Effects of serotoninergic agents on downregulation of beta-adrenoceptors by the selective serotonin reuptake inhibitor sertraline.

The results of the present study show that the down-regulation of beta-adrenoceptors of rat brain, induced by subacute administration of sertraline, is facilitated when this selective serotonin reuptake inhibitor was co-administered with the serotonin releaser, norfenfluramine, or the serotonin terminal autoreceptor antagonist, methiothepin. The respective drug combination produced a reduction in Bmax of [3H]dihydroalprenolol binding to cortical membranes of treated rats at a dose of the releaser, release enhancer, or sertraline, which was ineffective when administered alone. In a similar manner, the 5-HT1A agonists, gepirone and 8-OH-DPAT, were found to facilitate the downregulation of beta-adrenoceptors induced by sertraline. The 5-HT1B agonist, 3-trifluoromethylphenylpiperazine, and the 5-HT2 antagonist, ritanserin, showed neither facilitation nor antagonism of sertraline, but the 5-HT3 antagonist, ondansetron, attenuated the decrease of Bmax of [3H]dihydroalprenolol binding elicited by sertraline. Agents that putatively increase the serotoninergic activity facilitated the down-regulation of beta-adrenoceptors induced by sertraline, suggesting that the enhancement of serotonin transmission, expected of the selective serotonin reuptake inhibitor itself, may play a role in this effect of sertraline. Whether the downregulation of brain beta-adrenoceptors by sertraline plays any role in its antidepressant activity cannot be deduced from these experiments.

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.

Characterization of [3H]CP-96,501 as a selective radioligand for the serotonin 5-HT1B receptor: binding studies in rat brain membranes.

3-(1,2,5,6-Tetrahydro-4-pyridyl)-5-n-propoxyindole (CP-96,501) was found to be more selective ligand at the serotonin 5-HT1B receptor than the commonly used 5-HT1B agonist, 3-(1,2,5,6-tetrahydro-4-pyridyl)-5-methoxyindole (RU 24969). In rat brain membranes, the tritiated derivative, [3H]CP-96,501, was found to bind with a high affinity (KD, 0.21 nM) to a single binding site (nH, 1.0). The receptor density of this site (Bmax, 72 fmol/mg of protein) matched that of the 5-HT1B receptor determined with [3H]5-HT. Competition curves of 16 serotonergic compounds in [3H]CP-96,501 binding also indicated a single binding site. The rank order of their binding affinities with this new radioligand showed a high degree of correlation with their affinities at the 5-HT1B receptor determined with [3H]5-HT or [125I]iodocyanopindolol. Serotonergic compounds displayed competitive inhibition of [3H]CP-96,501 binding. In the presence of 5'-guanylylimidodiphosphate [Gpp(NH)p], [3H]CP-96,501 to displace [125I]iodocyanopindolol binding was also decreased. These findings are consistent with the agonist nature of CP-96,501. The results of this study suggest that [3H]CP-96,501 is a useful agonist radioligand for the 5-HT1B receptor.

Separation of alpha 1 adrenergic and N-methyl-D-aspartate antagonist activity in a series of ifenprodil compounds.

Ifenprodil (1) represents a new class of N-methyl-D-aspartate (NMDA) antagonist. This drug also possesses potent activity at several other brain receptors (most notably alpha 1 adrenergic receptors). We have prepared the enantiomers and diastereomers of ifenprodil along with a series of partial structures in order to explore the basic structure activity relations within this class of compounds. From this study, it is clear that alpha 1 adrenergic and NMDA receptor activities may be separated by selection of the threo relative stereochemistry. Examination of the optical isomers of threo-ifenprodil (2) reveals that no further improvement in receptor selectivity is gained from either antipode. Individual removal of most of the structural fragments from the ifenprodil molecule generally results in less active compounds although fluorinated derivative 9 with threo relative stereochemistry is somewhat more potent and substantially more selective for the NMDA receptor. Finally a minimum structure for activity in this series (14) has been identified. This stripped-down version of ifenprodil possesses nearly equivalent affinity for the NMDA receptor with no selectivity over alpha 1 adrenergic receptors.

