Fig. 1.

Naked Mole-Rat and Mouse Response to the Irritant Formalin. Quantification of pain behaviors in mice and naked mole-rats during the formalin test, and the effects of intrathecal (IT) injection of SP. A) Time spent performing pain behaviors (licking, biting, and lifting the formalin-injected foot) as a function of time. Data is shown in 5-minute increments. (n = 8 mice and NMR). B) The data are re-plotted and displayed as cumulative time to facilitate species comparisons within Phase I and Phase II. Phase I corresponds to the first 10 min after formalin application. Phase II corresponds to 10–90 min after formalin injection. Here, time of pain behaviors for phase II is summed for the entire 10–90-minute phase (note that all other Phase II data presented for mice correspond to 10–60 min as we did not observe robust pain behaviors after 60 min). C) Time spent in pain behaviors for Phase I of the formalin test after intrathecal injection of SP or saline control. (n = 4 mice, n = 7 NMR) D) Time spent in pain behaviors for Phase II after intrathecal injection of SP or saline control (same animals as C). E) Quantification of pain behaviors from formalin application following IT injection of SP or saline in naked mole-rats, displayed in 10-minute increments. NMR = naked mole-rat. SP = Substance P. (* p < .05, ** p < .01, Statistical analysis was performed using a paired T-test).