ABSENCE OF POSTNATAL TESTOSTERONE FAILS TO DEMASCULINIZE THE MALE-RATS CORPUS-CALLOSUM

We had previously shown that elimination of testosterone from embryoni c day 17 through adulthood reduced the midsagittal area of the male ra t corpus callosum (CC). However, day 1 castration, performed after the 2-h post-birth testosterone surge, was without effect. To elucidate t he contribution of this surge on the CC, male rats were delivered by c esarean section and castrated within 20 min. This procedure eliminated the 2-h postnatal rise in testosterone levels. The prenatal surge in testosterone, which occurs on embryonic day 18, remained intact. In ad ulthood, callosal area was examined in castrate males, sham males, and intact females. Castrate males and sham males had significantly large r CCs as compared to females, The two mate groups did not differ from each other. Body weight was significantly higher in sham versus castra te males, establishing the effectiveness of the castration. These resu lts show that hormonal organization of the CC in the male is the resul t of the independent action of-prenatal testicular; androgens, and sug gest that the end of this period marks the end of callosal sensitivity to testicular hormone influence. In addition, this report documents s exual dimorphism of the CC in a third rat strain.