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

THIS study was carried out to determine both the effect of systemic pa racetamol on the C-fibre evoked reflex activity, a test sensitive to c entrally acting analgesic drugs, and the influence of an intrathecally administered 5HT(3) receptor antagonist, tropisetron. Paracetamol (20 0, 300, 400 mg kg(-1), i.v.) dose-dependently decreased (maximal effec ts -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 eff ect of this drug and demonstrate the involvement of a spinal 5HT(3) me diated serotonergic mechanism.