Further characterisation of potential antidepressant action of flibanserin.

RATIONALE: Flibanserin has shown antidepressant-like properties in some animal models. In order to better define the probability that flibanserin may act as an antidepressant, its effects were tested in additional tests. OBJECTIVES: To assess the activity of flibanserin in the forced swimming test in rats, in the distress call frequency in isolated chicks, in the tail suspension test in mice and in muricidal rats. Flibanserin was also tested in mice performing an operant schedule of a food reinforcement fixed at an interval of 2 min. METHODS: Flibanserin was given intraperitoneally at a dose range between 0.5 and 32 mg/kg, 60 min before the muricidal test, 30 min before the tail suspension test, once (30 min) or three times (24, 5 and 1 h) before the forced swimming test, or just before testing (distress-induced calls in chicks). In the food reinforcement test in mice, flibanserin was given orally 60 min before testing. RESULTS: Flibanserin showed an antidepressant-like effect in the distress-induced calls in chicks (5 mg/kg) and in the muricidal test (16 and 32 mg/kg), but not in the tail suspension test (from 7.5 to 30 mg/kg). Flibanserin (8 and 16 mg/kg) increased immobility in the forced swimming test, either when administered once or for three times. Flibanserin increased the operant responses in the food reinforcement test (40 mg/kg). CONCLUSIONS: Flibanserin showed antidepressant-like effects in two out of four tests, and increased animal drive in the operant paradigm. These findings, together with others already published, may suggest that flibanserin will exert antidepressant activity in humans.

BIMT 17: a putative antidepressant with a fast onset of action?

BIMT 17, the only compound reported to be a full 5-HT1A agonist and a 5-HT2A antagonist at the frontal cortex, was assessed in three animal paradigms sensitive to antidepressants in rats: olfactory bulbectomy (OB), differential-reinforcement-of-low rate 72-s (DRL 72-s) and learned helplessness (LH). In the OB rats, BIMT 17, given once daily for 14 consecutive days at an i.p. dose of 10 mg/kg, but not of 20 mg/kg, reduced the increase in ambulation of OB rats, 24 h after the last administration. In the DRL 72-s test, BIMT 17 had a different profile than imipramine. A single i.p. injection of 5, 10, 15 or 20 mg/kg BIMT 17, in contrast to the same doses of imipramine, did not affect response and reinforcement rate in DRL 72-s 1 h after the administration. On the other hand, BIMT 17 slightly shifted the peak of the interresponse time (IRT) distribution towards shorter IRT duration, while imipramine shifted the peak of the IRT distribution towards longer IRT duration. In the LH test, acute oral doses (36, 48 or 60 mg/kg) of BIMT 17, given 30 min before testing, reduced the number of escape failures in LH without altering the intertrial crossings. This effect was also induced by a repeated, but not single, administration with 8 or 16 mg/kg imipramine. The plasma levels following i.p. 10 or oral 48 mg/kg BIMT 17 were in the same range. These results indicate that BIMT 17 does not behave like imipramine in all the tests, and suggest that BIMT 17 acts through different mechanisms of action than imipramine. Only clinical trials will tell whether these mechanisms will be relevant, but if so, BIMT 17 might induce a faster onset of therapeutic activity.

Central and peripheral components of dermorphin's effect on rat intestinal propulsion in comparison to morphine.

Dermorphin, injected intracerebroventricularly (ICV) to rats, provokes, like to morphine, an inhibition of intestinal propulsion linearly related to the log of the administered doses (in the range from 0.06 to 0.56 micrograms/rat), but it is 143 times more active than morphine. Naloxone, ICV or IP, antagonizes dermorphin less effectively than morphine. Quaternary naloxone ICV administered antagonizes the intestinal effect of ICV dermorphin, while IP administered it is not effective until 8 mg/kg. The dose of dermorphin maximally active by the ICV route (0.56 micrograms/rat) is completely inactive when injected IP. Increasing doses of dermorphin IP (from 12 to 6400 micrograms/kg) inhibit intestinal propulsion to the same extent irrespectively of the doses employed, but never by more than 50%. Only a high dose of naloxone (30 mg/kg/IP) antagonizes this IP effect. The central and peripheral components of this intestinal effect of dermorphin are discussed.

