Low magnification photomicrographs illustrating c-Fos (PC38) and tryptophan hydroxylase (Tph) immunostaining from different rostrocaudal levels of the rat dorsal raphe nucleus (DR) in Experiment 2. C-Fos (PC38) immunostaining can be identified by a dark blue/black nuclear stain. Tryptophan hydroxylase-immunoreactive (ir) neurons and dendrites can be identified by a red/brown cytoplasmic stain. The rostrocaudal levels selected for analysis were (A) −7.64 mm bregma, (B) −8.18 mm bregma, and (C) −8.54 mm bregma. The subdivisions of the DR that were analyzed at each rostrocaudal level are delineated by dashed lines. Abbreviations: Aq, cerebral aqueduct; DRC, dorsal raphe nucleus, caudal part; DRD, dorsal raphe nucleus, dorsal part; DRI, dorsal raphe nucleus, interfascicular part; DRV, dorsal raphe nucleus, ventral part; DRVL/VLPAG, dorsal raphe nucleus, ventrolateral part/ventrolateral periaqueductal gray; mlf, medial longitudinal fasciculus. Scale bar, 500 μm.