Biomedical subjects

G Le Fur

Publications and source records attributed to G Le Fur.

At least 37 records · Page 2Linked to original sources

PubMed1999

Stimulation of peripheral cannabinoid receptor CB2 induces MCP-1 and IL-8 gene expression in human promyelocytic cell line HL60.

Using the recently developed methodology of nucleic acid microarrays spotted with specific cDNAs probes belonging to different gene families, we showed for the first time that nanomolar concentrations of the cannabinoid ligand CP-55940 upregulated the expression of two different members of the chemokine gene family: the alpha-chemokine interleukin-8 (IL-8) and the beta-chemokine monocyte chemotactic protein-1 (MCP-1), in the promyelocytic cell line HL60 transfected with peripheral cannabinoid receptors (CB2). These genomic modulations observed on large-scale cDNA arrays were first confirmed by Northern blot studies. Furthermore, ELISA evaluations in culture supernatants indicated that the cannabinoid-induced activation of these two chemokine genes was followed by enhanced expression and secretion of the corresponding proteins. These upregulations initially observed in transfected HL60 cells overexpressing CB2 receptors, also occurred in normal non-transfected HL60 cells. The enhancement of IL-8 and MCP-1 gene transcription and protein production was shown to be pertussis toxin sensitive attesting that this phenomenon was a Gi protein-coupled receptor-mediated process as expected for cannabinoid receptors. More specifically, the abolition of the cannabinoid-induced effect by the specific CB2 antagonist SR 144528 indicated a strict peripheral cannabinoid-mediated process. Altogether, our data highlight a possible new function of peripheral cannabinoid receptors in the modulation of immune and inflammatory responses.

Analgesics↗

PubMed1999

Cloning and characterization of PRAX-1. A new protein that specifically interacts with the peripheral benzodiazepine receptor.

Using a cytoplasmic domain of the peripheral benzodiazepine receptor (PBR) as a bait in the yeast two-hybrid system, we have isolated a cDNA encoding a new protein that specifically interacts with PBR. We named it PRAX-1, for peripheral benzodiazepine receptor-associated protein 1. PRAX-1 is a 1857-amino acid protein, the sequence of which was structurally unrelated to any known proteins. The gene encoding PRAX-1 is located in the q22-q23 region of the long arm of the human chromosome 17. The PRAX-1 mRNA is 7.5 kilobase pairs, predominantly expressed in the central nervous system, pituitary gland, and thymus. At the protein level, we found the PRAX-1 as a single 220-250-kDa protein in the brain and in many different human cell lines tested using specific antibody raised against PRAX-1. Parallel analysis of the PRAX-1 mRNA and protein expression performed in mouse and rat gave similar results. Immunocytochemistry analysis carried out to define the distribution of the PRAX-1 protein in the rat brain showed that PRAX-1 was prevalent in the mesolimbic system, specially abundant in the CA1 subfield of the hippocampus. Exhibiting several domains involved in protein-protein interaction (three proline-rich domains, three leucine-zipper motifs, and an Src homology region 3-like domain), the PRAX-1 may be looked upon as a new adaptator protein. We show that both the Src homology region 3-like domain and a proline-rich domain in PRAX-1 are required for the interaction with PBR. PRAX-1 is a cytoplasmic protein that also partially colocalizes with PBR in the mitochondria, as determined by confocal microscopy and Western blotting. Altogether our observations support a model of interaction implicating PBR and this newly described protein, PRAX-1. As being the first cytoplasmic protein associated with PBR, PRAX-1 is a new tool that opens new fields for exploring PBR biological roles.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Blockade of neurokinin3 receptors antagonizes drug-induced population response and depolarization block of midbrain dopamine neurons in guinea pigs.

