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Biomedical subjects

I Creese

Publications and source records attributed to I Creese.

At least 55 records · Page 3Linked to original sources
PubMed1986

Forskolin potentiates the stimulation of rat striatal adenylate cyclase mediated by D-1 dopamine receptors, guanine nucleotides, and sodium fluoride.

We report here that forskolin acts in a synergistic manner with dopaminergic agonists, guanine nucleotides, or sodium fluoride to potentiate the stimulation of rat striatal adenylate cyclase mediated by these reagents. In the presence of 100 microM GTP, 100 microM guanyl-5'-yl imidodiphosphate [Gpp(NH)p], or 10 mM NaF, there is a greater than additive increase in forskolin-stimulated enzyme activity as well as a concomitant decrease (two- to fourfold) in the EC50 value for forskolin stimulation of striatal enzyme activity. In the presence of various concentrations of forskolin (10 nM-100 microM), the stimulation of adenylate cyclase elicited by GTP, Gpp(NH)p, and NaF is potentiated 194-1,825%, 122-1,141%, and 208-938%, respectively, compared with the stimulation by these agents above basal activity in the absence of forskolin. With respect to 3,4-dihydroxyphenylethylamine (dopamine) receptor-mediated stimulation of striatal enzyme activity, the stimulation of enzyme activity by dopaminergic agonists, in the absence or presence of forskolin, was GTP-dependent and could be antagonized by the selective D-1 antagonist SCH23390 (100 nM), indicating that these effects are mediated by D-1 dopamine receptors. In the presence of 100 microM GTP, forskolin at various concentrations markedly potentiates the stimulation elicited by submaximal as well as a maximally effective concentrations of dopamine (100 microM) and SKF38393 (1 microM). At higher concentrations of forskolin (10-100 microM) the stimulation elicited by the partial agonist SKF38393 is comparable to that of the full agonist dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1986

In vitro and in vivo irreversible blockade of cortical S2 serotonin receptors by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline: a technique for investigating S2 serotonin receptor recovery.

N-Ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) treatment, both in vitro and in vivo, results in an irreversible blockade of cortical S2 5-hydroxytryptamine (serotonin) receptors. Incubation of rat cortical homogenates with EEDQ in vitro results in a concentration-dependent (EC50 approximately 5 microM) and time-dependent decrease in the Bmax of [3H]ketanserin-labeled S2 serotonin receptors. Extensive washing of the homogenate following in vitro or in vivo EEDQ treatment does not result in an increase in the amount of [3H]ketanserin binding, indicating that EEDQ acts to modify irreversibly cortical S2 serotonin receptors. That the modification of S2 receptor binding by EEDQ occurs at the recognition site of the receptor is indicated by the finding that coincubation with the S2 receptor antagonist ketanserin, but not the D2 3,4-dihydroxyphenylethylamine (dopamine) receptor antagonist domperidone, selectively protects against the irreversible blockade of S2 serotonin receptors. Peripheral administration of EEDQ results in a dose-dependent reduction in cortical S2 serotonin receptors with maximal effects (approximately 90% reduction) observed following 10 mg/kg (i.p.). Seven days following peripheral administration of EEDQ there is a recovery of S2 serotonin receptors back to 74% of the original receptor population. These data demonstrate that EEDQ in vitro and in vivo acts as an irreversible antagonist of S2 serotonin receptors and that it can be used to investigate the recovery rate of these receptors.

Animals↗
PubMed1986

Characterization of alpha 1-adrenergic receptor subtypes in rat brain: a reevaluation of [3H]WB4104 and [3H]prazosin binding.

