N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide: a potent and selective dopamine D4 ligand

A series of new 1-aryl-4-alkylpiperazines containing a terminal benzamide fragment or a tetralin-1-yl nucleus on the alkyl chain were synthesized and tested for binding at cloned human dopamine D4 and D2 receptor subtypes. A SAFIR (structure-affinity relationship) study on this series is herein discussed. The most relevant D4 receptor affinities were displayed by N-[omega-[4-arylpiperazin-1-yl]alkyl]-methoxybenzamides (compounds 5, 16-20), their IC50 values ranging between 0.057 and 7.8 nM. Among these, N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (17) emerged since it exhibited very high affinity for dopamine D4 receptor (IC50 = 0.057 nM) with selectivity of >10 000 for the D4 versus the D2 receptor; compound 17 was also selective versus serotonin 5-HT1A and adrenergic alpha1 receptors.     

The partnership model: working with individuals, families, and communities toward a new vision of health

A novel irreversible 5-HT1A receptor binding ligand, NCS-MPP (4-(2'- methoxy-phenyl)-1-[2'-(N-2"-pyridyl)-p-isothiocyanobenzamido]- ethyl-piperazine), based on the new 5-HT1A receptor antagonist p-MPPI (4-(2'-methoxy-phenyl)-1-[2'-(N-2"-pyridyl)-p-iodobenzamido]-ethyl -piperazine ), was synthesized, and its binding characteristics were evaluated using in vitro homogenate binding with rat hippocampal membranes. The Ki value of NCS-MPP was estimated to be 1.8 +_ 0.2 nM using analysis of concentration-dependent inhibition for the binding of [125I]p-MPPI to 5-HT1A receptors. NovaScreen of NCS-MPP showed low to moderate binding affinities to alpha-1, alpha-2-adrenergic and 5-HT2 receptors, with Ki values of 350, 420, and 103 nM, respectively. These data strongly suggest that the ligand bound to 5-HT1A receptors with high affinity and high selectivity. Irreversible inhibition of [125I]p-MPPI binding by NCS-MPP following a 5 min incubation at room temperature was concentration dependent; the inhibition increased to 50% at a concentration less than 10 nM, and became more pronounced (90%) at 400 nM. Under similar assay conditions, NCS-MPP was significantly less efficient in irreversibly inhibiting agonist ligand [125I]8-OH-PIPAT binding to 5-HT1A receptors at lower concentrations (<10nM). After pretreatment of membranes with a low concentration of NCS-MPP (2nM), there was an apparent loss of [125I]p-MPPI binding sites, as expected, but no change in the binding affinity (Kd) was observed. However, the significant increase in Kd at a higher concentration of NCS-MPP (50 nM) indicated that there may be a secondary alkylation site, which may not be directly involved in p-MPPI binding to receptors; nevertheless, it would lead to an increased Kd value. The availability of an irreversible ligand, NCS-MPP, may provide a useful tool for studies of 5-HT1A receptors in the central nervous system.     

Systemic candidiasis with acute Epstein-Barr virus infection

The binding of a classical cannabinoid agonist, [3H]R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol[1,2 ,3-de]-1,4-benzoxazin-6-yl)(1-napthalenyl)methanone monomethanesulfonate ([3H] WIN55212-2), and a selective cannabinoid receptor (CB1) antagonist, N-(piperidin-1-yl)-5-(4-chlorophenyl)1-(2,4-dichlorophenyl)-4-meth yl-1H-pyrazole-3-carboxamide hydrochloride ([3H]SR141716A), to rat cannabinoid receptors was evaluated using rat cerebellar membranes. Guanine nucleotides inhibited [3H]WIN55212-2 binding by approximately 50% at 10 microM and enhanced [3H]SR141716A binding very slightly. In the same tissue, the binding of guanosine 5'-O-[gamma-[35S]thio]triphosphate ([35S]GTP-gamma-S) was characterized and the influence of cannabinomimetics evaluated on this binding. Cannabinoid receptor agonists enhanced [35S]GTP-gamma-S binding, whereas SR141716A was devoid of action by itself but antagonized the action of cannabinoid receptor agonists. The good correlation obtained between the half maximum efficient concentration (EC50) values in [35S]GTP-gamma-S binding and the IC50 values [3H]WIN55212-2 binding shows that [35S]GTP-gamma-S binding could be a good functional assay for brain cannabinoid receptors.     