In vivo extracellular recording techniques were used to investigate the effects of neurokinin3 (NK3) receptor blockade on the pharmacological activation of midbrain dopamine (DA) neurons in the guinea pig substantia nigra (A9) and ventral tegmental area (A10). The number of spontaneously active DA cells (population response) was largely increased in A10 and A9 by acute administration of haloperidol (1 and 0.5 mg/kg i.p., respectively) and this effect was dose-dependently prevented in both areas by the selective NK3 receptor antagonist SR142801 (0.3, 1, 3, and 1, 3, 10 mg/kg i.p., respectively). This compound, which was totally inactive by itself, also antagonized the increase of population response induced in A10 cells by the neurotensin receptor antagonist SR142948 (1 mg/kg i.p.) and in A9 cells by the NK2 receptor antagonist SR144190 (1 mg/kg i.p.). None of the effects of SR142801 were reproduced by SR142806, its (R)-enantiomer with 240-fold lower affinity for NK3 receptors. In addition, neither SR144190 (0.3 mg/kg i.p.) nor the NK1 receptor antagonist GR205171 (1 mg/kg i.p.) affected the haloperidol-induced response. The antagonistic effects of SR142801 (3 mg/kg i.p.) were also observed on the depolarization block-related decrease of A10 cell population response evoked by repeated administration (22 days) of haloperidol. Finally, SR142801 (3 mg/kg i.p.) prevented depolarization block induced in A10 cells by acute co-administration of SR142948 and haloperidol, both on population response and on single cell firing. These results on pharmacologically induced activation and depolarization block of dopamine neurons suggest that NK3 receptors play a key role in the midbrain DA function, presumably through activation by neurokinin B.

Animals↗

PubMed1999

Blockade of cannabinoid (CB1) receptors by 141716 selectively antagonizes drug-induced reinstatement of exploratory behaviour in gerbils.

RATIONALE: A cannabinoid hypothesis of schizophrenia has been proposed according to which cognitive dysfunction could be associated with dysregulation of an endogenous cannabinoid system. OBJECTIVE: The present study investigated whether SR 141716, a selective CB1 receptor antagonist, was able to reduce the hyperactivity induced in gerbils by various stimulant drugs known to produce or exacerbate schizophrenic symptoms. METHODS: Cocaine, d-amphetamine, morphine, and Win 55212-2 were administered intraperitoneally (IP) either immediately before placing the animals in the test apparatus (non-habituated gerbils) or after a 2- to 3-h habituation period in the actimeter (habituated gerbils). SR 141716 was given IP 30 min before the injection of stimulant drugs. Horizontal activity was recorded every 10 min for 1 h in Digiscan activity monitor. RESULTS: SR 141716 (0.3-3 mg/kg) dose-dependently suppressed the enhanced locomotor activity induced by each stimulant drug in habituated gerbils, but not in non-habituated animals. Clozapine, an atypical antipsychotic compound, but not haloperidol, shared with SR 141716, the ability to differentially affect drug-induced hyperactivity in habituated versus non-habituated gerbils. CONCLUSION: The activation of cannabinoid systems is a required, permissive element in the ability of cocaine, d-amphetamine, morphine, and Win 55212-2 to reinstate behaviour, i.e., to override stimulus satiation.

Animals↗

PubMed1999

Blockade of cannabinoid receptors by SR141716 selectively increases Fos expression in rat mesocorticolimbic areas via reduced dopamine D2 function.

The present study investigated, in rats, whether blockade of cannabinoid CB1 receptors may alter Fos protein expression in a manner comparable to that observed with antipsychotic drugs. Intraperitoneal administration of the selective CB1 receptor antagonist, SR141716, dose-dependently (1.0, 3.0 and 10 mg/kg) increased Fos-like immunoreactivity in mesocorticolimbic areas (prefrontal cortex, ventrolateral septum, shell of the nucleus accumbens and dorsomedial caudate-putamen), while motor-related structures such as the core of the nucleus accumbens and the dorsolateral caudate-putamen were unaffected. In the ventrolateral septum, taken as a representative structure, the Fos-inducing effect of SR141716 (10 mg/kg) was maximal 2 h after injection and returned to near control levels by 4 h. Within the prefrontal cortex, SR141716 increased the number of Fos-positive cells predominantly in the infralimbic and prelimbic cortices, presumptive pyramidal cells being the major cell types in which Fos was induced. The D1-like receptor antagonist, SCH23390 (0.1 mg/kg), did not prevent the Fos-inducing effect of SR141716 in any brain region examined (prefrontal cortex, nucleus accumbens, ventrolateral septum and dorsomedial caudate-putamen), although SCH23390 significantly reduced Fos expression induced by cocaine (20 mg/kg) in all these regions. By contrast, the dopamine D2-like agonist, quinpirole (0.25 mg/ kg), counteracted SR141716-induced Fos-like immunoreactivity in the ventrolateral septum, the nucleus accumbens and the dorsomedial caudate-putamen, while no antagonism was observed in the prefrontal cortex. Microdialysis experiments in awake rats indicated that SR141716, at doses which increased Fos expression (3 and 10 mg/kg), did not alter dopamine release in the shell of the nucleus accumbens. Finally, SR141716 increased the levels of neurotensin-like immunoreactivity in the nucleus accumbens, but not in the caudate-putamen. Collectively, the present results show that blockade of cannabinoid receptors increases Fos- and neurotensin-like immunoreactivity with characteristics comparable to those reported for atypical neuroleptic drugs.

