In the arthritic rat, the ventrolateral and not the dorsolateral columns of the PAG mediate prostanergic effects on spinal nociception. A, B, Ketoprofen injected into the dlPAG had no notable effect on EMG-derived withdrawal thresholds to preferential A- and C-nociceptor activation in the hindpaw secondary site (n = 4 for both groups). C, D, Ketoprofen injected into the vlPAG increased withdrawal threshold to A- and C-nociceptor activation in the hindpaw secondary site (C: two-way ANOVA main effect of treatment p < 0.0001, F(1,89) = 26.23, effect of time p = 0.0051, F(8,89) = 2.99, interaction p = 0.0061, F(8,89) = 2.92 with Sidak's post hoc test **p < 0.01, *p < 0.05, n = 7 for vehicle and n = 6 for ketoprofen; D: two-way ANOVA main effect of treatment p < 0.0001, F(1,88) = 40.57, effect of time p = 0.048, F(7,88) = 2.13 with Sidak's post hoc test ***p < 0.001, *p < 0.05, n = 5 for ketoprofen, n = 7 for vehicle). E, Ketoprofen injected into the vlPAG had a significantly greater effect on EMG thresholds evoked by A-nociceptors than that of a vehicle injection. In addition, when delivered into the vlPAG, ketoprofen had a significantly greater effect on EMG thresholds evoked by A-nociceptors compared with delivery into the dlPAG (one-way ANOVA p = 0.0001, F(2,14) = 18.98 with Bonferroni's post hoc test ***p < 0.001, **p < 0.01; n = 4 for dlPAG, n = 6 for vlPAG ket, n = 7 for vlPAG vehicle). F, Ketoprofen injected into the vlPAG had a greater effect on EMG thresholds evoked by C-nociceptor activation than that of vehicle. In addition, when delivered into the vlPAG, ketoprofen had a greater effect on EMG thresholds evoked by C-nociceptor activation compared with delivery into the dlPAG (one-way ANOVA p = 0.0012, F(2,13) = 11.83 with Bonferroni's post hoc test **p < 0.01; n = 4 for dlPAG, n = 5 for vlPAG ket, n = 7 for vlPAG vehicle).