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R Quirion

Publications and source records attributed to R Quirion.

At least 199 records · Page 11Linked to original sources
PubMed1993

Muscarinic potentiation of excitatory amino acid-evoked dopamine release in mesencephalic cells: specificity for the NMDA response and role of intracellular messengers.

Of the five cloned muscarinic receptor subtypes, dopamine (DA) neurons in the substantia nigra and ventral tegmental areas have been shown to be selectively enriched with the mRNA for the m5 subtype, suggesting that muscarinic modulation of DA neurons may have a distinct pharmacology. In the present study we have used dissociated cell cultures of fetal rat ventral mesencephalon to characterize muscarinic modulation of DA neurons. [3H]DA release stimulated by activation of N-methyl-D-aspartate (NMDA) receptors was potentiated by carbachol, a mixed muscarinic-nicotinic agonist, and by oxotremorine-M, a muscarinic agonist. Neither carbachol nor oxotremorine-M had an effect on [3H]DA release evoked by the non-NMDA agonists, kainate or quisqualate. A nicotinic agonist, DMPP, had no effect on NMDA-stimulated release. Potentiation of NMDA-stimulated [3H]DA release by oxotremorine-M was inhibited by the broad spectrum muscarinic antagonist, QNB, and by low concentrations of a putative M1 antagonist, pirenzepine, while much higher concentrations of a purported M2 antagonist, AF-DX 384, were required to reverse the oxotremorine-M effect. The muscarinic antagonist, 4-DAMP, was active in a concentration range between that required for pirenzepine and AF-DX 384. Further experiments examined intracellular messenger mechanisms coupled to the muscarinic receptors modulating NMDA-stimulated [3H]DA release. In contrast to oxotremorine-M, two muscarinic agents with only weak partial agonism with respect to phosphoinositide turnover, pilocarpine and arecoline, had no effect on NMDA-stimulated [3H]DA release.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaloids↗
PubMed1993

Autoradiographic localization of [125I-Tyr8]-bradykinin receptor binding sites in the guinea pig spinal cord.

The present study aimed to localize and characterize [125I-Tyr8]-BK binding sites in all major segments of the guinea pig spinal cord using in vitro quantitative receptor autoradiography. [125I-Tyr8]-BK specific binding sites were localized predominantly in superficial layers of the dorsal horn, with lamina II depicting the highest labelling. The density of specific binding in laminae I and III was moderate, whereas in other areas, i.e., laminae IV-X, lower amounts of labelling were noticed. The B2 receptor antagonists D-Arg[Hyp3,Thi5,D-Tic7,Oic8]-BK (Hoe 140), D-Arg[Hyp3,D-Phe7,Leu8]-BK, Tyr0,D-Arg[Hyp3,D-Phe7,Leu8]-BK, D-Arg[Tyr3,D-Phe7,Leu8]-BK, D-Arg[Hyp2,Thi5,8,D-Phe7]-BK, D-Arg[Hyp3,Leu8]-BK and D-Arg[Hyp3,Gly6,Leu8]-BK as well as unlabelled [Tyr8]-BK inhibited [125I-Tyr8]-BK binding with respective Ki values of 0.04, 12.4, 23.4, 34.5, 43.5, 33.5, 23.0, and 0.6 nM while B1 related molecules (Tyr0,des-Arg10-kallidin and [Leu8]-des-Arg9-BK) did not significantly inhibit [125I-Tyr8]-BK binding up to micromolar concentrations. These results indicate that the specific [125I-Tyr8]-BK binding sites present in the guinea pig spinal cord belong to the B2 receptor subtype. The high density of B2 binding sites in the substantia gelatinosa provides an anatomical evidence in favour of a role for BK as a modulator of nociceptive information.

Amino Acid Sequence↗
PubMed1993

Therapeutic potential of CNS-active M2 antagonists: novel structures and pharmacology.