Structure-activity relationship of quinazolinedione inhibitors of calcium-independent phosphodiesterase.

A series of quinazolinediones and azaquinazolinediones is described which possess potent inhibitory activity toward the calcium-independent phosphodiesterase enzyme (CaIPDE). In vivo testing showed that this in vitro activity translates to animal models predictive of chronic diseases such as depression and inflammation. These results support the hypothesis that inhibition of CaIPDE may lead to useful activity in such chronic diseases.

Calcium-independent phosphodiesterase inhibitors as putative antidepressants: [3-(bicycloalkyloxy)-4-methoxyphenyl]-2-imidazolidinones.

The synthesis and biological properties of a novel series of selective calcium-independent phosphodiesterase inhibitors are described. These compounds also inhibit the specific binding of [3H]rolipram to rat brain membranes and exhibit efficacy in preclinical models of antidepressant activity in mice, such as reducing immobility in the forced-swim test and reversing reserpine-induced hypothermia. Imidazolidinones 4 and 16 were found to be the most potent compounds studied.

Nicotinamide ethers: novel inhibitors of calcium-independent phosphodiesterase and [3H]rolipram binding.

The synthesis and biological properties of a series of nicotinamide ethers are described. These compounds, structurally novel calcium-independent phosphodiesterase inhibitors, also inhibit the binding of [3H]rolipram to rat brain membranes and reverse reserpine-induced hypothermia in the mouse. Several compounds exhibited potent in vivo activity comparable to the standard agent, rolipram.

Preclinical pharmacology of sertraline: a potent and specific inhibitor of serotonin reuptake.

Specific serotonin reuptake inhibitors constitute a new class of psychotherapeutic agents that promote enhanced central serotonergic neurotransmission in animal studies. Sertraline, a member of this class, exhibits considerable potency and specificity in inhibiting serotonin neuronal reuptake in preclinical studies. Thus, it is likely to exert antidepressant activity without significant anticholinergic, cardiovascular, and sedative side effects. Other animal studies demonstrating decreases in food intake and body weight and reduction in voluntary alcohol consumption after sertraline administration suggest a potential for wider clinical application.

4-Amino[1,2,4]triazolo[4,3-a]quinoxalines. A novel class of potent adenosine receptor antagonists and potential rapid-onset antidepressants.

A series of 4-amino[1,2,4]triazolo[4,3-a]quinoxalines has been prepared. Many compounds from this class reduce immobility in Porsolt's behavioral despair model in rats upon acute administration and may therefore have therapeutic potential as novel and rapid acting antidepressant agents. Optimal activity in this test is associated with hydrogen, CF3, or small alkyl groups in the 1-position, with NH2, NH-acetyl, or amines substituted with small alkyl groups in the 4-position, and with hydrogen or 8-halogen substituents in the aromatic ring. Furthermore, many of these 4-amino[1,2,4]triazolo[4,3-a]quinoxalines bind avidly, and in some cases very selectively, to adenosine A1 and A2 receptors. A1 affinity of these compounds was measured by their inhibition of tritiated CHA (N6-cyclohexyladenosine) binding in rat cerebral cortex membranes and A2 affinity by their inhibition of tritiated NECA (5'-(N-ethylcarbamoyl)adenosine) binding to rat striatal homogenate in the presence of cold N6-cyclopentyladenosine. Structure-activity relationship (SAR) studies show that best A1 affinity is associated with ethyl, CF3, or C2F5 in the 1-position, NH-iPr or NH-cycloalkyl in the 4-position, and with an 8-chloro substituent. Affinity at the A2 receptor is mostly dependent on the presence of an NH2 group in the 4-position and is enhanced by phenyl, CF3, or ethyl in the 1-position. The most selective A1 ligand by a factor of greater than 3000 is 121 (CP-68,247; 8-chloro-4-(cyclohexyl-amino)-1- (trifluoromethyl)[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 28 nM at the A1 receptor. The most potent A2 ligand is 128 (CP-66,713; 4-amino-8-chloro-1- phenyl[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 21 nM at the A2 receptor and a 13-fold selectivity for this receptor. Representatives from this series appear to act as antagonists at both A1 and A2 receptors since they antagonize the inhibiting action of CHA on norepinephrine-stimulated cAMP formation in fat cells and they decrease cAMP accumulation induced by adenosine in limbic forebrain slices. Thus certain members of this 4-amino[1,2,4]triazolo[4,3-a]quinoxaline series are among the most potent and A1 or A2 selective non-xanthine adenosine antagonists known.

