Ovaries of 6-month-old MC4R-deficient mice differ in morphology compared to MC4R+/+ mice. The figure shows representative ovary sections of mice with a mixed genetic C3H/B6 background. Under a B6 background, identical morphological changes were observed although less frequent. A and B: Ovaries of MC4R-/- mice (A) contain a cystic follicle (star) and no CL, while MC4R+/+ ovaries (B) show many CL (arrowheads). H.E. Scale bars: 200 μm. C and D: Collapsed zonae pellucidae as remnants of regressed follicles (arrows) are more obvious in MC4R-/- mice (C) compared to MC4R+/+ mice (D). PAS reaction. Scale bars: 50 μm. E and F: Interstitial gland cells are hypertrophied in MC4R-/- ovaries (E) compared to MC4R+/+ ovaries (F). H.E. Scale bars: 25 μm.