Article Figures & Data
Figures
- Fig. 1.
A, Repeated administration of clonidine produces tolerance to antinociception. Effect of PGE2 (E2), clonidine plus PGE2(Cl+E2), clonidine once hourly for 3 hr (Clx3), clonidine once hourly for 3 hr, and at the fourth hour clonidine plus PGE2 (Clx3, Cl+E2) on mechanical paw withdrawal threshold in the rat.B, Bidirectional cross-tolerance develops among A1, α2, and μ antinociception. Effect of clonidine plus PGE2 (Cl+E2), DAMGO once hourly for 3 hr (Dx3), DAMGO once hourly for 3 hr and at the fourth hour clonidine plus PGE2(Dx3,Cl+E2), CPA once hourly for 3 hr and at the fourth hour clonidine plus PGE2 (CPAx3, Cl+E2), CPA once hourly for 3 hr (CPAx3), clonidine once hourly for 3 hr and at the fourth hour DAMGO plus PGE2 (Clx3, D+E2), and clonidine once hourly for 3 hr and at the fourth hour CPA plus PGE2 (Clx3, CPA+E2) on mechanical paw withdrawal threshold in the rat.
- Fig. 2.
A, Yohimbine precipitates withdrawal hyperalgesia in clonidine tolerant paws. Effect of PGE2 (E2), clonidine plus PGE2(Cl+E2), clonidine once hourly for 3 hr (Clx3), clonidine once hourly for 3 hr (Clx3), clonidine once hourly for 3 hr, and at the fourth hour yohimbine (Clx3, Yo) on mechanical paw-withdrawal threshold in the rat. B, Bidirectional cross-withdrawal develops among A1, α2, and μ antinociception. Effect of clonidine once hourly for 3 hr and at the fourth hour naloxone (Clx3, N), clonidine once hourly for 3 hr and at the fourth hour PACPX (Clx3, PACPX), clonidine once hourly for 3 hr (Clx3), DAMGO once hourly for 3 hr and at the fourth hour yohimbine (Dx3, Yo), DAMGO once hourly for 3 hr (Dx3), CPA once hourly for 3 hr (CPAx3), CPA once hourly for 3 hr and at the fourth hour yohimbine (CPAx3, Yo), and CPA once hourly for 3 hr (CPAx3) on mechanical paw withdrawal threshold in the rat.
- Fig. 3.
μ, α2, and A1antagonists dose-dependently block μ, α2, and A1 antinociception, respectively. A, Naloxone dose-dependently blocks DAMGO antinociception. Effect of PGE2 (E2), DAMGO plus PGE2(D+E2) and various doses of naloxone (1 ng to 1 μg), and DAMGO plus PGE2 (N+D+E2), on mechanical paw withdrawal threshold in the rat. B, Yohimbine dose-dependently blocks clonidine antinociception. Effect of PGE2 (E2), clonidine plus PGE2(Cl+E2), and various doses of yohimbine (1 ng to 1 μg) and clonidine plus PGE2 (Yo+Cl+E2) on mechanical paw withdrawal threshold in the rat. C, PACPX dose-dependently blocks CPA antinociception. Effect of PGE2(E2), DAMGO plus PGE2(CPA+E2), and various doses of PACPX (1 ng to 1 μg) and CPA plus PGE2 (PACPX+CPA+E2) on mechanical paw withdrawal threshold in the rat.
- Fig. 4.
Multiple receptors are involved in μ, α2, and A1 antinociception. A, Clonidine α2 antinociception is blocked not only by yohimbine but also by naloxone and PACPX. Effect of PGE2(E2), clonidine plus PGE2(Cl+E2), yohimbine plus clonidine plus PGE2(Yo+Cl+E2), naloxone plus clonidine plus PGE2 (N+Cl+E2), and PACPX plus clonidine plus PGE2 (PACPX+Cl+E2) on mechanical paw withdrawal threshold in the rat. B, DAMGO μ antinociception is blocked not only by naloxone but also by yohimbine. Effect of PGE2 (E2), DAMGO plus PGE2 (D+E2), naloxone plus DAMGO plus PGE2 (N+D+E2), yohimbine plus DAMGO plus PGE2 (Yo+D+E2), and PACPX plus DAMGO plus PGE2 (PACPX+D+E2) on mechanical paw withdrawal threshold in the rat. C, CPA A1antinociception is blocked not only by PACPX but also by yohimbine. Effect of PGE2 (E2), CPA plus PGE2 (CPA+E2), PACPX plus CPA plus PGE2 (PACPX+CPA+E2), naloxone plus CPA plus PGE2 (N+CPA+E2), and yohimbine plus CPA plus PGE2 (Yo+CPA+E2) on mechanical paw withdrawal threshold in the rat.
- Fig. 5.
