Meeting Abstract

P3.195  Monday, Jan. 6 15:30  Sex steroid-independent effects of photostimulation on the song-control system of white-throated sparrows (Zonotrichia albicollis) HASSTEDT, M.R.*; ROBERTSON, B.D.; VANDERMEER, C.L.; MACDOUGALL-SHACKLETON, S.A.; Univ. of Western Ontario; Univ. of Western Ontario; Univ. of Western Ontario; Univ. of Western Ontario brober4@uwo.ca

Brain nuclei within the song-control system of songbirds are seasonally plastic during adulthood. These nuclei are larger in birds exposed to long, spring-like days than short, winter-like days. There is overwhelming evidence that this effect is mediated by testosterone (T). However, castration studies have also demonstrated that photoperiod can have gonad-independent effects on song-control system plasticity, but these studies rarely control for extra-gonadal sources of T. In this study, we used anti-androgen and anti-estrogen treatments in combination with castration to determine the sex steroid-independent effects of photostimulation in white-throated sparrows (Zonotrichia albicollis). Birds were kept on short days or photostimulated for 1 month. Photostimulated birds were intact, castrated and treated with anti-androgens and anti-estrogens, or castrated and treated with T. HVC volume of photostimulated intact birds and photostimulated castrated and T-treated birds did not differ, but were significantly larger than the HVC of short-day intact birds. HVC volume of castrated birds given anti-androgens/-estrogens was significantly smaller than the other photostimulated birds, but significantly larger than short-day birds, indicating a sex steroid-independent effect of photostimulation. Similar results were observed for RA. The number of migrating neurons (immunoreactive for doublecortin) in HVC did not differ between treatment groups. Our data support the view that photostimulation alone can drive song-control system nuclei growth, and that concurrent exposure to T potentiates this growth.