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.

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.

SR 144528, the first potent and selective antagonist of the CB2 cannabinoid receptor.

Based on both binding and functional data, this study introduces SR 144528 as the first, highly potent, selective and orally active antagonist for the CB2 receptor. This compound which displays subnanomolar affinity (Ki = 0.6 nM) for both the rat spleen and cloned human CB2 receptors has a 700-fold lower affinity (Ki = 400 nM) for both the rat brain and cloned human CB1 receptors. Furthermore it shows no affinity for any of the more than 70 receptors, ion channels or enzymes investigated (IC50 > 10 microM). In vitro, SR 144528 antagonizes the inhibitory effects of the cannabinoid receptor agonist CP 55,940 on forskolin-stimulated adenylyl cyclase activity in cell lines permanently expressing the h CB2 receptor (EC50 = 10 nM) but not in cells expressing the h CB1 (no effect at 10 microM). Furthermore, SR 144528 is able to selectively block the mitogen-activated protein kinase activity induced by CP 55,940 in cell lines expressing h CB2 (IC50 = 39 nM) whereas in cells expressing h CB1 an IC50 value of more than 1 microM is found. In addition, SR 144528 is shown to antagonize the stimulating effects of CP 55,940 on human tonsillar B-cell activation evoked by cross-linking of surface Igs (IC50 = 20 nM). In vivo, after oral administration SR 144528 totally displaced the ex vivo [3H]-CP 55,940 binding to mouse spleen membranes (ED50 = 0.35 mg/kg) with a long duration of action. In contrast, after the oral route it does not interact with the cannabinoid receptor expressed in the mouse brain (CB1). It is expected that SR 144528 will provide a powerful tool to investigate the in vivo functions of the cannabinoid system in the immune response.

Biochemical and pharmacological activities of SR 144190, a new potent non-peptide tachykinin NK2 receptor antagonist.

(R)-3-(1-[2-(4-benzoyl-2-(3,4-difluorophenyl)-morpholin-2-yl)- ethyl]-4-phenylpiperidin-4-yl)-1-dimethylurea (SR 144190) is a new non-peptide antagonist of tachykinin NK2 receptors. SR 144190 potently and selectively inhibited neurokinin A binding to NK2 receptors from various species, including humans. In in vitro functional assays, it was a potent, selective and competitive antagonist of NK2 receptors with apparent affinities (pA2 values) between 9.08 and 10.10. In vivo, SR 144190 blocked [Nle10]neurokinin A-(4-10)-induced bronchoconstriction in guinea pigs (ID50 = 21 micrograms kg-1 i.v. and 250 micrograms kg-1 i.d.) and [beta Ala8]neurokinin A-(4-10)-induced urinary bladder contraction in rats (ID50 = 11 micrograms kg-1 i.v. and 190 micrograms kg-1 i.d.). It prevented citric acid-induced cough and airway hyperresponsiveness to acetylcholine in guinea pigs (1 mg kg-1 i.p.) as well as castor oil-induced diarrhoea in rats (0.01-10 micrograms kg-1 s.c. or p.o). Finally, it blocked the turning behaviour induced by intrastriatal injections of [Nle10]neurokinin A-(4-10) in mice (ID50 = 3 micrograms kg-1 i.v. and 16 micrograms kg-1 p.o.).

Tachykinin-induced contractions of the guinea pig ileum longitudinal smooth muscle: tonic and phasic muscular activities.

In vitro tachykinin-induced contractions of guinea pig ileum longitudinal smooth muscle were investigated under isometric conditions by using selective agonists ([Sar9,Met(O2)11]substance P, [Nle10]neurokinin A-(4-10), senktide) and antagonists (SR 140333, SR 48968, SR 142801), respectively, for the tachykinin NK1, NK2, and NK3 receptors. [Sar9,Met(O2)11]Substance P (10 nM) induced a tonic contraction with superimposed phasic contractions. Both tonic and phasic muscular activities were completely abolished by SR 140333 (10 nM) and were not modified by SR 142801 (10 nM). SR 48968 (10 nM) and atropine (0.001 mM) did not modify the tonic muscular activity but inhibited the phasic muscular activity. [Nle10]Neurokinin A-(4-10) (10 nM) only caused a phasic contractile response that was inhibited by SR 48968. Atropine, SR 140333, and SR 142801 were without effect. Senktide (1 nM) induced combined tonic and phasic contractile responses. SR 142801 blocked the phasic and tonic muscular activities, whereas SR 48968 and SR 140333 were inactive. After addition of atropine, only tonic contractile response was abolished. These results showed fundamental differences in isometric tonic and phasic contractile responses of guinea pig ileum longitudinal smooth muscle to tachykinins.