Clinical trials with muscarinic agonists or acetylcholine esterase inhibitors for the treatment of Alzheimer's dementia have shown disappointing or equivocal results. An alternative treatment of this disease is the development of drugs which enhance the release of acetylcholine. It is believed, that of the five muscarinic receptor subtypes so far identified in the brain, M2 receptors are located presynaptically in the cortex and hippocampus and upon stimulation inhibit the release of acetylcholine. Based on this hypothesis, we initiated a drug discovery program with the aim of identifying selective and centrally active M2 antagonists which are capable of enhancing cholinergic transmission. These efforts resulted in the successful design and synthesis of novel muscarinic antagonists able to cross the blood brain barrier. Moreover, these compounds show few peripheral effects and possess a superior M2 versus M1 selectivity. The prototype of this novel class of M2 selective compounds, BIBN 99, could be a valuable tool to test the hypothesis that lipophilic M2 antagonists show beneficial effects in the treatment of cognitive disorders.

Animals↗
PubMed1993

Opioid and substance P receptor adaptations in the rat spinal cord following sub-chronic intrathecal treatment with morphine and naloxone.

The effect of continuous intrathecal infusion with morphine (5 mu/h) or naloxone (2 micrograms/h) was investigated with regard to analgesia and the apparent density of mu- and delta-opioid and neurokinin-I/substance P receptors in the rat spinal cord. Morphine infusion increased tail-flick and paw-pressure responses until day 4 after the mini-osmotic pump implant. A decline in antinociception, reflecting tolerance to morphine, was then apparent in both tests. Quantitative in vitro receptor autoradiography of [125I]FK-33824, [125I][D.Ala2]deltorphin-I and [125I] Bolton-Hunter substance P binding sites, as ligands of mu, delta and neurokinin-I/substance P receptors, respectively, was performed on lumbosacral spinal cord sections of seven-days tolerant animals. Treatments with morphine and naloxone induced a similar increase (37%) in the number of delta binding sites in the superficial laminae of the dorsal horn. In contrast, the density of mu-opioid receptors was only affected by naloxone (50% increase). Neurokinin-I/substance P binding parameters were not altered by these treatments. Thus, it appears that delta-opioid binding sites may be of special relevance with regard to the development of tolerance to opiates in the spinal cord.

Analgesics↗
PubMed1993

Entorhinal cortex lesion induces differential responses in [125I]insulin-like growth factor I, [125I]insulin-like growth factor II and [125I]insulin receptor binding sites in the rat hippocampal formation.

The hippocampus can be induced by deafferentation to selectively reorganize its neuronal input. Entorhinal cortex lesion, which causes degeneration of the perforant pathway, evokes sprouting of septal afferents as well as glutamatergic commissural/associational fibers in the deafferentated zone of the molecular layer of the dentate gyrus. Although the process of reactive synaptogenesis that follows deafferentation has been extensively studied, at present little is known about its molecular basis and the mechanism of initiation. In this study, following unilateral lesion of the entorhinal cortex, the time-course of possible alterations of insulin-like growth factors I and II, and insulin binding sites were evaluated by in vitro quantitative receptor autoradiography. [125I]Insulin-like growth factor I receptor binding sites did not exhibit any significant variation between the contralateral and ipsilateral hippocampal formation at any time periods following lesion except in the molecular layer of the dentate gyrus (P < 0.05) at day 8. However, when compared with the unlesioned animals, a differential time-dependent response of [125I]insulin-like growth factor I binding sites was noted in selective layers of the hippocampus. [125I]Insulin-like growth factor II receptor binding sites showed a significant decrease (P < 0.05) in the ipsilateral granular cell layer of the dentate gyrus only at day 14 post lesion. Interestingly, compared to controls, a dramatic bilateral increase (P < 0.05) in [125I]insulin-like growth factor II binding was evident between days 1 and 8 in most layers of the hippocampal formation. A lesion-induced bilateral increase (P < 0.05) in [125I]insulin binding sites was evident in all layers of the hippocampus between two to eight days and at 30 days post lesion. In selective layers, however, a significant increase (P < 0.05) in [125I]insulin binding sites was also observed at days 1 and 14 after lesion. These results, which are compatible with the process of degeneration and/or sprouting of the terminal fibers, suggest possible involvement of insulin-like growth factors and insulin in the sequence of molecular events that occur to facilitate neuronal repair and to promote neuronal survival following entorhinal cortex lesion.

