Pillai RLI, et al. - Researchers sought to identify 5-HT_1A differences in individual raphe nuclei using positron emission tomography (PET) in order to determine whether use of subnuclei would provide greater sensitivity and specificity of diagnosing major depressive disorder (MDD). In MDD, higher 5-HT_1A autoreceptor binding was observed selectively in the dorsal raphe nucleus (DRN). They found that 5-HT_1A autoreceptor binding in the combined DRN and median raphe nucleus (MRN) was a better biomarker for MDD than in the raphe as a whole.