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D Hoyer

Publications and source records attributed to D Hoyer.

At least 127 records · Page 7Linked to original sources
PubMed1993

Characterization of functional responses in A9 cells transfected with cloned rat 5-HT1C receptors.

Functional responses to stimulation of rat 5-HT1C receptors expressed in A9 cells were studied using whole cell voltage clamp and calcium recording techniques. Stimulation of 5-HT1C receptors evoked outward currents clamped at -50 mV. The outward currents were reduced when GTP was excluded from the intracellular recording solution or when GDP-beta-S was added. 8-Bromo cyclic AMP (5 mmol/l) neither produced an effect per se nor affected the 5-HT-induced outward current in A9 cells, thus excluding cAMP as a second messenger involved in 5-HT1C receptor activation. Phorbol myristic acetate (PMA; 10 mumol/l) did not affect the electrical activity of the transfected A9 cells but reduced the 5-HT-induced current amplitude to 71 +/- 9% of the control value (n = 12). This indicates that activation of protein kinase C does not play a direct role in the 5-HT-induced response in these cells. The 5-HT induced currents mainly involved potassium ions, although a small contribution of chloride ions was also observed. The 5-HT-induced current was inhibited by the K+ channel blocking agents tetraethylammonium (1 mmol/l), apamin (0,5 mumol/l) and 4-aminopyridine (5 mmol/l). The 5-HT-induced currents recorded at -50 mV were unaffected by removal of extracellular calcium, but inclusion of the calcium chelator BAPTA (5 mmol/l) in the intracellular solutions abolished the current. Measurement with the calcium indicator Fluo-3 revealed a 5-HT-induced increase in intracellular calcium which was not affected by removal of extracellular calcium but declined after repeated stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Endothelin receptors in the human coronary artery, ventricle and atrium. A quantitative autoradiographic analysis.

In the present experiments we investigated endothelin (ET) receptors in the human coronary artery, and in ventricular and atrial muscle using quantitative receptor autoradiography. Displacement of [125I]Sf6b (Sarafotoxin S6b) (30 pM)- and [125I]ET-1 (30 pM)-labeled binding sites was studied using ET-1, the ETA receptor selective ligand BQ-123 (cyclo[D-Asp-L-Pro-D-Val-L-Leu-D-Trp-]), and the ETB receptor selective ligand [Ala1, 3, 11, 15]ET-1. Specific binding was more dense in atrium and coronary artery (relative optical density (r.o.d.): 0.14 +/- 0.01 and 0.16 +/- 0.01, respectively) than in ventricular muscle (r.o.d.: 0.10 +/- 0.01). In the coronary artery, binding was especially dense in the media. ET-1 displaced [125I]ET-1 and [125I]Sf6b monophasically in atrium, ventricle and coronary artery. [Ala1,3,11,15]ET-1 and BQ-123 displaced [125I]ET-1 and [125I]Sf6b-labeled sites biphasically in the ventricle and in the atrium. In the human coronary artery, [Ala1,3,11,15]ET-1 and BQ-123 displaced [125I]ET-1-labeled sites monophasically (pIC50: ET-1 (9.72 +/- 0.12) > BQ-123 (6.84 +/- 0.08) > [Ala1,3,11,15]ET-1 (6.40 +/- 0.12). In contrast, [Ala1,3,11,15]ET-1 and BQ-123 displaced [125I]Sf6b-labeled coronary artery sites biphasically (high affinity pIC50: BQ-123, 9.03 +/- 0.25; [Ala1,3,11,15]ET-1, 8.40 +/- 0.14; low affinity pIC50: BQ-123, 7.24 +/- 0.14; [Ala1,3,11,15]ET-1, 6.99 +/- 0.09). These data indicate that both [125I]ET-1 and [125I] Sf6b-labeled ETA and ETB binding sites in human ventricular and atrial muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Partial agonists, full agonists, antagonists: dilemmas of definition.

The absence of selective antagonists makes receptor characterization difficult, and largely dependent on the use of agonists. However, there has been considerable debate as to whether certain drugs acting at G protein-coupled receptors are better described as agonists, partial agonists or antagonists. Indeed many agonists tend to display differences in intrinsic activity, depending on the preparation used to study receptor pharmacology. It has been argued that variations in intrinsic activity of drugs, may be a reflection of receptor subtypes rather than varying degrees of receptor-effector coupling. However, it has often been overlooked that classical receptor theory predicts that a drug acting at a given receptor type can display a range of intrinsic activities depending on the extent of receptor reserve. Furthermore, because any receptor can couple to different effector systems, different degrees of intrinsic activity may be observed for a given drug. Daniel Hoyer and Hendrikus Boddeke review recent data which provide explanations for why drugs display such variations in intrinsic activity.

