The putative 5-HT1B receptor agonist CP-93,129 suppresses rat hippocampal 5-HT release in vivo: comparison with RU 24969.

We have compared the ability of the new putatively specific 5-HT1B receptor agonist CP-93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b] pyrid-5-one) and the structurally related mixed 5-HT1A/5-HT1B receptor ligand RU 24969, to influence 5-HT release in brain in vivo, using microdialysis techniques in chloral hydrate-anaesthetised rats. CP-93,129 (3 or 10 microM, via the dialysis perfusion medium) caused a concentration-dependent and methiothepin (10 microM)-sensitive suppression of ventral hippocampal 5-HT output. The effect of RU 24969 on 5-HT output was dependent on whether or not the 5-HT reuptake blocker citalopram was present in the perfusion medium. Thus, RU 24969 (0.1 microM) induced a decrease, or an increase followed by a decrease (1 microM), in 5-HT output in the absence of citalopram, but monotonically decreased (1 microM) 5-HT release when citalopram (1 microM) was present. CP-93,129 decreased dialysate 5-HT in either condition. Our findings are consistent with the characterisation of CP-93,129 as a 5-HT1B receptor agonist, and may thus represent in vivo support for 5-HT1B autoreceptor-mediated feedback control of 5-HT release in the rat brain. The 5-HT1B selectivity of CP-93,129, and its lack of 5-HT reuptake blocking properties, suggests that the compound compares favourably with other purported 5-HT1B receptor agonists.     

Subthalamic 5-HT(1A) and 5-HT(1B) receptor modulation of RU 24969-induced behavioral profile in rats

The effects of systemic administration of the serotonin (5-HT)(1A/1B) agonist 5-methoxy-3-(1,2,3,6-tetrahydropyridin-4-yl)1H-indole (RU 24969) on locomotor and investigatory behavior in rats have been well characterized using the behavioral pattern monitor (BPM). To elucidate the neural circuitry underlying this behavioral profile, intracerebral dose--response studies were conducted at two sites with high densities of 5-HT(1B) receptors, the subthalamic nucleus (STN) and substantia nigra. Infusion of RU 24969 into the STN produced systemic RU 24969-like changes in locomotor activity and patterns but an uncharacteristic increase in investigatory holepokes. Intra-STN administration of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-N-propylamino)tetralin (8-OH-DPAT) produced RU 24969-like changes in locomotor patterns only, while the 5-HT(1B) receptor agonist 3(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride (CP-93,129) increased locomotor activity, produced no change in locomotor patterns and nonsignificantly increased holepokes. Intranigral infusion of RU 24969 produced systemic and intra-STN RU 24969-like increases in locomotor activity. Intranigral RU 24969, however, failed to produce any changes in locomotor patterns or investigatory holepokes. Intranigral infusions of CP-93,129 or 8-OH-DPAT had no effects on locomotor activity, locomotor patterns or investigatory holepokes. These results provide evidence for multiple-site mediation of the locomotor-activating effects of RU 24969 and for a dissociation of the neural substrates underlying locomotor and investigatory components of the RU 24969-induced behavioral profile.     

Novel potent 5-HT(1F) receptor agonists: structure-activity studies of a series of substituted N-[3-(1-methyl-4-piperidinyl)-1H-pyrrolo[3,2-b]pyridin-5-yl]amides

Compound 1a (LY334370), a selective 5-HT(1F) receptor agonist (SSOFRA), inhibited dural inflammation in the neurogenic plasma protein extravasation model of migraine and demonstrated clinical efficacy for the acute treatment of migraine. Although 1a was greater than 100-fold selective over both the 5-HT(1B) and 5-HT(1D) receptors, it exhibited appreciable 5-HT(1A) receptor affinity. Described here is the synthesis and evaluation of a series of pyrrolo[2,3-c]pyridine and pyrrolo[3,2-b]pyridine (2a and 3a) as well as pyrrolo[3,2-d]pyrimidine (4a) analogues of 1a, compounds prepared in an effort to identify SSOFRAs with improved selectivity over other 5-HT(1) receptor subtypes. The pyrrolo[3,2-b]pyridine analogue 3a showed high 5-HT(1F) receptor affinity but offered no improvement in selectivity compared to 1a. However, the C-5 acetamide derivative, 3b, was greater than 100-fold selective over the 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors. SAR studies of this series determined that alkylamides in particular exhibited high selectivity for the 5-HT(1F) receptor. Replacement at C-5 with other substituents decreased affinity or selectivity. These SAR studies identified SSOFRAs that demonstrated oral activity in the neurogenic plasma protein extravasation model, a model indicative of antimigraine activity.     

