by dopamine D2 receptor activation. The opposing action of SDZ GLC 756 on dopamine D1 and D2 receptors is also evident in vivo. SDZ GLC 756, like SCH23390, blocks apomorphine-induced rearing in mice. On the other hand, it inhibits prolactin secretion and produces circling in unilateral 6-OHDA-lesioned rats, which is compatible with stimulant properties at dopamine D2 receptors. This drug might be a new tool to study linkage between dopamine D1 and D2 receptors.

Acetylcholine↗

PubMed1996

Biphenyl-derivatives of 2-amino-7-phosphonoheptanoic acid, a novel class of potent competitive N-methyl-D-aspartate receptor antagonist--I. Pharmacological characterization in vitro.

Omega-Phosphono-substituted alpha-amino acids have long been known to be antagonists at the N-methyl-D-aspartate (NMDA) receptor. D-2-Amino-5-phosphonopentanoic (D-AP5) and D-2-amino-7-phosphonoheptanoic (D-AP7) acids are the "prototype" compounds of this kind. Insertion of a biphenyl-moiety in the middle of the AP7 chain results in increased affinity and reverses the enantioselectivity from a D- to an L-form preference (Müller et al., (1992) Helv. Chim. Acta 75: 855-864). We describe here a series of substituted biphenyl-AP7-derivatives, the most potent of which have affinities (in a [3H]CGP-39653 binding assay using native and recombinant receptors) and potencies (antagonism of NMDA-induced depolarizations in a cortical wedge preparation; inhibition of glutamate-stimulated [3H]MK-801 binding under non-equilibrium conditions) in the low nanomolar range. Structure-activity relationships show that hydroxy-substitution at the C5-atom in the AP7-chain as well as substitution in the second phenyl ring with space filling (such as chloro-)groups in the para- and especially the ortho-position (extending the torsion angle of the two rings) increase affinity and potency of these compounds. They have no relevant affinities for the strychnine-insensitive glycine co-agonist site or the MK-801/PCP channel blocking site on the NMDA receptor complex. AMPA- and kainate-induced responses were not affected by biphenyl-analogues. These compounds also do not interact with a number of other neurotransmitter receptor sites, and they do not inhibit the uptake of [3H] glutamate in rat brain synaptosomes. However, they display affinities in the (sub)micromolar range for a non-NMDA, non-AMPA, non-kainate binding site for [3H]glutamate, measured in the presence of calcium chloride, the functional correlate of which has not yet been elucidated.

2-Amino-5-phosphonovalerate↗

PubMed1996

Biphenyl-derivatives of 2-amino-7-phosphono-heptanoic acid, a novel class of potent competitive N-methyl-D-aspartate receptor antagonists--II. Pharmacological characterization in vivo.

A selection of biphenyl-analogues of 2-amino-7-phosphonoheptanoic acid (AP7), N-methyl-D-aspartate (NMDA) receptor antagonists with high affinity in vivo efficacy. The lead compound SDZ EAB 515 was found to inhibit L-phenylalanine uptake by the large neutral amino acid carrier in vitro and in vivo; active transport may thus confer a good bioavailability to this class of compounds. CNS effects were demonstrated by significant changes in 2-deoxyglucose-uptake in various brain regions at doses from 1 to 10 mg/kg i.p. With the most active agent, SDZ 220-581, full protection against maximal electroshock seizures (MES) was obtained at oral doses of 10 mg/kg in rats and in mice. The compound had a fast onset (< or = 1 hr) and a long duration (> or = 24 hr) of action. Motor-debilitating effects (impairment of rotarod performance) occurred at doses about 10 times higher than those required for protection against MES. Neuroprotective activity was demonstrated by the ability of the compounds to reduce the extent of quinolinic acid-induced striatal lesions in rats, in the dose range of 3-15 mg/kg (i.p.) or 10-50 mg/kg (p.o.). In the middle cerebral artery occlusion (MCAO) model of focal cerebral ischemia in rats, the test compounds reduced the infarct size by 40-50% when given i.v. before or by 20-30% when given i.v. 1 hr after MCAO. SDZ 220-581 provided 20-30% protection at > or = 2 x 10 mg/kg p.o. This compound also showed analgesic activity at low oral doses in a model of neuropathic pain, although higher doses were required in model of mechanical inflammatory hyperalgesia. Unexpectedly, SDZ 220-581 at low s.c. doses counteracted the antiparkinsonian effects of L-DOPA in MPTP-treated marmosets. (Sub)chronic administration of SDZ 220-581 did not reduce its ability to protect against quinolinic acid neurotoxicity, and no upregulation of NMDA receptors was detected using a [3H]CGP-39653 binding assay. In conclusion, from a series of biphenyl-AP7-derivatives, SDZ 220-581 is clearly the most active compound in vivo. Its pharmacological profile with a good, long-lasting oral activity might open up novel therapeutic applications for competitive NMDA receptor antagonists.