Animals↗
PubMed1993

5-hydroxytryptamine1 recognition sites in rat brain: heterogeneity of non-5-hydroxytryptamine1A/1C binding sites revealed by quantitative receptor autoradiography.

Quantitative in vitro receptor autoradiography was used to characterize the [3H]5-hydroxytryptamine binding sites which are not sensitive to 8-hydroxy-2-(di-N-propylamino)tetralin, mesulergine and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide, in a non-5-hydroxytryptamine1A/1B/1C/1D receptor population, in rat brain. Displacement of [3H]5-hydroxytryptamine [in the presence of 100 nM 8-hydroxy-2-(di-N-propyl-amino)tetralin and mesulergine, to block 5-hydroxytryptamine1A and 5-hydroxytryptamine1C sites] with (-)pindolol, 5-hydroxy-3(4-1,2,5,6-tetrahydropyridyl)-4-azaindole, sumatriptan and serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide yielded complex competition curves suggesting the presence of 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites and an additional [3H]5-hydroxytryptamine-sensitive component in rat brain. The non-5-hydroxytryptamine1A/1B/1C/1D binding sites were localized in olfactory tubercle, several nuclei of the amygdala, bed nucleus of the stria terminalis, caudate-putamen, CA3 field of the hippocampus, the frontoparietal cortex (motor area) and parts of the striate cortex. All the drugs used had low affinity for the unknown recognition site, which therefore might be comparable to the [3H]5-hydroxytryptamine binding site reported to display low affinity for sumatriptan and 5-carboxamidotryptamine in the brains of various species, the so-called 5-hydroxytryptamine1E site. A comparison of the density of sites labelled with [125I]serotonin-5-O-carboxy-methyl-glycyl-tyrosinamide (representing 5-hydroxytryptamine1B and 5-hydroxytryptamine1D sites) and [3H]5-hydroxytryptamine (under the conditions mentioned above) showed the density of [3H]5-hydroxytryptamine recognition sites to be higher in some structures.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1993

Effect of 5,7-dihydroxytryptamine lesion on mianserin-induced conditioned place aversion and on 5-hydroxytryptamine1C receptors in the rat brain.

The lesion of serotonergic neurons (by an intraventricular injection of 5,7-dihydroxytryptamine) potentiated the conditioned place aversion induced by the 5-hydroxytryptamine1C/5-hydroxytryptamine2 antagonist mianserin in rats. This effect was selective for mianserin as the same lesion suppressed the conditioned place aversion induced by the benzodiazepine inverse agonist FG-7142. Previous results had shown the involvement of the 5-hydroxytryptamine1C receptors in the conditioned place aversion induced by mianserin [Rocha et al. (1993) Behav. Pharmac. 4, 101-106]. It was thus of interest to investigate the effect of the lesion on these receptor binding sites. Autoradiographic binding studies showed that the lesion significantly increased the concentration of the 5-hydroxytryptamine1C binding sites in various brain regions, including the amygdala, the hippocampus and the nucleus accumbens. Contrastingly, in these same brain regions, in situ hybridization histochemistry did not reveal an alteration of the level of messenger RNA coding for these receptors. On the one hand, correlating potentiation of the aversive effects of mianserin and increase of 5-hydroxytryptamine1C binding sites in the limbic system represent an interesting step in the comprehension of the molecular and motivational effects of serotonergic drugs. On the other hand, showing a dissociation between the expression of 5-hydroxytryptamine1C receptors and their corresponding messenger RNA, suggest that post-transcriptional mechanisms are involved in the regulation of these receptors.

5,7-Dihydroxytryptamine↗
PubMed1993

The novel 5-HT1A receptor antagonist, SDZ 216-525, decreases 5-HT release in rat hippocampus in vivo.