[3H]Prazosin and [3H]WB4101 [2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4 benzodioxane] have both been proposed to label alpha 1-adrenergic receptors in the rat central nervous system. As many discrepancies between the binding of these two ligands have arisen, we conducted these studies in order to reevaluate their binding characteristics and resolve the similarities and differences in the pharmacological characteristics of their respective binding sites. [3H]Prazosin binding is characterized by a monophasic saturation isotherm. Prazosin, indoramine, and dihydroergocryptine competitions with [3H]prazosin are steep and monophasic, and model best to a single binding site. In contrast, phentolamine and WB4101 competition curves are shallow in rat cortex, exhibiting Hill coefficients significantly less than 1.0, and model to two binding sites of approximately equal proportions. The higher and lower affinity components are defined as alpha 1A and alpha 1B, respectively. [3H]WB4101 also labels two binding sites in rat cortex and hippocampus with picomolar and nanomolar affinity, respectively. However, the nanomolar binding site is serotonergic and not adrenergic. The picomolar site (KD = 150 pm) has characteristics of an alpha 1-receptor binding site: prazosin, WB4101, and phentolamine affinities for this [3H]WB4101 binding site correlate with their affinities for the highest affinity component (alpha 1A) of [3H]prazosin binding. In addition, the Bmax of this [3H] WB4101-labeled site is equal to one-half of the total [3H]prazosin Bmax. Agonist competitions with [3H]prazosin binding are multiphasic with pseudo-Hill slopes less than 1.0 and with a rank order of affinity of epinephrine greater than norepinephrine greater than phenylephrine. When binding to the alpha 1A component is blocked by a 30 nM phentolamine mask, the same rank order of agonist affinities is preserved. Although the affinities of epinephrine and norepinephrine at the two subtypes are identical, phenylephrine is weaker at the alpha 1B site. The ratio of the potency of phentolamine versus prazosin is about 4 at the alpha 1A component but about 80 at the alpha 1B binding site. We discuss these data in relation to the reported potencies of these antagonists in blocking alpha 1-receptor-mediated responses which may correlate with our designation of alpha 1A or alpha 1B binding sites.

Animals↗
PubMed1986

Effects of chronic SCH23390 treatment on the biochemical and behavioral properties of D1 and D2 dopamine receptors: potentiated behavioral responses to a D2 dopamine agonist after selective D1 dopamine receptor upregulation.

Chronic treatment of rats with SCH23390 (0.5 mg/kg/day s.c.), a D1 dopamine receptor antagonist, for 21 days resulted in an increase in D1 dopamine receptors but produced no change in D2 dopamine receptors. During habituation to locomotor activity cages the rats treated chronically with SCH23390 showed significantly higher locomotor activity than controls treated chronically with saline. When injected with the selective D1 dopamine receptor agonist SKF38393 (3 mg/kg), rats treated chronically with SCH23390 showed significantly greater stereotypy and locomotor activity responses. Surprisingly, rats treated chronically with SCH23390 also showed significantly higher locomotor activity and stereotypy responses when treated with the selective D2 dopamine receptor agonist, quinpirole (LY171555) (0.3 mg/kg). These results indicate that a selective increase in D1 receptors may not be necessary, but is sufficient, to lead to an enhanced behavioral response to either selective D1 or D2 dopamine receptor agonists. If, indeed, an enhanced stereotypy and locomotor activity response to dopaminergic agonists in rats after a brief chronic treatment with a neuroleptic drug is predictive of tardive dyskinesia potential in the clinical setting, these results can suggest that SCH23390 may also induce tardive dyskinesia in humans. Adenylate cyclase activity stimulated by guanine nucleotides, forskolin or dopamine was enhanced after chronic treatment with SCH23390. However, dopamine-stimulated adenylate cyclase activity was not potentiated detectably by the increase in receptor number over the more general increase in guanine nucleotide-stimulated cyclic AMP production. Additionally, no change was observed in dopamine competition for [3H]SCH23390 binding, with dopamine's RH/RL ratio remaining unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1986

Effects of in vivo and in vitro treatments with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline on putative muscarinic receptor subtypes in rat brain.

N-Ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was found to irreversibly decrease the Bmax of [3H](-)-quinuclidinyl-benzilate [(-)QNB] binding in rat brain following in vivo administration or by incubation of tissue homogenates with EEDQ in vitro. A greater reduction in the Bmax of [3H](-)QNB binding was observed in the hippocampus and cortex than in the brainstem following in vivo or in vitro treatment with EEDQ. Competition of pirenzepine for [3H](-)QNB binding was best described by computer-derived models assuming two binding sites in all brain regions. However, following EEDQ treatment there was a rightward shift in the pirenzepine competition curves for the remaining [3H](-)QNB-binding sites in all brain regions. Computer analysis of the pirenzepine competition curves indicated that this was due to a selective decrease in the number of [3H](-)QNB-binding sites having high affinity for pirenzepine. Although the binding of [3H](-)QNB to the site having lower affinity for pirenzepine was apparently unaltered, the affinity of pirenzepine for this binding site was significantly lowered following both in vivo and in vitro treatment with EEDQ. Thus, EEDQ differentially modifies muscarinic receptor-binding sites having high and low affinity for pirenzepine. The reduction in the Bmax of [3H](-)QNB binding and the rightward shift in the pirenzepine competition curve elicited by EEDQ both in vivo and in vitro could be prevented by coadministration of reversible muscarinic antagonists, thereby demonstrating that EEDQ interacts at the ligand recognition site of muscarinic receptors. These data suggest that the putative muscarinic receptor subtypes discriminated by pirenzepine may represent differences in the accessibility of pirenzepine and EEDQ to a homogeneous population of [3H](-)QNB-binding sites or, alternatively, that these muscarinic receptor-binding sites discriminated by pirenzepine and EEDQ represent structurally distinct molecular entities.

