Effects of the beta3-adrenoceptor (Adrb3) agonist SR58611A (amibegron) on serotonergic and noradrenergic transmission in the rodent: relevance to its antidepressant/anxiolytic-like profile.

SR58611A is a selective beta(3)-adrenoceptor (Adrb3) agonist which has demonstrated antidepressant and anxiolytic properties in rodents. The present study confirmed the detection of Adrb3 mRNA transcript in rodent brain sub-regions and evaluated the effect of SR58611A on serotonergic and noradrenergic transmission in rats and mice in an attempt to elucidate the mechanism(s) underlying these properties. SR58611A (3 and 10 mg/kg, p.o.) increased the synthesis of 5-HT and tryptophan (Trp) levels in several rodent brain areas (cortex, hippocampus, hypothalamus, striatum). Moreover, SR58611A (10 mg/kg, p.o.) increased the release of 5-HT assessed by in vivo microdialysis in rat prefrontal cortex. Systemic (3 mg/kg, i.v.) or chronic administration of SR58611A (10 mg/kg, p.o.), in contrast to fluoxetine (15 mg/kg, p.o.), did not modify the activity of serotonergic neurons in the rat dorsal raphe nucleus. The increase in 5-HT synthesis induced by SR58611A was not observed in Adrb3s knockout mice, suggesting a selective involvement of Adrb3s in this effect. SR58611A (3 and 10 mg/kg, p.o.) did not modify norepinephrine synthesis and metabolism but increased its release in rat brain. Repeated administration of SR58611A (10 mg/kg, p.o.) did not modify basal norepinephrine release in rat prefrontal cortex whereas it prevented its tail-pinch stress-induced enhancement similarly to reboxetine (15 mg/kg, p.o.). Finally SR58611A increased the firing rate of noradrenergic neurons in the rat locus coeruleus following systemic (3 mg/kg, i.v.) or local (0.01 and 1 microM) but not chronic (10 mg/kg, p.o.) administration. These results suggest that the anxiolytic- and antidepressant-like activities of SR58611A involve an increase of brain serotonergic and noradrenergic neurotransmissions, triggered by activation of Adrb3s.

Effects of the vasopressin (V1b) receptor antagonist, SSR149415, and the corticotropin-releasing factor 1 receptor antagonist, SSR125543, on FG 7142-induced increase in acetylcholine and norepinephrine release in the rat.

Arginine vasopressin and corticotropin-releasing factor are two neuroactive peptides that regulate hypothalamic-pituitary-axis and associated stress response. While the potential antidepressant and anxiolytic profiles of corticotropin-releasing factor 1 antagonists have been well studied, the concept of blockade of vasopressin system as another approach for the treatment of emotional processes has only been made available recently by the synthesis of the first non-peptide antagonist at the V1b receptor, SSR149415. In the present study SSR149415 has been compared with the corticotropin-releasing factor 1 antagonist SSR125543 and with anxiolytic and antidepressant drugs on the response of hippocampal cholinergic and cortical noradrenergic systems to the anxiogenic benzodiazepine receptor inverse agonist FG 7142. Acute (0.3-10 mg/kg, i.p.) and long-term administration (10 mg/kg, i.p., 21 days) of SSR149415 and SSR125543 reduced the FG 7142-induced increase in extracellular concentrations of acetylcholine in the hippocampus of anesthetized rats measured by microdialysis. By contrast acute and long-term administration of SSR149415 failed to reduce the FG 7142-induced increase in the release of norepinephrine in the cortex of freely moving rats. The present results demonstrate that the two compounds have similar profiles in a model of activation by an anxiogenic drug of the hippocampal cholinergic system and they suggest that SSR149415 and SSR125543 may have anti-stress anxiolytic and antidepressant effects via a mechanism of action different from classical benzodiazepine ligands and noradrenergic antidepressants.

2-Chloro-N-[(S)-phenyl [(2S)-piperidin-2-yl] methyl]-3-trifluoromethyl benzamide, monohydrochloride, an inhibitor of the glycine transporter type 1, increases evoked-dopamine release in the rat nucleus accumbens in vivo via an enhanced glutamatergic neurotransmission.