1. Recent evidence suggests that the novel compound SDZ 216-525 is a selective and possibly silent 5-HT1A receptor antagonist. Here we have examined the action of SDZ 216-525 on central 5-HT1A autoreceptor function. The experiments involved measurement of drug effects on extracellular 5-HT in the ventral hippocampus of the chloral hydrate anaesthetized rat by use of microdialysis. 2. Acute injection of SDZ 216-525 (0.1, 0.3, 1.0 and 3 mg kg-1, s.c.) caused a dose-related decrease in 5-HT output with an estimated ED50 of at least 0.3 mg kg-1. This ED50 value is 20-30 times greater than ED50 values previously obtained for 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) and NAN-190. In comparison, SDZ 216-525 is reported to have slightly higher affinity for the 5-HT1A site than 8-OH-DPAT and NAN-190. 3. The inhibitory effect of SDZ 216-525 (1 mg kg-1, s.c.) on 5-HT was blocked by the 5-HT1/beta-adrenoceptor antagonist, (-)-pindolol (8 mg kg-1, s.c.) but not by a combination of the beta 1- and beta 2-selective adrenoceptor antagonists metoprolol and ICI 118,551 (4 mg kg-1, each). 4. Although in several experimental models SDZ 216-525 has high affinity, selectivity and lacks intrinsic activity at the 5-HT1A receptor, our experiments show that the drug decreases extracellular 5-HT in ventral hippocampus of the chloral hydrate anaesthetized rat via a pindolol-sensitive mechanism. We conclude that either SDZ 216-525 promotes (with low potency in vivo) 5-HT1A receptor/G-protein interactions, or that the 5-HTlA autoreceptor is a 5-HT1A receptor subtype different from the postsynaptic 5-HT1A receptor.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1992

Evidence for the presence of 5-HT1B receptor messenger RNA in neurons of the rat trigeminal ganglia.

In situ hybridization histochemistry and receptor autoradiography were used to determine the presence of 5-HT1B receptor messenger RNA (mRNA) and 5-HT1B receptor proteins, respectively, in rat trigeminal ganglia. Receptor autoradiography on rat trigeminal ganglia, using appropriate 5-HT1B radioligands, did not demonstrate any specific labelling. In contrast, in situ hybridization showed that many ganglion cells contain 5-HT1B receptor mRNA, suggesting the presence of presynaptic 5-HT1B receptors on trigeminovascular neurons.

Animals↗
PubMed1992

Cloning and functional characterization of the rat stomach fundus serotonin receptor.

A DNA segment homologous to the third exons of the serotonin 1C and 2 receptor genes was isolated from a mouse genomic library. The positions of the introns flanking these exons were conserved in the three genes. To examine whether the new fragment was part of an active gene, we used a quantitative PCR protocol to analyse rat RNAs from different tissues and ages. The gene was expressed in stomach fundus at an abundance of 1 x 10(5) mRNA molecules. This tissue contracts in response to serotonin via a receptor that has previously resisted classification. We constructed a cDNA library from rat stomach fundus and isolated clones containing 2020 bp inserts with open reading frames of 465 amino acids comprising seven putative membrane-spanning regions. The protein was transiently expressed in COS cells and binding of serotonergic ligands to the membranes was analysed. The pharmacological profile resembled that described for the serotonin-stimulated contraction of the stomach fundus. After expression of this receptor in Xenopus oocytes, the application of serotonin triggered the typical chloride current which presumably results from the activation of phospholipase C. The coupling to this response system was less efficient than that of the 5-HT1C or 5-HT2 receptors.

Amino Acid Sequence↗
PubMed1992

Agonist/antagonist interactions with cloned human 5-HT1A receptors: variations in intrinsic activity studied in transfected HeLa cells.

The characteristics of 5-HT1A-recognition sites and receptor-mediated release of intracellular calcium were established in two transfected HeLa cell lines (HA 6 and HA 7) expressing different levels of human 5-HT1A receptors (about 3000 and 500 fmol/mg protein, Fargin et al. 1989; 1991; Raymond et al. 1989). The pharmacological profiles of the binding (determined with [3H]8-OH-DPAT) and the calcium response (measured using Fura-2) were clearly of the 5-HT1A type. Compounds such as 5-HT, 5-CT and 8-OH-DPAT acted as full agonists on the calcium response in both HeLa cell lines. In addition, methiothepin, pindolol, NAN 190 and SDZ 216-525 (Seiler et al. 1991) acted as silent and potent antagonists. Marked differences were observed in the responses mediated in the two cell lines. EC50 values of agonists (particularly 5-HT, 5-CT, flesinoxan and 8-OH-DPAT) were higher in HA 7 cells (up to 80-fold) than in other 5-HT1A receptor models (e.g. inhibition of adenylate cyclase in calf hippocampus). Further, a variety of compounds (ipsapirone, buspirone, spiroxatrine, MDL 73005) acted as agonists in HA 6 cells, whereas they behaved as silent antagonists in HA 7 cells (which express fewer receptors). By contrast, KB values for antagonists were comparable in HA 6 and HA 7 cells. The present data show that EC50 values and intrinsic activity for a given drug are subject to large variations depending on the number of receptors expressed in the target tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1992