How often does oral treatment of toenail onychomycosis produce a disease-free nail? An analysis of published data

A series of N-(1-ethyl-4-methylhexahydro-1,4-diazepin-6-yl)nicotinamide derivatives were prepared and evaluated for their binding to 5-HT3 and dopamine D2 receptors. Among them, the 5-bromo-2-methoxy-6-methylaminonicotinamide 16 and its (R)-isomer were found to have potent affinities for both receptors. The affinities of (R)-16 for 5-HT3 and dopamine D2 receptors are approximately 3-fold higher than those of the corresponding benzamide (R)-1 (IC50: 1.1 and 12 nM vs. 2.9 and 35 nM, respectively).     

Stimulated [35S]GTP gamma S binding by 5-HT1A receptor agonists in recombinant cell lines. Modulation of apparent efficacy by G-protein activation state

G-protein activation by different 5-HT receptor ligands was investigated in h5-HT1A receptor-transfected C6-glial and HeLa cells using agonist-stimulated [35S]-GTP gamma S binding to membranes in the presence of excess GDP. 5-HT (10 microM) stimulated [35S]GTP gamma S binding in the C6-glial membrane preparation to a larger extent than in the HeLa preparation; maximal responses with 30 microM GDP were 490 +/- 99 and 68 +/- 12%, respectively. With the 5-HT receptor agonists that were being investigated, the two preparations displayed the same rank order of potency for stimulation of [35S]GTP gamma S binding. In the C6-glial preparation at 0.3 microM GDP, the rank order of maximal effects was: 5-HT (1.00) > 8-OH-DPAT (0.90) = R(+)-8-OH-DPAT (0.87) = 5-CT (0.86) = L694247 (0.84) > S(-)8-OH-DPAT (0.68) = buspirone (0.67) = spiroxatrine (0.67) = flesinoxan (0.64) > ipsapirone (0.53) = (-)-pindolol (0.50) > SDZ216525 (0.25). However, differences in maximal response in the C6-glial preparation were magnified by increasing the GDP concentrations, indicating that the activity state of G-proteins can affect the maximal response. With the exception of 5-CT and L694247, increasing the amount of GDP to 30 microM and higher concentrations resulted in an attenuation of both the ligand's maximal effect (24 to 56%) and apparent potency (6 to 24-fold). Each of the [35S]GTP gamma S binding responses was mediated by a 5-HT1A receptor as indicated by the competitive blockade by WAY100635 and spiperone. Only 5-CT and L694247 in some conditions displayed an efficacy similar to that of 5-HT at the h5-HT1A receptor; the other agents with intrinsic activity are partial agonists at this receptor. The data also suggest that the activity state of the G-proteins is involved in the maximal effects that can be produced by activating the h5-HT1A receptor.     

Detection and quantitation of human papillomavirus by using the fluorescent 5' exonuclease assay

Some 1-aryl-4-[(5-methoxy-1,2,3, 4-tetrahydronaphthalen-1-yl)-n-propyl]piperazines and their alkylamino and alkylamido analogues, previously studied as 5-HT1A ligands, were prepared in enantiomerically pure form, and their absolute configuration was determined by chemical correlation or by chiroptical properties. They were evaluated for in vitro 5-HT1A, D2, and alpha1 receptor affinity by radioligand binding assays, to study the influence of the chiral carbon atom of the tetrahydronaphthalene nucleus on the 5-HT1A affinity and selectivity. Results indicated that, as regarding the 5-HT1A receptor affinity, there was no difference in affinity between (-)- and (+)-enantiomers as well as the racemate of each compound. The stereochemistry, instead, influenced the selectivity: all (-)-enantiomers displayed affinity values higher than those of (+)-isomers at D2 receptors, and conversely, all (+)-enantiomers displayed affinity values higher than those of (-)-isomers at alpha1 receptors. As a result of this trend, it is not possible to predict the isomer with a better selectivity profile. However, compounds (S)-(+)-2, (S)-(+)-4, and (R)-(+)-6 displayed high affinity for the 5-HT1A receptor (IC50 values ranging between 7.0 and 2.3 nM) and good selectivity (>/=250-fold) versus both D2 and alpha1 receptors. Furthermore, compounds (S)-(+)-4 and (R)-(-)-4 were submitted to the [35S]GTPgammaS binding assay for a preliminary evaluation of their intrinsic activity on the 5-HT1A receptor.     