CP-94,253: a selective serotonin1B (5-HT1B) agonist that promotes satiety

The selective 5-HT_1B agonist CP-94,253 (3-(1,2,5,6-tetrahydro-4-pyridyl)-5-propoxypyrrolo[3,2-b] pyridine) (5–40 μmol/kg) reduced the intake of both pellets and a 10% solution of sucrose (ID₅₀ = 12.5 and 22.8 μmol/kg, respectively) in mildly deprived rats. Time-sampled observations revealed that CP-94,253 terminated feeding earlier, without disrupting the continuity of feeding. CP-94,253 increased standing but did not promote resting during satiation. Microstructural analysis of licking indicated that CP-94,253 decreased the frequency, but not the size, of bursts and clusters of licks without altering oral motor efficiency. The peripherally acting 5-HT_1B agonist, CP-93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one) had no effect on food intake. These results imply that CP-94,253 probes a role for central 5-HT_1B receptors in the regulation of meal size and duration, but that recruitment of other 5-HT receptor subtypes may be needed for the full expression of satiety. Received: 30 July 1996/Final version: 11 December 1996     

Inhibition of amino acid release by 5-HT1B receptor agonist in the rat prefrontal cortex

In vivo microdialysis in conscious rats was used to evaluate the effect of 5-HT1A agonist (+/-)-8-hydroxy-2-(n-dipropylamino)tetralin (8-OH-DPAT), 5-HT2A/2C agonist (+/-)- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and 5-HT1B receptor agonist 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo-[3,2-b]pyrid-5-one (CP 93129) on the veratridine-evoked glutamate (Glu) and aspartate (Asp) release in the rat prefrontal cortex. CP 93129 at concentrations between 50-500 microM significantly reduced Glu and Asp release. The effect of CP 93129 was attenuated by intraperitoneal (ip) administration of the selective 5-HT1B receptor antagonist N-[3-[3-(dimethylamino)ethoxy]-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-[ 1, 1'-biphenyl]-4-carboxamide (SB 216641) at a dose of 2 mg/kg. Neither DOI (100 microM) nor 8-OH-DPAT given locally at concentration of 100 microM or peripherally at doses of 0.1 and 1 mg/kg ip, influenced stimulated Glu and Asp release. We suggest that cortical glutamatergic neurons possess 5-HT1B heteroceptors and their activation may be responsible for the inhibitory effect of 5-HT on Glu and Asp release.     

Parabrachial infusion of D-fenfluramine reduces food intake. Blockade by the 5-HT(1B) antagonist SB-216641

Systemic administration of the serotonin (5-HT) releaser/reuptake inhibitor, D-fenfluramine decreases consumption of food in mammals. This hypophagic action involves loci at several levels of the neuraxis. Indirect evidence implicates the parabrachial nucleus (PBN) of the pons as one of these regions. Consistent with this hypothesis, unilateral infusion of D-fenfluramine (200, 280, and 400 nmol/0.5 microl) directly into the lateral PBN (LPBN) of male rats reduced food intake by 33%, 56%, and 66% from baseline (7.3 +/- 0.7 g) during a 30-min test with chow. Infusions lateral, medial, and dorsal to the PBN were ineffective. Stimulating 5-HT(1B) receptors in the PBN also reduces feeding. Administration of the selective 5-HT(1B) agonist CP-93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one) (0, 0.625, 2.5, and 10 nmol/0.5 microl) into the PBN reduced food intake by 25--79%. The selective 5-HT(1B) antagonist SB-216641 (N-[3-[3-(dimethylamino(ethoxy]-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-[1,1'-biphenyl]-4-carboxamide) (2.5 nmol) completely blocked the hypophagic action of the approximate ED(50) doses of CP-93,129 (2.5 nmol) and D-fenfluramine (280 nmol). These data strongly suggest that directly or indirectly activating 5-HT(1B) receptors in the LPBN inhibits feeding and implicates this pontine region in the serotonergic regulation of eating and satiation.     