Animals↗

PubMed1999

Effect of the neuroprotective compound SR57746A on nerve growth factor synthesis in cultured astrocytes from neonatal rat cortex.

The neurotrophic factor promoting activity of the neuroprotective compound SR57746A was evaluated in primary cultures of neonatal rat cortical astrocytes by studying the synthesis of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). A concentration- and time-dependent increase of nerve growth factor mRNA was induced by SR57746A (10 nM-1 microM). In these astrocytes, BDNF mRNA contents were increased to a significant but smaller extent, and beta-actin mRNA showed no variation. SR57746A (1 microM) induced increases of both de novo protein translation after 6 h of incubation and NGF release into the extracellular medium after 6-24 h. These effects were preceded by a transient augmentation of junB, c-fos and c-jun mRNA contents. These increases of AP-1 family mRNA were associated with increased nuclear AP-1 binding activity. The results show that SR57746A can increase the synthesis and release of NGF in rat cortical astrocytes. Such effects may contribute to the drug's previously described neuroprotective effects.

Animals↗

PubMed1999

Blockade of neurotensin receptors suppresses the dopamine D1/D2 synergism on immediate early gene expression in the rat brain.

A remarkable feature of dopamine functioning is that the concomitant activation of D1-like and D2-like receptors acts to intensify the expression of various dopamine-dependent effects, in particular the expression of the immediate-early genes, c-fos and zif268. Using non-peptide neurotensin receptor antagonists, including SR48692, we have determined that blockade of neurotensin receptors reduced the cooperative responses of direct acting D2-like (quinpirole) and partial D1-like (SKF38393) dopamine agonists on the expression of Fos-like antigens and zif268 mRNA. Pretreatment with SR48692 (3 and 10 mg/kg) reduced the number of Fos-like immunoreactive cells produced by the combined administration of SKF38393 (20 mg/kg) and quinpirole (1 mg/kg) in the caudate-putamen, nucleus accumbens, globus pallidus and ventral pallidum. High-affinity neurotensin receptors are likely to be involved in these D1-like/D2-like cooperative responses, as compounds structurally related to SR48692, SR48527 (3 mg/kg) and its (-)antipode, SR49711 (3 mg/kg), exerted a stereospecific antagonism in all selected brain regions. Pretreatment with SR48692 (10 mg/kg) also diminished Fos induction by the indirect dopamine agonist, cocaine (25 mg/kg), particularly at the rostral level of the caudate-putamen. In situ hybridization experiments in the caudate-putamen indicated that SR48692 (10 mg/kg) markedly reduced zif268 mRNA labelling produced by SKF38393 plus quinpirole in cells not expressing enkephalin mRNA, but was unable to affect the concomitant decrease of zif268 mRNA labelling in enkephalin-positive cells. Taken together, the results of the present study indicate that neurotensin is a key element for the occurrence of cooperative responses of D2-like and partial D1-like agonists on immediate-early gene expression.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1999

SR146131: a new potent, orally active, and selective nonpeptide cholecystokinin subtype 1 receptor agonist. I. In vitro studies.

SR146131 inhibited the binding of [125I]-Bolton Hunter (BH)-sulfated cholecystokinin octapeptide (CCK-8S) for the human recombinant cholecystokinin subtype 1 (CCK1) receptor (IC50 = 0.56 nM) with high (300-fold) selectivity to the CCK2 receptor. The biological activity of SR146131 was characterized in vitro in a NIH-3T3 cell line expressing the human recombinant CCK1 receptor (3T3-hCCK1). Measuring intracellular calcium release, SR146131 behaved as a full agonist with an efficacy comparable with that of CCK-8S (EC50 = 1.38 +/- 0.06 nM). On individual cells, SR146131 induced, like CCK-8S, Ca2+ oscillations at subnanomolar concentrations and sustained responses at higher concentrations. Like CCK-8S, SR146131 also fully stimulated inositol monophosphate formation (EC50 = 18 +/- 4 nM). SR146131 partially activated mitogen-activated protein kinase and enhanced the expression of the immediate early gene krox 24. In the human CHP212 and IMR32 neuroblastoma cell lines, which constitutively express the CCK1 receptor, SR146131 behaved as a partial agonist on intracellular calcium release and inositol monophosphate formation. All of these effects of SR146131 were inhibited by the CCK1 receptor antagonists SR27897B and devazepide, suggesting that the effects of SR146131 were entirely mediated by the CCK1 receptor. In contrast, high concentrations (>1 microM) of SR146131 had only minimal effects on CCK-8S-stimulated and unstimulated Chinese hamster ovary (CHO) cells expressing the human CCK2 receptor, indicating that SR146131 is functionally inactive on the CCK2 receptor. In conclusion, these in vitro experiments show that SR146131 is a highly potent and selective agonist of the CCK1 receptor.

