Analysis of ovary morphology, steroid hormone levels, reproductive performance, and Bruce effect test. (A-E) Normal breeding performance in cGαo-/- females during a four-month interval, analyzed as litter size (A), number of litters (B), litter interval (C), relative fecundity (D), and latency to first litter (E) (analysis of variance (ANOVA): F2,26 = 0.44 to 0.95, P = 0.40 to 0.65). Circles/triangles in E represent individual subjects, red squares indicate mean values. (F) Plasma estradiol and progesterone levels at proestrus did not differ between B6 control and cGαo-/- mice measured in juveniles (4 to 5 weeks) and adults (12 to 16 weeks) (t-test: P = 0.61 (juveniles) and 0.2 (adults) for estradiol; P = 0.68 for progesterone). (G) Near-maximum levels of non-pregnant females are observed in cGαo-/- females in the Bruce effect assay when tested with familiar urine or under unstimulated conditions (ANOVA: F2,78 = 6.52, least significant difference (LSD): *P <0.05). B6 females perform normally and discriminate familiar versus unfamiliar urine cues (LSD: *P <0.05, **P <0.01). (H) Histological sections of ovaries from both adult B6 control (top) and cGαo-/- mice (bottom) show the presence of follicles with antrum at different stages of folliculogenesis (arrows indicate small- or medium-sized follicles arrowheads indicate large follicles ) as well as of corpora lutea (*). Scale bar, 250 μm. (I) Number of corpora lutea and follicles with antrum did not differ between B6 and cGαo-/- mice (t-test: P = 0.18 to 0.56). Follicles were divided into three categories according to their size: 100 to 199 μm (small), 200 to 299 μm (medium), >300 μm (large or preovulatory). ns, non-significant.