Search

Several lines of evidence indicate that inhibition of the metabotropic glutamate (mGlu) receptor 5 produces anxiolytic-like effects in rodents. Peptide neurotransmitter neuropeptide Y (NPY) produces an anxiolytic effect in rats after intraventricular or intra-amygdalar administration. Many classes of anxiolytic drugs exert their effect through the GABA-benzodiazepine (BZD) receptor complex. Therefore, in the present study we have investigated whether the anxiolytic action of MPEP (2-methyl-6-(phenylethynyl)pyridyne), an mGlu5 receptor antagonist, is mediated by a mechanism involving either the GABA-BZD receptor complex or NPY receptor. In the behavioral studies, the anxiolytic activity of MPEP (10 mg/kg, i.p.) was examined using plus-maze test. The BZD antagonist flumazenil (10 mg/kg, i.p.) was given to one group of rats and Y I receptor antagonist BIBO 3304 (((R)-N-[[4-(aminocarbonylaminomethyl) phenyl] methyl]-N2-(diphenylacetyl)-argininamide trifluoroacetate)3304) (200 pmol/site, intra-amygdala) to the other. It was found that anxiolytic effects of MPEP were not changed by flumazenil, but were abolished by BIBO 3304. Immunohistochemical studies showed a high density of mGlu5 receptor immunoreactivity (IR) in the amygdala. The effect of MPEP on NPY expression in the amygdala was studied using immunohistochemistry (IH) and radioimmunoassay (RIA). Both methods showed a diminution of NPY IR expression, to about 43% (IH) or 81% (RIA) of the control level after multiple administrations, but we observed an increase up to 148% of the control after single MPEP administration. These effects may suggest a release of NPY from nerve terminals after MPEP administration. Our results indicate that the anxiolytic action of MPEP is conveyed through NPY neurons with the involvement of YI receptors in the amygdala and that BZD receptors do not significantly contribute to these effects. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the selective 5-hydroxytryptamine1B (5-HT1B) receptor agonist 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-pyrrolo[3,2-b]pyridine (CP 94253) and the 5-HT1A/1B/1D receptor agonist 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridyl)-1H-indole (RU 24969) in maximal electroshock- and pentylenetetrazol-induced seizures in mice was examined. CP 94253 (10–40 mg/kg) afforded no protection against maximal electroshock-evoked convulsions, but produced anticonvulsant action in the pentylenetetrazol-induced seizures (ED50 =29 mg/kg). The anticonvulsant effect of CP 94253 was abolished by the selective 5-HT1B receptor antagonist N-[3-(2-dimethylamino)ethoxy-4-methoxyphenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1′-biphenyl)-4-carboxamide (SB 216641; 20 mg/kg) but it was maintained following the p-chlorophenylalanine (p-CPA; 3×300 mg/kg)-induced 5-HT depletion. Interestingly, CP 94253 potentiated the anticonvulsant activity of diazepam in the pentylenetetrazol test; on the other hand, the benzodiazepine receptor antagonist, flumazenil (10 mg/kg), did not modify the anticonvulsant effect of CP 94253. RU 24969 (5 mg/kg) evoked no effect in the maximal electroshock model, but it produced anticonvulsant activity in the pentylenetetrazol assay, the latter effect being attenuated by the selective 5-HT1A receptor antagonist N-(2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl)-N-(2-pyridyl)-cyclohexanecarboxamide (WAY 100635; 0.3 mg/kg) and SB 216641 (10–20 mg/kg). The obtained results suggest that CP 94253 exerts anticonvulsant activity on pentylenetetrazol-induced seizures in mice, as a consequence of stimulation of 5-HT1B receptors (probably located postsynaptically and/or as heteroreceptors); the antiseizure activity of RU 24969 seems to depend on the stimulation of both 5-HT1A and 5-HT1B receptors. [Copyright &y& Elsevier]