Afferent Pathways↗
PubMed1993

Interleukin-2 modulates evoked release of [3H]dopamine in rat cultured mesencephalic cells.

Mesencephalic cell cultures were used as a model to investigate the effects of interleukin-2 (IL-2) on evoked release of [3H]dopamine ([3H]DA) and gamma-[3H]-aminobutyric acid ([3H]GABA). At low concentrations (10(-13)-10(-12) M), IL-2 potentiated [3H]DA release evoked by the excitatory amino acids N-methyl-D-aspartate (NMDA) and kainate, whereas higher IL-2 concentrations (10(-9)-10(-8) M) had no effect. IL-2 (10(-14)-10(-8) M) modulated K(+)-evoked [3H]DA release in a biphasic manner, with low concentrations (10(-12)-10(-11) M) of IL-2 potentiating and higher concentrations (10(-9)-10(-8) M) inhibiting K(+)-induced [3H]DA release. IL-2 (10(-14)-10(-8) M) by itself failed to alter spontaneous [3H]DA release. The inhibition by IL-2 of K(+)-evoked [3H]DA release was reversible and not due to neurotoxicity, as preexposure to IL-2 (10(-8) M) had no significant effect on the subsequent ability of dopaminergic cells to take up and to release [3H]DA. Under our experimental conditions, IL-2 (10(-8) M) did not alter Ca(2+)-independent [3H]GABA release evoked by either K+ or NMDA. The results of this study indicate that IL-2 is able to potentiate [3H]DA release evoked by a number of different stimuli, including K+ depolarization and activation of both NMDA and non-NMDA receptor subtypes in mesencephalic cell cultures. IL-2 is active at very low concentrations, a finding that indicates a potent effect of IL-2 on dopaminergic neurons and implicates a physiological role for this cytokine in the modulation of DA release.

Animals↗
PubMed1993

Levomepromazine receptor binding profile in human brain--implications for treatment-resistant schizophrenia.

The receptor binding profile of levomepromazine (LMP) in human brain was compared with that of clozapine (CLOZ) and chlorpromazine (CPZ). LMP showed significantly greater binding affinity for both alpha-1 and serotonin-2 binding sites than either CLOZ or CPZ, and significantly greater binding to alpha-2 sites than CPZ. A potent pharmacological effect at these receptor sites may explain the beneficial effect of LMP on psychotic symptoms and akathisia in treatment-resistant schizophrenia recently described in 2 open studies. LMP requires further appraisal as a potentially useful neuroleptic in the management of treatment-resistant schizophrenia.

Adolescent↗
PubMed1993

Cholinergic markers in Alzheimer disease and the autoregulation of acetylcholine release.

The status of various cholinergic markers was compared in Alzheimer's and Parkinson's diseases. Rather unexpectedly, similar decrements were observed in choline acetyltransferase (ChAT) activity and in density of muscarinic M2 and nicotinic receptors in various cortical areas in these two disorders. This may relate to the existence of important functional interactions between cholinergic and dopaminergic systems in cortical and hippocampal areas. Additionally, the parallel decrements in nicotinic and muscarinic M2 receptor subtypes, with that of ChAT activities in these disorders suggest their presynaptic location. A series of pharmacological data do in fact reveal that nicotinic receptors may act as positive autoreceptors modulating basal acetylcholine release while muscarinic M2 receptors could act as negative autoreceptors. This information may have significance for the development of new treatment strategies (for example, M2 antagonists) of disorders associated with cholinergic hypofunction.

Acetylcholine↗
PubMed1993

Modulation of hippocampal acetylcholine release: a potent central action of interleukin-2.

