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P M Laduron

Publications and source records attributed to P M Laduron.

At least 73 records · Page 4Linked to original sources
PubMed1987

Two populations of neurotensin binding sites in murine brain: discrimination by the antihistamine levocabastine reveals markedly different radioautographic distribution.

Monoiodo-[125I-Tyr3]neurotensin (NT) bound to a high affinity, low capacity binding component and a lower affinity, high capacity component in rat brain synaptic membranes. The antihistamine H1 agent levocabastine, which bears no structural relationship to NT, selectively and totally inhibited NT binding to its low affinity binding sites. The IC50 for levocabastine was 7 nM. Lowering the temperature of the binding assay from 25 to 4 degrees C markedly reduced the affinity of the high affinity NT binding site but did not affect the ability of levocabastine to discriminate between high and low affinity NT binding sites in rat brain membranes and tissue sections. Radioautographic studies of [125I-Tyr3]NT binding to rat brain tissue sections in the absence and presence of levocabastine revealed markedly different regional distributions of the two NT binding components. The levocabastine-sensitive NT binding site was present in membranes from rat and mouse brain but absent from rabbit brain membranes and from human brain tissue sections. It was also absent from mouse neuroblastoma N1E115 and human colonic adenocarcinoma HT29 cell membranes, two cell lines which have previously been shown to possess NT receptors functionally coupled to intracellular second messenger-generating systems. These findings are discussed in the light of the known properties of the high and low affinity NT binding sites in rat brain.

Animals↗
PubMed1987

Enhanced axonal transport of receptor-bound opiate in ethanol-treated rats.

The retrograde transport of receptor-bound opiate was markedly enhanced in the vagus nerves of rats housed for 25 days in an atmosphere of ethanol vapor. This increase disappeared after 8 days of withdrawal as did the animal preference for ethanol. In contrast, the axonal transport of muscarinic receptors in sciatic nerves was slightly reduced. This provides more evidence for the idea that chronic alcoholization and morphine addiction share a common denominator and that the retrograde transport of receptor-bound signal molecules represents a link between the synapses and the cell-body of neurones.

Animals↗
PubMed1987

Axonal transport of the synaptic vesicle monoamine carrier identified by [3H]dihydrotetrabenazine binding in rat sciatic nerve.

The monoamine carrier of noradrenergic synaptic vesicles was assayed in the rat sciatic nerve by in vitro binding of [3H]dihydrotetrabenazine. The number of binding sites increased with time on both sides of a ligature, indicating fast anterograde and retrograde axoplasmic transports of comparable amplitude. Anterogradely and retrogradely transported binding sites had similar pharmacological properties, which were characteristic of binding to the monoamine carrier embedded within a lipid bilayer. Contrary to the secreted synaptic vesicle matrix constituents, the intrinsic monoamine carrier assayed by [3H]dihydrotetrabenazine binding is a marker adapted to retrograde transport studies.

Animals↗
PubMed1987

Different postnatal ontogeny of two [3H]neurotensin binding sites in rat brain.

Two distinct neurotensin binding sites have been identified in rat brain: the NT1-acceptor site (levocabastine-sensitive) and the NT2-receptor site. In rat forebrain, NT2-receptors were present at birth, revealed a maximal level (13.8 fmol/mg tissue) on day 10 of postnatal life but a much lower plateau (3.0 fmol/mg tissue) in adult rats. NT1-acceptors were not detected before day 10 and became maximal at day 30. It is suggested that the loss of NT2-receptor sites during the postnatal development may be the expression of the regression of a transient redundancy of neuronal connections.

Animals↗
PubMed1987

Identification of the serotonin-S2 receptor ligand binding site by photoaffinity labelling with 7-azido-8-[125I]ketanserin ([125I]AZIK).

7-Azido-8-[125I]ketanserin ([125I]AZIK) was characterized as a potent photoaffinity probe for serotonin-S2 receptors. In reversible binding experiments, [125I]AZIK bound with high affinity (Kd = 0.69 nM) to rat frontal cortex membranes. When incubation with [125I]AZIK was followed by UV irradiation, the binding was found to be irreversible. Protection experiments with various drugs demonstrated the serotonin-S2 nature of the photoaffinity labelling. SDS-polyacrylamide gel electrophoresis of the photolabelled membranes allowed one to identify the serotonin-S2 receptor ligand binding site as a single polypeptide with a molecular mass of approx. 67,500 Da. [125I]AZIK will be a valuable tool for the elucidation of the serotonin-S2 receptor structure.

Affinity Labels↗
PubMed1987

Axonal transport of neuroreceptors: possible involvement in long-term memory.

