Affinity For M1 Receptors Research Articles

Pharmacological considerations in antipsychotic drug selection for prevention of drug-induced dysphagia.

Antipsychotic drugs have the ability to induce dysphagia. The aim of this study was to determine the association between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, and to identify factors that prevent antipsychotic drug-induced dysphagia. We used the receptor affinity of 13 antipsychotic drugs for which data were reported in an in vitro test using human receptors, extracted time-to-onset dysphagia from the Japan Adverse Drug Event Report database, and used data from 46 patients to evaluate the correlation between receptor affinity and time-to-onset of dysphagia. We found a negative correlation between D₂ receptor affinity and time-to-onset of dysphagia (r = -0.4572, p = 0.0016), and a positive correlation between H1, M1, and M₃ receptor affinity and time-to-onset of dysphagia (r = 0.5006, p = 0.0006; r = 0.4130, p = 0.0059; and r = 0.4149, p = 0.0057, respectively). Antipsychotic drugs with a strong D₂ receptor-blocking action may accelerate the onset of dysphagia, whereas a strong H1, M1, and M₃ receptor-blocking action may delay the onset of dysphagia. The current study revealed the relationship between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, which should aid in the selection of antipsychotic drugs, while preventing dysphagia.

Excitatory effect of acotiamide on rat and human bladder: Implications for underactive bladder treatment

ObjectiveTo evaluate whether approved gastroprokinetic agent, acotiamide exerts a direct excitatory effect on bladder to help explain the reported meaningful reduction of post-void residual urine volume (PVR) in detrusor underactivity (DU) patients after thrice daily oral intake of acotiamide 100 mg for 2 weeks. MethodsEffect of acotiamide [1–16 μM] was assessed on nerve-mediated contractions evoked by electrical field stimulation (EFS) for 5 s with 5 ms pulse trains of 10 V in longitudinal, mucosa intact rat and human bladder strips to construct frequency response curve (1–32 Hz) and repeat 10 Hz stimulation at 60s interval. Effect of acotiamide 2 μM on spontaneous and carbachol evoked contractions was also assessed. ResultsAcotiamide 2 μM significantly enhanced the Atropine and Tetrodotoxin (TTX)-sensitive EFS evoked contractions of rat and human bladder at 8–32 Hz (Two-way ANOVA followed Sidak's multiple comparison; *p < 0.01) and on repeat 10 Hz stimulation (Paired Student's t-test; *p < 0.05), while producing a modest effect on the spontaneous contractions and a negligible effect on the carbachol evoked contractions. ConclusionsEnhancement of TTX-sensitive evoked contractions of rat and human bladder by acotiamide is consistent with the enhancement of excitatory neuro-effector transmission mainly through prejunctional mechanisms. Findings highlight immense therapeutic potential of antimuscarinics with low M3 receptor affinity like acotiamide in Underactive bladder (UAB)/DU treatment.

Differently fluorescence-labelled dibenzodiazepinone-type muscarinic acetylcholine receptor ligands with high M2R affinity.

A series of fluorescent dibenzodiazepinone-type muscarinic acetylcholine M2 receptor (M2R) ligands was synthesized using various fluorescent dyes (5-TAMRA, λ ex/λ em ≈ 547/576 nm; BODIPY 630/650, λ ex/λ em ≈ 625/640 nm; pyridinium dye Py-1, λ ex/λ em ≈ 611/665 nm and pyridinium dye Py-5, λ ex/λ em ≈ 465/732 nm). All fluorescent probes exhibited high M2R affinity (pK i (radioligand competition binding): 8.75-9.62, pK d (flow cytometry): 8.36-9.19), a very low preference for the M2R over the M1 and M4 receptors and moderate to pronounced M2R selectivity compared to the M3 and M5 receptors. The presented fluorescent ligands are considered useful molecular tools for future studies using methods such as fluorescence anisotropy and BRET based MR binding assays.

Brexpiprazole: so far so good.

