Figure 2. Effect of sex and HD mutation on saccharin-preference test and total fluid intake. (A) We found a significant interaction between sex and genotype (F(1,44) = 5.84, p,0.05) on saccharin preference (expressed as % of total fluid intake). Indeed compared to WT animals, only HD female mice exhibited reduced saccharin preference. (B) Interestingly looking at total fluid intake (expressed in mL), we revealed an overall effect of genotype (F(1,44) = 12.3, p,0.01) but no significant effect of sex or interactions. Values represent means (6 SEM) of n = 8–14 mice per group. WT vs. HD: (*) p,0.05, (**) p,0.01. doi:10.1371/journal.pone.0022133.g002 Wilk test), we also ran non-parametric tests and found an overall significant group difference (p,0.01, Kruskal Wallis test). Compared to WT animals, only female HD mice exhibited augmented time to feed (p,0.01, Mann-Whitney test). Our observations were not due to altered appetite motivations since there was no difference in the amount of food consumed after NSFT (Fig. 3B). Sex-specific increased 8-OH-DPAT-induced hypothermia in female HD mice We assessed the hypothermic response to the 5-HT1A receptor agonist 8-OH-DPAT to evaluate 5-HT1A autoreceptor function in vivo. The involvement of 5-HT1A autoreceptors in mediating the 8- OH-DPAT-induced hypothermia is well-established in the mouse [35] but also see [36,37]. There were no differences in baseline temperatures between the sexes or genotypes prior to drug administration (data not shown). Considering the change in body temperature for 1 h post-injection (Figure 4), we found that acute administration of 8-OH-DPAT significantly decreased rectal temperatures in a dose-dependent manner in both male (Fig. 4A) and female (Fig. 4B) mice compared to saline-treated animals (treatment effect: F(2,116) = 142, p,0.001). There were significant effects of both sex (F(1,116) = 6.48, p,0.05) and genotype (F(1,116) = 4.61, p,0.05) as well as significant interactions between the 3 factors. Indeed 20–30 min following 8-OH-DPAT (0.3 mg/ kg) administration, only female HD mice exhibited an enhanced hypothermia when compared to WT animals (p,0.05). Functional analysis of 5-HT1A and 5-HT2 heteroreceptors We assessed 5-HT1A post-synaptic receptor function in vivo, by measuring the effect of the 5-HT1A receptor agonist 8-OH-DPAT on the plasma corticosterone levels in both male and female animals. Regardless of sex and genotype, the acute administration of 8-OH-DPAT (0.3 mg/kg, s.c.) significantly increased cortico- sterone levels (Fig. 5A & 5B). There was a significant overall drug effect (F(1,38) = 31.7, p,0.001) but no effect of sex or genotype. Figure 3. Effect of sex and HD mutation on the novelty suppressed feeding test (NSFT). (A) Analyzing the time (expressed in sec) to complete the task in the NSFT, we found a significant interaction between sex and genotype (F(1,55) = 4.2, p,0.05). Indeed compared to WT animals, only HD female mice exhibited greater delay to complete the NSFT. (B) Interestingly measuring the amount of food consumed after NSFT, we did not find any effect of genotype (F(1,55) = 1.7, p = 0.19) or interaction with the sex (F(1,55) = 0.39, p = 0.54). Values represent means (6 SEM) of n = 12–17 mice per group. WT vs. HD: (***) p,0.001. doi:10.1371/journal.pone.0022133.g003 PLoS ONE | www.plosone.org 3 July 2011 | Volume 6 | Issue 7 | e22133