Several lines of evidence suggest a crucial involvement of glutamate in the mechanism of action of anxiolytic drugs including the involvement of group I metabotropic glutamate (mGlu) receptors. Given the recent discovery of a selective and brain penetrable mGlu5 receptor antagonists, the effect of 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]-pyridine (MTEP), i.e. the most potent mGlu5 antagonist, was evaluated in established models of anxiety after single or repeated administration. We also studied if the anxiolytic effect of MTEP is mediated by mechanism involving the GABA–benzodiazepine (BZD) receptor complex. Experiments were performed on male Wistar rats or male Albino Swiss mice. The anxiolytic-like effects of MTEP were tested in the conflict drinking test and the elevated plus-maze test in rats as well as in the four-plate test in mice. MTEP (0.3–3.0 mg/kg) induced anxiolytic-like effects in the conflict drinking test (after single and repeated administration) and in the elevated plus-maze test in rats. In the four-plate test in mice, it exerted anxiolytic activity at a dose of 20 mg/kg. MTEP had no effect on the locomotor activity of animals. The anxiolytic-like effect of MTEP was not changed by BZD antagonist flumazenil. Moreover, a synergistic interaction between non-effective doses of MTEP and diazepam was observed in the conflict drinking test. These data suggest that selective mGlu5 receptor antagonists mediated anxiolysis is not dependent on GABA-ergic system and that these agents may play a role in the therapy of anxiety. [Copyright &y& Elsevier]

In the present paper, we examined the effect of lesions of 5-hydroxytryptamine (5-HT) neurons, produced by p-chloroamphetamine (p-CA; 2×10 mg/kg), and the influence of flumazenil (Ro 15-1788, 10 mg/kg), a benzodiazepine receptor antagonist, on the anticonflict activity of N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl)cyclohexanecarboxamide (WAY 100635) and trans-1-(2-methoxy-phenyl)-4-[4-succinimidocyclohexyl]piperazine (MP 349), pre- and postsynaptic 5-HT1A receptor antagonists, and 1-(2-methoxyphenyl)-4-(4-succinimidobutyl)piperazine (MM 77), a postsynaptic 5-HT1A receptor antagonist, in the Vogel conflict drinking test in rats. Diazepam was used as a reference compound. WAY 100635 (0.5–1 mg/kg), MP 349 (0.25–0.5 mg/kg), MM 77 (0.03–0.25 mg/kg) and diazepam (2.5–5 mg/kg) significantly increased the number of shocks accepted during experimental sessions in the conflict drinking test. In p-chloroamphetamine-pretreated rats, neither WAY 100635 (1 mg/kg) nor MP 349 (0.25 mg/kg) induced an anticonflict effect, whereas MM 77 (0.06 mg/kg) did produce it. Flumazenil fully blocked the anticonflict effects of WAY 100635 (1 mg/kg) and diazepam (5 mg/kg), and it partly but significantly reduced the anticonflict effects of MP 349 (0.25 mg/kg) and MM 77 (0.06 mg/kg). p-Chloroamphetamine and flumazenil alone were inactive in the conflict drinking test. The present results suggest that, first, the anticonflict effect of the 5-HT1A receptor antagonists, WAY 100635 and MP 349, but not MM 77, is linked to the presynaptically located 5-HT1A receptors, and second, benzodiazepine receptors are indirectly involved in such effects of WAY 100635, MP 349 and MM 77, due maybe to a possible interaction between the 5-HT and the γ-aminobutyric acid (GABA)/benzodiazepine systems. [Copyright &y& Elsevier]

Abstract: The synthesis of 5-(cyclo)alkyl-5-phenyl- and 5-spiroimidazolidine-2,4-dione derivatives with an arylpiperazinylpropyl moiety (12–23) and their in vitro and in vivo pharmacological properties and molecular characteristics were described. The investigated compounds exhibited high affinity for 5-HT1A (13–22) and 5-HT2A (18, 20, 21, 23) receptors and diversified pharmacological profile. Compounds 17, 20 and 22 showed antagonistic, partial agonistic and agonistic activity, respectively, toward 5-HT1A receptor and they were investigated as potential antidepressants and/or anxiolytics. The most interesting compound 22 (1-[3-(4-(2-methoxyphenyl)piperazin-1-yl)propyl]-3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione), a pre- and postsynaptic 5-HT1A receptor agonist produced an antidepressant-like effect, which was more pronounced than that of imipramine in the forced swim test in mice, without affecting locomotor activity. Moreover, compound 22 produced a weak anxiolytic-like effect in the four-plate test in mice. Molecular docking studies of compound 22 to the homology model of the 5-HT1A receptor showed that a 3′,4′-dihydro-2′H-spiro[imidazolidine-4,1′-naphthalene]-2,5-dione moiety played an important role in stabilizing the ligand–receptor complex. [Copyright &y& Elsevier]