This article describes the role of a newly approved antipsychotic agent brexpiprazole in the treatment of schizophrenia and major depressive disorder. This drug has high affinity for 5-HT1A, 5-HT2A, D2 and α1B,2C receptors. It displays partial agonism at 5-HT1A and D2 receptors and potent antagonism at 5-HT2A and α1B,2C adrenergic receptors. It also has some affinity (antagonism) for D3, 5-HT2B, 5-HT7 and α1A,1D receptors, and moderate affinity for H1 and low affinity for M1 receptors. These all lead to a favorable antipsychotic profile in terms of improvement of cognitive performance and sleep patterns, as well as effects on affective states and potential to treat core symptoms in schizophrenia and major depressive disorder, including cognitive deficits with a low risk of adverse effects (extrapyramidal symptoms, metabolic complications, weight gain, akathisia potential) that are commonly encountered with other typical and second-generation antipsychotic drugs. In our review, we have made an attempt to decipher the pharmacological profile of brexpiprazole from two major trials (VECTOR and BEACON). We have also tried to give a concise but detailed overview of brexpiprazole by head to head comparison of the pharmacological profile of brexpiprazole and its earlier congeners aripiprazole and prototype antipsychotic drug chlorpromazine by accessing individual summaries of product characteristics from the US Food and Drug Administration database, 2015. Relevant preclinical and clinical studies associated with this drug have been discussed with emphasis on efficacy and safety concerns. From the studies done so far, it can be concluded that brexpiprazole can be an effective monotherapy for schizophrenia and as an adjunct to other antidepressant medications in major depressive disorder.

The potency and efficacy of anticholinergics to inhibit haloperidol-induced catalepsy in rats correlates with their rank order of affinities for the muscarinic receptor subtypes

Extrapyramidal syndromes (EPS) caused by antipsychotic therapy are currently treated with anticholinergics that lack selectivity for the five muscarinic receptor subtypes. Since these receptors are heterogeneously expressed among the different classes of striatal neurons and their afferents, it can be expected that their simultaneous blockade will cause distinct, sometimes opposed, effects within the striatal circuitry. In order to test the hypothesis that the differential blockade of the muscarinic receptor subtypes would influence their potency and efficacy to prevent EPS, here we tested four anticholinergics with varying order of affinities for the muscarinic receptor subtypes, and compared their dose–response curves to inhibit haloperidol-induced catalepsy in male rats. Drugs were applied into the lateral ventricle 15 min before haloperidol (2 mg/kg, s.c.). Catalepsy was measured in the bar test at 15 min intervals during 5 h. The preferential M1/M4 antagonist pirenzepine (3, 10, 30, 100, and 300 nmol) caused a dose-dependent inhibition of catalepsy intensity: ED50 = 5.6 nmol [95% CI, 3.9–8.1], and latency: ED50 = 5.6 nmol [95% CI, 3.7–8.6]. Pirenzepine had the steepest dose–response curve, producing maximal inhibition (84 ± 5%) at the dose of 10 nmol, while its effect tended to reverse at higher doses (62 ± 11%). The purported M1/M3 antagonist 4-DAMP (30, 100, and 300 nmol) also caused a dose-dependent inhibition of catalepsy intensity: ED50 = 29.5 nmol [95% CI, 7.0 to 123.0], and latency: ED50 = 28.5 nmol [95% CI, 2.2 to 362.0]. However, the curve for 4-DAMP had a less pronounced slope, reaching its maximal effect (63 ± 14%) at the dose of 300 nmol. The M2/M4 antagonist AF-DX 116 (10, 30, and 300 nmol) only caused a partial inhibition of catalepsy (30 ± 11%) at the dose of 30 nmol, but this changed to a non-significant increment (15 ± 10%) at the dose of 100 nmol. The alleged M4 antagonist tropicamide (30, 100, 300, and 600 nmol) produced a partial inhibition of catalepsy (36 ± 12%) at the dose of 300 nmol, but lacked effect at higher or lower doses. Concurrent treatment with pirenzepine (10 nmol) and tropicamide (300 nmol) produced an effect similar to that of tropicamide alone. The greater potency and efficacy of pirenzepine for catalepsy inhibition could be due to its higher affinity for M1 receptors and, to a lesser extent, for M4 receptors. It is suggested that selective M1 antagonists would be more effective than M2, M3 or M4 antagonists to prevent EPS caused by antipsychotic drugs.