5-HT1D binding sites in various species: similar pharmacological profile in dog, monkey, calf, guinea-pig and human brain membranes.

Radioligand binding studies were performed in membranes of calf caudate, guinea-pig cortex, dog caudate and whole brain, monkey caudate and whole brain, and human caudate using the novel iodinated radioligand, Serotonin-5-O-Carboxymethyl-Glycyl[125I] Tyrosinamide (abbreviated [125I]GTI for the sake of simplicity), a ligand known to label 5-HT1B and 5-HT1D sites. In all membrane preparations tested, [125I]GTI labelled high affinity sites with the following rank order of affinity: 5-carboxamidotryptamine greater than 5-HT = DHE = ergotamine greater than or equal to sumatriptan greater than or equal to metergoline = CGS 12066 greater than or equal to yohimbine = methysergide greater than or equal to methiothepin greater than 8-OH-DPAT greater than or equal to mianserin greater than or equal to CP 93129 greater than or equal to (-)pindolol = ketanserin greater than or equal to isamoltane = mesulergine greater than or equal to corynanthine = spiperone greater than MDL 72222. The affinity profiles were very similar in the membranes of the different species, especially in dog, monkey and human brain. The pharmacological profile of [125I]GTI binding (determined with up to 25 different drugs) was fully comparable to the binding profile reported previously in human substantia nigra (using [125I]GTI) or in a variety of brain preparations known to contain 5-HT1D sites using [3H]5-HT as a radioligand.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

"5-HT1R" or 5-HT1D sites? Evidence for 5-HT1D binding sites in rabbit brain.

Radioligand binding studies were performed in membranes of rabbit whole brain and striatum using the novel iodinated radioligand for 5-hydroxytryptamine 5-HT1B and 5-HT1D sites, Serotonin-5-O-Carboxymethyl-Glycyl[125I]Tyrosinamide ([125I]GTI). [125I]GTI labelled a finite number of high affinity sites in rabbit brain membranes, Bmax = 191 +/- 47 fmol/mg protein, pKD (-log mol/l) = 8.50 +/- 0.13, n = 5. The pharmacological profile of [125I]GTI binding was fully comparable to that reported previously in human and other brain preparations known to possess 5-HT1D sites (using either [3H]5-HT or [125I]GTI) and displayed a characteristic rank order of affinity: 5-carboxamido-tryptamine greater than 5-HT = dihydroergotamine greater than or equal to ergotamine greater than or equal to sumatriptan greater than or equal to CGS 12066 greater than or equal to metergoline greater than yohimbine greater than or equal to methysergide greater than ICYP greater than 8-OH-DPAT greater than or equal to CP 93129 greater than (-)pindolol greater than ketanserin greater than isamoltane greater than mesulergine greater than corynanthine greater than buspirone greater than MDL 72222. Autoradiographic studies were performed on rabbit brain slices using [3H]5-HT in the presence of 100 nmol/l 8-OH-DPAT and mesulergine (in order to mask 5-HT1A and 5-HT1C binding sites) and [125I]CYP (iodocyanopindolol) in the presence of 3 mumol/l isoprenaline and 100 nmol/l 8-OH-DPAT (in order to mask beta adrenoceptor and 5-HT1A binding sites). There was no detectable specific binding of [125I]CYP through the brain, thus excluding the presence of 5-HT1B sites in rabbit brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Direct visualization of serotonin1D receptors in the human brain using a new iodinated radioligand.

