CNVs conferring risk of autism or schizophrenia affect cognition in controls.

In a small fraction of patients with schizophrenia or autism, alleles of copy-number variants (CNVs) in their genomes are probably the strongest factors contributing to the pathogenesis of the disease. These CNVs may provide an entry point for investigations into the mechanisms of brain function and dysfunction alike. They are not fully penetrant and offer an opportunity to study their effects separate from that of manifest disease. Here we show in an Icelandic sample that a few of the CNVs clearly alter fecundity (measured as the number of children by age 45). Furthermore, we use various tests of cognitive function to demonstrate that control subjects carrying the CNVs perform at a level that is between that of schizophrenia patients and population controls. The CNVs do not all affect the same cognitive domains, hence the cognitive deficits that drive or accompany the pathogenesis vary from one CNV to another. Controls carrying the chromosome 15q11.2 deletion between breakpoints 1 and 2 (15q11.2(BP1-BP2) deletion) have a history of dyslexia and dyscalculia, even after adjusting for IQ in the analysis, and the CNV only confers modest effects on other cognitive traits. The 15q11.2(BP1-BP2) deletion affects brain structure in a pattern consistent with both that observed during first-episode psychosis in schizophrenia and that of structural correlates in dyslexia.

Persistent gating deficit and increased sensitivity to NMDA receptor antagonism after puberty in a new mouse model of the human 22q11.2 microdeletion syndrome: a study in male mice.

BACKGROUND: The hemizygous 22q11.2 microdeletion is a common copy number variant in humans. The deletion confers high risk for neurodevelopmental disorders, including autism and schizophrenia. Up to 41% of deletion carriers experience psychotic symptoms. METHODS: We present a new mouse model (Df(h22q11)/+) of the deletion syndrome (22q11.2DS) and report on, to our knowledge, the most comprehensive study undertaken to date in 22q11.2DS models. The study was conducted in male mice. RESULTS: We found elevated postpubertal N-methyl-D-aspartate (NMDA) receptor antagonist-induced hyperlocomotion, age-independent prepulse inhibition (PPI) deficits and increased acoustic startle response (ASR). The PPI deficit and increased ASR were resistant to antipsychotic treatment. The PPI deficit was not a consequence of impaired hearing measured by auditory brain stem responses. The Df(h22q11)/+ mice also displayed increased amplitude of loudness-dependent auditory evoked potentials. Prefrontal cortex and dorsal striatal elevations of the dopamine metabolite DOPAC and increased dorsal striatal expression of the AMPA receptor subunit GluR1 was found. The Df(h22q11)/+ mice did not deviate from wild-type mice in a wide range of other behavioural and biochemical assays. LIMITATIONS: The 22q11.2 microdeletion has incomplete penetrance in humans, and the severity of disease depends on the complete genetic makeup in concert with environmental factors. In order to obtain more marked phenotypes reflecting the severe conditions related to 22q11.2DS it is suggested to expose the Df(h22q11)/+ mice to environmental stressors that may unmask latent psychopathology. CONCLUSION: The Df(h22q11)/+ model will be a valuable tool for increasing our understanding of the etiology of schizophrenia and other psychiatric disorders associated with the 22q11DS.

Assessing the Cognitive Translational Potential of a Mouse Model of the 22q11.2 Microdeletion Syndrome.

A chromosomal microdeletion at the 22q11.2 locus is associated with extensive cognitive impairments, schizophrenia and other psychopathology in humans. Previous reports indicate that mouse models of the 22q11.2 microdeletion syndrome (22q11.2DS) may model the genetic basis of cognitive deficits relevant for neuropsychiatric disorders such as schizophrenia. To assess the models usefulness for drug discovery, a novel mouse (Df(h22q11)/+) was assessed in an extensive battery of cognitive assays by partners within the NEWMEDS collaboration (Innovative Medicines Initiative Grant Agreement No. 115008). This battery included classic and touchscreen-based paradigms with recognized sensitivity and multiple attempts at reproducing previously published findings in 22q11.2DS mouse models. This work represents one of the most comprehensive reports of cognitive functioning in a transgenic animal model. In accordance with previous reports, there were non-significant trends or marginal impairment in some tasks. However, the Df(h22q11)/+ mouse did not show comprehensive deficits; no robust impairment was observed following more than 17 experiments and 14 behavioral paradigms. Thus - within the current protocols - the 22q11.2DS mouse model fails to mimic the cognitive alterations observed in human 22q11.2 deletion carriers. We suggest that the 22q11.2DS model may induce liability for cognitive dysfunction with additional "hits" being required for phenotypic expression.