Effects of triiodothyronine and imipramine on basal 5-HT levels and 5-HT(1) autoreceptor activity in rat cortex

Clinical studies have shown that triiodothyronine (T3) both augments and accelerates the therapeutic response to antidepressant drugs, particularly tricyclics. There is evidence that this effect is mediated by the serotonergic system. We show here that T3 administered daily for 7 days over the range 0.02-0.5 mg/kg increases basal serotonin (5-hydroxytryptamine, 5-HT) levels, as measured by in vivo microdialysis in rat cortex, in a dose-dependent fashion. All the doses of T3 examined reduced 5-HT(1A) autoreceptor activity, as measured by the effect of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 0.05 mg/kg s.c.) to decrease 5-HT levels in frontal cortex. T3 administered daily for 14 days at 0.02 mg/kg also reduced 5-HT(1B) autoreceptor activity, as measured by the effect of locally administered 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129, 10 microM) to decrease 5-HT levels. In animals administered imipramine (10 mg/kg/day by osmotic minipump) concurrently with T3 injections, no further changes in either 5-HT(1A) or 5-HT(1B) autoreceptor activity were seen. We suggest that the effect of T3 to accelerate the therapeutic actions of antidepressant drugs may be due to a combination of the actions of T3 at autoreceptors and the actions of the drugs at postsynaptic 5-HT(1A) receptors.     

Chronic fluoxetine-induced desensitization of 5-HT1A and 5-HT1B autoreceptors: regional differences and effects of WAY-100635

Desensitization of 5-HT(1A) and 5-HT(1B) autoreceptors is thought to be the mechanism underlying the therapeutic effects of fluoxetine and other selective serotonin reuptake inhibitors when these are administered chronically. The blockade of 5-HT(1A) autoreceptors occurring on administration of a selective serotonin reuptake inhibitor together with a 5-HT(1A) autoreceptor antagonist is responsible for the acute increase in 5-hydroxytryptamine (serotonin, 5-HT) levels observed under these circumstances. The effects of repeated administration of selective serotonin reuptake inhibitors together with 5-HT(1A) receptor antagonists have not been widely studied. In this work, we found that the effects of fluoxetine (5 mg/kg, i.p., daily for 12 days) to desensitize 5-HT(1B) autoreceptors in the frontal cortex, as measured by the effect of the locally administered 5-HT(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129), and to desensitize 5-HT(1A) autoreceptors as measured by the action of the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 50 microg/kg, s.c.) to reduce 5-HT levels in cortex, were prevented by concomitant administration of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide (WAY-100635; 0.3 mg/kg, s.c.). 5-HT(1B) receptor activity in the hypothalamus, as measured by the effects of locally administered CP 93129, and 5-HT(1A) autoreceptor activity, as determined by the effects of subcutaneous 8-OH-DPAT to reduce 5-HT levels in hypothalamus, were not altered either by fluoxetine alone or by fluoxetine in the presence of WAY-100635. The data suggest that the regulation of extracellular levels of 5-HT in the cortex and hypothalamus is subject to different autoregulatory mechanisms.     

Mechanistic investigation of the stimulus properties of 1-(3-trifluoromethylphenyl)piperazine.