[3H] sertraline binding to rat brain membranes.

Tritiated sertraline, a radiolabeled form of a potent and selective inhibitor of serotonin uptake, was found to bind with high affinity to rat whole brain membranes. Characterization studies showed that [3H] sertraline binding occurred at a single site with the following parameters: KD 0.57 nM, Bmax 821 fmol/mg protein, nH 1.06. This binding was reversible; the dissociation constant calculated from kinetic measurements (KD 0.81 nM) agreed with that determined by saturation binding experiments. [3H] Sertraline binding in the presence of serotonin, paroxetine, fluoxetine or imipramine suggested competitive inhibition of binding (large increase in KD with little change in Bmax). The rank order of potency of inhibition of [3H] sertraline binding was similar to that of inhibition of serotonin uptake for known uptake inhibitors and the 1-amino-4-phenyltetralin uptake blockers. A marked decrease in ex vivo [3H] sertraline binding in the brain of rats 7 days after treatment with p-chloroamphetamine was consistent with the loss of serotonin uptake sites induced by this agent. The results of our study indicated that [3H] sertraline labels serotonin uptake sites in rat brain.

(+)-[3H]3-(3-hydroxyphenyl)-N-(1-propyl)-piperidine binding to sigma receptors in mouse brain in vivo.

Binding of i.v. administered (+)-[3H]3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ([3H]3-PPP) in the brain of intact mice is antagonized dose responsively by sigma receptor ligands. The correlation of potencies for inhibition of binding in vivo and in vitro indicates that sigma receptors in mouse brain are labeled in vivo by i.v. [3H]3-PPP. 3-PPPP, the N-phenylpropyl derivative of norpropyl-3-PPP exhibits very high affinity for sigma receptors in vitro and in vivo.

A novel class of "GABAergic" agents: 1-aryl-3-(aminoalkylidene)oxindoles.

Antagonism of mercaptopropionic acid (MPA) induced convulsions, reflecting a GABAergic mechanism, was observed in a series of 1-aryl-3-(aminoalkylidene)oxindoles. Optimal MPA antagonism was associated with 3-halo, 3-alkyl, and/or 4-alkoxy substituents in the pendant aryl ring and with (dimethylamino)methylene, 1-(dimethylamino)-ethylidene and N-methyl-2-pyrrolidinylidene side chains. The precise mechanism of action of these agents is unclear at this time; however, they are not GABA mimics and they do not affect GABA levels. Like other GABAergic agents, these compounds are potent enhancers of benzodiazepine binding and they antagonize cyclic GMP elevations induced by isoniazid. Compounds from this series may therefore have potential therapeutic utility as anticonvulsants or anxiolytics.

Treatment with sertraline, a new serotonin uptake inhibitor, reduces voluntary ethanol consumption in rats.

Serotonin uptake blockers have been shown to produce a robust and reliable reduction in voluntary ethanol consumption in rats. These compounds are currently under investigation as potential treatments for alcohol abuse in humans. It is uncertain whether serotonin uptake blockers exert their effects directly through serotonergic mechanisms or whether an interaction between the serotonin and noradrenergic systems is involved. The present series of experiments was designed to examine the effects of sertraline, a new selective serotonin uptake blocker, on voluntary ethanol intake. Sertraline produced a robust reduction in voluntary ethanol intake. It appears therefore, that increasing selectivity for serotonin blockade does not alter the efficacy of these compounds as antialcohol agents. The drug also reduced the consumption of a saccharin solution indicating that sertraline's effects are not specific to ethanol intake.

Pharmacology of sertraline: a review.