Abstract: New, flexible (7, 9, 11 and 13) and rigid (8, 10, 12 and 14) imides with a 1-(m-trifluorophenyl)piperazine fragment and a tetramethylene or a 1e,4e-cyclohexylene spacer, respectively, showed very high affinity (K i =0.3–34nM) and agonistic in vivo activity for 5-HT1A receptors. Flexible new compounds and the previously described 5 also bound to 5-HT7 receptors (K i =21–134nM). Selected glutarimide derivatives, that is, the most potent postsynaptic 5-HT1A receptor agonist rigid compound 8 and its flexible analogue 7, as well as the previously described full agonist—rigid compound 6 and the partial agonist—its flexible counterpart 5 exhibited moderate affinity for α1-adrenoceptors (K i =85–268nM), but were practically devoid of any affinity for dopamine D2 sites. Those glutarimides demonstrated anxiolytic- (5 and 7) and antidepressant-like (5, 6 and 8) activity in the four-plate and the swim tests in mice, respectively; at the same time, however, they inhibited the locomotor activity of mice. The antidepressant-like effect of 8 was significantly stronger than that induced by imipramine used as a reference antidepressant. [Copyright &y& Elsevier]

Abstract: Novel arylpiperazines with N-acylated amino acids, selected on the basis of a preliminary screening of two libraries previously synthesized on SynPhase™ Lanterns, were prepared in solution and their affinity for 5-HT1A, 5-HT2A, and D2 receptors was evaluated. The compounds bearing (3-acylamino)pyrrolidine-2,5-dione (19–26) and N-acylprolinamide (29–34) moieties showed high affinity for 5-HT1A (K i =3–47nM), high-to-low for 5-HT2A (K i =4.2–990nM), and low for D2 receptors (K i =0.77–21.19 μM). All the new o-methoxy derivatives of (3-acylamino)pyrrolidine-2,5-diones tested in vivo revealed agonistic activity at postsynaptic 5-HT1A receptors, while m-chloro derivatives were classified as antagonists of these sites; similar relations were observed for o-methoxy (29) and m-chlorophenylpiperazine derivatives of N-acylprolinamides. The reported results show that the amino acid-derived terminal fragment modified the in vivo functional profile. Finally, the selected compounds 19 and 20, a 5-HT1A partial agonist and a full agonist, respectively, and 26, a mixed 5-HT1A/5-HT2A antagonist, were evaluated in preclinical animal models of depression and anxiety. The project allowed selecting the lead compound 20 which exhibited an anxiolytic-like effect in the four-plate test in mice and revealed distinct antidepressant-like effects in the forced swimming and tail suspension tests in mice. [Copyright &y& Elsevier]

Abstract: Using the forced swimming test in mice, we examined the effect of the following antidepressants: citalopram, imipramine, desipramine and moclobemide (which are characterized by different mechanisms of action), administered in combination with the selective 5-HT7 receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB 269970). All those drugs were given in doses which did not shorten the immobility time of mice. Citalopram (1.25 mg/kg), imipramine (10 mg/kg), desipramine (5 mg/kg) or moclobemide (10 mg/kg) administered jointly with SB 269970 (5 mg/kg), produced a significant antidepressant-like effect. None of the compounds studied, given alone or in combination, increased the spontaneous locomotor activity of mice. The obtained results indicate that blockade of 5-HT7 receptors may facilitate the anti-immobility effect of antidepressants in mice. [Copyright &y& Elsevier]

Abstract: Introduction of 1,4-disubstituted cyclohexane ring in the structure of flexible long chain arylpiperazines resulted in linearly constrained, potent serotonin (5-HT)1A ligands. In order to trace structure–intrinsic activity relationships in this group, a new series of 1-substituted 4-(4-arylpiperazin-1-yl)cyclohexane derivatives with different cyclic imide/amide termini, and their flexible, tetramethylene analogues were synthesized and pharmacologically evaluated for 5-HT1A receptors. In vitro binding experiments revealed that all the compounds were potent 5-HT1A receptor agents (K i =1.9–74nM). Some derivatives tested additionally showed also high affinity for α1-adrenergic receptors (K i =2.9–101nM) and for 5-HT7 receptors. Functional in vivo examination revealed that rigid ligands with o-OCH3 group in the aryl moiety and cyclic imide system in the opposite terminal behaved like postsynaptic 5-HT1A receptor antagonists. On the other hand, unsubstituted, m-Cl, or m-CF3 substituted derivatives as well as those with cyclic amide group in the terminal fragment exhibited agonistic or partial agonistic activity. Three out of four derivatives tested, that is, postsynaptic 5-HT1A antagonists 9 and 10, and partial agonist 16, showed anxiolytic-like activity in the conflict drinking (Vogel) test in rats. [Copyright &y& Elsevier]