Using a standard two-lever operant procedure with rats trained to discriminate 1-(3-trifluoromethylphenyl)piperazine (TFMPP) (0.5 mg/kg) from saline, tests of stimulus antagonism and stimulus generalization were performed to better understand the stimulus properties of this agent. The agents examined for ability to antagonize the TFMPP stimulus were prazosin, quipazine, zacopride, buspirone, 8-hydroxy-2-(di-N-propylamino) tetralin (8-OH-DPAT), 1-(2-methoxyphenol)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190), haloperidol, and 1-(2-pyrimidinyl)piperazine (1-PP); only buspirone attenuated the response to TF-MPP. In separate experiments, the lowest nondisrupting dose of buspirone (1.2 mg/kg) caused a rightward shift of the TFMPP dose-response curve (TFMPP alone, ED50 = 0.19 mg/kg; TFMPP + buspirone, ED50 = 0.43 mg/kg). In addition, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93, 129), 7-trifluoromethyl-4-(4-methyl-1-piperazinyl)pyrolo[1,2-a]quinox ali ne (CGS 12066B), 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), 3-chlorophenylbiguanide (mCPBG), NAN-190, nisoxetine, zacopride, 1-PP, (+)-N-allylnormetazocine ((+)-NANM), and N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) were analyzed in tests of stimulus generalization. The TFMPP stimulus generalized only to CGS 12066B (ED50 = 4.2 mg/kg) and (+)-NANM (ED50 = 8.8 mg/kg). Tests with DOI and MDMA resulted in partial generalization. Up to doses that disrupted behavior, all other agents had little effect on TFMPP-appropriate responding. The results of these and other published studies suggest roles for 5-hydroxytryptamine 1B (5-HT1B), 5-HT1C, and, possibly, sigma-receptors in the mediation of the TFMPP stimulus and indicate a lack of involvement of 5-HT1A, 5-HT2, dopaminergic, and adrenergic mechanisms in this behavior.     

Activation of 5-HT(1B/1D) receptors in the mesolimbic dopamine system increases dopamine release from the nucleus accumbens: a microdialysis study

This study was designed to investigate the role of 5-hydroxytryptamine (5-HT)(1B) receptors located in the ventral tegmental area and nucleus accumbens in the modulation of accumbal dopaminergic transmission. The selective 5-HT(1B) receptor agonist CP 93129 [3-(1,2,5,6-tetrahydro-4-pyridyl)pyrrolo[3,2-b]pyrid-5-one] was administered into the ventral tegmental area or nucleus accumbens of freely moving Sprague-Dawley rats via retrograde microdialysis. The effects of intra-accumbal and intra-tegmental CP 93129 on extracellular dopamine levels in the nucleus accumbens were measured using one- and dual-probe microdialysis, respectively. For dual-probe microdialysis, one probe was in the ventral tegmental area for drug administration and the other in the ipsilateral nucleus accumbens for dopamine measurement. The results show that infusion of CP 93129 (2, 5 and 10 microM) into the nucleus accumbens increased local dopamine levels in a concentration-related manner. Infusion of CP 93129 (10 and 20 microM) into the ventral tegmental area also increased dopamine levels in the ipsilateral nucleus accumbens. The increased dopamine release in the nucleus accumbens produced by intra-accumbal or intra-tegmental CP 93129 was antagonized by co-infusion of cyanopindolol (5 microM), a 5-HT(1B/1A) receptor antagonist, but not by WAY-100635 [N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-2-pyridinyl-cyclohexanecarboxamide] (5 microM), a highly selective 5-HT(1A) receptor antagonist. In addition, augmentations of dopamine release in the nucleus accumbens induced by intra-accumbal CP 93129 were sensitive to Na(+) channel blockade with tetrodotoxin. These results are not in opposition to the concept that 5-HT(1B) receptors within the ventral tegmental area and nucleus accumbens are all involved in the modulation of dopamine release in the terminal area of the mesolimbic dopamine system.     

Infusion of the serotonin1B (5-HT1B) agonist CP-93,129 into the parabrachial nucleus potently and selectively reduces food intake in rats

Unilateral infusion of the selective 5-HT_1B agonist, CP-93,129 (3-(1,2,5,6-tetrahydropyrid-4-yl) pyrrolo[3,2-b]pyrid-5-one) into the parabrachial nucleus (PBN) of the pons reduced food consumption by rats. The hypophagia was dose-related (ED₅₀ ≈ 1 nmol) and associated with fewer observations of feeding and more periods of inactivity. Water intake, grooming and exploratory activity were unaffected. CP-93,129 also decreased food intake when injected into the hypothalamic paraventricular nucleus, but this action was 50-fold less potent than administration into the PBN. Autoradiography demonstrated 5-HT_1B sites in the PBN; this binding was displaced by CP-93,129. The results implicate parabrachial 5-HT_1B receptors in mediating serotonergic enhancement of satiation. Received: 11 November 1997/Final version: 20 November 1997     

