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Biomedical subjects

P M Laduron

Publications and source records attributed to P M Laduron.

At least 19 recordsLinked to original sources
PubMed2000

Axonal transport of TREK and TRAAK potassium channels in rat sciatic nerves.

The recent cloning, functional expression and brain localization of two new potassium channels, TREK and TRAAK, led us to examine whether both channels are present in peripheral nerves and can move along axons by means of axonal transport mechanisms. Using specific antibodies directed against TREK and TRAAK peptides, we found that immunoreactivity for both potassium channels accumulates above and below a ligature in rat sciatic nerves. The process was rapid and bidirectional suggesting that the channels are associated with vesicles. This represents the first report on the axonal transport of potassium channels.

Animals↗
PubMed1999

Riluzole series. Synthesis and in vivo "antiglutamate" activity of 6-substituted-2-benzothiazolamines and 3-substituted-2-imino-benzothiazolines.

Two series of analogues of riluzole, a blocker of excitatory amino acid mediated neurotransmission, have been synthesized: monosubstituted 2-benzothiazolamines and 3-substituted derivatives. Of all the compounds prepared in the first series, only 2-benzothiazolamines bearing alkyl, polyfluoroalkyl, or polyfluoroalkoxy substituents in the 6-position showed potent anticonvulsant activity against administration of glutamic acid in rats. The most active compounds displaying in vivo "antiglutamate" activity were the 6-OCF(3) (riluzole), 6-OCF(2)CF(3), 6-CF(3), and 6-CF(2)CF(3) substituted derivatives with ED(50) values between 2.5 and 3.2 mg/kg i.p. Among the second series of variously substituted benzothiazolines, compounds as active as riluzole or up to 3 times more potent were identified in two series: benzothiazolines bearing a beta-dialkylaminoethyl moiety and compounds with an alkylthioalkyl chain and their corresponding sulfoxides and sulfones. The most potent derivatives were 2-imino-3-(2-methylthio)- and 2-imino-3-(2-methylsulfinyl)-ethyl-6-trifluoromethoxybenzothiazolines (61 and 64, ED(50) = 1.0 and 1.1 mg/kg i.p., respectively). In addition, intraperitoneal administration of some of the best benzothiazolines protected mice from mortality produced by hypobaric hypoxia.

Animals↗
PubMed1997

Fractionation of human brain by differential and isopycnic equilibration techniques.

Fractionation of brain tissue by either differential or isopycnic centrifugation is a useful cytological and biochemical tool to study the intracellular localization of neuronal elements involved in neurotransmission. Several neuroreceptors and uptake sites were found to display a subcellular bimodal distribution in rat brain. However, in the human brain, little is known about the subcellular distribution of neurotransmitter receptors and amine uptake sites. Despite the inevitable post-mortem delay which seems to induce many more morphological changes than modifications of enzymatic or receptor distribution profile from the subcellular fractions, fractionation of human brain areas remains a valid procedure to explore the subcellular localization of neuronal constituents. This paper describes the methods used to separate human brain tissue. As we have previously demonstrated in rat and dog brains, our results indicate that differential and isopycnic fractionation techniques, used with a large number of markers such as enzymes, receptors and uptake sites, make it possible to separate tissue fractions enriched in nerve endings, dendrites, dendritic spines, plasma membranes or vesicles.

Brain↗
PubMed1995

Subcellular distribution of receptor sites in human brain: differentiation between heavy and light structures of high and low density.

