Fig. 5. Averaged data from the three groups of rats given formalin into the ipsilateral hindpaw to illustrate effects of systemic administration of CP-96,345 and of CP-96,344 on the second phase of excitation in the response to formalin injection. A, Time histogram. The cross-hatchedhistogram represents animals that received no pharmacological manipulation (n = 9), thediagonal-hatched histogram represents the group of rats given CP-96,344 (n = 8), and theclear histogram represents animals treated with the NK-1 receptor antagonist CP-96,345 (n = 9) at 40 min after formalin injection. The vertical axis represents the mean number of spikes in 5 min periods, normalized to the value at 40 min. The horizontal axis represents time. For each time after 40 min, a comparison was made in each treatment group between the normalized mean number of spikes at that point and 100%. (*p < 0.05; **p < 0.01; ***p < 0.001) B, Graph showing the time course of the mean changes in rate of discharge beginning 40 min after formalin injection, the time of intravenous administration of CP-96,345 or CP-96,344. Each value represents the normalized mean number of spikes for each 5 min period expressed as a percent of the number of spikes at 40 min after formalin injection. Comparison of the groups reveals a significant difference between the number of spikes from neurons in rats treated with CP-96,345 compared with the number from rats treated with the inactive isomer CP-96,344 (++p < 0.01 at 45, 50, 55, and 60 min). Comparison of the group of rats that received no pharmacological manipulation and the group that received CP-96,345 reveals a significant difference. ***p < 0.001 at 45 and 50 min; **p < 0.01 at 55 and 60 min.