Binding Profiles of a Series of 2-Arylpropionic Acid Esters on Cloned Human Muscarinic Receptor Subtypes (m1-m5) and Their Relationship to Nootropic Activity

The muscarinic binding profile of a series of 2-arylpropionic acid esters on cloned human muscarinic receptor subtypes (m1-m5) was determined to investigate whether there is a correlation between pharmacological activity and muscarinic receptor subtype selectivity. Among the tested compounds, 1, 7 and 9 showed the highest affinity for the m2 and m4 receptors. Compounds 1, 7 and 9 show good affinity for m4 receptors (pKi = 7.87; 7.73 and 7.10, respectively) and are able to discriminate 10-60 fold between m4/m1, m4/m3, and m4/m5 subtypes. Conversely, these compounds are able only to weakly discriminate between m4/m2. Compounds 1 (50-300 micrograms kg-1 i.p.) and 7 (1-10 micrograms kg-1 i.p.), injected 20 min before the training session, are able to prevent the amnesia induced by dicyclomine (2 mg kg-1 i.p.) in the mouse passive-avoidance test. Compounds 1 and 7, at the highest antiamnesic doses, do not modify motor coordination and spontaneous motility as evaluated by the rota-rod test and Animex apparatus experiments.

Muscarinic receptor 1 agonist activity of novel N-arylthioureas substituted 3-morpholino arecoline derivatives in Alzheimer’s presenile dementia models

As part of our continuing effort aimed at the development of selective, efficacious and centrally active M1 muscarinic agonists for the treatment of Alzheimer’s presenile dementia, a series of N-arylthioureas substituted 3-morpholino arecoline derivatives 9(a–j) were synthesized by using N-benzyl amino ethanol coupling with α-bromo acetyl pyridine followed by reduction and cyclization to develop a new class of M1 receptor agonists. Subsequently the synthesized compounds were subjected to in vitro radioligand M1 receptor affinity studies, IP3 formation studies and also to in vivo pharmacological evaluation of memory and learning in male Wistar rats. Derivatives with chloro ( 9f) and methoxy ( 9c) groups on the para position of the benzene ring attached to the nitrogen of thiourea showed several fold high affinity for the M1 receptor (in vitro) among all the synthesized molecules 9( a–j), and also significantly elevated IP3 levels and as well elicited beneficial effects in vivo in memory and learning models in rats (rodent memory evaluation, plus and Y maze studies).

Hyperglycemia and Diabetes in Patients With Schizophrenia or Schizoaffective Disorders

We thank Jindal and Keshavan (1) for their contribution explaining the results of our study (2), which stated that in a cross-sectional design ( n = 200), no differences in the prevalence of diabetes or hyperglycemia between typical- or atypical-treated patients were found. We would like to make two comments on this statement. First, although the muscarinic M3 receptor affinity fits well with the diabetogenic properties of …

N-8-Substituted benztropinamine analogs as selective dopamine transporter ligands

A series of N-8-substituted benztropinamines was synthesized and evaluated for binding at the dopamine (DAT), serotonin (SERT), norepinephrine (NET) transporters, and muscarinic M1 receptors. In general, the isosteric replacement of the C-3 benzhydrol ether of benztropine by a benzhydryl amino group was well tolerated at the DAT. However, for certain N-8 substituted derivatives, selectivity over muscarinic M1 receptor affinity was reduced.