2-Chloro-N-S-phenyl 2S-piperidin-2-yl methyl]-3-trifluoromethyl benzamide, monohydrochloride (SSR504734) is a potent and selective inhibitor of the glycine transporter type 1, which increases central N-methyl-D aspartate glutamatergic tone. Since glutamate has been shown to play a role in the regulation of the dopaminergic system in dopamine-related disorders, such as schizophrenia, we investigated the possibility that SSR504734 may modify the basolateral amygdala-elicited stimulation of dopamine release in the nucleus accumbens via an augmentation of glutamate receptor-mediated neurotransmission. First, our data confirmed that SSR504734 is an inhibitor of GlytT1. In the nucleus accumbens of anesthetized rat, SSR504734 (10 mg/kg, i.p.) induced an increase of extracellular levels of glycine as measured by microdialysis coupled with capillary electrophoresis with laser-induced fluorescence detection. Second, the data demonstrated that SSR504734 (10 mg/kg, i.p.) enhanced the facilitatory influence of glutamatergic afferents on dopamine neurotransmission in the nucleus accumbens. Using an electrochemical technique, we measured dopamine release in the nucleus accumbens evoked by an electrical stimulation of the basolateral amygdala. SSR504734 facilitated dopamine release evoked by a 20 or a 40 Hz frequency basolateral amygdala stimulation. This facilitatory effect was dependent on glutamatergic tone, as intra-nucleus accumbens application of 6-7-dinitroquinoxaline-2,3-dione (10(-3) M) or DL-2-amino-5-phosphonopentanoic acid (10(-3) M), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and N-methyl-D aspartate receptors antagonists, respectively, inhibited dopamine release evoked by basolateral amygdala stimulation. Furthermore DL-2-amino-5-phosphonopentanoic acid co-administrated with SSR504734 hampered the dopamine-evoked release facilitation. These data underline the in vivo implication of the glycine uptake mechanism in the control of subcortical glutamate/dopamine interactions.

The cannabinoid CB1 receptor antagonist SR141716 increases Acrp30 mRNA expression in adipose tissue of obese fa/fa rats and in cultured adipocyte cells.

This study investigates the effects of SR141716, a selective CB(1) receptor antagonist that reduces food intake and body weight of rodents, on Acrp30 mRNA expression in adipose tissue. Acrp30, a plasma protein exclusively expressed and secreted by adipose tissue, has been shown to induce free fatty acid oxidation, hyperglycemia and hyperinsulinemia decrease, and body weight reduction. We report that N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR141716) treatment once daily (10 mg/kg/d, i.p.) from 2 to 14 days reduced body weight and stimulated Acrp30 mRNA expression in adipose tissue of obese Zucker (fa/fa) rats. In parallel, the hyperinsulinemia associated with this animal model was reduced by SR141716 treatment. In cultured mouse adipocytes (3T3 F442A), SR141716 (25 to 100 nM) also induced an overexpression of Acrp30 mRNA and protein. In addition, in adipose tissue of CB(1)-receptor knockout mice, SR141716 had no effect on Acrp30 mRNA expression, demonstrating a CB(1) receptor mediating effect. Furthermore, RT-PCR analysis revealed that rat adipose tissue and 3T3 F442A adipocytes expressed CB(1) receptor mRNA. Relative quantification of this expression revealed an up-regulation (3- to 4-fold) of CB(1) receptor mRNA expression in adipose tissue of obese (fa/fa) rats and in differentiated 3T3 F442A adipocytes compared with lean rats and undifferentiated adipocytes, respectively. Western blot analysis revealed the presence of CB(1) receptors in 3T3 F442A adipocytes, and their expression was up-regulated in differentiated cells. These results show that SR141716 stimulated Acrp30 mRNA expression in adipose tissue by an effect on adipocytes, and reduced hyperinsulinemia in obese (fa/fa) rats. These hormonal regulations may participate in the body weight reduction induced by SR141716 and suggest a role of metabolic regulation in the antiobesity effect of SR141716.

Selective blockade of neurokinin-2 receptors produces antidepressant-like effects associated with reduced corticotropin-releasing factor function.

The present study investigated the effects of the selective neurokinin-2 (NK2) receptor antagonist SR48968 in behavioral, electrophysiological, and biochemical tests sensitive to the action of prototypical antidepressants (fluoxetine, imipramine) or to corticotropin-releasing factor (CRF) receptor antagonists, which have been proposed recently as potential antidepressants. Results showed that SR48968 (0.3-10 mg/kg i.p.) produced antidepressant-like activity because it reduced immobility in the forced swimming test in both mice and rats, and decreased the amount of maternal separation-induced vocalizations in guinea pig pups. This latter effect appears to involve a reduction of stress-induced substance P release because SR48968 reduced the separation-induced increase in the number of neurons displaying neurokinin-1 receptor internalization in the amygdala. Furthermore, SR48968 increased the expression of the cAMP response-element binding protein mRNA in the rat hippocampus after repeated (1 mg/kg i.p., 21 days), but not acute administration. Finally, neuronal firing of the locus coeruleus (LC) and noradrenergic (NE) release in the prefrontal cortex both elicited by an uncontrollable stressor or an intraventricular administration of CRF were reduced by SR48968 (0.3-1 mg/kg i.p.). The finding that SR48968 (1 mg/kg i.p.) blocked the cortical release of NE induced by an intra-LC infusion of the preferential NK2 receptor agonist neurokinin A suggested the presence of NK2 receptors in this latter region. Importantly, SR48965 (1-10 mg/kg i.p.), the optical antipode of SR48968, which is devoid of affinity for the NK2 receptor, was inactive in all the models used. These data suggest that NK2 receptor blockade may constitute a novel mechanism in the treatment of depression and CRF-related disorders.