Abstract: A series of new 3-[4-(4-arylpiperazinyl)-butyl]-β-tetralonohydantoins (8a–13a) were synthesized. The compounds exhibited high affinity for 5-HT1A receptors (K i =6 to 55 nM) combined with moderate-to-high 5-HT2A receptor affinities (K i =45 to 213 nM). The results of in vivo studies indicated that of the compounds tested, 3-[4-(4-phenylpiperazinyl)-butyl-β-tetralonohydantoin (8a) showed features of full (pre- and postsynaptic) 5-HT1A receptor agonists, whereas compounds 9a–13a behaved like antagonists of postsynaptic 5-HT1A receptors; additionally, compound 13a produced an effect characteristic of presynaptic 5-HT1A receptor agonists. Moreover, compounds 8a and 10a–13a exhibited properties of 5-HT2A receptor antagonists. Due to the most interesting 5-HT1A/5-HT2A functional profile compounds 8a and 13a were further tested for their potential psychotropic activity. In fact, compound 8a (but not 13a) showed diazepam—like anxiolytic activity and behaved like a weak antidepressant. [Copyright &y& Elsevier]

Abstract: The mechanism of the antidepressant-like activity of the selective 5-hydroxytryptamine1B (5-HT1B) receptor agonist 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-pyrrolo[3,2-b]pyridine (CP 94253) was studied in the forced swimming test in mice. CP 94253 administered intraperitoneally at a single dose of 5 mg/kg potently shortened the immobility time of mice. The anti-immobility effect of CP 94253 was wholly blocked by the selective 5-HT1B receptor antagonist N-[3-(2-dimethylamino)ethoxy-4-methoxyphenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1′-biphenyl)-4-carboxamide (SB 216641, 5 mg/kg), the dopamine D2-like receptor antagonist sulpiride (50 mg/kg) and the α2-adrenoceptor antagonist idazoxan (2 mg/kg), but was not modified in animals with a lesion of the 5-HT system produced by p-chlorophenylalanine (p-CPA, 3×300 mg/kg). The obtained results suggest that the anti-immobility effect of CP 94253 is mediated by activation of 5-HT1B receptors—most probably located postsynaptically and/or as heteroreceptors, and that the dopamine and the noradrenaline systems are involved in this action. [Copyright &y& Elsevier]

Abstract: Starting with the structure of potent 5-HT1A ligands, that is, MM77 [1-(2-methoxyphenyl)-4-(4-succinimidobutyl)piperazine, 4] and its constrained version 5 (MP349), previously obtained in our laboratory, a series of their direct analogues with differently substituted aromatic ring (R=H, m-Cl, m-CF3, m-OCH3, p-OCH3) were synthesized. The flexible and the corresponding 1e,4e-disubstituted cyclohexane derivatives were designed in order to investigate the influence of rigidification on 5-HT1A affinity, selectivity for 5-HT2A, 5-HT7, D1, and D2 binding sites and functional profile at pre- and postsynaptic 5-HT1A receptors. The new compounds 19–25 were found to be highly active 5-HT1A receptor ligands (Ki=4–44nM) whereas their affinity for other receptors was: either significantly decreased after rigidification (5-HT7), or controlled by substituents in the aromatic ring (α1), or influenced by both those structural modifications (5-HT2A), or very low (D2, Ki=5.3–31μM). Since a distinct disfavor towards rigid compounds was observed for 5-HT7 receptors only, it seems that the bioactive conformation of chain derivatives at those sites should differ from the extended one. Several in vivo models were used to asses functional activity of 19–25 at pre- (hypothermia in mice) and postsynaptic 5-HT1A receptors (lower lip retraction in rats and serotonin syndrome in reserpinized rats). Unlike the parent antagonists 4 and 5, all the new derivatives tested were classified as partial agonists with different potency, however, similar effects were observed within pairs (flexible and rigid) of the analogues. The obtained results indicated that substitution in the aromatic ring, but not spacer rigidification, controls the 5-HT1A functional activity of the investigated compounds. Moreover, an o-methoxy substituent in the structure of 5 seems to be necessary for its full antagonistic properties. Of all the new compounds studied, trans-4-(4-succinimidocyclohexyl)-1-(3-trifluoromethylphenyl)piperazine 24 was the most potent 5-HT1A receptor ligand in vitro (Ki=4nM) and in vivo, with at least 100-fold selectivity for the other receptors tested. [Copyright &y& Elsevier]