Pharmacological characterization of SR 142801: a new non-peptide antagonist of the neurokinin NK-3 receptor.

Pharmacological and biochemical assays were performed to characterize SR 142801, a new NK-3 receptor antagonist, and its [R]-enantiomer, SR 142806. The compounds were tested (1) in the guinea pig isolated ileum stimulated with [MePhe7]NKB (NK-3 system) in order to evaluate onset and duration of action and to estimate the apparent affinity of the antagonist in terms of pA2 at 140 min after application; (2) in 6 selected monoreceptor systems, the rabbit (rb) vena cava for the NK-1rb receptor, the rabbit pulmonary artery and the hamster (hs) urinary bladder for the NK-2rb and NK-2hs receptors, the rat (r) portal vein for the NK-3r receptor, and in two multireceptor systems adequately treated with NK-1 or NK-2 receptor antagonists to obtain monoreceptor-mediated biological responses (the rat urinary bladder treated with SR 48968 for evaluating the NK-1r and the guinea pig-gp-ileum treated with CP-99994 for measuring the antagonist affinity on the NK-3gp receptor), in order to evaluate the antagonist selectivity, and (3) in various plasma membrane preparations containing NK-3-binding sites from rats, guinea pigs, and man. The data presented indicate that SR 142801 is a potent, fairly selective non-peptide antagonist of the functional (pA2 9.4) and binding (Ki 0.11 nmol/l) site of the guinea pig and human (Ki 0.21 nmol/l) NK-3 receptors, while being much less active on the Nk-3 receptors of other species, particularly the rat (pA2 7.0; Ki 15 nmol/l). SR 142801 shows a slow onset of action and acts as a long-lasting irreversible antagonist, specific for neurokinin receptors, especially the NK-3 sites of guinea pigs and man.

Characterization and distribution of binding sites for [3H]-SR 141716A, a selective brain (CB1) cannabinoid receptor antagonist, in rodent brain.

SR 141716A belongs to a new class of compounds (diarylpyrazole) that inhibits brain cannabinoid receptors (CB1) in vitro and in vivo. The present study showed that [3H]-SR 141716A binds with high affinity (Kd=0.61 +/- 0.06 nM) to a homogenous population of binding sites (Bmax=0.72 +/- 0.05 pmol/mg of protein) in rate whole brain (minus cerebellum) synaptosomes. This specific binding was displaced by known cannabinoid receptor ligands with the following rank order of potency SR 141716A > CP 55,940 > WIN 55212-2 = delta9-THC > anandamide. Apart from anandamide, all these compounds were found to interact competitively with the binding sites labeled by [3H]-SR 141716A. On the other hand, agents lacking affinity for cannabinoid receptors were unable to displace [3H]-SR 141716A from its binding sites (IC50 > 10 microM). In addition, the binding of [3H]-SR 141716A was insensitive to guanyl nucleotides. Regional rat brain distribution of CB1 cannabinoid receptors detected by [3H]-SR 141716A saturation binding and autoradiographic studies, showed that this distribution was very similar to that found for [3H]-CP 55,940. In vivo, the [3H]-SR 141716A binding was displaced by SR 141716A with ED50 values of 0.39 +/- 0.07 and 1.43 +/- 0.29 mg/kg following intraperitoneal and oral administration, respectively. Finally, the [3H]-SR 141716A binding sites remained significantly occupied for at least 12 hr following oral administration of 3 mg/kg SR 141716A. Taken together, these results suggest that SR 141716A in its tritiated form is a useful research tool for labeling brain cannabinoid receptors (CB1) in vitro and in vivo.

Biochemical and pharmacological characterisation of SR141716A, the first potent and selective brain cannabinoid receptor antagonist.

