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A Dumbrille-Ross

Publications and source records attributed to A Dumbrille-Ross.

17 recordsLinked to original sources
PubMed1988

Identification of an altered splice site in Ashkenazi Tay-Sachs disease.

Tay-Sachs disease is an autosomal recessive genetic disorder resulting from mutation of the HEXA gene encoding the alpha-subunit of the lysosomal enzyme, beta-N-acetylhexosaminidase A (ref. 1). A relatively high frequency of carriers (1/27) of a lethal, infantile form of the disease is found in the Ashkenazi Jewish population, but it is not yet evident whether this has resulted from a founder effect and random genetic drift or from a selective advantage of heterozygotes. We have identified a single-base mutation in a cloned fragment of the HEXA gene from an Ashkenazi Jewish patient. This change, the substitution of a C for G in the first nucleotide of intron 12 is expected to result in defective splicing of the messenger RNA. A test for the mutant allele based on amplification of DNA by the 'polymerase chain rection and cleavage of a DdeI restriction site generated by the mutation revealed that this case and two other cases of the Ashkenazi, infantile form of Tay-Sachs disease are heterozygous for two different mutations. The occurrence of multiple mutant alleles warrants further examination of the selective advantage hypothesis.

Base Sequence↗
PubMed1988

Characterization of the human HEXB gene encoding lysosomal beta-hexosaminidase.

The lysosomal enzyme beta-hexosaminidase A contains alpha- and beta-subunits that are encoded by the HEXA and HEXB genes, respectively. The human HEXB gene has been isolated and characterized. It is 45 kb long and is split into 14 exons. Of the 13 introns, 12 interrupt the coding sequences at homologous positions in the HEXA and HEXB genes. The 5' flanking region contains the functional HEXB gene promoter. While a fine-structure analysis has yet to be done, we note that the sequence is GC rich and has several GC boxes and one CAAT box. There are also sequences related or identical to a progesterone response element and an AP-1 binding motif.

Amino Acid Sequence↗
PubMed1987

Dopamine agonist high-affinity state in solubilized D2 receptors in striatum, but not in anterior pituitary.

To determine whether brain and pituitary dopamine D2 receptors have similar characteristics on solubilization, canine striatal and bovine anterior pituitary tissues were solubilized with digitonin, and their D2 dopamine receptors were characterized by competition studies and by high pressure liquid chromatography. Solubilized striatal membranes retained the ability to bind agonists with high affinity and retained sensitivity to guanine nucleotides. In contrast, however, solubilized pituitary membranes no longer revealed high-affinity binding of agonists and sensitivity to guanine nucleotide unless they had been solubilized in the presence of agonist. Agonist-pre-labelled pituitary receptors were of larger apparent molecular weight than antagonist-pre-labelled receptors. However, striatal receptors pre-labelled by agonist or antagonist were of similar apparent molecular weight. Thus, unlike the pituitary, striatal receptors probably remain associated with a guanine nucleotide binding protein (N) upon solubilization.

Animals↗
PubMed1986

Dopamine D1 receptors characterized with [3H]SCH 23390. Solubilization of a guanine nucleotide-sensitive form of the receptor.

Dopamine D1 receptors were solubilized from canine and bovine striatal membranes with the detergent digitonin. The receptors retained the pharmacological characteristics of membrane-bound D1 receptors, as assessed by the binding of the selective antagonist [3H]SCH 23390. The binding of [3H]SCH 23390 to solubilized receptor preparations was specific, saturable, and reversible, with a dissociation constant of 5 nM. Dopaminergic antagonists and agonists inhibited [3H]SCH 23390 binding in a stereoselective and concentration-dependent manner with an appropriate rank order of potency for D1 receptors. Moreover, agonist high affinity binding to D1 receptors and its sensitivity to guanine nucleotides was preserved following solubilization, with agonist dissociation constants virtually identical to those observed with membrane-bound receptors. To ascertain the molecular basis for the existence of an agonist-high affinity receptor complex, D1 receptors labeled with [3H] dopamine (agonist) or [3H]SCH 23390 (antagonist) prior to, or following, solubilization were subjected to high pressure liquid steric-exclusion chromatography. All agonist- and antagonist-labeled receptor species elute as the same apparent molecular size. Treatment of brain membranes with the guanine nucleotide guanyl-5'-yl imidodiphosphate prior to solubilization prevented the retention of [3H]dopamine but not [3H]SCH 23390-labeled soluble receptors. This suggests that the same guanine nucleotide-dopamine D1 receptor complex formed in membranes is stable to solubilization and confers agonist high affinity binding in soluble preparations. These results contrast with those reported on the digitonin-solubilized dopamine D2 receptor, and the molecular mechanism responsible for this difference remains to be elucidated.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1985

Dopamine D2 receptors photolabeled by iodo-azido-clebopride.

