Source:Brain Research Bulletin
Author(s): Bradford D. Fischer, Raymond J. Schlitt, Bryan Z. Hamade, Sabah Rehman, Margot Ernst, Michael M. Poe, Guanguan Li, Revathi Kodali, Leggy A. Arnold, James M. Cook
γ-Aminobutyric acid type A (GABAA) receptors are located in spinal nociceptive circuits where they modulate the transmission of pain sensory signals from the periphery to higher centers. Benzodiazepine-type drugs bind GABAA, receptors containing α1, α2, α3, and α5 subunits (α1GABAA, α2GABAA, α3GABAA, and α5GABAA receptors, respectively) through which they inhibit the transmission of these signals. However, the role of these different GABAA receptor subtypes in the antihyperalgisic properties of benzodiazepine-type drugs has not been characterized fully and is limited by currently available compounds. In the present study we describe the novel benzodiazepine site positive allosteric modulator modulator methyl 8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazo[1,5-a][1,4]diazepine-3-carboxylate (MP-III-024). MP-III-024 displayed preference for α2GABAA and α3GABAA receptors relative to α1GABAA and α5GABAA receptors as well as an improved metabolic profile relative to subtype-selective positive modulators that are available currently. MP-III-024 produced a dose- and time-dependent reversal of mechanical sensitivity. On locomotor activity and schedule-controlled responding, MP-III-024 was ineffective across the doses tested. These data provide further evidence that α2GABAA and α3GABAA receptors play an important role in the antihyperalgiesic effects and may not be involved in some of the off target effects of benzodiazepine-like drugs. Further, these findings suggest that MP-III-024 is an ideal research tool for investigating the role of α2GABAA and α3GABAA receptors in the behavioral properties of benzodiazepine-like drugs in mice.
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