Amino Acids↗

PubMed1996

Extracts from rhizomes of Cyperus articulatus (Cyperaceae) displace [3H]CGP39653 and [3H]glycine binding from cortical membranes and selectively inhibit NMDA receptor-mediated neurotransmission.

The marshland plant Cyperus articulatus (Cyperaceae) is commonly used in traditional medicine in Africa and Latin America to treat a wide variety of human diseases ranging from headache to epilepsy. We tested the hypothesis that the purported anti-epileptic effect of this plant might be due to a functional inhibition of excitatory amino acid receptors. One or several component(s) contained in the extracts inhibited the binding of [3H]CGP39653 to the NMDA recognition site and of [3H]glycine to the strychnine-insensitive glycine site of the NMDA receptor complex from rat neocortex. Water extracts from rhizomes of Cyperus articulatus dose-dependently reduced spontaneous epileptiform discharges and NMDA-induced depolarizations in the rat cortical wedge preparation at concentrations at which AMPA-induced depolarizations were not affected. We conclude that the purported beneficial effects of Cyperus articulatus might at least partially be due to inhibition of NMDA-mediated neurotransmission.

2-Amino-5-phosphonovalerate↗

PubMed1994

The pharmacology of SDZ EAA 494, a competitive NMDA antagonist.

SDZ EAA 494 (D-CPPene) was characterized as a competitive NMDA antagonist, having a pA2 value against NMDA depolarizations in frog spinal cord and rat neocortex of 6.7-6.8 and a pKi of 7.5 in a [3H]CGP39653 binding assay, with no action on other receptors or amine reuptake. The compound was orally active in rodent maximal electroshock models with an ED50 of around 16 mg/kg, was protective in rats even 24 hours after oral application and had an oral therapeutic index of around 8. Muscle relaxation, ataxia, flattened body posture and reduced acquisition of a passive avoidance task, suggesting potential effects on memory formation, occurred at supra-anticonvulsant doses in rodents, with PCP-like stimulatory effects produced only by high i.p. doses or constant i.v. infusions. This favourable profile is discussed in relation to the negative outcome of a recent trial of the compound in patients with intractable epilepsy. The conclusion is drawn that standard models for screening new anticonvulsants are inappropriate to seeking drugs active in patients with a protracted convulsive history. The anti-ischaemic action of SDZ EAA 494 encourages further testing in brain trauma, in which the anticonvulsant action of the compound may be an added benefit.

Animals↗

PubMed1992

Biochemical and thermodynamic aspects of the binding of [3H]glycine to its strychnine-insensitive recognition site associated with the N-methyl-D-aspartate receptor complex.

