Prenatal testosterone masculinizes synaptic input to gonadotropin-releasing hormone neurons in sheep

In sheep, the control of tonic and surge GnRH secretion is sexually differe ntiated by testosterone in utero, However, GnRH neurons are not sexually di morphic with respect to number, distribution, or gross morphology. Therefor e, this study tested the hypothesis that prenatal steroids influence synapt ic input to GnRH neurons. We compared the number of synapses on GnRH neuron s from male, female, and androgenized female lambs (n = 5 each). Androgeniz ed females were exposed to testosterone during mid-gestation, Yearling lamb s were perfused, and GnRH neurons were visualized using the LR-1 antibody. Five to seven GnRH neurons from the rostral preoptic area in each animal we re viewed at the ultrastructural level. Afferent synapses and glial ensheat hment on each neuron were counted in a single section through the plane of the nucleus, GnRH neurons from females received approximately twice as many contacts (3.6 +/- 0.7 synapses/100 mu m plasma membrane) as those from mal e lambs (1.6 +/- 0.3; p < 0.05), similar to previous reports in rats. In ad dition, the number of synapses on GnRH neurons from androgenized female lam bs (1.5 +/- 0.5) was similar to that from male lambs, suggesting that prena tal steroids give rise to sex differences in synaptic input to GnRH neurons .