Abstract
In experiment 1, we used autoradiographic procedures to examine whether tamoxifen could displace 3H‐estradiol labeling in the anterior hypothalamus and the caudal nucleus of the ventral hyperstriatum (HVc) of ovariectomized 20‐day‐old female zebra finches. There was no significant reduction in labeling of cells by 3H‐estradiol in birds preinjected with unlabeled tamoxifen. In experiment 2, we found that injections of 3H‐tamoxifen causedweak labeling of cells in the anterior hypothalamus of 20‐day‐old male and female zebra finches. These results are compatible with the idea that tamoxifen does not block the action of estradiol in the brain of zebra finches, and suggest that the effects of early tamoxifen treatment on the morphology of the song system may reflect central action of tamoxifen.