A Pharmacogenetic ‘Restriction-of-Function’ Approach Reveals Evidence for Anxiolytic-Like Actions Mediated by α5-Containing GABAA Receptors in Mice

Abstract

Benzodiazepines have been widely used for their anxiolytic actions. However, the contribution of GABA A receptor subtypes to anxiolysis is still controversial. Studies with mutant mice harboring diazepam-insensitive α-subunits α1, α2, α3, or α5 have revealed that α2-containing GABA A receptors (α2-GABA A Rs) are required for diazepam-induced anxiolysis, with no evidence for an involvement of any other α-subunit, whereas TP003, described as a selective modulator of α3-containing GABA A receptors, was shown to be anxiolytic. Here, we describe a novel, systematic approach to evaluate the role of positive allosteric modulation of each of the four diazepam-sensitive α-subtypes in anxiety-related behavioral paradigms. By combining H to R point mutations in three out of the four diazepam-sensitive α-subunits in mice with a 129X1/SvJ background, diazepam becomes a subtype-specific modulator of the remaining non-mutated α-subtype. Modulation of α5-GABA A Rs, but not of α2-GABA A Rs, increased the time in the light side of the light-dark box as well as openarm exploration in the elevated plus maze. In contrast, modulation of α3-GABA A Rs decreased open-arm exploration, whereas modulation of α2-GABA A Rs increased time in the center in the open-field test. Modulation of any single α-subtype had no effect on stress-induced hyperthermia. Our results provide evidence that modulation of α5-GABA A Rs elicits anxiolytic-like actions, whereas our data do not provide evidence for an anxiolytic-like action of α3-GABA A Rs. Thus, α5-GABA A Rs may be suitable targets for novel anxiolytic drugs.

Somatostatin-Positive Gamma-Aminobutyric Acid Interneuron Deficits in Depression: Cortical Microcircuit and Therapeutic Perspectives

“…Based on restricted corticolimbic distribution of α5-GABA A Rs (138), and that these receptors partially mediate SST interneuron inhibition, SH-053-2′F-R-CH3, a compound with α5-selective positive allosteric modulation activity demonstrated antidepressant-like properties in female mice exposed to chronic stress (139). However, others found anxiolytic-, but not antidepressant-like effects of benzodiazepines, which act as GABA A R positive allosteric modulators, mediated specifically by α5-GABA A Rs in rodents (140). Although depressive- and anxiety-like behaviors are closely related in animal models (141), a thorough behavioral characterization of SST interneuron potentiation will provide further insight on how deficits in this system contribute to symptom emergence.…”

Novel Benzodiazepine-Like Ligands with Various Anxiolytic, Antidepressant, or Pro-Cognitive Profiles

“…However, the relations are not straightforward; for instance, high activity at α1-GABAA-Rs induces sedation and contributes to amnesia, but the same receptor subtype is also implicated in cognition by co-localizing with α5 and γ2 subunits [15]. The BZ anxiolytic properties are mediated predominantly by α2-GABAA-Rs [16] and also by α5-GABAA-Rs [17, 18]. Selective activity at α5-GABAA-Rs has also been suggested to play a critical role in alleviating “behavioral emotionality” (anxiety and depressive-like behaviors) in a mouse model of depression (using chronic stress in mice [19]) or cognitive dysfunctions in mouse models of schizophrenia [20] or in old rats [21].…”

“…Selective activity at α5-GABAA-Rs has also been suggested to play a critical role in alleviating “behavioral emotionality” (anxiety and depressive-like behaviors) in a mouse model of depression (using chronic stress in mice [19]) or cognitive dysfunctions in mouse models of schizophrenia [20] or in old rats [21]. The α5-GABAA-Rs have predominant distribution in the neocortex and hippocampus [22] suggesting a role in cognition and emotion [17, 23], while α1-GABAA-Rs have ubiquitous distribution and are very abundant [24], potentially explaining their effect on sedation [25] and their controversial role in cognition [15, 26]. …”

Ester to amide substitution improves selectivity, efficacy and kinetic behavior of a benzodiazepine positive modulator of GABAA receptors containing the α5 subunit

“…It is less clear how these results can be linked with the recent suggestions that generalization of fear and anxiety is mediated by α5-subunit containing neurons in the central nucleus of the amygdala, where reduced expression of α5-GABA A Rs was proved to be anxiogenic (Botta et al, 2015), or that the anxiolytic effect of diazepam is preserved in mice rendered sensitive to its modulatory action solely via α5-GABA A Rs (Behlke et al, 2016). The latter studies were performed in genetically modified mice, while the present study dealt with native rats, so that both, species and genetic diversity may have been the source of variability.…”

“…Development of positive allosteric modulators of α5GABA A Rs has been recognized more recently as a potentially fruitful approach in treatment of aging-related dementia (Koh et al, 2013) and cognitive impairment in schizophrenia (Gill et al, 2011) and autism (Mendez et al, 2013). Moreover, the results obtained in mice with the central nucleus of the amygdala–specific deletion of α5-GABA A Rs (Botta et al, 2015) as well as in mice bearing three point-mutated subunits (Behlke et al, 2016), suggest that positive allosteric modulation of α5-GABA A Rs could be expected to interfere with maladaptive fear generalization and/or induce anxiolytic activity, which is an additional impetus for development of the appropriate selective ligands.…”