SR141716A is a selective, potent and orally active antagonist of the brain cannabinoid receptor with a long duration of action. This compound shows high affinity for the central cannabinoid receptor (Ki = 2 nM), displays low affinity for the peripheral cannabinoid receptor (Ki > 1000 nM). In vitro, SR141716A antagonizes the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and dopamine-stimulated adenylyl cyclase activities in rat brain membranes. After oral administration SR141716A totally inhibited the ex vivo [3H]-CP55,940 binding to cerebral membranes with a ED50 value of 3.5 mg/kg. Furthermore SR141716A antagonizes the classical pharmacological responses elicited by cannabinoid receptor agonists. In addition, SR141716A reverses the inhibitory effect of WIN55212-2 on isoniazid-induced elevation of cGMP in rat cerebellum. This compound will provide a powerful tool for studying the in vivo functions of the anandamide/cannabinoid system.

Immunopharmacological profile of SR 31747: in vitro and in vivo studies on humoral and cellular responses.

In our preceding paper, we demonstrated that both human and rat lymphocytes possess saturable high-affinity binding sites for the new sigma ligand SR 31747. Here we investigate the potential activity of this ligand on immune responses. In vitro, our study shows that SR 31747 exerts a concentration- and time-dependent inhibition of proliferative response to mitogens on mouse and human lymphocytes without affecting cell viability. This suppressive effect elicited by SR 31747 occurs over a concentration range which correlates with the pharmacological profile of the molecule in binding assays, strongly suggesting that SR 31747 acts through a receptor-mediated process. We showed that the SR 31747 effect, which was observed on purified T lymphocytes, affects a late event in the activation process which occurs after the G1 during the S phase of the cell cycle. Interestingly, no anti-proliferative effect was observed in a variety of tumor cell lines, supporting a specific effect limited to normal immune cells. In vivo, in mice, treatment with SR 31747 prevented both graft-versus-host disease and delayed-type hypersensitivity granuloma formation, while antibody response to sheep red blood cells was not affected. These results strongly suggest that the sigma-related receptor recognized by SR 31747 is very likely coupled to a biological function of lymphocytes.

Allosteric modulation of peripheral sigma binding sites by a new selective ligand: SR 31747.

The interactions of a new compound SR 31747 with sigma sites were examined in rat spleen membranes and in human peripheral blood leukocytes (PBL). Nanomolar concentrations of SR 31747 selectively inhibited in a non-competitive manner the binding of the prototypic sigma ligands [3H](+)-pentazocine, [3H](+)-3PPP and [3H]DTG on rat spleen membranes. Characterization of SR 31747 binding sites using [3H]SR 31747 as a ligand showed that this compound binds reversibly, with high affinity to one class of sites on rat spleen membranes (Kd 0.66 nM, Bmax 5646 fmol/mg protein). The pharmacological profile of [3H]SR 31747 binding sites was consistent with the presence of specific sites distinct from classical sigma 1 and sigma 2 receptor subtypes strongly suggesting an allosteric modulation of sigma sites by SR 31747. Similarly, [3H]SR 31747 binding sites were demonstrated on human PBL and also on purified subpopulations of human mononuclear cells (granulocytes, NK cells, T4, T8 and B lymphocytes). Administered to mice by i.p. or oral route 30 min before sacrifice, SR 31747 strongly inhibited the binding of [3H](+)-3PPP to mice spleen membranes with ED50 values of 0.18 and 1.43 mg/kg, respectively. Taken together these results could suggest a potential immunological activity of SR 31747 either directly or through allosteric modulation of peripheral sigma sites.

Evidence for a common molecular mode of action for chemically distinct nonpeptide antagonists at the neurokinin-1 (substance P) receptor.

The molecular mechanism of action of three chemically distinct nonpeptide antagonists, SR 140,333, FK 888, and RP 67,580, was compared with that of the previously characterized compound CP 96,345, using a series of chimeric constructs between their common target, the rat neurokinin (NK)-1 (substance P) receptor, and the homologous nonresponsive NK-3 (NKB) receptor. The ability of all four nonpeptide compounds to displace radiolabeled substance P from the NK-1 receptor and their ability to inhibit the peptide-induced increase in inositol phosphate turnover were critically dependent on structural elements located in an area from the middle of the second extracellular loop through transmembrane segments V and VI to the middle of the third extracellular loop of the NK-1 receptor. Dissection of the domain around the outer part of transmembrane segments V and VI into smaller segments demonstrated that the individual nonpeptide antagonists, in agreement with their distinct chemical structures, were dependent on different subepitopes within the common putative binding domain. Full NK-1-like susceptibility to SR 140,333, FK 888, and CP 96,345 could be transferred to the NK-3 receptor by exchange of transmembrane segments V and VI and adjacent parts with corresponding segments from the NK-1 receptor. For SR 140,333 and CP 96,345, almost the same effect could be achieved by transfer of two discontinuous segments around the top of transmembrane segments V and VI. RP 67,580 shared interaction sites with the other compounds around the top of transmembrane segment VI but appeared also to be dependent on transmembrane segment VII. It is concluded that four nonpeptide antagonists, despite overt chemical differences, appear to block NK-1 receptor function by interacting in distinct ways with a common site located spatially around the outer part of transmembrane segment VI.

