Identity of inhibitory presynaptic 5-hydroxytryptamine (5-HT) autoreceptors in the rat brain cortex with 5-HT1B binding sites

In rat brain cortex slices preincubated with [3H]5-HT, the potencies of 17 5-HT receptor agonists to inhibit the electrically evoked 3H overflow and the affinities of 13 antagonists (including several beta-adrenoceptor blocking agents) to antagonize competitively the inhibitory effect of unlabelled 5-HT on evoked 3H overflow were determined. The affinities of the compounds for 5-HT1B and 5-HT2 binding sites in rat brain cortex membranes (labelled by [125I]cyanopindolol = [125I]-CYP in the presence of 30 mumol/l isoprenaline and [3H]ketanserin, respectively), for 5-HT1A binding sites in pig and rat brain cortex membranes (labelled by [3H]8-hydroxy-2-(di-n-propylamino)tetralin = [3H]8-OH-DPAT) and for 5-HT1C binding sites in pig choroid plexus membranes (labelled by [3H]mesulergine) were also determined. The affinities of the drugs for the various 5-HT recognition sites ranged over 4-5 log units (the functional experiments revealed the same range of differences between the drugs). There were no significant correlations between the affinities of the drugs at 5-HT1C and 5-HT2 binding sites and their potencies or affinities, determined for the 5-HT autoreceptors. In contrast, significant correlations were found between the potencies or affinities of the drugs for the autoreceptors and their affinities at 5-HT1A or 5-HT1B binding sites; the best correlations were obtained with the 5-HT1B binding site. Some of the drugs investigated were not included in the correlation since their agonistic or antagonistic effects on the autoreceptors were weak and pEC30 or apparent pA2 values could not be determined (less than 5.5).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological characterization of two novel and potent 5-HT4 receptor agonists, RS 67333 and RS 67506, in vitro and in vivo.

1. The pharmacology of two novel 5-HT4 receptor agonists, RS 67333 (1-(4-amino-5-chloro-2-methoxy-phenyl)-3-[1(n-butyl)-4-piperidinyl]-1- propanone HCl) and RS 67506 (1-(4-amino-5-chloro-2-methoxy-phenyl)-3-[1-(2-methyl sulphonylamino)ethyl-4-piperidinyl]-1-propanone HCl) have been assessed in vitro and in vivo. 2. RS 67333 and RS 67506 exhibited affinities (pKi = 8.7 and 8.8, respectively) for the 5-HT4 binding sites, labelled with [3H]-GR 113808, in guinea-pig striatum. The Hill coefficients from these displacement curves were not significantly different from unity. The compounds exhibited lower affinities (< 6.0) at several other receptors including 5-HT1A, 5-HT1D, 5-HT2A, 5-HT2C, dopamine D1, D2 and muscarinic M1-M3 receptors. However, RS 67333 and RS 67506 did exhibit affinities for the sigma 1 (pKi = 8.9 and 7.9, respectively) and sigma 2 (pKi = 8.0 and 7.3, respectively) binding sites. 3. At the 5-HT4 receptor mediating relaxation of the carbachol-precontracted oesophagus, RS 67333 and RS 67506 acted as potent (pEC50 8.4 and 8.6, respectively), partial agonists (intrinsic activities, with respect to 5-HT were 0.5 and 0.6, respectively) with respect to 5-HT. Relaxant responses to RS 67333 or RS 67506 were surmountably antagonized by GR 11308 (10 nM), with apparent affinities (pKB) of 9.1 and 9.0, respectively. RS 67333 and RS 67506 induced dose-dependent increases in heart rate of the anaesthetized micropig (ED50 4.9 and 5.4 micrograms kg-1, i.v.), with maximal increases of 35 and 47 beats min-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for common pharmacological properties of [3H]5-hydroxytryptamine binding sites,presynaptic 5-hydroxytryptamine autoreceptors in CNS and inhibitory presynaptic 5-hydroxytryptamine receptors on sympathetic nerves

