Search PubMed⌕ Search

Biomedical subjects

P Seeman

Publications and source records attributed to P Seeman.

At least 127 records · Page 7Linked to original sources
PubMed1990

Dopamine uptake sites and dopamine receptors in Parkinson's disease and schizophrenia.

Dopamine uptake sites, labelled by 3 nM [3H]GBR 12935, were reduced by 28-34% in post-mortem Parkinson's diseased striata (n = 22) compared to control striata (n = 28). There was no significant difference between post-mortem striata from schizophrenics (n = 16) and controls. Both dopamine D1 and D2 receptors are consistently elevated in Parkinson's diseased striata from patients who have not been medicated with L-dopa pre-mortem. Both these receptors are down-regulated by L-dopa pre-mortem. In schizophrenia, however, while the density of D1 receptors is similar to control, the D2 receptors are consistently elevated.

Adult↗
PubMed1989

2-Haloaporphines as potent dopamine agonists.

The synthesis of 2-amino- and 2-halo-substituted aporphines is described. The key step is the substitution of a hydroxy group in the 2-position with an amino group effected by a Smiles rearrangement reaction of the 2-methylpropanamide derivative 6. The affinity of the new compounds for the dopamine D-2 receptor in the anterior pituitary gland was evaluated. 2-Fluoroapomorphine was the most potent compound, being 1.5 times more potent than (-)-apomorphine. The structure-activity relationships are discussed in relation to a previously proposed receptor model.

Animals↗
PubMed1989

Link between D1 and D2 dopamine receptors is reduced in schizophrenia and Huntington diseased brain.

Dopamine receptor types D1 and D2 can oppose or enhance each other's actions for electrical, biochemical, and psychomotor effects. We report a D1-D2 interaction in homogenized tissue as revealed by ligand binding. D2 agonists lowered the binding of [3H]raclopride to D2 receptors in striatal and anterior pituitary tissues. Pretreating the tissue with the D1-selective antagonist SCH 23390 prevented the agonist-induced decrease in [3H]raclopride binding to D2 sites in the striatum but not in the anterior pituitary, which has no D1 receptors. Conversely, a dopamine-induced reduction in the binding of [3H]SCH 23390 to D1 receptors could be prevented by the D2-selective antagonist eticlopride. Receptor photolabeling experiments confirmed both these D1-D2 interactions. The blocking effect by SCH 23390 was similar to that produced by a nonhydrolyzable guanine nucleotide analogue, and SCH 23390 reduced the number of agonist-labeled D2 receptors in the high-affinity state. Thus, the D1-D2 link may be mediated by guanine nucleotide-binding protein components. The link may underlie D1-D2 interactions influencing behavior, since the link was missing in over half the postmortem striata from patients with schizophrenia and Huntington disease (both diseases that show some hyperdopamine signs) but was present in human control, Alzheimer, and Parkinson striata.

Affinity Labels↗
PubMed1988

Photoaffinity labeling of dopamine D1 receptors.

A high-affinity radioiodinated D1 receptor photoaffinity probe, (+/-)-7-[125I]iodo-8-hydroxy-3-methyl-1-(4-azidophenyl)-2,3,4,5-tetra hyd ro- 1H-3-benzazepine ([125I]IMAB), has been synthesized and characterized. In the absence of light, [125I]IMAB bound in a saturable and reversible manner to sites in canine brain striatal membranes with high affinity (KD approximately equal to 220 pM). The binding of [125I]IMAB was stereoselectively and competitively inhibited by dopaminergic agonists and antagonists with an appropriate pharmacological specificity for D1 receptors. The ligand binding subunit of the dopamine D1 receptor was visualized by autoradiography following photoaffinity labeling with [125I]IMAB and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon photolysis, [125I]IMAB incorporated into a protein of apparent agents in a stereoselective manner with a potency order typical of dopamine D1 receptors. In addition, smaller subunits of apparent Mr 62,000 and 51,000 were also specifically labeled by [125I]IMAB in these species. Photoaffinity labeling in the absence or presence of multiple protease inhibitors did not alter the migration pattern of [125I]IMAB-labeled subunits upon denaturing electrophoresis in both the absence or presence of urea or thiol reducing/oxidizing reagents. [125I]IMAB should prove to be a useful tool for the subsequent molecular characterization of the D1 receptor from various sources and under differing pathophysiological states.