3T3 Cells↗

PubMed1999

SR146131: a new potent, orally active, and selective nonpeptide cholecystokinin subtype 1 receptor agonist. II. In vivo pharmacological characterization.

SR146131 is a potent and selective agonist at cholecystokinin subtype 1 (CCK1) receptors in vitro. The present study evaluates the activity of the compound in vivo. SR146131 completely inhibited gastric and gallbladder emptying in mice (ED50 of 66 and 2.7 micrograms/kg p.o., respectively). SR146131 dose dependently reduced food intake in fasted rats (from 0.1 mg/kg p.o.), in nonfasted rats in which food intake had been highly stimulated by the administration of neuropeptide Y (1-36) (from 0.3 mg/kg p.o.), in fasted gerbils (from 0.1 mg/kg p.o.), and in marmosets maintained on a restricted diet (from 3 mg/kg p.o.). SR146131 (10 mg/kg p.o.) also increased the number of Fos-positive cells in the hypothalamic paraventricular nucleus of rats. Locomotor activity of mice was reduced by orally administered SR146131 (from 0.3 mg/kg p.o.). When administered intrastriatally, SR146131 elicited contralateral turning behavior in mice. Furthermore, orally administered SR146131 (0.3-10 mg/kg), also reduced the levels of cerebellar cyclic GMP. Finally, SR146131 (0.1 microgram/kg to 1 mg/kg, p.o.) significantly and dose dependently antagonized fluphenazine-induced mouth movements in rats. The CCK1 antagonist SR27897B prevented all the effects of SR146131. Conversely, SR146131 was unable to elicit any agonist or antagonist effects in a model of CCK2 receptor stimulation in vivo. SR146131 is a very potent and selective nonpeptide CCK1 agonist in vivo. SR146131 is more potent than any other CCK1 agonists reported to date. Because pharmacodynamic studies suggest that SR146131 should have a high absolute bioavailability, it may be a promising drug for the treatment of eating and motor disorders in humans.

Animals↗

PubMed1998

Neurotensin is an antagonist of the human neurotensin NT2 receptor expressed in Chinese hamster ovary cells.

The human levocabastine-sensitive neurotensin NT2 receptor was cloned from a cortex cDNA library and stably expressed in Chinese hamster ovary (CHO) cells in order to study its binding and signalling characteristics. The receptor binds neurotensin as well as several other ligands already described for neurotensin NT1 receptor. It also binds levocabastine, a histamine H1 receptor antagonist that is not recognised by neurotensin NT1 receptor. Neurotensin binding to recombinant neurotensin NT2 receptor expressed in CHO cells does not elicit a biological response as determined by second messenger measurements. Levocabastine, and the peptides neuromedin N and xenin were also ineffective on neurotensin NT2 receptor activation. Experiments with the neurotensin NT1 receptor antagonists SR48692 and SR142948A, resulted in the unanticipated discovery that both molecules are potent agonists on neurotensin NT2 receptor. Both compounds, following binding to neurotensin NT2 receptor, enhance inositol phosphates (IP) formation with a subsequent [Ca2+]i mobilisation; induce arachidonic acid release; and stimulate mitogen-activated protein kinase (MAPK) activity. Interestingly, these activities are antagonised by neurotensin and levocabastine in a concentration-dependent manner. These activities suggest that the human neurotensin NT2 receptor may be of physiological importance and that a natural agonist for the receptor may exist.

Amino Acid Sequence↗

PubMed1998

Stimulation by neurotensin of (3H)5-hydroxytryptamine (5HT) release from rat frontal cortex slices.