3H]Alnespirone: a novel specific radioligand of 5-HT1A receptors in the rat brain

Determination of the optimal assay conditions for the specific binding of a tritiated derivative of the novel potential anxiolytic drug alnespirone (S-20499, (+)-4-[N-(5-methoxy-chroman-3-yl)-N-propylamino]butyl-8-azaspiro-( 4,5)-decane-7,9-dione) allowed the demonstration that this radioligand bound with a high affinity (Kd = 0.36 nM) to a homogeneous class of sites in rat hippocampal membranes. The pharmacological properties of [3H]alnespirone specific binding sites matched exactly (r = 0.95) those of 5-HT1A receptors identified with [3H]8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) as radioligand. Furthermore, membrane binding experiments and autoradiographic labeling of tissue sections showed that the regional distribution of [3H]alnespirone specific binding sites in the rat brain and spinal cord superimposed over that of 5-HT1A receptors specifically labeled by [3H]8-OH-DPAT. However, the differential sensitivity of [3H]alnespirone and [3H]8-OH-DPAT specific binding to various physicochemical effectors (temperature, pH, Mn2+, N-ethyl-maleimide) supports the idea that these two agonist radioligands did not recognize 5-HT1A receptors exactly in the same way. These differences probably account for the reported inability of alnespirone, in contrast to 8-OH-DPAT, to induce some 5-HT1A receptor-mediated behavioural effects in rats.     

Response of SCC-12F, a human squamous cell carcinoma cell line, to complement attack

Serotonin 5-HT1A receptors belong to the superfamily of G-protein-coupled receptors. Receptor activation of G-proteins can be determined by agonist-stimulated [35S]GTPgammaS binding in the presence of excess GDP, and in vitro autoradiographic adaptation of this technique allows visualization of receptor-activated G-proteins in tissue sections. The present study was performed to examine 5-HT1A receptor activation of G-proteins using 8-OH-DPAT-stimulated [35S]GTPgammaS binding in membranes and brain sections. In hippocampal membranes, 8-OH-DPAT stimulated [35S]GTPgammaS binding by twofold, with an ED50 value of 25 nM. 5-HT1 antagonists, but not 5-HT2 antagonists, increased the ED50 of 8-OH-DPAT in a manner consistent with competitive antagonists. Scatchard analysis of [35S]GTPgammaS binding showed that 8-OH-DPAT induced the formation of high affinity [35S]GTPgammaS binding sites with a KD for GTPgammaS of 3.2 nM. [35S]GTPgammaS autoradiography, performed in brain sections with the 5-HT1A agonist 8-OH-DPAT, revealed high levels of 5-HT1A-stimulated [35S]GTPgammaS binding in the hippocampus, lateral septum, prelimbic cortex, entorhinal cortex, and dorsal raphe nucleus. 5-HT1A-stimulated [35S]GTPgammaS binding in sections was blocked by the addition of the 5-HT1 antagonist methiothepin. These results show that the use of agonist-stimulated [35S]GTPgammaS autoradiography for the 5-HT1A receptor system should provide new information regarding signal transduction in specific brain regions.     

