Figure 6.

5-HT neurons are selectively missing in the raphe nuclei of Lmx1b^f/f/p mice. A–D, Immunocytochemical staining of 5-HT in B7 (A, B) and the caudal part (B1–B3) (C, D) of the raphe nuclei of wild-type mice (A, C) and Lmx1b^f/f/p mice (B, D). Only a few 5-HT⁺ cells were detected in the mutant (arrow in B). E, F, Nissl staining showed the loss of B6 in the raphe nuclei of Lmx1b^f/f/pr mice (F, arrow) compared with B6 in wild-type mice (arrow pointing to dark staining of B6 in E). G, H, Immunocytochemical staining with anti-β-gal antibody in B7 nucleus of Lmx1b^f/+/pr mice (G) and Lmx1b^f/f/pr mice (H). Arrows in H indicate a few remaining cells in mutants. Small insets in G and H showed higher magnification of confocal images of anti-β-gal⁺ cells. I, HPLC analysis of 5-HT and 5-HIAA in the brain and spinal cord of Lmx1b^f/f/p mice (n = 4) and wild-type littermates (n = 4). There was severe deficiency of the levels of 5-HT and its metabolite 5-HIAA in the CNS of Lmx1b^f/f/p mice. Two-tailed t test. Asterisk indicates the cerebral aqueduct. WT, Wild type; wet weight, wet tissue weight. Scale bars: 100 μm; insets, 10 μm.