Fig 2. Serotonin immunostaining of the dorsal raphe nucleus (DRN) immediately caudal to oculomotor nucleus.

(Bregma -4.48 mm). Representative examples of sections processed for 5-HT immunostaining and visualized with Ni²⁺-DAB (blue-black stain) from virgin female mice (A; n = 3) and lactating mice (B; n = 4). C: Average optical density of cell bodies (background-subtracted; threshold detection) in the field as demarcated by the dashed lines in A and B. D: Average number of detectable stained cells in the field. Aq, Aqueduct of Sylvius; DRD, dorsal raphe-dorsal part; DRV, dorsal raphe-ventral part; VLPAG, ventrolateral aspect of the periaqueductal gray; mlf, medial longitudinal fasciculus. Student’s t-test comparison of the means: *p<0.05, **p<0.01 compared to virgin controls.