Neuropharmacological characterization of SR 140333, a non peptide antagonist of NK1 receptors.

SR 140333 (1-[2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl) piperidin-3-yl]ethyl]-4-phenyl-1-azonia-bicyclo[2.2.2]octane , chloride), a potent non peptide ligand of the substance P (SP) NK1 receptor subtype with high affinity for NK1 receptors from both rat cortical membranes and human IM9 cells (Ki = 0.02 nM and 0.01 nM, respectively) was studied in vivo on various effects induced by NK1 agonists in rats and mice. SR 140333 given intraperitoneally (i.p.) in mice antagonized dose-dependently and in a stereoselective manner the scratching responses induced by intracerebroventricular SP and septide (ID50 = 0.73 and 0.08 mg/kg, respectively) and the turning behavior elicited by intrastriatal SP and septide (ID50 = 0.07 and 0.06 mg/kg, respectively). This compound had little effect on the scratching responses and the turning behavior elicited by [Sar9, Met(O2)11]-SP. When SR 140333 was coadministered with the peptide agonist, the compound reduced the scratching responses elicited by SP, [Sar9, Met(O2)11]-SP and septide injected intrathecally (i.t.) in mice (ID50 = 72.0, 64.3 and 52.5 ng i.t., respectively). SR 140333 antagonized the salivation induced by SP, [Sar9, Met(O2)11]-SP and septide in rats (ID50 = 0.13, 0.18 and 0.09 mg/kg i.p., respectively). SR 140333 abolished the facilitation of the tail-flick reflex induced by noxious heat in rats (total reversal at 0.06 mg/kg, i.p.). This compound was also found to inhibit the turning behavior induced by intrastriatal apomorphine in mice (ID50 = 0.1 mg/kg, i.p.). In conclusion, these results indicate that SR 140333 behaves as a potent, selective and centrally active NK1 receptor antagonist.

Identification of binding sites for SR 46349B, a 5-hydroxytryptamine2 receptor antagonist, in rodent brain.

SR 46349B belongs to a new class of compounds (propenone oxime ether derivative) that inhibit 5-hydroxytryptamine (HT)2 receptors in vitro and in vivo. (3H) SR 46349B has been shown to bind with high affinity (Kd = 1.20 nM) to a single class of sites in rat prefrontal cortical membranes. The maximum binding capacity (Bmax = 0.262 pmol/mg of protein) is similar to that found for other classes of 5-HT2 receptor antagonists. Although the highest density of specific (3H) SR 46349B binding was found in cortex tissue, specific binding was also detectable in other brain areas. Among various receptor or channel ligands [including alpha or beta adrenergic, dopamine (D1 or D2), histamine (H1 or H2), 5-HT subclasses (5-HT1, 5-HT3), muscarinic and Na+ and Ca2+ channel blockers] only 5-HT2 receptor effectors were able to displace (3H) SR 46349B. In addition, the type of inhibition exerted by known 5-HT2 receptor antagonists such as ketanserin and ritanserin was investigated by saturation studies. In vivo, (3H) SR 46349B bound predominantly in mouse brain regions containing 5-HT2 receptors. This binding was displaced by SR 46349B, ketanserin and ritanserin following oral administration. From these results we suggest that SR 46349B in its tritiated form is a useful tool to label the 5-HT2 receptor in vitro and in vivo.

Two nonpeptide tachykinin antagonists act through epitopes on corresponding segments of the NK1 and NK2 receptors.