Mechanism of action of flibanserin in the learned helplessness paradigm in rats.

The mechanism of action of flibanserin, a 5-HT(1A) receptor agonist and a 5-HT(2A) receptor antagonist, was investigated in learned helplessness in rats. The effect of flibanserin (32 mg/kg, i.p. 30 min before testing) on learned helplessness was not antagonized by the (a) 5-HT synthesis inhibitor parachlorophenylalanine (pCPA; 150 mg/kg p.o.x3 times), which reduced brain 5-HT by 89%; (b) 5-HT(1A) receptor antagonists (+/-)-N-tert-butyl-3-4-(2-ethoxyphenyl)piperazin-1yl-2-phenyl propionamide [WAY100135; 10 mg/kg, i.p. 30 min before flibanserin, or 40 mg/kg, s.c. 15 min before flibanserin] and tertatolol (2.5 and 5 mg/kg, i.p. 30 min before flibanserin); and (c) 5-HT(2) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI; 3 mg/kg, s.c. simultaneously with flibanserin). The effect of flibanserin on learned helplessness was antagonized by the dopamine D(1) receptor antagonist [R]-3-methyl-7-chloro-8-hydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390; 0.1 mg/kg, i.p. 30 min before flibanserin) and by the opioid receptor antagonist naloxone (3 mg/kg, s.c. 15 min before flibanserin). Flibanserin (32 and 64 mg/kg) did not induce conditioned place preference. In conclusion, flibanserin improved rats' performance in the learned helplessness paradigm, by stimulating dopamine D1 and opioid receptors, probably indirectly, since flibanserin has a low affinity for these receptors.

Evidence that imipramine activates 5-HT1C receptor function.

The anti-immobility effect of imipramine (15 mg/kg) in the forced swimming test in mice was antagonized by the non-selective 5-hydroxytryptamine (5-HT) antagonist, metitepine (0.5 mg/kg), by the 5-HT1C/5-HT2 antagonist, mesulergine (15 mg/kg), and by the dopamine D2 antagonist, d,l-sulpiride (50 mg/kg). These three antagonists did not alter the behaviour of imipramine-treated mice in an open-field and did not reduce imipramine brain levels. The 5-HT2 antagonist, ritanserin (0.06 mg/kg), the 5-HT1A/5-HTB antagonist, l-propranolol (20 mg/kg), and the 5-HT3 antagonists, endo-2,3-dihydro-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2-oxo-1H- benzimidazole-1-carboxamide hydrochloride (DAU 6215; 0.1 mg/kg) and 1,2,3,9-tetrahydro-9-methyl-3[(2-methyl-1H-imidazol-1-yl)methyl]-4H- carbazol-4-one, HCl.2H2O) (GR 38032F; 0.1 mg/kg), failed to reduce imipramine-induced anti-immobility. Subthreshold doses of 8-hydroxy-2-(di-n-propylamino)tetralin hydrochloride (8-OH-DPAT; 0.5 mg/kg) and imipramine (7.5 mg/kg) did not synergize in reducing immobility. d,l-Sulpiride, but not mesulergine, antagonized the effect of desipramine (15 mg/kg) in the forced swimming test. All compounds were administered i.p. 6 min before imipramine or desipramine, given i.p. 30 min before the testing. Imipramine produced 50% inhibition of [3H]mesulergine binding to 5-HT1C receptors at 10 microM, a concentration below that obtained following i.p. imipramine administration. The results suggest a contribution of 5-HT1C receptors in the mechanism of the imipramine effect in the forced swimming test.

Involvement of periaqueductal gray matter in intestinal effect of centrally administered morphine.