Evidence is presented that neuroreceptors move bidirectionally along axons of neurons through fast axoplasmic transport mechanisms. The retrograde transport of receptor-bound signal molecules from nerve terminals to the perikaryon represents a corridor of information between synapses and the cell body of neurons. It is speculated that this process could be involved in long-term memory.

Animals↗
PubMed1987

Axonal transport of receptors: characterization, role in receptor regulation and possible involvement in learning.

There is an increasing amount of evidence indicating that presynaptic receptors move antero- and retrogradely along axons of neurones through axoplasmic transport mechanisms. The main features of this dynamic process will be presented: it is bidirectional, fast, microtubule dependent and associated with vesicles which are presumably recycled in the cell body. Receptor axonal transport is impaired or enhanced in certain pathological conditions. The implications of this process and its possible involvement in long-term memory will be discussed.

Animals↗
PubMed1986

TPP+ accumulation in rat brain synaptosomes as a probe for Na+ channels.

Tetraphenylphosphonium (TPP+) accumulation in rat brain synaptosomes was measured in the presence of various stimuli. TPP+ accumulation was sensitive to an increase of extracellular K+ or to the presence of Na+ channel neurotoxins. Examination of the effects of drugs with different physico-chemical properties on TPP+ accumulation showed that there was no effect under low and high K+ conditions; pimozide, flunarizine and buterizine were active in the presence of veratridine or scorpion venom. These results were compared to data obtained for the specific binding of [3H]BTX-B, a selective marker for the Na+ channel. It can be concluded that certain drugs, although active on [3H]BTX-B binding, are not necessarily identified when TPP+ is used as probe.

Animals↗
PubMed1986

Structure-linked latency of muscarinic receptors in axonal transport.

Muscarinic receptors that accumulated above a ligature in rat sciatic nerves were labelled in vitro under isotonic conditions with N-[3H]methylscopolamine. The addition of 0.005% of digitonin doubled the binding in proximal segments above and close to the ligature but not in the intermediary segments between two ligatures. Osmotic shock and freeze-thawing treatments also enhanced the binding. Digitonin did not affect the affinity of muscarinic receptors but revealed a greater number of sites by increasing the membrane permeability to the hydrophilic ligand. We conclude that presynaptic muscarinic receptors that undergo fast axonal transport in rat sciatic nerves exist under a latent form because they are associated with vesicles. This is the first demonstration of a structure-linked latency for receptors.

Animals↗
PubMed1986

Impaired axonal transport of opiate and muscarinic receptors in streptozocin-diabetic rats.

Axonal transport of receptors was studied in streptozocin-diabetic rats using two different binding models. Streptozocin-induced hyperglycemia caused a reduced accumulation of muscarinic receptors above a ligature placed on rat sciatic nerves when the binding assay was performed in vitro with [3H]QNB. In the vagus nerve, the retrograde axonal transport of receptor-bound opiate was strongly decreased in the streptozocin-treated rats when [3H]lofentanil was used in vivo to label opiate receptors. Insulin partly reversed the changes observed in the streptozocin-treated rats. These findings suggest that impaired axonal transport of receptors may explain part of the neurological disturbance which is seen in diabetic patients.

Animals↗
PubMed1986

[3H]Batrachotoxinin A 20-alpha-benzoate binding to sodium channels in rat brain: characterization and pharmacological significance.

Attempts were made to find whether [3H]batrachotoxinin A 20-alpha-benzoate provides a specific probe for measuring interactions of local anesthetics with the sodium channel complex. [3H]Batrachotoxinin A 20-alpha-benzoate binding, [14C]guanidine and 22Na uptake were investigated in rat brain crude synaptosomal preparations and the potencies of drugs belonging to various chemical and pharmacological classes were compared. The results show that [14C]guanidine uptake seems to be a good model for measuring Na+ fluxes. An allosteric interaction between site 2 and 3 of the Na+ channel is apparent since (i) scorpion venom was able to increase further the guanidine or Na+ stimulation of site 2 toxins to a maximal level and (ii) in the presence of scorpion venom, binding of [3H]BTX-B to site 2 of the Na+ channel was enhanced. A good correlation exists between drug potencies in the binding and uptake experiments. Inhibition by drugs was not restricted to drugs known as local anesthetics. It can be concluded that many drugs seem to interfere with the Na+ channel of rat brain. This may play a role not only in the major effects of local anesthetic drugs but also in the side-effects of drugs from other classes.

Animals↗
PubMed1986

Evidence for a displaceable non-specific [3H]neurotensin binding site in rat brain.