The affinities of 16 5-hydroxytryptamine (5-HT) receptor agonists (indole derivatives) and 7 5-HT receptor antagonists for [3H]5-hydroxytryptamine [( 3H]5-HT) binding sites in rat cerebral cortex membranes were determined. In addition, the potencies of the agonists for inhibiting the electrically induced tritium overflow from rat brain cortex slices preincubated with [3H]5-HT and from canine saphenous veins preincubated with [3H]noradrenaline were measured. Furthermore, the potencies of the indole derivatives for inducing contractile responses of canine saphenous veins were recorded. In addition, the interaction of the antagonists with unlabelled 5-HT at the 5-HT autoreceptor was studied in rat brain cortex slices. There was a good correlation between the binding affinities of the indole derivatives for the [3H]5-HT sites of rat brain cortex membranes and their potencies for inhibiting the evoked tritium overflow from both rat brain cortex slices and strips of canine saphenous vein. Comparison of the inhibition constants derived from the overflow experiments in both tissues again revealed a high correlation coefficient while there was only weak correlation between the binding affinities in rat brain cortex and the contractile potencies of the drugs in canine saphenous vein strips. When 5-HT receptor antagonists were investigated, metitepin and metergoline showed moderate affinities for the 5-HT autoreceptors in rat brain cortex slices, whereas quipazine had only weak affinity, and ketanserin, metoclopramide, cinanserin and cyproheptadine exhibited no antagonistic property. In binding experiments, the competition curves of most 5-HT receptor antagonists were biphasic, suggesting that the [3H]5-HT binding sites are heterogeneous.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence for mediation by 5-HT2 receptors of 5-hydroxytryptamine-induced contraction of canine basilar artery

Summary The agonist potencies of 8 indole derivatives and the potencies of 19 recognized antagonists to inhibit constrictor responses to 5-hydroxytryptamine (5-HT) of canine basilar artery were established. In addition the affinities of the indole derivatives for [³H]5-hydroxytryptamine ([³H]5-HT) binding sites and the affinities of the antagonists for [¹²⁵Iodo]LSD ([¹²⁵I]LSD) binding sites in rat brain cortex membranes were determined. Comparison was also made between the potencies of the antagonists on canine basilar artery and the K _D values published for displacement of [³H]ketanserin binding (Leysen et al. 1982).There was a good correlation between the affinities of the antagonists for 5-HT₂ binding sites labelled by both [¹²⁵I]LSD and [³H]ketanserin and the affinity parameters calculated for inhibition of constrictor responses to 5-HT of canine basilar artery. No correlation could be found between the affinities of the indole derivatives for 5-HT₁ binding sites labelled by [³H]5-HT and their potencies to constrict canine basilar artery.It is concluded that constrictor responses to 5-HT of canine basilar artery are mediated by 5-HT₂-like receptors.     

Cloned human 5-HT1A receptor pharmacology determined using agonist binding and measurement of cAMP accumulation

Twenty agonists and nine antagonists were evaluated for their ability to compete for [3H]-8-hydroxy-2-(di-n-propylamino)tetralin ([3H]-8-OH-DPAT) binding to the cloned human serotonin-1A (ch-5-HT1A) receptor expressed in Chinese hamster ovary cells and for their ability to alter adenylyl cyclase activity in the same cells. The most potent full agonists of high affinity included N,N-dipropyl-5-carboxamidotryptamine (pEC50=9.6 +/- 0.1), MDL 73005EF (pEC50=9.3 +/- 0.2), 5-methyl-urapidil (pEC50=9.2 +/- 0.1), 5-carboxamidotryptamine (pEC50=9.1 +/- 0.2), R(+)-8-OH-DPAT (pEC50=8.6 +/- 0.1) and BMY-7378 (pEC50=8.6 +/- 0.1). WB-4101 (pEC50=8.3 +/- 0.2; IA=79%), clozapine (pEC50=8.1 +/- 0.3; IA=29%), (buspirone (pEC50=7.6 +/- 0.2; IA=79%), quipazine (pEC50 <5; IA=45%) and R-DOI (pEC50 < 5; IA=31%) were weaker agonists with partial agonist properties. The most potent antagonists were WAY-100,635 (pKi=10.2 +/- 0.1), methiothepin (pKi=8.8 +/- 0.2), spiperone (pKi=8.7 +/- 0.2) and NAN-190 (pKi=8.5 +/- 0.2). The receptor affinities and functional potencies were well correlated (r=0.88; P <0.0001). Our binding data correlated well with the pharmacology of endogenous 5-HT1A receptors in the rabbit iris-ciliary body (r=0.91; P <0.001) and rat hippocampus (r=0.93, P <0.0001). Our functional cAMP data correlated well with other cAMP accumulation data (r=0.8, P <0.01 vs calf hippocampus) but less so with [35S]-GTPgammaS binding to the ch-5-HT(1A) receptor as a functional activity read-out (r=0.58, P <0.05). The present study provides a detailed pharmacological characterization of the ch-5-HT1A receptor using binding and functional assays.     

