Time course of effects of intrathecal treatment with PDBu, 0.1–10 nmol/10 ml, compared to vehicle and the inactive compound 4-α-PDBu. The withdrawal thresholds for 1, 3 and 10 nmol PDBu groups are significantly less than vehicle controls or 4-a-PDBu. Inset shows that GF109203X. 0.5 nmol/10 ml, significantly prevents the decreases in withdrawal thresholds that normally occurs after intrathecal delivery of 1–3 nmol PDBu. Data are represented as mean +/- S.E.M. *, significantly different from vehicle controls.