Fig. 4. Examination of the relationship between the antinociceptive activity of 200 μg spinally administered paracetamol (APAP) per rat, administered intrathecally, or 50 μg 5-HT per rat, administered intrathecally, and the 5-HT^1Areceptor using 40 μg WAY 100,635 per rat, administered intrathecally, on the biting and licking time produced by 2.5% formalin. Nociceptive responses were measured 0 to 5 min (phase 1) and 20 to 40 min (phase 2) after intraplantar formalin injection (50 μL). The results are expressed as mean ± standard error of mean. *P < 0.05 compared with the NaCl 0.9%-receiving group using analysis of variance followed by Student-Newman-Keuls test (n = 8).