In CNS, the 5-hydroxytryptamine1A (5-HT1A) receptors exist in two different populations with different behavioural and physiological effects: (1) somatodendritic autoreceptors located pre-synaptically of 5-HT containing neurons and (2) receptors located post-synaptic to 5-HT containing neurons. Clinical studies have shown that 5-HT1A partial agonists have anxiolytic properties, while antagonists of pre-synaptical autoreceptors shorten the onset time of selective serotonin reuptake inhibitors (SSRIs). In the present study, the pre- and post-synaptic activity of structural analogues of buspirone was evaluated in animal models. A three dimensional model of the 5-HT1A receptor was used to study their interaction modes and helical displacements upon receptor binding. The predicted receptor–ligand interactions indicated similarities in the receptor binding modes for all buspirone analogues, and no clear relationship between receptor contact residues and activity at pre- and post-synaptic receptors. Comparative molecular dynamics (MD) simulations for 650 ps indicated that pre-synaptic antagonistic behaviour is connected to large displacements of transmembrane helix (TMH) 7 upon binding, while pre-synaptic agonistic behaviour is connected to large displacements of TMH2 and small displacements of TMH7. Post-synaptic partial agonist behaviour is connected to large displacements of TMH4 and TMH5 upon binding, while post-synaptic antagonists only slightly displace these helices. [Copyright &y& Elsevier]

In the present study, we examined effects of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor citalopram, the 5-HT/noradrenaline reuptake inhibitor imipramine, the selective noradrenaline reuptake inhibitor desipramine or the monoamine oxidase-A inhibitor moclobemide, administered in combination with the 5-HT1A receptor antagonist N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridynyl)cyclohexanecarboxamide (WAY 100635) or the 5-HT1B/1D receptor antagonist N-[4-methoxy-3-(4-methyl-1-piperazinyl)phenyl]-2′-methyl-4′-(5-methyl-[1,2,4]oxadiazol-3-yl)1,1′-biphenyl-4-carboxamide (GR 127935) and the 5-HT1B receptor antagonist N-[3-(2-dimethylamino) ethoxy-4-methoxyphenyl]-2′-methyl-4′-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1′-biphenyl)-4-carboxamide (SB 216641) in the forced swimming test in rats. When given alone, citalopram (20 and 30 mg/kg), imipramine (20 mg/kg), desipramine (20 mg/kg), moclobemide (20 mg/kg), WAY 100635 (0.1 and 1 mg/kg), GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) did not shorten the immobility time of rats. Co-administration of WAY 100635 (0.1 and 1 mg/kg) and citalopram (20 mg/kg), or imipramine (20 mg/kg), or moclobemide (20 mg/kg) did not affect the immobility time of rats, whereas WAY 100635 given jointly with desipramine (20 mg/kg) induced a weak anti-immobility effect. GR 127935 (10 and 20 mg/kg) or SB 216641 (2 mg/kg) co-administered with imipramine, desipramine or moclobemide, but not citalopram, produced a significant anti-immobility action in the forced swimming test in rats. These results indicate that the blockade of 5-HT1B rather than 5-HT1A receptors may facilitate the anti-immobility effect of imipramine, desipramine or moclobemide in the forced swimming test. No interaction was observed between 5-HT1A or 5-HT1B/1D receptor antagonists and citalopram. [Copyright &y& Elsevier]

On the basis of systematic studies on the structure–activity relationships in arylpiperazine group of serotonin ligands, 12 new derivatives containing quinazolidin-4(3H)-one (1–4), 2-phenyl-2,3-dihydrophthalazine-1,4-dione (5–8) or 1-phenyl-1,2-dihydropyridazine-3,6-dione (9–12) fragments were synthesized. The majority of the tested compounds (2, 4, 7, 8 and 10–12) showed a high affinity for 5-HT1A receptors (Ki=11–54 nM) and two (1, 2) were found active at 5-HT2A sites (16 and 68 nM, respectively). All the new 5-HT1A ligands tested in vivo revealed an antagonistic activity at postsynaptic 5-HT1A receptors, and three of them behaved as agonists at presynaptic ones. Additionally, both the meta-chlorophenylpiperazine derivatives containing quinazolidin-4-one fragment showed features of 5-HT2A receptor antagonists. The dual 5-HT1A/5-HT2A receptor ligand (2) was further tested for its potential psychotropic activity. It showed a distinct anxiolytic-like activity in a conflict drinking test in rats and the observed effect was more potent in terms of the active dose, than that produced by diazepam (used as a reference drug). [Copyright &y& Elsevier]