Multiple receptors are involved in α2, μ, and A1 tolerance and withdrawal.A, Yohimbine withdrawal is blocked not only by clonidine but also by DAMGO and CPA. Effect of clonidine once hourly for 3 hr and at the fourth hour yohimbine (Clx3,Yo), clonidine once hourly for 3 hr and at the fourth hour clonidine plus yohimbine (Clx3,Cl+Yo), clonidine once hourly for 3 hr and at the fourth hour DAMGO plus yohimbine (Clx3,D+Yo), and clonidine once hourly for 3 hr and at the fourth hour CPA plus yohimbine (Clx3,CPA+Yo) on mechanical paw withdrawal threshold in the rat. B, Naloxone withdrawal is blocked not only by DAMGO but also by clonidine. Effect of DAMGO once hourly for 3 hr and at the fourth hour naloxone (Dx3,N), DAMGO once hourly for 3 hr and at the fourth hour DAMGO plus naloxone (Dx3,D+N), DAMGO once hourly for 3 hr and at the fourth hour clonidine plus naloxone (Dx3,Cl+N), and DAMGO once hourly for 3 hr and at the fourth hour CPA plus naloxone (Dx3,CPA+N) on mechanical paw withdrawal threshold in the rat. C, PACPX withdrawal is blocked not only by CPA but also by clonidine. Effect of CPA once hourly for 3 hr and at the fourth hour PACPX (CPAx3,PACPX), CPA once hourly for 3 hr and at the fourth hour CPA plus PACPX (CPAx3,CPA+PACPX), CPA once hourly for 3 hr and at the fourth hour clonidine plus PACPX (CPAx3,Cl+PACPX), and CPA once hourly for 3 hr and at the fourth hour DAMGO plus naloxone (CPAx3,D+PACPX) on mechanical paw withdrawal threshold in the rat.
- Fig. 6.
Antisense μ ODN treatment blocks not only μ antinociception but also α2 antinociception. A1 antinociception is unaffected. A, Effect of PGE2 (E2), DAMGO plus PGE2(D+E2), μ-antisense (AS) ODN 1 μg intrathecally on alternate days × 3 and DAMGO plus PGE2 [μ-(AS)x3,D+E2], μ-sense (S) ODN 1 μg intrathecally on alternate days × 3, and DAMGO plus PGE2 [μ-(S)x3,D+E2] on mechanical paw-withdrawal threshold. B, Effect of PGE2 (E2), clonidine plus PGE2(Cl+E2), μ-(AS) ODN 1 μg intrathecally on alternate days × 3, and clonidine plus PGE2[μ-(AS)x3,Cl+E2], μ-(S) ODN 1 μg intrathecally on alternate days × 3, and clonidine plus PGE2[μ-(S)x3,Cl+E2] on mechanical paw-withdrawal threshold. C, Effect of PGE2(E2), CPA plus PGE2 (CPA+E2), μ-(AS) ODN 1 μg intrathecally on alternate days × 3, CPA plus PGE2 [μ-(AS)x3,CPA+E2], μ-(S) ODN 1 μg intrathecally on alternate days × 3, and CPA plus PGE2 [μ-(S)x3,CPA+E2] on mechanical paw withdrawal threshold in the rat.
- Fig. 7.
Antisense α2C ODN treatment blocks not only α2 antinociception but also μ and A1 antinociception. A, Effect of PGE2 (E2), clonidine plus PGE2(Cl+E2), α2-(AS) ODN 1 μg intrathecally on alternate days × 3, and clonidine plus PGE2[α2-(AS)x3,CCl+E2], α2-(S) ODN 1 μg intrathecally on alternate days × 3, and clonidine plus PGE2 [α2-(S)x3,Cl+E2] on mechanical paw withdrawal threshold in the rat. B, Effect of PGE2 (E2), DAMGO plus PGE2 (D+E2), α2-(AS) ODN 1 μg intrathecally on alternate days × 3, and DAMGO plus PGE2 [α2-(AS)x3,D+E2], α2-(S) ODN 1 μg intrathecally on alternate days × 3, and DAMGO plus PGE2[α2-(S)x3,D+E2] on mechanical paw withdrawal threshold in the rat. C, Effect of PGE2(E2), CPA plus PGE2 (CPA + E2), α2-(AS) ODN 1 μg intrathecally on alternate days × 3, and CPA plus PGE2 [α2-(AS)x3,CPA+E2], α2-(S) ODN 1 μg intrathecally on alternate days × 3, and CPA plus PGE2[α2-(S)x3,CPA+E2] on mechanical paw withdrawal threshold in the rat.
- Fig. 8.
