A. Representative Calbindin immunostained dorsal and ventral coronal hippocampal sections of adult control mice. Boxes indicate approximate locations of high magnification micrographs in B. B. Representative high magnification images of calbindin immunostained dorsal and ventral DG and CA3 from adult and middle-aged mice. C. Calbindin labeling intensity, calculated from six hemisections per mouse, is decreased in select regions in adult and middle-aged hippocampus following 4 weeks of fluoxetine treatment (18mg/kg/day). The mean intensity (±SEM) of calbindin labeling is expressed as percentage of control labeling in the respective region in age-matched controls. *, P<0.05; **, P<0.01. Scale bar: 200μM (A), 50μM (B).