Selective visualization of rat brain 5-HT2A receptors by autoradiography with [3H]MDL 100,907

The recently developed 5-HT2A receptor selective antagonist [3H]MDL100,907 ((+/-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol]) has been characterized as a radioligand for the autoradiographic visualization of these receptors. [3H]MDL100,907 binding to rat brain tissue sections was saturable, had sub-nanomolar affinity (Kd = 0.2-0.3 nM), and presented a pharmacological profile consistent with its binding to 5-HT2A receptors (rank order of affinity for [3H]MDL100,907-labelled receptors: MDL100,907 > spiperone > ketanserin > mesulergine). The distribution of receptors labelled by [3H]MDL100,907 was compared to the autoradiographical patterns obtained with [3H]Ketanserin, [3H]Mesulergine, and [3H]RP62203 (N-[3-[4-(4-fluorophenyl)piperazin-1-y1]propyl]-1,8-naphtalenes ultam) and to the distribution of 5-HT2A receptor mRNA as determined by in situ hybridization. As opposed to the other radioligands, [3H]MDL100,907 labelled a single population of sites (5-HT2A receptors) and presented extremely low levels of non-specific binding. The close similarity of the distributions of [3H]MDL100,907-labelled receptors and 5-HT2A mRNA further supports the selectivity of this radioligand for 5-HT2A receptors and suggests a predominant somatodendritic localization of these receptors. The present results point to [3H]MDL100,907 as the ligand of choice for the autoradiographic visualization of 5-HT2A receptors.     

Characterization of 5-HT1A receptor-mediated [35S]GTPgammaS binding in rat hippocampal membranes

Stimulation of [35S]GTPgammaS binding by serotonin (5-hydroxytryptamine, 5-HT) receptor ligands was characterized in rat hippocampal membranes. The optimized assay contained 30-50 microg protein, 300 microM GDP and 0.1 nM [35S]GTPgammaS, incubated at 37 degrees C for 20 min. At 10 microM, the 5-HT1A receptor agonist R(+)-8-hydroxy-2-(di-n-propylamino)tetralin [R(+)-8-OH-DPAT] stimulated GTPgammaS binding from 27.1 +/- 2.5 to 45.7 +/- 4.2 fmol/mg protein. Increasing the protein concentration did not affect the absolute difference between basal and maximal GTPgammaS binding nor the EC50, but decreased the percent stimulation. The non-selective agonists serotonin and 5-carboxamidotryptamine were 30-35% more efficacious, whereas the partial agonists buspirone and S(-)-8-hydroxy-2-(di-n-propylamino)tetralin stimulated GTPgammaS binding by 19 +/- 1 and 43 +/- 3%, respectively, compared to R(+)-8-OH-DPAT. Neither the 5-HT2 receptor agonist [(+/-)1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl] (DOI) nor the 5-HT1A receptor antagonists WAY 100,635 (n-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-n-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) and spiperone altered basal GTPgammaS binding. WAY 100,635 abolished the effect of R(+)-8-OH-DPAT, but only reduced the effect of serotonin by 88 +/- 3%. Finally, methiothepin antagonized R(+)-8-OH-DPAT-stimulated GTPgammaS binding and reduced basal GTPgammaS binding by itself. The reduction was not affected by WAY 100,635. We have characterized a method to assess functional activity at 5-HT1A receptors in rat hippocampal membranes by measuring agonist-induced [35S]GTPgammaS binding.     

Prognosis and immunomorphological characteristics in rectal cancer: results of a multivariate analysis

A new model of 4-alkyl-1-arylpiperazines containing a terminal dihydronaphthalene fragment on the alkyl chain was synthesized in order to have mixed serotonergic and dopaminergic activity and to pursue the recent alternative approaches to the discovery of novel antipsychotic and anxiolytic agents. Title compounds were evaluated for in vitro activity on dopamine D-2 and serotonin 5-HT1A and 5-HT2 receptors by radioreceptor binding assays. They show high nanomolar affinity for 5-HT1A, moderate affinity for D-2, and low affinity for 5-HT2 receptors, and in particular, two compounds, 4-[3-(1,2-dihydro-6-methoxynaphthalen-4-yl)-n-propyl]-1-(2- methoxyphenyl)piperazine (8) and 4-[3-(1,2-dihydro-8-methoxynaphthalen-4-yl)-n-propyl]-1-(2- pyridyl)piperazine (15), show values (nM) of IC50 = 2.0 and 1.4 for 5-HT1A and IC50 = 90.6 and 119.3 for D-2, respectively. Some in vivo behavioral studies show compound 8 to be an antagonist on 5-HT1A receptors. These first findings place the new arylpiperazines on the same level as that of the azaspirone class, e.g., 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)-n-butyl]piperazine (NAN-190) and buspirone.     