Iodo-azido-clebopride, a photoaffinity compound for dopamine D2 receptors, had high affinity for canine brain striatal dopamine D2 receptors with a dissociation constant (Kd) of 14 nM. Irradiation of striatal homogenate with iodo-azido-clebopride irreversibly inactivated 50% of dopamine D2 receptors at 20 nM (as indicated by subsequent [3H]spiperone binding). Dopamine agonists and antagonists prevented this photo-inactivation with the appropriate rank-order of potency. Striatal dopamine D1, serotonin (S2), alpha 1- and beta-adrenoceptors were not significantly inactivated following irradiation with iodo-azido-clebopride. Thus, iodo-azido-clebopride is a selective photoaffinity probe for dopamine D2 receptors, the radiolabelled form of which may aid in the molecular characterization of these proteins.

Affinity Labels↗
PubMed1983

Temperature-sensitive reversible loss of [3H]imipramine binding sites: evidence suggesting different conformational states.

Previous studies have indicated that the tertiary tricyclic antidepressant imipramine binds with high affinity to a site related to the serotonin uptake mechanism. We have further characterized this site with regards to the effects of temperature, pH and calcium ions on both rat cerebral cortex homogenates and outdated human platelets. The binding of [3H]imipramine to these sites is maximal at 4 degrees C. When the assay temperature is increased to 23 degrees C, there is approximately a 50% decrease in the maximal number of binding sites (Bmax) with no apparent change in the affinity for the ligand. On further raising the temperature to 37 degrees C there is no further decrease in Bmax but there is an increase in the dissociation constant (KD). These temperature related changes are reversed when the assay temperature is again lowered to 4 degrees C. Decreasing the pH of the incubation mixture from 7.5 to 7 (which is the pH change also observed upon changing the temperature of the incubation mixture from 4 to 37 degrees C) decreased [3H]imipramine binding by 10-20%, an amount which does not account for the changes observed. Similarly, neither calcium nor EDTA altered these reversible changes. Irreversible loss of binding sites was observed on prolonged incubation at 23 or 37 degrees C. After 20 h preincubation at 23 or 37 degrees C, 15 or 30% of the binding respectively could not be restored by lowering the temperature to 4 degrees C. This permanent loss was enhanced by calcium and inhibited by EDTA. These results suggest that reversible conformational changes in the [3H]imipramine binding site can be observed.

Animals↗
PubMed1983

Manipulations of synaptic serotonin: discrepancy of effects on serotonin S1 and S2 sites.

The effect of repeated treatment (28 day) with D-fenfluramine, a serotonin (5HT) releaser, L-tryptophan, a 5HT precursor, or fluoxetine, a 5HT uptake inhibitor, on 3H-5HT and 3H-spiperone binding in the rat cerebral cortex was investigated. Treatment with fenfluramine and fluoxetine caused a significant decrease in the number of 3H-5HT binding sites (Bmax). Fenfluramine also decreased binding of 3H-spiperone in the cortex, but fluoxetine treatment increased this binding. Treatment with L-tryptophan produced no change in the binding of either 3H-5HT or of 3H-spiperone significantly. The data show that manipulation of synaptic 5HT concentration does not always result in parallel changes in S1 and S2 receptors. This suggests that the 5HT S1 and S2 receptors may be subject to different regulatory mechanisms.

Animals↗
PubMed1983

Noradrenergic and serotonergic input necessary for imipramine-induced changes in beta but not S2 receptor densities.

Chronic imipramine administration decreases the density of serotonin S2 and beta-adrenergic receptors. The mode of action is not clear but might be assumed to be a result of imipramine interacting with its high affinity binding sites on presynaptic serotonin neurons. To investigate this possibility and the role of the serotonergic and noradrenergic systems on imipramine-induced receptor down-regulations, the effects of raphe lesions and 6-hydroxydopamine lesions were examined. The theory that imipramine acts through the serotonin system to down-regulate beta-adrenergic receptors was supported by the observation that raphe lesions attenuated the imipramine-induced beta receptor denumeration. However, the effect of imipramine on the S2 site may not be a result of serotonin uptake blockade. Raphe lesions which diminish 3H-imipramine high affinity binding did not alter the imipramine-induced decrease in S2 receptor numbers. 6-Hydroxydopamine lesions prevented the reduction in beta but not S2 binding. Imipramine may exert its effect on S2 binding through a site other than the high affinity, serotonin uptake site.