Microinjections of morphine in the rat periaqueductal gray matter (PAG) inhibited intestinal transit in linear relation to the log of the dose administered (in the range from 5 to 20 micrograms/rat). This linear regression was parallel with that obtained on intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administration of morphine and the intracerebral (i.c.) route was calculated to be 4 times more potent than the i.c.v. route and 189 times more potent than the i.p. route. Monolateral electrolytic lesions into the PAG abolished the intestinal effect of i.c.v. morphine to a large extent. The relevance of other brain areas and the type of opiate receptors involved in this central effect of morphine are discussed.

Pharmacological properties of a novel class of 5-HT3 receptor antagonists.

The pharmacological profile of six representative members of a novel class of 5-HT3 receptor antagonists is described. The compounds are esters and amides of benzimidazolone-1-carboxylic acid with a basic azabicycloalkyl moiety (compounds 1-3) and their respective ethyl derivatives (compounds 4-6). In isolated preparations (rabbit heart and guinea pig ileum) all compounds antagonized the 5-HT3 receptor-mediated effects of serotonin, with potencies comparable with those of the reference compounds, ICS 205.930 and GR 38032F (-log IC50 9.30-11.9 and 6.8-8.20, in heart and ileum, respectively). In the anaesthetised rat, all agents potently inhibited the Bezold-Jarisch reflex whether given i.v. or i.d. I.v. administration of compounds prevented cisplatin-induced emesis in dogs (ID50 ranging from 3.7 to 147 micrograms/kg). All agents accelerated gastric emptying of solids in rats (ED50 about 10-160 micrograms/kg i.p.). In addition, compounds 4 and 5 were able to stimulate 5-HT4 receptors in the isolated guinea pig ileum, as well as enhance contractile activity in the Heidenhain gastric pouch of dogs, showing clearcut prokinetic properties.

Gastroprokinetic properties of the benzimidazolone derivative BIMU 1, an agonist at 5-hydroxytryptamine4 and antagonist at 5-hydroxytryptamine3 receptors.

We have investigated the in vivo motor stimulating and gastroprokinetic properties of the azabicycloalkyl benzimidazolone derivative BIMU 1 (3-ethyl-2,3-dihydro-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2-oxo-1H- benzimidazole-1-carboxamide hydrochloride) and its binding profile at 5-hydroxytryptamine3 and 5-hydroxytryptamine4 receptors, in an attempt to assess the serotonergic mechanism underlying its prokinetic action. BIMU 1 dose-dependently (0.01-0.3 mg/kg i.v.) increased the motility of a denervated pouch of canine stomach. This excitatory action was sensitive to muscarinic blockade. A similar stimulatory effect was exerted by the benzamidic prokinetic agent cisapride (0.03-0.3 mg/kg i.v.) but not by the 5-HT3 receptor antagonist ondansetron (up to 1 mg/kg i.v.). The significance for propulsive efficacy of the motor stimulating activity of BIMU 1 was evaluated in a model of gastric emptying of liquids in the conscious dog. The emptying rate of a non-caloric liquid meal instilled through a gastric fistula was accelerated by both BIMU 1 (0.01-1 mg/kg i.v. and 0.1-3 mg/kg p.o.) and cisapride (0.03-1 mg/kg i.v. and 0.3-10 mg/kg p.o.). Ondansetron (1 mg/kg i.v.) did not show any effect. The activity of the 5-HT4 receptor antagonist DAU 6285 was evaluated in the gastric emptying model per se and in interaction experiments on the accelerating action of BIMU 1 (0.3 mg/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of BIMT 17, a new potential antidepressant, in the forced swimming test in mice.

