Inhibition of strychnine-allodynia is mediated by spinal adenosine A1- but not A2-receptors in the rat

Intrathecal (i.t.) strychnine produces localized allodynia in the rat without peripheral or central nerve injury. Intrathecal CPA (A(1)-selective agonist) and CGS-21680 (A(2)-selective agonist) dose-dependently inhibited strychnine-allodynia but with a 50-fold difference in potency (0.02-0.07 vs. 2.7-3.1 mu g, respectively). The anti-allodynic effect of CPA and CGS was completely blocked by pretreatment with the A(1)-selective antagonist, DPCPX (10 mu g i.t.), but unaffected by the A(2)-selective antagonist, CSC (2 mu g i.t.). The results indicate that spinal A(1)-, but not A(2)-, receptors modulate abnormal somatosensory input in the strychnine model, and suggest a difference in spinal purinergic modulation in injury vs. non-injury models of allodynia. (C) 1998 Published by Elsevier Science B.V. All rights reserved.