The effect of neurotensin (NT) on the K+-evoked (3H)5HT release from brain frontal cortex slices was studied in rats. NT(1-13) and NT(8-13) increased (3H)5HT release with EC50 values in the nanomolar range and Emax values in the range of 100% of control, whereas D-tyr11-NT was inactive. Concerning NT receptor antagonists, SR 48692 and SR 142948A antagonized with IC50 values of 4.8+/-1.8 nM and 4.5+/-1.8 nM respectively, the NT stimulated K+-evoked (3H)5HT release. SR 48527 also antagonized NT induced (3H)5HT release with an IC50 value of 0.95+/-0.06 nM whereas the inactive R(-) enantiomer SR 49711 only inhibited this effect with IC50 value close to 10(-6)M. The 5HT-releasing effect of NT was completely inhibited by tetrodotoxin suggesting that NT receptors involved in the control of 5-HT release are not located on 5-HT terminals. After a first NT (10(-7)M) application, the NT (10(-7)M, 10(-6)M) effect under K+ depolarization was drastically decreased, indicating that the NT receptor could be desensitized. No potentiating effect of NT on K+-evoked (3H)5HT release was observed in striatal and hippocampal slices. These results suggest that, in the rat frontal cortex, NT regulates 5HT release through a high affinity NT receptor not associated with 5HT terminals.

Adamantane↗

PubMed1998

Activation of dopaminergic and cholinergic neurotransmission by tachykinin NK3 receptor stimulation: an in vivo microdialysis approach in guinea pig.

The regulation of dopaminergic and cholinergic function by neurokinin-3 (NK3) receptor activation was examined in vivo in urethane-anaesthetized guinea pigs with microdialysis probes. The local application of the NK3 tachykinin receptor agonist senktide in the region of dopamine cell bodies (pars compacta of the substantia nigra and ventral tegmental area) and in the area of cholinergic cell bodies (septal area) markedly enhanced the extracellular dopamine (DA) and acetylcholine (ACh) concentration throughout their respective target areas, i.e. striatum, nucleus accumbens, prefrontal cortex for dopaminergic systems and hippocampus for cholinergic neurons. The enhancing effect of senktide on neurotransmitter release was dose dependently blocked by the selective non-peptide NK3 receptor antagonist SR142801 (0.1-1 mg/kg, i.p.), whereas its inactive S-enantiomer SR142806 (0.3-1 mg/kg, i.p.) did not exert any antagonistic activity on the effect of intranigral or intraseptal application of senktide. These results demonstrate that NK3 receptors can modulate the activity of central DA and ACh systems.

Acetylcholine↗

PubMed1998

Facilitation of striatal acetylcholine release by dopamine D1 receptor stimulation: involvement of enhanced nitric oxide production via neurokinin-2 receptor activation.

The regulation of striatal cholinergic function by dopamine D1 receptor activation was examined in vivo in urethane-anaesthetized rats with microdialysis probes. Extracellular acetylcholine levels were enhanced by activation of D1 receptors either directly by a striatal application of the D1 receptor agonist (+)-SKF-38393 (3 microM) or indirectly by the release of dopamine evoked by striatal application of neurotensin (0.1 microM) under D2 receptor blockade. SR 144190, a new potent and selective non-peptide neurokinin-2 receptor antagonist (0.03-1 mg/kg, i.p.), dose-dependently reduced the acetylcholine release induced by (+)-SKF-38393 or neurotensin. Furthermore, intrastriatal application of SR 144190 (1 nM) blocked the increase in acetylcholine release induced by the local application of (+)-SKF-38393 (3 microM), neurokinin A (1 microM) or substance P (1 microM). Finally, a role for nitric oxide in mediating the effects of D1 neurokinin-2 receptor activation on acetylcholine release is proposed since local infusion of the competitive inhibitor of nitric oxide synthase, N(G)-monomethyl-L-arginine (0.01-10 microM), blocked the increase in acetylcholine release induced by (+)-SKF-38393 (3 microM), neurotensin (0.1 microM) or neurokinin A (1 microM) without affecting the enhancing effect of the neurokinin-1 agonist septide (0.1 microM).

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1998

Electrophysiological evidence for putative subtypes of neurotensin receptors in guinea-pig mesencephalic dopaminergic neurons.

