A masculinized skeletomusculature is not necessary for male-typical patterns of food-protective movement

Although sexual dimorphism in movement has been documented in rodents, the extent to which it relates to dimorphic neural control versus dimorphic body size/structure is unclear. We have shown previously that male and female rats are sexually dimorphic with regards to the lateral movements and hindpaw stepping they use to protect a food item. We addressed the question of whether this sexual dimorphism is due to sex differences in peripheral skeletomusculature or in the CNS by examining the movement composition used during dodging to protect a food item by tfm-affected males and their wild-type male (WTM) and female (WTF) controls. The tfm-affected male, while genetically male, develops internal testes that secrete testosterone, but is phenotypically female due to a failure of androgen receptor-mediated masculinization of the periphery. Masculinization of the CNS of tfm-affected males, however, is primarily accomplished by the actions of testosterone's aromatized metabolite estradiol acting via estrogen receptors. Thus the tfm-affected male provides an assay by which the relative contributions of the skeletomusculature or CNS to sex differences in movement organization can be addressed. We found that female wild-type animals were significantly different from both the tfm-affected and wild-type males. There were no significant differences in dodge patterns used by tfm-affected males and their wild-type male controls. This study provides evidence that the sex differences in dodging patterns are mediated primarily by CNS mechanisms and are not primarily dependent on a male- or female-typical skeletomusculature.