Figure 7. Concentrations of 5-HT and 5-HIAA in brain tissue. Using the HPLC system, we measured the tissue levels of serotonin (5-HT) and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in several brain areas. Both 5-HT and 5-HIAA concentrations were decreased in the hippocampus (A/B), the cortex (C/D) and the striatum (E/F) in female HD mice when compared to WT animals. Levels of 5-HIAA were also reduced in male HD. Finally, male mice exhibited higher hippocampal tissue levels of both 5-HT and 5-HIAA when compared to female animals. 5-HT and 5-HIAA are expressed in ng/g tissue. Values represent means (6 SEM) of n = 6–8 mice per group. WT vs. HD: (*) p,0.05, (**) p,0.01, (***) p,0.001. Male vs. female: (##) p,0.01. doi:10.1371/journal.pone.0022133.g007 not affected by the HD mutation or underwent additional opposite adaptive changes. This putative adaptation could be related to the altered DPAT-induced hypothermia and the increased fluid intake (previously observed in R6/2 HD mice [67]) we reported here. Indeed, the hypothalamus is known to be involved in the regulation of body temperature and water balance. Whether such putative region-specific changes are link to the hypothalamic capacity to regulated endocrine activity still need to be addressed. PLoS ONE | www.plosone.org 7 July 2011 | Volume 6 | Issue 7 | e22133