Assessment of affinities and dissociation potencies of several 5-HT2 antagonists to and from M2 muscarinic receptor in rat heart membranes

The aim of the present study was to investigate the binding affinities and dissociation potencies of several 5-HT(2) antagonists in M(2) muscarinic receptor of rat heart membranes using [(3)H]QNB as a radioligand. The 5-HT(2) antagonists used in this study were sarpogrelate, ketanserin and cyproheptadine. The results showed that sarpogrelate and ketanserin had very weak binding affinities to M(2) muscarinic receptor, whereas cyproheptadine had higher binding affinity to this receptor than the muscarinic receptor antagonist, atropine. All of these three 5-HT(2) antagonists as well as muscarinic receptor antagonists (atropine and pirenzepine) were readily dissociated from M(2) muscarinic receptor in rat heart membranes after washing. Therefore, the findings of the present investigation suggest that the dissociation potencies of neither 5-HT(2) antagonists nor muscarinic antagonists used correlate with their binding affinities to M(2) muscarinic receptors in rat heart.     

Interactions of dopaminergic agonists and antagonists with dopaminergic D3 binding sites in rat striatum. Evidence that [3H]dopamine can label a high affinity agonist-binding state of the D1 dopamine receptor

The interactions of dopaminergic agonists and antagonists with 3H-agonist labeled D3 dopaminergic binding sites of rat striatum have been characterized by radioligand-binding techniques. When the binding of [3H]dopamine and [3H]apomorphine to D2 dopamine receptors is blocked by the inclusion of D2 selective concentrations of unlabeled spiroperidol or domperidone, these ligands appear to label selectively the previously termed "D3" binding site. Antagonist/[3H]dopamine competition curves are of uniformly steep slope (nH = 1.0), suggesting the presence of a single D3 binding site. The relative potencies of antagonists to inhibit D3 specific [3H]dopamine binding are significantly correlated with their potencies to block D1 dopamine receptors as measured by the inhibition of both dopamine-stimulated adenylate cyclase and [3H]flupentixol-binding activities. The affinities of agonists to inhibit D3 specific [3H]dopamine binding are also correlated with estimates of these agonists' affinities for the high affinity binding component of agonist/[3H]flupentixol competition curves. Both D3 specific [3H] dopamine binding and the high affinity agonist-binding component of dopamine/[3H]flupentixol competition curves show a similar sensitivity to guanine nucleotides. Taken together, these data strongly suggest that the D3 binding site is related to a high affinity agonist-binding state of the D1 dopamine receptor.     

Novel histamine H3 receptor antagonists: affinities in an H3 receptor binding assay and potencies in two functional H3 receptor models.