Affinity Labels↗
PubMed1988

Dopamine D1 receptors with enhanced agonist affinity and reduced antagonist affinity revealed by chemical modification.

In order to investigate the possibility that there may be two conformationally distinct dopamine D1 binding sites, the effect of lysine-modifying agents on striatal dopamine D1 receptors was investigated. Treatment with the distilbene derivative, 4,4'-diisothiocyanostilbene-2,2'-disulfonate, (DIDS), resulted in an irreversible D1 receptor inactivation that was associated with a 70% loss of binding sites. The remaining DIDS-insensitive sites displayed both a decreased affinity (approximately 5 fold) for the D1 antagonist SCH-23390 and an enhanced affinity of dopaminergic agonists (approximately 10 fold) for the agonist high-affinity form of the receptor. Pretreatment with Gpp(NH)p, a non-hydrolysable guanine nucleotide, prevented the formation of the agonist high-affinity form, indicating that these sites are G-protein-linked. Prior occupancy of D1 receptors with dopaminergic agonists and antagonists afforded no protection against DIDS inactivation, suggesting that a site outside the ligand binding subunit of the D1 receptor was modified. Taken together, these data suggest that [3H]SCH-23390 labels two conformationally distinct populations of dopamine D1 receptors.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Glycoprotein nature of D2 dopamine receptors.

The glycoprotein nature of the ligand binding subunit of photoaffinity-labeled striatal D2 receptors was investigated. Upon photolysis, [125I]N-azidophenethylspiperone covalently incorporated into a major band of Mr 94000 with an appropriate pharmacological profile for D2 receptors as assessed by autoradiography following SDS-polyacrylamide gel electrophoresis. The exoglycosidase, neuraminidase, altered the electrophoretic mobility of the 94 kDa labeled band to 54 kDa with a slight modification in the binding affinity of [3H]spiperone. Endoglycosidase treatment (glycopeptidase-F) produced a further increase in the mobility of the 94 kDa peptide to approximately 43 kDa. A smaller specifically photolabeled D2 receptor peptide of 34 kDa does not contain terminal sialic acid but is an N-linked glycoprotein as assessed by lectin affinity chromatography and susceptibility to digestion by glycopeptidase-F to a peptide of approximately 23 kDa.

Animals↗
PubMed1988

Dopamine D1 and D2 receptor selectivities of agonists and antagonists.

The selectivities of various dopamine agonists and antagonists for dopamine D1 and D2 receptors were obtained by comparing their relative dissociation constants for inhibiting the binding of [3H]SCH 23390 at D1 receptors (calf caudate nucleus) and at D2 receptors (pig anterior pituitary tissue). The most selective agonists were SK&F 38393 (for D1) and (+)-PHNO (for D2), while the most selective antagonists were SCH 23390 (for D1) and raclopride or eticlopride (for D2).

Animals↗
PubMed1988

Dopamine D2 receptors retain agonist high-affinity form and guanine nucleotide sensitivity after removal of sialic acid.

The ligand binding subunit of the D2 dopamine receptor (Mr approximately equal to 94,000) can be visualized by autoradiography following photoaffinity labeling with [125I]N-azidophenethylspiperone and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Following removal of sialic acids with the exoglycosidase, neuraminidase, [125I]N-azidophenethylspiperone photoincorporated into a protein of Mr = 54,000 with the appropriate pharmacological profile for D2 receptors. The desialylated D2 receptor bound dopaminergic agonists with high affinity and was capable of coupling to a functional G-protein as indexed by: 1) pertussis-toxin mediated [32P]ADP ribosylation of proteins of Mr = 42,000 and 39,000, and 2) the conversion of the agonist high affinity form of D2 receptors to one displaying low affinity for agonists in the presence of guanine nucleotides. These data suggest that sialic acid residues do not contribute significantly to the ligand binding characteristics of D2 receptors despite the large change produced in the estimated molecular mass of the binding subunit.