Electrophysiologically identified mesencephalic dopaminergic neurons were examined by means of extra- and intracellular microelectrodes in coronal slices of guinea-pig brain. Neurotensin and its C-terminal fragment (8-13) were equipotent in the enhancement of spontaneous neuronal firing rate (EC50 values 81.9 and 72.6nM, respectively). The duration of response was significantly longer and more variable for neurotensin compared to neurotensin fragment (8-13) (mean half-time of recovery 423+/-44 and 100+/-14 s, respectively, for peptides applied at 300 nM). The initial fast phase of excitatory responses to neurotensin receptor agonists was associated with membrane depolarization (when assessed in current-clamp mode) or with inward currents (when assessed in voltage-clamp mode), whereas prolonged excitation was associated with a slowly occurring and long-lasting change in the late afterhyperpolarization. Two kinetically distinct components were revealed in responses to neurotensin and neurotensin fragment (8-13) by the use of SR48692 and SR142948, two selective non-peptide neurotensin receptor antagonists. SR142948 (100 nM) potently antagonized responses to both agonists [response was reduced by 661 5% and 74+/-9% for neurotensin and neurotensin fragment (8-13), respectively] and caused a rightward shift in the concentration-response curve for neurotensin. On the other hand, SR48692 (100 nM) selectively inhibited the slow (late afterhyperpolarization-dependent) component, without altering the response amplitude; the half-time of recovery was reduced by 71+/-6% and 65+/-5% of control values for responses induced by neurotensin (300 nM) and neurotensin fragment (8-13) (300 nM), respectively. In addition, neurotensin, but not neurotensin fragment (8-13), provoked SR48692-sensitive and long-lasting attenuation of dopamine-induced inhibitory responses. It is suggested that two subtypes of neurotensin receptors are present in dopaminergic neurons, based on the differences in agonist and antagonist sensitivity, kinetic properties and the membrane mechanisms involved.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1998

In vitro characterization of tachykinin NK2-receptors modulating motor responses of human colonic muscle strips.

1. Human in vitro preparations of transverse or distal colonic circular smooth muscle were potently and dose-dependently contracted by neurokinin A (EC50, 4.9 nM), the tachykinin NK2-receptor selective agonist [beta-Ala8]neurokinin A (4-10) ([beta-Ala8]NKA (4-10)) (EC50, 5.0 nM), neurokinin B (EC50, 5.3 nM) and substance P (EC50, 160 nM), but not by the tachykinin NK1-receptor selective agonist [Sar9Met(O2)11] substance P, or the NK3-receptor selective agonists, senktide and [MePhe7] neurokinin B. No regional differences between transverse and distal colon were observed in response to [beta-Ala8]NKA (4-10). 2. Atropine (1 microM) and tetrodotoxin (1 microM) did not significantly inhibit responses to [beta-Ala8]NKA (4-10), neurokinin A, substance P or neurokinin B. 3. The newly developed non-peptide antagonists for tachykinin NK2-receptors SR 48968, SR 144190 and its N-demethyl (SR 144743) and N,N-demethyl (SR 144782) metabolites, were used to challenge agonist responses, as appropriate. SR 144190 and the metabolites all potently and competitively antagonized the response to [beta-Ala8]NKA (4-10), with similar potency (Schild plot pA2 values 9.4, 9.4 and 9.3, slope = 1). SR 48968 antagonism was not competitive: the Schild plot slope was biphasic with a high (X intercept approximately 9.3) and a low (X intercept 8.4, slope 1.6) affinity site. Co-incubation of SR 48968 (10, 100 nM) and SR 144782 (10 nM) produced additive effects; in this experimental condition, SR 48968 apparent affinity (pKB) was 8.2. In addition, SR 144782 (0.1 microM) antagonized responses to neurokinin A, substance P and neurokinin B, with pKB consistent with its affinity for tachykinin NK2-receptors. The potent and selective NK1 and NK3-receptor antagonists, SR 140333 and SR 142801 (both 0.1 microM), failed to inhibit contractions induced by SP or NKB. 4. In conclusion, the in vitro mechanical responses of circular smooth muscle preparations from human colon are strongly consistent with the presence of non-neuronal tachykinin NK2-receptors, but not tachykinin NK1- or NK3-receptors. Our findings with SR 48968 suggest the existence of two tachykinin NK2-receptor subtypes, that it seems to distinguish, unlike SR 144190 and its metabolites. However, the precise nature of SR 48968 allotopic antagonism remains to be elucidated, since allosteric effects at the tachykinin NK2-receptor might well account for the complexity of the observed interaction.

