Increased 5-hydroxytryptamine transporter (5-HTT) expression leads to reduced fear recruitment of parvalbumin-expressing interneurons (PVINs) in the basal amygdala (BA). (a) Reduced freezing responses in 5-HTT-overexpressing (5-HTTOE) mice in the conditioned stimulus–unconditioned stimulus (CS–US) paired condition during fear testing session (paired: wild type (WT), n=14, 5-HTTOE, n=12; unpaired: WT, n=7, 5-HTTOE, n=7; tone alone: WT, n=8, 5-HTTOE, n=8). (b) Representative c-Fos expression in the BA following the fear testing session. Arrows indicate c-Fos+ neurons. Scale bar: 100 μm. (c) Immunoreactivity of a representative neuron for PV and c-Fos. Scale bar: 10 μm. (d) Overall numbers of c-Fos+ neurons in the basolateral amygdala (BLA) do not differ between WT and 5-HTTOE mice following the fear testing session (n=5 per genotype and condition). (e) Overall numbers of PV+ neurons in the BA do not differ between WT and 5-HTTOE mice following the fear testing session (n=5 per genotype). (f) Reduced numbers of c-Fos+/PV+ in the BA of 5-HTTOE in the paired condition. No significant difference between WT and 5-HTTOE in the unpaired and tone-alone condition (n=5 per genotype and condition). *P<0.05. The color reproduction of this figure is available on the Neuropsychopharmacology journal online.