BIMT 17 inhibits cortical electrical activity through the activation of cortical 5-HT(1A) receptors combined with the antagonism of 5-HT(2) receptors. The aim of this study was to evaluate the potential antidepressant activity of BIMT 17 and its mechanism of action by using the forced swimming test in mice. BIMT 17, when administered i.p. (16mg/kg), s.c. (8mg/kg) and orally (32mg/kg), increased the struggling time in mice forced to swim. With i.p. administration, BIMT 17 did not alter locomotor activity. The effect of BIMT 17 seems to be mediated by 5-HT(1A) receptors since it was antagonised by WAY 100135 (10mg/kg i.p.), a selective 5-HT(1A) antagonist. The 5-HT(2) component does not seem to modulate BIMT 17 activity since the administration of DOI (1mg/kg i.p.), a 5-HT(2A/2C) agonist, did not modify the BIMT 17 effect. Antagonism of BIMT 17 was also produced by buspirone (30mg/kg p.o.), alpha-methyl-p-tyrosine (250mg/kg i.p.) and sulpiride (50mg/kg i.p.) but not by pindolol (20mg/kg i.p.). Neither the reduction of 5-HT synthesis brought about by p-chlorophenylalanine nor the selective destruction of 5-HT containing neurons by 5,7-dihydroxytryptamine reduced the BIMT 17 effect, suggesting that BIMT 17 acts postsynaptically in increasing struggling behaviour.

Mesulergine antagonism towards the fluoxetine anti-immobility effect in the forced swimming test in mice.

The anti-immobility effect of fluoxetine (40 mg kg-1) in the forced swimming test in mice was antagonized by the 5-HT1c/2 antagonist mesulergine (7.5 mg kg-1) and the dopamine D2 antagonist (+/-)-sulpiride (12.5 mg kg-1) but not by the 5-HT2/1C antagonist ritanserine (2 mg kg-1), the 5-HT1A/1B antagonist (-)-propranolol (20 mg kg-1) or the 5-HT3 antagonist DAU 6215 (0.1 mg kg-1). All compounds were administered intraperitoneally (i.p.) 6 min before fluoxetine, given i.p. 30 min before testing. The anti-immobility effect of fluoxetine was also prevented by pretreatment with p-chlorophenylalanine (300 mg kg-1 twice daily for 3 days) which produced an 80% reduction of 5-HT in brain. The results suggest that fluoxetine reduces immobility time in mice forced to swim, by acting indirectly through a mesulergine-sensitive site, probably the 5-HT1C receptor.

The effect of DAU 6215, a novel 5HT-3 antagonist, in animal models of anxiety.

The aim of the present study was to evaluate the effect of DAU 6215 (N-(endo-8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2, 3-dihydro-2-oxo-1H-benzimidazol-1-carboxamide, hydrochloride), which is a 5HT-3 receptor antagonist, chemically different from the other 5HT-3 antagonists, on a wide variety of animal models sensitive to anxiolytics. Nine animal models were used. DAU 6215 was active in reducing (i) aversion to a brightly lit environment in the light/dark exploratory test in mice, (ii) unpleasant properties of an aversive drug in rats (naloxone-induced place aversion), and (iii) aggressiveness in monkeys. DAU 6215 was effective at doses ranging (a) between 10 and 1000 micrograms/kg given i.p. in mice, (b) between 15 and 30 micrograms/kg given s.c. in rats and (c) between 1 and 10 micrograms/kg given orally in monkeys. DAU 6215 was inactive in (iv) the elevated plus maze, (v) conflict test and (vi) emotional hypophagia in rats and in (vii) the four plates test, (viii) staircase test and (ix) stress-induced hyperthermia in mice. Diazepam was active in all tests. In contrast to diazepam, DAU 6215 did not induce place preference, suggesting the possible lack of addictive properties.

Lack of interaction between flibanserin and antidepressants in inducing serotonergic syndrome in rats.

This study was aimed at evaluating the ability of flibanserin, a 5-HT1A receptor full agonist with antidepressant potential, to induce the 5-HT syndrome (flat body posture, hindlimb abduction and forepaw treading) in rats previously administered with clinically active antidepressants imipramine, fluoxetine or paroxetine. The 5-HT syndrome was observed for 50 min after intraperitoneal administration of flibanserin (0, 8 or 64 mg/kg) given 10 min after antidepressants (0 or 15 mg/kg). Flibanserin induced flat body posture and very slight hindlimb abduction only at 64 mg/kg. No dose of flibanserin elicited forepaw treading. Similar but milder symptoms were induced by antidepressants. No interaction between flibanserin and antidepressants was observed. A dose of 10 mg/kg flibanserin did not change the flat body posture induced by 8 mg/kg (+/-)-8-OH-DPAT but antagonized (+/-)-8-OH-DPAT-induced forepaw treading.