Expression of tachykinin NK2 receptor mRNA in human brain.

Tachykinin NK2 receptors have been suggested to play an important role in the central nervous system. This study, using reverse transcription-polymerase chain reaction revealed a detectable expression of NK2 receptor mRNA in various human brain regions, including the caudate nucleus, the putamen, the hippocampus, the substantia nigra and the cerebral cortex. The distribution of NK2 receptor expression in the cortex revealed a major expression in frontal and temporal cortex compared to occipital and parietal areas. These results provide a molecular basis for considering a role of NK2 receptors in human pathophysiology.

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.

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.

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.

Biochemical and pharmacological activities of SR 142948A, a new potent neurotensin receptor antagonist.

SR 142948A, 2-[[5-(2,6-dimethoxyphenyl)-1-(4-(N-(3-dimethylaminopropyl)-N-methylc arbamoyl)-2-isopropylphenyl)-1H-pyrazole3-carbonyl]amino] adamantane-2-carboxylic acid, hydrochloride, a new and extremely potent neurotensin (NT) receptor antagonist, has been characterized in comparison with SR 48692. This selective compound possesses nanomolar affinities for NT receptors, recognizes the two binding sites described for the NT receptor and fully displaces [3H]SR 48692 specific binding. SR 142948A antagonizes the classical in vitro NT effects, i.e., inositol monophosphate formation in HT 29 cells (IC50 = 3.9 nM) or intracellular calcium mobilization in Chinese hamster ovary cells transfected with the human receptor. It dose-dependently (0.04-640 x 10(-3) mg/kg p.o.) inhibits the turning behavior induced by unilateral intrastriatal injection of NT in mice, with the biphasic profile previously seen for SR 48692. At 0.1 mg/kg (i.p.), it completely antagonizes NT-evoked acetylcholine release in the rat striatum. In contrast to SR 48692, SR 142948A (p.o.) blocks both hypothermia and analgesia induced by i.c.v. injection of NT (mice and/or rats) but is unable to modify the dopamine release evoked by NT injection into the ventral tegmental area. In summary, SR 142948A retains the properties of the lead compound SR 48692 (no intrinsic agonist activity, oral bioavailability, long duration of action and good brain access), reveals a wider spectrum of activity than SR 48692 (probably due to the inhibition of NT receptor subtypes) and represents an additional tool for further exploration of the therapeutic potential of this class of compounds.

Characterization of CB1 receptors on rat neuronal cell cultures: binding and functional studies using the selective receptor antagonist SR 141716A.

This study was undertaken to characterize further the central cannabinoid receptors in rat primary neuronal cell cultures from selected brain structures. By using [3H]SR 141716A, the specific CB1 receptor antagonist, we demonstrate in cortical neurons the presence of a high density of specific binding sites (Bmax = 139 +/- 9 fmol/mg of protein) displaying a high affinity (KD = 0.76 +/- 0.09 nM). The two cannabinoid receptor agonists, CP 55940 and WIN 55212-2, inhibited in a concentration-dependent manner cyclic AMP production induced by either 1 microM forskolin or isoproterenol with EC50 values in the nanomolar range (4.6 and 65 nM with forskolin and 1.0 and 5.1 nM with isoproterenol for CP 55940 and WIN 55212-2, respectively). Moreover, in striatal neurons and cerebellar granule cells, CP 55940 was also able to reduce the cyclic AMP accumulation induced by 1 microM forskolin with a potency similar to that observed in cortical neurons (EC50 values of 3.5 and 1.9 nM in striatum and cerebellum, respectively). SR 141716A antagonized the CP 55940- and WIN 55212-2-induced inhibition of cyclic AMP accumulation, suggesting CB1 receptor-specific mediation of these effects on all primary cultures tested. Furthermore, CP 55940 was unable to induce mitogen-activated protein kinase activation in either cortical or striatal neurons. In conclusion, our results show nanomolar efficiencies for CP 55940 and WIN 55212-2 on adenylyl cyclase activity and no effect on any other signal transduction pathway investigated in primary neuronal cultures.

