Biomedical subjects

N Griffon

Publications and source records attributed to N Griffon.

45 records · Page 3Linked to original sources

PubMed1995

The dopamine D3 receptor and schizophrenia: pharmacological, anatomical and genetic approaches.

Antipsychotic drug therapy mainly rests on the use of antagonists of dopamine D2-like (D2, D3 and D4) receptors, for which all clinically active compounds have high affinity. The D3 receptor has a restricted expression in brain limbic areas, associated with cognitive functions and motivated behavior. D3 selective agonists and antagonists reveal an inhibitory role on motor behaviors for the D3 receptor, opposite to that of the D2 receptor. An opposing role for D2 and D3 receptors is also suggested by the contrasted effects of D2/D3 antagonists on neurotensin expression in discrete subdivisions of nucleus accumbens, where D2 and D3 receptors are selectively expressed. Tolerance to the motor but not to the therapeutic effects of neuroleptics is observed after repeated administration, which upregulates the D2, but not the D3 receptor in animals. In genetic association studies, an excess of homozygosity for both alleles of the BalI polymorphism at the D3 receptor gene was found in schizophrenic patients, suggesting that this gene may have subtle influence on the liability to develop schizophrenia. These results suggest the D3 receptor as an important target for antipsychotic drug action, and D3 receptor selective antagonists as promising therapeutic agents.

Animals↗

PubMed1995

Oxygen delivery and autoxidation of hemoglobin.

Hemoglobin can be considered to exist in active and inactive states. When the iron atom is in the ferrous form, the protein is active and can bind oxygen reversibly; high and low affinity substates account for the cooperativity of ligand binding. However, like bulk metal, the iron can rust. The oxidation to the ferric form (metHb) leads to an inactive protein. The oxidation rate will therefore limit the useful lifetime of oxygen transporters; this is especially critical for cell free Hb solutions. This problem is compounded by the fact that Hb is a tetramer. A single oxidized heme effects the other three subunits within the same tetramer. The statistics are different from those for a monomeric system. For example, a random distribution of 20% ferric iron would imply 58% of the tetramers with at least one oxidized subunit. The oxidized subunits remain liganded (with water or OH) and will change the oxygenation curve for the neighbouring subunits. Since the tetramer will no longer make a full transition to the deoxy state, the oxygenation curves are shifted towards higher affinities. Thus the oxygen delivery will decrease for two reasons: the direct loss of active hemes, and the secondary influence on the remaining ferrous subunits. Control of the oxidation rate is also complicated by the intercorrelation of parameters. The rate is globally correlated with the oxygen affinity; it is also increased for hemoglobin dimers relative to tetramers. One must therefore accept a compromise of these parameters, in order to obtain a useful transporter.

Biological Transport↗

PubMed1995

Hb Arta [beta 45 (CD4) Phe-->Cys]: a new unstable haemoglobin with reduced oxygen affinity in trans with beta-thalassaemia.

The interaction of rare Hb variants with beta(0)-thalassaemia results in a quasihomozygous state where the erythrocytes contain the variant as the only major adult Hb component. Such a situation is a unique model that enables functional studies even in the case of a neutral variant that could not be isolated from Hb A. We report here an unusual patient carrying Hb Arta, a novel Hb variant [beta 45 (CD4) Phe-->Cys], in trans with beta(0)-thalassaemia gene (beta(0) 39). The aminoacid substitution at the critical CD corner of this Hb molecular renders the molecule unstable. In addition, haem is displaced in a position that favours the deoxy (T) conformation of the variant, but less than in Hb Cheverly [beta 45 (CD4) Phe-->Ser], and results in a p50 of 43 mmHg (pH 7.4, 37 degrees C) in the red cells with preservation of cooperativity. Solution studies of the almost pure Hb Arta show a 50% decrease in oxygen affinity and normal cooperativity; the Bohr effect and the interaction with organic phosphates are similar to those of Hb A. Hb Arta retains both normal homo- and heterotropic effects allowing a well-preserved oxygen transport in vivo despite a mild anaemia.

Adult↗

PubMed1995

Nafadotride, a potent preferential dopamine D3 receptor antagonist, activates locomotion in rodents.