Associating in vitro target binding and in vivo CNS occupancy of serotonin reuptake inhibitors in rats: the role of free drug concentrations.

The present study aimed at investigating the theory that free (unbound) active site concentrations are the best predictors of target binding of compounds blocking the serotonin transporter (Sert) in the central nervous system (CNS). Thirteen serotonin reuptake inhibitors were evaluated for their Sert-binding affinities in vitro and in vivo in rats together with their unbound fractions in plasma and brain. Cortical Sert occupancy was used in vivo to acquire EC50-estimates from total plasma, free plasma, whole brain, and free brain concentrations after acute drug administration. The in vitro-in vivo Sert occupancy analyses showed that the best correlation was achieved when unbound brain concentrations were employed. Unbound brain concentrations also provided a better correlation when compared with unbound plasma concentrations, which could be related to lack of equilibrium between plasma and brain at time of measurements or involvement of active brain efflux processes. In addition, brain-free fractions were shown to be directly correlated to the lipophilicity of the compounds. These data emphasize the use and impact of applying free fraction data in assessment of pharmacological in vitro-in vivo correlations and demonstrates its use to validate in vivo Sert occupancy as pharmacodynamic marker for serotonin reuptake inhibitors in rats.

Separable neural mechanisms for the pleiotropic association of copy number variants with neuropsychiatric traits.

22q11.2, 15q13.3, and 1q21.1 microdeletions attract considerable interest by conferring high risk for a range of neuropsychiatric disorders, including schizophrenia and autism. A fundamental open question is whether divergent or convergent neural mechanisms mediate this genetic pleiotropic association with the same behavioral phenotypes. We use a combination of rodent microdeletion models with high-field neuroimaging to perform a comparative whole-brain characterization of functional and structural mechanisms linked to high-risk states. Resting-state functional and structural magnetic resonance imaging data were acquired on mice carrying heterozygous microdeletions in 22q11.2 (N = 12), 15q13.3 (N = 11), and 1q21.1 (N = 11) loci. We performed network-based statistic, graph, and morphometric analyses. The three microdeletions did not share significant systems-level features. Instead, morphometric analyses revealed microcephaly in 1q21.1 and macrocephaly in 15q13.3 deletions, whereas cerebellar volume was specifically reduced in 22q11.2 deletion. In function, 22q11.2 deletion mice showed widespread cortical hypoconnectivity, accompanied by opposing hyperconnectivity in dopaminergic pathways, which was confirmed by graph analysis. 1q21.1 exhibited distinct changes in posterior midbrain morphology and function, especially in periaqueductal gray, whereas 15q13.3 demonstrated alterations in auditory/striatal system. The combination of cortical hypoconnectivity and dopaminergic hyperconnectivity and reduced cerebellum in 22q11.2 deletion mirrors key neurodevelopmental features of schizophrenia, whereas changes in midbrain and auditory/striatal morphology and topology in 1q21.1 and 15q13.3 rather indicate focal processes possibly linked to the emergence of abnormal salience perception and hallucinations. In addition to insights into pathophysiological processes in these microdeletions, our results establish the general point that microdeletions might increase risk for overlapping neuropsychiatric phenotypes through separable neural mechanisms.

The multimodal antidepressant vortioxetine may facilitate pyramidal cell firing by inhibition of 5-HT3 receptor expressing interneurons: An in vitro study in rat hippocampus slices.