Place Conditioning and Locomotor Effects of N-Substituted, 4′,4′′-Difluorobenztropine Analogs in Rats

Previous studies demonstrated that analogs of benztropine [3alpha-(diphenyl-methoxy)tropane (BZT)] bind to the dopamine (DA) transporter with high affinity, inhibit DA uptake, but do not maintain rates of responding in self-administration procedures comparable with those maintained by cocaine. Some BZT analogs have an onset of action that is slower than that for cocaine that may contribute to this decreased effectiveness. In addition, some BZT analogs have affinity for muscarinic-M1 receptors that may interfere with reinforcing effects. The present study assessed effects of BZT analogs in place-conditioning procedures designed to accommodate variations in onset of effect. BZT analogs with variations in relative affinities for the DA transporter over M1 receptors from equal [AHN 1-055 (3alpha-[bis(4'-fluorophenyl)methoxy]-tropane)] to 16-fold [JHW 007 (N-(n-butyl)-3alpha-[bis(4'-fluorophenyl)methoxy]-tropane)] were compared with cocaine and the muscarinic antagonist, atropine. Cocaine (10-20 mg/kg) but not atropine (1.0-5.6 mg/kg) produced dose-related place conditioning. The N-methyl-substituted BZT analog, AHN 1-055, was without significant effects at doses that ranged from 0.3 to 3.0 mg/kg and when administered up to 90 min before conditioning trials. In contrast, effects of AHN 2-005 (N-allyl-3alpha-[bis(4'-fluorophenyl)methoxy]-tropane; 0.1-10.0 mg/kg) were significant, and those of JHW 007 approached significance when administered 45 min but not immediately or 90 min before trials. Atropine blocked the effect of AHN 2-005 and approached significant antagonism of cocaine. The present study further supports and extends previous results showing minimal preclinical indications of abuse liability of BZT analogs and suggests that these differences from cocaine are not entirely accounted for by a slower onset of action or muscarinic M1 receptor affinity.

Effect of M4-cholinoceptor blockade on haloperidol-produced catatonic syndrome in rats.

We studied the relationship between the efficiency of muscarinic receptor antagonists in preventing haloperidol-induced catatonia and their activity in tests for the interaction of ligands with various subtypes of muscarinic receptors (M1-M4) in rats. Mathematical modeling showed that affinity of the ligand for M4 receptors positively affects its ability to correct extrapyramidal disorders (catatonic syndrome) produced by haloperidol, while affinity for M2 receptors had a negative effect on this characteristic.

Orally active and selective benzylidene ketal M2 muscarinic receptor antagonists for the treatment of Alzheimer's disease

AbstractNumerous studies have implicated the cholinergic system as a target for Alzheimer's disease (AD) therapy. The currently marketed drugs for treatment of AD are acetylcholinesterase inhibitors, which increase levels of the neurotransmitter acetylcholine (ACh) by blocking its metabolic degradation. However, this mechanism results in a non‐selective enhancement of cholinergic activity in peripheral organs as well as brain, which could lead to detrimental side effects. Cholinergic enhancement in brain can also be achieved by blocking presynaptic release‐regulating autoreceptors. M2 muscarinic receptor activation inhibits ACh release in brain regions that are critical for learning and memory processes. Thus, M2 antagonists may prove beneficial for relief of cognitive deficits in AD. In this review, early discoveries of M2 muscarinic antagonists based on dibenzodiazepinones, natural products, piperazines, and piperidines are described. More specifically, the development of a benzylidene ketal class of M2 muscarinic antagonists is reviewed. Characterization and optimization of these agents have led to the identification of compounds with high M2 receptor affinity and subtype selectivity. These M2 antagonists also facilitate ACh release and enhance cognition in preclinical experimental paradigms. While clinical efficacy of these compounds has not been evaluated, M2 antagonists represent a promising treatment for AD. Drug Dev. Res. 56:310–320, 2002. © 2002 Wiley‐Liss, Inc.