Nafadotride (N[(n-butyl-2-pyrrolidinyl)methyl]-1-methoxy-4-cyano naphtalene-2-carboxamide) is a novel compound, which inhibits potently and stereoselectively [125I]iodosulpride binding at recombinant human dopamine D3 receptors. the levoisomer displays an apparent Ki value of 0.3 nM at the dopamine D3 receptor, but is 10 times less potent at the human recombinant dopamine D2 receptor. In comparison, the dextroisomer displays 20-fold less apparent affinity at the dopamine D3 receptor and reduced (2-fold) selectivity. l-Nafadotride displays iow, micromolar affinity at dopamine D1 and D4 receptors and negligible apparent affinity at various other receptors. In dopamine D3 receptor-transfected NG-108 15 cells, in which dopamine agonists increase mitogenesis, l-nafadotride has no intrinsic activity, but competitively antagonizes the quinpirole-induced mitogenetic response, monitored by [3H]thymidine incorporation with a pA2 of 9.6. In dopamine D2 receptor-transfected Chinese Hamster Ovary cells, l-nafadotride also behaves as a competitive antagonist of quinpirole-induced mitogenesis with an 11-fold lower potency. These studies establish nafadotride as a pure, extremely potent, competitive and preferential dopamine D3 receptor antagonist in vitro. l-Nafadotride displaces in vivo N-[3H]propylnorapomorphine accumulation at lower dosage and for longer periods in limbic structures, containing both dopamine D2 and D3 receptors than in the stratum, containing dopamine D2 receptor only. At low dosage (0.1-1 mg/kg), nafadotride, unlike haloperidol, a dopamine D2 receptor-preferring antagonist, increases spontaneous locomotion of habituated rats and climbing behavior of mice, at doses that do not modify striatal homovanillic acid levels. At high dosage (1-100 mg/kg), nafadotride, like haloperidol, produces catalepsy and antagonizes apomorphine-induced climbing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The D3 receptor and its relevance in psychiatry.

A large fraction of neurotensin neurons in the ventromedial shell subdivision of nucleus accumbens express D3 receptors. Blockade of D2/D3 receptors by antipsychotic agents paradoxically decreases neurotensin gene expression in these neurons whereas it enhances it in other striatal areas expressing the D2 receptor. This suggests that D2 and D3 receptors mediate opposite actions of dopamine. In support of this view low doses of nafadotride, a novel D3 receptor-preferring antagonist, enhances locomotor activity in rodents, a behavioral response opposite to that of current neuroleptics. The action of D3 receptor-preferring agonists was characterized by the mitogenic response they elicit in transfected NG 108-15 cells. Finally, gene expression of the D3 receptor is in opposition to that of the D2 receptor, being decreased by denervation and unaffected by chronic blockade by neuroleptics.

Antipsychotic Agents↗

PubMed1994

Opposing roles for dopamine D2 and D3 receptors on neurotensin mRNA expression in nucleus accumbens.

Using in situ hybridization histochemistry in rat nucleus accumbens, we show that the dopamine D3 receptor mRNA is expressed in the ventromedial part of the shell subdivision, where its gross distribution matches that of neurotensin mRNA. In addition, hybridization studies at the cellular level show that a large fraction of the neurotensin neurons co-express the D3 receptor mRNA in this restricted area. In contrast, the dopamine D2 receptor mRNA is expressed mainly in the core and marginally in the shell, at the level of the cone. In rats treated by haloperidol and sulpiride, two D2-like receptor antagonists, but not by SCH 23390, a D1-like receptor antagonist, proneurotensin mRNA was increased in the D2 receptor mRNA-rich areas but decreased in the D3 receptor mRNA-rich areas. This suggests that the D2 and D3 receptors control neurotensin mRNA expression negatively and positively, respectively.

Animals↗

PubMed1994

Functional coupling of the human dopamine D3 receptor in a transfected NG 108-15 neuroblastoma-glioma hybrid cell line.