The multimodal antidepressant vortioxetine is thought to mediate its pharmacological effects via 5-HT1A receptor agonism, 5-HT1B receptor partial agonism, 5-HT1D, 5-HT3, 5-HT7 receptor antagonism and 5-HT transporter inhibition. Here we studied vortioxetine's functional effects across species (canine, mouse, rat, guinea pig and human) in cellular assays with heterologous expression of 5-HT3A receptors (in Xenopus oocytes and HEK-293 cells) and in mouse neuroblastoma N1E-115 cells with endogenous expression of 5-HT3A receptors. Furthermore, we studied the effects of vortioxetine on activity of CA1 Stratum Radiatum interneurons in rat hippocampus slices using current- and voltage-clamping methods. The patched neurons were subsequently filled with biocytin for confirmation of 5-HT3 receptor mRNA expression by in situ hybridization. Whereas, both vortioxetine and the 5-HT3 receptor antagonist ondansetron potently antagonized 5-HT-induced currents in the cellular assays, vortioxetine had a slower off-rate than ondansetron in oocytes expressing 5-HT3A receptors. Furthermore, vortioxetine's but not ondansetron's 5-HT3 receptor antagonistic potency varied considerably across species. Vortioxetine had the highest potency at rat and the lowest potency at guinea pig 5-HT3A receptors. Finally, in 5-HT3 receptor-expressing GABAergic interneurons from the CA1 stratum radiatum, vortioxetine and ondansetron blocked depolarizations induced by superfusion of either 5-HT or the 5-HT3 receptor agonist mCPBG. Taken together, these data add to a growing literature supporting the idea that vortioxetine may inhibit GABAergic neurotransmission in some brain regions via a 5-HT3 receptor antagonism-dependent mechanism and thereby disinhibit pyramidal neurons and enhance glutamatergic signaling.

4-aryl-5-(4-piperidyl)-3-isoxazolol GABAA antagonists: synthesis, pharmacology, and structure-activity relationships.

A series of 4-aryl-5-(4-piperidyl)-3-isoxazolol GABAA antagonists have been synthesized and pharmacologically characterized. The meta-phenyl-substituted compounds 9k and 9m and the para-phenoxy-substituted compound 9l all display high affinities (Ki=10-70 nM) and antagonist potencies in the low nanomolar range (Ki=9-10 nM). These potencies are significantly higher than those of previously reported 4-PIOL antagonists and considerably higher than that of the standard GABAA antagonist SR 95531.

New 4-Functionalized Glutamate Analogues Are Selective Agonists at Metabotropic Glutamate Receptor Subtype 2 or Selective Agonists at Metabotropic Glutamate Receptor Group III.

The metabotropic glutamate (Glu) receptors (mGluRs) play key roles in modulating excitatory neurotransmission in the brain. In all, eight subtypes have been identified and divided into three groups, group I (mGlu1,5), group II (mGlu2,3), and group III (mGlu4,6-8). In this article, we present a L-2,4-syn-substituted Glu analogue, 1d, which displays selective agonist activity at mGlu2 over the remaining mGluR subtypes. A modeling study and redesign of the core scaffold led to the stereoselective synthesis of four new conformationally restricted Glu analogues, 2a-d. Most interestingly, 2a retained a selective agonist activity profile at mGlu2 (EC50 in the micromolar range), whereas 2c/2d were both selective agonists at group III, subtypes mGlu4,6,8. In general, 2d was 20-fold more potent than 2c and potently activated mGlu4,6,8 in the low-mid nanomolar range.

A mouse model of the 15q13.3 microdeletion syndrome shows prefrontal neurophysiological dysfunctions and attentional impairment.

RATIONALE: A microdeletion at locus 15q13.3 is associated with high incidence rates of psychopathology, including schizophrenia. A mouse model of the 15q13.3 microdeletion syndrome has been generated (Df[h15q13]/+) with translational utility for modelling schizophrenia-like pathology. Among other deficits, schizophrenia is characterised by dysfunctions in prefrontal cortical (PFC) inhibitory circuitry and attention. OBJECTIVES: The objective of this study is to assess PFC-dependent functioning in the Df(h15q13)/+ mouse using electrophysiological, pharmacological, and behavioural assays. METHOD: Experiments 1-2 investigated baseline firing and auditory-evoked responses of PFC interneurons and pyramidal neurons. Experiment 3 measured pyramidal firing in response to intra-PFC GABAA receptor antagonism. Experiments 4-6 assessed PFC-dependent attentional functioning through the touchscreen 5-choice serial reaction time task (5-CSRTT). Experiments 7-12 assessed reversal learning, paired-associate learning, extinction learning, progressive ratio, trial-unique non-match to sample, and object recognition. RESULTS: In experiments 1-3, the Df(h15q13)/+ mouse showed reduced baseline firing rate of fast-spiking interneurons and in the ability of the GABAA receptor antagonist gabazine to increase the firing rate of pyramidal neurons. In assays of auditory-evoked responses, PFC interneurons in the Df(h15q13)/+ mouse had reduced detection amplitudes and increased detection latencies, while pyramidal neurons showed increased detection latencies. In experiments 4-6, the Df(h15q13)/+ mouse showed a stimulus duration-dependent decrease in percent accuracy in the 5-CSRTT. The impairment was insensitive to treatment with the partial α7nAChR agonist EVP-6124. The Df(h15q13)/+ mouse showed no cognitive impairments in experiments 7-12. CONCLUSION: The Df(h15q13)/+ mouse has multiple dysfunctions converging on disrupted PFC processing as measured by several independent assays of inhibitory transmission and attentional function.