1. We determined the affinities of ten novel H3 receptor antagonists in an H3 receptor binding assay and their potencies in two functional H3 receptor models. The novel compounds differ from histamine in that the aminoethyl side chain is replaced by a propyl or butyl chain linked to a polar group (amide, thioamide, ester, guanidine, guanidine ester or urea) which, in turn, is connected to a hexocyclic ring or to an alicyclic ring-containing alkyl residue [corrected]. 2. The specific binding of [3H]-N alpha-methylhistamine to rat brain cortex membranes was monophasically displaced by each of the ten compounds at pKi values ranging from 7.56 to 8.68. 3. Inhibition by histamine of the electrically evoked tritium overflow from mouse brain cortex slices preincubated with [3H]-noradrenaline was antagonized by the ten compounds and the concentration-response curve was shifted to the right with apparent pA2 values ranging from 7.07 to 9.20. 4. The electrically induced contraction in guinea-pig ileum strips (which was abolished by atropine) was inhibited by the H3 receptor agonists R-(-)-alpha-methylhistamine (pEC50 7.76), N alpha-methylhistamine (7.90) and imetit (8.18). The concentration-response curve of R-(-)-alpha-methylhistamine was shifted to the right by thioperamide (apparent pA2 8.79) and by the ten novel compounds (range of pA2 values 6.64-8.81). 5. The affinities and potencies were compared by linear regression analysis. This analysis was extended to thioperamide, the standard H3 receptor antagonist, which is also capable of differentiating between H3A and H3B sites.(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of affinity and dissociation ability of a newly synthesized 5-HT2 antagonist, AT-1015: comparison with other 5-HT2 antagonists

This study investigated the binding affinities of a newly synthesized 5-HT2 antagonist, AT-1015 (N-[2-[4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)-piperidino]ethyl]-1-formyl-4-piperidinecarboxamide monohydrochloride monohydrate) for [3H]ketanserin bindings to 5-HT2 receptors in the rabbit cerebral cortex membranes using the radioligand binding assay method. The affinity of this compound was also compared with other 5-HT2-selective antagonists such as ketanserin, sarpogrelate, cyproheptadine and ritanserin, and the results showed that AT-1015 has a high pKi value for the 5-HT2 receptor. The rank order of these antagonists are: ritanserin > ketanserin approximately equal to AT-1015 > cyproheptadine approximately equal to sarpogrelate. We also evaluated the dissociation ability (slow or rapid) of AT-1015 in the rabbit cerebral cortex membrane and compared it with other 5-HT2 antagonists using the radioligand binding assay method. The blockade of [3H]ketanserin binding sites in the rabbit cerebral cortex induced by ketanserin and sarpogrelate was readily reversed by washing, whereas the inhibition by AT-1015, cyproheptadine and ritanserin was not readily reversed by washing. The % of control after washing are 76.10% and 49.55% for AT-1015 at 10(-7.5) and 10(-7.0) M, 67.32% and 50.17% for cyproheptadine at 10(7.5) and 10(-7.0) M, and 72.38% and 39.80% for ritanserin at 10(-9.5) and 10(-9.0) M concentrations, respectively. Thus, these findings suggest that AT-1015 has antagonistic properties towards the 5-HT2 receptor and also shows that AT-1015 slowly dissociates from the 5-HT2 receptor, whereas, ketanserin and sarpogrelate dissociate rapidly from the 5-HT2 receptor, which do not correlate with their affinity.     

5-HT2 antagonists and minaprine block the 5-HT-induced inhibition of dopamine release from rat brain striatal slices

5-Hydroxytryptamine (5-HT) inhibited the K+-induced [3H]dopamine [( 3H]DA) release from slices of rat striatum. Minaprine (3-(2-morpholinoethylamino)-4-methyl-6-phenylpyridazine) attenuated the inhibitory effect of 5-HT in a dose-dependent manner. 5-HT2 receptor antagonists, ketanserin and mianserin, prevented the effect of 5-HT as well as minaprine did. The inhibitory effect of 5-HT was not mimicked by a 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), and was not prevented by a 5-HT1A and 5-HT1B mixed receptor antagonist, propranolol. Minaprine was a potent inhibitor of the binding of [3H]ketanserin to binding sites in the striatum over the concentration range 10(-6)-10(-4) M. Lesion of the medial forebrain bundle with 6-hydroxydopamine (6-OHDA) significantly reduced the K+-induced [3H]DA release from the striatum and release was no longer inhibited by 5-HT. Lesioning, however, did not change significantly the [3H]ketanserin binding in the striatum. These results suggest that minaprine suppresses the inhibitory effect of 5-HT on DA release in the striatum via the inhibition of 5-HT binding at the 5-HT2 receptor on the nerve terminal of the DA-ergic neuron and, further, that the proportion of the 5-HT2 receptor site which is located on the nerve terminal of the DA-ergic neuron is small in the striatum.     

