SPINAL R-PHENYL-ISOPROPYL ADENOSINE INHIBITS SPINAL DORSAL HORN NEURONS RESPONDING TO NOXIOUS HEAT STIMULATION IN THE ABSENCE AND PRESENCE OF SENSITIZATION

The effects of spinally administered R(-)N-6-(2-phenylisopropyl) adeno sine (R-PIA) on spinal dorsal horn neurons were investigated in anesth etized rats. Extracellular, single-unit recordings were measured durin g noxious heating of receptive fields on the hind paw. Three series of experiments were carried out to characterize the effects of R-PIA on spinal dorsal horn neuronal activity. In the first set of experiments, R PIA dose-dependently suppressed noxiously evoked activity of spinal dorsal horn neurons. In the second set of experiments, R-PIA suppress ed noxiously evoked activity in neurons sensitized by the topical appl ication of mustard oil to a region of skin adjacent to their receptive fields. In the third set of experiments, R-PIA prevented mustard oil induced sensitization of dorsal horn neurons. In all cases, the adenos ine receptor antagonist theophylline reversed the action of R-PIA. The results of these investigations indicate the involvement of spinal ad enosine receptors in spinal pathways of central sensitization and in t he modulation of somatically induced noxious pain. (C) 1998 Internatio nal Association for the Study of Pain. Published by Elsevier Science B .V.