Design and development of selective muscarinic agonists for the treatment of Alzheimer's disease: characterization of tetrahydropyrimidine derivatives and development of new approaches for improved affinity and selectivity for M1 receptors

Cholinergic neurons degenerate in Alzheimer's disease, resulting in cognitive impairments and memory deficits, and drug development efforts have focused on selective M1 muscarinic agonists. 5-(3-Ethyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidine trifluoroacetic acid (CDD-0102) stimulates M1 muscarinic receptors in rat brain [Messer, W.S., Jr., Abuh, Y.F., Liu, Y., Periyasamy, S., Ngur, D.O., Edgar, M.A., El-Assadi, A.A., Sbeih, S., Dunbar, P.G., Roknich, S., Rho, T., Fang, Z., Ojo, B., Zhang, H., Huzl, J.J., III, Nagy, P.I., 1997a. J. Med. Chem. 40, 1230–1246.] and improves memory function in rats with lesions of the basal forebrain cholinergic system. Moreover, CDD-0102 exhibits oral bioavailability, few side effects and low toxicity, and thus represents a viable candidate for clinical studies. Despite the development of functionally selective agonists such as xanomeline and CDD-0102, there is room for improvements in ligand affinity and selectivity. The high degree of amino acid homology within transmembrane domains has hindered the development of truly selective agonists. Site-directed mutagenesis, biochemical and molecular modeling studies have identified key amino acid residues such as Thr192 and Asn382 in the binding of agonists to M1 receptors [Huang, X.P., Nagy, P.I., Williams, F.E., Peseckis, S.M., Messer, W.S., Jr., 1999. Br. J. Pharmacol. 126, 735–745.]. Recent work has implicated residues at the top of transmembrane domain VI in the binding of muscarinic agonists and activation of M1 receptors [Huang, X.P., Williams, F.E., Peseckis, S.M., Messer, W.S., Jr., 1998. J. Pharmacol. Exp. Ther. 286, 1129–1139.]. Thus, residues such as Ser388 represent molecular targets for the further development of agonists with improved M1 receptor affinity, selectivity and activity.

New (sulfonyloxy)piperazinyldibenzazepines as potential atypical antipsychotics: chemistry and pharmacological evaluation.

A series of 2- or 8-trifluoromethylsulfonyloxy (TfO) and 2- or 8-methylsulfonyloxy (MsO) 11-piperazinyldibenzodiazepines, -oxazepines, and -thiazepines were synthesized and evaluated in pharmacological models for their potential clozapine-like properties. In receptor binding assays, the 2-TfO analogues (18a, GMC2-83; 24, GMC3-06; and previously reported GMC1-169, 9a) of the dibenzazepines have profiles comparable to that of clozapine, acting on a variety of CNS receptors except they lack M1 receptor affinity. Introduction of 2-TfO to clozapine leads to compound 9e (GMC61-39) which has a similar binding profile as that of clozapine including having M1 receptor affinity. Interestingly, the MsO analogues, as well as the 8-TfO analogues, have no or weak dopaminergic and serotonergic affinities, but all 8-sulfonyloxy analogues do have M1 affinities. In behavioral studies performed to indicate the potential antipsychotic efficacy and the propensity to induce EPS, 2-TfO analogues blocked effectively the apomorphine-induced climbing in mice in a dose-dependent manner with ED50 values (mg/kg) of 2.1 sc for 9a, 1.3 po for 18a, 2.6 sc for 24, and 8.2 sc for 9e. On the other hand, they showed a clear dose separation with regard to their ED50 values (mg/kg) for indicating catalepsy in rats (>44 sc for 9a, 28 po for 18a, 30 sc for 24, and >50 sc for 9e, respectively), thus implicating a more favorable therapeutic ratio (K/A, ED50 climbing/ED50 catalepsy) in comparison with typical neuroleptics such as haloperidol and isoclozapine. Furthermore, compound 18a was also demonstrated to be an orally potent DA antagonist with an ED50 value of 0.7 mg/kg po in the ex vivo L-DOPA accumulation model. The present study contributes to the SAR of 11-piperazinyldibenzazepines, and the 2-TfO analogues of 11-piperazinyldibenzazepines are promising candidates as clozapine-like atypical antipsychotics with low propensity to induce EPS.

6beta-Acetoxynortropane: a potent muscarinic agonist with apparent selectivity toward M2-receptors.