Characterization of the effect of SR48692 on inositol monophosphate, cyclic GMP and cyclic AMP responses linked to neurotensin receptor activation in neuronal and non-neuronal cells.

1. Neurotensin stimulated inositol monophosphate (IP1) formation in both human colonic carcinoma HT29 cells and in mouse neuroblastoma N1E115 cells with EC50 values of 3.5 +/- 0.5 nM (n = 4) and 0.46 +/- 0.02 nM (n = 3), respectively. Neurotensin also stimulated cyclic GMP production with an EC50 of 0.47 +/- 1.2 nM and inhibited cyclic AMP accumulation induced by forskolin (0.5 microM) with an IC50 of 1.33 +/- 1.5 nM (n = 3) on the N1E115 cell line. 2. The competitive antagonism by the non-peptide neurotensin receptor antagonist, SR48692 of neurotensin-induced IP1 formation revealed pA2 values of 8.7 +/- 0.2 (n = 3) for HT29 and 10.1 +/- 0.2 (n = 3) for N1E115 cells. SR48692 also antagonized the cyclic GMP and cyclic AMP responses induced by neurotensin in the N1E115 cell line with pA2 values of 10.7 +/- 0.7 (n = 3) and 9.8 +/- 0.3 (n = 3), respectively. 3. In CHO cells transfected with the rat neurotensin receptor, neurotensin stimulated IP1 and cyclic AMP formation with EC50 values of 3.0 +/- 0.5 nM (n = 3) and 72.2 +/- 20.7 nM (n = 3), respectively. Both effects were antagonized by SR48692, giving pA2 values of 8.4 +/- 0.1 (n = 3) for IP1 and 7.2 +/- 0.4 (n = 3) for cyclic AMP responses. 4. Radioligand binding experiments, performed with [125I]-neurotensin (0.2 nM), yielded IC50 values of 15.3 nM (n = 2) and 20.4 nM (n = 2) for SR48692 versus neurotensin receptor binding sites labelled in HT29 and N1E115 cells, respectively. 5 In conclusion, SR48692 appears to be a potent, species-independent antagonist of the signal transduction events triggered by neurotensin receptor activation in both neuronal and non-neuronal cell systems.

Functional characterization of the nonpeptide neurokinin3 (NK3) receptor antagonist, SR142801 on the human NK3 receptor expressed in Chinese hamster ovary cells.

The effects of SR142801, a nonpeptide tachykinin neurokinin (NK3) receptor antagonist, were investigated on the functional events linked to NK3 receptor activation by using Chinese hamster ovary (CHO) cells transfected with the human NK3 receptor. Radioligand binding conducted with [125I]iodohistidyl-[MePhe7]-NKB revealed a competitive inhibition by SR142801 and its (-)-antipode SR142806 with Ki values of 0.21 +/- 0.03 and 32.0 +/- 5.0 nM, respectively. NK3 agonists such as [MePhe7]-NKB and senktide stimulated inositol monophosphate formation with EC50 values of 2.0 +/- 1.4 and 2.1 +/- 0.7 nM, respectively. SR142801 antagonized the stimulatory effect of [MePhe7]-NKB (10(-8) M) with an IC50 of 14.3 +/- 2.6 nM and of senktide (10(-8) M) with an IC50 of 4.8 +/- 1.5 nM. The [3H]arachidonic acid release induced by either [MePhe7]-NKB (EC50 of 2.6 +/- 0.2 nM) or senktide (EC50 of 4.2 +/- 2.9 nM) also was inhibited by SR142801 with IC50 values of 16.1 +/- 0.5 and 8.0 +/- 1.7 nM, respectively. The cyclic AMP accumulation induced by 10(-7) M [MePhe7]-NKB (EC50 of 54 +/- 2 nM) also was antagonized by SR142801 with an IC50 value of 4.0 +/- 0.7 nM. These antagonistic effects were stereospecific and NK3 receptor specific because the (-)-antipode, SR142806, was much less effective than SR142801 in NK3 agonist-evoked responses, whereas the nonpeptide NK1 (SR140333) and NK2 (SR48968) receptor antagonists were almost inactive. The activity of SR142801 also was evaluated on the [Ca++]i increase induced by 10(-9) M [MePhe7]-NKB.(ABSTRACT TRUNCATED AT 250 WORDS)

SR 120819A, an orally-active and selective neuropeptide Y Y1 receptor antagonist.