Muscarinic cholinergic agonists and antagonists of the 3-(3-alkyl-1,2,4-oxadiazol-5-yl)-1,2,5,6-tetrahydropyridine type. Synthesis and structure-activity relationships

A series of 3-(3-alkyl-1,2,4-oxadiazol-5-yl)-1,2,5,6-tetrahydro-1-methylpyr idines (2a-q) were synthesized and tested for central muscarinic cholinergic receptor binding affinity by using [3H]oxotremorine-M and [3H]QNB as ligands and in a functional assay using guinea pig ileum. The analogues with unbranched C1-8-alkyl substituents (2a-g) were agonists, whereas the compounds with branched or cyclic substituents (2h-m) were antagonists. The alkyl ether analogues (2o-q) were also agonists but had lower receptor binding affinity than the corresponding alkyl analogues. The 3-(5-alkyl-1,2,4-oxadiazol-3-yl)-1,2,5,6-tetrahydro-1-methylpyridi ne analogues had only ver low affinity for the central muscarinic receptors and were weak antagonists in the ileum assay. A few 3-(3-butyl-1,2,4-oxadiazol-5-yl)-1,2,5,6-tetrahydro-1-methylpyr idines substituted with methyl or hydrogen in the 1-, 5-, or 6-position were synthesized and tested. N-Desmethyl analogue 7 was a potent muscarinic agonist, whereas N-desmethyl-5-methyl analogue 11 and N-methyl-6-methyl analogue 13 both were antagonists with lower muscarinic receptor affinity. The 3-(3-butyl-1,2,4-oxadiazol-5-yl)quinuclidine (17) and tropane (15) analogues were both very potent antagonists with high affinity for central muscarinic receptors. The ratio [IC50(QNB)/IC50(Oxo-M)] x 0.162 proved to be a good indicator of the efficacy of the compounds in the guinea pig ileum assay.     

Novel N-[omega-[4-(2-methoxyphenyl)piperazin-1-yl]-ethyl]pyrid-2(1H)-ones with diversified 5-HT1A receptor activity

Novel omega-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl derivatives 1-6 containing 4-, 5- and/or 6-arylsubstituted pyrid-2(1H)-one moiety were synthesized. All the new compounds were examined in vitro to assess their 5-HT1A and 5-HT2A receptor affinities. Compounds 3 and 4 with a 5- or a 6-phenylsubstituted pyridone ring demonstrated high 5-HT1A receptor affinity (Ki = 17 and 38 nM, respectively) and were tested in behavioral functional models. Derivative 3 can be regarded as a weak 5-HT1A postsynaptic antagonist, whereas 4 showed features of a weak partial agonist of 5-HT1A receptors (an agonist of pre- and an antagonist of postsynaptic ones). Binding affinities and in vivo results were discussed in comparison with those for the previously described tetramethylene analogs. The obtained results showed that the shortening of the aliphatic chain to two methylene groups exposed the intrinsic activity of the ligand 4 at 5-HT1A receptor sites.     

Substitution mode of the amide fragment in some new N-[omega-[4-(2-methoxyphenyl)piperazin-1-yl]alkyl]pyrid-2(1H)-ones and their 5-HT1A/5-HT2A activity

