PubMed Health⌕ Search

Biomedical subjects

P M Laduron

Publications and source records attributed to P M Laduron.

At least 109 records · Page 6Linked to original sources
PubMed1983

Characterization and regional distribution of serotonin S2-receptors in human brain.

[3H]Ketanserin binding was characterized in vitro in human brain homogenates and the regional distribution of the sites was determined. In human brain, [3H]ketanserin was found to bind on serotonin (5-HT) S2-receptors; only 5-HT antagonists competed with the labelled ligand at nanomolar concentrations; other drugs were much less active or inactive. Special attention was paid to the choice of a displacer, here methysergide, to determine the blank value (non-displaceable binding). [3H]Ketanserin binding in human brain displayed similar binding characteristics to the S2-receptor in the rat frontal cortex, high affinity (Kd 0.69 nM) and relatively slow dissociation rate. The regional distribution of serotonin S2-receptors labelled with [3H]ketanserin was studied in 30 different regions of human brain. The highest number of receptors was measured in the cortex. However, within the cortex the distribution was also inhomogeneous, a much lower number of sites being found in the pre- and post-central gyri. In the dopaminergic areas and the cerebellum the number of sites was quite low, and only few binding sites were detected in the corpus callosum, the medulla and the hypophysis. The large number of serotonin S2-receptors in the human cortex suggests that serotonin has an important role in this brain region.

Brain↗
PubMed1983

Trapping of labelled ligands in intact cells: a pitfall in binding studies.

Binding on/in whole cells seems to be a more appropriate approach for studying receptor sites in physiological conditions. However, certain difficulties encountered throughout the characterization of [3H]spiperone binding in human lymphocytes led us to reconsider this problem. The IC50 values of [3H]spiperone binding to human lymphocytes did not correlate with those found in rat striatum; domperidone was inactive in lymphocytes whereas it is one of the most potent dopamine antagonists in rat striatal preparations in vitro. In contrast, chloroquine, a lysosomotropic drug, displaced [3H]spiperone at low concentration in intact lymphocytes but did not in the striatum. [3H]Spiperone binding was not displaceable in the membrane preparation of lymphocytes. Similar results were obtained with other intact cells, fibroblasts, hepatocytes and neuroblastoma cells using [3H]spiperone and other ligands, such as [3H]haloperidol, [3H]pyrilamine and [3H]ketanserin. Here again, displaceable binding was only present in intact cells but not in membrane fractions. Such a 'displaceable' binding was not related to receptor sites but may be regarded as non-specific binding which should correspond to a trapping phenomenon presumably in the lysosomes. Binding studies on intact cells need more caution than when performed on membrane preparations; indeed, permeation or trapping of ligands in the nanomolar range represents a serious drawback which, sometimes, can give the illusion of specific binding.

Animals↗
PubMed1983

Short-term disappearance of muscarinic cell surface receptors in carbachol-induced desensitization.

A rapid carbachol-induced disappearance of muscarinic cell surface receptors was shown using [3H]methyl scopolamine as ligand on intact 108CC15 hybrid cells or rat cerebellar cells. This phenomenon is temperature-dependent, correlated to agonist stimulation and reversible. In these short time periods (less than or equal to 30 min), no change was observed in the total receptor amount measured on membrane preparations. This disappearance of cell surface receptors could represent the first event in cell desensitization which could be followed by receptor recycling in physiological conditions or by receptor degradation if the stimulation by agonists persists, as in long-term regulation.

Animals↗
PubMed1983

Analytical subcellular fractionation of rat cortex: resolution of serotonergic nerve endings and receptors.

An analytical procedure for the subcellular fractionation of rat brain cortex is presented; it consists of a two-step procedure involving a differential centrifugation using the five-fraction scheme and an isopycnic centrifugation in continuous sucrose gradients. All fractions obtained were analyzed for their content of various constituents, such as receptor binding, uptake, and several marker enzymes. Special attention was paid to the subcellular distribution of the serotonin S2 receptors; they were mainly recovered in the microsomal P fraction, but a significant amount was also associated with the mitochondrial (M and L) fractions. After equilibration in density gradients, serotonin S2 receptors revealed two peaks, which were similarly affected after treatment with amitriptyline and/or yohimbine. There is no evidence to suggest that serotonin S2 receptors are associated with nerve endings containing the neurotransmitter serotonin. Although three main profiles, a microsomal, a mitochondrial, and a mixed one, clearly appear from the differential centrifugation, subgroups of these main profiles were also found. For instance, the microsomal distribution patterns of serotonin S2 receptors and 5'-nucleotidase are very similar, but differ from that of UDP-galactosyltransferase. Similarly, the mitochondrial profiles of cytochrome oxidase and 5-HT (serotonin) uptake are different. An analytical approach for brain fractionation, when performed with appropriate measurements (cytochrome oxidase, amine uptake, 5'-nucleotidase, and receptor binding), is rapid and clearly differentiates pre- and postsynaptic constituents.

Animals↗
PubMed1983

Failure of a peripheral dopaminergic marker in Parkinson's disease.

