HTR1A and depressive disorder: Consistent with the above model for depression, there is evidence of a 50% reduction in major depression of calbindin-positive interneurons (which are 5-HT1A+ by in situ hybridization de Almeida and Mengod, 2008) and not of parvalbumin-positive interneurons (which lack 5-HT1A RNA) (Rajkowska et al., 2007).