UP 202-56, an adenosine analogue, selectively acts via A1 receptors to significantly decrease noxiously-evoked spinal c-Fos protein expression.
The effects of oral administration of UP 202-56, an adenosine analogue, were assessed on carrageenan-induced spinal c-Fos protein expression and peripheral oedema. Three hours after intraplantar injection of carrageenan (6 mg/150 microl of saline), in awake rats, numerous c-Fos-like immunoreactive (c-Fos-LI) neurons in the dorsal horn of L4-L5 lumbar segments of the spinal cord (191 +/- 8; 184 +/- 10; 205 +/- 7 c-Fos-LI neurons per 40 microm section, for carrageenan controls in three experimental series performed in this study, respectively) and an extensive peripheral oedema were observed. Oral UP 202-56 (10, 30 or 50 mg/kg) dose-dependently reduced the number of carrageenan-induced c-Fos-LI neurons (r = 0.931. P < 0.0001), with the highest dose of UP 202-56 producing 72 +/- 4% reduction of the total number of carrageenan-induced spinal c-Fos-LI neurons, and 12 +/- 3% and 33 +/- 6% of reduction of control carrageenan oedema at paw and ankle levels, respectively. DPCPX (1 mg/kg i.p.), a selective adenosine A1 receptor antagonist, which injected alone had no effect on carrageenan-induced spinal c-Fos expression and peripheral oedema, blocked the effects of UP 202-56 (30 mg/kg p.o.) on the number of carrageenan-induced c-Fos-LI neurons. In addition, DPCPX did not modify the effects of UP 202-56 on carrageenan-induced peripheral oedema. DMPX (1 mg/kg i.p.), a somewhat selective adenosine A2 receptor antagonist, which injected alone had no significant effect on carrageenan-induced spinal c-Fos protein expression and peripheral oedema, did not influence the effects of UP 202-56 (30 mg/kg p.o.) on both carrageenan-induced spinal c-Fos expression and peripheral oedema. Our results demonstrate that UP 202-56 dose-dependently reduced the spinal c-Fos protein expression in carrageenan model of inflammatory pain. The ability of DPCPX to block the effect of UP 202-56, in contrast to the lack of effect of DMPX, increased evidence for a predominant role of adenosine A1 receptors activation in the mechanism of action of UP 202-56. These results increase evidence for a role of adenosine in the modulation of nociceptive transmission and support the antinociceptive action of adenosine analogues, such as UP 202-56, in inflammatory pain processes.
Honoré
P
P
Physiopharmacologie du Système Nerveux, INSERM U.161 and EPHE, Paris, France.
Buritova
J
J
Chapman
V
V
Besson
J M
JM
D000241:Adenosine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000284:Administration, Oral; D000818:Animals; D002351:Carrageenan / Q000494:pharmacology*; D004487:Edema / Q000139:chemically induced; D006614:Hindlimb; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D016760:Proto-Oncogene Proteins c-fos / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011687:Purines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018047:Receptors, Purinergic P1 / Q000502:physiology*; D013116:Spinal Cord / Q000378:metabolism*; D013805:Theobromine / Q000031:analogs & derivatives / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D007211:Indoles; D016760:Proto-Oncogene Proteins c-fos; D011687:Purines; D018047:Receptors, Purinergic P1; C112540:UP 202-56; D014970:Xanthines; C057837:3,7-dimethyl-1-propargylxanthine; D002351:Carrageenan; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000241:Adenosine; D013805:Theobromine