Potent 4-aryl- or 4-arylalkyl-substituted 3-isoxazolol GABA(A) antagonists: synthesis, pharmacology, and molecular modeling.

We have previously described a series of competitive GABA(A) antagonists derived from the low-efficacy partial agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 4). The 2-naphthylmethyl analogue, 4-(2-naphthylmethyl)-5-(4-piperidyl)-3-isoxazolol (5), provided affinity for the GABA(A) receptor site higher than that of the standard GABA(A) receptor antagonist, SR 95531 (3). Molecular modeling studies of these compounds exposed a cavity at the receptor recognition site capable of accommodating aromatic groups of substantial size in the 4-position in the 3-isoxazolol ring. Here we present a series of analogues of 5, with various substituents in different positions in the naphthyl ring system (6a-k), and compounds with aromatic substituents directly attached to the 4-position of the 3-isoxazolol ring (7l-n). The compounds have been pharmacologically characterized using receptor-binding assays and electrophysiological whole-cell patch-clamp techniques. All of the tested compounds show affinity for the GABA(A) receptor site. While the 5-, 7-, and 8-bromo analogues, 6b-d, showed receptor affinities (K(i) = 45, 109, and 80 nM, respectively) comparable with that of 5 (K(i) = 49 nM), the 1-bromo analogue, 6a, provided the highest receptor affinity of the series (K(i) = 10 nM). Introduction of a series of different substituents in the 1-position in the 2-naphthyl ring system led to compounds, 6e-k, with retained high affinity for the GABA(A) receptor (K(i) = 16-250 nM). Introduction of a phenyl ring directly into the 4-position on the 3-isoxazolol ring gave a 41-fold increase in affinity relative to that of 4-PIOL. In whole-cell patch-clamp recordings from cultured cerebral cortical neurons, all of the tested compounds were able to inhibit the effect of the specific GABA(A) agonist isoguvacine, 6a showing antagonist potency (IC(50) = 42 nM) markedly higher than that of 3 (IC(50) = 240 nM). Molecular modeling studies, based on the compounds described, emphasized the importance of the distal ring in 5 for receptor affinity and the considerable dimensions of the proposed receptor cavity. Furthermore, the phenyl rings in 7l and in 6k were shown to represent highly favorable positions for an aromatic ring in previously unexplored receptor regions in terms of a pharmacophore model.

Selective antagonists at group I metabotropic glutamate receptors: synthesis and molecular pharmacology of 4-aryl-3-isoxazolol amino acids.

Homologation of (S)-glutamic acid (Glu, 1) and Glu analogues has previously provided ligands with activity at metabotropic Glu receptors (mGluRs). The homologue of ibotenic acid (7), 2-amino-3-(3-hydroxy-5-isoxazolyl)propionic acid (HIBO, 8), and the 4-phenyl derivative of 8, compound 9a, are both antagonists at group I mGluRs. Here we report the synthesis and molecular pharmacology of HIBO analogues 9b-h containing different 4-aryl substituents. All of these compounds possess antagonist activity at group I mGluRs but are inactive at group II and III mGluRs.

Three-dimensional structure of the ligand-binding core of GluR2 in complex with the agonist (S)-ATPA: implications for receptor subunit selectivity.

Two X-ray structures of the GluR2 ligand-binding core in complex with (S)-2-amino-3-(5-tert-butyl-3-hydroxy-4-isoxazolyl)propionic acid ((S)-ATPA) have been determined with and without Zn(2+) ions. (S)-ATPA induces a domain closure of ca. 21 degrees compared to the apo form. The tert-butyl moiety of (S)-ATPA is buried in a partially hydrophobic pocket and forces the ligand into the glutamate-like binding mode. The structures provide new insight into the molecular basis of agonist selectivity between AMPA and kainate receptors.