Transfection of a human dopamine D3 receptor cDNA in a neuroblastoma-glioma hybrid cell line (NG 108-15) provided clonal cell lines stably expressing up to 600 fmol per mg protein of [125I]iodosulpiride binding sites. Dopamine and several agonists distinguished two receptor-affinity states in membranes. In the case of dopamine, the high-affinity state (Ki = 0.9 nM, 30% of total binding) was completely converted into a low-affinity state (Ki = 57 nM) in the presence of 10 microM guanosine-5'-O-(3-thiotriphosphate). In addition to these two sites, a site with a very low affinity for dopamine was evidenced in whole cells. The dopamine D3 receptor mediated two responses: c-fos activation, as measured by the appearance of Fos-like immunoreactivity, and increased mitogenesis, as measured by incorporation of [3H]thymidine. The Fos-like immunoreactivity appeared within 30 min, lasted 2 h and was blocked by the partially selective dopamine D3 receptor compound (+)-UH 232 (cis-(+)-5-methoxy-1-methyl-2-(di-n-propylamino)tetralin). The mitogenic effect, which occurred after a lag time (over 2 h stimulation), was produced with subnanomolar potency and full intrinsic activity by several compounds previously identified as dopamine D2 receptor agonists, e.g. quinpirole, (+)-7-OH-DPAT ((+)-7-hydroxy-2-(di-n-propylamino)tetralin) and RU 24926 (N-n-propyl-di-beta(3-hydroxyphenyl)-ethylamine), and was reversibly blocked by (+)-UH 232 (Ki = 9 nM). Talipexole (B-HT 920, 5-allyl-2-amino-5,6,7,8-tetrahydro-4H-thiazolo[4,5-d]azepin) was identified as a partial agonist at the dopamine D3 receptor. Dopamine D3 receptor-mediated mitogenesis was potentiated by a phorbol ester and was abolished by pretreatment with pertussis toxin. A mitogenic effect of same amplitude was elicited by bradykinin or carbachol, both acting through constitutive receptors. Bradykinin markedly activated inositol phosphate turnover, and had no effect on forskolin-stimulated cyclic AMP accumulation. Carbachol inhibited forskolin-stimulated cyclic AMP accumulation and had no effect on inositol-phosphate turnover. Quinpirole had no effect on any of these second messenger pathways. Thus, in transfected NG 108-15 cells, the dopamine D3 receptor is coupled to a pertussis toxin-sensitive G protein and mediates two possibly unrelated biological effects, through initial biochemical events that remain to be identified.

Animals↗

PubMed1994

Molecular cloning and characterization of the rat fifth melanocortin receptor.

Adrenocorticotropic hormone (ACTH) and melanocortin peptides (alpha, beta and gamma MSH) have numerous activities in both central nervous system and peripheral tissues, namely the adrenals. Recently, five melanocortin receptors were cloned and characterized. We report here the cloning, pharmacological characterization and expression of the rat fifth melanocortin receptor (MC5), starting from the dopamine D3 receptor sequence to screen a genomic DNA library. The MC5 comprises a sequence of 325 amino acids, displaying 45-62% identity with other melanocortin receptors and 82% identity with its human counterpart that we cloned thereafter. The sequence of the latter is identical to that of a so-called 'MC2' receptor (Chhajlani et al., 1993, Biochem. Biophys. Res. Comm. 195, 866-873). The MC5, stably expressed in CHO cells, mediates increase in cAMP accumulation with a characteristic pharmacology: alpha MSH is twice as potent as NDP alpha MSH, 10 times as ACTH and 100 times as gamma MSH. Very low expression levels were detected in brain, while high levels were found in adrenals, stomach, lung and spleen. In addition, in situ hybridization studies show the MC5 expressed in the three layers of the adrenal cortex, predominantly in the aldosterone-producing zona glomerulosa cells.

Adrenal Cortex↗

PubMed1994

Multiple dopamine receptors: the D3 receptor and actions of substances of abuse.

Our knowledge of dopamine receptor diversity has markedly increased during the past few years as a result of discovery of five distinct genes, splice variants and polymorphic receptors. The genes can be classified in two subfamilies: the intronless genes that encode the D1 and D5 receptors positively linked to adenylyl cyclase and genes with introns that encode the two isoforms of the D2 receptor and the D3 and D4 receptors. The various dopamine receptor subtypes can be distinguished by their sequence, intracellular signalling systems, pharmacology and localisation. The localisation of the D3 receptor in the shell of nucleus accumbens suggests its participation in brain reward circuits and actions of substances of abuse.

Animals↗