The molecular mechanism of interaction between glycine and its strychnine-insensitive binding site linked to the N-methyl-D-aspartate receptor was investigated by examining on the one hand the thermodynamic properties of glycine binding, and, on the other hand, the effects of various functional group modifying agents on ligand binding. Raising the incubation temperature from 0 degrees to 37 degrees resulted in a consistent decrease of glycine binding affinity. Calculation of thermodynamic parameters from the corresponding Van't Hoff plot showed that the binding of glycine was mainly entropy-driven, the change in enthalpy contributing only little (25-30%) to the change in Gibbs free energy. Chemical modification with the sulfhydryl-directed agents p-hydroxy-mercuribenzoate and N-ethyl-maleimide showed free -SH groups to be critical for ligand binding to the receptor site. Furthermore, guanidino groups on arginyl residues, sensitive to 2,3-butanedione, were also found to participate in glycine binding. Both the -SH and the guanidino groups could be protected against their inactivation by co-incubation with glycine, indicating a direct involvement of these functional groups in the binding process. Dithiothreitol, a disulfide-reducing agent, likewise prevented [3H]glycine binding, suggesting that the glycine recognition site is stabilized by at least one disulfide bridge. It is concluded that the binding of glycine probably involves a strong ion-ion interaction between its carboxyl group and a positively charged guanidino group at the receptor site, resulting in a thermodynamically favorable increase in entropy by displacement of water molecules from the latter and a concomitant decrease in enthalpy. Furthermore, at least one free sulfhydryl group seems to participate in the binding process.

Animals↗

PubMed1990

Partial dopamine-agonistic and atypical neuroleptic properties of the amino-ergolines SDZ 208-911 and SDZ 208-912.

The aminoergolines SDZ 208-911 [N-[(8-alpha)-2,6-dimethylergoline-8-yl]-2,2- dimethylpropanamide] and SDZ 208-912 [N-[8-alpha)-2-chloro-6-methylergoline-8-yl]- 2,2-dimethylpropanamide] exhibit nonclassical, neuroleptic-like properties in rodents. Thus, they are equipotent to haloperidol as inhibitors of apomorphine-induced gnawing behavior and conditioned avoidance responding, but are essentially devoid of cataleptogenic activity. In addition, they show high affinity for central D-2 receptors in vitro and elevate striatal homovanillic acid levels. In contrast to haloperidol, however, SDZ 208-911 and 208-912 strongly inhibit prolactin secretion and induce contralateral circling behavior in 6-hydroxydopamine-lesioned animals. These profiles are consistent with the drugs exhibiting varying degrees of partial agonistic activity at dopamine D-2 receptors, with SDZ 208-911 being considerably more agonistic than SDZ 208-912. Support for this contention stems from the ability of SDZ 208-911 to reduce the elevation of striatal L-dopa formation induced by gamma-butyrolactone, and SDZ 208-912's partial reversal of apomorphine's inhibitory action on gamma-butyrolactone activity. SDZ 208-911's effects are reduced after the partial alkylation of D-2 receptors with N-ethoxy-carbonyl-2-ethoxy-1,2-dihydroquinoline, confirming its partial agonistic properties. SDZ 208-911 and SDZ 208-912 could be effective against both the positive and negative symptoms of schizophrenia, while exhibiting a reduced incidence of dystonic and parkinsonian side-effects. In addition, their clinical testing might throw more light on the central dopaminergic status of schizophrenic subjects.

4-Butyrolactone↗

PubMed1989

Biochemical and behavioural properties of clozapine.

The selection and early development of clozapine was based upon its gross behavioural, arousal-inhibiting, sleep-promoting, and caudate spindle-prolonging properties. Compared to classical neuroleptics, clozapine causes only a short-lasting elevation of plasma prolactin levels, elevates both striatal homovanillic acid and dopamine content, is devoid of marked apomorphine-inhibitory or cataleptogenic activity and fails to induce supersensitivity of striatal dopaminergic systems after chronic administration. Clozapine's intrinsic anticholinergic activity, while stronger than that of other neuroleptic agents, does not appear to underlie either its failure to induce tardive dyskinesias or its superior antipsychotic activity. Furthermore, the overlap between clozapine and several classical neuroleptics with regard to alpha-adrenergic-, serotonin- and histamine-blocking activity makes it unlikely that one or more of these properties is the key to its atypical characteristics. More recent findings show that clozapine and classical neuroleptics differ with regard to their indirect effects on nigral GABA-ergic mechanisms implicated in the induction of tardive dyskinesias and, possibly in keeping with this, that clozapine and similar agents exhibit preferential blockade of D-1 dopamine receptors in the whole animal. Such an action of clozapine in man could well explain both its low EPS liability and, in some subjects, its superior antipsychotic activity.

