Figure 6. NRTN-OE mice have increased sensitivity to innocuous cold temperature and oral menthol.

A) A two-temperature choice test was performed in which mice explored two adjacent temperature-controlled keys for 5 min. The control key was held at a constant 32°C while the test key ranged from 4 to 32°C. Data are plotted as percentage of time spent on the test key (y-axis) as a function of test temperature (x-axis). No preference was displayed by NRTN-OE (n=20) or WT (n=20) mice at test temperatures of 29°C and 32°C; i.e., they spent ca. 50% of the time on both keys . When the temperature of the test key was <29°C, both NRTN-OE and WT mice spent less time on the test key relative to the control key, indicating a preference for 32°C. NRTN-OE mice spent significantly less time than WT mice at the 17°C and 20°C test temperatures (*indicates NRTN-OE < WT; t-tests at each temperature). B) NRTN-OE mice have decreased sensitivity to noxious cold on wet ice block. Plot shows NRTN-OE mice placed on a -20°C surface have a longer latency to their first nocifensive response than WT mice (t-test; p <0.05). C) NRTN-OE mice also had fewer responses during the ice block trial period. (t-test; p <0.05). D) WT (n=6) and NRTN-OE (n=6) mice were tested for oral sensitivity to menthol using a two-bottle drinking aversion assay. One bottle contained water with vehicle (0.07% ethanol) and the other bottle contained water with menthol (0.1, 1 and 5 mM). At the lowest concentration (0.1 mM), both WT and NRTN-OE mice drank equal amounts of vehicle and menthol solutions, exhibiting no preference. At menthol concentrations of 1 and 5 mM, both WT and NRTN-OE mice drank less menthol solution compared to baseline, and NRTN-OE mice drank significantly less menthol-water than WT mice (*indicates NRTN-OE < WT; two-way ANOVA and Bonferroni post-hoc test. p<0.05).