Alniditan, a new 5-hydroxytryptamine1D agonist and migraine-abortive agent: ligand-binding properties of human 5-hydroxytryptamine1D alpha, human 5-hydroxytryptamine1D beta, and calf 5-hydroxytryptamine1D receptors investigated with [3H]5-hydroxytryptamine and [3H]alniditan

Alniditan is a new migraine-abortive agent. It is a benzopyran derivative and therefore structurally unrelated to sumatriptan and other indole-derivatives and to ergoline derivatives. The action of sumatriptan is thought to be mediated by 5-hydroxytryptamine (5-HT)1D-type receptors. We investigated the receptor-binding profile in vitro of alniditan compared with sumatriptan and dihydroergotamine for 28 neurotransmitter receptor subtypes, several receptors for peptides and lipid-derived factors, ion channel-binding sites, and monoamine transporters. Alniditan revealed nanomolar affinity for calf substantia nigra 5-HT1D and for cloned h5-HT1D alpha, h5-HT1D beta and h5-HT1A receptors (Ki = 0.8, 0.4, 1.1, and 3.8 nM, respectively). Alniditan was more potent than sumatriptan at 5-HT1D-type and 5-HT1A receptors. Alniditan showed moderate-to-low or no affinity for other investigated receptors; sumatriptan showed additional binding to 5-HT1F receptors. Dihydroergotamine had a much broader profile with high affinity for several 5-HT, adrenergic and dopaminergic receptors. In signal transduction assays using cells expressing recombinant h5-HT1D alpha, h5-HT1D beta, or h5-HT1A receptors, alniditan (like 5-HT) was a full agonist for inhibition of stimulated adenylyl cyclase (IC50 = 1.1, 1.3, and 74 nM, respectively, for alniditan). Therefore, in functional assays, the potency of alniditan was much higher at 5-HT1D receptors than at 5-HT1A receptors. We further compared the properties of [3H]alniditan, as a new radioligand for 5-HT1D-type receptors, with those of [3H]5-HT in membrane preparations of calf substantia nigra, C6 glioma cells expressing h5-HT1D alpha, and L929 cells expressing h5-HT1D beta receptors. [3H]Alniditan revealed very rapid association and dissociation binding kinetics and showed slightly higher affinity (Kd = 1-2 nM) than [3H]5-HT. We investigated 25 compounds for inhibition of [3H]alniditan and [3H]5-HT binding in the three membrane preparations; Ki values of the radioligands were largely similar, although some subtle differences appeared. Most compounds did not differentiate between 5-HT1D alpha and 5-HT1D beta receptors, except methysergide, ritanserin, ocaperidone, risperidone, and ketanserin, which showed 10-60-fold higher affinity for the 5-HT1D alpha receptor. The Ki values of the compounds obtained with 5-HT1D receptors in calf substantia nigra indicated that these receptors are of the 5-HT1D beta-type. We demonstrated that alniditan is a potent agonist at h5-HT1D alpha and h5-HT1D beta receptors; its properties probably underlie its cranial vasoconstrictive and antimigraine properties.     

2-aminotetralin-derived substituted benzamides with mixed dopamine D2, D3, and serotonin 5-HT1A receptor binding properties: a novel class of potential atypical antipsychotic agents