Animals↗

PubMed1989

Mono- and divalent cations modulate the affinities of brain D1 and D2 receptors for dopamine by a mechanism independent of receptor coupling to guanyl nucleotide binding proteins.

In order to clarify the question of whether the modulatory effects of cations on dopamine receptor affinities are brought about by shifts in the equilibrium of receptor - G protein - coupling, it was investigated whether mono- and divalent cations were still able to modulate rat striatal D1 and D2 receptor affinities after selective inactivation of the G-proteins linked to the two receptors. The Gs-protein coupled to the D1 receptor was eliminated by mild thermal inactivation, and the Gi- (or Go-) protein associated with the D2 receptor by alkylation with a low concentration of N-ethyl-maleimide. Incubation of striatal membranes at 60 degrees C completely abolished the specific binding of 3H-GTP. Both treatments resulted in an increase of the IC50-values for dopamine as a displacer of 3H-SCH 23390 from D1- and of 3H-spiperone from D2 receptors. Concomitantly, the formerly shallow D1 displacement curves became steeper, with their Hill coefficients increasing. This effect was less evident at D2 receptors. Guanosine triphosphate (GTP), which increased the IC50's of dopamine for both receptors approximately two-fold in control membranes, was without effect in pretreated samples, indicating an effective inactivation of the G-proteins. Na+ ions were still able to lower, and Ca2+ ions to increase the affinities of D1 and D2 receptors for dopamine after such inactivation of the respective G-proteins. It is concluded that the mechanism underlying the regulation of dopamine receptor affinities by mono- and divalent cations is independent of and superimposed upon the coupling of these receptors to guanyl nucleotide binding proteins.

Animals↗

PubMed1989

Partial brain dopamine D2 receptor agonists in the treatment of schizophrenia.

Partial dopamine agonists showing high affinity but low efficacy at D2 receptors can act as dopaminergic "buffers," reducing dopaminergic activity when it is excessive, and promoting it when reduced. This makes them of interest as potential therapeutic agents for the treatment of both positive and negative symptoms in schizophrenia, where they should also result in fewer or less severe motor disturbances than classical neuroleptics. SDZ 208-911 and SDZ 208-912 are amino-ergolines exhibiting partial agonistic properties in the rat, where they inhibit apomorphine-induced stereotypies, are only weakly cataleptogenic, induce varying degrees of circling behavior after unilateral lesioning of the nigrostriatal pathway, and strongly suppress prolactin secretion. The least agonistically acting agent, SDZ 208-912, should be effective against positive symptoms, whereas SDZ 208-911 could be suitable for the treatment of negative symptoms. In addition to possible therapeutic effects, the clinical testing of this class of agent should help to elucidate the status of central dopaminergic function in schizophrenic psychosis.

Brain Chemistry↗

PubMed1988

6,7-Dichloro-3-hydroxy-2-quinoxalinecarboxylic acid is a relatively potent antagonist at NMDA and kainate receptors.

The 6,7-dichloro derivative of 3-hydroxy-2-quinoxalinecarboxylic acid (diCl-HQC) is a relatively potent antagonist at the two excitatory amino acid receptor subtypes activated by N-methyl-D-aspartate (NMDA) and kainic acid. It antagonizes NMDA-induced excitation in the frog spinal cord (pA2 5.8), i.e. with a potency similar to D-2-amino-7-phosphonoheptanoate (D-AP-7). It also antagonizes NMDA-induced sodium efflux from rat brain slices (pA2 5.6). The compound inhibits kainic acid-induced sodium efflux from rat brain slices with a pA2 of 5.4 and it inhibits [3H]kainic acid binding to rat brain membranes with a pKi of 5.4. DiCl-HQC is only weakly active at the quisqualate receptor. This spectrum of activities may make this compound a useful tool to investigate the pharmacology of excitatory amino acid receptors.

Animals↗