Phenothiazine drug metabolites: dopamine D2 receptor, alpha 1- and alpha 2-adrenoceptor binding

The in vitro binding affinities of levomepromazine, chlorpromazine, fluphenazine, perphenazine and methoxypromazine and their main metabolites to dopamine D2 receptors, alpha 1- and alpha 2-adrenoceptors in rat brain, were examined using [3H]spiperone, [3H]WB 4101 and [3H]yohimbine binding. All compounds had 10-500 times lower affinities to alpha 2-adrenoceptors than to dopamine D2 receptors and alpha 1-adrenoceptors. Ring-hydroxylated and N-demethylated metabolites had relative potencies for dopamine D2 receptor and alpha 1-adrenoceptor binding ranging from 20 to 70%, compared to that of the parent drugs. The ring sulphoxides of levomepromazine, chlorpromazine and perphenazine, except dextro levomepromazine sulphoxide, were virtually inactive in all binding systems. The results indicate that the metabolites having the highest binding affinities for dopamine D2 receptor and alpha 1-adrenoceptor binding may contribute significantly to the therapeutic effect and side-effects of the drugs, and should be measured together with the parent drugs in blood level-effect studies.     

In vivo receptor occupancy of NRA0045, a putative atypical antipsychotic, in rats.

We have previously reported that (R)-(+)-2-amino-4-(4-fluorophenyl)-5-[1-[4-(4-fluorophenyl)-4-oxobutyl]+ ++pyrrolidin-3-yl]thiazole (NRA0045) is a novel antipsychotic agent with affinities for dopamine D4, 5-hydroxytryptamine 2A (5-HT2A) and alpha1 receptors. In the present study, in vivo receptor occupancy of 5-HT2A, alpha1, dopamine D2 and D3 receptors by NRA0045 was assessed, based on in vivo and ex vivo receptor binding, and findings were compared to reference antipsychotic drugs (haloperidol, risperidone, clozapine). Intraperitoneal administration of haloperidol highly occupied the dopamine D2 receptor in the striatum and nucleus accumbens, and alpha1 adrenoceptors in the frontal cortex. Occupation of the 5-HT2A receptor in the frontal cortex and the dopamine D3 receptor in the nucleus accumbens and islands of Cajella was moderate. By contrast, atypical antipsychotics such as risperidone and clozapine dose-dependently occupied the 5-HT2A receptor in the frontal cortex, with moderate to negligible occupancy of the D2 receptor in the striatum and the nucleus accumbens. Clozapine and risperidone also occupied the alpha1 adrenoceptor in the frontal cortex, and clozapine did not occupy the dopamine D3 receptor. As seen with other atypical antipsychotics, intraperitoneal administration of NRA0045 dose-dependently occupied the 5-HT2A receptor and the alpha1 adrenoceptor in the frontal cortex, while it was without effect on dopamine D2 and D3 receptors in the striatum, nucleus accumbens and islands of Cajella. Thus, the strong occupancy of 5-HT2A and alpha1 receptors is involved in the pharmacological action of NRA0045.     

Neuroleptic drug interactions with norepinephrine alpha receptor binding sites in rat brain.