Studies of the subcellular localization of neuroreceptors in the rat brain have shown that most of them are associated with light and low density subcellular fractions. In two human brain areas, quite different subcellular distributions were observed. After fractionation by differential centrifugation of frontal cortex homogenates, benzodiazepine and serotonin 5-HT2 receptors were mainly found in the heavy mitochondrial (M) fraction, whereas mu-opiate and muscarinic cholinergic receptors were mainly concentrated in the microsomal (P) fraction. In human putamen, the presynaptic markers of dopaminergic nerve terminals (neurotensin receptors, dopamine uptake sites and amine vesicular transporter-binding sites), benzodiazepine receptors and serotonin uptake sites were recovered both in the high and low density fractions, whereas the muscarinic, opiate and, to a lesser extent, dopamine D2 receptors were mostly concentrated in the microsomal fraction. In the cerebral cortex, after isopycnic centrifugation in sucrose gradients, neuroreceptors were found in the high density fractions where the peaks of cytochrome oxidase and that of nerve endings, as identified by amine uptake and by means of electron microscopy were also found. A single peak of benzodiazepine receptors was observed in high density (1.15-1.17 g/ml) fractions suggesting that these receptors are much more concentrated in the nerve terminals or dendrites rather than in the dendritic spines or vesicles. The fact that muscarinic and opiate receptors were recovered in the P fraction with plasma membrane constituents and also in M and L fractions, which is confirmed by a bimodal distribution in sucrose gradient, suggests that they are localized in both the nerve terminals or dendrites and in the small vesicles or dendritic spines. In the putamen, much of the specific binding to uptake sites for dopamine and serotonin was recovered in the high density fractions, but the existence of another peak at a lower density indicates the presence of microsomal uptake sites. The results indicate that differential and isopycnic fractionation methods performed on human brain samples, make it possible to separate tissue fractions enriched in nerve endings, dendrites, dendritic spines, plasma membranes or vesicles.

Binding, Competitive↗
PubMed1995

Interleukin-1 beta induces long-term increase of axonally transported opiate receptors and substance P.

Interleukin-1 is known to exert pleiotropic effects in host defence mechanisms and in inflammation. Chronic pain, inflammation and interleukin-1 beta enhance the production of substance P. Recently, axonal transport of opiate receptors was found to increase in rat sciatic nerves in the model of Freund's adjuvant-induced arthritis. Here we show that a single intraplantar injection of interleukin-1 beta is able to enhance the axonal transport of mu and kappa opiate receptors and substance P. Indeed, their accumulation was markedly increased in the proximal part of ligated sciatic nerves, but only in the paw injected with interleukin-1. The time course revealed a delayed onset and, more importantly, a long-term increase lasting at least six days, which is in contrast with the short-term pyrogenic effect of interleukin-1. Pretreatment of rats with capsaicin or administration of dexamethasone completely prevented the interleukin-1 beta effect. The present results suggest that interleukin-1 beta may serve as a mediator to sensitize nociceptors in chronic inflammation and possibly in hyperalgesia through long-term changes in neuronal plasticity.

Animals↗
PubMed1995

Functional consequences of retrograde axonal transport of receptor-bound neurotensin.

Transport mechanisms or trafficking systems in axons allow neuronal constituents to reach nerve terminals. Accordingly, presynaptic receptors undergo axonal transport through a process that is fast and bidirectional. However, axonal transport of receptors also appears to be involved in the 'flow' of information from membrane receptors to genome. The most compelling evidence that retrograde axonal transport of receptor-bound neuropeptide represents a long-distance signalling system in gene expression, discussed here by Pierre Laduron, comes from the recent observation that neurotensin injected in the striatum undergoes retrograde transport in dopaminergic neurones to the substantia nigra, where it induces in the cell bodies an increase of tyrosine hydroxylase mRNA. Although the molecular mechanisms of this remain to be elucidated, the present data suggest the existence of retrograde signal molecules, or 'third messengers', which have to be associated with synaptic or endocytotic vesicles in order to gain entry into the cell bodies, where they may modulate gene expression.

Animals↗
PubMed1994

IL-1 beta-like Freund's adjuvant enhances axonal transport of opiate receptors in sensory neurons.

Chronic pain and inflammation increase substance P in sensory fibres of peripheral nerves in which opiate receptors are known to undergo axonal transport. The aim of the present study was to evaluate a possible modulation of axonal transport of opiate receptors in peripheral nerves during inflammation. After intraplantar injection of Freund's adjuvant to rats, the accumulation of mu and kappa opiate receptors increased on both sides of ligature in sciatic nerves of the injected paw. The contralateral side was unaffected and may serve as control. When IL-1 beta was injected into rat paws, the axonal transport of opiate receptors was increased in a similar way. This suggests that IL-1 beta represents a major mediator to sensitize nociceptors during inflammation through a process requiring retrograde signals.