The molecular mechanism of action for two chemically distinct and highly selective, nonpeptide antagonists, CP-96,345 and SR-48,968, was studied by development of a series of chimeric constructs between their respective target receptors, the NK1 (substance P) and NK2 (neurokinin A) receptors. The binding affinities of the natural peptide ligands, substance P and neurokinin A, were not affected by exchanging almost the entire C-terminal half of the NK1 receptor with the corresponding segment of the NK2 receptor. In contrast, it was found that transfer from the NK2 to the NK1 receptor of a segment corresponding to transmembrane segment VI, the amino-terminal half of transmembrane segment VII, and the connecting extracellular loop 3 completely switched the susceptibility for the nonpeptide antagonists. This chimeric exchange, corresponding to 17 nonconserved residues, conveyed full susceptibility for the NK2-specific compound SR-48,968 to the previously unresponsive NK1 receptor--i.e., the Ki value for inhibition of binding of 125I-labeled substance P decreased from > 10,000 to 0.97 nM. At the same time the affinity for the NK1-selective compound CP-96,345 decreased > 30-fold. The actual binding site for SR-48,968 was localized to this region of the NK2 receptor by use of [3H]SR-48,968, which did not bind to the NK1 receptor but bound with similar high affinities to the wild-type NK2 receptor and to the chimeric NK1 receptor with the NK2 receptor segment incorporated around transmembrane segments VI and VII, Kd = 1.5 nM and 1.0 nM, respectively. Our data indicate that two chemically very different nonpeptide antagonists, CP-96,345 and SR-48,968, act through epitopes located around transmembrane segment VI on their respective target receptors and that at least the nonconserved residues in these epitopes are not important for the binding of the natural peptide ligands, substance P and neurokinin A.

The NK2 receptor antagonist SR48968 inhibits thalamic responses evoked by thermal but not mechanical nociception.

Extracellular recordings were made in the thalamic posterior nuclear group of anesthetized rats to study the effects of SR48968, a non-peptide NK2 receptor antagonist, on the responses evoked by thermal or mechanical nociceptive cutaneous stimulation. SR48968 (0.125-0.5 mg/kg, i.v. route) inhibited the responses to thermal stimulation while being ineffective on mechanically evoked responses in doses up to 2 mg/kg i.v. This effect was stereoselective since SR48965, the (R) enantiomer of SR48968 with a 2000-fold lower affinity for NK2 receptors, did not modify thermally evoked responses at a dose of 1 mg/kg i.v. These results support the notion that NK2 receptors are involved in thermal nociception.

Neuropharmacological profile of a novel and selective ligand of the sigma site: SR 31742A.

The biochemical, electrophysiological and behavioural effects of SR 31742A, a novel and selective ligand of sigma sites in brain, labelled with (+)-[3H]3PPP (Ki = 5.3 +/- 0.3 nM), were investigated in rodents and compared with those of DA antagonists having (haloperidol) or not (spiroperidol) a high affinity for sigma sites. Like haloperidol but unlike spiroperidol, SR 31742A, (ED50 = 0.065 mg/kg, i.p., and 0.21 mg/kg, p.o.) antagonized sigma-dependent turning behaviour in mice and inhibited (0.5 mg/kg, i.v.) the spontaneous firing of hippocampal (CA3) neurones in urethane-anaesthetized rats. In chloral hydrate-anaesthetized rats, like classical antipsychotic compounds, SR 31742A (0.625-5 mg/kg, i.p.) increased the number of spontaneously active A9 and A10 DA cells after single administration and produced an opposite effect after repeated injections. The drug SR 31742A reduced (2.5, 5, 10 mg/kg, i.p.) the hyperactivity elicited by various drugs including that produced by injection of (+)-amphetamine into the nucleus accumbens and impaired avoidance responses at doses (5, 10 mg/kg, i.p.), sparing escape behaviour. SR 31742A lacked affinity for DA receptors and neither did the compound induce catalepsy nor antagonize such effects elicited by apomorphine as climbing, hypothermia, stereotypy or the inhibition of firing of DA neurones. SR 31742A did not affect the basal metabolism of DA but at 10 mg/kg (i.p.) it significantly reduced the amphetamine-induced rise in levels of 3-MT in the striatum of mice. Together, these results indicate a modulatory role for sigma sites upon the activity of hippocampal and DA systems and that sigma ligands exert effects, which suggest antipsychotic potential.

Up-regulation of 5-HT2 receptors in the rat brain by repeated administration of SR 46349B, a selective 5-HT2 receptor antagonist.

