We recently reported that intrathecal (i.t.) administration of prostaglandin E 2 (PGE 2 ) to conscious mice induced allodynia, a state of discomfort and pain evoked by innocuous tactile stimuli. In the present study, we examined the effect of the PGE receptor EP 1 subtype antagonist ONO-NT-012, the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801, and the NO synthase inhibitorN ω -nitro-l-arginine methyl ester (l-NAME) on the allodynia. The PGE 2 -induced allodynia was blocked by simultaneous i.t. injection of ONO-NT-012, MK-801, or l-NAME. However, 5 min after i.t. injection of PGE 2 , the allodynia was significantly blocked by i.t.l -NAME, but not by i.t. ONO-NT-012 or MK-801. These results demonstrate that the PGE 2 -induced allodynia, once developed, does not require the continued agonist occupancy of EP 1 and NMDA glutamate receptor sites.