Animals↗
PubMed1994

Neuroprotective effects of colchicine in the gerbil model of cerebral ischaemia.

The tropolonic alkaloid colchicine significantly reduces the behavioural, electroencephalographic and histological damage seen after a 6-min occlusion of the two common carotid arteries of the Mongolian gerbil if the compound is administered at 2 or 4 mg/kg i.p. immediately upon reperfusion. A 45% increase in high-frequency ECoG activity and significant reduction of 80% in the hypermotility of the gerbils, with 63% less faults in a passive avoidance paradigm, were observed in conjunction with considerable protection of the hippocampus, after a single dose of 4 mg/kg colchicine. No adverse effects of colchicine treatment on animal movement and body weight were observable. Colchicine's possible mode of action, via inhibition of cellular transport systems, is discussed.

Animals↗
PubMed1994

From receptor internalization to nuclear translocation. New targets for long-term pharmacology.

Receptors involved in intercellular communication at the cell surface share the capacity to desensitize through molecular and cellular mechanisms. Cellular desensitization is a rapid and dynamic process whereby membrane receptors internalize in response to an excess of agonists. The internalized receptors may recycle rapidly or undergo down-regulation when following a degradative pathway. However, receptor internalization does not necessarily mean degradation; it also represents the initial step of a retrograde signalling system whereby an "interiorized" message, the ligand-receptor complex, can be transported in contrast to second messengers, along axons or in the cytoplasm leading to long-term effects in the nucleus. Such "third messengers" have to undergo nuclear translocation to serve as transcriptional regulators in the control of gene expression. The "third messengers" are thus cytoplasmic proteins, including the receptor itself, which may be associated with internalized vesicles and released by mechanisms which have not yet been elucidated. They represent already good targets for the development of new drugs, and multi-targeting and synergistic approaches are likely to increase their usefulness.

Biological Transport↗
PubMed1994

Retrograde axonal transport of neurotensin in rat nigrostriatal dopaminergic neurons. Modulation during ageing and possible physiological role.

Biochemical and anatomical data are reported which demonstrate for the first time the existence of a retrograde axonal transport process for a neuropeptide, neurotensin, in rat brain. Neurotensin receptors are mainly located in the striatum on nerve terminals of the nigrostriatal dopaminergic pathway. Thus, the association of specific neurotensin receptors on a well defined pathway provides an excellent model to investigate the existence of such a process. Two hours after the intrastriatal injection of iodinated neurotensin, radioactivity started to accumulate in the ipsilateral substantia nigra. The levels were maximal during the fourth hour. The appearance of this labelling was prevented by injection of a large excess of unlabelled neurotensin or of neurotensin 8-13, an active neurotensin fragment, but not by neurotensin 1-8 which had no affinity for neurotensin receptors. These results suggest that the appearance of radioactivity in the ipsilateral substantia nigra was dependent on the initial binding of this peptide to its receptors in the striatum. HPLC studies demonstrated that the radioactivity found in the substantia nigra corresponded to intact neurotensin and to degradation products of this peptide. Moreover, it has been shown that this retrograde transport was microtubule-dependent and occurred in dopaminergic nigrostriatal neurons. Light and electron microscopic data confirmed and extended the present results. Four and a half hours after intrastriatal injection of iodinated neurotensin, silver grains were mainly detected in dopaminergic perikarya of the substantia nigra pars compacta. The vast majority were associated with neuronal elements and their localization within cell bodies suggests that retrogradely transported neurotensin may be processed along a variety of intracellular pathways including those mediating recycling in the rough endoplasmic reticulum and degradation in lysosomes. However, the presence of silver grains over the nucleus, as well as the increase in tyrosine-hydroxylase mRNA expression in the ipsilateral substantia nigra 4 hr after intrastriatal injection of neurotensin support the concept that neurotensin alone, or associated with its receptor, might be involved in the regulation of gene expression. Finally, we have demonstrated that in old rats the quantity of retrogradely transported neurotensin was significantly decreased as compared to that observed in young adult rats. This retrograde axonal transport of a neuropeptide may represent, as already suggested for growth factors, an important dynamic process conveying information from nerve terminals to the cell body.

