PARTICIPATION OF NUCLEUS-RETICULARIS GIGANTOCELLULARIS IN THE ANTINOCICEPTIVE EFFECT OF ANGIOTENSIN-III IN THE RAT

We evaluated the participation of nucleus reticularis gigantocellulari s (NRGC), a medullary nucleus that plays an important role in the regu lation of nociceptive processes, in the antinociceptive effect of angi otensin III (AIII), a biologically active peptide of the renin-angiote nsin system. Adult, male Sprague-Dawley rats anesthetized with pentoba rbital sodium (40 mg/kg, i.p., with 10 mg/kg/h i.v. infusion supplemen t) were used. Bilateral, site-specific microinjection of AIII (80 or 1 60 pmol) into the NRGC produced a dose-related increase in the latency of tail-flick response to noxious thermal stimuli (50-degrees-C hot w ater). Such an antinociceptive action of AIII was blocked by concomita nt administration of the AIII receptor antagonist, Ile7-angiotensin II I (Ile7-AIII, 10 nmol). At the neuronal level, microiontophoretic appl ication of AIII suppressed, Ile7-AIII reversibly, the responsiveness o f nociception-related neurons in the NRGC to tail-clamping. These resu lts demonstrated that central AIII may elicit antinociception via a pr ocess that may at least take place at the NRGC.