The potential of the T-cell growth factor interleukin-2 (IL-2) to modulate the release of ACh from rat hippocampus was studied in vitro, as a means to investigate the possible functional significance of this cytokine in the CNS. Hippocampal slices were superfused with Krebs' buffer medium, and endogenous ACh released into the superfusate was measured using a radioenzymatic assay. Recombinant human IL-2 present during a stimulation with 25 mM KCl altered, in a concentration-dependent manner, the evoked transmitter release. At a concentration of 15 U/ml (< or = 1 nM), IL-2 inhibited ACh release by more than 50% of the control level (evoked ACh release from the untreated contralateral hemispheres). Inhibition was observed within 20 min of tissue exposure to IL-2 and lasted for up to 1 hr. The inhibitory effect of IL-2 was reversible since transient tissue exposure to IL-2 did not affect subsequent evoked ACh release. IL-2 at this concentration also significantly decreased evoked ACh in frontal cortical slices, but was ineffective in the parietal cortex and striatum, revealing that IL-2 selectively modulates the release of ACh from certain, but not all, cholinergic nerve terminals in the CNS. At very low concentrations (1.5 mU/ml, < or = 0.1 pM), IL-2 transiently increased hippocampal evoked ACh release, resulting in a biphasic dose-response profile with no significant effect observed at 0.015 mU/ml (< or = 1 fM). Other cytokines (IL-1 alpha, IL-3, IL-5, IL-6, interferon alpha), tested in hippocampal slice incubations, failed to modulate ACh release.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

Evidence for in vivo interactions between neuropeptide Y-related peptides and sigma receptors in the mouse hippocampal formation.

Recently, it was proposed that neuropeptide Y (NPY) and peptide YY (PYY) could act as endogenous ligands for sigma binding sites, as both NPY and PYY competed with high affinity (nanomolar) for 3H-(+)SKF 10,047 binding sites in rat brain membrane homogenates (Roman et al., 1989). However, various laboratories failed to replicate these in vitro findings. In order to clarify this apparent discrepancy and investigate further possible interactions between NPY and sigma related sites, we evaluated the effects of NPY, PYY and homologs, as well as nonrelated peptides, on in vivo 3H-(+)SKF 10,047 binding parameters in the mouse hippocampal formation. As expected, haloperidol (2 mg/kg), a prototypical sigma receptor ligand, competed for 90% of in vivo hippocampal labeling observed following a peripheral intravenous injection of 3H-(+)SKF 10,047. Intracerebroventricular injections of 300-3000 pmol of either NPY, PYY, NPY2-36, or the Y1 agonist Leu31,Pro34-NPY inhibited significant proportions (17-35%) of haloperidol-sensitive in vivo 3H-(+)SKF 10,047 hippocampal labeling. However, a Y2 receptor agonist, NPY13-36, and nonrelated peptides such as neurotensin and vasoactive intestinal polypeptide, as well as adrenalin, failed to alter in vivo 3H-(+)SKF 10,047 hippocampal binding. It thus appears that NPY, PYY, and a selective Y1 agonist can interact in a concentration-dependent manner, with in vivo 3H-(+)SKF 10,047 labeling in the mouse hippocampal formation. This effect demonstrates selectivity as a Y2 agonist, unrelated peptides, and adrenalin failed to alter in vivo sigma labeling. This in vivo interaction may be relevant to some of the respective biological actions of NPY and sigma-related molecules.

Animals↗
PubMed1993

Comparative characterization and autoradiographic distribution of neuropeptide Y receptor subtypes in the rat brain.

Some evidence has suggested the existence and differential distribution of neuropeptide Y (NPY) receptor subtypes in the mammalian brain (Dumont et al., 1990; Aicher et al., 1991). We now report on the extensive characterization and visualization of at least two classes of NPY receptor sites using a highly selective Y1 analog, [Leu31,Pro34]-NPY or [Pro34]-NPY, and a relatively specific Y2 competitor, NPY13-36. Autoradiographic studies using 125I-peptide YY (125I-PYY) clearly reveal that the Y1 receptor subtype is most abundant in various cortical areas, the dentate gyrus of the hippocampal formation, the claustrum, and the reuniens nucleus of the thalamus. In most other regions, 125I-PYY binding is potently inhibited by increasing concentrations of either NPY2-36 or NPY13-36, suggesting a Y2-like profile. Furthermore, binding assays using homogenates from discrete brain regions clearly demonstrate that various NPY fragments and analogs compete for 125I-PYY labeling with profiles indicative of heterogeneity of NPY receptor subtypes, even in the presence of a selective Y1 blocker. Thus, it is likely that, in addition to the Y1 receptor, which is particularly concentrated in cortical areas, the rat brain is enriched with a receptor class (Y2) that can exist under high- or low-affinity states or with additional receptor subtypes that are recognized by 125I-PYY. These findings cannot be explained by the existence of the very recently reported Y3 receptor subtype, since PYY does not possess significant affinity to this site (Grundemar et al., 1991). Further experiments are currently in progress to determine the nature and functional significance of each of these NPY/PYY receptor sites.

