In the formalin model of tonic nociceptive pain, 8-OH-DPAT produces 5-HT1Areceptor-mediated, behaviorally specific analgesia

The experiments examined antinociceptive and intrinsic behavioral effects i nduced by the prototypical 5-HT1A receptor agonist 8-OH-DPAT (8-hydroxy-2-[ di-n-propylamino] tetralin) in rats. 8-OH-DPAT (0.01-2.5 mg/kg, subcutaneou s (s.c.)) reduced both the paw licking and paw elevation induced by (2.5%) formalin injection into the plantar surface of the right hindpaw; it also p roduced forepaw treading. All of these effects were completely blocked by p retreatment with WAY 100635 (N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl} -N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride) (0.16 mg/kg, s.c. ); prazosin (0.63 mg/kg, s.c.) inhibited forepaw treading, but not 8-OH-DPA T's action on paw elevation and paw licking. Repeated injection of 8-OH-DPA T (0.63 mg/kg, s.c.) twice daily for 4 days, markedly reduced 8-OH-DPAT's a bility to produce forepaw treading, but exerted only little and inconsisten t effects on its paw licking and paw elevation-inhibiting action. The data indicate that 8-OH-DPAT exerts an analgesic action in the formalin model of tonic nociceptive pain; this action is mediated by 5-HT1A receptors, and i s not confounded by the productive sign (i.e., forepaw treading) of the 5-H T syndrome which 8-OH-DPAT also induces. (C) 2001 Published by Elsevier Sci ence B.V.