Animals↗
PubMed1985

Up-regulation of serotonergic binding sites labeled by [3H]WB4101 following fimbrial transection and 5,7-dihydroxytryptamine-induced lesions.

Lesions of the serotonergic afferents to the hippocampus, by fimbrial transection or by 5,7-dihydroxytryptamine treatment, produce an increase in the Bmax of [3H]WB4101 to its nanomolar affinity binding site, with no effect on its picomolar affinity binding site or on [3H]prazosin binding. The nanomolar site is serotonergic as the serotonergic agonists, serotonin and 8-hydroxydipropylaminotetraline (8-OH-DPAT) have nanomolar affinity for [3H]WB4101 binding when studied in the presence of a prazosin mask (30 nM) of the alpha-1 component of [3H]WB4101 binding. The serotonin receptor antagonists metergoline, lysergic acid diethylamide and lisuride also have high nanomolar affinities while ketanserin, yohimbine, prazosin and noradrenergic agonists have affinities in the micromolar range. Fimbrial transection or 5,7-dihydroxytryptamine injections produced 32% and 44% increases in the Bmax of [3H]WB4101 binding in the presence of a prazosin mask. Serotonin competition for [3H]WB4101 binding was identical in control and experimental tissue from each lesion experiment. Although specific binding of [3H]WB4101 was increased, there was no change in the affinities or the percentages of the two binding components for serotonin competition with [3H]WB4101. These data suggest that removal of the serotonergic input to the hippocampus produces an increase in the Bmax of serotonin receptor binding sites labeled by [3H]WB4101.

5,7-Dihydroxytryptamine↗
PubMed1985

D2 dopamine receptor-mediated inhibition of forskolin-stimulated adenylate cyclase activity in rat striatum.

Forskolin markedly stimulates striatal adenylate cyclase activity in a concentration-dependent manner, and at 10(-4) M produces an approximate 40-fold increase in enzyme activity above basal levels. Dopamine (in the presence of 100 nM SCH 23390), bromocryptine and quinpirole (LY 171555) significantly inhibit both basal and forskolin-stimulated adenylate cyclase activity. There is a significant increase in the absolute but not in the percent inhibition of enzyme activity by dopaminergic agonists as a function of forskolin concentration. This inhibition is agonist-concentration dependent and antagonized by the D2 antagonist, spiperone. These results suggest that forskolin may be used as a tool for amplifying the abolute D2-receptor-mediated inhibition of adenylate cyclase in rat striatal homogenates.

Adenylyl Cyclases↗
PubMed1985

Alteration of nicotinic cholinergic agonist binding sites in hippocampus after fimbria transection.

Nicotinic cholinergic agonist binding sites were studied in rat hippocampus by the binding of [3H]acetylcholine in the presence of 1.5 microM atropine sulfate. Following transection of the fimbria/fornix there was a 49% increase in the binding of [3H]acetylcholine reflecting an increase in the affinity of the receptor binding site from Kd = 18.82 +/- 3.6 nM in control animals to Kd = 9.06 +/- 1.2 nM in experimental tissue. Chronic administration of the agonist nicotine (4 mg/kg/day) by osmotic minipumps produced an increase in the binding of 10 nM [3H]acetylcholine after 14 days (49% increase over control) and after 28 days (141% increase over controls). These data are consistent with the suggestion that [3H]acetylcholine labels a nicotinic cholinergic receptor in rat brain. Further they support the notion that some of the termination sites of the septal-cholinergic projection to the hippocampus are nicotinic.

Acetylcholine↗
PubMed1985

Identification of subtypes of [3H]prazosin-labelled alpha 1 receptor binding sites in rat brain.