Animals↗
PubMed1992

Effects of L- and N-type Ca2+ channel antagonists on excitatory amino acid-evoked dopamine release.

In the present study we tested the effect of dihydropyridine (DHP) Ca2+ channel antagonists and of omega-conotoxin GVIA on [3H]dopamine (DA) release evoked by the activation of excitatory amino acid (EAA) receptors in cultures of fetal rat ventral mesencephalon, in order to investigate the role of voltage-sensitive L- and N-type Ca2+ channels in these EAA-mediated processes. Micromolar concentrations (10-30 microM) of DHP L-type Ca2+ channel antagonists inhibited [3H]DA release evoked by N-methyl-D-aspartate (NMDA), kainate, quisqualate or veratridine. [3H]DA release evoked by the L-type Ca2+ channel agonist, Bay K 8644, was inhibited by lower concentrations (0.1-1 microM) of the DHP antagonist, nitrendipine, than was the release evoked by EAAs. The DHP antagonist, (+)-PN 200-110, was more potent than (-)-PN 200-110 in inhibiting [3H]DA release evoked by Bay K 8644, but the two stereoisomers were equipotent in inhibiting NMDA-evoked release. These results indicate that activation of L-type Ca2+ channels is able to evoke [3H]DA release. However activation of L-type channels is not involved in EAA-induced [3H]DA release and therefore inhibition of EAA-induced [3H]DA release by micromolar concentrations of DHPs must be mediated by actions other than inhibition of L-type Ca2+ channels. omega-Conotoxin GVIA (3 microM) had no effect on [3H]DA release evoked by Bay K 8644, indicating that the toxin may selectively inhibit N-type channels in this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1992

Further evidence for differential affinity states of the serotonin1A receptor in rat hippocampus.

The binding profile of [3H]8-hydroxy-2-(di-N-propylamino)-tetralin ([3H]8-OH-DPAT) to serotonin1A (5-HT1A) sites in rat hippocampal, frontocortical and striatal membranes has been compared. In these regions, [3H]8-OH-DPAT labels both a high and a low-affinity binding site; the affinity values for each of the two sites are comparable in the different brain regions, but have different maximal capacity. By modifying the experimental conditions in a series of hippocampal membrane preparations, reciprocal changes in the proportion of the two sites were observed suggesting that they represent, at least in this region, different conformations or affinity states of a single receptor protein. In contrast to the lower affinity state, it appears that the high-affinity state is stabilized by coupling with a G-protein. Evidence supporting this statement is provided by addition of the guanine nucleotide Gpp(NH)p, breakage of labile disulfide bonds using N-ethylmaleimide and increasing membrane rigidity with ascorbate-induced lipid peroxidation, conditions which all reduced the density of receptors in the high-affinity state. Moreover, the high-affinity state appears to be stabilized at the expense of the lower affinity state in the presence of Mn2+. On the other hand, a complete shift to the low-affinity binding state was observed after a 24 h in vivo treatment with inhibitors of monoamine oxidase A (phenelzine or clorgyline) but not of monoamine oxidase B (deprenyl). This disappearance of the high-affinity state with a concomitant increase in the binding capacity of the low-affinity state was reproduced by inhibiting monoamine oxidase A in vitro, as well as by reducing preincubation washout periods. Also, competitors of the [3H]8-OH-DPAT binding site, such as serotonin and unlabelled 8-OH-DPAT, display two affinity states while others like (+/-)-propranolol, tryptamine and spiperone recognize a single affinity component. These results suggest that the 5-HT1A binding site may exhibit at least two different affinity states depending upon its microenvironment and the intrinsic activity of the ligand used.

