Neuropharmacology
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The aim of the current study was to investigate the role of the rostroventromedial medulla (RVM) in alpha 2-adrenoceptor-mediated antinociception. Medetomidine or clonidine, selective alpha 2-adrenoceptor agonists were microinjected into the RVM in unanesthetized rats with a chronic guide cannula. The antinociceptive effects were evaluated using the tail-flick and hot-plate tests. ⋯ Microinjections of medetomidine into the cerebellum or the PAG produced an identical dose-response curve in the tail-flick test as that obtained following microinjection into the RVM. In spinalized rats the antinociceptive effect (tail-flick test) induced by medetomidine microinjected into the RVM was not less effective than in intact rats. Lidocaine (5%) or atipamezole (5 micrograms) microinjected into the RVM did not attenuate the antinociception induced by systemically administered medetomidine (100 micrograms/kg, s.c.).(ABSTRACT TRUNCATED AT 250 WORDS)