The development of the new ligand serotonin-5-O-carboxymethyl-glycyl [125I]tyrosinamide (abbreviated [125I]GTI) allows for the direct visualization of serotonin1B and serotonin1D (5-HT1B/1D) sites. Autoradiographic techniques were used to demonstrate the selective binding of this ligand to 5-HT1D sites in human post-mortem brain materials. The distribution of [125I]GTI binding sites was compared to [3H]5-HT sites in the presence of different displacers. The results show the selective binding of [125I]GTI to sites in the basal ganglia and substantia nigra which corresponds to 5-HT1D receptors.

Aged↗
PubMed1991

Interaction of the alpha-adrenoceptor agonist oxymetazoline with serotonin 5-HT1A, 5-HT1B, 5-HT1C and 5-HT1D receptors.

Oxymetazoline was recognized with nanomolar affinity by 5-HT1A, 5-HT1B and 5-HT1D binding sites and mimicked the effects of 5-hydroxytryptamine with about the same potency and intrinsic activity as the endogenous amine in the corresponding functional tests. At 5-HT1C receptors, oxymetazoline behaved as a mixed agonist-antagonist. Clonidine had minimal activity. Methiothepin antagonized the effects of oxymetazoline (7.4 less than pKB less than 8.8). Thus, oxymetazoline is a full and potent agonist at 5-HT1A, 5-HT1B and 5-HT1D receptors and a partial agonist at 5-HT1C receptors.

Adrenergic alpha-Agonists↗
PubMed1991

Competitive antagonism by recognized 5-HT2 receptor antagonists at 5-HT1C receptors in pig choroid plexus.

The effects of several antagonists, known to interact with 5-HT2 receptors (ritanserin, LY 53857, ICI 169,369, methysergide, mesulergine and ketanserin), were tested against 5-HT-stimulated production of inositol phosphate in pig choroid plexus, a 5-HT1C receptor model. These antagonists produced dextral shifts of the concentration response curve to 5-HT in a parallel manner, without depressing significantly the maximal response. The following pA2 values (in parentheses) were obtained: mesulergine (8.88), methysergide (8.85), LY 53857 (8.69), ritanserin (8.69), ICI 169,369 (7.86), and ketanserin (6.57). These pA2 values were in good agreement with the pKD values determined in radioligand binding studies performed in pig choroid plexus with [3H]mesulergine. The present data demonstrate that several drugs described as 5-HT2 receptor selective antagonists (e.g. ritanserin, LY 53857 and ICI 169,369) are also potent, competitive and surmountable antagonists at 5-HT1C receptors. Thus, the results provide further evidence for the pharmacological similarity of 5-HT1C and 5-HT2 receptors. However, in contrast to the situation described with methysergide, ritanserin and LY 53857 in several 5-HT2 receptor models, none of these antagonists acted in a non-competitive or unsurmountable fashion at 5-HT1C receptors. These results suggest, but do not firmly rule out, that at least in the presence of the drugs tested in the present study, 5-HT1C receptors in the choroid plexus do not undergo an allosteric modulation; these findings are apparently in contrast to a model proposed previously for 5-HT2 receptors (Kaumann and Frenken 1985, Naunyn-Schmiedeberg's Arch Pharmacol 328:295-300).

Allosteric Regulation↗
PubMed1991

Interaction between systemic circulation and brain injuries in newborns.

In several studies different pathogenetic mechanisms of metabolic and/or cardiovascular origin were shown depending on the type of hypoxic or hypoxic/hypercapnic stress and conditions of animals (normal developed or intrauterine growth retarded newborn piglets). Thus, in normal-weight piglets the prevention of compensatory hyperventilation owing to severe hypoxia (artificially ventilated animals) leads to critical, i.e. lethal acidosis. In intrauterine growth retarded piglets, a severe hypoxia cannot be vitally compensated because of the restricted circulatory centralization. Moreover, a limited cerebrovascular dilatation during moderate hypoxia/hypercapnia produces a critical state of the metabolic supply in those animals.

Adaptation, Physiological↗
PubMed1991

Investigations of cerebral glucose utilization into the newborn brain: a [18F]-FDG positron emission tomography study using a high resolution multiwire proportional chamber detector device.

An experimental approach is presented, where for the first time positron emission tomography (PET, the most important method for in vivo measuring the key functions of brain physiology and metabolism) was applied together with other techniques for quantitative-topological estimation of key parameters such as rCMRGlu in normal and disturbed brain function states in the newborn period.

Animals↗