Novel class of potent 4-arylalkyl substituted 3-isoxazolol GABA(A) antagonists: synthesis, pharmacology, and molecular modeling.

A number of analogues of the low-efficacy partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL, 5), in which the 4-position of the 3-isoxazolol ring was substituted by different groups, were synthesized and tested as GABA(A) receptor ligands. Substituents of different size and structural flexibility such as alkyl, phenylalkyl, diphenylalkyl, and naphthylalkyl were explored. Pharmacological characterization of the synthesized compounds was carried out using receptor binding assays and by electrophysiological experiments using whole-cell patch-clamp techniques. Whereas none of these compounds significantly affected GABA(B) receptor sites or GABA uptake, they did show affinity for the GABA(A) receptor site. While alkyl or benzyl substitution, compounds 7a-h, provided receptor affinities comparable with that of 5 (K(i) = 9.1 microM), diphenylalkyl and naphthylalkyl substitution, as in compounds 7m-t, resulted in a dramatic increase in affinity relative to 5. The 3,3-diphenylpropyl and the 2-naphthylmethyl analogues, compounds 7s and 7m, respectively, showed the highest affinities of the series (K(i) = 0.074 microM and K(i) = 0.049 microM). In whole-cell patch-clamp recordings from cultured cerebral cortical neurons, all of the tested compounds were able to inhibit the effect of the specific GABA(A) agonist isoguvacine (1), compounds 7m and 7s showing antagonist potency (IC(50) = 0.37 microM and IC(50) = 0.02 microM) comparable with or markedly higher than that of the standard GABA(A) antagonist 4 (IC(50) = 0.24 microM). Highly potent convulsant activity was demonstrated in mice with compounds 7m (ED(50) = 0.024 micromol/kg) and 7s (ED(50) = 0.21 micromol/kg) after intracerebroventricular administration, whereas no effects were found after subcutaneous administration. According to a previously proposed pharmacophore model for GABA(A) receptor agonists, a receptor cavity in the vicinity of the 4-position of the 3-isoxazolol ring in 4-PIOL exists. A molecular modeling study, based on compounds 7o,m,l,q,s, was performed to explore the dimensions and other properties of the receptor cavity. This study demonstrates the importance of the arylalkyl substituents in 7m and 7s and the considerable dimensions of this proposed receptor cavity.

Selective agonists at group II metabotropic glutamate receptors: synthesis, stereochemistry, and molecular pharmacology of (S)- and (R)-2-amino-4-(4-hydroxy[1,2,5]thiadiazol-3-yl)butyric acid.

Homologation of analogues of the central excitatory neurotransmitter glutamic acid (Glu), in which the distal carboxy group has been bioisosterically replaced by acidic heterocyclic units, has previously provided subtype selective ligands for metabotropic Glu receptors (mGluRs). The (S)-form of the 1,2,5-thiadiazol-3-ol Glu analogue, 2-amino-3-(4-hydroxy[1,2,5]thiadiazol-3-yl)propionic acid (TDPA, 6), is an 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor agonist, which in addition stereospecifically activates group I mGluRs. We have now synthesized the (S)- and (R)-forms of 2-amino-4-(4-hydroxy[1,2,5]thiadiazol-3-yl)butyric acid (homo-TDPA, 7) and shown that whereas neither enantiomer interacts with AMPA receptors, (S)- and (R)-7 appear to be selective and equipotent agonists at group II mGluRs as represented by the mGluR2 subtype. The activities of (S)- and (R)-7 are rationalized by conformational analysis, comparison with the potent and specific group II mGluR agonist (-)-LY379268 [(-)-12], and docking to a homology model of mGluR2.

Synthesis and anticonvulsant activity of novel bicyclic acidic amino acids.

Bicyclic acidic amino acids (+/-)-6 and (+/-)-7, which are conformationally constrained homologues of glutamic acid, were prepared via a strategy based on a 1,3-dipolar cycloaddition. The new amino acids were tested toward ionotropic and metabotropic glutamate receptor subtypes; both of them behaved as antagonists at mGluR1,5 and as agonists at mGluR2. Furthermore, whereas (+/-)-6 was inactive at all ionotropic glutamate receptors, (+/-)-7 displayed a quite potent antagonism at the NMDA receptors. In the in vivo tests on DBA/2 mice, the compounds displayed an anticonvulsant activity. The interesting pharmacological profile of (+/-)-7 qualifies it as a lead of novel neuroprotective agents.