Alpha adrenergic receptor sites in mammalian brain tissue can be labeled by the binding of [³H]WB-4101 (2-([2′,6′-dimethoxy] phenoxyethylamino) methyl benzodioxan), a potent α-adrenergic antagonist. Numerous neuroleptic drugs of phenothiazine, butyrophenone and thioxanthene classes are potent in competing for [³H]WB-4101 binding, with affinities resembling those of classic α-antagonists such as phentolamine and phenoxybenzamine. The potencies of neuroleptics in competing for WB-4101 binding sites correlate closely with their potencies in antagonizing norepinephrine and epinephrine induced lethality in rats, confirming that affinity for WB-4101 binding sites predicts α-receptor antagonism in vivo. The relative affinities of neuroleptics for WB-4101 binding sites and for dopamine receptors as labeled by [³H]haloperidol provides an index of the relative propensities of these drugs for eliciting autonomic side effects such as orthostatic hypotension and sedation.     

Asenapine: a novel psychopharmacologic agent with a unique human receptor signature

Asenapine is a novel psychopharmacologic agent under development for the treatment of schizophrenia and bipolar disorder. We determined and compared the human receptor binding affinities and functional characteristics of asenapine and several antipsychotic drugs. Compounds were tested under comparable assay conditions using cloned human receptors. In comparison with the antipsychotics, asenapine showed high affinity and a different rank order of binding affinities (pKi) for serotonin receptors (5-HT1A [8.6], 5-HT1B [8.4], 5-HT2A [10.2], 5-HT2B [9.8], 5-HT2C [10.5], 5-HT5 [8.8], 5-HT6 [9.6] and 5-HT7 [9.9]), adrenoceptors (alpha1 [8.9], alpha2A [8.9], alpha2B [9.5] and alpha2C [8.9]), dopamine receptors (D1 [8.9], D2 [8.9], D3 [9.4] and D4 [9.0]) and histamine receptors (H1 [9.0] and H2 [8.2]). It had much lower affinity (pKi相似文献   

The role of the 5-HT1D receptor as a presynaptic autoreceptor in the guinea pig

The present study investigated the role of the 5-hydroxytryptamine (5-HT, serotonin)1D receptor as a presynaptic autoreceptor in the guinea pig. In keeping with the literature, the 5-HT1B selective antagonist, 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydrospiro [furo[2,3-f]indole-3,4'-piperidine]oxalate (SB224289) potentiated [3H]5-HT outflow from pre-labelled slices of guinea pig cerebral cortex confirming its role as a presynaptic autoreceptor in this species. In addition, the 5-HT1D receptor-preferring antagonists, 1-[2-[4-(6-fluoro-1H-indol-3-yl)-3,6-dihydro-2H-pyridin-1-yl]-ethyl]-3-pyridin-4-yl-methyl-tetrahydro-pyrimidin-2-one (LY367642), (R)-1-[2-(4-(6-fluoro-1H-indol-3-yl-)-3,6-dihydro-1(2H)-pyridinyl)ethyl]-3,4-dihydro-1H-2-benzopyran-6-carboxamide (LY456219), (S)-1-[2-(4-(6-fluoro-1H-indol-3-yl-)-3,6-dihydro-1(2H)-pyridinyl)ethyl]-3,4-dihydro-1H-2-benzopyran-6-carboxamide (LY456220) and 1-[2-[4-(4-fluoro-benzoyl)-piperidin-1-yl]-ethyl]-3,3-dimethyl-1,2-dihydro-indol-2-one (LY310762), potentiated [3H]5-HT outflow from this preparation with potencies (EC50 values=31-140 nM) in the same range as their affinities for the guinea pig 5-HT1D receptor (Ki values=100-333 nM). The selective 5-HT1D receptor agonist, R-2-(4-fluoro-phenyl)-2-[1-[3-(5-[1,2,4]triazol-4-yl-1H-indol-3-yl)-propyl]-piperidin-4-ylamino]-ethanol dioxylate (L-772,405), inhibited [3H]5-HT outflow. In microdialysis studies, administration of either SB224289 or LY310762 at 10 mg/kg by the intraperitoneal (i.p.) route, potentiated the increase in extracellular 5-HT concentration produced by a maximally effective dose of the selective serotonin re-uptake inhibitor, fluoxetine (at 20 mg/kg i.p.). In addition, the 5-HT1D receptor-preferring antagonist and 5-HT transporter inhibitor, LY367642 (at 10 mg/kg i.p.), elevated extracellular 5-HT concentrations to a greater extent than a maximally effective dose of fluoxetine. It is concluded that the 5-HT1D receptor, like the 5-HT1B receptor, may be a presynaptic autoreceptor in the guinea pig.     