Sertraline is a member of a new class of psychotherapeutic agents that selectively inhibit serotonin reuptake in the brain. Animal studies have demonstrated that inhibition of serotonin reuptake leads to enhanced serotonergic neurotransmission and indirectly results in a down-regulation of beta-adrenoceptors. The preclinical pharmacology of sertraline predicts antidepressant activity without accompanying anticholinergic, cardiotonic, or sedative side effects. Recent laboratory and clinical observations pertaining to body weight and obsessive compulsive disorder suggest the possibility of broader clinical indications for selective serotonin reuptake blockers such as sertraline.

[3H]Ro 15-1788 binding to benzodiazepine receptors in mouse brain in vivo: marked enhancement by GABA agonists and other CNS drugs.

Administration of the benzodiazepine receptor antagonist, [3H]Ro 15-1788, to mice intravenously was found to label these receptors in brain. Binding of [3H]Ro 15-1788 in vivo was strongly blocked by pretreating mice with clonazepam or diazepam. Marked enhancement of [3H]Ro 15-1788 binding in vivo was induced by progabide or sodium valproate. This effect was greater than a similar enhancement of [3H]flunitrazepam binding. The increased membrane-bound [3H]Ro 15-1788 elicited by progabide was completely dissociated on subsequent incubation with Ro 15-1788, diazepam or clobazam, indicating that the enhanced binding occurred at benzodiazepine receptors. Compounds that exert diazepam-like actions and/or indirect GABAergic activity (cartazolate, pentobarbital, methaqualone, levonantradol, phenytoin) elicited enhancement of [3H]Ro 15-1788 in vivo. Other CNS agents (atypical neuroleptics, GABA antagonists, baclofen, some 5-HT1 agonists) also induced elevation of [3H]Ro 15-1788 binding in vivo, as did drugs exerting vasodilatatory effects (papaverine, nimodipine, verapamil, prazosin, N6-cyclohexyladenosine). Possible explanations for enhancement of [3H]Ro 15-1788 binding in vivo include increase in the number of benzodiazepine receptors induced by GABA or GABAergic drugs or effects of binding enhancers that elevate brain levels of [3H]Ro 15-1788, such as accelerating cerebral blood flow, competing for radioligand binding sites in plasma or increasing metabolic stability of the radioligand.

Sertraline, a selective inhibitor of serotonin uptake, induces subsensitivity of beta-adrenoceptor system of rat brain.

Subacute administration (b.i.d. for 4 days) of sertraline, a potent and selective inhibitor of serotonin uptake, was found to reduce cyclic AMP generation by the norepinephrine receptor-coupled adenylate cyclase in rat limbic forebrain slices and decrease the number of beta-adrenoceptors in rat cerebral cortex without affecting the affinity of [3H]dihydroalprenolol binding. Co-administration of sertraline and the serotonin agonist, quipazine, at doses at which neither agent had an effect, resulted in desensitization of norepinephrine receptor-coupled adenylate cyclase and down-regulation of beta-adrenoceptors. These findings suggest that increased serotonergic activity may be involved in the induction of subsensitivity of the beta-adrenoceptor system of rat brain by sertraline.

Neuroleptics from the 4a,9b-cis- and 4a,9b-trans-2,3,4,4a,5,9b-hexahydro-1H-pyrido[4,3-b]indole series. 2.

Compounds derived from 4a,9b-trans-2,3,4,4a,5,9b-hexahydro-1H-pyrido[4, 3-b]indole are consistently efficacious in displacing [3H]spiroperidol from striatal dopamine receptors in vitro. Derivatives bearing substituents at position 2, particularly those derived from butyrophenone moieties, are exceptionally potent in vivo. Compounds from the corresponding 4a,9b-cis series are substantially less potent in both in vivo and in vitro assays of neuroleptic activity. Although the cis and trans derivatives have, in some conformations, similar basic nitrogen atom to aromatic ring separations of about 5.1 A, the distance at which the basic nitrogen atom lies above or below the plane of the aromatic ring differs substantially between the two series. Consideration of these results in terms of this and earlier work indicates that the out-of-plane distance for the basic nitrogen in neuroleptic molecules may range from about 0 to about 0.90 A but may be optimized at about 0.55 A.