Fig. 4. Effect of pretreatment on the effect of 9 μg intrathecal adenosine in animals after spinal nerve ligation. Animals were pretreated with saline and then received adenosine, or were pretreated with the A1-preferring adenosine antagonist, DCPX, the A2-preferring adenosine antagonist, 3,7-dimethyl-1-propargylxanthine, the α²-adrenergic antagonist, idazoxan, or the noradrenergic neurotoxin, DSP-4. Response is depicted as percent maximum possible effect (%MPE), defined as return of withdrawal threshold to presurgery levels. Values are mean ± SE of five to six animals. *  P < 0.05 compared with saline pretreatment.