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. 2022 Feb 16;42(7):1196–1210. doi: 10.1523/JNEUROSCI.1982-21.2021

Figure 4.

Figure 4.

Role of Gαo in hyperalgesia and hyperalgesic priming induced by systemic sub-AD fentanyl and morphine. Rats received injection of AS-ODN (120 μg in 20 μl/d, i.t.) or SE-ODN (120 μg in 20 μl/d, i.t.) against Gαo mRNA daily for 3 consecutive days. On the fourth day, at which time the mechanical nociceptive threshold was not different from the pre-ODN baselines (A: SE-ODN-treated group: t(5) = 0.67; p = 0.53; AS-ODN-treated group: t(5) = 0.65; p = 0.54; B: SE-ODN-treated group: t(5) = 0.74; p = 0.49; AS-ODN-treated group: t(5) = 1.66; p = 0.15, when the mechanical nociceptive threshold is compared before and ∼17 h after the third ODN injection; paired Student's t test), sub-AD fentanyl (A, 0.01 mg/kg, s.c.) or morphine (B, 0.03 mg/kg, s.c.) was administered and the mechanical nociceptive threshold was evaluated 1 h later. In the group of rats treated with Gαo AS-ODN, systemic sub-AD fentanyl-induced hyperalgesia was prevented (A, F(1,10) = 53.3, ****p < 0.0001, when the hyperalgesia in the Gαo SE-ODN-treated and the AS-ODN-treated groups was compared at 1 h after systemic sub-AD fentanyl; two-way repeated-measures ANOVA followed by Bonferroni's post hoc test). However, systemic sub-AD morphine-induced hyperalgesia was not affected by the treatment with Gαo AS-ODN (B, F(1,10) = 0.24, p = 0.63, when the hyperalgesia in the Gαo SE-ODN-treated and the AS-ODN-treated groups was compared at 1 h after systemic sub-AD morphine; two-way repeated-measures ANOVA followed by Bonferroni's post hoc test). At the end of the fourth day, rats again received intrathecal Gαo AS-ODN or SE-ODN. Five days after systemic sub-AD fentanyl and morphine, when the mechanical nociceptive threshold was not different from preopioid baselines (C: SE-ODN-treated group: t(5) = 0.75; p = 0.48; AS-ODN-treated group that received sub-AD fentanyl: t(5) = 2.15; p = 0.08; D: SE-ODN-treated group: t(5) = 0.68; p = 0.53; AS-ODN-treated group that received sub-AD morphine: t(5) = 1.90; p = 0.11, when the mechanical nociceptive threshold is compared before and 5 d after systemic sub-AD opioids; paired Student's t test), PGE2 (100 ng/5 μl, i.d.) was administered and the mechanical nociceptive threshold was evaluated 30 min and 4 h later. Treatment with Gαo AS-ODN did not prevent the prolongation of PGE2-induced hyperalgesia in both fentanyl-treated (C) and morphine-treated (D) groups of rats (C: F(1,10) = 2.15, p = 0.17; D: F(1,10) = 0.18, p = 0.68, when the hyperalgesia in the Gαo SE-ODN-treated and the AS-ODN-treated groups is compared at the fourth hour after intradermal PGE2; two-way repeated-measures ANOVA followed by Bonferroni's post hoc test). These findings support the suggestion that the Gαo subunit plays a role in OIH produced by systemic sub-AD fentanyl, but not morphine, and is not involved in hyperalgesic priming produced by sub-AD fentanyl and morphine. (n = 6 paws/6 rats/group).