Figure 3. Estrogen receptor alpha (ERα) regulates the induction of hyperalgesic priming by ryanodine in female rats.

(a) Female rats were treated with ODN antisense (black bars) or mismatch (white bars) for estrogen receptor alpha (ERα, left panel) or beta (ERβ, right panel), for 6 consecutive days. Ryanodine (1 pg) was injected on the dorsum of the hind paw on the 4^th day of ODN treatment. On the 7^th day, PGE₂ (100 ng) was injected at the same site as ryanodine, and the mechanical nociceptive threshold was evaluated, 30 min and 4 h later. No difference (NS) was observed in the mechanical nociceptive thresholds before the injection of ryanodine and immediately before injection of PGE₂ (see Supplementary Table S1). PGE₂-induced hyperalgesia was still present 4 h after injection in all groups, except in the group treated with ODN antisense for ERα (F_1,10 = 16.22; **p = 0.0024, when the groups treated with ERα ODN are compared; F_1,10 = 0.2610; p =s0.6205, NS, when the groups treated with ERβ ODN are compared; two-way repeated measures ANOVA followed by Bonferroni post-hoc test); (b) The dose of ryanodine that induced priming in male rats (100 ng) was injected on the dorsum of the hind paw of female rats that have been treated intrathecally with ODN antisense or mismatch for ERα. The ODN treatment was performed for 6 consecutive days, and ryanodine was injected on the 4^th day. PGE₂ (100 ng) was injected at the same site as ryanodine on the 7^th day, and the mechanical hyperalgesia was evaluated 30 min and 4 h later. No significant difference in the mechanical thresholds before the injection of ryanodine and before injection of PGE₂ was observed (see Supplementary Table S1). We found that the hyperalgesia induced by PGE₂ was still present 4 h after injection, with no attenuation, in both groups (F_1,10 = 0.3839; p = 0.5494, NS, when both groups are compared). Together, these results support the suggestion that ERα regulates the capacity of ryanodine to induce priming in the female rat. (N = 6 paws, all groups).