A new chemical class of potential atypical antipsychotic agents, based on the pharmacological concept of mixed dopamine D2 receptor antagonism and serotonin 5-HT1A receptor agonism, was designed by combining the structural features of the 2-(N,N-di-n-propylamino)tetralins (DPATs) and the 2-pyrrolidinylmethyl-derived substituted benzamides in a structural hybrid. Thus, a series of 35 differently substituted 2-aminotetralin-derived substituted benzamides was synthesized and the compounds were evaluated for their ability to compete for [3H]-raclopride binding to cloned human dopamine D2A and D3 receptors, and for [3H]-8-OH-DPAT binding to rat serotonin 5-HT1A receptors in vitro. The lead compound of the series, 5-methoxy-2-[N-(2-benzamidoethyl)-N-n-propylamino]tetralin (12a), displayed high affinities for the dopamine D2A receptor (Ki = 3.2 nM), the dopamine D3 receptor (Ki = 0.58 nM) as well as the serotonin 5-HT1A receptor (Ki = 0.82 nM). The structure-affinity relationships of the series suggest that the 2-aminotetralin moieties of the compounds occupy the same binding sites as the DPATs in all three receptor subtypes. The benzamidoethyl side chain enhances the affinities of the compounds for all three receptor subtypes, presumably by occupying an accessory binding site. For the dopamine D2 and D3 receptors, this accessory binding site may be identical to the binding site of the 2-pyrrolidinylmethyl-derived substituted benzamides.     

Selective in vivo labelling of brain 5-HT1A receptors by [3H]WAY 100635 in the mouse

The novel selective 5-HT1A receptor antagonist radioligand [3H]WAY 100635 ([O-methyl-3H]N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2- pyridyl)cyclohexane-carboxamide) was injected i.v. to mice in an attempt to label in vivo central 5-HT1A receptors. Although 5 min after the i.v. injection of [3H]WAY 100635 (4-7.6 muCi per mouse) the amount of tritium found in the whole brain only accounted for 1.5-1.8% of the injected radioactivity, regional differences in 3H accumulation already corresponded to those of 5-HT1A receptor density. Optimal data were obtained 1 h after [3H]WAY 100635 injection as the distribution of 3H in brain was exactly that of 5-HT1A receptor binding sites in mouse brain sections labelled in vitro with [3H]WAY 100635. In particular, high level of labelling was found in the lateral septum, gyrus dentatus and CA1 area of Ammon's horn in the hippocampus, dorsal raphe nucleus and entorhinal cortex. No labelling was found in he substantia nigra, and 3H accumulated in the cerebellum represented only 12-14% of that found in the hippocampus. Pretreatment with various drugs indicated that only 5-HT1A receptor ligands were able to decrease the accumulation of 3H in all the brain areas examined except in the cerebellum. Assuming that only non-specific binding took place in the latter structure, it was possible to calculate the ID50 values of 5-HT1A receptor agonists (8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin), S 14506 (1-[2-(4-fluorobenzoylamino)ethyl]-4-(7-methoxynaphthyl+ ++)piperazine) and S 20499 ((+)-4-[N-(5-methoxy-chroman-3-yl)-N-propylamino]butyl-8- azaspiro-(4,5)-decane-7,9-dione)) and antagonists (spiperone, (-)-tertatolol, (+)-WAY 100135 (N-tert-butyl-3,4-(2-methoxyphenyl)piperazin-1-yl-2-phenyl- propanamide)) as inhibitors of 3H accumulation in the hippocampus of [3H]WAY 100635-injected mice. Comparison of these values with the in vitro affinity of the same ligands for hippocampal 5-HT1A receptors revealed marked variations in the capacity of 5-HT1A receptor agonists and antagonists to reach the brain when injected via the subcutaneous route in mice.     

Reconstitution of receptors and GTP-binding regulatory proteins (G proteins) in Sf9 cells. A direct evaluation of selectivity in receptor.G protein coupling