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

Quantitative autoradiographic distribution of calcitonin gene-related peptide (hCGRP alpha) binding sites in the rat and monkey spinal cord.

Calcitonin gene-related peptide (CGRP) has been implicated in various spinal functions on the basis of its presence in the substantia gelatinosa and motoneurons and the biological effects induced by intrathecal CGRP injections. We investigated here the comparative distribution of [125I]hCGRP alpha binding sites in various segments of the rat and monkey spinal cord. The immunocytochemical localization of CGRP-like material in rat spinal cord was also evaluated for comparison. In the rat spinal cord, high densities of [125I]hCGRP alpha binding sites were observed in lamina I, in a U-shaped band that included lamina X and the medial parts of laminae III-IV and in the intermediolateral and intermediomedial nuclei. The substantia gelatinosa (lamina II) contained relatively lower, but still significant, densities of [125I]hCGRP alpha binding sites, while the ventral horn showed low amounts of specific labeling. CGRP-like immunoreactive fibers, on the other hand, were heavily concentrated in laminae I-II and in the reticulated portion of lamina V of the dorsal horn. Immunoreactivity to CGRP antiserum was also noted in fibers around the central canal and in a number of motoneurons of the ventral horn. In the monkey spinal cord, [125I]hCGRP alpha binding sites were present in lamina I in a U-shaped band that included lamina X and the medial portions of laminae V-VI. Relatively low levels of [125I]hCGRP alpha binding were detected in laminae II to IV of the dorsal horn, while the ventral horn was more enriched with specific [125I]hCGRP alpha binding sites. Thus, it appears that the autoradiographic distribution of [125I]hCGRP alpha sites is species dependent in the spinal cord. Additionally, some differences are observed between the localization of [125I]hCGRP alpha binding sites and immunoreactive material in the rat spinal cord. These differences may be relevant to the purported roles of CGRP-like peptides in spinal functions such as nociception, control of sympathetic output, and motor control.

Animals↗
PubMed1992

Characterization and autoradiographic distribution of [3H]AF-DX 384 binding to putative muscarinic M2 receptors in the rat brain.

The novel radioligand [3H]AF-DX 384 binds specifically and saturably to putative muscarinic M2 receptor sites in homogenates of rat cerebral cortex. In saturation studies, [3H]AF-DX 384 appears to bind to two subpopulations of sites/states, one of high affinity (Kd1 = 0.28 +/- 0.08 nM) and another of low affinity (Kd2 = 28.0 +/- 5.0 nM). The maximal binding capacity (Bmax) of [3H]AF-DX 384 binding sites represented 9.7 +/- 2.3 fmol/mg protein (Bmax1) and 1993 +/- 551 fmol/mg protein (Bmax2) for the high and low affinity sites/states, respectively. The ligand selectivity profile of [3H]AF-DX 384 (at 2 nM) revealed that (-)-quinuclidinyl benzylate = atropine greater than 4-diphenylacetoxy-N-methylpiperidine methobromide greater than AQ-RA 741 greater than AF-DX 384 greater than UH-AH 371 much greater than methoctramine greater than oxotremorine-M greater than hexahydro-sila-defenidol much greater than pirenzepine greater than carbamylcholine much much greater than nicotine. This suggests that under our assay conditions [3H]AF-DX 384 binds mostly to M2-like muscarinic receptors in the rat central nervous system. This is further supported by the clear M2-like pattern of distribution observed using quantitative receptor autoradiography. High densities of specific labelling were seen in areas such as the hypoglossal nucleus, the pontine nucleus, the superior colliculus, the motor trigeminal nucleus, various thalamic nuclei and certain cortical laminae. Compared to [3H]AF-DX 116, the percentage of specific binding detected with [3H]AF-DX 384 was much higher. This is likely to be related to the greater chemical stability and affinity of [3H]AF-EX 384. In addition, autoradiograms obtained with [3H]AF-DX 384 (2 nM) are of better quality with film exposure periods five shorter than those needed for [3H]AF-DX 116 (10 nM). Therefore, [3H]AF-DX 384 displays a good selectivity for muscarinic M2 sites and offers major advantages, including higher affinity and greater stability, over previously used ligands.

Animals↗