In the present paper, we describe affinities to 5-HT1A and 5-HT2A receptors of several new 1,2,4-trisubstituted piperazine derivatives. The affinities were compared with those described earlier for 1,4-disubstituted piperazines and the influence of the third (methyl) substituent on the affinity to both receptors is discussed. The difference between two- and three-substituted derivatives was rationalised in terms of molecular modelling of the respective ligand–receptor complexes. Additionally, the functional activity of some 1,2,4-trisubstituted piperazines for 5-HT1A receptor was examined in behavioural and biochemical models. The obtained results have shown that some trisubstituted compounds exhibited a higher affinity to 5-HT2A receptors than their respective disubstituted analogues (with the affinity to 5-HT1A receptors remaining the same or somewhat improving). The molecular dynamics simulations suggested that the presence of the third substituent in the piperazine ring of those compounds may induce stabilising effect on the ligand–receptor complexes. The results of the in vivo studies have shown that some of the examined trisubstituted piperazines (10–13, 16, 17) exhibited properties of postsynaptic 5-HT1A partial agonists. Moreover, compounds 13 and 16 exhibited features of 5-HT1A presynaptic agonists in in vitro test, and compound 16 also in in vivo tests. [Copyright &y& Elsevier]

GABAergic hypothesis of anxiety was introduced many years ago, however, a limited number of supporting data were accumulated so far and the role of GABA(B) receptors in behavioral processes related to the anxiety disorders has not been resolved. In the present study, we examined anxiolytic activity of CGP 36742, a potent and selective GABA(B) receptor antagonist, in rodent tests/models. We have demonstrated that CGP 36742 (30 mg/kg) is active in several animal tests detecting anxiolytic activity (the elevated plus-maze, conflict drinking test and four-plate test). Moreover, we examined the effects of another antagonist--CGP51176 and agonist--CGP 44532 of GABA(B) receptor in the four-plate test in mice. CGP 51176 (5 or 8 mg/kg) was inactive, while CGP 44532 (0.125 mg/kg) exhibited anxiogenic-like effect. These preclinical data further implicate GABA(B) receptor function in anxiety, and support the GABAergic hypothesis of this disorder.

Recent literature data and the results of our earlier pharmacological studies, have provided evidence that antagonists of group I metabotropic glutamate receptors (mGluRs) and agonists of group II mGluRs show anxiolytic-like properties in preclinical and clinical studies. Out of all glutamate receptors, the role of group III mGluRs in anxiety-like states is the least investigated because of the lack of specific pharmacological tools, moreover all group III receptor ligands synthesized so far are not systemically active, so they have to be administered centrally. In the present study, we investigated the anxiolytic-like activity of group III mGlu receptor ligands including a nonselective group III mGlu receptor agonist (1S,3R,4S)-1-aminocyclopentane-1,3,4-tricarboxylic acid (ACPT-I), group III mGlu receptor antagonist, (RS)-alpha -cyclopropyl-4-phosphonophenylglycine (CPPG) and a positive allosteric modulator of mGluR4 (-)-N-phenyl-7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxamide (PHCCC). The Vogel conflict drinking test in rats was used to test the anxiolytic-like effects. The hippocampus was chosen as a site of the injection of drugs, as this brain regions is involved in the regulation of anxiety-related behavior. Intrahippocampal injections (CA1 region of the hippocampus) of PHCCC (12 nmol) but not of CPPG (75 nmol ) produced an anxiolytic-like response, moreover, the effect of PHCCC was totally blocked by CPPG. The anxiolytic-like effects of ACPT-I (7.5 nmol) or PHCCC (12 nmol) were significantly attenuated by flumazenil (10 mg/kg), indicating an involvement of GABAergic system in the anxiolytic-like response.

Substances acting as agonists of group III mGlu receptors were shown to induce an antianxiety-like effect after intrahippocampal administration to rats. The purpose of the present study was to establish whether the selective mGlu8 receptor agonist (S)-3,4-dicarboxyphenylglycine ((S)-3,4-DCPG) induced an anxiolytic-like effect after injection into the basolateral amygdala nuclei or the CA1 region of the hippocampus in the conflict drinking Vogel test in rats. The obtained results indicate that (S)-3,4-DCPG (10, 50 and 100 nmol/rat) produces no anticonflict effect in rats. We conclude that selective stimulation of mGlu8 receptors (a subtype of group III mGluRs) does not evoke anxiolytic-like activity, and that the mGlu8 receptors are of no significance for anxiolytic-like effects of group III mGluR agonists.

