Abstract
In male songbirds, the motivation to sing is largely regulated by testosterone action in the medial preoptic area, whereas testosterone acts on song control nuclei to modulate aspects of song quality. Stereotaxic implantation of testosterone in the medial preoptic nucleus (POM) of castrated male canaries activates a high rate of singing activity, albeit with a longer latency than after systemic testosterone treatment. Systemic testosterone also increases the occurrence of male-like song in female canaries. We hypothesized that this effect is also mediated by testosterone action in the POM. Females were stereotaxically implanted with either testosterone or with estradiol targeted at the POM and their singing activity was recorded daily during 2 hours for 28 days until brains were collected for histological analyses. Following identification of implant localizations, 3 groups of subjects were constituted that had either testosterone or estradiol implanted in the POM or had an implant that had missed the POM (Out). Testosterone and estradiol in POM significantly increased the number of songs produced and the percentage of time spent singing as compared with the Out group. The songs produced were in general of a short duration and of poor quality. This effect was not associated with an increase in HVC volume as observed in males, but testosterone in POM enhanced neurogenesis in HVC, as reflected by an increased density of doublecortin-immunoreactive multipolar neurons. These data indicate that, in female canaries, testosterone acting in the POM plays a significant role in hormone-induced increases in the motivation to sing.
Significance Systemic testosterone increases male-like song in adult female canaries. We demonstrate by stereotaxic implantation of testosterone or estradiol that this effect is mediated, as has been demonstrated in males, by hormone action in the preoptic area. These implants significantly increased the number of songs produced and the percentage of time spent singing, but the songs produced remained short in duration and simple in structure. This singing activity did not result in an increase in HVC volume, as observed in males, but there was an enhanced density of doublecortin-immunoreactive new neurons supporting the notion that HVC neurogenesis is at least in part activity–dependent. These data also indicate that neural mechanisms regulating testosterone-induced singing are similar in males and females.
Footnotes
Authors report no conflict of interest
This work was supported by grant RO1NS104008 from the National Institute of Neurological Disorders and Stroke to GFB, JB and CAC, grant SSTC IAP P7/17 from the Belgian Science Policy to JB and CAC and a grant from the University of Liege (Fonds Spéciaux pour la Recherche 2017) to CAC. CAC is a senior F.R.S.-FNRS Research Associate.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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