Fig. 2. Effect of MK801 on 2 nmol of dynorphin A (1-13)-induced tactile allodynia. Saline, 0.9%, (group S; circle, n = 7), 10 nmol of MK801 (group M10; triangle, n = 7), or 5 nmol of MK801(group M5; square, n = 7) was intrathecally administered 20 min before intrathecal injection of 2 nmol of dynorphin A (1-13), and paw withdrawal thresholds were assessed by using von Frey filaments. * P < 0.05 versus control; † P < 0.05 versus group S. Data are expressed as mean ± SEM.