A series of tropane derivatives, related in structure to baogongteng A (1), an alkaloid from a Chinese herb, were synthesized. 6beta-Acetoxynortropane (5) had weak affinity (Ki 22 microM) for central (M1) muscarinic receptors in a [3H]quinuclidinyl benzilate binding assay but had extremely high affinity (Ki 2.6 nM) and selectivity for M2-muscarinic receptors expressed in CHO cells. It had 13-fold lower affinity for M4-receptors, 260-fold lower affinity for M3-receptors, and 8200-fold lower affinity for M1-receptors expressed in CHO cells. The 6beta-carbomethoxy analogue (14) of baogongteng A had only weak affinity for M2-muscarinic receptors, as did 6beta-carbomethoxynortropane (13) and 6beta-acetoxytropane (4). In transfected CHO cells, 6beta-acetoxynortropane (5) was an agonist at M2-receptors, based on a GTP-elicited decrease in affinity, and a full agonist with an IC50 of 11 nM at M4-receptors, based on inhibition of cyclic AMP accumulation, while being a full agonist at M1-receptors with an EC50 of 23 nM and a partial agonist at M3-receptors with an EC50 of 3.6 nM, based in both cases on stimulation of phosphoinositide breakdown. All of the 16 tropane derivatives had weak affinities for central alpha4beta2-nicotinic receptors with 6beta-carbomethoxynortropane (13) having the highest affinity, which was still 150-fold less than that of nicotine. 6beta-Acetoxynortropane (5) represents a potent muscarinic agonist with apparent selectivity toward M2-receptors.

Synthesis and muscarinic activity of a series of quinolines and naphthalenes with a 1-azabicyclo[3.3.0]octane moiety.

In order to discover a medicine effective against Alzheimer's disease, we synthesized a series of quinoline derivatives having a characteristic 1-azabicyclo[3.3.0]octane amine ring, and performed pharmacological evaluation of them. Acetylcholine esterase inhibitory activities of these derivatives were unexpectedly weak. Tests for central nervous muscarinic cholinergic receptor binding affinity indicated that these compounds had higher affinities to muscarinic M1 receptors than to M2 receptors. A series of naphthalene derivatives substituted with the 1-azabicyclo[3.3.0]octane ring were also synthesized and muscarinic M1 and M2 receptor binding affinity determined. These compounds had much higher affinity for M1 receptors than the quinoline derivatives, and 1-[N-(1-azabicyclo[3.3.0]octan-5-yl)methyl-N-methylamino]-4-nitronaph tha lene showed the highest affinity and selectivity. The ability of this compound to improve cognitive function was assessed using the passive avoidance test in scopolamine-induced mice.

WAY-131256 is an orally active, efficacious, and in vivo functionally selective M1 agonist

Computer modeling of carbachol docked in the human m1 receptor binding pocket has been used to discover a series of carbamate and thiocarbamate chiral, conformationally restricted analogues of carbachol based on azabicyclo[2.2.1]heptan-3-ol. These molecules have been evaluated for affinity and efficacy at human muscarinic receptors (m1–m5) transfected into a CHO cell line. None of these compounds was selective in binding. Thiocarbamate analogues had greater affinity for the m1 receptor subtype, but lower efficacy based on comparison of their ability to induce phosphoinositide (PI) turnover. Carbamate analogues had lower affinity for m1 receptors than thiocarbamates and varied in efficacy from 10% to 100% of the carbachol response in phosphoinositide (PI) turnover. One of these analogues 3S,4R-azabicyclo[2.2.1]heptan-3-methylcarbamate, WAY-131256, (VI) has been characterized as an m1/m2 agonist in vitro. (VI) was equi-efficacious to the standard m1 agonist, xanomeline (Phase III) in vivo in a scopolamine-impaired radial arm maze paradigm (MED 1 mg/kg, 5.88 mmol/kg for VI and MED 1 mg/kg, 3.55 mmoles/kg for xanomeline) and was approximately equal to xanomeline in an AF64A-impaired radial arm maze paradigm. Despite its lack of m1 selectivity in vitro, in vivo experiments on (VI) indicated no significant effect on blood pressure or heart rate at 10 mg/kg (58.78 mmol/kg) (i.p.), and no peripheral side effects attributed to stimulation of either the m2 or m3 receptors (salivation, lacrimation, and chromodacryorrhea) up to doses of 30 mg/kg, 176.2 mmol/kg. These results may be explained by different receptor densities in various brain regions not accounted for in a transfected cell line or by metabolism of (VI) to a m1 selective agonist in vivo. Drug Dev. Res. 40:185–192, 1997. © 1997 Wiley-Liss, Inc.