The selectivity in coupling of various receptors to GTP-binding regulatory proteins (G proteins) was examined directly by a novel assay entailing the use of proteins overexpressed in Spodoptera frugiperda (Sf9) cells. Activation of G proteins was monitored in membranes prepared from Sf9 cells co-expressing selected pairs of receptors and G proteins (i.e. alpha, beta1, and gamma2 subunits). Membranes were incubated with [35S]guanosine 5'-(3-O-thio)triphosphate (GTPgammaS) +/- an agonist, and the amount of radiolabel bound to the alpha subunit was quantitated following immunoprecipitation. When expressed without receptor (but with beta1gamma2), the G protein subunits alphaz, alpha12, and alpha13 did not bind appreciable levels of [35S]GTPgammaS, consistent with a minimal level of GDP/[35S]GTPgammaS exchange. In contrast, the subunits alphas and alphaq bound measurable levels of the nucleotide. Co-expression of the 5-hydroxytryptamine1A (5-HT1A) receptor promoted binding of [35S]GTPgammaS to alphaz but not to alpha12, alpha13, or alphas. Binding to alphaz was enhanced by inclusion of serotonin in the assay. Agonist activation of both thrombin and neurokinin-1 receptors promoted a modest increase in [35S]GTPgammaS binding to alphaz and more robust increases in binding to alphaq, alpha12, and alpha13. Binding of [35S]GTPgammaS to alphas was strongly enhanced only by the activated beta1-adrenergic receptor. Our data identify interactions of receptors and G proteins directly, without resort to measurements of effector activity, confirm the coupling of the 5-HT1A receptor to Gz and extend the list of receptors that interact with this unique G protein to the receptors for thrombin and substance P, imply constitutive activity for the 5-HT1A receptor, and demonstrate for the first time that the cloned receptors for thrombin and substance P activate G12 and G13.     

Lesbians, bisexual women, and body image: an investigation of gender roles and social group affiliation

In our previous study, we demonstrated that chronic ethanol (EtOH) exposure down-regulated the cannabinoid receptors (CB1) in mouse brain synaptic plasma membrane (SPM) (Basavarajappa et al., Brain Res. 793 (1998) 212-218). In the present study, we investigated the effect of chronic EtOH (4-day inhalation) on the CB1 agonist stimulated guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTP gamma S) binding in SPM from mouse. Our results indicate that the net CP55,940 stimulated [35S]GTP gamma S binding was increased with increasing concentrations of CP55,940 and GDP. This net CP55,940 (1.5 microM) stimulated [35S]GTP gamma S binding was reduced significantly (-25%) in SPM from chronic EtOH group (175 +/- 5.25%, control; 150 +/- 8.14%, EtOH; P < 0.05). This effect occurs without any significant changes on basal [35S]GTP gamma S binding (152.1 +/- 10.7 for control, 147.4 +/- 5.0 fmol/mg protein for chronic EtOH group, P > 0.05). Non-linear regression analysis of net CP55,940 stimulated [35S]GTP gamma S binding in SPM showed that the Bmax of cannabinoid stimulated binding was significantly reduced in chronic EtOH exposed mouse (Bmax = 7.58 +/- 0.22 for control; 6.42 +/- 0.20 pmol/mg protein for EtOH group; P < 0.05) without any significant changes in the G-protein affinity (Kd = 2.68 +/- 0.24 for control; 3.42 +/- 0.31 nM for EtOH group; P > 0.05). The pharmacological specificity of CP55,940 stimulated [35S]GTP gamma S binding in SPM was examined with CB1 receptor antagonist, SR141716A and these studies indicated that CP55,940 stimulated [35S]GTP gamma S binding was blocked by SR141716A with a decrease (P < 0.05) in the IC50 values in the SPM from chronic EtOH group. These results suggest that the observed down-regulation of CB1 receptors by chronic EtOH has a profound effect on desensitization of cannabinoid-activated signal transduction and possible involvement of CB1 receptors in EtOH tolerance and dependence.     

Antidepressant effects of pramipexole, a novel dopamine receptor agonist

These studies compared the effects of the 5-HT1B/1D receptor agonists sumatriptan, CP-122 288 ((R)-N-methyl-[3-(1-methyl-2-pyrrolidinylmethyl)-1H-indol-5-yl] methanesulphonamide succinate) and CP-93 129 (3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one dihydrochloride) on neurogenic dural extra-vasation and vasodilation in anaesthetized rats. Dural extravasation, evoked by high intensity (1.2 mA) stimulation of the trigeminal ganglion, was measured using the radioactive plasma marker 125I-labelled bovine serum albumin. Dural vasodilation produced by lower intensity (50-300 microA) stimulation of trigeminal fibres, was measured through a closed cranial window using intravital microscopy. All compounds inhibited dural extravasation (rank order of potency: CP-122 288 > > sumatriptan > CP-93 129) and dural vasodilation (rank order of potency: CP-93 129 > > sumatriptan = CP-122 288). Comparison of the potency of these compounds with their potencies in an in vitro functional model, agonist-induced [35S]GTP gamma S binding, suggests that blockade of dural extravasation was consistent with an action at rat 5-HT1D receptors, but activity at another, unknown, "extravasation receptor" could also be involved. In contrast, inhibition of dural vasodilation was consistent with an action at rat 5-HT1B receptors. We suggest that in our preparations, production of dural vasodilation involves activation of trigeminal A delta-fibres whereas production of dural extravasation involves activation of trigeminal C-fibres. The differential effects of compounds on dural extravasation and vasodilation may therefore be due to the different receptor subtypes involved and to the selective localization of these subtypes on different populations of trigeminal sensory fibre.     