Aging↗
PubMed1993

Is the sigma 2 receptor in rat brain related to the K+ channel of class III antiarrhythmic drugs?

The sigma 2 receptor subtype was studied in rat cerebral cortex and in C6 glioma cells homogenates using various compounds including class III antiarrhythmic drugs. The characteristics of (+)-[3H]-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ((+)-[3H]-3-PPP) binding were assessed in competition experiments with different displacers which revealed the presence of sigma 2 receptors. Various class III antiarrhythmic drugs inhibited (+)-[3H]-3-PPP binding with high affinity and their binding affinity was found to correlate with the potency of these compounds to increase the duration of action potentials measured in Purkinje fibers in electrophysiological studies. Since class III antiarrhythmic drugs are known to interact with voltage-dependent K+ channels, the present results provide evidence that the (+)-[3H]-3-PPP binding sites in rat brain possess the characteristics of K+ channels of class III antiarrhythmic drugs.

Action Potentials↗
PubMed1993

Postnatal ontogeny of the rat brain neurotensin receptor mRNA.

Total RNA was purified from rat forebrain at different postnatal ages and analyzed by Northern blot using a specific neurotensin receptor RNA probe. The rat neurotensin receptor mRNA was present in high amount during the first 10 days of life. Thereafter, it rapidly decreased and was undetected after 20 days. [3H]neurotensin binding experiments performed on the same tissues indicated that the total amount of neurotensin receptors increased during the first week and was maximal between day 7 and day 10. This plateau was followed by an important loss (70%) of neurotensin receptors. These results indicate that an important reduction in the genetic expression of the neurotensin receptor after day 10 may probably account for the [3H]neurotensin binding profile observed in rat forebrain during the postnatal ontogeny.

Aging↗
PubMed1993

Axonal transport of dopamine-containing vesicles labelled in vivo with [3H]reserpine.

Axonal transport of the vesicular monoamine transporter was assayed in the rat brain by in vivo binding of the specific ligand [3H]reserpine. Because of the marked localization of reserpine binding sites in dopaminergic cell bodies and nerve terminals, the dopaminergic nigrostriatal pathway was chosen for the study of the axonal transport of the monoamine carrier present in the membrane of synaptic vesicles. When labelled reserpine was injected into the substantia nigra, a delayed accumulation of radioactivity in the ipsilateral striatum was observed approximately 4 h after the injection. Similarly, injection into the right striatum was followed by a substantial accumulation of radioactivity in the ipsilateral substantia nigra, which was prevented by peripheral injection of unlabelled reserpine or tetrabenazine. This process was rapid and dependent on microtubules. In senescent rats, the amount of retrogradely transported [3H]reserpine was significantly reduced. These results demonstrate that labelled reserpine may be used to monitor in vivo fast axonal transport in central neurons.

Aging↗
PubMed1993

Interaction of the substance P receptor antagonist RP 67580 with the rat brain NK1 receptor expressed in transfected CHO cells.