An orally-active antagonist of neuropeptide Y (NPY) Y1 receptors, SR 120819A, has been characterized. This compound displays highly selective and competitive affinity for rat, guinea-pig and human (Ki = 15 nM) NPY Y1 receptors. In vitro, SR 120819A blocks the inhibitory effect of NPY on adenylyl cyclase activity in human SK-N-MC cells and that of the selective Y1 agonist, [Leu31,Pro34]NPY, on rabbit vas deferens contraction (pA2 = 7.20 +/- 0.07). In vivo, by intravenous route, this compound acts as an antagonist in anesthetized guinea-pigs and, notably, after oral administration, SR 120819A counteracts the pressor response of [Leu31,Pro34]NPY (5 micrograms/kg i.v.) with a long duration of action (> 4 h at 5 mg/kg p.o.). Thus, SR 120819A is the first orally-effective NPY Y1 receptor antagonist yet described. It could be a useful tool for exploring the role of NPY and the therapeutic relevance of an antagonist at NPY Y1 receptors.

SR 140333, a novel, selective, and potent nonpeptide antagonist of the NK1 tachykinin receptor: characterization on the U373MG cell line.

The effects of a novel nonpeptide NK1 tachykinin receptor antagonist, SR 140333, on the functional consequences of NK1 receptor activation in a human astrocytoma cell line, U373MG, were investigated. Radioligand binding conducted with 125I-Bolton-Hunter substance P revealed a competitive inhibition by SR 140333 and its R enantiomer SR 140603 with Ki values of 0.74 and 7.40 nM, respectively. The NK1-selective agonist, [Sar9,Met(O2)11]-substance P, stimulated the formation of inositol phosphates with an EC50 of 3.8 x 10(-9) M. SR 140333 blocked the stimulatory effect of this agonist (10(-7) M) with an IC50 of 1.6 x 10(-9) M, whereas the effect of another NK1 agonist, septide (EC50 = 1.5 x 10(-8) M) was antagonized with an IC50 of 2.1 x 10(-10) M. Enhancement of [3H]taurine release by [Sar9,Met(O2)11]-substance P (EC50 = 7.4 x 10(-9) M) was also inhibited by SR 140333 with an IC50 of 1.8 x 10(-9) M. SR 140603 was 10-fold less potent than SR 140333 in inhibiting inositol monophosphate formation and [3H]taurine release. The calcium mobilization induced by [Sar9,Met(O2)11]-substance P (10(-8) M) was totally prevented by 10(-8) M SR 140333. Patch-clamp experiments showed that SR 140333 depressed the outward current evoked by 5 x 10(-8) M [Sar9, Met(O2)11]-substance P with an IC50 of 1.3 x 10(-9) M. The expression of c-fos was stimulated by [Sar9,Met(O2)11]substance P with an EC50 of 2.5 x 10(-10) M, an effect that was also inhibited by SR 140333 with an IC50 of 1.1 x 10(-9) M.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

SR 46559A: a novel and potent muscarinic compound with no cholinergic syndrome.

The cholinergic activities of SR 46559A, 3-[N-(2 diethyl-amino-2-methylpropyl)-6-phenyl-5-propyl] pyridazinamine sesquifumarate, have been investigated in vitro and in vivo, in rodents. Using rat brain cortical membranes, SR 46559A was a competitive ligand (Ki = 112 nM) at muscarinic M1 receptors, its affinity for muscarinic M2 (cardiac) and M3 (glandular) receptors being 6-7 times lower. SR 46559A did not interact with brain nicotinic receptors and high affinity choline uptake sites nor did it inhibit brain acetylcholinesterase activity. In contrast to reference muscarinic agonists, SR 46559A (1 mM) did not inhibit the forskolin-induced activation of cAMP synthesis nor did it stimulate phosphoinositides breakdown in various brain preparations. However, this compound enhanced (+67% at 1 mM) diacylglycerol formation in rat striatal miniprisms, an effect fully reversed by atropine. As shown with reference agonists, SR 46559A inhibited (IC50 = 10 microM) the K(+)-evoked release of [3H]GABA from rat striatal slices and reduced at 0.5 and 1 microM, the population spike amplitude of the CA1 pyramidal cells induced by stimulation of the Schaffer's collateral commissural pathway in rat hippocampal slices. In mice, SR 46559A at a near lethal dose (200 mg/kg PO) did not induce the typical cholinergic syndrome nor did it modify at 30 mg/kg PO the oxotremorine-induced hypothermia. Like muscarinic agonists, SR 46559A (1 mg/kg PO) potentiated haloperidol-induced catalepsy in rats and inhibited (ED50 = 0.12 mg/kg PO) rotations induced in mice by intrastriatal injection of pirenzepine.(ABSTRACT TRUNCATED AT 250 WORDS)

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.