Abstract

The present study investigated 1) antihyperalgesic actions of a novel and selective adenosine kinase (AK) inhibitor, A-134974 (IC₅₀ = 60 pM), in the carrageenan model of thermal hyperalgesia; 2) effects of A-134974 on locomotor activity; and 3) relative contributions of supraspinal, spinal, and peripheral sites to the actions of A-134974. Systemic A-134974 (i.p.) dose dependently reduced hyperalgesia (ED₅₀ = 1 μmol/kg) and at higher doses, reduced locomotor activity (ED₅₀ = 16 μmol/kg). Administration of A-134974 intrathecally (i.t.) was more potent (ED₅₀ = 6 nmol) at producing antihyperalgesia than delivering the compound by intracerebralventricular (ED₅₀ = 100 nmol, i.c.v.) or intraplantar (ED₅₀ >300 nmol) routes. In contrast, i.c.v. administration of A-134974 was more effective in reducing locomotor activity than i.t. administration (ED₅₀ values were 1 and >100 nmol, respectively). Increasing the pretreatment time for i.t.-delivered A-134974 caused a greater reduction in locomotor activity (ED₅₀ = 10 nmol). This was due to diffusion of A-134974 (i.t.) to supraspinal sites. The antihyperalgesic effects of systemic A-134974 were antagonized by the adenosine receptor antagonist theophylline (THEO, 30–500 nmol) administered i.t., but not i.c.v. In the locomotor assay, i.t.-injected THEO did not antagonize hypomobility caused by systemic or i.t. administration of A-134974. However, i.c.v. infusion of THEO did block the hypomotive actions of i.c.v.-, i.t.-, and i.p.-administered A-134974. These data demonstrate that the novel AK inhibitor A-134974 potently reduces thermal hyperalgesia primarily through interactions with spinal sites, whereas its ability to depress locomotor activity is predominantly mediated by supraspinal sites.