Affinity Labels↗
PubMed1988

Tardive dyskinesia, dopamine receptors, and neuroleptic damage to cell membranes.

The long-term treatment of schizophrenic patients with neuroleptics is associated with neuroleptic accumulation in neuromelanin-containing cells with ensuing nigral cell damage. Thus, in addition to early or short-term up-regulation of D2 dopamine receptors, the late stage denervation supersensitivity may result in a further proliferation of D2 dopamine receptors in those parts of the human striatum controlling mouth-lips-tongue motion. Young individuals, upon reduction or removal of the neuroleptic, may have neural sprouting with subsequent D2 down-regulation and reversal of their dyskinesia. Older individuals may not readily exhibit sprouting and D2 down-regulation, possibly accounting for a more persistent form of dyskinesia.

Animals↗
PubMed1988

Psychosis and positron tomography.

The new technology of positron emission tomography (PET) offers hope in developing objective biological indices and correlates of various psychotic states, including schizophrenia. PET is of the order of a million to a billion times more sensitive than MRI (magnetic resonance imaging) and is now successfully measuring the densities of various brain neurotransmitter receptors in health and disease. PET data in schizophrenia patients confirm that delusions and hallucinations are controlled by neuroleptics when the D2 dopamine receptors are specifically blocked. D1 receptors are not involved. The elevation of D2 receptors as a possible basis for psychotic symptoms needs additional investigation because of technical difficulties which need to be resolved. The rapid development of PET indicates its promise for differential diagnosis as well as its value in treating the psychoses.

Affective Disorders, Psychotic↗
PubMed1988

Dopamine D1 receptors of the calf parathyroid gland: identification and characterization.

The dopamine D1 receptor was identified in the calf parathyroid gland. The binding of the selective D1 receptor antagonist [3H]SCH-23390 to membranes of calf parathyroid was specific, reversible, and saturable with a dissociation constant of approximately 200 pM and a receptor density of 30 fmol/mg of protein. Dopaminergic agonists and antagonists inhibited [3H]SCH-23390 binding in a concentration-dependent and stereoselective manner with an appropriate pharmacological specificity for D1 dopamine receptors. Moreover, potent dopaminergic agonists recognized two affinity forms of the receptor, one displaying high affinity for agonists, termed D1 High, and one with low affinity, D1 Low. The addition of the nonhydrolyzable guanine nucleotide guanyl 5'-yl-imidodiphosphate caused the complete transition of the agonist high affinity form (D1 High) of the receptor to one displaying only low affinity for agonists (D1 Low). Sodium ions, however, caused a approximately 5-fold decrease in the affinity of agonists at both D1 High and D1 Low. Virtually identical results were obtained on D1 receptor preparations of neural origin. The D1 receptor identified here appears to be the one responsible for the physiological effects on the parathyroid gland, because dopamine-stimulated cAMP accumulation is stereoselectively blocked by the D1 receptor antagonist SCH-23390 in dispersed cells of the parathyroid gland. Moreover, a series of nine dopaminergic antagonists and agonists shows an excellent correlation between their potency in [3H]SCH-23390 binding assays and their corresponding effects on cAMP accumulation. In the case of agonists, Ka for activation of cAMP accumulation agrees most closely with the agonist low affinity site in binding experiments. Specific [3H]spiperone binding to D2 dopamine receptors was not detected in this tissue and as such, the calf-parathyroid gland provides a model system in which to study the molecular characteristics of dopamine D1 receptor-mediated events.