WAL 2014 FU (talsaclidine): A preferentially neuron activating muscarinic agonist for the treatment of Alzheimer's disease

The functional selectivity of WAL 2014 FU with regard to stimulation of the neuronal muscarinic M1 receptor subtype in vitro and in vivo is shown in different receptor preparations, isolated organ models, whole animal testing, and finally humans. From receptor binding experiments in membrane preparations from rat tissues and from Chinese hamster ovary cells expressing human muscarinic receptor subtypes, it can be delineated that the ratio between M1 and M2 (hm1 and hm2) is shifted in favour of the M1 receptor affinity, when compared to several classic muscarinic agonists such as carbachol, arecoline, and oxotremorine. The intermediate GTP-shift of 7.5 for WAL 2014 FU in a M2 muscarinic receptor preparation (rat heart) indicates only partial agonistic activity at this subtype, carbachol (e.g., shows a shift of 51). Moreover, the ratio from agonist to antagonist receptor binding comparing the affinities using [3H]cis-methyldioxolane and [3H]N-methylscopolamine as radioligands, suggests only a partial agonist behaviour at M2 receptors, too. In functional assays in vitro, such as phosphoinositide breakdown measured in cerebral cortex slices from guinea pig brain, WAL 2014 FU is as effective (27.8% compared to carbachol 100%) as arecoline (27.6%), but is more effective than RS 86 (22.1%), oxotremorine (21.6%) or McN-A-343 (14.7%). WAL 2014 FU is about as effective as RS 86 and McN-A-343 in stimulating the secretion of N-acetyl-glucosaminidase from RBL cells transfected with the human m1 receptor subtype. Investigating the proton efflux from CHO cells expressing hm1, hm2, and hm3 muscarinic receptor with cytosensor technology WAL 2014 FU was clearly more effective at human m1 receptors (66.3% compared to carbachol 100%) than at hm3 receptors (18.6%) and showed no measurable effect at hm2 receptor expressing cells. The efficacy in isolated organ preparations and in whole animals has already been reported [Ensinger et al., 1993] and shows the functional selectivity of WAL 2014 FU quite impressively. The general receptor profile of WAL 2014 FU demonstrates a nearly specific interaction with muscarinic receptors, having only weak binding affinity for a1- and nicotinic receptors. Results from pharmacokinetic studies in rats and humans indicate high oral bioavailability (>95% in rats) and very low interindividual variation in plasma levels. Furthermore, good penetration of the blood brain barrier with 2.5- to 3-fold higher concentrations of WAL 2014 FU in brain than in plasma could be measured. The advantageous and stable pharmacokinetic profile of WAL 2014 FU and its functional M1 selectivity establish WAL 2014 FU as a promising candidate for drug treatment of Alzheimer's disease. In addition to its role for symptomatic treatment, WAL 2014 FU may also have a disease-modifying potential because of its stimulatory effects on APPs secretion. Drug Dev. Res. 40:144–157, 1997. © 1997 Wiley-Liss, Inc.