[3H]-spiperone binding on human lymphocytes did not reveal the occurrence of dopamine receptors. However, lower values were observed in Parkinsonism and the displaceable binding was increased after levodopa treatment although this was not specific only for levodopa and, furthermore, was not correlated with the clinical symptomatology. This non-specific binding in lymphocytes corresponds to trapping, presumably in lysosomes and thus does not reflect the dopaminergic receptors state in Parkinson's disease.

Adult↗
PubMed1982

Axoplasmic transport and possible recycling of opiate receptors labelled with 3H-lofentanil.

3H-Lofentanil, an extremely potent opiate drug with a very long duration of action was injected intravenously into rats immediately after a ligature had been tied around the vagus nerve. Radioactivity accumulated on both sides of the ligature 24 hours and, to a larger extent, 48 hours after the injection. In contrast, there was no accumulation in animals pretreated with naloxone, neither in ligated sciatic nerves nor between two ligatures in the vagus nerve. An accumulation of stereospecific 3H-lofentanil binding sites measured in vitro was only detected above the ligature, thus in the proximal part of the nerve. When 3H-lofentanil was injected at different time intervals after ligation, we observed a tremendous drop of labelling in the distal and also but more slowly in the proximal part of the nerve. This could be due to a possible recycling or re-utilization of 3H-lofentanil binding sites. The present data are compatible with an axoplasmic flow and a possible recycling of opiate receptors labelled in vivo after intravenous injection of 3H-lofentanil.

Animals↗
PubMed1982

In vivo binding of [3H]ketanserin on serotonin S2-receptors in rat brain.

In vivo binding of [3H]ketanserin was studied in various brain regions in rats. After i.v. injection of [3H]ketanserin (5 micrograms . kg-1), the highest labelling was found in the frontal cortex. Brain disposition of labelled drug correlated with the distribution of serotonin S2-receptors detected in vitro. The binding was saturable in the serotonergic areas but not in the cerebellum. Various drugs were tested for their ability to displace or to prevent [3H]ketanserin binding: these results were then compared to those obtained with [3H]spiperone in the frontal cortex. Although [3H]spiperone can be used to differentiate the affinity of a drug for serotonin (frontal cortex) and dopamine (striatum) receptors, the great advantage of [3H]ketanserin is that it labels serotonin S2-receptors exclusively.

Animals↗
PubMed1982

In vitro and in vivo binding characteristics of a new long-acting histamine H1 antagonist, astemizole.

Binding characteristics of astemizole were studied in vitro in various receptor binding models and in vivo by determining the occupancy of histamine H1 receptors in guinea pig lung and cerebellum. In vitro, astemizole was found to have a high affinity for histamine H1 receptors, but great difficulties were encountered in proving this because of its high affinity for nonspecific binding sites. Since the equilibrium conditions were not reached in vitro, the real affinity of astemizole remains unclear and its receptor profile must be interpreted with caution. Nevertheless, the drug is certainly much more potent on histamine H1 receptors than on serotonin S2 and adrenergic alpha 1-receptors. Moreover, it was found to be devoid of antimuscarinic and antidopaminergic properties. The most striking property of this drug is its extremely slow dissociation rate from H1 receptors when assayed in vitro using [3H]-pyrilamine. Ex vivo experiments were performed in guinea pigs; astemizole was given orally to the animals, and the occupancy of H1 receptors in the lung and the cerebellum was determined in vitro by the [3H]-pyrilamine binding assay. Astemizole was found to occupy H1 receptors in lung at very low doses. Here again the most striking receptor binding property was its very long duration. The occupancy of H1 receptors in lung began to decline only 4-6 days after administration of the drug. However, there was a marked difference between the occupancy of peripheral and central receptors; indeed, in contrast to pyrilamine, astemizole at pharmacological doses did not reach the H1 receptors in the cerebellum, presumably because the drug does not readily cross the blood-brain barrier.

Animals↗
PubMed1982

Characterization of solubilized serotonin (S2) receptors in rat brain.

[3H]Spiperone binding sites were solubilized from rat frontal cortex and striatum by means of the mild detergent, lysolecithin. In the frontal cortex, the binding sites were extracted from a microsomal membrane fraction which was found to be enriched in serotonin (S2) receptors when labeled either with [3H]spiperone or with [3H]lysergic acid diethylamide. Although the extraction yield was relatively low, the [3H]spiperone binding sites solubilized from the frontal cortex retained the high-affinity characteristics of serotonin (S2) receptors in the original membrane: low KD (1.4 nM); binding saturable, reversible, and stereospecific; and displaying a high affinity toward the most potent serotonin antagonists (pirenperone, pipamperone, ketanserin, methysergide, and mianserin). There was a very good correlation between the drug potencies in both soluble and membrane preparations. The molecular dispersion of the soluble extract was assessed by several criteria, including a low sedimentation coefficient in sucrose gradient. No specific binding sites could be extracted from the cerebellum. In contrast, few binding sites endowed with the characteristics of serotonin (S2) receptors were detected in lysolecithin extracts from rat striatum. However, the S2 sites became more apparent when a tetralin derivative was added to the incubation medium in order to prevent [3H]spiperone binding on solubilized dopamine receptors. In contrast, when microsomal membranes from rat striatum were treated with digitonin, the solubilized [3H]spiperone binding sites were only of a dopaminergic nature.

Animals↗