Paradoxical hypermasculinization of the XXXX song system by an antiestrogen.

@entity172 @entity1 @entity440 @entity53 @entity12128 @entity4520
Exogenous @entity172 , when administered to hatchling female zebra finches, masculinize the morphology and function of their neural vocal control system. The first of two experiments evaluated whether @entity440 is an antiestrogen in zebra finches, and the second determined whether it would block the masculinization hypothesized to be caused in hatchling males by the males' endogenous @entity53 . In the first experiment adult female zebra finches were ovariectomized and injected for 10 days with @entity4520 (EB), @entity440 , EB and @entity440 combined, or vehicle (control). The dependent variable was oviduct weight. The EB-stimulated growth of the oviduct was blocked by @entity440 , which had no effects when administered alone. Thus, @entity440 acts as an antiestrogen in the @entity12128 oviduct. In Experiment 2, male and female zebra finches were treated with @entity440 or vehicle for the first 20 days after hatching. The males were castrated at 20 days. At 60 days we compared the song control regions of experimental and control males and females. In both sexes @entity440 increased the somatic areas of neurons in RA (robust nucleus of the archistriatum), HVc (caudal nucleus of the ventral hyperstriatum), and @entity1 (magnocellular nucleus of the anterior neostriatum). @entity440 also increased the volumes of HVc, RA, @entity1 , and Area X in males. Thus, @entity440 failed to block masculinization of males, but masculinized females and hypermasculinized males. @entity440 's hypermasculinization of the male and masculinization of the female song system is paradoxical given that (1) @entity53 does not have similar effects on the male song system, and (2) @entity440 antagonizes the effects of EB in the oviduct.