Chronic administration (twice a day for three days and on the morning of the fourth day) of SR 46349B (trans-4-[(3Z)3-(2-dimethylaminoethyl)oxyimino-3-(2-fluoroph enyl)propen-1- yl]phenol hemifumarate) (10 mg/kg, orally), a selective 5-HT2 receptor antagonist, caused 24 h later a marked increase (+42%) of the maximum binding capacity of [3H]ketanserin in rat brain cortical membranes without change in its affinity constant. Further, administration of the 5-HT2 receptor agonist, (+/-)-DOI((+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) (1 mg/kg, i.p.), produced in chronic SR 46349B treated rats a significant increase in the amount of [3H]-inositol phosphate compared to corresponding controls. In addition, subacute administration of SR 46349B caused a 2-fold increase in the head-twitch response to (+/-)-DOI (0.5 mg/kg, i.p.). This enhanced response was blocked by an acute administration of ritanserin (6-(2-[4-[bis(4-fluorophenyl)methylene]-1-piperidinyl]ethyl]-7- methyl-5H-thiazolo[3,2-a]pyrimidin-5-one) (10 mg/kg). Finally, a significant enhancement (+29%) of 5-HT2 receptor mRNA levels was observed in the cortex. Taken together, these data showed that an up-regulation of 5-HT2 receptors occurred in rats following repeated treatment with a selective 5-HT2 receptor antagonist. The effects of SR 46349B on 5-HT2 receptors might implicate pre-translational regulation.

Characterization of the binding sites of [3H]SR 48968, a potent nonpeptide radioligand antagonist of the neurokinin-2 receptor.

[3H]SR 48968, a radiolabeled nonpeptide antagonist of NK-2 receptor, has been tested in ligand-receptor binding assays using rat duodenum, hamster urinary bladder and guinea pig ileum membranes. [3H]SR 48968 bound to a single class of high affinity binding sites. Its affinity was slightly species-dependent. Its binding was inhibited by neurokinins, following the rank order of potency NKA > NKB > SP. It was also inhibited by peptide antagonists of NK-2 receptor (MEN 10,376, L 659,877), but their relative potencies were highly species-dependent. Unlabeled SR 48968, but not its R-enantiomer (SR 48965), also potently inhibited its binding. These data show that [3H]SR 48968 potently binds to NK-2 receptor and therefore is a useful tool to study NK-2 receptor.

Turning behavior induced in mice by a neurokinin A receptor agonist: stereoselective blockade by SR 48968, a non-peptide receptor antagonist.

The intrastriatal injection of [Nle10]-NKA(4-10), a neurokinin A agonist, (0.05-5 ng/mouse) elicited vigorous contralateral rotations. This behavior was dose-dependently antagonized by SR 48968 (ED50: 0.15 mg/kg i.p.: 0.19 mg/kg p.o.), a selective non-peptide antagonist of NK-2 receptors, but it was not affected by spiroperidol. This suggests that NK-2 receptor stimulation may affect the activity of the striatum without necessarily involving dopaminergic systems.

Repeated administration of SR 46349B, a selective 5-hydroxytryptamine2 antagonist, up-regulates 5-hydroxytryptamine2 receptors in mouse brain.

Adaptive changes in 5-hydroxytryptamine (5-HT)2 receptors were investigated in mice after repeated administration of SR 46349B, a potent, selective, and competitive 5-HT2 receptor antagonist (Kl = 0.72 +/- 0.05 nM). Repeated administration (twice per day for 3 days and once on the morning of the fourth day) of SR 46349B (5 or 10 mg/kg, orally) caused 24 hr later a marked increase in 5-HT2 receptor number (+41% and +75%, respectively), measured ex vivo in brain cortical membranes with [3H] ketanserin, without affecting its affinity constant. Further, administration of the 5-HT2 agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane produced, in SR 46349B (10 mg/kg, orally)-treated mice, a significant stimulation of the 5-HT2 receptor-linked phosphoinositide turnover in vivo in the brain. In addition, subacute administration of SR 46349B (5 or 10 mg/kg, orally) caused a significant increase of the head-twitch response to L-5-hydroxytryptophan. This enhanced response was blocked by an acute administration of ritanserin (1 mg/kg). These results show that repeated administration of SR 46349B produced a parallel enhancement in 5-HT2 receptor number, in 5-HT2 receptor-linked signal transduction, and in 5-HT2 receptor-mediated behavioral responses in mice. These findings suggest for the first time that an up-regulation of 5-HT2 receptors can occur after repeated treatment with a selective 5-HT2 antagonist.