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Horm Behav. 2018 Jul;103:80-96. doi: 10.1016/j.yhbeh.2018.06.004. Epub 2018 Jun 28.

Behavioral evidence for sex steroids hypersensitivity in castrated male canaries.

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GIGA Neurosciences, University of Liege, Liège, Belgium.
Department of Psychology, University of Maryland, College Park, MD 20742, United States of America.
INSERM UMR 1195 and Université Paris Sud and University Paris-Saclay, Le Kremlin-Bicêtre Cedex, France.
GIGA Neurosciences, University of Liege, Liège, Belgium. Electronic address:


In seasonally breeding songbirds such as canaries, singing behavior is predominantly under the control of testosterone and its metabolites. Short daylengths in the fall that break photorefractoriness are followed by increasing daylengths in spring that activate singing via both photoperiodic and hormonal mechanisms. However, we observed in a group of castrated male Fife fancy canaries maintained for a long duration under a short day photoperiod a large proportion of subjects that sang at high rates. This singing rate was not correlated with variation in the low circulating concentrations of testosterone. Treatment of these actively singing castrated male canaries with a combination of an aromatase inhibitor (ATD) and an androgen receptor blocker (flutamide) only marginally decreased this singing activity as compared to control untreated birds and did not affect various measures of song quality. The volumes of HVC and of the medial preoptic nucleus (POM) were also unaffected by these treatments but were relatively large and similar to volumes in testosterone-treated males. In contrast, peripheral androgen-sensitive structures such as the cloacal protuberance and syrinx mass were small, similar to what is observed in castrates. Together these data suggest that after a long-term steroid deprivation singing behavior can be activated by very low concentrations of testosterone. Singing normally depends on the activation by testosterone and its metabolites of multiple downstream neurochemical systems such as catecholamines, nonapeptides or opioids. These transmitter systems might become hypersensitive to steroid action after long term castration as they probably are at the end of winter during the annual cycle in seasonally breeding temperate zone species.


Antiandrogen; Aromatase inhibition; HVC; Singing motivation; Song control system; Songbirds; Testosterone

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