Aged↗

PubMed1998

In vitro functional evidence of neuronal cannabinoid CB1 receptors in human ileum.

We investigated the effect of the cannabinoid agonist (+)WIN-55212-2 on human ileum longitudinal smooth muscle preparations, either electrically stimulated or contracted by carbachol. Electrical field stimulation mostly activated cholinergic neurons, since atropine and tetrodotoxin (TTX), alone or coincubated, reduced twitch responses to a similar degree (85%). (+)WIN-55212-2 concentration-dependently inhibited twitch responses (IC50 73 nM), but had no additive effect with atropine or TTX. The cannabinoid CB1 receptor antagonist SR 141716 (pA2 8.2), but not the CB2 receptor antagonist, SR 144528, competitively antagonized twitch inhibition by (+)WIN-55212-2. Atropine but not (+)WIN-55212-2 or TTX prevented carbachol-induced tonic contraction. These results provide functional evidence of the existence of prejunctional cannabinoid CB1-receptors in the human ileum longitudinal smooth muscle. Agonist activation of these receptors prevents responses to electrical field stimulation, presumably by inhibiting acetylcholine release. SR 141716 is a potent and competitive antagonist of cannabinoid CB1 receptors naturally expressed in the human gut.

Adult↗

PubMed1998

Expression and presence of septal neurokinin-2 receptors controlling hippocampal acetylcholine release during sensory stimulation in rat.

We examined the expression and presence of NK2 receptors in the septal area of rat brain, and investigated their functional role in the regulation of the septohippocampal cholinergic system. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, we showed the presence of NK2 receptor mRNA expression in the septal area, and detected septal NK2 binding sites by using a fluorescent-tagged neurokinin A (NKA) derivative. In vivo microdialysis was employed to explore the functional role of NK2 receptors in the release of hippocampal acetylcholine evoked by tactile stimulation in freely moving rats. Two sessions of stroking of the neck and back of the rat for 30 min, at 90 min intervals, produced a marked and reproducible increase in hippocampal acetylcholine release. This effect was dose-dependently prevented by intraperitoneal administration of the two selective non-peptide tachykinin NK2 receptor antagonists SR144190 (0.03-0.3 mg/kg, i.p.) and SR48968 (0.3 and 1 mg/kg, i.p.), but not by the inactive enantiomer of SR48968 (SR48965, 1 mg/kg) nor by the two non-peptide NK1 receptor antagonists SR140333 (3 mg/kg, i.p.) and GR205171 (1 mg/kg, i.p.). Furthermore, the intraseptal application of SR144190 (10(-8) M) reduced the sensory response. Finally, intraseptal perfusion of neurokinin A (0.01-10 microM) in anaesthetized rats produced a concentration-dependent increase in hippocampal acetylcholine release. The response to neurokinin A (0.1 microM) was prevented by SR144190 (0.03-0.3 mg/kg, i.p.) and SR48968 (0.3-1 mg/kg, i.p.). In conclusion, this study provides direct evidence for the role of endogenous NKA/substance P, through the activation of NK2 receptors, in regulating the septohippocampal cholinergic function.

Acetylcholine↗

PubMed1998

Effects of SR140333, a selective non-peptide NK1 receptor antagonist, on trigemino-thalamic nociceptive pathways in the rat.

Trigeminal stimulation of C-fibers increased c-fos expression within the trigeminal nucleus caudalis (NtV) and thalamic neuronal activity which both reflect the transmission of a nociceptive message. We examined the effects on both these phenomena of the selective NK1 and NK2 receptor antagonists, SR140333 and SR48968. SR140333 (0.3, 1 and 3 micrograms/kg intravenously [i.v.]) dose-dependently, reversibly and stereoselectively antagonized the increase of contralateral thalamic activity. This compound, when given i.v. (30 micrograms/kg) or orally (10 mg/kg), also reduced the number of Fos-like immunoreactive cells particularly at the medial and caudal level of the NtV. In contrast, SR48968 did not exert any antagonistic effect either on thalamic activity or on Fos-like immunoreactivity. The data strongly suggest a preferential involvement of NK1 vs NK2 receptors in nociceptive transmission following trigeminal ganglion stimulation. Taken together, our results indicate that SR140333 could provide a potent drug for the relief of pain occurring under excessive activity of sensory trigeminal fibers.

Administration, Oral↗