Schematic diagram of hypothesized topological/physical arrangement of the three receptors for peripheral antinociception in the cell membrane. μ (DAMGO), α2C (Clonidine), and A1(CPA) agonism all result in peripheral antinociception mediated through a common second messenger pathway, leading to complete symmetrical cross-tolerance and cross-dependence. However, the asymmetrical interactions are proposed to be a result of the central position of the α2C receptor leading to bidirectional interactions between this receptor and the two other receptors but no interaction between the μ and A1 receptors.
Tables
Abbreviation(s) Agent Action PGE2or E2 Prostaglandin E2 Hyperalgesic inflammatory mediator DAMGO or D [d-Ala2,N-Me-Phe4,gly5-ol] enkephalin μ-opioid receptor agonist N Naloxone Opioid receptor antagonist Cl Clonidine α2-adrenergic agonist Yo Yohimbine α2-adrenergic antagonist CPA N6-cyclopentyl-adenosine A1-adenosine receptor agonist PACPX 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine A1-adenosine receptor antagonist μ-antisense μ-opioid receptor oligodeoxynucleotide (ODN) Downregulation of μ-opioid receptors μ-sense No effect α2-antisense α2C-adrenergic receptor oligodeoxynucleotide (ODN) Downregulation of α2C-adrenergic receptors α2-sense No effect Group N Treatment Dose(s) I–A 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 Clonidine hourly × 3 100 ng × 3 4 12 Clonidine hourly × 3, fourth hour clonidine + PGE2 100 ng × 3, 100 ng + 100 ng I–B 1 12 DAMGO hourly × 3, fourth hour clonidine + PGE2 1 μg × 3, 100 ng + 100 ng 2 12 CPA hourly × 3, fourth hour clonidine + PGE2 1 μg × 3, 100 ng + 100 ng 3 16 Clonidine + PGE2 100 ng + 100 ng 4 12 Clonidine hourly × 3, fourth hour DAMGO + PGE2 100 ng × 3, 1 μg + 100 ng 5 6 DAMGO + PGE2 1 μg + 100 ng 6 6 DAMGO hourly × 3 1 μg × 3 7 6 CPA hourly × 3 1 μg × 3 8 12 Clonidine hourly × 3, fourth hour CPA + PGE2 100 ng × 3, 1 μg + 100 ng 9 6 CPA + PGE2 1 μg + 100 ng II-A 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 Clonidine × 3 100 ng × 3 4 8 Clonidine hourly × 3, fourth hour yohimbine 100 ng × 3, 100 ng II-B 1 10 Clonidine hourly × 3, fourth hour naloxone 100 ng × 3, 200 ng 2 10 Clonidine hourly × 3, fourth hour PACPX 100 ng × 3, 100 ng 3 6 Clonidine × 3 100 ng × 3 4 10 DAMGO hourly × 3, fourth hour yohimbine 1 μg × 3, 100 ng 5 6 DAMGO × 3 1 μg × 3 6 10 CPA hourly × 3, fourth hour yohimbine 1 μg × 3, 100 ng 7 6 CPA hourly × 3 1 μg × 3 III-A 1 24 PGE2 100 ng 2 6 DAMGO + PGE2 1 μg + 100 ng 3 6 Naloxone + DAMGO + PGE2 1 ng + 1 μg + 100 ng 4 6 Naloxone + DAMGO + PGE2 10 ng + 1 μg + 100 ng 5 6 Naloxone + DAMGO + PGE2 100 ng + 1 μg + 100 ng 6 6 Naloxone + DAMGO + PGE2 1 μg + 1 μg + 100 ng III-B 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 Yohimbine + clonidine + PGE2 1 ng + 100 ng + 100 ng 4 6 Yohimbine + clonidine + PGE2 10 ng + 100 ng + 100 ng 5 6 Yohimbine + clonidine + PGE2 100 ng + 100 ng + 100 ng 6 6 Yohimbine + clonidine + PGE2 1 μg + 100 ng + 100 ng III-C 1 24 PGE2 100 ng 2 6 CPA + PGE2 1 μg + 100 ng 3 6 PACPX + CPA + PGE2 1 ng + 1 μg + 100 ng 4 6 PACPX + CPA + PGE2 10 ng + 1 μg + 100 ng 5 6 PACPX + CPA + PGE2 100 ng + 1 μg + 100 ng 6 6 PACPX + CPA + PGE2 1 μg + 1 μg + 100 ng IV-A 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 Yohimbine + clonidine + PGE2 100 ng + 100 ng + 100 ng 4 10 Naloxone + clonidine + PGE2 200 ng + 100 ng + 100 ng 5 10 PACPX + clonidine + PGE2 100 ng + 100 ng + 100 ng IV-B 1 24 PGE2 100 ng 2 6 DAMGO + PGE2 1 μg + 100 ng 3 6 Naloxone + DAMGO + PGE2 200 ng + 1 μg + 100 ng 4 8 Yohimbine + DAMGO + PGE2 100 ng + 1 μg + 100 ng 5 6 PACPX + DAMGO + PGE2 100 ng + 1 μg + 100 ng IV-C 1 24 PGE2 100 ng 2 6 CPA + PGE2 1 μg + 100 ng Group N Treatment Dose(s) IV-C 3 6 PACPX + CPA + PGE2 100 ng + 1 μg + 100 ng 4 8 Naloxone + CPA + PGE2 200 ng + 1 μg + 100 ng 5 6 Yohimbine + CPA + PGE2 100 ng + 1 μg + 100 ng V-A 1 8 Clonidine hourly × 3, fourth hour yohimbine 100 ng × 3, 100 ng 2 6 Clonidine hourly × 3, fourth hour clonidine + yohimbine 100 ng × 3, 100 ng + 100 ng 3 8 Clonidine hourly × 3, fourth hour DAMGO + yohimbine 100 ng × 3, 1 μg + 100 ng 4 8 Clonidine hourly × 3, fourth hour CPA + yohimbine 100 ng × 3, 1 μg + 100 ng V-B 1 6 DAMGO hourly × 3, fourth hour naloxone 1 μg × 3, 200 ng 2 6 DAMGO hourly × 3, fourth hour DAMGO + naloxone 1 μg + 1 μg + 200 ng 3 8 DAMGO hourly × 3, fourth hour clonidine + naloxone 1 μg + 100 ng + 200 ng 4 8 DAMGO hourly × 3, fourth hour CPA + naloxone 1 μg + 1 μg + 200 ng V-C 1 8 CPA hourly × 3, fourth hour PACPX 1 μg × 3, 100 ng 2 6 CPA hourly × 3, fourth hour CPA + PACPX 1 μg + 1 μg + 100 ng 3 8 CPA hourly × 3, fourth hour clonidine + PACPX 1 μg + 100 ng + 100 ng 4 8 CPA hourly × 3, fourth hour DAMGO + PACPX 1 μg + 1 μg + 100 ng VI-A 1 24 PGE2 100 ng 2 6 DAMGO + PGE2 1 μg + 100 ng 3 6 μ-antisense intrathecally alternate days × 3, 24 hr after DAMGO + PGE2 1 μg × 3, 1 μg + 100 ng 4 6 μ-sense intrathecally alternate days × 3, 24 hr after DAMGO + PGE2 1 μg × 3, 1 μg + 100 ng VI-B 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 μ-antisense intrathecally alternate days × 3, 24 hr after clonidine + PGE2 1 μg × 3, 100 ng + 100 ng 4 6 μ-sense intrathecally alternate days × 3, 24 hr after clonidine + PGE2 1 μg × 3, 100 ng + 100 ng VI-C 1 24 PGE2 100 ng 2 6 CPA + PGE2 1 μg + 100 ng 3 6 μ-antisense intrathecally alternate days × 3, 24 hr after CPA + PGE2 1 μg × 3, 1 μg + 100 ng 4 6 μ-sense intrathecally alternate days × 3, 24 hr after CPA + PGE2 1 μg × 3, 1 μg + 100 ng VII-A 1 24 PGE2 100 ng 2 6 DAMGO + PGE2 1 μg + 100 ng 3 6 α2-antisense intrathecally alternate days × 3, 24 hr after DAMGO + PGE2 1 μg × 3, 1 μg + 100 ng 4 6 α2-sense intrathecally alternate days × 3, 24 hr after DAMGO + PGE2 1 μg × 3, 1 μg + 100 ng VII-B 1 24 PGE2 100 ng 2 16 Clonidine + PGE2 100 ng + 100 ng 3 6 α2-antisense intrathecally alternate days × 3, 24 hr after clonidine + PGE2 1 μg × 3, 100 ng + 100 ng 4 6 α2-sense intrathecally alternate days × 3, 24 hr after clonidine + PGE2 1 μg × 3, 100 ng + 100 ng VII-C 1 24 PGE2 100 ng 2 6 CPA + PGE2 1 μg + 100 ng 3 6 α2-antisense intrathecally days × 3, 24 hr after CPA + PGE2 1 μg × 3, 1 μg + 100 ng 4 6 α2-sense intrathecally alternate days × 3, 24 hr after CPA + PGE2 1 μg × 3, 1 μg + 100 ng Abbreviations: PGE2, Prostaglandin E2 (EP receptor agonist); DAMGO, [d-Ala2, N-Me-Phe4, gly5-ol] (μ-opioid receptor agonist); Cl, clonidine (α2 agonist); Yo, yohimbine (α2 antagonist); CPA, N6-cyclopentyl adenosine (A1-adenosine agonist); PACPX, 1,3-dipropyl-8-(2-amino-4-chlorophenyl)-xanthine (A1-adenosine antagonist). There are repetitions for the sake of comparison.
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