Expression of sex steroid receptors and sex differences of Otp glutamatergic neurons of the medial extended amygdala

The medial extended amygdala (EAme) is part of the social behavior network and its subdivisions show expression of sex steroid receptors, which participate in the regulation of sexually dimorphic behaviors. However, EAme subdivisions are highly heterogeneous in terms of neuron subtypes, with different subpopulations being involved in regulation of different aspects of social and non-social behaviors. To further understand the role of the different EAme neurons and their contribution to sexual differences, here we studied one of its major subtypes of glutamatergic neurons, those derived from the telencephalon-opto-hypothalamic domain that coexpress Otp and Foxg1 genes during development. Our results showed that the vast majority of the Otp glutamatergic neurons of the medial amygdala and BSTM in both sexes express Ar, Esr1 (ER) and Esr2 (ER{beta}) mRNA. Moreover, the high percentage of receptors expression in the Otp neurons (between 93 and 100%) indicates that probably the majority of the Otp neurons of EAme are coexpressing the three receptors. In addition, Otp neurons of the posterodorsal medial amygdala have a larger soma and occupy more space in males than in females. These and other features of the Otp neurons regarding their expression of sex steroid receptors likely contribute to some of the sexually-dimorphic behaviors regulated by EAme.