A series of omega-[4-(2-methoxyphenyl)piperazin-1-yl]alkyl derivatives with terminal pyrid-2(1H)-one fragments was synthesized and evaluated for their 5-HTIA and 5-HT2A activity. Enlargement of the aromatic amide system by its substitution with phenyl and/or p-methoxyphenyl in positions 4, 5 and/or 6, as well as modification of an aliphatic spacer allowed us to better understand structure-activity relationships in that group of compounds. The results of in vitro and in vivo experiments showed that only unsubstituted (1b) and monosubstituted (2b-4b) derivatives with the tetramethylene spacer demonstrated high 5-HTIA receptor affinity (Ki = 15-40 nM) and 5-HT1A/5-HT2A selectivity; they exhibited features of 5-HTIA antagonists. Those results suggested that the mode of substitution of the terminal amide moiety in the tested tetramethylene arylpiperazines was not significant for their 5-HTIA receptor activity. Conformational analysis calculations indicated that despite its great capacity for adaptation at 5-HTIA receptor site, an aryl substituent in position 4 in the pyrid-2(1H)-one ring destabilized the ligand-5-HT1A receptor complex formation in the case of trimethylene derivatives. Diarylsubstituted derivatives (5a-8a and 5b-8b) were characterized by a low 5-HT2A affinity (Ki > 446 nM) regardless of the spacer length, while those with the tetramethylene aliphatic chain had a higher 5-HT2A affinity than the remaining investigated compounds.     

New 3-[4-(2,3-dihydro-14-benzodioxin-5-yl)piperazin-1-yl]-1-(5-substituted benzo[b]thiophen-3-yl)propanol derivatives with dual action at 5-HT(1A) serotonin receptors and serotonin transporter as a new class of antidepressants

Compounds derived from 2,3-dihydro-(1,4-benzodioxin-5-yl)piperazine and benzo[b]thiophene with different substituents in 5 position (H, F, NO2, NH2, CH3 and OH) have been synthesized in order to obtain new dual antidepressant drugs. The final compounds were evaluated for in vitro 5-HT(1A) receptor affinity and serotonin reuptake inhibition by radioligand assays. Compounds 1-(5-nitrobenzo[b]thiophen-3-yl)-3-[4-(2,3-dihydro-1,4-benzodioxin-5-yl)piperazin-1-yl]propan-1-ol (4c) (Ki = 6.8 for 5-HT(1A) receptor and Ki = 14 for 5-HT transporter) and 1-(5-hydroxybenzo[b]thiophen-3-yl)-3-[4-(2,3-dihydro-1,4-benzodioxin-5-yl)piperazin-1-yl] propan-1-ol (4f) (Ki = 6.2 for 5-HT(1A) receptor and Ki = 18.2 for 5-HT transporter) showed the best results for both activities.     

1-(2-Aminoethyl)-3-methyl-8,9-dihydropyrano[3,2-e]indole: a rotationally restricted phenolic analog of the neurotransmitter serotonin and agonist selective for serotonin (5-HT2-type) receptors.

A series of rotationally restricted phenolic analogs of the neurotransmitter serotonin has been synthesized with the 5-hydroxyindole portion of serotonin replaced by a dihydropyrano[3,2-e]-indole (1, 3, 4, and 5) and a dihydropyrano[2,3-f]indole (2). The receptor binding profile of these compounds has been studied and compared to the natural substrate serotonin. The dihydropyrano[3,2-e]indole derivatives (1, 3, 4, and 5) possess lower affinity for 5-HT1 receptors but equal or greater affinity for 5-HT2 receptors. Like serotonin, these compounds dose-dependently stimulated phosphatidylinositol turnover in rat brain slices. Moreover, the response to 1-(2-aminoethyl)-3-methyl-8,9-dihydropyrano[3,2-]indole (5, CP-132,484) and 1-(2-aminoethyl)-8,9-dihydropyrano[3,2-e]indole (4) is selectively antagonized by 5-HT2 receptor antagonists establishing these tryptamines as selective 5-HT2 receptor agonists. The high affinity and potency of 5 for 5-HT2 receptors suggests that the C5-hydroxy group in serotonin can function as a hydrogen bond acceptor in a 5-HT2 receptor with a directionality of interaction which is down and away from C6 in serotonin (Figure 5). Furthermore, the potent affinity of these compounds for 5-HT2 receptors coupled with their poor affinity for 5-HT1 receptors indicates that the aminoethyl side chain of serotonin adopts significantly different conformations in 5-HT1 versus 5-HT2 receptors.     

