The Male Bias in the Number of Purkinje Cells and the Size of the Murine Cerebellum may Require Müllerian Inhibiting Substance/Anti‐Müllerian Hormone

There is a male bias in the size of the cerebellum, with males, on average, having more Purkinje cells than females. The critical periods in cerebellum development occur when the immature testes secrete Müllerian inhibiting substance (MIS; synonym anti‐Müllerian hormone) but only trace levels of testosterone. This suggests that the male bias in the cerebellum is generated by a different mechanism to the testosterone‐sensitive reproductive nuclei. Consistent with this, in the present study, we report that Purkinje cells and other cerebella neurones express receptors for MIS, and that MIS −/− male mice have female‐like numbers of Purkinje cells and a female‐like size to other parts of their cerebellum. The size of the cell bodies of Purkinje cells was also dimorphic, although only a minority of this was a result of MIS. This suggests that MIS induces the initial male bias in the cerebellum, which is then refined by pubescent testosterone and/or other sex‐specific factors.