Stereoselective interaction of uncharged esters at four muscarinic receptor subtypes

We investigated the binding and pharmacological properties of the esters of 3,3-dimethylbutan-1-ol (the carbon analogue of choline) with either diphenylglycolic acid, (R)-phenylcyclohexylglycolic acid, or (S)-phenylcyclohexylglycolic acid [BS-6181, (R)-BS-7826 and (S)-BS-7826, respectively] at muscarinic M1, M2, M3 (Hm3) and M4 receptors. The three uncharged compounds were muscarinic receptor antagonists, with pA2 or pKi values between 7.9 5.6. The achiral ester BS-6181 displayed highest affinity for M1, M3 (Hm3) and M4 receptors (pA2 or pKi = 7.2−7.6) and lower affinity for M2 receptors (pA2 or pKi = 6.7and6.8). The four muscarinic receptor subtypes were able to distinguish between the two enantiomers of the cyclohexyl derivative of BS-6181 [(R)- and (S)-BS-7826], with a preference for the (R)-isomer (up to 79-fold). Interestingly, the (S)-enantiomer of BS-7826, being the distomer, was found to be M4 selective (pKi/M4= 6.9; pA2 or pKi/M1-M3 (Hm3) = 5.6−6.2). These results indicate that uncharged compounds may (stereo)selectively bind to muscarinic receptors via hydrophobic interactions. Thus, an ionic bond between muscarinic ligands and an anionic site of the receptor is not absolutely necessary for recognition of muscarinic receptors.

Evidence for a selective CCK A and CCK B receptor mediated regulation of GABA and dopamine release in rat nucleus accumbens. A combined receptor binding and microdialysis study

Extrapyramidal syndromes (EPS) caused by antipsychotic therapy are currently treated with anticholinergics that lack selectivity for the five muscarinic receptor subtypes. Since these receptors are heterogeneously expressed among the different classes of striatal neurons and their afferents, it can be expected that their simultaneous blockade will cause distinct, sometimes opposed, effects within the striatal circuitry. In order to test the hypothesis that the differential blockade of the muscarinic receptor subtypes would influence their potency and efficacy to prevent EPS, here we tested four anticholinergics with varying order of affinities for the muscarinic receptor subtypes, and compared their dose–response curves to inhibit haloperidol-induced catalepsy in male rats. Drugs were applied into the lateral ventricle 15 min before haloperidol (2 mg/kg, s.c.). Catalepsy was measured in the bar test at 15 min intervals during 5 h. The preferential M1/M4 antagonist pirenzepine (3, 10, 30, 100, and 300 nmol) caused a dose-dependent inhibition of catalepsy intensity: ED50 = 5.6 nmol [95% CI, 3.9–8.1], and latency: ED50 = 5.6 nmol [95% CI, 3.7–8.6]. Pirenzepine had the steepest dose–response curve, producing maximal inhibition (84 ± 5%) at the dose of 10 nmol, while its effect tended to reverse at higher doses (62 ± 11%). The purported M1/M3 antagonist 4-DAMP (30, 100, and 300 nmol) also caused a dose-dependent inhibition of catalepsy intensity: ED50 = 29.5 nmol [95% CI, 7.0 to 123.0], and latency: ED50 = 28.5 nmol [95% CI, 2.2 to 362.0]. However, the curve for 4-DAMP had a less pronounced slope, reaching its maximal effect (63 ± 14%) at the dose of 300 nmol. The M2/M4 antagonist AF-DX 116 (10, 30, and 300 nmol) only caused a partial inhibition of catalepsy (30 ± 11%) at the dose of 30 nmol, but this changed to a non-significant increment (15 ± 10%) at the dose of 100 nmol. The alleged M4 antagonist tropicamide (30, 100, 300, and 600 nmol) produced a partial inhibition of catalepsy (36 ± 12%) at the dose of 300 nmol, but lacked effect at higher or lower doses. Concurrent treatment with pirenzepine (10 nmol) and tropicamide (300 nmol) produced an effect similar to that of tropicamide alone. The greater potency and efficacy of pirenzepine for catalepsy inhibition could be due to its higher affinity for M1 receptors and, to a lesser extent, for M4 receptors. It is suggested that selective M1 antagonists would be more effective than M2, M3 or M4 antagonists to prevent EPS caused by antipsychotic drugs.