Gastric cytoprotective, antisecretory and antiulcer activities of (E)-4-oxo-4-(3,4,5-trimethoxyphenyl)-2-butenoic acid (RU 38086).

As a result of trials of a large series of compounds, RU 38086 (E)-4-oxo-4-(3,4,5-trimethoxyphenyl)-2-butenoic acid) was selected because of its cytoprotective, antisecretory and antiulcer properties. In pylorus-ligated rats, RU 38086 dose-dependently decreased the total acid output, at 2.5, 5 and 10 mg/kg orally and at 10 and 50 mg/kg intraduodenally. In the perfused rat stomach, 1.2 mg/kg RU 38086 in situ inhibited acid secretion stimulated by histamine or pentagastrin but was inactive against carbachol. In the same test 5 mg/kg intravenously did not antagonize pentagastrin-induced acid secretion. In the cat Heidenhain pouch, 0.6 mg/kg RU 38086 was also antisecretory, reducing the acid concentration when in contact with the mucosa of the pouch. In ulcers induced in rats by ligature of the pylorus plus acetylsalicylic acid, RU 38086 at 2.5 and 5 mg/kg demonstrated much more striking activity after oral than after intraduodenal administration. It also had antiulcer activity against stress ulcers (restraint plus cold), starting at a dose of 5 mg/kg orally. RU 38086 had marked gastric cytoprotective activity in rats against the necrotizing effects of ethanol from the low dose of 0.3 mg/kg orally. This cytoprotective activity was not significantly affected by indomethacin pre-treatment. At 4 and 20 mg/kg orally, RU 38086 strongly increased prostaglandin E2 levels in gastric juice of pylorus-ligated rats and in stomach tissue of normal rats. These data indicate that RU 38086 is an orally effective cytoprotective, antisecretory and antiulcer agent.

New classes of antimuscarinic agents endowed with selective antispasmodic properties. 1-Arylsulfonyl pyrrolidin-2-ones and 2-thiones, 1-arylsulfonyl piperidin-2-ones and 2-thiones and 1-arylsulfonyl hexahydro-2H-azepin-2-one.

A series of 1-arylsulfonylpyrrolidin-2-ones (and 2-thiones), 1-aryl sulfonylpiperidin-2-ones (and 2-thiones) and 1-arylsulfonyl hexahydro-2H-azepin-2-one were synthesized and submitted to a battery of binding assays. The compounds showed little or no affinity for the receptors tested other than muscarinic receptors labelled either with [3H]pirenzepine or with [3H]quinuclidinyl benzilate. When tested in the isolated guinea pig ileum, they antagonized the contractions induced by acetylcholine and behaved as competitive muscarinic antagonists. After parenteral administration in mice, most compounds inhibited carbachol-induced diarrhoea but were less effective in counteracting salivation and lacrimation and showed little or no mydriatic action, thus displaying selectivity at the intestinal level. The reference drugs tested, atropine, butyl scopolamine and cimetropium bromide were far less selective. maximal in vivo activity was obtained by introducing diethylamino or 1-piperidino or 1-hexahydroazepinyl groups in the 4-position of the phenyl ring while the enlargement of a 5- to a 6-membered lactam ring or its conversion into a thiolactam had a less marked effect. The most interesting compounds were further evaluated for their ability to antagonize carbachol-induced colonic hypermotility in the rat and arecoline-induced analgesia in mice. The effect on gastric acid secretion in the rat was also investigated. The overall in vivo data showed that compounds 14, 15, 26 and 27, i.e. those bearing a 1-hexahydroazepinyl group in the 4-position of the phenyl ring, were the most potent and selective compounds.(ABSTRACT TRUNCATED AT 250 WORDS)