The 5HT(1B) receptor agonist, CP-93129, inhibits [(3)H]-GABA release from rat globus pallidus slices and reverses akinesia following intrapallidal injection in the reserpine-treated rat

This study examined whether activation of 5HT(1B) receptors in the rodent globus pallidus (GP) could reduce GABA release in vitro and reverse reserpine-induced akinesia in vivo. Microdissected slices of GP from male Sprague Dawley rats (300-350 g) were preloaded with [(3)H]-GABA. During subsequent superfusion, 4 min fractions were collected for analysis of release. The effects of the 5HT(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3, 2-b]pyrid-5-one (CP-93129), on 25 mM KCl-evoked release were examined using a standard dual stimulation paradigm. Male Sprague Dawley rats (270 - 290 g), stereotaxically cannulated above the GP, were rendered akinetic by injection of reserpine (5 mg kg(-1) s.c.). Eighteen hours later, the rotational behaviour induced by unilateral injection of CP-93129 was examined. CP-93129 (0.6-16.2 microM) produced a concentration-dependent inhibition of 25 mM KCl-evoked [(3)H]-GABA release reaching a maximum inhibition of 52.5+/-4.5%. The effect of a submaximal concentration of CP-93129 (5.4 microM) was fully inhibited by the 5HT(1B) receptor antagonist, isamoltane (10 microM). Following intrapallidal injection, CP-93129 (30-330 nmol in 0.5 microl) produced a dose-dependent increase in net contraversive rotations reaching a maximum of 197+/-32 rotations in 240 min at 330 nmol. Pre-treatment with isamoltane (10 nmol in 1 microl) inhibited the effects of a submaximal dose of CP-93129 (220 nmol) by 84+/-6%. These data suggest that at least some 5HT(1B) receptor function as heteroreceptors in the GP, reducing the release of GABA. Moreover, CP-93129-mediated activation of these receptors in the GP provides relief of akinesia in the reserpine-treated rat model of PD.     

Specific labelling of serotonin 5-HT(1B) receptors in rat frontal cortex with the novel, phenylpiperazine derivative, [3H]GR125,743. A pharmacological characterization

Although several tritiated agonists have been used for radiolabelling serotonin (5-hydroxytryptamine, 5-HT)(1B) receptors in rats, data with a selective, radiolabelled antagonist have not been presented. Inasmuch as [3H]GR125,743 specifically labels cloned, human and native guinea pig 5-HT(1B) receptors and has been employed for characterization of cerebral 5-HT(1B) receptor in the latter species [Eur. J. Pharmacol. 327 (1997) 247.], the present study evaluated its utility for characterization of native, cerebral 5-HT(1B) sites in the rat. In homogenates of frontal cortex, [3H]GR125,743 (0.8 nM) showed rapid association (t(1/2)=3.4 min), >90% specific binding and high affinity (K(d)=0.6 nM) for a homogeneous population of receptors with a density (B(max)) of 160 fmol/mg protein. In competition binding studies, affinities were determined for 15 chemically diverse 5-HT(1B) agonists, including 2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl]-1H-indole-3-yl]ethylamine (L694,247; pK(i), 10.4), 5-carboxamidotryptamine (5-CT; 9.7), 3-[3-(2-dimethylamino-ethyl)-1H-indol-6-yl]-N-(4-methoxybenzyl)acrylamide (GR46,611; 9.6), 5-methoxy-3-(1,2,5,6-tetrahydro-4-pyridinyl)-1H-indole (RU24,969; 9.5), dihydroergotamine (DHE; 8.6), 5-H-pyrrolo[3,2-b]pyridin-5-one,1,4-dihydro-3-(1,2,3,6-tetrahydro-4-pyridinyl (CP93,129; 8.4), anpirtoline (7.9), sumatriptan (7.4), 1-[2-(3-fluorophenyl)ethyl]-4-[3-[5-(1,2,4-triazol-4-yl)-1H-indol-3-yl]propyl]piperazine (L775,606; 6.4) and (minus sign)-1(S)-[2-[4-(4-methoxyphenyl)piperazin-1-yl]ethyl]-N-methyl-3,4-dihydro-1H-2-benzopyran-6-carboxamide (PNU109,291; <5.0). Similarly, affinities were established for 13 chemically diverse antagonists, including N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-3-methyl-4-(4-pyridyl)benzamide (GR125,743; pK(i), 9.1), (-)cyanopindolol (9.0), (-)-tertatolol (8.2), N-(4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiozol-3-yl)biphenyl-4-carboxamide (GR127,935; 8.2), N-[3-(1,4-benzodioxan-5-yl)piperidin-4-yl]N-(indan-2yl)amine (S18127; 7.9), metergoline (7.8), (-)-pindolol (7.6), 1'-methyl-5-[2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-biphenyl-4-ylcarbonyl]-2,3,6,7-tetrahydro-5H-spiro[furo[2,3-f]indole-3,4'-piperidine] (SB224,289; 7.5) and ketanserin (<5.0). These rank orders of affinity correspond to the binding profile of 5-HT(1B) rather than 5-HT(1D) receptors. The low affinities of L775,066 and PNU109,291 versus L694,247 should be noted, as well as the low affinity of ketanserin as compared to SB224,289. Finally, in line with species differences, the affinities of several ligands including CP93,129, RU24,969, (-)-pindolol and (-)-propanolol in rat 5-HT(1B) sites were markedly different to guinea pig 5-HT(1B) sites labelled with [3H]GR125,743. In conclusion, [3H]GR125,743 is an appropriate tool for the radiolabelling of native, rat 5-HT(1B) receptors and permitted determination of the affinities of an extensive series of ligands at these sites.     

