Testosterone or estradiol when implanted in the medial preoptic nucleus trigger short low-amplitude songs in female canaries

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.