Figure 1. The comparison of preinjury versus postinjury treatment (A). In the preinjury group, the drug is administered before formalin injection and is active during phase 1 of the formalin test. In the postinjury group, drug is administered at the end of phase 1. The paradigm for studies of receptor antagonism (B). To further establish the preemptive effect of the anesthetic, antagonist administration at the end of phase 1 (drug active during phase 1) is compared with administration with the drug before formalin injection (drug antagonized during phase 1). Shaded stripe depicts the approximate duration of action of the administered agents.