Animals↗
PubMed1988

Dopamine D2 receptor binding subunits of Mr congruent to 140,000 and 94,000 in brain: deglycosylation yields a common unit of Mr congruent to 44,000.

The ligand-binding subunit of the porcine striatal dopamine D2 receptor was identified by photoaffinity labeling with [125I]N-azidophenethylspiperone ([125I]NAPS). Upon photolysis, [125I]NAPS covalently incorporated into a broad band of apparent Mr congruent 140,000 with an appropriate pharmacological profile for D2 receptors as assessed by autoradiography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Smaller subunits of apparent Mr congruent 94,000 and 34,000 were specifically labeled by [125I]NAPS with an appropriate D2 receptor profile and were similar to the major ligand-binding subunits of photoaffinity-labeled canine striatal D2 receptors. Photoaffinity labeling in the absence or presence of multiple protease inhibitors did not alter the migration pattern of the Mr congruent to 140,000/94,000 subunits upon denaturing electrophoresis in either the absence or presence of thiol-reducing/alkylating reagents. In order to investigate the possible basis for the existence of these high molecular weight forms of the D2 receptor, we assessed the carbohydrate nature of photolabeled D2 ligand-binding subunits by the use of lectin affinity chromatography and specific exo- and endoglycosidase treatments. Both photoaffinity-labeled D2 receptor proteins from porcine striatum (Mr congruent to 140,000 and 94,000) were glycoproteins as indexed by their absorption and specific elution from wheat germ agglutinin lectin resins. The exoglycosidase neuraminidase altered the electrophoretic mobility of both the Mr congruent to 140,000 and 94,000 labeled subunits to a single band of apparent Mr congruent to 51,000. Prior removal of sialic acid residues did not alter the reversible binding characteristics of [3H]spiperone to D2 receptors. Complete removal of receptor-associated N-linked carbohydrate by the endoglycosidase glycopeptidase F (peptide-N4[N-acetyl-beta-glucosaminyl]asparagine amidase) produced a further increase in the mobility of the Mr congruent to 51,000 subunit to apparent Mr congruent to 44,000. The porcine Mr congruent to 34,000 photolabeled peptide is an N-linked glycoprotein as assessed by lectin affinity chromatography and susceptibility to digestion by glycopeptidase F to a peptide of apparent Mr congruent to 23,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Affinity Labels↗
PubMed1987

Dopamine D-2 receptors in canine brain: ionic effects on [3H]neuroleptic binding.

In order to determine the effects of monovalent cations on the binding of 3H-neuroleptics to canine striatal dopamine D-2 receptors, a study of the effects of ions on the binding of two 3H-neuroleptics from different drug classes was undertaken. Dopamine D-2 receptors are selectively labeled in a sodium-sensitive manner by the benzamide ligand [3H]YM-09151-2. In the presence of 120 mM NaCl, [3H]YM-09151-2 had a dissociation constant of 55 pM and a maximal receptor density of 34 pmol/g of tissue. In the absence of NaCl, the dissociation constant was 440 pM with no change in the receptor density. The binding of [3H]YM-09151-2 (52 pM) was increased by 700% with 150 mM Na+, 440% with 500 mM Li+ and 290% with 500 mM K+. The ion concentrations producing half-maximal increases in binding were 4 mM Na+, 8.5 mM Li+ and 115 mM K+. The ionic strength control, N-methyl-D-glucamine, did not increase [3H]YM-09151-2 binding. [3H]Spiperone binding was much less affected by monovalent cations. Analysis of saturable binding showed that these changes were due to changes in binding affinity, independent of changes in receptor density. The sulfhydryl alkylating agent, N-ethylmaleimide, inactivated [3H]YM-09151-2 binding. Sodium ions at 120 mM protected approximately 40% of the susceptible sites while lithium and potassium ions (120 mM) did not. The anion exchange blocker, 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid (DIDS), has been shown to be capable of blocking the effect of Na+ on the binding of agonists to alpha 2-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
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↗