Fig. 8. Dynamic bone histomorphometric analysis and osteoblast proliferation after a 4-week treatment with 40 µg/kg PTH. (A) Fluorescent micrographs (200x) of undecalcified sections of lumbar spine trabecular bone showing double calcein labels in both wild-type Cx43+/fl (WT) and heterozygous equivalent Cx43/fl (Het) mice, but only single labels in conditional knockout ColCre;Cx43/fl (cKO) mice. (B) Mineral apposition rate (MAR) in the lumbar spine was significantly lower in cKO ColCre;Cx43/fl mice than in either HT or WT Cx43+/fl group (n=5-6). (C) Calcein labeling and (D) mineral apposition rate in the endosteal surface of the tibia showing attenuated response to PTH in cKO mice (n=5-6). (E) BrdU stain of endosteal tibial surface, showing positively stained cells equally in mice of all genotypes (n=3-4). (F) Osteoblast mitotic index, expressed as percentage of BrdU-labeled cells per total number of cells on the bone surface. *P<0.05 versus Cx43+/fl, one-way ANOVA.