Stereological determination of TH+ dopaminergic neurons and morphological analysis of Iba1+ microglia at 21 DPI revealed that pre-treatment with MnCl2 during juvenile development induced persistent morphological changes in microglia consistent with an activated phenotype and increased their reactivity to a subsequent infection with H1N1, characterized by retraction of cytoplasmic processes and adoption of an amoeboid phenotype (Fig 1B–1I). Here, TH is linked to infection.