EVIDENCE OF A CENTRAL ANTINOCICEPTIVE EFFECT OF PARACETAMOL INVOLVING SPINAL 5HT(3) RECEPTORS

THIS study was carried out to determine both the effect of systemic paracetamol on the C-fibre evoked reflex activity, a test sensitive to centrally acting analgesic drugs, and the influence of an intrathecally administered 5HT(3) receptor antagonist, tropisetron. Paracetamol (200, 300, 400 mg kg(-1), i.v.) dose-dependently decreased (maximal effects -60+/-8%) the C-evoked responses for a duration of 90 min (for the lowest dose). This effect was totally suppressed by tropisetron (1 mu g, i.t.). These data confirm previous studies suggesting a central effect of this drug and demonstrate the involvement of a spinal 5HT(3) mediated serotonergic mechanism.