Characterization of (S)-des-4-amino-3-[125I]iodozacopride ([125I]DAIZAC), a selective high-affinity radioligand for 5-hydroxytryptamine3 receptors

The 5-hydroxytryptamine(HT)3 receptor subtype is present in the central nervous system (CNS) in low abundance, and few selective radiolabeled antagonists with high specific activity are available to study these sites. DAIZAC [desamino-3-iodo-(S)-zacopride; (S)-5-chloro-3-iodo-2-methoxy-N-(1-azobicyclo-[2.2. 2]oct-3-yl)benzamide] is a compound with high affinity and selectivity for the 5-HT3 receptor. Scatchard analysis of specific binding to NCB-20 cell membranes gave a Bmax of 340 +/- 58 fmol/mg protein and a KD of 0.14 +/- 0.03 nM, which is in agreement with the value previously reported in rat brain (KD = 0.15 nM). Nonspecific binding of [125I]DAIZAC in NCB-20 cells was <1% of total binding at the KD for DAIZAC compared with 17% in the rat brain preparation. Unlabeled DAIZAC (10 microM) showed minimal ability to displace binding of radiolabeled ligands selected for their affinities for other CNS receptor and uptake carrier binding sites. The discrimination ratio of DAIZAC for the 5-HT3 receptor over the M1 muscarinic binding site, the non-5-HT3 site at which it was most potent, was >2800. Serotonergic antagonists at every other known CNS serotonergic binding sites (3-30 microM) were ineffective in displacing [125I]DAIZAC binding in rat brain membranes. Similarly, antagonists (3-30 microM) for other nonserotonergic receptors and uptake sites were ineffective in displacing [125I]DAIZAC binding. Autoradiographic studies showed highest specific binding in area postrema and nucleus solitarius, with intermediate levels of binding in entorhinal cortex and hippocampus. DAIZAC inhibited 5-HT3 receptor-mediated inward cation current in NCB-20 cells with an IC50 of 0.24 nM. [125I]DAIZAC is a potent and highly selective ligand for in vitro studies of the 5-HT3 receptor.     

Diagnostic value of otoacoustic emissions. 1

Analogues of the potent and selective 5-HT1A ligand, WAY 100635, were synthesized and examined as potential candidates for imaging 5-HT1A receptors by positron emission tomography (PET). Several of the analogues displayed nanomolar affinity for the 5-HT1A receptor, comparable to WAY 100635. Three of these were examined in a model of human liver metabolism vis-à-vis WAY 100635. All showed a markedly lower propensity for amide hydrolysis than WAY 100635. Radiolabelling of these three potential PET radiotracers with carbon-11 was readily achieved from [11C]-iodomethane, and the newly synthesized radioligands were tested in vivo in rats for binding to 5-HT1A receptors. Whereas two of the ligands failed to bind to 5-HT1A receptors in vivo, one was successful. The latter, [11C]-7 [4-(2'-methoxyphenyl)-1-[2'-[N-(2'-pyridinyl)-2-bicyclo[2.2.2]octanec arboxamido]ethyl]-piperazine], showed good brain penetration, hippocampal:cerebellar ratios of 10:1 at 45 min postinjection. Blocking studies with a variety of drugs demonstrated that the binding of [11C]-7 in vivo was selective for 5-HT1A receptors. [11C]-7 is a promising candidate as a ligand for imaging 5-HT1A receptors by PET.