(S)-2-Amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid, a potent and selective agonist at the GluR5 subtype of ionotropic glutamate receptors. Synthesis, modeling, and molecular pharmacology.

We have previously described (RS)-2-amino-3-(3-hydroxy-7,8-dihydro-6H-cyclohepta[d]isoxazol-4-yl)propionic acid (4-AHCP) as a highly effective agonist at non-N-methyl-d-aspartate (non-NMDA) glutamate (Glu) receptors in vivo, which is more potent than (RS)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) but inactive at NMDA receptors. However, 4-AHCP was found to be much weaker than AMPA as an inhibitor of [(3)H]AMPA binding and to have limited effect in a [(3)H]kainic acid binding assay using rat cortical membranes. To shed light on the mechanism(s) underlying this quite enigmatic pharmacological profile of 4-AHCP, we have now developed a synthesis of (S)-4-AHCP (6) and (R)-4-AHCP (7). At cloned metabotropic Glu receptors mGluR1alpha (group I), mGluR2 (group II), and mGluR4a (group III), neither 6 nor 7 showed significant agonist or antagonist effects. The stereoisomer 6, but not 7, activated cloned AMPA receptor subunits GluR1o, GluR3o, and GluR4o with EC(50) values in the range 4.5-15 microM and the coexpressed kainate-preferring subunits GluR6 + KA2 (EC(50) = 6.4 microM). Compound 6, but not 7, proved to be a very potent agonist (EC(50) = 0.13 microM) at the kainate-preferring GluR5 subunit, equipotent with (S)-2-amino-3-(5-tert-butyl-3-hydroxyisothiazol-4-yl)propionic acid [(S)-Thio-ATPA, 4] and almost 4 times more potent than (S)-2-amino-3-(5-tert-butyl-3-hydroxyisoxazol-4-yl)propionic acid [(S)-ATPA, 3]. Compound 6 thus represents a new structural class of GluR5 agonists. Molecular modeling and docking to a crystal structure of the extracellular binding domain of the AMPA subunit GluR2 has enabled identification of the probable active conformation and binding mode of 6. We are able to rationalize the observed selectivities by comparing the docking of 4 and 6 to subtype constructs, i.e., a crystal structure of the extracellular binding domain of GluR2 and a homology model of GluR5.

Design, synthesis, and pharmacological characterization of novel, potent NMDA receptor antagonists.

The two diastereomeric pairs of acidic amino acids 5-(2-amino-2-carboxyethyl)-4,5-dihydroisoxazole-3-carboxylic acid (8A/8B) and 4-(2-amino-2-carboxyethyl)-5,5-dimethyl-4,5-dihydroisoxazole-3-carboxylic acid (10A/10B) were prepared via a strategy based on a 1,3-dipolar cycloaddition. The four amino acids were tested at ionotropic and metabotropic glutamate receptors. None of the compounds was active, neither as agonists nor as antagonists, at 1 mM on metabotropic receptors (mGluR1, -2, -4, and -5 expressed in CHO cell lines). Conversely, the pair of stereoisomers 8A/8B showed a remarkable affinity, antagonist potency, and selectivity for NMDA receptors, when tested on ionotropic glutamate receptors. The affinity of 8A proved to be 5 times higher than that of diastereomer 8B (K(i) values 0.21 and 0.96 microM, respectively). Furthermore, compounds 8A and 8B exhibited a noteworthy anticonvulsant activity in in vivo tests on DBA/2 mice. Derivative 10A was inactive at all ionotropic glutamate receptors, whereas its stereoisomer 10B displayed a seizable binding to both NMDA and AMPA receptors.

Novel 1-hydroxyazole bioisosteres of glutamic acid. Synthesis, protolytic properties, and pharmacology.