Development of a radioligand binding assay for 5-HT4 receptors in guinea-pig and rat brain.

1. The 5-HT4 receptor antagonist, GR113808, has been radiolabelled to a high specific activity with tritium. 2. Characterization of specific [3H]-GR113808 binding in homogenates of guinea-pig striatum and hippocampus revealed a single site of high affinity (Kd values 0.20 and 0.13 nM respectively). 3. [3H]-GR113808 binding was reversible and displayed rapid kinetics such that association and dissociation were complete within 3 min. 4. Specific [3H]-GR113808 binding was potently and stereoselectively inhibited by agonists and antagonists acting at the 5-HT4 receptor but not by compounds selective for other 5-HT receptors or other neurotransmitter receptors. 5. Autoradiographic analysis revealed a discrete localization in both guinea-pig and rat brain with high concentrations of binding in brain areas such as the striatum, substantia nigra and olfactory tubercle. 6. [3H]-GR113808 binding to homogenates of guinea-pig striatum meets the criteria for labelling of the 5-HT4 receptor and, as such, represents the first characterization of this receptor in a radioligand binding assay.     

Effect of amperozide on rat cortical 5-HT2 and striatal and limbic dopamine D2 receptor occupancy: implications for antipsychotic action.

Amperozide (FG 5606, N-ethyl-4-[4',4'-bis(p-fluorophenyl)butyl]-1-piperazine-carboxamide) is an atypical antipsychotic drug which has relatively weak in vitro affinity for striatal dopamine2 (D2) receptors and strong affinity for cortical 5-HT2 receptors. The in vivo affinity for 5-HT2 binding sites in rat cortex was 1.1 mg/kg. In striatum or olfactory tubercle, doses of amperozide up to 40 mg/kg did not displace radioligand binding to D2 receptors. Amperozide, haloperidol and ritanserin had similar in vivo potency in blocking the 5-HT2 binding site, but only haloperidol displaced D2 receptor binding. Based on the clinically effective dose of amperozide (0.14-0.28 mg/kg per day), it is suggested that the antipsychotic effect of amperozide is related, in part, to its in vivo interaction with the 5-HT2 receptor and that amperozide cannot be expected to exert its antipsychotic action by blockade of D2 receptors in the striatum or limbic regions.     

Characteristics of [3H]sultopride binding to rat brain

The binding of [3H]sultopride, a benzamide drug, to rat brain was investigated in vitro. Specific [3H]sultopride binding was observed in dopaminergic regions: striatum, nucleus accumbens, olfactory tubercle, substantia nigra, frontal cortex and anterior pituitary. Specific [3H]sultopride binding to striatum was saturable and had one high affinity binding site with a KD of 5.8 nM and a total density of receptors 25.7 pmol/g. [3H]Sultopride binding was stereoselectively displaced by (-)- and (+)-sultopride. Inhibition studies indicated that all neuroleptic drugs and dopamine were capable of displacing sultopride from its binding sites. A highly significant correlation was observed between IC50 values against [3H]sultopride and those against [3H]spiperone binding. Specific [3H]sultopride binding was highly dependent on the presence of sodium ions. The results suggest that the characteristics of sultopride binding sites seem to be similar to those of the D2-receptor labeled by spiperone and haloperidol. The sultopride binding site was highly dependent on the presence of sodium ions and may thus be characterized as a sodium-dependent D2-receptor.     

The interaction of RS 25259-197, a potent and selective antagonist, with 5-HT3 receptors, in vitro.