In the present study, we describe the effects of RP 67580, a substance P non-peptide antagonist, in binding and second messenger experiments performed using transfected Chinese hamster ovary cells expressing the rat NK1 receptor. The cDNA sequence encoding the rat brain substance P receptor was transfected in Chinese hamster ovary cells, and cellular clones which stably express the corresponding protein were isolated. [3H]Substance P binding was performed in homogenates of these transfected cells and revealed the presence of NK1 receptors in displacement experiments, using peptide analogs of three mammalian tachykinins (substance P, neurokinin A, neurokinin B). Scatchard analysis indicated a KD value of 0.33 +/- 0.13 nM and a Bmax value of 5.83 +/- 1.16 pmol/mg of protein. RP 67580, a selective NK1-receptor antagonist was found to displace the specific binding of [3H]substance P. When [3H]RP 67580 was used as a ligand, it displayed a high affinity (KD value: 1.22 +/- 0.27 nM) in transfected cell homogenates and only competed with NK1 receptor ligands. Substance P stimulated the hydrolysis of phosphoinositide in a time- and concentration-dependent manner and this effect was mimicked by selective agonists of the NK1 receptor ([Pro9]SP and septide). RP 67580 did not induce any accumulation of inositol phosphates, but was found to inhibit the inositol phosphate increase mediated by substance P, without affecting the maximal response. From these results, one may conclude that the receptor expressed by the transfected Chinese hamster ovary cells revealed similar binding characteristics as the NK1 receptor present in the rat brain and also confirmed the high affinity and the antagonist properties of RP 67580.

Animals↗
PubMed1993

A non-peptide NK1-receptor antagonist, RP 67580, inhibits neurogenic inflammation postsynaptically.

1. The non-peptide neurokinin NK1-receptor antagonist, RP 67580 (3aR, 7aR), a perhydroisoindolone derivative, powerfully reduced plasma extravasation in rat hind paw skin induced by local application of xylene (ID50 = 0.03 mg kg-1, i.v.) or capsaicin (ID50 = 0.06 mg kg-1, i.v.), or by i.v. injection of exogenous substance P (SP) or septide ([pGlu6,Pro9]SP(6-11)) (ID50 = 0.04-0.05 mg kg-1, i.v.). RP 67580 (1 mg kg-1, i.v.) also abolished capsaicin-induced nasal fluid hypersecretion (by 82 +/- 5%). These effects were found to be stereospecific, the enantiomer, RP 68651 (3aS, 7aS), being inactive at 1 mg kg-1, i.v. 2. In rats neonatally treated with capsaicin (50 mg kg-1, s.c.), plasma extravasation induced by SP was significantly increased (by 43 +/- 7%). RP 67580 (1 mg kg-1, i.v.) completely inhibited the SP-induced plasma extravasation in capsaicin neonatally treated-animals, as it did in control animals. This result suggests that RP 67580 acts at the postsynaptic level for the inhibition of plasma extravasation. 3. Opioid receptor agonists, mu-(morphine) and kappa-(PD-117302) at 10 mg kg-1, s.c., in contrast to NK1-receptor antagonists, did not inhibit plasma extravasation induced by exogenous SP. They were, however, partially effective against plasma extravasation induced by electrical nerve stimulation (74 +/- 4% and 48 +/- 9% inhibition at 10 mg kg-1, s.c. of morphine and PD-117302, respectively, compared to 90 +/- 3% inhibition obtained with RP 67580, 3 mg kg-1, s.c.). These results indicate the presynaptic action of opioid receptor agonists, in contrast to the postsynaptic action of NK1-receptor antagonists for the inhibition of plasma extravasation.4. Ligature of the saphenous nerve distal to the point of electrical stimulation, local application of lignocaine to the saphenous nerve, neonatal capsaicin pretreatment, and colchicine at very low doses(120 microg kg-1 day-1 given for 3 days) were found to prevent plasma extravasation elicited by electrical nerve stimulation.5. The foregoing results demonstrate that the non-peptide NK1-receptor antagonist, RP67580, is a potent inhibitor of plasma extravasation induced in skin by NK1-receptor agonists, by local application of chemical irritants (capsaicin or xylene) or by electrical nerve stimulation. Moreover, opioid receptor agonists and colchicine inhibit plasma extravasation induced by electrical nerve stimulation but not that elicited by exogenous SP. Therefore, it is possible to inhibit neurogenic inflammation either at the presynaptic level with opioid receptor agonists and colchicine, or at the postsynaptic level withNK1-receptor antagonists, and that the new non-peptide NK1-receptor antagonists may have a great potential for alleviation of inflammation in various pathological syndromes in man.

Animals↗