Preclinical evaluation of flesinoxan as a potential anxiolytic and antidepressant drug

The putative 5-HT1A receptor antagonist DU125530 blocks the discriminative stimulus of the 5-HT1A receptor agonist flesinoxan in pigeons

Twelve homing pigeons were trained to discriminate the 5-HT1A receptor agonist flesinoxan (0.25 mg/kg p.o.) from its vehicle in a fixed ratio (FR) 30 two-key operant drug discrimination procedure. Tests for generalization and antagonism showed that compounds with agonistic action at the 5-HT1A receptor, such as 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), buspirone and ipsapirone all substituted for the flesinoxan cue. Compounds with mixed agonistic action at the 5-HT(1A/1B) receptor fully (eltoprazine) or partially (RU24969 (5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl-1H-indole)) substituted for flesinoxan. TFMPP (1-(3-trifluoromethylphenyl)piperazine) and mCPP (1-(3-chlorophenyl)piperazine), both acting at the 5-HT(1B/2C) receptor, did not substitute for flesinoxan, neither did the selective 5-HT re-uptake inhibitor fluvoxamine. The results of the antagonism tests showed that the 5-HT1A receptor antagonists NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine), WAY 100635 ((N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclo-he xane-carboxamide) and the newly developed DU125530 (2-[4-[4-(7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-1-piperazinyl ]butyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxide) fully (more than 80%) blocked the flesinoxan cue without having substantial effects when given alone. WAY100135 (N-tert-butyl-3-(4-(2-methoxyphenyl)piperazine-1-yl)-2-phenylpropanamide ), (+/-)-pindolol and (S)-UH-301 ((S)-5-fluoro-8-hydroxy-2-(dipropylamino)-tetralin) all partially antagonized the flesinoxan cue. However, both WAY100135 as well as (+/-)-pindolol also partially substituted for flesinoxan in generalization tests. NAN190, (S)-UH-301, WAY100635 and DU125530 were without any activity in the generalization test at the doses tested. The putative 5-HT1A receptor antagonist S15535 (4-benzodioxan-5-yl) 1-(indan-2-yl)piperazine) was identified as a full agonist in the present procedure. Taken together these results suggest that the flesinoxan cue in pigeons is mediated by the 5-HT1A receptor and that DU125530 acts as a full antagonist on the 5-HT1A receptor.

The effects of the 5-HT1A agonist flesinoxan, in three paradigms for assessing antidepressant potential in the rat

5-HT1A receptor agonists have been shown to be effective clinically in the treatment of depression and anxiety. Flesinoxan is an example which is highly selective for the 5-HT1A receptor subtype. The objective of this study was to appraise the antidepressant potential of flesinoxan (1 and 3 mg/kg s.c.) in three tests which are indicative of antidepressant activity. These are (1) the forced swim test, following sub-acute administration, (2) 'open field' activity in the olfactory bulbectomised (OB) rat, following chronic administration, and (3) 8-OH-DPAT-induced hypothemia following chronic treatment. Both doses of flesinoxan significantly reduced the immobility time in the sham and OB groups when compared to their respective controls. In the 'open field', there was a significant increase in the ambulation of the OB control group. The higher dose of flesinoxan significantly reduced this deficit. In addition both doses of flesinoxan significantly attenuated the 8-OH-DPAT-induced hypothermic response. These effects of flesinoxan are quantitatively similar to those seen following the chronic administration of antidepressants. These studies illustrate the potential antidepressant properties of flesinoxan, and hence further emphasise the role of the 5-HT1A receptor in the pathogenesis of depression.

Novel 5-HT2-like receptor mediates neurogenic relaxation of the guinea-pig proximal colon

The aim of the current investigation was to characterize the 5-HT receptors that mediate neurogenic relaxation of the guinea-pig proximal colon. After blockade of 5-HT2A, 5-HT3 and 5-HT4 receptor-mediated contractions, 5-hydroxytryptamine (5-HT) induced relaxations yielding a biphasic concentration-response curve. Other tryptamines were also agonists with the following rank order of potency: 5-HT > 5-carboxamidotryptamine = 5-methoxytryptamine > or = alpha-methyl-5-HT (partial agonist) > tryptamine (partial agonist). 5-Hydroxytryptophan, 2-methyl-5-HT and N-methyltryptamine were virtually inactive as agonists. The curve to 5-HT was not affected by pargyline, citalopram, phentolamine, or by the 5-HT4 receptor antagonists 2-methoxy-4-amino-5-chloro-benzoic acid 2-(diethylamino)ethyl ester (SDZ 205-557) and (1-butyl-4-piperidinylmethyl)-8-amino-7-chloro-1,4-benzodioxan+ ++-5-carboxylate (SB 204070). 8-Hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), 5-methoxy-3[1,2,3,6-tetrahydroxypyridin-4-yl]-1H-indole (RU 24969), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane (WB 4101), 1-(3-chlorophenyl)piperazine (mCPP), 1-(m-trifluoromethylphenyl)-piperazine (TFMPP), flesinoxan, sumatriptan and 6-chloro-2-(piperazinyl)-pyrazine (MK212) were inactive as 5-HT receptor agonists. The first phase of the curve to 5-HT was inhibited by: metergoline (pA2 = 8.8 +/- 0.3, against 5-methoxytryptamine 9.3 +/- 0.3), methysergide (non-surmountable), methiothepin (non-surmountable), spiroxatrine (non-surmountable), MK212 (non-surmountable), mesulergine (7.8 +/- 0.3), mCPP (7.1 +/- 0.1), mianserin (7.0 +/- 0.4), ritanserin (8.9 +/- 0.2), rauwolscine (7.0 +/- 0.2), yohimbine (6.2 +/- 0.2), 1-(1-naphthyl)-piperazine (7.7 +/- 0.2) and RU 24969 (6.4 +/- 0.1), but not by 1-(2-methoxyphenyl)4-[4-(2-phthalimidobtyl]-piperazine (NAN-190), spiperone, sumatriptan, 8-OH-DPAT and flesinoxan. It is suggested that the 5-HT receptor under study could be considered an unknown 5-HT2-like receptor.

Flesinoxan shows antidepressant activity in a DRL 72-s screen

Schedules which selectively reinforce low rates of responding (DRL, differential reinforcement of low rate) distinguish between antidepressants and other types of drugs. In a DRL schedule a subject is required to pause for a specified minimum period of time between two consecutive responses in order to obtain a reinforcer. The dependent variables are rate of responding and rate of reinforcement. Response patterns of rats treated with clinically effective antidepressant drugs such as imipramine (2.0-32.0 mg/kg) or fluvoxamine (4.0-32.0 mg/kg) are characterized by a decrease in response rate and an increase in reinforcement rate. Treatment with the 5-HT1A agonist flesinoxan (0.1-3.0 mg/kg) also dose-dependently decreased response rates while at the same time increasing reinforcement rates. Chlordiazepoxide (2.5-20.0 mg/kg) and diazepam (0.25-2.0 mg/kg) had no effects in the present experiment. d-Amphetamine increased response rates at low doses (0.5-2.0 mg/kg), and decreased it at the higher doses (4.0 mg/kg), but reinforcement rates were unaltered. Overall analysis of the effects of haloperidol (0.02-0.32 mg/kg) showed decreased responding and increased reinforcement rates. Post hoc analysis, however, clearly differentiated between haloperidol's profile and that of the antidepressants. As such, the results of the present experiment show that flesinoxan might possess antidepressant activity in humans.