1. A series of isoquinolines have been identified as 5-HT3 receptor antagonists. One of these, RS 25259-197 [(3aS)-2-[(S)-1-azabicyclo[2.2.2]oct-3-yl]-2,3,3a,4,5,6-hexahydro- 1- oxo-1H-benzo[de]isoquinoline-hydrochloride], has two chiral centres. The remaining three enantiomers are denoted as RS 25259-198 (R,R), RS 25233-197 (S,R) and RS 25233-198 (R,S). 2. At 5-HT3 receptors mediating contraction of guinea-pig isolated ileum, RS 25259-197 antagonized contractile responses to 5-HT in an unsurmountable fashion and the apparent affinity (pKB), estimated at 10 nM, was 8.8 +/- 0.2. In this tissue, the -log KB values for the other three enantiomers were 6.7 +/- 0.3 (R,R), 6.7 +/- 0.1 (S,R) and 7.4 +/- 0.1 (R,S), respectively. The apparent affinities of RS 25259-197 and RS 25259-198, RS 25233-197 and RS 25233-198 at 5-HT3 receptors in membranes from NG-108-15 cells were evaluated by a [3H]-quipazine binding assay. The -log Ki values were 10.5 +/- 0.2, 8.4 +/- 0.1, 8.6 +/- 0.1 and 9.5 +/- 0.1, respectively, with Hill coefficients not significantly different from unity. Thus, at these 5-HT3 receptors, the rank order of apparent affinities was (S,S) > (R,S) > (S,R) = (R,R). 3. RS 25259-197 displaced the binding of the selective 5-HT3 receptor ligand, [3H]-RS 42358-197, in membranes from NG-108-15 cells, rat cerebral cortex, rabbit ileal myenteric plexus and guinea-pig ileal myenteric plexus, with affinity (pKi) values of 10.1 +/- 0.1, 10.2 +/- 0.1, 10.1 +/- 0.1 and 8.3 +/- 0.2, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Subnanomolar dopamine D3 receptor antagonism coupled to moderate D2 affinity results in favourable antipsychotic-like activity in rodent models: I. neurochemical characterisation of RG-15

RG-15 (trans-N-{4-[2-[4-(3-cyano-5-trifluoromethyl-phenyl)-piperazine-1-yl]-ethyl]-cyclohexyl}-3-pyridinesulfonic amide dihydrochloride) displayed subnanomolar affinity to human and rat dopamine D₃ receptors (pKi 10.49 and 9.42, respectively) and nanomolar affinity to human and rat D₂ receptors (pKi 8.23 and 7.62, respectively). No apparent interactions were found with the other 44 receptors and four channel sites tested in this study. RG-15 inhibited dopamine-stimulated [³⁵S]GTPγS binding in membranes from rat striatum, in murine A9 cells expressing human D_2L receptors and in CHO cells expressing human D₃ receptors (IC₅₀ values were 21.2, 36.7 and 7.2 nM, respectively). In these tests RG-15 showed the highest affinity toward D₃ receptors when compared to amisulpride, haloperidol and SB-277011. RG-15, similar to haloperidol and amisulpride, dose-dependently inhibited in vivo [³H]raclopride binding in mouse striatum, enhanced dopamine turnover and synthesis rate in mouse and rat striatum and olfactory tubercle. SB-277011 did not change [³H]raclopride binding in mouse striatum nor biosynthesis or turnover rates in either region in mice or rats. RG-15 and haloperidol, but not SB-277011, antagonised dopamine synthesis inhibition induced by the D₃/D₂ full agonist 7-OH-DPAT in GBL-treated mice. RG-15, but not SB-277011, elevated plasma prolactin levels. In vitro receptor binding and functional experiments demonstrated that RG-15 had an antagonist profile on both D₃ and D₂ receptors. with high selectivity for dopamine D₃ receptors over D₂ receptors. However, in vivo, its neurochemical actions were similar to those of D₂ receptor antagonists. Neurochemical comparison of RG-15 with antagonists having a different affinity and selectivity toward D₃ and D₂ receptors indicate that D₃ receptors have little, if any, role in the control of presynaptic dopamine biosynthesis/release in dopaminergic terminal regions.