Syntheses and 5-HT2 antagonist activity of bicyclic 1,2,4-triazol-3(2H)-one and 1,3,5-triazine-2,4(3H)-dione derivatives.

A series of bicyclic 1,2,4-triazol-3(2H)-one and 1,3,5-triazine-2,4(3H)-dione derivatives with a 4-[bis(4-fluoro-phenyl)methylene]piperidine or 4-(4-fluorobenzoyl)piperidine group has been prepared and tested for 5-HT2 and alpha 1 receptor antagonist activity. Among the compounds prepared, 2-[2-[4-[bis(4-fluorophenyl)methylene]-piperidin-1-yl]ethyl]- 5,6,7,8-tetrahydro-1,2,4-triazolo[4,3-a]pyridin-3(2H)-one (7b) had the most potent 5-HT2 antagonist activity, which was greater than ritanserin (2), while 7b did not show alpha 1 antagonist activity in vivo. The central 5-HT2 receptor antagonism was approximately 1/30 that of 2 when tested for the ability to block head twitches induced by 5-hydroxytryptophan. Compound 21b, 3-[2-[4-(4-fluorobenzoyl)piperidin-1-yl]ethyl]-6,7,8,9-tetrahydro- 2H- pyrido[1,2-a]-1,3,5-triazine-2,4(3H)-dione also displayed potent 5-HT2 antagonist activity. The compound had moderate alpha 1 receptor antagonism, and the potency inhibiting head twitches was about one-third that of ketanserin (1). These results indicate that 5,6,7,8-tetrahydro-1,2,4-triazolo[4,3-a]pyrimidin-3(2H)-one and 6,7,8,9-tetrahydro-2H-pyrido-[1,2-a]-1,3,5-triazine-2,4(3H)-dione ring systems are useful components of 5-HT2 antagonists.     

New 3-[4-(3-substituted phenyl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propanol derivatives with dual action at 5-HT1A serotonin receptors and serotonin transporter as a new class of antidepressants

In this paper a series of new 3-[4-(3-substituted phenyl)piperazin-1-yl]-1-(benzo[b]thiophen-3-yl)propanol derivatives is presented as a new class of antidepressant drugs with dual activity at 5-HT1A serotonin receptors and serotonin transporter. The 5-HT1A receptor and 5-HT transporter binding affinities of hydroxylic compounds 4 a-e have been determined. The new compounds present nanomolar affinity for both activities, and 1-(benzo[b]thiophen-3-yl)-3-[4-(3-methoxyphenyl)piperazin-1-yl]propan-1-ol (4d) shows values (nM) of Ki = 86 for 5-HT1A receptors and Ki = 76 for the serotonin transporter, respectively.