Two series of novel 4-ethyl- or 4-propyl-1-arylpiperazines (5-12) with the 4,4'-disubstituted diphenylmethylamino (series a) or the diphenylmethoxy (series b) terminal fragment were synthesized and evaluated for their binding affinity at 5-HT1A and 5-HT2A receptors. The influence of the introduction of 4-methyl, 4-chloro or 4-fluoro substituents at both phenyl rings of that terminal moiety on in vitro and in vivo 5-HT1A receptor activity of those modified compounds was discussed. Compounds 5a, 6a, 9a-12a, 5b, 6b, 9b, 11b and 12b displayed high to fairly high affinity for 5-HT1A receptors (Ki = 2.4-72 nM). Compounds of both series showed low or very low 5-HT2A receptor affinity (Ki = 155-5400 nM). Amines 5a, 6a, 11a, and their ether analogs 5b, 6b and 11b, also possessed high or moderate alpha(1)-adrenoceptor affinity (K(i) = 6-104 nM). The functional activity of compounds 5a, 6a, 9a-12a, 5b, 8b, 9b, 11b and 12b was tested in vivo in the commonly used animal models. The majority of those ligands behaved like 5-HT1A receptor antagonists, their influence on the pre- and/or postsynaptic sites being diverse, though. They exhibited characteristics of partial agonists of postsynaptic 5-HT1A receptors (11a), of weak antagonists of pre- and postsynaptic sites (12a, 9b), of antagonists of presynaptic (5a) or of antagonists of postsynaptic 5-HT(1A) receptors (9a, 10a, 5b, 8b, 11b and 12b) while, 6a was devoid of functional activity at those receptors. The above findings indicate that introduction of 4-methyl, 4-chloro or 4-fluoro substituents to the diphenylmethyl part of the 1-(2-methoxyphenyl)piperazines tested in vivo may modify their 5-HT1A receptor functional activity.

A series of 15 new 2-H- and 2-substituted 5-[omega-[4-(2-methoxyphenyl)-piperazinyl]-alkyl]-1,2,3,4-tetrahydro-gamma-carboline derivatives were prepared, and their affinity for 5-HT1A and 5-HT2A serotonin receptors was determined. Most of those hybrid compounds were found to bind with high affinity to 5-HT1A sites (Ki < 50 nM; 2d, 3a, 3b, 3d, 3e, 4b, 4d, 4e) and moreover two of them (4d, 4e) were mixed 5-HT1A/5-HT2A ligands. The results of a lower lip retraction test in rats indicated that the 2-acetyl derivative with a dimethylene spacer (2d) had features of a postsynaptic 5-HT1A receptor agonist, whereas its analogues with longer chains (3d and 4d) behaved like antagonists. Both 5-HT2A receptor ligands (4d, 4e) at high doses inhibited the (+/-)-DOI-induced head twitches in mice and were classified as weak antagonists of those receptors.

Two series of 4-alkyl-1-arylpiperazines (1-4) and 1,2,3,4-tetrahydroiso-quinolines (5, 6) with diphenylmethylamino (series a) or diphenylmethoxy (series b) fragment were synthesized in order to obtain potential ligands of 5-HT1A and/or 5-HT2A and dopamine D2 receptors. Four new arylpiperazines (1a, 3a, 1b, 3b) were found to demonstrate high 5-HT1A receptor affinity (Ki = 1.5-35 nM); among them, 3a exhibited satisfactory 5-HT2A receptor affinity (Ki = 74 nM). Only compounds 1b and 2b showed moderate affinity for D2 receptor sites (Ki = 123 and 128 nM, respectively). Compounds 1a, 3a, 1b and 3b were investigated in vivo to determine their functional activity at 5-HT1A receptors; additionally, 3a was tested for 5-HT2A receptor activity. Derivatives 1a, 1b and 3b produced effects characteristic of antagonists of postsynaptic 5-HT1A receptors. Moreover, 1b exhibited features of an agonist of presynaptic 5-HT1A receptors, while 3a behaved like a partial agonist of postsynaptic 5-HT1A sites. The latter derivative may also be classified as a 5-HT2A receptor antagonist. Thus, novel potent 5-HT1A receptor ligands were successfully obtained, and the most promising compound 3a showed mixed 5-HT1A/5-HT2A receptor activity in in vitro and in vivo tests.

Novel N-[3-(4-phenylpiperazin-1-yl)-propyl] derivatives of 3-spiro-cyclo-hexanepyrrolidine-2,5-dione (5-7) and 3-spiro-beta-tetralonepyrrolidine-2,5-dione (8-10) were synthesized and their 5-HT1A and 5-HT2A receptor affinities were determined. All tested compounds exhibited moderate to low 5-HT1A receptor affinity, whereas compounds 5-7 demonstrated high 5-HT2A receptor affinity (Ki = 27, 46 and 15 nM, respectively) and features of 5-HT2A receptor antagonists. Introduction of a beta-tetralone fragment in the 3-position of pyrrolidine-2,5-dione ring (8-10) did not affect 5-HT1A but decreased 5-HT2A receptor affinity.

