Operant reward licking events for three different strains of mice. Hairless mice significantly increased their reward licking events (A) when fasted overnight (N = 13–27/session). Unfasted animals had significantly lower (+P < 0.05) licking events in session 1 as compared to session 2, but there was no difference between session 2 and 3, and overall the fasted sessions produced significantly higher performance as compared to the unfasted sessions. Hairless (B) and C57/BL6 (C) mice demonstrated a stimulus response such that increasing temperatures significantly reduced the number of reward licking events, indicating aversion to the more noxious stimuli. The TRPV1 knock-out mice (D) were relatively insensitive to temperatures ≤ 52°C, as their responses in the noxious heat range of 46–52°C produced responses similar to baseline 37°C testing conditions. These knock-out mice only demonstrated a significant decrease in reward licking events when they were tested at the highest stimulus temperature of 55°C. A total of N = 10 hairless, N = 5 CB57BL6, and N = 5 TRPV1 knock-out mice were used to generate these data. N.T. = not tested. *Significantly higher (P < 0.05). Note that there were no significant differences between male and female mice when comparing the number of licking events during the unfasted and fasted sessions, therefore their data was pooled.
Neubert et al. Molecular Pain 2008 4:43 doi:10.1186/1744-8069-4-43