A successful unified pharmacophore/receptor model which has guided the synthesis of subtype selective compounds is reviewed in light of recent developments both in ligand synthesis and structural studies of the binding site itself. The evaluation of experimental data in combination with a comparative model of the alpha1beta2gamma2 GABA(A) receptor leads to an orientation of the pharmacophore model within the Bz BS. Results not only are important for the rational design of selective ligands, but also for the identification and evaluation of possible roles which specific residues may have within the benzodiazepine binding pocket.

Classical benzodiazepines (BZs) exert anxiolytic, sedative, hypnotic, muscle relaxant, anticonvulsive, and amnesic effects through potentiation of neurotransmission at GABA A receptors containing a 1 , a 2 , a 3 or a 5 subunits. Genetic studies suggest that modulation at the a 1 subunit contributes to much of the adverse effects of BZs, most notably sedation, ataxia, and amnesia. Hence, BZ site ligands functionally inactive at GABA A receptors containing the a 1 subunit are considered to be promising leads for novel, anxioselective anxiolytics devoid of sedative properties. In pursuing this approach, we used two-electrode voltage clamp experiments in Xenopus oocytes expressing recombinant GABA A receptor subtypes to investigate functional selectivity of three newly synthesized BZ site ligands and also compared their in vivo behavioral profiles. The compounds were functionally selective for a 2 -, a 3 -, and a 5 -containing subtypes of GABA A receptors (SH-053-S-CH3 and SH-053-S-CH3-2 0 F) or essentially selective for a 5 subtypes (SH-053-R-CH3). Possible influences on behavioral measures were tested in the elevated plus maze, spontaneous locomotor activity, and rotarod test, which are considered primarily predictive of the anxiolytic, sedative, and ataxic influence of BZs, respectively. The results confirmed the substantially diminished ataxic potential of BZ site agonists devoid of a 1 subunit-mediated effects, with preserved anti-anxiety effects at 30 mg/kg of SH-053-S-CH3 and SH-053-S-CH3-2 0 F. However, all three ligands, dosed at 30 mg/kg, decreased spontaneous locomotor activity, suggesting that sedation may be partly dependent on activity mediated by a 5 -containing GABA A receptors. Hence, it could be of importance to avoid substantial agonist activity at a 5 receptors by candidate anxioselective anxiolytics, if clinical sedation is to be avoided.

Benzodiazepine (BZ) site ligands affect vigilance, anxiety, memory processes, muscle tone and epileptogenic propensity through modulation of neurotransmission at GABA A receptors containing α 1 , α 2 , α 3 or α 5 subunits, and may have numerous experimental and clinical applications. The ability of nonselective BZ site inverse agonists to enhance cognition, documented in animal models and human studies, is clinically not feasible due to potentially unacceptable psychomotor effects. Most investigations to date have proposed the α 1 and/or α 5 subunit-containing GABA A receptors as comprising the memory-modulating population of these receptors. The novel ligand PWZ-029, which we synthesised and characterized electrophysiologically, possesses in vitro binding selectivity and moderate inverse agonist functional selectivity at α 5 -containing GABA A receptors. This ligand has also been examined in rats in the passive and active avoidance, spontaneous locomotor activity, elevated plus maze and grip strength tests, primarily predictive of the effects on the memory acquisition, basal locomotor activity, anxiety level and muscle tone, respectively. The improvement of task learning was detected at the dose of 5 mg/kg in the passive, but not active avoidance test. The inverse agonist PWZ-029 had no effect on anxiety or muscle tone, whereas at higher doses (10 and 20 mg/kg) it decreased locomotor activity. This effect was antagonized by flumazenil and also by the lower (but not the higher) dose of an agonist (SH-053-R-CH3-2'F) selective for GABA A receptors containing the α 5 subunit. The hypolocomotor effect of PWZ-029 was not antagonized by the

Over the last years, genetic studies have greatly improved our knowledge on the receptor subtypes mediating various pharmacological effects of positive allosteric modulators at GABA A receptors. This stimulated the development of new benzodiazepine (BZ)-like ligands, especially those inactive/low-active at GABA A receptors containing the α 1 subunit, with the aim of generating more selective drugs. Hereby, the affinity and efficacy of four recently-synthesized BZ site ligands: SH-053-2'N, SH-053-S-CH3-2'F, SH-053-R-CH3-2'F and JY-XHe-053 were assessed. They were also studied in behavioral tests of spontaneous locomotor activity, elevated plus maze, and water maze in rats, which are considered predictive of, respectively, the sedative, anxiolytic, and amnesic influence of BZs. The novel ligands had moderately low to low affinity and mild to partial agonistic efficacy at GABA A receptors containing the α 1 subunit, with variable, but more pronounced efficacy at other BZ-sensitive binding sites. While presumably α 1 receptor-mediated sedative effects of GABA A modulation were not fully eliminated with any of the ligands tested, only SH-053-2'N and SH-053-S-CH3-2'F, both dosed at 30 mg/kg, exerted anxiolytic effects. The lack of clear anxiolytic-like activity of JY-XHe-053, despite its efficacy at α 2 -and α 3 -GABA A receptors, may have been partly connected with its preferential affinity at α 5 -GABA A receptors © 2010 Elsevier Inc. All rights reserved. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. coupled with weak agonist activity at α 1 -containing subtypes. The memory impairment in watermaze experiments, generally reported with BZ site agonists, was completely circumvented with all four ligands. The results suggest that a substantial amount of activity at α 1 GABA A receptors is needed for effecting spatial learning and memory impairments, while much weaker activity at α 1 -and α 5 -GABA A receptors is sufficient for eliciting sedation. NIH Public Access

The clinical use of benzodiazepines (BZs) is hampered by sedation and cognitive deterioration. Although genetic and pharmacological studies suggest that α1- and α5-containing GABAA receptors mediate and/or modulate these effects, their molecular substrate is not fully elucidated. By the use of two selective ligands : the α1-subunit affinity-selective antagonist β-CCt, and the α5-subunit affinity- and efficacy-selective antagonist XLi093, we examined the mechanisms of behavioural effects of diazepam in the tests of spontaneous locomotor activity and water-maze acquisition and recall, the two paradigms indicative of sedative- and cognition-impairing effects of BZs, respectively. The locomotor-activity decreasing propensity of diazepam (significant at 1.5 and 5 mg/kg) was antagonized by β-CCt (5 and 15 mg/kg), while it tended to be potentiated by XLi093 in doses of 10 mg/kg, and especially 20 mg/kg. Diazepam decreased acquisition and recall in the water maze, with a minimum effective dose of 1.5 mg/kg. Both antagonists reversed the thigmotaxis induced by 2 mg/kg diazepam throughout the test, suggesting that both GABAA receptor subtypes participate in BZ effects on the procedural component of the task. Diazepam-induced impairment in the declarative component of the task, as assessed by path efficiency, the latency and distance before finding the platform across acquisition trials, and also by the spatial parameters in the probe trial, was partially prevented by both, 15 mg/kg β-CCt and 10 mg/kg XLi093. Combining a BZ with β-CCt results in the near to control level of performance of a cognitive task, without sedation, and may be worth testing on human subjects.