Detailed antagonist competition curves for [3H]prazosin-labelled binding sites in rat cerebral cortex membranes reveal anomalous binding characteristics. Dihydroergocryptine and indoramine compete in a steep, monophasic manner while WB4101 and phentolamine exhibit shallow competition curves. Computer-assisted analysis of binding data indicate that both WB4101 and phentolamine discriminate identical subpopulations of [3H]prazosin binding sites, which each comprise approximately 50% of specific [3H]prazosin binding. These data suggest the presence of subtypes of [3H]prazosin-labelled alpha 1 adrenergic receptors in rat cerebral cortex.

Animals↗
PubMed1985

[3H]WB4101 labels the 5-HT1A serotonin receptor subtype in rat brain. Guanine nucleotide and divalent cation sensitivity.

In the presence of a 30 nM prazosin mask, [3H]-2-(2,6-dimethoxyphenoxyethyl) aminomethyl-1,4-benzodioxane ([3H]WB4101) can selectively label 5-HT1 serotonin receptors. Serotonin exhibits high affinity (Ki = 2.5 nM) and monophasic competition for [3H] WB4101 binding in cerebral cortex. Furthermore, we have found a significant correlation (r = 0.96) between the affinities of a number of serotonergic and nonserotonergic compounds at [3H]WB4101-binding sites in the presence of 30 nM prazosin and [3H] lysergic acid diethylamide ([3H]LSD)-labeled 5-HT1 serotonin receptors in homogenates of rat cerebral cortex. Despite similar pharmacological profiles, distribution studies indicate that, in the presence of 5 mM MgSO4, the Bmax of [3H]WB4101 is significantly lower than the Bmax of [3H]LSD in various brain regions. WB4101 competition for [3H] LSD-labeled 5-HT1 receptors fits best to a computer-derived model assuming two binding sites, with the KH for WB4101 being similar to the KD of [3H]WB4101 binding derived from saturation experiments. This suggests that [3H]WB4101 labels only one of the subtypes of the 5-HT1 serotonin receptors labeled by [3H]LSD. Interestingly, the selective 5-HT1A serotonin receptor antagonist, spiperone, and the selective 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetraline, exhibit high affinity and monophasic competition for [3H]WB4101 but compete for multiple [3H]LSD 5-HT1 binding sites. These data indicate that [3H]WB4101 selectively labels the 5-HT1A serotonin receptor, whereas [3H] LSD appears to label both the 5-HT1A and the 5-HT1B serotonin receptor subtypes. The divalent cations, Mn2+, Mg2+, and Ca2+ were found to markedly increase the affinity and Bmax of [3H]WB4101 binding in cerebral cortex. Conversely, the guanine nucleotides guanylylimidodiphosphate and GTP, but not the adenosine nucleotide ATP, markedly reduce the Bmax of [3H]WB4101 binding. These characteristics are typical of agonists interacting with receptors which modulate cellular function via a guanine nucleotide-regulatory subunit.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1985

Interactions of dopamine agonists with brain D1 receptors labeled by 3H-antagonists. Evidence for the presence of high and low affinity agonist-binding states.

The interactions of dopaminergic agonists and antagonists with 3H-antagonist labeled D1 dopamine receptors of rat striatum have been characterized. [3H]Flupentixol has been found to selectively label D1 dopamine receptors when its binding to D2 dopamine receptors is blocked by the inclusion of D2 selective concentrations of unlabeled spiroperidol or domperidone. Antagonist/3H-antagonist competition curves are of uniformly steep slope (nH = 1.0) suggesting the presence of a single D1 dopamine receptor. Agonist/3H-antagonist competition curves are extremely shallow (nH less than or equal to 0.5) for agonists of high relative efficacy, suggesting the presence of heterogeneous populations of agonist-binding states of the D1 dopamine receptor. Computer-modeling techniques were used to estimate affinities and relative site densities for these heterogeneous binding states. This analysis indicates that the ratio of agonist affinities for low and high affinity agonist-binding states is correlated with agonist relative efficacies in activating adenylate cyclase in membrane homogenates. Under the assay conditions employed, the addition of saturating concentrations of guanine nucleotides reduced, but did not abolish, the relative density of high affinity agonist-binding sites. These binding data can, at least in part, be explained by postulating two states of the D1 dopamine receptor, inducible by agonists but not by antagonists and modulated by guanine nucleotides.

Animals↗
PubMed1985

Interactions of dopaminergic agonists and antagonists with dopaminergic D3 binding sites in rat striatum. Evidence that [3H]dopamine can label a high affinity agonist-binding state of the D1 dopamine receptor.