We examined the anxiolytic-like activity of (1S,3R,4S)-1-aminocyclopentane-1,3,4-tricarboxylic acid (ACPT-I) using the Vogel conflict drinking test, while antidepressant-like effects of this compound were evaluated using Porsolt's test. ACPT-I, a selective group III mGlu receptor agonist, produced a dose-dependent anticonflict effect after intrahippocampal injections and antidepressant-like effect in rats after intraventricular injections. These data suggest that selective group III mGlu receptor agonists may become a new class of anxiolytics and/or antidepressants.

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.

Clinical data suggest that coadministration of pindolol, a 5-HT1A/5-HT1B/beta-adrenoceptor antagonist, and selective serotonin reuptake inhibitors (SSRIs) may shorten the time of onset of a clinical action and may increase beneficial effects of the therapy of drug-resistant depression. Effects of combined administration of SSRIs and 5-HT receptor ligands are currently evaluated in animal models for the detection of an antidepressant-like activity; however, the obtained results turned out to be inconsistent. The aim of the present study was to investigate effects of a 5-HT1A antagonist (WAY 100635), 5-HT1B antagonists (SB 216641 and GR 127935) or pindolol, given in combination with paroxetine or fluoxetine (SSRIs), in the forced swimming test in rats (Porsolt test). When given alone, paroxetine (10 and 20 mg/kg), fluoxetine (10 and 20 mg/kg), WAY 100635 (0.1 and 1 mg/kg), SB 216641 (2 mg/kg), GR 127935 (10 and 20 mg/kg) and pindolol (4 and 8 mg/kg) did not shorten the immobility time of rats in that test. Interestingly, SB 216641 administered alone at a dose of 4 mg/kg produced a significant reduction of the immobility time in that test. A combination of paroxetine (20 mg/kg) and WAY 100635 or pindolol failed to reveal a significant interaction; on the other hand, when paroxetine was given jointly with SB 216641 (2 mg/kg) or GR 127935 (10 and 20 mg/kg), that combination showed a significant antiimmobility action in the forced swimming test in rats. The active behaviors in that test did not reflect increased general activity because combined administration of both the 5-HT1B antagonists and paroxetine failed to alter the locomotor activity of rats, measured in the open field test. Coadministration of fluoxetine and all the antagonists used did not affect the behavior of rats in the forced swimming test. The obtained results seem to indicate that blockade of 5-HT1B receptors, but not 5-HT1A ones, can facilitate the antidepressant-like effect of paroxetine in the forced swimming test in rats. No interaction was observed between fluoxetine and 5-HT1A/5-HT1B receptor antagonists.

In this study, we examined the role of 5-hydroxytryptamine (5-HT)1A and alpha1-adrenergic receptors in the hypothermia induced by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190) and its analogs, 1-(2-methoxyphenyl)-4-[(4-succinimido)butyl]piperazine (MM77) and trans-1(2-methoxyphenyl)-4-[4-(2-phthalimido)cyclohexyl]piperazine (MP245), which--like NAN-190--showed a high affinity for 5-HT1A and alpha1-adrenoceptors. Administration of NAN-190 (a partial agonist of presynaptic and an antagonist of postsynaptic 5-HT1A receptors and alpha1-adrenoceptors), MM77 and MP245 (antagonists of postsynaptic 5-HT1A receptors), as well as 8-OH-DPAT (a 5-HT1A agonist) and prazosin (an alpha1-adrenoceptor antagonist) induced a dose-dependent hypothermia in mice. The silent antagonist of 5-HT1A receptors, WAY 100635, which abolished the hypothermic effect of 8-OH-DPAT, inhibited the hypothermia induced by NAN-190 administered at a dose of 1 mg/kg (but not 2 mg/kg) and by MP245 (0.5 and 1 mg/kg), but failed to change the MM77 (1 and 4 mg/kg)-induced decrease in body temperature in mice. The alpha1-adrenoceptor agonist St 587, which reduced the hypothermic effect of prazosin, inhibited the decrease in body temperature evoked by NAN-190 at the higher dose and by MP245 at both the doses used, but did not affect the MM77-induced hypothermia in mice. The obtained results suggest that the hypothermia in mice induced by NAN-190 and its constrained analog MP245 is connected with stimulation of 5-HT1A receptors and with blockade of alpha1-adrenoceptors, participation of these receptors not being equivalent, though. The origin of the hypothermia evoked by MM77 is still unknown.