The goal of this work is an understanding of how steroid hormones influence the development of connections within a sexually dimorphic forebrain nucleus, the posterodorsal subnucleus of the medial amygdala (MeApd). My hypothesis is that the high levels of androgens present in neonatal male rats act on the MeApd to modify its synaptic architecture. We will test this using whole-cell voltage clamp recording of synaptic currents and electron microscopy in the following experiments: (1) I will test whether the synaptic organization of the MeApd is sexually dimorphic by comparing the physiology and anatomy of the MeApd in prepubertal rats; (2) I will give gonadal steroids to neonatal female rats to evaluate whether gonadal steroid receptor activation is necessary to masculinize MeApd synapses; (3) I will create organotypic explants of the MeApd to test whether gonadal steroids influence the intrinsic synapses of the MeApd. This research will contribute to our understanding of how gonadal steroids influence the amygdala, a nucleus that has been implicated in the incidence of several psychiatric disorders that vary by gender, such as autism and depression [unreadable] [unreadable]