A number of 1-hydroxyazole derivatives were synthesized as bioisosteres of (S)-glutamic acid (Glu) and as analogues of the AMPA receptor agonist (R,S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA, 3b). All compounds were subjected to in vitro pharmacological studies, including a series of Glu receptor binding assays, uptake studies on native as well as cloned Glu uptake systems, and the electrophysiological rat cortical slice model. Compounds 7a,b, analogues of AMPA bearing a 1-hydroxy-5-pyrazolyl moiety as the distal carboxylic functionality, showed only moderate affinity for [3H]AMPA receptor binding sites (IC(50) = 2.7 +/- 0.4 microM and IC(50) = 2.6 +/- 0.6 microM, respectively), correlating with electrophysiological data from the rat cortical wedge model (EC(50) = 280 +/- 48 microM and EC(50) = 586 +/- 41 microM, respectively). 1-Hydroxy-1,2,3-triazol-5-yl analogues of AMPA, compounds 8a,b, showed high affinity for [3H]AMPA receptor binding sites (IC(50) = 0.15 +/- 0.03 microM and IC(50) = 0.13 +/- 0.02 microM, respectively). Electrophysiological data showed that compound 8a was devoid of activity in the rat cortical wedge model (EC(50) > 1000 microM), whereas the corresponding 4-methyl analogue 8b was a potent AMPA receptor agonist (EC(50) = 15 +/- 2 microM). In accordance with this disparity, compound 8a was found to inhibit synaptosomal [3H]D-aspartic acid uptake (IC(50) = 93 +/- 25 microM), as well as excitatory amino acid transporters (EAATs) EAAT1 (IC(50) = 100 +/- 30 microM) and EAAT2 (IC(50) = 300 +/- 80 microM). By contrast, compound 8b showed no appreciable affinity for Glu uptake sites, neither synaptosomal nor cloned. Compounds 9a-c and 10a,b, possessing 1-hydroxyimidazole as the terminal acidic function, were devoid of activity in all of the systems tested. Protolytic properties of compounds 7a,b, 8b, and 9b were determined by titration, and a correlation between the pK(a) values and the activity at AMPA receptors was apparent. Optimized structures of all the synthesized ligands were fitted to the known crystal structure of an AMPA-GluR2 construct. Where substantial reduction or abolition of affinity at AMPA receptors was observed, this could be rationalized on the basis of the ability of the ligand to fit the construct. The results presented in this article point to the utility of 1-hydroxypyrazole and 1,2,3-hydroxytriazole as bioisosteres of carboxylic acids at Glu receptors and transporters. None of the compounds showed significant activity at metabotropic Glu receptors.

Ibotenic acid and thioibotenic acid: a remarkable difference in activity at group III metabotropic glutamate receptors.

In this study, we have determined and compared the pharmacological profiles of ibotenic acid and its isothiazole analogue thioibotenic acid at native rat ionotropic glutamate (iGlu) receptors and at recombinant rat metabotropic glutamate (mGlu) receptors expressed in mammalian cell lines. Thioibotenic acid has a distinct pharmacological profile at group III mGlu receptors compared with the closely structurally related ibotenic acid; the former is a potent (low microm) agonist, whereas the latter is inactive. By comparing the conformational energy profiles of ibotenic and thioibotenic acid with the conformations preferred by the ligands upon docking to mGlu1 and models of the other mGlu subtypes, we propose that unlike other subtypes, group III mGlu receptor binding sites require a ligand conformation at an energy level which is prohibitively expensive for ibotenic acid, but not for thioibotenic acid. These studies demonstrate how subtle differences in chemical structures can result in profound differences in pharmacological activity.

Design and synthesis of a new series of 4-alkylated 3-isoxazolol GABA A antagonists.

A number of analogues of the low-efficacy partial GABA(A) agonist 5-(4-piperidyl)-3-isoxazolol (4-PIOL), in which the 4-position of the 3-isoxazolol ring is substituted by different groups, were synthesized and tested as GABA(A) receptor ligands. While alkyl and benzyl substitution provided affinities and antagonist potencies comparable to those of 4-PIOL, diphenylalkyl and naphthylalkyl substitution resulted in marked increase in both affinity and potency. The 2-naphthylmethyl and the 3,3-diphenylpropyl analogues showed antagonist potencies comparable or markedly higher than that of the standard antagonist SR 95531. Molecular modeling studies exposed a large cavity in the vicinity of the 4-position of 4-PIOL, in which there seems to be additional sites for specific receptor interactions.