The interactions of dopaminergic agonists and antagonists with 3H-agonist labeled D3 dopaminergic binding sites of rat striatum have been characterized by radioligand-binding techniques. When the binding of [3H]dopamine and [3H]apomorphine to D2 dopamine receptors is blocked by the inclusion of D2 selective concentrations of unlabeled spiroperidol or domperidone, these ligands appear to label selectively the previously termed "D3" binding site. Antagonist/[3H]dopamine competition curves are of uniformly steep slope (nH = 1.0), suggesting the presence of a single D3 binding site. The relative potencies of antagonists to inhibit D3 specific [3H]dopamine binding are significantly correlated with their potencies to block D1 dopamine receptors as measured by the inhibition of both dopamine-stimulated adenylate cyclase and [3H]flupentixol-binding activities. The affinities of agonists to inhibit D3 specific [3H]dopamine binding are also correlated with estimates of these agonists' affinities for the high affinity binding component of agonist/[3H]flupentixol competition curves. Both D3 specific [3H] dopamine binding and the high affinity agonist-binding component of dopamine/[3H]flupentixol competition curves show a similar sensitivity to guanine nucleotides. Taken together, these data strongly suggest that the D3 binding site is related to a high affinity agonist-binding state of the D1 dopamine receptor.

Animals↗
PubMed1984

Interactions of agonists with D-2 dopamine receptors: evidence for a single receptor population existing in multiple agonist affinity-states in rat striatal membranes.

Several lines of evidence previously indicated that [3H]spiroperidol (SPIRO) or [3H]domperidone (DOMP) might label heterogeneous populations of striatal dopamine receptors in radioligand binding studies. We have examined this possibility in rat striatum using computerized non-linear curve fitting and a method to block the unwanted [3H]SPIRO binding to S-2 serotonergic receptors. In the absence of a serotonergic antagonist, [3H]SPIRO saturation data produce curved Scatchard plots which are best computer fit by assuming the presence of two sites of different [3H]SPIRO affinities. In the presence of appropriate concentrations of ketanserin to block S-2 serotonergic binding, Scatchard plots are linear, with data modeling best to a single population of homogeneous binding sites. The D-2 dopamine receptor Bmax and [3H]SPIRO KD determined in this fashion are indistinguishable from that obtained for the higher affinity binding site by computer analysis of data obtained in the absence of ketanserin. [3H]DOMP produced indistinguishable values for D-2 receptor Bmax as well. Competitions by (-)sulpiride, metoclopramide, and DOMP for [3H]SPIRO binding sites in the presence of ketanserin are steep (Hill slope approximately 1), demonstrating that the previously observed heterogeneity of these sites is due entirely to serotonergic [3H]SPIRO binding. In contrast, agonist/3H-antagonist competition curves in the presence of ketanserin are best computer fit by assuming two independent receptor sites of high (RH) and low (RL) agonist affinity. With the addition of 5'-guanylylimidodiphosphate [Gpp(NH)p] computer analyses of agonist/3H-antagonist competition curves show an increased ratio RL/RH concomitant with apparent decreases in agonist affinities for both sites. Under some conditions, some agonist/3H-antagonist competition curves are best fit by a single site model in which agonist affinity is indistinguishable from the agonist's affinity at RL determined in the absence of Gpp(NH)p. These data are consistent with the presence of a single dopaminergic 3H-butyrophenone binding site, representing the D-2 receptor, which exists in two interconverting states differing in agonist affinity.

Animals↗
PubMed1984

Sulpiride isomers exhibit reversed stereospecificity for D-1 and D-2 dopamine receptors in the CNS.

We have investigated the stereospecificity of the interaction of (-) and (+)sulpiride with [3H]cis-flupentixol and [3H]spiperone binding to D-1 and D-2 dopamine receptors respectively in rat striatum. Both isomers of sulpiride compete more potently at D-2 vs. D-1 dopamine receptors. (-)Sulpiride is 50-fold more potent than (+)sulpiride in blocking D-2 receptors, while (+)sulpiride is 3-fold more potent than (-)sulpiride at D-1 receptors. This reversed stereospecificity of sulpiride interactions with CNS D-1 and D-2 dopamine receptors is similar to the stereospecificity of sulpiride interactions at DA1 and DA2 dopamine receptors in peripheral vascular beds.

Animals↗