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Background and PurposeThe GABAA receptors are ligand‐gated ion channels, which play an important role in neurotransmission. Their variety of binding sites serves as an appealing target for many clinically relevant drugs. Here, we explored the functional selectivity of modulatory effects at specific extracellular α+/β− interfaces, using a systematically varied series of pyrazoloquinolinones.Experimental ApproachRecombinant GABAA receptors were expressed in Xenopus laevis oocytes and modulatory effects on GABA‐elicited currents by the newly synthesized and reference compounds were investigated by the two‐electrode voltage clamp method.Key ResultsWe identified a new compound which, to the best of our knowledge, shows the highest functional selectivity for positive modulation at α6β3γ2 GABAA receptors with nearly no residual activity at the other αxβ3γ2 (x = 1–5) subtypes. This modulation was independent of affinity for α+/γ− interfaces. Furthermore, we demonstrated for the first time a compound that elicits a negative modulation at specific extracellular α+/β− interfaces.Conclusion and ImplicationsThese results constitute a major step towards a potential selective positive modulation of certain α6‐containing GABAA receptors, which might be useful to elicit their physiological role. Furthermore, these studies pave the way towards insights into molecular principles that drive positive versus negative allosteric modulation of specific GABAA receptor isoforms.

γ‐Aminobutyric acid type A (GABAA) receptors containing the α6 subunit are located in trigeminal ganglia, and their reduction by small interfering RNA increases inflammatory temporomandibular and myofascial pain in rats. We thus hypothesized that enhancing their activity may help in neuropathic syndromes originating from the trigeminal system. Here, we performed a detailed electrophysiological and pharmacokinetic analysis of two recently developed deuterated structurally similar pyrazoloquinolinone compounds. DK‐I‐56‐1 at concentrations below 1 µM enhanced γ‐aminobutyric acid (GABA) currents at recombinant rat α6β3γ2, α6β3δ and α6β3 receptors, whereas it was inactive at most GABAA receptor subtypes containing other α subunits. DK‐I‐87‐1 at concentrations below 1 µM was inactive at α6‐containing receptors and only weakly modulated other GABAA receptors investigated. Both plasma and brain tissue kinetics of DK‐I‐56‐1 were relatively slow, with half‐lives of 6 and 13 hr, respectively, enabling the persistence of estimated free brain concentrations in the range 10–300 nM throughout a 24‐hr period. Results obtained in two protocols of chronic constriction injury of the infraorbital nerve in rats dosed intraperitoneally with DK‐I‐56‐1 during 14 days after surgery or with DK‐I‐56‐1 or DK‐I‐87‐1 during 14 days after trigeminal neuropathy were already established, demonstrated that DK‐I‐56‐1 but not DK‐I‐87‐1 significantly reduced the hypersensitivity response to von Frey filaments. Significance Neuropathic pain induced by trigeminal nerve damage is poorly controlled by current treatments. DK‐I‐56‐1 that positively modulates α6 GABAA receptors is appropriate for repeated administration and thus may represent a novel treatment option against the development and maintenance of trigeminal neuropathic pain.

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