γ-aminobutyric acid type A (GABAA) receptors are located in spinal nociceptive circuits where they mediate 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.

MP‐III‐024 is a benzodiazepine (BZ) analog that, based on pharmacophore modeling, is predicted to exhibit agonist activity at the BZ site on the GABA‐A receptor. The present study assessed the behavioral effects of MP‐III‐024 on four endpoints in C57BL/6 mice. First, the antihyperalgesic effects of MP‐III‐024 were assessed in a model of inflammatory pain. Here, mechanical sensitivity was assessed following subcutaneous injection of the yeast extract zymosan A into the plantar surface of the footpad. MP‐III‐024 (1 – 32 mg/kg) produced dose‐ and time‐dependent reversal of mechanical sensitivity on this endpoint. Second, the anxiolytic‐like effects of MP‐III‐024 were assessed in a Vogel conflict procedure. In this procedure, MP‐III‐024 produced dose‐dependent increases in rates of suppressed responding up to a dose of 32 mg/kg, and decreases in responding below vehicle levels were observed at 100 mg/kg. Next, ambulatory behavior was assessed in locomotor activity chambers. In this procedure, MP‐III‐024 (1 – 32 mg/kg) failed to produce effects that were significantly different from vehicle. Finally, the response rate‐decreasing effects of MP‐III‐024 were examined in an assay of schedule controlled responding. Across the dose range tested, MP‐III‐024 (10‐100 mg/kg) failed to alter response rates in this procedure. Together, these observations will help provide a framework for studying GABA‐A receptor pharmacology which in turn should help guide the development of improved therapeutic agents for the treatment of pain‐ and anxiety‐related disorders.