Animals↗
PubMed1983

Binding of [3H]Ro 11-2465. Possible identification of a subclass of [3H]imipramine binding sites.

Ro 11-2465 is a cyanide derivative of imipramine. In cerebral cortex homogenates, [3H] Ro 11-2465 displays a binding profile similar to that of [3H]imipramine. Agents compete with binding of [3H]Ro 11-2465 in an order of potency similar to their ability to block serotonin uptake, and raphe lesions greatly decrease the binding of [3H]Ro 11-2465. These observations suggest that the sites labeled by [3H]Ro 11-2465 are presynaptic. The binding of [3H]Ro 11-2465 is sodium ion-dependent, as are both the binding of [3H] imipramine and the serotonin uptake mechanism. In the presence of sodium ions, binding of [3H]Ro 11-2465 to brain tissue or platelets at 4 degrees is apparently irreversible. Binding is not displaced by high concentrations of the displacing agent desipramine or by repeated washing. However, by either removing sodium or increasing the assay temperature to 23 degrees, the ligand dissociates from the tissue. In tissue where [3H]Ro 11-2465 is irreversibly bound to receptor at 4 degrees, subsequent [3H]imipramine binding is decreased by about 50%. At temperatures greater than 23 degrees, [3H]Ro 11-2465 binding displays a temperature dependency similar to that of [3H]imipramine; that is, when temperatures are raised from 23 degrees to 30 degrees or 37 degrees there is no change in the Bmax, but the affinity of the ligand for the receptor is decreased. These data suggest that [3H]Ro 11-2465 binds to a discrete population of [3H]imipramine binding sites, comprising about one-half of the total [3H] imipramine binding sites.

Animals↗
PubMed1982

Lack of effect of raphe lesions on serotonin S2 receptor changes induced by amitriptyline and desmethylimipramine.

Spiperone binding was studied in rat cortical and striatal homogenates by direct binding assay after chronic (10 mg/kg/day i.p. for 21 days) treatment with the tricyclic antidepressants amitriptyline (AMT) and desmethylimipramine (DMI). Both AMT (a potent serotonin reuptake inhibitor) and DMI (a weak serotonin reuptake inhibitor) treatment were associated with decreased specific binding of 3H-spiperone and 3H-mianserin in the cortex (markers for serotonin S2 receptors) of 31-45% of normal rats, but not the binding of 3H-spiperone in the striatum (a marker for dopamine D2 receptors). The same chronic treatment of raphe-lesioned rats with AMT or DMI produced equivalent (38-40%) decreased specific binding of these ligands in the cortex but no change in striatum. These results suggest that synaptic serotonin concentration may not be the factor responsible for the decreased number of spiperone binding sites observed after chronic antidepressant treatment.

Amitriptyline↗
PubMedDate not supplied

Dopamine receptor elevation by cholecystokinin.

High concentrations of cholecystokinin (CCK) in the striatum and limbic areas of the brain suggest that this peptide may influence dopaminergic transmission. Thus, the effect of CCK on dopamine D2 receptors in the striatum and nucleus accumbens of the rat brain both in vitro and in vivo (central and peripheral administration) was studied by determining the binding of 3H-spiperone. The density (Bmax) of D2 receptors was elevated (a) by 20% in the accumbens upon in vitro co-incubation with 10(-6) M CCK. (A non-significant drop of 10% occurred in the striatum); (b) by about 40% in the accumbens and 25% in the striatum after continuous intraventricular infusion of CCK for 24 hr. The increase in receptor density in the accumbens was maintained for 14 days and in both tissues was specific to CCK (neurotensin infusion did not alter 3H-spiperone binding); (c) by 20% in the accumbens and 15% in the striatum 3 hr after a single IP injection of 50 micrograms/kg CCK or caerulein, and maintained up to 14 days later. These results suggest that CCK elevates dopamine D2 receptors in the accumbens and striatum and may be a physiological modulator of the dopaminergic system.

Animals↗