Levocabastine is a potent antihistamine drug, structurally unrelated to neurotensin. In rat and mouse brain but not in other animal species, it inhibited 60% of the [3H]neurotensin binding displaced by unlabelled neurotensin or neurotensin(8-13). The levocabastine-sensitive site or "site 1" displayed high affinity properties for levocabastine (IC50 = 25 nM) and was highly sterospecific (IC50-value higher than 10 microM for one of the isomers). Binding to the "site 1" in rat brain corresponded to the [3H]neurotensin binding displaceable by 1 microM levocabastine, whereas binding to the "site 2" corresponded to the binding displaced by 1 microM neurotensin when the "site 1" was occluded by 1 microM levocabastine. Both "site 1" and "site 2" appeared to be saturable. Scatchard plots obtained in rat bulbus olfactorius allowed to calculate a KD-values of 7.1 nM and a Bmax-values of 37.2 fmol/mg original tissue for "site 1", while "site 2" displayed a KD-value of 0.7 nM and a Bmax-value of 16.3 fmol/mg original tissue. The regional distributions of both sites showed marked differences. The "site 1" was homogeneously distributed throughout all rat brain areas, whereas the amount of "site 2" binding was markedly different in separate brain areas: bulbus olfactorius and substantia nigra had the highest amounts (8.9 and 7.8 fmol/mg tissue) while cerebellum had the lowest (0.4 fmol/mg tissue). In spite of its high affinity and stereospecificity, "site 1" has to be considered as an acceptor or recognition site for [3H]neurotensin because of its species-link, low saturability and homogeneous distribution in all rat brain areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

In vitro labeling of serotonin-S2 receptors: synthesis and binding characteristics of [3H]-7-aminoketanserin.

[3H]-7-Aminoketanserin (7-amino-3-[2-[4-(2-tritio-4-fluorobenzoyl)-1- piperidinyl]ethyl]-2,4-(1H,3H)-quinazolinedione), an amino derivative of the selective serotonin-S2 antagonist ketanserin, was synthesized and tested for in vitro labeling of serotonin-S2 receptors. The compound showed a very high affinity for both membrane-bound and detergent-solubilized serotonin-S2 receptors with KD values of 0.35 and 2.03 nM, respectively. At nanomolar concentrations, binding to serotonin-S1 sites was totally absent. Serotonin-S2 receptor binding was characterized by a slow dissociation and a very low nonspecific binding. In rat frontal cortex preparations, binding could be displaced by nanomolar concentrations of different serotonin antagonists and micromolar concentrations of serotonin agonists. Compounds with other pharmacological profiles were poorly or not active. Introduction of an amino function in this new radioligand led to a decreased lipophilicity. Therefore, besides being a valuable radioligand for routine binding studies, [3H]-7-aminoketanserin will probably be a good ligand for labeling serotonin-S2 receptors on intact cells.

Animals↗
PubMed1986

Different subcellular localization of muscarinic and serotonin (S2) receptors in human, dog, and rat brain.

Cortex from rat, dog, and human brain was submitted to subcellular fractionation using an analytical approach consisting of a two-step procedure. First, fractions were obtained by differential centrifugation and were analyzed for their content of serotonin S2 and muscarinic receptors, serotonin uptake, and marker enzymes. Second, the cytoplasmic extracts were subfractionated by equilibration in sucrose density gradient. In human brain, serotonin and muscarinic receptors were found associated mostly with mitochondrial fractions which contain synaptosomes, whereas in rat brain they were concentrated mainly in the microsomal fractions. Density gradient centrifugation confirmed a more marked synaptosomal localization of receptors in human than in rat brain, the dog displaying an intermediate profile. In human brain, indeed, more receptor sites were found to be associated with the second peak characterized in electron microscopy by the largest number of nerve terminals. In addition, synaptosomes from human brain are denser than those from rat brain and some marker enzymes reveal different subcellular distribution in the three species. These data indicate that more receptors are of synaptosomal nature in human brain than in other species and this finding is compatible with a larger amount of synaptic contacts in human brain.

Adult↗
PubMed1986

Reconstitution of solubilized serotonin-S2 receptors into phospholipid vesicles.

Serotonin-S2 receptors from rat frontal cortex were solubilized using CHAPS/sodium chloride. Reconstitution of the solubilized receptors was achieved by dilution of the soluble preparation, followed by centrifugation to remove the detergent. The receptors were truly reconstituted as judged by sedimentation, increased thermostability and electron microscopy. The reconstituted preparation showed high-affinity binding of [3H]7-aminoketanserin. The binding characteristics resembled those obtained for membrane-bound receptors.

Animals↗